Directory UMM :Data Elmu:jurnal:A:Agricultural Water Management:Vol43.Issue1.Feb2000:
Agricultural Water Management 43 (2000) 51±74
Strategies for water management in gravity
sprinkle irrigation systems
A.A. Ramalana,*, R.W. Hillb
a
Agricultural Engineering Department, Ahmadu Bello University, Zaria PMB 1044, Nigeria
Biological and Irrigation Engineering Department, Utah State University, Logan, UT 84321-4105, USA
b
Accepted 17 March 1999
Abstract
The study examined various management strategies implementable for equitable allocation of
water among users in a gravity sprinkle irrigation system (GSIS). A computer model was developed
and employed to effect allocations under three scenarios or variations thereof, namely, on-demand,
rotation, and continuous supply. Historical streamflow records and climatic data for 3 years, 1979,
1986 and 1983, representing normal, dry and wet years, respectively, were used. Equitable water
distribution consideration took into account shares of stock for water held by each user in the
irrigation company. Allocations were proportionately determined in relation to the numeric strength
of the users' stock when the demand for water was constrained by the available streamflow. The
developed management strategies were applied to a real-life irrigation project, the Richmond
Irrigation Company at Richmond, UT. Pure on-demand strategy proved to be the most beneficial
project-wide, costs of augmentation notwithstanding. # 2000 Elsevier Science B.V. All rights
reserved.
Keywords: Gravity-sprinkle; On-demand; On-request; Strategies; Water-rights; Users
1. Introduction
The water source for the gravity sprinkle irrigation system provides water as well as the
energy for operating the system. No pumping is required to lift water and pressurize the
line as is the case in a conventional sprinkler system. The water source at certain
mountain top locations is several hundred meters in elevation above underlying farm
* Corresponding author. Tel.: +234-069-50571; fax: +234-069-50563.
E-mail address: aramalan@abu.edu.ng. (A.A. Ramalan)
0378-3774/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 8 - 3 7 7 4 ( 9 9 ) 0 0 0 4 6 - 3
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A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
lands. Thus, the elevation difference provides the pressure energy needed to deliver
irrigation water at the sprinkler nozzle. The system is fed directly with water from rivers
and creeks by the use of simple intake structures in open channels. Typically, these runof-the-river irrigation systems are characterized by absence of any flood detention or
storage structures.
In dry years, as a consequence of low snow pack on the mountain, streamflow in rivers
and creeks resulting from snow melt in the spring are deficient. Coupled with the high
crop water use in the summer, system performance diminishes. Equitable distribution of
water among users constitutes a serious water management problem to irrigation
companies1. Studies by Kaewkulaya (1980); Bishop and Long (1983); Khanjani and Bush
(1983); (Kim et al., 1983) examined methods for water allocation in open-ditch surface
irrigation systems. Information is, however, lacking on techniques for water allocation in
a gravity sprinkle irrigation system (GSIS).
A study to examine management strategies to adopt to effect such allocations was
undertaken. The nine strategies which evolved integrated with hydrological, soil and
climatic factors of the area, crop water use, and the amount of shares held by users in
company stock for water. As part of the study, a computer model to effect allocation was
developed. The model was tested using data from a real-life irrigation project in northern
Utah.
2. Objectives
The general objective of the study was to evolve techniques for improving water
management in gravity sprinkle irrigation systems. The specific objectives include
identifying and evaluating practical management strategies that could be used by GSIS
companies to aid water management. In addition, the study was to compare the attributes
of the various strategies and quantify the benefits associated with each.
3. Procedure
The water available to users in an irrigation company is a common commodity by
virtue of the legal provisions in water rights. Such waters may be either directly from a
diversion of surface source or from groundwater. The challenge for management of
mutual irrigation companies is to translate share of stock values into realistic water
allocations to users that are fair and equitable. Equity is viewed here in relation to
individuals getting their fair share of water. Time is an important element in the allocation
process because crop production occurs in sequential phenological phases that respond to
environmental changes. Water allocated to users must be in amounts and at times
1
Users constitute mutual irrigation companies, granted water-rights through an instrument of State Law to
divert and distribute water to all share holders. The companies assess fees seasonally for each share of water
stock held by the user.
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53
Table 1
A listing of the strategies used for the water allocation studies in gravity sprinkle irrigation system (GSIS) at
Richmond, Utah
Strategy
Composition
Pure on-demand
Unlimited access to water by all users
fields treated as single entities.
Modified on-demand
Users' supply placed on request
One-time delivery
fields treated as single entities.
fields treated as single entities.
Rotation
Users grouped in rotation blocks
Supply based on crop category
Min±max Ranking system
Systems-related strategy
Low labour cost schemes
Continuous supply
Continuous supply to users
contiguous fields as rotation blocks (three blocks)
each crop type forms a block (three blocks)
range in shares of stock, each range constitutes a block (four blocks)
hand-move and wheel-move lateral system each constitute a block
(two blocks)
Off-farm and on-farm users constitute a block each (two blocks)
fields treated singly.
reasonable to make the commodity usable and effective. Various management strategies,
or operational schemes, have been evolved as means to effect delivery to users. Table 1
gives a listing of the strategies used. A description of each strategy is presented below.
Except for the continuous supply strategy, the other strategies under on-demand and
rotation schemes are modified versions of the system used in open ditch irrigation
systems. Allocations based on selected strategy were implemented using the computer
model GSIS, developed as part of the study, which integrated soil, water and
environmental factors. The model and the submodels are illustrated in Fig. 1(a±d).
3.1. Descriptions of the management strategies used in the study
3.1.1. Pure on-demand (unlimited access to water by all users)
This is a strategy that seeks to allow all users, access to water at all times. The
implementation of this strategy is possible early in the season when an ample supply of
water is available and crop water requirements are relatively low. Irrigation durations are
similarly expected to be low. No intensive policing of the system is desirable.
The manner with which users may connect for service is expected to follow a random
pattern. The main constraint anticipated is with the capacity of the system hydraulics to
satisfy demand from users needing water within the same time frame.
3.1.2. Users placed on request
This strategy is a modified demand delivery system. It places some responsibility on
the user. It requires that he made known his request for water in advance of time of use to
allow a sufficient time lag for scheduling and balancing of deliveries and total system
flow rates by the project. Because this strategy allocates water subject to constraint in
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Fig. 1. Flow diagram of gravity sprinkle irrigation system (GSIS) computer allocation model. (b) Flow diagram
of GSIS submodel HYDRA. (c) Flow diagram of GSIS soil-water budget submodel SWBAL. (d) Flow diagram
of GSIS submodel ATTR.
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
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Fig. 1. (Continued )
supply, the users' request may or may not be honoured at the requested time. Some
waiting may be imminent.
The strategy is particularly expedient during the latter part of the season when water
shortages are expected and irrigation amounts and/or frequencies are likely to be high.
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Fig. 1. (Continued )
Users' requests are likely to be highest during times of critical crop growth stages. While
it may be possible to anticipate incoming requests for water, it may not be possible that
all requests made for deliveries at specific times will be met.
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Fig. 1. (Continued )
3.1.3. One-time delivery
This strategy considers supplying the user his allocation of water in a one-time
delivery. The one-time allocation will be estimated based on a quantity of water that
would refill the entire root zone of his crop in a one-time delivery. Users, through mutual
agreements, may trade water among themselves; management must be notified of such
deals in advance of trades.
3.1.4. Users grouped in rotation blocks
Users' holdings are grouped in rotation blocks. Each block is of a pre-determined size
(in hectares). Each user/field in the block is allowed access to a fixed continuous flow
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amount and duration. The frequency is usually fixed, but may also be variable. Individual
users within each block irrigating at the same time are grouped as rotation units. Users
will have allocations figured out relative to their stock shares. Rotations are expected to
be rigid and all were to take their flows only when due. One rotation unit made up of one
or more blocks received water at any one time.
3.1.5. Supply users based on crop category
This strategy invokes the use of crop categories in allocation, taking into consideration
the economic benefits derivable from the array of crops irrigated. Ranking of users' crops
was in effect and allocations were to be along specific crop categories.
First to be allocated water were users who grew crops with the highest economic value,
and so on, to users who grow economically least-derivable-benefit crops, such as pasture.
The strategy is particularly well adapted to periods of diminishing streamflow.
3.1.6. Min±max ranking system
A ranking system was evolved whereby allocations were begun with users who hold
the highest number of shares of stock taking all the flow. This group of users was
followed by the next lower level of users and finally by users who held the least stocks.
When operating under deficit flow conditions, each user at any of the levels will have
water for a time period commensurate with his shares.
3.1.7. Systems-related strategy
This strategy relates to the two major gravity sprinkle irrigation systems, the handmove and the wheel-move lateral systems. Users were classified into the two groups
depending on the type of system each operates.
Allocations using this strategy were along system types, in other words, users operating
wheel moves will be expected to be irrigating at about the same time. The exact time
individuals within system groups are delivered water depended on the overall system
hydraulic analysis.
3.1.8. Low labour cost scheme
This management strategy is invoked whereby certain users are to receive their
allocations during the low labour cost hours. The scheme differentiates on-farm from offfarm users. Under certain circumstances and locations, the cost of irrigation labour to the
farmer is lower during weekday first-shift hours compared to other shifts. The first shift is
between 8 a.m. and 4 p.m. The strategy is to make water available to the farmer during
the least labour cost hours.
Urban and non-agricultural irrigation stockholders who use water for lawn sprinkling
and backyard gardens will have access to water during the second and third shifts on
Saturdays and all three shifts on Sundays.
3.1.9. Continuous supply with monitoring
Continuous supply of water to users is to be maintained day or night as rationed to
users. Each user's ration is to be monitored by estimating and counting the number of
sprinklers he has operating continuously. The rations are available to the user whether or
not they are needed.
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4. The computer model
The GSIS model is developed for use in mutual irrigation companies that operate under
gravity sprinkle systems. The model is comprised of four submodels, the first being the
main programme. The second, third and fourth are designated HYDRA, SWBAL and
ATTR submodels, respectively. The main programme serves the primary function of
controlling programme flow. It also carries out non-repetitive calculations. The submodel
HYDRA provides a work area in which routine calculations of crop water requirements
and the need for irrigation are performed. The submodel SWBAL maintains the soil water
balance sheet for all fields and the ATTR submodel evaluates the attributes of the various
strategies.
The model invokes a strategy to implement allocations, then estimates a field service
priority, and determines sprinkler discharges based on operating pressures at delivery
points. It also uses stored data on soils, crop and climate to compute crop evapotranspiration at various growth stages for maize (field corn), spring wheat, pasture and alfalfa from:
Et Kc Ks Etr
(1)
Where Et is the estimated crop evapotranspiration, Etr is the reference crop
evapotranspiration computed from the Jensen±Haise equation. Kc, the crop coefficient,
is the ratio of the actual crop evapotranspiration to reference crop evapotranspiration. The
value varies with crop variety or species, time of planting, and growth stages. It is
computed by the use of a phenology clock for each crop for the specific Julian day
depending on planting, effective cover and harvest dates. The mean crop coefficients, Kcm
used in the model were adapted from (Allen et al. (1988) based on tabular values
presented by Wright (1981, 1982); Doorenbos and Pruitt (1977) rev.). In the equation, Ks
is the soil moisture stress coefficient. For an irrigation system in which maximum Et is
allowed, Ks 1. The coefficient varies with evaporative demand, soil moisture content,
soil and the crop. This study used the model proposed by (Hill et al., 1984).
The Jensen and Haise (1963) temperature-radiation equation for estimating Etr was
used to program a Datapod (Omnidata International DP 219) to accumulate the calculated
Etr on a daily basis. The data used including air temperature and solar radiation were
sampled at Newton, UT (the nearest weather station to Richmond). Thus,
Etr Ct Cf T ÿ Tx Rs
(2)
where Etr is the reference crop evapotranspiration (mm), T is the average daily
temperature (8C), Tx is the intercept on the temperature axis, Rs is incident solar radiation
(langleys/day), and Ct is a temperature coefficient. Values for Ct and Tx as 0.025 and ÿ3,
respectively, were reported in Hansen et al. (1979). Both factors are site-specific. For this
reason, they further gave a relationship for estimating Ct and Tx for other areas taking into
account altitude above mean sea level and saturation vapour pressures of water for the
warmest month of the year in the location. Allen et al. (1988) gave Ct (in English units) as
0.009 and 0.011, respectively, for valleys with extensive irrigated or wetland areas, and
for surroundings of predominantly arid lands. A fifth power polynomial equation was
derived that best fit the Datapod data relating Etr with day of year. The equation was used
in the model to estimate Etr for the Richmond site.
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The hydraulic network submodel, HYDRA, simulates pressures in the distribution
main pipes, the laterals and sprinkler nozzles. The relationships given in Keller (1986)
were used to estimate average lateral pressures and nozzle discharges using data relating
to pipe type and size, friction head loss coefficient, and allowable head loss due to
elevation changes. It also provided for corrections for environmental and spray
conditions.
The submodel also estimates the allocation time for each user to irrigate with the
allotted volume of water, qt. The allotted volume was estimated by
qt 2:8 a d
(3)
where q is equal to field/user flow capacity (lps); t is equal to time to apply the irrigation
(h); a is equal to field area (ha) and d is equal to gross depth of irrigation (mm)
The time of water application, t, was related to infiltration rate of the soil in order to
prevent surface runoff and/or ponding. Therefore, the application rate, which is only
constrained by the soil infiltration rate, was calculated in the submodel using
i
3600 qs
Sm Sl
(4)
where I is equal to application rate (mm/h); qs is equal to discharge per sprinkler (lps); Sm
equal to lateral spacing along mainline, and Sl is equal to sprinkler spacing along laterals
(m).
Once allocations are completed, programme execution is transferred to submodel
SWBAL, the soil water balance submodel.
The submodel SWBAL maintains a soil±water budget. This is a daily book-keeping
process of where water is in the soil/crop environment. The soil±water budget equation is
SWSn SWSnÿ1 Prn IRn ÿ Etn ÿ DRn
(5)
where SWSn is the soil water content at the end of the present day, SWSnÿ1 was the soil
water content the day before, Prn, Irn, Etn, and Drn are, respectively, the precipitation
amount, irrigation depth, actual crop evapotranspiration and drainage loss for the present
day. Drainage occurred only if SWSn for any day exceeded the field capacity storage of
the soil. The present day n subscript refers to a specific day of the year. In the
development of the submodel, assumptions were made that the soils within the layers
found were homogeneous, infiltration occurred at the same rate in fields, there was no
upward movement of water into the root zone, all farmers (users) used the correct nozzle
sizes on their sprinklers at all times, and the management allowed depletion was 50% of
available water in the root zone (Ramalan, 1988).
As soil water storage capacity is tied to rooting depth, the model uses a root growth
function to estimate crop root depth in relation to time. The function assumes that root
growth progresses linearly from a minimum root depth at the time of planting (or begin
growth in the case of alfalfa) to a maximum root depth value at crop full cover.
Crop yield is estimated by the model using the method of Hill et al. (1984) based on
the ratio of actual to potential transpiration for each growth stage. Influence of
each growth stage has an effect on the estimate because of the multiplicative nature of
the relationship. Crop growth progression through a number of growth stages, was
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
61
estimated using a phenology clock based on growing degree-days proposed by Gilmore
and Rogers (1958).
The submodel ATTR is invoked to evaluate attributes of the various strategies,
including costs, returns, and benefits. In addition, waiting time with respect to elapsed
time before a user receives service, and equitability indices are estimated in this
submodel. The monetary benefit was simply estimated from total returns from sale of
produce minus cost of production. Returns were estimated as
Returns Price per unit weight
Yield
BYP
ha
(6)
where unit weight was based on tonnage or kg. In the case of pasture the unit weight was
replaced by animal unit month (AUM), as 1 AUM 360 kg DM (Scarnecchia and
Kothmann, 1982). Yield was based on production per unit area, tonne/ha. BYP was the
revenue from sale of bye-products, such as wheat straw. All the costs toward production
were partitioned as yield-dependent, constant or fixed, area-dependent, or capital costs.
Thus on-farm total production cost per hectare was estimated as
TC Cy Cc Ca Ck
(7)
where TC is equal to total cost/ha; Cy to yield-dependent costs such as of fertilizers and
fertilizing; swathing and baling for alfalfa; and clipping for pasture. Cc is equal to
constant costs, such as the cost associated with land tax; Ca to area-dependent costs, such
as water assessment and irrigating costs. Ck is equal to capital costs, such as costs
associated with machinery and tools. Its value depends on the investment cost of the item,
interest rate and pay-back period on loan amount.
The submodel ATTR estimated annual cost of capital items using capital recovery
factor CRF, thus,
Annual cost investment cost CRF
(8)
where
CRF
i 1 in
1 in ÿ 1
i is equal to annual interest rate expressed in decimal and n is equal to pay-back period for
the loan sum in years.
The input data for calculations in this routine were stored in ECON.DAT for the four
crop enterprises in the study.
5. Application of the model
5.1. The site
The Richmond Irrigation Company (RIC) project was the site of the study conducted in
the summer of 1986. The project, located in Richmond (418430 N, 1118470 W) in north
Cache County, UT, as shown in Fig. 2, was developed in stages following the company's
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Fig. 2. Location map for Richmond Irrigation Company.
formation in the year 1860 by a group of farmers (users). The sole purpose of the
company was to effect distribution of water among members for irrigation and municipal
uses. The source water is by direct diversion from High Creek, near Richmond. The area
of the watershed contributing flow in the creek is 26.1 km2. From historical records
(1944±1985), the mean discharge at the main diversion gauging station is about 83 lps.
The extreme maximum and extreme minimum discharges ever recorded were 14,000 lps
and 70 lps, respectively.
The users who are the stockholders in the company, own and operate farms within the
project. The profile of stockholders showed that there were 457 of them in the register
who collectively owned 6067 shares. The maximum, average and minimum number of
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63
shares held by stockholders are 229, 13.28, and 1, respectively, and all were acquired as
sprinkle irrigation stock. The farms were flood-irrigated until 1970, when construction of
the gravity sprinkle irrigation system was begun (USDA ± Soil Conservation Service,
Logan, 1974). The RIC had a total of 10,000 ha for which water-rights were granted by
the Utah Division of Water Resources through the Kimball Decree Awards #38. The
priority date for the first right to the company was issued on 1 May 1860. Three other
irrigation companies in the vicinity which also have water-rights on the High Creek are
Coveville, Webster, and Mt. Home.
The interpretation of these awards (Ramalan, 1988) which are in three parts gives RIC
the right to divert 78.4% of the flow in High Creek for all flows between 141.2 lps (5 cfs)
and 1412 lps (50 cfs). If the flow in the creek is greater than 1412 lps (50 cfs) and up to
2613 lps (92.2 cfs), RIC has an additional award to divert 20.2% of flow that is in excess
of 1412 lps (50 cfs). At this 2613 lps (92.2 cfs) flow, which is regarded as maximum ditch
flow, the company by virtue of the two awards has rights to divert a total of 1338 lps
(47.2 cfs). The third award comes into effect if the flow in the creek exceeds 2613 lps
(92.2 cfs). The third award allows the company an additional 20.2% subject to an upper
ceiling of 1984 lps (70 cfs). At the time of study the RIC had not operated any ground
water rights.
5.2. Pumping
Four electrical deep well turbine pumps exist within the project. The pumps with rated
discharges of 60 lps (900 gpm) at heads 80 m (260 ft) were to pump from 30 cm diameter,
98.8 m deep wells. The pumps were located in a fenced pump house in sector four close
to the Logan±Richmond highway. The location was a few hundred meters from the pipe
intake structure across the road. The pumps feed the project mainline which in turn feed
distribution lines servicing different farmers' fields. The pumps were not designed to
serve individual fields rather they feed into the common pipelines arranged in branching
hydraulic network. The study took cognisance of these facilities to include the possibility
of need for flow augmentation by use of ground water.
5.3. Procedure for estimating augmentation and costs
The general procedure used to estimate augmentation requirement and its costs,
especially in relation to strategies 1 and 8 is summarized below. The energy type was
electricity and a Utah Power and Light Company (UPLC), schedule of charges used.
Augmentation requirement was estimated
Qaug DQJd ÿ HQJd
if Qaug > 0
(9)
and
Vaug 8:64 10ÿ3 Qaug
(10)
where Qaug is equal to the required flow augmentation in lps; DQJd is equal to the demand
flow on a particular Julian date in lps; HQJd equal to historical streamflow for the
particular Julian date in lps; Vaug is equal to volume of augmentation in ha m.
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It was anticipated by the project designers that augmentation, if needed, would not
exceed 226.7 lps (8 cfs) even in dry years. Such need is to be met by the output from the
four pumps installed. Each pump was rated at 56.67 lps (2 cfs) and powered by 75 hp
motors connected to three-phase, 415 V power source. The number of pumps needed to
supply augmentation on any day was estimated by (rounding up to next integer)
PUMPN
Qaug
56:67
(11)
i.e., one pump if 0 < Qaug 56:67 lps; two pumps if 56:67 lps < Qaug 113:33 lps;
three pumps if 113:34 lps < Qaug 170:00 lPs; and four pumps if 170:00 lps < Qaug
226:66 lps; where PUMPN is equal to number of pumps operating.
The electric power requirement for the pumps to supply the augmentation flow was
estimated
Power
Qaug h
56:6 Ep
(12)
where Power is equal to required power of electric motor in kW; h to pumping depth in
m; Ep is equal to pump efficiency (expressed in decimal) and Qaug as previously defined.
The energy requirement was calculated as
Energy Power Time
(13)
where Energy and Time were measured in kW h and h, respectively. Both power and
energy were tallied to obtain monthly and seasonal totals. Monthly power and energy
costs were estimated using option A of the UPLC schedule. Monthly bills for
augmentation were estimated in the model by
MNBILL FXCOST SERVCHG MISCOST DEMCOST ENECOSTmn
(14)
where MNBILL is equal to monthly bill in US$; FXCOST is equal to fixed cost
representing amortized costs for wells, motors and pumps, and shelter based 30, 20, and
10 year lives, respectively, at 12% interest rate. All cost details were obtained from the
local equipment dealer. SERVCHG is equal to service charge per connection by the
Utility company. MISCOST is equal to miscellaneous costs, which are associated with
attendance, lubrication and repairs on per 100 h basis for the month. DEMCOST is equal
to UPLC monthly power demand cost based on $8.04/kW, first 100 kW; and $5.33/kW all
additional kW; ENECOST is equal to UPLC monthly energy cost based on 10.0345
cents/kW h first 100 kW h per kW; 5.3803 cents/kW h next 25,000 kW h; and 3.5702
cents/kW h all additional kW h, and mn is subscript referring to the specific month.
Discounts were applied to the monthly bill to obtain the net monthly bill. The discounts
were with respect to term and voltage. Term discounts were not in operation at the time of
the study. Voltage discounts were rated based on power demand and were contingent
upon the customer providing and maintaining the transformer and necessary equipment.
The voltage discount rates operated by UPLC are: $1.17/kW, first 100 kW of power; and
$0.62/kW, all additional kW.
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Seasonal bill is a summation of monthly net bill minus off-season costs. The off-season
costs are equipment costs for which payment must be made during and off-irrigation
season. These data were entered in a data file, AUGMENT.DAT for use in the model.
5.4. Farm and field characteristics
The RIC project is in four sectors. Each sector is served by an intake structure that
feeds water into the mainline for the fields in the sector. The data collected for this study
were gathered in the fourth sector which has an area of 251 ha.
For at least the purpose of this study, a field was considered a piece of land with unique
crop, soil, and physical characteristics. The field was, therefore, expected to consist of
one crop on essentially one soil type. The field had physical boundaries based on either
soil or crop differentiation. One or more fields constituted a farm. Records of field sizes
obtained through direct interview with the farmers varied from 2 to 32 ha with a mean of
11 ha.
Soil types defined by textural classification given in the soil survey data of the area
showed that Trenton silty clay loam was the most common. About 70% of the area under
this soil type is cropped with irrigated crops such as alfalfa, small grains, sugar beet, and
pasture. This soil and others elsewhere on the site are moderately well drained though
slowly permeable. Runoff is low and hazards to erosion slight. Water-table depth is
commonly more than 100 cm.
Crops in the project fall within the categories of irrigated or dryland commercial crops.
Their distribution among fields, however, varied with climatic and soil conditions,
economics and farmers preferences. For the 1986 crop year, aerial distribution of crops
among fields in the study area was as follows: alfalfa, 65%; small grain, 13%; silage corn,
9%; and pasture, 13% on land areas of 181, 14, 24, and 32 ha, respectively. About 177 ha,
out of the 251 ha, were on Trenton silty clay loam and Nibley silty clay loam soils.
Water for irrigation was distributed through a branching pipe network. The irrigation
systems in the farms are sprinklers of either hand-move or the periodic wheel-move
systems. Water channelled from the creek in open ditches was fed to the pipe inlet at
canal turnout about 60 m in elevation above the lowest farm delivery points. Most
delivery points were located about 52 m below the elevation of canal turnout. Excess
pressures not used in the pipeline were dissipated at pressure relief valves strategically
located within the network. Pipe sizes of standard lengths of 6 m made from welded steel
or asbestos cement and fittings were joined and buried to constitute the network.
At delivery points, the network terminated to 100 mm stand valves equidistantly
spaced on laterals along fence lines of individuals' properties. Valve openers facilitated
release of water into individual sprinkler systems.
5.5. The model implementation
The computer model was invoked for each of the nine allocation strategies and for the
3 years representing dry (1979), normal (1986) and wet (1983) years. These
representative years were selected from the water-year records of High Creek (October
1978 through September 1987). For these years, the available streamflow diversions to
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the study area, as allowed for by the water rights, varied from 14 lps to a maximum of
178 lps. Daily streamflow data adjusted with water-right awards factor (as a percentage)
represents the allowable diversion due to RIC. These daily estimates were stored in an
array variable HQ in data files CLIM.DRY, CLIM.NOM and CLIM.WET. They were
read for each computer run. Recorded precipitation are also included on a daily basis as
part of the input files. Each computer run called the relevant subroutine after having
previously opened and read all input data files. All the calculations carried out in the subroutines are written in output data files before exiting to the main programme.
6. Results and discussions
For the test years, with allocation on demand, the study showed that it was infeasible to
operate the strategy for allocation without augmentation throughout the growing season.
This is evidently so because demand flow rates on the system outstripped supply in some
instances, as depicted by the hydrographs in Fig. 3 particularly in the flow receding
region where demand-to-supply ratio exceeded 8 : 1. In the normal and wet years, it was
possible to operate on-demand from day of year 101 through Day 135 and Day 175,
respectively. Within these periods demand flows could easily be satisfied by supply. But
the supply hydrograph for the dry year showed significant deficit as to make allocations
on-demand inoperative. Scanty precipitation coupled with low stream flows preclude
operating on-demand except intermittently for some 10 days throughout the growing
season. The model showed that in addition at least one pump needed to be operated
continuously.
Beyond those periods when on-demand allocations were feasible in the normal and wet
year, constraints in delivery were inevitable. From these days onward, on-demand was
viable only to the extent that water supply was augmented through conjunctive water use
by tapping groundwater sources. The total costs for augmentation in order to continue to
operate on-demand were $44,679, $96,257, and $144,735 in wet, normal and dry years
respectively. A substantial proportion of this cost was for energy for pumping. In the only
alternative, as would be the case for most run-of-the-river GSIS with no groundwater
rights, the schedule of allocations has to change to a less flexible system such as rotation
or continuous supply.
The data on seasonal crop water use for the test years for the three strategies are given
in Table 2. The average seasonal actual crop Et's were 760, 510, 580 and 710 mm for
alfalfa, corn, small grain, and pasture, respectively. The number and net depths of
irrigation were highest under the continuous supply strategy. Drainage, estimated by the
model as the component of applied water or rain that had percolated below root zones,
was least with the on-demand mode, where values exceeded 25 mm per season. These
drainage amounts were mainly in corn and grain fields. The seasonal rainfall received in
alfalfa and pasture fields was about 280 mm with about 178 mm on the corn and small
grain fields.
Benefits accrued to individuals were calculated through the itemization of costs and
returns. Crop yield using the technique of Hill et al. (1984) provided vital data for
estimating the financial returns. The fields under pastures sustained financial loss. When
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
Fig. 3. Available and demand flow hydrographs for irrigation on-demand, precipitation, number of pumps for supply augmentation, and number of users irrigating based
on Dry Year (1979) data, RIC.
67
68
Table 2
Summary of water use (seasonal totals) by field/user during a normal year with the on-demand, rotation, and continuous supply strategies invoked
Crop
CARI430
CAR1593
CARI688
CARI836
CARI525
CARI750
CARI142
CARI950
CARI011
CARI066
CARI122
CARI474
CARI299
CARI869
CARI958
CARI481
CARI986
CARI399
CARI640
CARI059
CARI618
CARI181
CARI714
ALFALFA
ALFALFA
S/GRAIN
PASTURE
PASTURE
S/GRAIN
PASTURE
ALFALFA
ALFALFA
ALFALFA
ALFALFA
ALFALFA
ALFALFA
ALFALFA
CORN/SL
ALFALFA
S/GRAIN
CORN/SL
ALFALFA
ALFALFA
ALFALFA
ALFALFA
ALFALFA
Area
(ha)
Rain
(mm)
On-demand
Rotation
No.
of
irrg
Net
irrg
(mm)
Drain
(mm)
RT-Z
depl
(mm)
Crop
Et
(mm)
No.
of
irrg
Net
irrg
(mm)
16
16
16
20
4
8
8
32
6
12
6
12
12
14
10
12
4
4
4
10
20
2.8
2
281.9
281.9
188.0
289.6
281.9
200.7
289.6
281.9
281.9
281.9
289.6
289.6
289.6
281.9
172.7
281.9
175.3
172.7
281.9
292.1
297.2
281.9
289.6
3
3
6
7
6
6
7
2
3
3
3
3
3
3
3
4
6
4
3
3
2
3
3
408.9
414.0
464.8
495.3
416.6
472.4
487.7
436.9
408.9
403.9
406.4
424.2
408.9
408.9
317.5
510.5
467.4
396.2
406.9
411.5
340.4
403.9
401.3
0.0
5.1
83.8
55.9
45.7
91.4
58.4
0.0
2.5
10.2
15.2
17.8
7.6
2.5
5.1
17.8
76.2
50.8
0.0
22.9
0.0
2.5
12.7
61.0
61.0
15.2
2.5
66.0
2.5
15.2
ÿ27.9
63.5
76.2
68.6
53.3
61.0
63.5
33.0
ÿ22.9
15.2
5.1
68.6
71.1
119.4
68.6
71.1
754.4
751.8
584.2
731.5
718.8
584.2
734.1
690.9
751.8
751.8
751.8
751.8
751.8
751.8
518.2
751.8
581.7
525.8
756.9
749.3
756.9
754.4
751.8
10
10
10
10
10
10
10
10
10
10
11
11
10
10
10
10
10
9
9
10
9
9
10
449.6
574.0
398.8
355.6
566.4
317.5
599.4
66.0
571.5
569.0
594.4
594.4
576.6
294.6
452.1
444.5
825.5
538.5
388.6
289.6
396.2
490.2
619.8
Continuous supply
Drain
(mm)
147.3
236.2
243.8
162.6
279.4
208.3
297.2
0.0
221.0
226.1
236.2
238.8
228.6
78.7
137.2
149.9
538.5
200.7
94.0
88.9
106.7
165.1
261.6
Note: NET IRRG: applied water that infiltrated the soil surface; RT-Z DEPL: root zone depletion.
RT-Z
depl
(mm)
170.2
132.1
157.5
127.0
132.1
154.9
119.4
208.3
119.4
129.5
101.6
104.1
114.3
208.3
12.7
177.8
119.4
5.1
177.8
193.0
170.2
144.8
101.6
Crop
Et
(mm)
No.
of
irrg
Net
irrg
(mm)
Drain
(mm)
RT-Z
depl
(mm)
Crop
Et
(mm)
754.4
751.8
500.4
609.6
701.0
464.8
708.7
558.8
751.81
751.8
751.8
751.8
751.8
706.1
502.9
751.8
581.7
515.6
756.9
685.8
756.9
754.4
751.8
16
16
13
16
16
13
16
16
16
16
16
16
16
16
14
16
13
14
16
16
16
16
16
457.2
586.7
419.1
363.2
574.0
325.1
599.4
68.6
581.7
584.2
599.4
609.6
581.7
302.3
533.4
411.5
777.2
510.5
363.2
279.4
370.8
457.2
581.7
137.2
223.5
248.9
152.4
266.7
203.2
287.0
0.0
218.4
228.6
233.7
238.8
221.0
76.2
182.9
129.5
487.7
175.3
81.3
88.9
91.4
139.7
223.5
152.4
106.7
160.0
127.0
129.5
157.5
124.5
208.3
106.7
114.3
91.4
88.9
101.6
208.3
7.6
188.0
119.4
5.1
193.0
193.0
180.3
152.4
101.6
754.4
751.8
518.2
627.4
718.8
482.6
729.0
558.8
751.8
751.8
751.8
751.8
751.8
716.3
528.3
751.8
581.7
513.1
756.9
675.6
756.9
754.4
751.8
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
Field/
user code
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
69
crops were not water-stressed, average benefit to users who engaged in the following
crop enterprises were as follows: alfalfa, $746/ha ($44/tonne); silage corn, $832/ha
($15/tonne); small grains, $281/ha ($474/tonne); and pasture, ÿ$84/ha (ÿ$14/tonne).
With constrained allocations, results showed that benefits accruing to users are lower
and indeed some alfalfa fields returned negative benefits in the dry year. The
aggregated benefits resulting from the use of each strategy are included in Table 3 for
the test years.
The relative ratios of user allocations and stock for water held in the company were
compared to draw inferences regarding equitability of allocations among users. The
results given in Table 2 for the normal year using the strategies showed that some users
received more or less water than their shares of stock would otherwise entitle them to. In
the on-demand mode no restrictions were imposed, each field received as much water as
it needed. Those fields/users that got far less relative to their shares had far more shares
than they needed. While no absolute agreement between the ratios was expected and
obtained with on-demand, the non-flexible strategies attempted to ration water based on
shares of stock.
Waiting time or stress-days for this study was calculated based on number of days since
50% available soil moisture storage was depleted. It varied with strategy used and the test
year. For the on-demand strategy waiting time in the dry, normal and wet years were 11,
7, and 5 days, respectively. Waiting time for other strategies were also estimated. The
durations varied between 28 and 101 days. Waiting time with continuous supply was
shortest, because users received water on a daily basis. Waiting time for all strategies
were longest during the dry year and shortest in the wet year. There was evidently a
relationship between waiting time and crop yield achieved. It appeared that the longer the
waiting time with a given strategy, the more the individual fields are stressed and the less
the crop yields and potential benefits to users.
The resource utilization ratio (RUR), provided a measure of how closely total
allocations to users related to available water resources at the disposal of the company. In
the dry season, RUR amounted to 1.84, thus users required 84% more water in volumetric
terms on a seasonal basis than they had water rights for in order to operate on-demand.
The specific times to inject additional water can be seen on observation of demand and
supply hydrographs, given as Fig. 3. In normal and wet years, the ratios potrayed a
standpoint of sufficiency in meeting seasonal demands; this is to be realized only if
assumption of trading surplus water at the beginning of the season holds. If not,
augmentation from groundwater had to be in effect. To match allocations closely with
what was available, the ratios had to be less than 1.0. The data on Table 3 showed that
RUR ranged 0.32 and 0.94 for the other non-flexible strategies. With one-time delivery
strategy, where only one heavy irrigation was given to refill the root zones, in the normal
year just about 35% of the streamflow was utilized. Augmentation was needed only if
streamflow was low to satisfy the commitment for the one-time delivery.
The data in Table 4 represent the average of five runs and summarize the results of the
response of the irrigation system to all of the allocation strategies in what are described as
`attributes' of the management strategies. On-demand strategy returned the highest
benefit to users only if augmentation is at no cost (such as when water is traded). But, if it
has to be paid for, on-demand in spite of its flexibility is a lower revenue-earning option
70
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
Table 3
A summary of attributes for management strategies implemented in the dry, normal, and wet years (1979, 1986
and 1983), respectively
Strategy
On demand
Unlimited access to waterc
Unlimited access to waterd
Modified demand
User on request
One time deliverye
Rotation
Users in rotation blocks
Among crop categories
Stock ranks
System types
Labor cost scheme
Continuous supply
Continuous supply
a
Season
type
Benefit
$
Wait time
days
Water supplieda
dry
norm.
wet
dry
norm.
wet
143464
153961
154331
ÿ5214
51111
105509
11
7
5
11
7
5
80.9
72.0
87.2
80.7
74.3
89.0
dry
norm.
wet
dry
norm.
wet
64268
89183
136231
5294
84175
117441
74
58
34
101
67
65
90.7
72.0
92.6
46.6
47.8
47.4
dry
norm.
wet
dry
norm.
wet
dry
norm.
wet
dry
norm.
wet
dry
norm.
wet
34203
110330
127400
19651
105760
125414
28757
109227
128314
28280
106015
125889
21426
103073
123639
79
38
29
91
43
37
81
40
35
83
42
38
90
43
38
84.0
126.5
130.4
83.5
123.8
127.4
86.0
127.6
132.1
82.4
126.5
131.0
84.6
125.7
131.3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.84
0.91
0.89
0.83
0.89
0.87
0.86
0.92
0.90
0.82
0.91
0.89
0.85
0.90
0.90
dry
norm.
wet
23841
102651
117763
80
35
28
89.6
130.1
135.6
0
0
0
0.89
0.94
0.93
Stream
RURb
Augm.
103.0
67.2
28.9
103.0
67.2
28.9
0
0
0
24.3
0.85
0.13
1.84
1.00
0.79
1.84
1.02
0.80
0.91
0.52
0.63
0.71
0.35
0.63
Water supplied, measured in ha m.
Resource utilization ratio (RUR), defined as the ratio of water supplied (stream plus augmentation) and
allocated to users to streamflow resource available to project for which water-right is granted.
c
Assumes unlimited access to water, with no cost supply augmentation during times when flow demand
exceeds available supply hydrographs.
d
Augmentation costs included were $144,735, $96,257, and $44,679 for dry, normal, and wet years,
respectively.
e
Augmentation costs included were $38,405, $5,665, and $4,479 for dry, normal, and wet years,
respectively.
b
Table 4
Field/user stock relative to allocation of water received (and expressed in percentage) using on-demand strategy in a normal year
CARI430
CARI593
CARI688
CARI836
CARI525
CARI750
CARI142
CARI950
CARI011
CARI066
CARI122
CARI474
CARI299
CARI869
CARI958
CARI481
CARI986
CARI399
CARI640
CARI059
CARI618
CARI181
CARI714
User
stock (%)
40
51
40
39
12.5
15
26
12
19
38
19
38
38
23
20
27
19
8
8
14
41
7
6.3
User as a ratio of
company stock (%)
7.1
9.1
7.1
7.0
2.2
2.7
4.6
2.11
3.4
6.8
3.4
6.8
6.8
4.1
3.6
4.8
3.4
1.4
1.4
2.5
7.3
1.2
1.1
On-demand
Rotation
User
allocation
(%)
User as a
ratio of all
allocations
(ha m)
User
allocation
(%)
8.4
8.5
10.0
12.6
2.2
5.2
5.1
9.2
3.2
6.4
3.1
6.9
6.8
7.3
4.1
8.2
2.5
2.1
2.2
5.5
9.3
1.5
1.1
6
6
7.1
8.9
1.6
3.7
3.6
13.6
2.3
4.5
2.2
4.9
4.8
5.2
2.9
5.8
1.8
1.5
1.6
3.9
6.6
1
0.8
9.4
12.1
8.4
9.2
3.0
3.2
6.3
2.4
4.5
8.9
4.7
9.1
8.4
4.5
5.3
5.9
4.1
3.3
1.9
2.5
8.4
1.8
1.6
Continuous supply
User allocation
as a ratio of
all allocations
(ha m)
7.5
9.5
6.6
7.3
2.3
2.6
5
1.9
3.6
7
3.7
7.2
6.7
3.6
4.2
4.6
3.3
2.6
1.5
2
4.7
4.7
1.3
User
allocation
(%)
9.6
12.3
8.9
9.5
3.0
3.4
6.4
2.6
4.6
9.1
4.7
9.6
9.2
5.2
6.6
5.4
3.9
2.6
1.8
2.6
6.0
1.7
1.5
User allocation
as a ratio of
all allocations
7.4
9.5
6.8
7.3
2.3
2.6
4.9
2
3.5
7
3.6
7.4
7
4
5.1
4.1
3
2
1.4
2
4.6
1.3
1.2
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
Field/user
code
71
72
Table 4 (Continued )
Month
User
stock (%)
Aug. (ha m)
April
May
June
July
August
September
0
0
9.46
21.85
32.83
3.02
Total vol. of
augmentation
(ha m)
Total aug. cost
Total benefit
to project
Average waiting
time (days)
Total water
allocated (ha m)
Resource
utilization ratio
67.2 0
User as a ratio of
company stock (%)
Vol. (h)
On-demand
Rotation
Continuous supply
User
allocation
(%)
User as a
ratio of all
allocations
(ha m)
User
allocation
(%)
User allocation
as a ratio of
all allocations
(ha m)
User
allocation
(%)
User allocation
as a ratio of
all allocations
Aug. (kW h)
Hour ($)
Energy ($)
Costs ($)
Discounts ($)
Netbill ($)
0
0
432
744
744
216
0
0
19336
44663
67117
6177
0
0
$96,257.00
$51,111.00
0
$110,330.00
0
$102,651,00
7
38
35
141.5
126.4
130.2
0.94
1.02
0.91
713.75
713.75
14502.15
31799.81
46976.20
5317.71
0
0
554.52
1208.81
1788.87
214.56
713.75
713.75
13947.64
30591.01
45187.34
5103.15
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
Field/user
code
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
73
to the project. On-request, because of its bias toward the more profitable crops and
enhanced productivity, returned higher benefits to the project relative to the amount of
water supplied. The higher productivity was, however, at the expense of equity. One-time
delivery performed almost as well as on-request in the normal year. The one heavy
dosage of irrigation given to refill the root zone was not beneficial to grain crops in
particular as some fields failed, more so in the dry year. Continuous supply performed no
better than any of the modified rotation strategies; it had slightly lower average waiting
time in the dry year.
7. Conclusions
The study addressed a felt need in run-of-river gravity sprinkle irrigation system. The
strategies developed for managing water allocations using the GSIS computer model
provides a valuable management-decision tool for simulation as well as operation.
In implementing allocations in normal and wet years, on-demand strategy is an obvious
choice since emphasis are on higher monetary benefit to the project and less waiting time.
No attempt should be made to operate on-demand in the dry years. At these times, it is
incumbent on the project to deliver water to all users to satisfy the legal provision of the
water-rights. To such end, continuous supply or rotation strategies facilitate allocations
more equitably, though at the expense of achieving high productivity. Augmentation in a
dry year is not advisable because it results in financial loss unless cheaper energy for
pumping is available.
Acknowledgements
The work reported here enjoyed partial support from the Utah Division of Water
Resources to which we are gratefully appreciative. Gratitude is also expressed to the
President and several members of the Richmond Irrigation Company for granting
unlimited access to their lands for data collection and to the staff of USDA ± NRCS
(formerly SCS) Cache Valley office in Logan for assisting us with construction drawings
of the pipe network. Finally, the skill and patience of Becky Andrus for finalizing the
figures and equations and Peggy Shumway for retyping the revised manuscript is greatly
appreciated.
References
Allen, L. Neil., Hill, Robert W., 1988. Crop irrigation requirement model for Utah. Proceedings: Planning Now
for Irrigation and Drainage in the 21st Century. Specialty Conference of the Irrigation and Drainage
Division. ASCE, Lincoln, NE, pp. 724±731.
Bishop, A.A., Long, A.K., 1983. Irrigation water delivery for equity between user. J. Irrig. Drainage Eng. ASCE,
vol. 109(4). Proc. Paper 18454, December, pp. 349±356.
Doorenbos, J., Pruitt, W.O., 1977. Irrigation water requirements. FAO Irrigation and Drainage Paper 24. United
Nations, Rome, Italy.
74
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
Gilmore Jr., E.C., Rogers, J.S., 1958. Heat units as a method of measuring maturity in corn. Agron. J. 50, 611±
615.
Hansen, Vaughn E., Israelsen, Orson W., Stringham, Glen, E., 1979. Irrigation Principles and Practices, fourth
edn. Wiley, New York, 417p.
Hill, R.W., Hanks, R. John., Wright, James, L., 1984. Crop yield models adapted to irrigation scheduling
programs. Research Report 99, Utah Agricultural Experiment Station. Utah State University, Logan, Utah.
Jensen, M.E., Haise, H.R., 1963. Estima
Strategies for water management in gravity
sprinkle irrigation systems
A.A. Ramalana,*, R.W. Hillb
a
Agricultural Engineering Department, Ahmadu Bello University, Zaria PMB 1044, Nigeria
Biological and Irrigation Engineering Department, Utah State University, Logan, UT 84321-4105, USA
b
Accepted 17 March 1999
Abstract
The study examined various management strategies implementable for equitable allocation of
water among users in a gravity sprinkle irrigation system (GSIS). A computer model was developed
and employed to effect allocations under three scenarios or variations thereof, namely, on-demand,
rotation, and continuous supply. Historical streamflow records and climatic data for 3 years, 1979,
1986 and 1983, representing normal, dry and wet years, respectively, were used. Equitable water
distribution consideration took into account shares of stock for water held by each user in the
irrigation company. Allocations were proportionately determined in relation to the numeric strength
of the users' stock when the demand for water was constrained by the available streamflow. The
developed management strategies were applied to a real-life irrigation project, the Richmond
Irrigation Company at Richmond, UT. Pure on-demand strategy proved to be the most beneficial
project-wide, costs of augmentation notwithstanding. # 2000 Elsevier Science B.V. All rights
reserved.
Keywords: Gravity-sprinkle; On-demand; On-request; Strategies; Water-rights; Users
1. Introduction
The water source for the gravity sprinkle irrigation system provides water as well as the
energy for operating the system. No pumping is required to lift water and pressurize the
line as is the case in a conventional sprinkler system. The water source at certain
mountain top locations is several hundred meters in elevation above underlying farm
* Corresponding author. Tel.: +234-069-50571; fax: +234-069-50563.
E-mail address: aramalan@abu.edu.ng. (A.A. Ramalan)
0378-3774/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 8 - 3 7 7 4 ( 9 9 ) 0 0 0 4 6 - 3
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A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
lands. Thus, the elevation difference provides the pressure energy needed to deliver
irrigation water at the sprinkler nozzle. The system is fed directly with water from rivers
and creeks by the use of simple intake structures in open channels. Typically, these runof-the-river irrigation systems are characterized by absence of any flood detention or
storage structures.
In dry years, as a consequence of low snow pack on the mountain, streamflow in rivers
and creeks resulting from snow melt in the spring are deficient. Coupled with the high
crop water use in the summer, system performance diminishes. Equitable distribution of
water among users constitutes a serious water management problem to irrigation
companies1. Studies by Kaewkulaya (1980); Bishop and Long (1983); Khanjani and Bush
(1983); (Kim et al., 1983) examined methods for water allocation in open-ditch surface
irrigation systems. Information is, however, lacking on techniques for water allocation in
a gravity sprinkle irrigation system (GSIS).
A study to examine management strategies to adopt to effect such allocations was
undertaken. The nine strategies which evolved integrated with hydrological, soil and
climatic factors of the area, crop water use, and the amount of shares held by users in
company stock for water. As part of the study, a computer model to effect allocation was
developed. The model was tested using data from a real-life irrigation project in northern
Utah.
2. Objectives
The general objective of the study was to evolve techniques for improving water
management in gravity sprinkle irrigation systems. The specific objectives include
identifying and evaluating practical management strategies that could be used by GSIS
companies to aid water management. In addition, the study was to compare the attributes
of the various strategies and quantify the benefits associated with each.
3. Procedure
The water available to users in an irrigation company is a common commodity by
virtue of the legal provisions in water rights. Such waters may be either directly from a
diversion of surface source or from groundwater. The challenge for management of
mutual irrigation companies is to translate share of stock values into realistic water
allocations to users that are fair and equitable. Equity is viewed here in relation to
individuals getting their fair share of water. Time is an important element in the allocation
process because crop production occurs in sequential phenological phases that respond to
environmental changes. Water allocated to users must be in amounts and at times
1
Users constitute mutual irrigation companies, granted water-rights through an instrument of State Law to
divert and distribute water to all share holders. The companies assess fees seasonally for each share of water
stock held by the user.
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53
Table 1
A listing of the strategies used for the water allocation studies in gravity sprinkle irrigation system (GSIS) at
Richmond, Utah
Strategy
Composition
Pure on-demand
Unlimited access to water by all users
fields treated as single entities.
Modified on-demand
Users' supply placed on request
One-time delivery
fields treated as single entities.
fields treated as single entities.
Rotation
Users grouped in rotation blocks
Supply based on crop category
Min±max Ranking system
Systems-related strategy
Low labour cost schemes
Continuous supply
Continuous supply to users
contiguous fields as rotation blocks (three blocks)
each crop type forms a block (three blocks)
range in shares of stock, each range constitutes a block (four blocks)
hand-move and wheel-move lateral system each constitute a block
(two blocks)
Off-farm and on-farm users constitute a block each (two blocks)
fields treated singly.
reasonable to make the commodity usable and effective. Various management strategies,
or operational schemes, have been evolved as means to effect delivery to users. Table 1
gives a listing of the strategies used. A description of each strategy is presented below.
Except for the continuous supply strategy, the other strategies under on-demand and
rotation schemes are modified versions of the system used in open ditch irrigation
systems. Allocations based on selected strategy were implemented using the computer
model GSIS, developed as part of the study, which integrated soil, water and
environmental factors. The model and the submodels are illustrated in Fig. 1(a±d).
3.1. Descriptions of the management strategies used in the study
3.1.1. Pure on-demand (unlimited access to water by all users)
This is a strategy that seeks to allow all users, access to water at all times. The
implementation of this strategy is possible early in the season when an ample supply of
water is available and crop water requirements are relatively low. Irrigation durations are
similarly expected to be low. No intensive policing of the system is desirable.
The manner with which users may connect for service is expected to follow a random
pattern. The main constraint anticipated is with the capacity of the system hydraulics to
satisfy demand from users needing water within the same time frame.
3.1.2. Users placed on request
This strategy is a modified demand delivery system. It places some responsibility on
the user. It requires that he made known his request for water in advance of time of use to
allow a sufficient time lag for scheduling and balancing of deliveries and total system
flow rates by the project. Because this strategy allocates water subject to constraint in
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Fig. 1. Flow diagram of gravity sprinkle irrigation system (GSIS) computer allocation model. (b) Flow diagram
of GSIS submodel HYDRA. (c) Flow diagram of GSIS soil-water budget submodel SWBAL. (d) Flow diagram
of GSIS submodel ATTR.
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
55
Fig. 1. (Continued )
supply, the users' request may or may not be honoured at the requested time. Some
waiting may be imminent.
The strategy is particularly expedient during the latter part of the season when water
shortages are expected and irrigation amounts and/or frequencies are likely to be high.
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Fig. 1. (Continued )
Users' requests are likely to be highest during times of critical crop growth stages. While
it may be possible to anticipate incoming requests for water, it may not be possible that
all requests made for deliveries at specific times will be met.
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57
Fig. 1. (Continued )
3.1.3. One-time delivery
This strategy considers supplying the user his allocation of water in a one-time
delivery. The one-time allocation will be estimated based on a quantity of water that
would refill the entire root zone of his crop in a one-time delivery. Users, through mutual
agreements, may trade water among themselves; management must be notified of such
deals in advance of trades.
3.1.4. Users grouped in rotation blocks
Users' holdings are grouped in rotation blocks. Each block is of a pre-determined size
(in hectares). Each user/field in the block is allowed access to a fixed continuous flow
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amount and duration. The frequency is usually fixed, but may also be variable. Individual
users within each block irrigating at the same time are grouped as rotation units. Users
will have allocations figured out relative to their stock shares. Rotations are expected to
be rigid and all were to take their flows only when due. One rotation unit made up of one
or more blocks received water at any one time.
3.1.5. Supply users based on crop category
This strategy invokes the use of crop categories in allocation, taking into consideration
the economic benefits derivable from the array of crops irrigated. Ranking of users' crops
was in effect and allocations were to be along specific crop categories.
First to be allocated water were users who grew crops with the highest economic value,
and so on, to users who grow economically least-derivable-benefit crops, such as pasture.
The strategy is particularly well adapted to periods of diminishing streamflow.
3.1.6. Min±max ranking system
A ranking system was evolved whereby allocations were begun with users who hold
the highest number of shares of stock taking all the flow. This group of users was
followed by the next lower level of users and finally by users who held the least stocks.
When operating under deficit flow conditions, each user at any of the levels will have
water for a time period commensurate with his shares.
3.1.7. Systems-related strategy
This strategy relates to the two major gravity sprinkle irrigation systems, the handmove and the wheel-move lateral systems. Users were classified into the two groups
depending on the type of system each operates.
Allocations using this strategy were along system types, in other words, users operating
wheel moves will be expected to be irrigating at about the same time. The exact time
individuals within system groups are delivered water depended on the overall system
hydraulic analysis.
3.1.8. Low labour cost scheme
This management strategy is invoked whereby certain users are to receive their
allocations during the low labour cost hours. The scheme differentiates on-farm from offfarm users. Under certain circumstances and locations, the cost of irrigation labour to the
farmer is lower during weekday first-shift hours compared to other shifts. The first shift is
between 8 a.m. and 4 p.m. The strategy is to make water available to the farmer during
the least labour cost hours.
Urban and non-agricultural irrigation stockholders who use water for lawn sprinkling
and backyard gardens will have access to water during the second and third shifts on
Saturdays and all three shifts on Sundays.
3.1.9. Continuous supply with monitoring
Continuous supply of water to users is to be maintained day or night as rationed to
users. Each user's ration is to be monitored by estimating and counting the number of
sprinklers he has operating continuously. The rations are available to the user whether or
not they are needed.
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4. The computer model
The GSIS model is developed for use in mutual irrigation companies that operate under
gravity sprinkle systems. The model is comprised of four submodels, the first being the
main programme. The second, third and fourth are designated HYDRA, SWBAL and
ATTR submodels, respectively. The main programme serves the primary function of
controlling programme flow. It also carries out non-repetitive calculations. The submodel
HYDRA provides a work area in which routine calculations of crop water requirements
and the need for irrigation are performed. The submodel SWBAL maintains the soil water
balance sheet for all fields and the ATTR submodel evaluates the attributes of the various
strategies.
The model invokes a strategy to implement allocations, then estimates a field service
priority, and determines sprinkler discharges based on operating pressures at delivery
points. It also uses stored data on soils, crop and climate to compute crop evapotranspiration at various growth stages for maize (field corn), spring wheat, pasture and alfalfa from:
Et Kc Ks Etr
(1)
Where Et is the estimated crop evapotranspiration, Etr is the reference crop
evapotranspiration computed from the Jensen±Haise equation. Kc, the crop coefficient,
is the ratio of the actual crop evapotranspiration to reference crop evapotranspiration. The
value varies with crop variety or species, time of planting, and growth stages. It is
computed by the use of a phenology clock for each crop for the specific Julian day
depending on planting, effective cover and harvest dates. The mean crop coefficients, Kcm
used in the model were adapted from (Allen et al. (1988) based on tabular values
presented by Wright (1981, 1982); Doorenbos and Pruitt (1977) rev.). In the equation, Ks
is the soil moisture stress coefficient. For an irrigation system in which maximum Et is
allowed, Ks 1. The coefficient varies with evaporative demand, soil moisture content,
soil and the crop. This study used the model proposed by (Hill et al., 1984).
The Jensen and Haise (1963) temperature-radiation equation for estimating Etr was
used to program a Datapod (Omnidata International DP 219) to accumulate the calculated
Etr on a daily basis. The data used including air temperature and solar radiation were
sampled at Newton, UT (the nearest weather station to Richmond). Thus,
Etr Ct Cf T ÿ Tx Rs
(2)
where Etr is the reference crop evapotranspiration (mm), T is the average daily
temperature (8C), Tx is the intercept on the temperature axis, Rs is incident solar radiation
(langleys/day), and Ct is a temperature coefficient. Values for Ct and Tx as 0.025 and ÿ3,
respectively, were reported in Hansen et al. (1979). Both factors are site-specific. For this
reason, they further gave a relationship for estimating Ct and Tx for other areas taking into
account altitude above mean sea level and saturation vapour pressures of water for the
warmest month of the year in the location. Allen et al. (1988) gave Ct (in English units) as
0.009 and 0.011, respectively, for valleys with extensive irrigated or wetland areas, and
for surroundings of predominantly arid lands. A fifth power polynomial equation was
derived that best fit the Datapod data relating Etr with day of year. The equation was used
in the model to estimate Etr for the Richmond site.
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The hydraulic network submodel, HYDRA, simulates pressures in the distribution
main pipes, the laterals and sprinkler nozzles. The relationships given in Keller (1986)
were used to estimate average lateral pressures and nozzle discharges using data relating
to pipe type and size, friction head loss coefficient, and allowable head loss due to
elevation changes. It also provided for corrections for environmental and spray
conditions.
The submodel also estimates the allocation time for each user to irrigate with the
allotted volume of water, qt. The allotted volume was estimated by
qt 2:8 a d
(3)
where q is equal to field/user flow capacity (lps); t is equal to time to apply the irrigation
(h); a is equal to field area (ha) and d is equal to gross depth of irrigation (mm)
The time of water application, t, was related to infiltration rate of the soil in order to
prevent surface runoff and/or ponding. Therefore, the application rate, which is only
constrained by the soil infiltration rate, was calculated in the submodel using
i
3600 qs
Sm Sl
(4)
where I is equal to application rate (mm/h); qs is equal to discharge per sprinkler (lps); Sm
equal to lateral spacing along mainline, and Sl is equal to sprinkler spacing along laterals
(m).
Once allocations are completed, programme execution is transferred to submodel
SWBAL, the soil water balance submodel.
The submodel SWBAL maintains a soil±water budget. This is a daily book-keeping
process of where water is in the soil/crop environment. The soil±water budget equation is
SWSn SWSnÿ1 Prn IRn ÿ Etn ÿ DRn
(5)
where SWSn is the soil water content at the end of the present day, SWSnÿ1 was the soil
water content the day before, Prn, Irn, Etn, and Drn are, respectively, the precipitation
amount, irrigation depth, actual crop evapotranspiration and drainage loss for the present
day. Drainage occurred only if SWSn for any day exceeded the field capacity storage of
the soil. The present day n subscript refers to a specific day of the year. In the
development of the submodel, assumptions were made that the soils within the layers
found were homogeneous, infiltration occurred at the same rate in fields, there was no
upward movement of water into the root zone, all farmers (users) used the correct nozzle
sizes on their sprinklers at all times, and the management allowed depletion was 50% of
available water in the root zone (Ramalan, 1988).
As soil water storage capacity is tied to rooting depth, the model uses a root growth
function to estimate crop root depth in relation to time. The function assumes that root
growth progresses linearly from a minimum root depth at the time of planting (or begin
growth in the case of alfalfa) to a maximum root depth value at crop full cover.
Crop yield is estimated by the model using the method of Hill et al. (1984) based on
the ratio of actual to potential transpiration for each growth stage. Influence of
each growth stage has an effect on the estimate because of the multiplicative nature of
the relationship. Crop growth progression through a number of growth stages, was
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
61
estimated using a phenology clock based on growing degree-days proposed by Gilmore
and Rogers (1958).
The submodel ATTR is invoked to evaluate attributes of the various strategies,
including costs, returns, and benefits. In addition, waiting time with respect to elapsed
time before a user receives service, and equitability indices are estimated in this
submodel. The monetary benefit was simply estimated from total returns from sale of
produce minus cost of production. Returns were estimated as
Returns Price per unit weight
Yield
BYP
ha
(6)
where unit weight was based on tonnage or kg. In the case of pasture the unit weight was
replaced by animal unit month (AUM), as 1 AUM 360 kg DM (Scarnecchia and
Kothmann, 1982). Yield was based on production per unit area, tonne/ha. BYP was the
revenue from sale of bye-products, such as wheat straw. All the costs toward production
were partitioned as yield-dependent, constant or fixed, area-dependent, or capital costs.
Thus on-farm total production cost per hectare was estimated as
TC Cy Cc Ca Ck
(7)
where TC is equal to total cost/ha; Cy to yield-dependent costs such as of fertilizers and
fertilizing; swathing and baling for alfalfa; and clipping for pasture. Cc is equal to
constant costs, such as the cost associated with land tax; Ca to area-dependent costs, such
as water assessment and irrigating costs. Ck is equal to capital costs, such as costs
associated with machinery and tools. Its value depends on the investment cost of the item,
interest rate and pay-back period on loan amount.
The submodel ATTR estimated annual cost of capital items using capital recovery
factor CRF, thus,
Annual cost investment cost CRF
(8)
where
CRF
i 1 in
1 in ÿ 1
i is equal to annual interest rate expressed in decimal and n is equal to pay-back period for
the loan sum in years.
The input data for calculations in this routine were stored in ECON.DAT for the four
crop enterprises in the study.
5. Application of the model
5.1. The site
The Richmond Irrigation Company (RIC) project was the site of the study conducted in
the summer of 1986. The project, located in Richmond (418430 N, 1118470 W) in north
Cache County, UT, as shown in Fig. 2, was developed in stages following the company's
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Fig. 2. Location map for Richmond Irrigation Company.
formation in the year 1860 by a group of farmers (users). The sole purpose of the
company was to effect distribution of water among members for irrigation and municipal
uses. The source water is by direct diversion from High Creek, near Richmond. The area
of the watershed contributing flow in the creek is 26.1 km2. From historical records
(1944±1985), the mean discharge at the main diversion gauging station is about 83 lps.
The extreme maximum and extreme minimum discharges ever recorded were 14,000 lps
and 70 lps, respectively.
The users who are the stockholders in the company, own and operate farms within the
project. The profile of stockholders showed that there were 457 of them in the register
who collectively owned 6067 shares. The maximum, average and minimum number of
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63
shares held by stockholders are 229, 13.28, and 1, respectively, and all were acquired as
sprinkle irrigation stock. The farms were flood-irrigated until 1970, when construction of
the gravity sprinkle irrigation system was begun (USDA ± Soil Conservation Service,
Logan, 1974). The RIC had a total of 10,000 ha for which water-rights were granted by
the Utah Division of Water Resources through the Kimball Decree Awards #38. The
priority date for the first right to the company was issued on 1 May 1860. Three other
irrigation companies in the vicinity which also have water-rights on the High Creek are
Coveville, Webster, and Mt. Home.
The interpretation of these awards (Ramalan, 1988) which are in three parts gives RIC
the right to divert 78.4% of the flow in High Creek for all flows between 141.2 lps (5 cfs)
and 1412 lps (50 cfs). If the flow in the creek is greater than 1412 lps (50 cfs) and up to
2613 lps (92.2 cfs), RIC has an additional award to divert 20.2% of flow that is in excess
of 1412 lps (50 cfs). At this 2613 lps (92.2 cfs) flow, which is regarded as maximum ditch
flow, the company by virtue of the two awards has rights to divert a total of 1338 lps
(47.2 cfs). The third award comes into effect if the flow in the creek exceeds 2613 lps
(92.2 cfs). The third award allows the company an additional 20.2% subject to an upper
ceiling of 1984 lps (70 cfs). At the time of study the RIC had not operated any ground
water rights.
5.2. Pumping
Four electrical deep well turbine pumps exist within the project. The pumps with rated
discharges of 60 lps (900 gpm) at heads 80 m (260 ft) were to pump from 30 cm diameter,
98.8 m deep wells. The pumps were located in a fenced pump house in sector four close
to the Logan±Richmond highway. The location was a few hundred meters from the pipe
intake structure across the road. The pumps feed the project mainline which in turn feed
distribution lines servicing different farmers' fields. The pumps were not designed to
serve individual fields rather they feed into the common pipelines arranged in branching
hydraulic network. The study took cognisance of these facilities to include the possibility
of need for flow augmentation by use of ground water.
5.3. Procedure for estimating augmentation and costs
The general procedure used to estimate augmentation requirement and its costs,
especially in relation to strategies 1 and 8 is summarized below. The energy type was
electricity and a Utah Power and Light Company (UPLC), schedule of charges used.
Augmentation requirement was estimated
Qaug DQJd ÿ HQJd
if Qaug > 0
(9)
and
Vaug 8:64 10ÿ3 Qaug
(10)
where Qaug is equal to the required flow augmentation in lps; DQJd is equal to the demand
flow on a particular Julian date in lps; HQJd equal to historical streamflow for the
particular Julian date in lps; Vaug is equal to volume of augmentation in ha m.
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It was anticipated by the project designers that augmentation, if needed, would not
exceed 226.7 lps (8 cfs) even in dry years. Such need is to be met by the output from the
four pumps installed. Each pump was rated at 56.67 lps (2 cfs) and powered by 75 hp
motors connected to three-phase, 415 V power source. The number of pumps needed to
supply augmentation on any day was estimated by (rounding up to next integer)
PUMPN
Qaug
56:67
(11)
i.e., one pump if 0 < Qaug 56:67 lps; two pumps if 56:67 lps < Qaug 113:33 lps;
three pumps if 113:34 lps < Qaug 170:00 lPs; and four pumps if 170:00 lps < Qaug
226:66 lps; where PUMPN is equal to number of pumps operating.
The electric power requirement for the pumps to supply the augmentation flow was
estimated
Power
Qaug h
56:6 Ep
(12)
where Power is equal to required power of electric motor in kW; h to pumping depth in
m; Ep is equal to pump efficiency (expressed in decimal) and Qaug as previously defined.
The energy requirement was calculated as
Energy Power Time
(13)
where Energy and Time were measured in kW h and h, respectively. Both power and
energy were tallied to obtain monthly and seasonal totals. Monthly power and energy
costs were estimated using option A of the UPLC schedule. Monthly bills for
augmentation were estimated in the model by
MNBILL FXCOST SERVCHG MISCOST DEMCOST ENECOSTmn
(14)
where MNBILL is equal to monthly bill in US$; FXCOST is equal to fixed cost
representing amortized costs for wells, motors and pumps, and shelter based 30, 20, and
10 year lives, respectively, at 12% interest rate. All cost details were obtained from the
local equipment dealer. SERVCHG is equal to service charge per connection by the
Utility company. MISCOST is equal to miscellaneous costs, which are associated with
attendance, lubrication and repairs on per 100 h basis for the month. DEMCOST is equal
to UPLC monthly power demand cost based on $8.04/kW, first 100 kW; and $5.33/kW all
additional kW; ENECOST is equal to UPLC monthly energy cost based on 10.0345
cents/kW h first 100 kW h per kW; 5.3803 cents/kW h next 25,000 kW h; and 3.5702
cents/kW h all additional kW h, and mn is subscript referring to the specific month.
Discounts were applied to the monthly bill to obtain the net monthly bill. The discounts
were with respect to term and voltage. Term discounts were not in operation at the time of
the study. Voltage discounts were rated based on power demand and were contingent
upon the customer providing and maintaining the transformer and necessary equipment.
The voltage discount rates operated by UPLC are: $1.17/kW, first 100 kW of power; and
$0.62/kW, all additional kW.
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65
Seasonal bill is a summation of monthly net bill minus off-season costs. The off-season
costs are equipment costs for which payment must be made during and off-irrigation
season. These data were entered in a data file, AUGMENT.DAT for use in the model.
5.4. Farm and field characteristics
The RIC project is in four sectors. Each sector is served by an intake structure that
feeds water into the mainline for the fields in the sector. The data collected for this study
were gathered in the fourth sector which has an area of 251 ha.
For at least the purpose of this study, a field was considered a piece of land with unique
crop, soil, and physical characteristics. The field was, therefore, expected to consist of
one crop on essentially one soil type. The field had physical boundaries based on either
soil or crop differentiation. One or more fields constituted a farm. Records of field sizes
obtained through direct interview with the farmers varied from 2 to 32 ha with a mean of
11 ha.
Soil types defined by textural classification given in the soil survey data of the area
showed that Trenton silty clay loam was the most common. About 70% of the area under
this soil type is cropped with irrigated crops such as alfalfa, small grains, sugar beet, and
pasture. This soil and others elsewhere on the site are moderately well drained though
slowly permeable. Runoff is low and hazards to erosion slight. Water-table depth is
commonly more than 100 cm.
Crops in the project fall within the categories of irrigated or dryland commercial crops.
Their distribution among fields, however, varied with climatic and soil conditions,
economics and farmers preferences. For the 1986 crop year, aerial distribution of crops
among fields in the study area was as follows: alfalfa, 65%; small grain, 13%; silage corn,
9%; and pasture, 13% on land areas of 181, 14, 24, and 32 ha, respectively. About 177 ha,
out of the 251 ha, were on Trenton silty clay loam and Nibley silty clay loam soils.
Water for irrigation was distributed through a branching pipe network. The irrigation
systems in the farms are sprinklers of either hand-move or the periodic wheel-move
systems. Water channelled from the creek in open ditches was fed to the pipe inlet at
canal turnout about 60 m in elevation above the lowest farm delivery points. Most
delivery points were located about 52 m below the elevation of canal turnout. Excess
pressures not used in the pipeline were dissipated at pressure relief valves strategically
located within the network. Pipe sizes of standard lengths of 6 m made from welded steel
or asbestos cement and fittings were joined and buried to constitute the network.
At delivery points, the network terminated to 100 mm stand valves equidistantly
spaced on laterals along fence lines of individuals' properties. Valve openers facilitated
release of water into individual sprinkler systems.
5.5. The model implementation
The computer model was invoked for each of the nine allocation strategies and for the
3 years representing dry (1979), normal (1986) and wet (1983) years. These
representative years were selected from the water-year records of High Creek (October
1978 through September 1987). For these years, the available streamflow diversions to
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A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
the study area, as allowed for by the water rights, varied from 14 lps to a maximum of
178 lps. Daily streamflow data adjusted with water-right awards factor (as a percentage)
represents the allowable diversion due to RIC. These daily estimates were stored in an
array variable HQ in data files CLIM.DRY, CLIM.NOM and CLIM.WET. They were
read for each computer run. Recorded precipitation are also included on a daily basis as
part of the input files. Each computer run called the relevant subroutine after having
previously opened and read all input data files. All the calculations carried out in the subroutines are written in output data files before exiting to the main programme.
6. Results and discussions
For the test years, with allocation on demand, the study showed that it was infeasible to
operate the strategy for allocation without augmentation throughout the growing season.
This is evidently so because demand flow rates on the system outstripped supply in some
instances, as depicted by the hydrographs in Fig. 3 particularly in the flow receding
region where demand-to-supply ratio exceeded 8 : 1. In the normal and wet years, it was
possible to operate on-demand from day of year 101 through Day 135 and Day 175,
respectively. Within these periods demand flows could easily be satisfied by supply. But
the supply hydrograph for the dry year showed significant deficit as to make allocations
on-demand inoperative. Scanty precipitation coupled with low stream flows preclude
operating on-demand except intermittently for some 10 days throughout the growing
season. The model showed that in addition at least one pump needed to be operated
continuously.
Beyond those periods when on-demand allocations were feasible in the normal and wet
year, constraints in delivery were inevitable. From these days onward, on-demand was
viable only to the extent that water supply was augmented through conjunctive water use
by tapping groundwater sources. The total costs for augmentation in order to continue to
operate on-demand were $44,679, $96,257, and $144,735 in wet, normal and dry years
respectively. A substantial proportion of this cost was for energy for pumping. In the only
alternative, as would be the case for most run-of-the-river GSIS with no groundwater
rights, the schedule of allocations has to change to a less flexible system such as rotation
or continuous supply.
The data on seasonal crop water use for the test years for the three strategies are given
in Table 2. The average seasonal actual crop Et's were 760, 510, 580 and 710 mm for
alfalfa, corn, small grain, and pasture, respectively. The number and net depths of
irrigation were highest under the continuous supply strategy. Drainage, estimated by the
model as the component of applied water or rain that had percolated below root zones,
was least with the on-demand mode, where values exceeded 25 mm per season. These
drainage amounts were mainly in corn and grain fields. The seasonal rainfall received in
alfalfa and pasture fields was about 280 mm with about 178 mm on the corn and small
grain fields.
Benefits accrued to individuals were calculated through the itemization of costs and
returns. Crop yield using the technique of Hill et al. (1984) provided vital data for
estimating the financial returns. The fields under pastures sustained financial loss. When
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
Fig. 3. Available and demand flow hydrographs for irrigation on-demand, precipitation, number of pumps for supply augmentation, and number of users irrigating based
on Dry Year (1979) data, RIC.
67
68
Table 2
Summary of water use (seasonal totals) by field/user during a normal year with the on-demand, rotation, and continuous supply strategies invoked
Crop
CARI430
CAR1593
CARI688
CARI836
CARI525
CARI750
CARI142
CARI950
CARI011
CARI066
CARI122
CARI474
CARI299
CARI869
CARI958
CARI481
CARI986
CARI399
CARI640
CARI059
CARI618
CARI181
CARI714
ALFALFA
ALFALFA
S/GRAIN
PASTURE
PASTURE
S/GRAIN
PASTURE
ALFALFA
ALFALFA
ALFALFA
ALFALFA
ALFALFA
ALFALFA
ALFALFA
CORN/SL
ALFALFA
S/GRAIN
CORN/SL
ALFALFA
ALFALFA
ALFALFA
ALFALFA
ALFALFA
Area
(ha)
Rain
(mm)
On-demand
Rotation
No.
of
irrg
Net
irrg
(mm)
Drain
(mm)
RT-Z
depl
(mm)
Crop
Et
(mm)
No.
of
irrg
Net
irrg
(mm)
16
16
16
20
4
8
8
32
6
12
6
12
12
14
10
12
4
4
4
10
20
2.8
2
281.9
281.9
188.0
289.6
281.9
200.7
289.6
281.9
281.9
281.9
289.6
289.6
289.6
281.9
172.7
281.9
175.3
172.7
281.9
292.1
297.2
281.9
289.6
3
3
6
7
6
6
7
2
3
3
3
3
3
3
3
4
6
4
3
3
2
3
3
408.9
414.0
464.8
495.3
416.6
472.4
487.7
436.9
408.9
403.9
406.4
424.2
408.9
408.9
317.5
510.5
467.4
396.2
406.9
411.5
340.4
403.9
401.3
0.0
5.1
83.8
55.9
45.7
91.4
58.4
0.0
2.5
10.2
15.2
17.8
7.6
2.5
5.1
17.8
76.2
50.8
0.0
22.9
0.0
2.5
12.7
61.0
61.0
15.2
2.5
66.0
2.5
15.2
ÿ27.9
63.5
76.2
68.6
53.3
61.0
63.5
33.0
ÿ22.9
15.2
5.1
68.6
71.1
119.4
68.6
71.1
754.4
751.8
584.2
731.5
718.8
584.2
734.1
690.9
751.8
751.8
751.8
751.8
751.8
751.8
518.2
751.8
581.7
525.8
756.9
749.3
756.9
754.4
751.8
10
10
10
10
10
10
10
10
10
10
11
11
10
10
10
10
10
9
9
10
9
9
10
449.6
574.0
398.8
355.6
566.4
317.5
599.4
66.0
571.5
569.0
594.4
594.4
576.6
294.6
452.1
444.5
825.5
538.5
388.6
289.6
396.2
490.2
619.8
Continuous supply
Drain
(mm)
147.3
236.2
243.8
162.6
279.4
208.3
297.2
0.0
221.0
226.1
236.2
238.8
228.6
78.7
137.2
149.9
538.5
200.7
94.0
88.9
106.7
165.1
261.6
Note: NET IRRG: applied water that infiltrated the soil surface; RT-Z DEPL: root zone depletion.
RT-Z
depl
(mm)
170.2
132.1
157.5
127.0
132.1
154.9
119.4
208.3
119.4
129.5
101.6
104.1
114.3
208.3
12.7
177.8
119.4
5.1
177.8
193.0
170.2
144.8
101.6
Crop
Et
(mm)
No.
of
irrg
Net
irrg
(mm)
Drain
(mm)
RT-Z
depl
(mm)
Crop
Et
(mm)
754.4
751.8
500.4
609.6
701.0
464.8
708.7
558.8
751.81
751.8
751.8
751.8
751.8
706.1
502.9
751.8
581.7
515.6
756.9
685.8
756.9
754.4
751.8
16
16
13
16
16
13
16
16
16
16
16
16
16
16
14
16
13
14
16
16
16
16
16
457.2
586.7
419.1
363.2
574.0
325.1
599.4
68.6
581.7
584.2
599.4
609.6
581.7
302.3
533.4
411.5
777.2
510.5
363.2
279.4
370.8
457.2
581.7
137.2
223.5
248.9
152.4
266.7
203.2
287.0
0.0
218.4
228.6
233.7
238.8
221.0
76.2
182.9
129.5
487.7
175.3
81.3
88.9
91.4
139.7
223.5
152.4
106.7
160.0
127.0
129.5
157.5
124.5
208.3
106.7
114.3
91.4
88.9
101.6
208.3
7.6
188.0
119.4
5.1
193.0
193.0
180.3
152.4
101.6
754.4
751.8
518.2
627.4
718.8
482.6
729.0
558.8
751.8
751.8
751.8
751.8
751.8
716.3
528.3
751.8
581.7
513.1
756.9
675.6
756.9
754.4
751.8
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
Field/
user code
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
69
crops were not water-stressed, average benefit to users who engaged in the following
crop enterprises were as follows: alfalfa, $746/ha ($44/tonne); silage corn, $832/ha
($15/tonne); small grains, $281/ha ($474/tonne); and pasture, ÿ$84/ha (ÿ$14/tonne).
With constrained allocations, results showed that benefits accruing to users are lower
and indeed some alfalfa fields returned negative benefits in the dry year. The
aggregated benefits resulting from the use of each strategy are included in Table 3 for
the test years.
The relative ratios of user allocations and stock for water held in the company were
compared to draw inferences regarding equitability of allocations among users. The
results given in Table 2 for the normal year using the strategies showed that some users
received more or less water than their shares of stock would otherwise entitle them to. In
the on-demand mode no restrictions were imposed, each field received as much water as
it needed. Those fields/users that got far less relative to their shares had far more shares
than they needed. While no absolute agreement between the ratios was expected and
obtained with on-demand, the non-flexible strategies attempted to ration water based on
shares of stock.
Waiting time or stress-days for this study was calculated based on number of days since
50% available soil moisture storage was depleted. It varied with strategy used and the test
year. For the on-demand strategy waiting time in the dry, normal and wet years were 11,
7, and 5 days, respectively. Waiting time for other strategies were also estimated. The
durations varied between 28 and 101 days. Waiting time with continuous supply was
shortest, because users received water on a daily basis. Waiting time for all strategies
were longest during the dry year and shortest in the wet year. There was evidently a
relationship between waiting time and crop yield achieved. It appeared that the longer the
waiting time with a given strategy, the more the individual fields are stressed and the less
the crop yields and potential benefits to users.
The resource utilization ratio (RUR), provided a measure of how closely total
allocations to users related to available water resources at the disposal of the company. In
the dry season, RUR amounted to 1.84, thus users required 84% more water in volumetric
terms on a seasonal basis than they had water rights for in order to operate on-demand.
The specific times to inject additional water can be seen on observation of demand and
supply hydrographs, given as Fig. 3. In normal and wet years, the ratios potrayed a
standpoint of sufficiency in meeting seasonal demands; this is to be realized only if
assumption of trading surplus water at the beginning of the season holds. If not,
augmentation from groundwater had to be in effect. To match allocations closely with
what was available, the ratios had to be less than 1.0. The data on Table 3 showed that
RUR ranged 0.32 and 0.94 for the other non-flexible strategies. With one-time delivery
strategy, where only one heavy irrigation was given to refill the root zones, in the normal
year just about 35% of the streamflow was utilized. Augmentation was needed only if
streamflow was low to satisfy the commitment for the one-time delivery.
The data in Table 4 represent the average of five runs and summarize the results of the
response of the irrigation system to all of the allocation strategies in what are described as
`attributes' of the management strategies. On-demand strategy returned the highest
benefit to users only if augmentation is at no cost (such as when water is traded). But, if it
has to be paid for, on-demand in spite of its flexibility is a lower revenue-earning option
70
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
Table 3
A summary of attributes for management strategies implemented in the dry, normal, and wet years (1979, 1986
and 1983), respectively
Strategy
On demand
Unlimited access to waterc
Unlimited access to waterd
Modified demand
User on request
One time deliverye
Rotation
Users in rotation blocks
Among crop categories
Stock ranks
System types
Labor cost scheme
Continuous supply
Continuous supply
a
Season
type
Benefit
$
Wait time
days
Water supplieda
dry
norm.
wet
dry
norm.
wet
143464
153961
154331
ÿ5214
51111
105509
11
7
5
11
7
5
80.9
72.0
87.2
80.7
74.3
89.0
dry
norm.
wet
dry
norm.
wet
64268
89183
136231
5294
84175
117441
74
58
34
101
67
65
90.7
72.0
92.6
46.6
47.8
47.4
dry
norm.
wet
dry
norm.
wet
dry
norm.
wet
dry
norm.
wet
dry
norm.
wet
34203
110330
127400
19651
105760
125414
28757
109227
128314
28280
106015
125889
21426
103073
123639
79
38
29
91
43
37
81
40
35
83
42
38
90
43
38
84.0
126.5
130.4
83.5
123.8
127.4
86.0
127.6
132.1
82.4
126.5
131.0
84.6
125.7
131.3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.84
0.91
0.89
0.83
0.89
0.87
0.86
0.92
0.90
0.82
0.91
0.89
0.85
0.90
0.90
dry
norm.
wet
23841
102651
117763
80
35
28
89.6
130.1
135.6
0
0
0
0.89
0.94
0.93
Stream
RURb
Augm.
103.0
67.2
28.9
103.0
67.2
28.9
0
0
0
24.3
0.85
0.13
1.84
1.00
0.79
1.84
1.02
0.80
0.91
0.52
0.63
0.71
0.35
0.63
Water supplied, measured in ha m.
Resource utilization ratio (RUR), defined as the ratio of water supplied (stream plus augmentation) and
allocated to users to streamflow resource available to project for which water-right is granted.
c
Assumes unlimited access to water, with no cost supply augmentation during times when flow demand
exceeds available supply hydrographs.
d
Augmentation costs included were $144,735, $96,257, and $44,679 for dry, normal, and wet years,
respectively.
e
Augmentation costs included were $38,405, $5,665, and $4,479 for dry, normal, and wet years,
respectively.
b
Table 4
Field/user stock relative to allocation of water received (and expressed in percentage) using on-demand strategy in a normal year
CARI430
CARI593
CARI688
CARI836
CARI525
CARI750
CARI142
CARI950
CARI011
CARI066
CARI122
CARI474
CARI299
CARI869
CARI958
CARI481
CARI986
CARI399
CARI640
CARI059
CARI618
CARI181
CARI714
User
stock (%)
40
51
40
39
12.5
15
26
12
19
38
19
38
38
23
20
27
19
8
8
14
41
7
6.3
User as a ratio of
company stock (%)
7.1
9.1
7.1
7.0
2.2
2.7
4.6
2.11
3.4
6.8
3.4
6.8
6.8
4.1
3.6
4.8
3.4
1.4
1.4
2.5
7.3
1.2
1.1
On-demand
Rotation
User
allocation
(%)
User as a
ratio of all
allocations
(ha m)
User
allocation
(%)
8.4
8.5
10.0
12.6
2.2
5.2
5.1
9.2
3.2
6.4
3.1
6.9
6.8
7.3
4.1
8.2
2.5
2.1
2.2
5.5
9.3
1.5
1.1
6
6
7.1
8.9
1.6
3.7
3.6
13.6
2.3
4.5
2.2
4.9
4.8
5.2
2.9
5.8
1.8
1.5
1.6
3.9
6.6
1
0.8
9.4
12.1
8.4
9.2
3.0
3.2
6.3
2.4
4.5
8.9
4.7
9.1
8.4
4.5
5.3
5.9
4.1
3.3
1.9
2.5
8.4
1.8
1.6
Continuous supply
User allocation
as a ratio of
all allocations
(ha m)
7.5
9.5
6.6
7.3
2.3
2.6
5
1.9
3.6
7
3.7
7.2
6.7
3.6
4.2
4.6
3.3
2.6
1.5
2
4.7
4.7
1.3
User
allocation
(%)
9.6
12.3
8.9
9.5
3.0
3.4
6.4
2.6
4.6
9.1
4.7
9.6
9.2
5.2
6.6
5.4
3.9
2.6
1.8
2.6
6.0
1.7
1.5
User allocation
as a ratio of
all allocations
7.4
9.5
6.8
7.3
2.3
2.6
4.9
2
3.5
7
3.6
7.4
7
4
5.1
4.1
3
2
1.4
2
4.6
1.3
1.2
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
Field/user
code
71
72
Table 4 (Continued )
Month
User
stock (%)
Aug. (ha m)
April
May
June
July
August
September
0
0
9.46
21.85
32.83
3.02
Total vol. of
augmentation
(ha m)
Total aug. cost
Total benefit
to project
Average waiting
time (days)
Total water
allocated (ha m)
Resource
utilization ratio
67.2 0
User as a ratio of
company stock (%)
Vol. (h)
On-demand
Rotation
Continuous supply
User
allocation
(%)
User as a
ratio of all
allocations
(ha m)
User
allocation
(%)
User allocation
as a ratio of
all allocations
(ha m)
User
allocation
(%)
User allocation
as a ratio of
all allocations
Aug. (kW h)
Hour ($)
Energy ($)
Costs ($)
Discounts ($)
Netbill ($)
0
0
432
744
744
216
0
0
19336
44663
67117
6177
0
0
$96,257.00
$51,111.00
0
$110,330.00
0
$102,651,00
7
38
35
141.5
126.4
130.2
0.94
1.02
0.91
713.75
713.75
14502.15
31799.81
46976.20
5317.71
0
0
554.52
1208.81
1788.87
214.56
713.75
713.75
13947.64
30591.01
45187.34
5103.15
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
Field/user
code
A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
73
to the project. On-request, because of its bias toward the more profitable crops and
enhanced productivity, returned higher benefits to the project relative to the amount of
water supplied. The higher productivity was, however, at the expense of equity. One-time
delivery performed almost as well as on-request in the normal year. The one heavy
dosage of irrigation given to refill the root zone was not beneficial to grain crops in
particular as some fields failed, more so in the dry year. Continuous supply performed no
better than any of the modified rotation strategies; it had slightly lower average waiting
time in the dry year.
7. Conclusions
The study addressed a felt need in run-of-river gravity sprinkle irrigation system. The
strategies developed for managing water allocations using the GSIS computer model
provides a valuable management-decision tool for simulation as well as operation.
In implementing allocations in normal and wet years, on-demand strategy is an obvious
choice since emphasis are on higher monetary benefit to the project and less waiting time.
No attempt should be made to operate on-demand in the dry years. At these times, it is
incumbent on the project to deliver water to all users to satisfy the legal provision of the
water-rights. To such end, continuous supply or rotation strategies facilitate allocations
more equitably, though at the expense of achieving high productivity. Augmentation in a
dry year is not advisable because it results in financial loss unless cheaper energy for
pumping is available.
Acknowledgements
The work reported here enjoyed partial support from the Utah Division of Water
Resources to which we are gratefully appreciative. Gratitude is also expressed to the
President and several members of the Richmond Irrigation Company for granting
unlimited access to their lands for data collection and to the staff of USDA ± NRCS
(formerly SCS) Cache Valley office in Logan for assisting us with construction drawings
of the pipe network. Finally, the skill and patience of Becky Andrus for finalizing the
figures and equations and Peggy Shumway for retyping the revised manuscript is greatly
appreciated.
References
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for Irrigation and Drainage in the 21st Century. Specialty Conference of the Irrigation and Drainage
Division. ASCE, Lincoln, NE, pp. 724±731.
Bishop, A.A., Long, A.K., 1983. Irrigation water delivery for equity between user. J. Irrig. Drainage Eng. ASCE,
vol. 109(4). Proc. Paper 18454, December, pp. 349±356.
Doorenbos, J., Pruitt, W.O., 1977. Irrigation water requirements. FAO Irrigation and Drainage Paper 24. United
Nations, Rome, Italy.
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A.A. Ramalan, R.W. Hill / Agricultural Water Management 43 (2000) 51±74
Gilmore Jr., E.C., Rogers, J.S., 1958. Heat units as a method of measuring maturity in corn. Agron. J. 50, 611±
615.
Hansen, Vaughn E., Israelsen, Orson W., Stringham, Glen, E., 1979. Irrigation Principles and Practices, fourth
edn. Wiley, New York, 417p.
Hill, R.W., Hanks, R. John., Wright, James, L., 1984. Crop yield models adapted to irrigation scheduling
programs. Research Report 99, Utah Agricultural Experiment Station. Utah State University, Logan, Utah.
Jensen, M.E., Haise, H.R., 1963. Estima