Calibration of Monthly Spatial Runoff from the Root Zone using Water Balance Method (A Case Study in Cicatih Watershed, Sukabumi, West Java)

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CALIBRATION OF MONTHLY SPATIAL RUNOFF FROM THE ROOT

ZONE USING WATER BALANCE METHOD (A Case Study in Cicatih

Watershed, Sukabumi, West Java)

TEUKU ACHMAD IQBAL

DEPARTMENT OF GEOPHYSICS AND METEOROLOGY

FACULTY OF MATHEMATICS AND NATURAL SCIENCES

BOGOR AGRICULTURAL UNIVERSITY

2006

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ABSTRACT

TEUKU ACHMAD IQBAL. Calibration of Monthly Spatial Runoff from the Root Zone Using Water Balance Method (A Case Study in Cicatih Watershed, Sukabumi, West Java). Under the direction of DANIEL MURDIYARSO.

This study calibrated the monthly spatial runoff from the root zone using simple water balance in Cicatih watershed, Sukabumi, West Java. Soil layer of 10-30 cm was taken to represent the root zone. The method of monthly runoff by Xiong and Guo (1999) was applied. Geographic information system (GIS) was used to estimate spatial and monthly runoff distributions. The result was satisfactory. The value of R2 for Cicatih watershed was 66.15 % and the relative error (RE)

was 1.4 %. It was capable of describing the monthly spatial runoff and had produced quite good estimation. Spatially distributed runoff clearly indicated the influence of rainfall, land cover types, and water holding capacity (WHC). However, monthly runoff was only affected by the rainfall. The runoff contribution from the garden areas was the highest. The lowest contiribution of runoff was found in the grass areas. Monthly runoff from the forest areas was the highest over the year. It was found that runoff increased as the significant increased of rainfall.

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CALIBRATION OF MONTHLY SPATIAL RUNOFF FROM THE ROOT

ZONE USING WATER BALANCE METHOD (A Case Study in Cicatih

Watershed, Sukabumi, West Java)

TEUKU ACHMAD IQBAL

(G 24101023)

Research Report

To fulfill the requirement for a Bachelor Degree in Science

At the Department of Geophysics and Meteorology

Faculty of Mathematics and Natural Sciences

DEPARTMENT OF GEOPHYSICS AND METEOROLOGY

FACULTY OF MATHEMATICS AND NATURAL SCIENCES

BOGOR AGRICULTURAL UNIVERSITY

2006

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Title : CALIBRATION OF MONTHLY SPATIAL RUNOFF FROM THE

ROOT ZONE USING WATER BALANCE METHOD (A Case Study

in Cicatih Watershed, Sukabumi, West Java)

Name : Teuku Achmad Iqbal

Nrp : G 24101023

Approved by:

Supervisor

Prof. Dr. Daniel Murdiyarso

NIP. 130804892

Dean of Faculty of Mathematics and Natural Sciences

Bogor Agricultural University

Dr. Ir. Yonny Koesmaryono, M.Si

NIP. 131473999

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BIOGRAPHY

Teuku Achmad Iqbal was born in Jakarta at August 30, 1983 with parents name Teuku Syarif and Kemala Sari. He has two brothers.

After graduation from the SMA 109 Jakarta in 2001, he was enrolled IPB through the USMI process. He joined the Department of Geophysics and Meteorology, Faculty of Mathematics and Natural Sciences in 2002/2003. He was a member of a student association interested in Agricultural Meteorology, HIMAGRETO. Iqbal was the assistant of Hydrometeorology Practical Class in 2005/2006.

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ACKNOWLEDGEMENTS

Bismillahirrahmanirrahim

Praise and thanks to Allah SWT who has given the author opportunity to carry out and prepare this report and pursue a Bachelor Degree in Meteorology at the Department of Geophysics and Meteorology, Bogor Agricultural University.

The author is grateful to Prof. Daniel Murdiyarso as a supervisor from the Department of Geophysics and Meteorology, Bogor Agricultural University for the patience and helpful comments on the draft of this paper.

The author wish to thank individuals and institutions who contributed to the research: 1. Mr Idung Risdiyanto M.Sc and Mr Heny Suharsono MS as the examiners.

2. Parents and brothers for their support and prayers.

3. The members of research team in Hydrometeorology Laboratory. 4. CIFOR for providing research facility and fund.

5. All of the lecturers and staff at Department of Geophysics and Meteorology. 6. My classmates in the Department Geophysics and Meteorology.

7. Lux Style and Wisma Galih crew.

8. Everyone who gives contribution and support for the author.

Advices and comments are really needed to make this report much better. Finally, the author hopes that this report will be useful for others.

Bogor, March 2006

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Page

LIST OF FIGURE………..…….……….….…vi

LIST OF TABEL……….………..………..……..vi

LIST OF APPENDICES………...vi

I. INTRODUCTION 1.1 Background………..…..1

1.2 Objective………..….….1

II. LITERATURE REVIEW 2.1 Rainfall-runoff methods………...…..…....1

2.2 Total runoff………..………..…………1

2.3 Relationships between rainfall and runoff………..…..…….1

2.4 Relationships between runoff and land covers………….…...2

2.5 Relationships between runoff and soil characteristic ….………...2

2.6 Calibration criteria………...…….2

III. MATERIALS AND METHODS 3.1 Study area……….………..…...3

3.2 Software and Data requirements….………..……...3

3.3 Methods……….………..…...5

IV. RESULTS AND DISCUSSION 4.1 Water balance components………….………..………...9

4.2 Runoff distributions of Cicatih watershed…………..………..……...11

V. CONCLUSIONS AND SUGGESTION 5.1 Conclusions………...17

5.2 Suggestion………..….……...17

VI. REFERENCES………..…………...17

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List of Table

Page

1. Rainfall-runoff relationships in the Western Ghats in South India .……..………..…..……2

2. Land cover types of each subwatershed..………..…………..………...5

3. Percent of land covers interception in various locations………....7

4. Water balance of each subwatershed (mm)………..…………..………..10

5. Monthly runoff distributions in Cicatih watershed, Sukabumi……..….….…..………..………13

List of Figure

1. The study area……….………..………..………….………..….4

2. Map of Rainfall stations and their polygons ....………..4

3. Conceptual of water balance method…...5

4. Flowchart of monthly spatial runoff calculation………….…………....….………….……..…...8

5. The observed and calculated monthly runoff hydrograph of Cicatih watershed, Sukabumi in 1999..………..………...11

6. Predicted flow directions using PC Raster …….……….12

7. Predicted runoff accumulation in January using PC Raster and their stream orders…….……..12

8. Stream orders of Cicatih watershed, Sukabumi………..……….13

9. Calculated monthly spatial runoff distributions in January-April……….……….…………..…14

10.Calculated monthly spatial runoff distributions in May-August………15

11. Calculated monthly spatial runoff distributions in September-December…………...……....16

List of Appendices

1. Map of Soil Types in Cicatih watershed ………...21

2. Mean of monthly temperature during 1988-1999 periods………22

3. Monthly rainfall of 1999 in Cicatih watershed………. ………...23

4. Area rainfall of Cicatih watershed estimated using Thiesen Polygon ………..…………...24

5. Digital Elevation Model (DEM) (m)….………...25

6. Map of 34 disturbed soil sampling points in Cicatih watershed …..…….………..25

7. Map of water holding capacity (WHC) in Cicatih watershed ……….………26

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I. INTRODUCTION

1.1 Background

Watershed hydrological processes are complicated and widely affected by climatic and physiographic factors that vary in time and space (Mehrota and Singh 1998). Knowledge about hydrological processes has become important because water has turn out to be scarce resource in some areas (Ladekarl 1998). Simple conceptual water balance methods are useful for water resources planning and management, and for use in forecasting (Xu 1999). Several water balance methods on rainfall-runoff relationship have been developed based on conceptual representations of the physical processes in entire watershed area (Madsen 2000). Simulation of hydrograph of streamflow using simple water balance methods would be a valuable tool in watershed management (Xu 1997). An application of Geographic information system (GIS) can be used in describing spatial and temporal variability (Kurnianto 2004). GIS could offer those capabilities for the efficient integration of spatial variation in hydrology (Adhikari 2003).

In Cicatih watershed, water demand for agricultural, industrial competes with the needs for direct household. For that reason, well-envisioned and management of watershed are needed to enhance and maintain their hydrological services from the processes. In this paper, the hydrological processes of watershed are described as monthly spatial runoff from the root zone using simple water balance method. The monthly spatial runoff is applied in 1999 period. Soil layer of 10-30 cm is taken to represent the root zone. GIS is used to estimate spatial and monthly runoff distributions.

1.2 Objective

The objective of the study is to calculate and calibrate the monthly spatial runoff from the root zone using simple water balance method in Cicatih watershed, Sukabumi, West Java.

II. LITERATURE REVIEW

2.1 Rainfall-runoff methods

In general, the study of the water balance methods typically used in rainfall-runoff assessment and planning have been developed based on conceptual representations of the physical processes (lumped conceptual type of models). Lumped conceptual models are computationally efficient and provide the solutions to many hydrological related problems (Mehrotra and Singh 1998). Examples of this type are proposed by several studies, such as: Khan (2002) applied two storages, Mehrotra and Singh (1998) developed models with four storages, Xu (1997) used ones storage, Abulohom (2001) used ones storage and two functions to find simulated runoff, and Makhlouf and Michel (1994) with their two parameters. In addition, Madsen (2000) studied the performance of conceptual rainfall-runoff models. The results showed that the traditional concept of automatic model calibration is inappropriate.

2.2 Total runoff

As shown in several rainfall-runoff methods, the total runoff which is determined by the runoff components is considered as the streamflow. For example: Xu (1997) describes the total runoff as the streamflow, which was calculated by summing two runoff components: fast runoff and slow runoff. Fast runoff was described as the surface runoff and slow runoff was being similar to baseflow.

In the method of the models proposed by Mehrotra and Singh (1998), historical streamflow data was used as the historical runoff to judge the models performance. For the soil conservation service (SCS) model, runoff is considered to be made up of two components: surface runoff and Baseflow. The present calculation considers Ro as the only component for calculating the total runoff and uses streamflow data as observed runoff to judge the model performance. In accordance, Khan (2002) have validated their model by using the observed streamflow data as the observed total runoff data.

2.3 Relationships between rainfall and runoff

Numerous investigations described that runoff increases as well as the significant increase of rainfall intensity. For example, Putty and Prasad (2000) in the Western Ghat in South India (see Table. 1). Lewis (2000) in a California oak woodland watershed found

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that peak monthly effective rainfall corresponded to peak monthly runoff. Furthermore, a review of rainfall-runoff relationships is supported by previous researches, such as: Xu (1997), Xu and Singh (1998), Strasser and Mauser (2001), and Li (2005).

Table 1. Rainfall-runoff relationships in the Western Ghats in South India

Watersheds Rainfall (mm) Observed Runoff (mm) HonamanaHalla YettinaHole KonganaHole Lakshmanatirtha Malathi Harangi Hemavathi 1447 3044 2461 2429 5660 3177 2888 895 2099 1639 1667 4701 1929 1959

Source: Putty and Prasad 2000

2. 4 Relationships between runoff and land covers

A long term study in the Weser catchments, Germany showed that maximum runoff occurs in the mountainous regions (600 mm), where intensively covered by forest followed by settlements (400 mm) due to their small actual evapotranspiration (AET) and infiltration capacity (Strasser and Mauser 2001). A study in Lestijoki catchment, Finland reported that forests areas contribute greater runoff than peat and field, because forests were the most common land cover types in the catchments (Karvonen 1999). Hence, the relationship between land cover and runoff has also shown in Kurnianto (2004).

Management of wetland forest on cypress-pine flatwoods in the southern United States described runoff from the maximum disturbance watershed was significantly higher but reduced from 150 - 65 % after the management was undergone (Sun 2001). In the investigation of forest conversion from

eucalypts to Pinus radiata by Putuhena and Cordery (2000) showed that runoff decreased as the plantation grew. Research in South Island, New Zealand described an estimated reduction in runoff of 340 mm within 5 years at one of their catchments studied (Fahey and

Jackson 1997). Calder (2002) gained a new understanding of evaporation from forests in dry and wet conditions based on process studies. Those studies indicate decreased runoff from areas under forest as compared with areas under shorter crop. However, cloud forest and very old forest was excluded from the description above. Kaimowitz (2004) argued that the water falling will be grater infiltrated than quickly running off in the well established forest cover. Studied by Sun (2002) in tree forest ecosystem in the Southern US reported that runoff/rainfall ratio was greater in upland than in wetland areas. A studied that had examined runoff-dependent of forest types by Ollinger (1998) described that runoff was generally higher for hardwood than coniferous forest. In addition, the Mountain Ash species (Eucalyptus regnans)

showed the affect between forest age and catchments water balance, where annual runoff increased from 429 mm at age 15 years to 889 mm at age 240 years (Vertessy 2001). Another studied in Mountain Ash shows that runoff was smaller when the regenerating forest was aged 13-16 years (Cornish and Vertessy 2001).

2. 5 Relationships between runoff and soil characteristic

Texture is one of soil characteristic that affect runoff through its influenced to the depth of vegetation root (Kurnianto 2004). Previous study in La Copita, Texas, United States reported by Fernandes-Illescas (2001) figured that runoff constituted a negligible portion of the waterbalance at their site and its variability within the soil triangle appears to follow gradients in mean soil moisture, for example: clay soils with higher mean values of soil moisture were associated with larger amounts of runoff. Hence, Karvonen (1999) found that various texture types in agricultural regions contribute small runoff portion.

2. 6 Calibration criteria

The criterion of Nash-Sucliffe (1970) had been used in numerous rainfall-runoff studied, for example: Xiong and Guo (1999) and Mehrota and Singh (1998) used the Nash-Sucliffe criterion to judge the model performance on the basis of comparison between the calculated and historical runoff data, Karvonen (1999) used as an optimization criterion. Johansson and Chen (2005) used the Nash-Sucliffe criterion as one of their criteria to evaluate the model performance. Vandewiele (1992) used the transformation

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CALIBRATION OF MONTHLY SPATIAL RUNOFF FROM THE ROOT

ZONE USING WATER BALANCE METHOD (A Case Study in Cicatih

Watershed, Sukabumi, West Java)

TEUKU ACHMAD IQBAL

DEPARTMENT OF GEOPHYSICS AND METEOROLOGY

FACULTY OF MATHEMATICS AND NATURAL SCIENCES

BOGOR AGRICULTURAL UNIVERSITY

2006

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ABSTRACT

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CALIBRATION OF MONTHLY SPATIAL RUNOFF FROM THE ROOT

ZONE USING WATER BALANCE METHOD (A Case Study in Cicatih

Watershed, Sukabumi, West Java)

TEUKU ACHMAD IQBAL

(G 24101023)

Research Report

To fulfill the requirement for a Bachelor Degree in Science

At the Department of Geophysics and Meteorology

Faculty of Mathematics and Natural Sciences

DEPARTMENT OF GEOPHYSICS AND METEOROLOGY

FACULTY OF MATHEMATICS AND NATURAL SCIENCES

BOGOR AGRICULTURAL UNIVERSITY

2006

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Title : CALIBRATION OF MONTHLY SPATIAL RUNOFF FROM THE

ROOT ZONE USING WATER BALANCE METHOD (A Case Study

in Cicatih Watershed, Sukabumi, West Java)

Name : Teuku Achmad Iqbal

Nrp : G 24101023

Approved by:

Supervisor

Prof. Dr. Daniel Murdiyarso

NIP. 130804892

Dean of Faculty of Mathematics and Natural Sciences

Bogor Agricultural University

Dr. Ir. Yonny Koesmaryono, M.Si

NIP. 131473999

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BIOGRAPHY

Teuku Achmad Iqbal was born in Jakarta at August 30, 1983 with parents name Teuku Syarif and Kemala Sari. He has two brothers.

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ACKNOWLEDGEMENTS

Bismillahirrahmanirrahim

The author wish to thank individuals and institutions who contributed to the research: 1. Mr Idung Risdiyanto M.Sc and Mr Heny Suharsono MS as the examiners.

2. Parents and brothers for their support and prayers.

3. The members of research team in Hydrometeorology Laboratory. 4. CIFOR for providing research facility and fund.

5. All of the lecturers and staff at Department of Geophysics and Meteorology. 6. My classmates in the Department Geophysics and Meteorology.

7. Lux Style and Wisma Galih crew.

8. Everyone who gives contribution and support for the author.

Advices and comments are really needed to make this report much better. Finally, the author hopes that this report will be useful for others.

Bogor, March 2006

(17)

Page

LIST OF FIGURE………..…….……….….…vi

LIST OF TABEL……….………..………..……..vi

LIST OF APPENDICES………...vi

I. INTRODUCTION 1.1 Background………..…..1

1.2 Objective………..….….1

II. LITERATURE REVIEW 2.1 Rainfall-runoff methods………...…..…....1

2.2 Total runoff………..………..…………1

2.3 Relationships between rainfall and runoff………..…..…….1

2.4 Relationships between runoff and land covers………….…...2

2.5 Relationships between runoff and soil characteristic ….………...2

2.6 Calibration criteria………...…….2

III. MATERIALS AND METHODS 3.1 Study area……….………..…...3

3.2 Software and Data requirements….………..……...3

3.3 Methods……….………..…...5

IV. RESULTS AND DISCUSSION 4.1 Water balance components………….………..………...9

4.2 Runoff distributions of Cicatih watershed…………..………..……...11

V. CONCLUSIONS AND SUGGESTION 5.1 Conclusions………...17

5.2 Suggestion………..….……...17

VI. REFERENCES………..…………...17

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List of Table

Page

1. Rainfall-runoff relationships in the Western Ghats in South India .……..………..…..……2

2. Land cover types of each subwatershed..………..…………..………...5

3. Percent of land covers interception in various locations………....7

4. Water balance of each subwatershed (mm)………..…………..………..10

5. Monthly runoff distributions in Cicatih watershed, Sukabumi……..….….…..………..………13

List of Figure

1. The study area……….………..………..………….………..….4

2. Map of Rainfall stations and their polygons ....………..4

3. Conceptual of water balance method…...5

4. Flowchart of monthly spatial runoff calculation………….…………....….………….……..…...8

5. The observed and calculated monthly runoff hydrograph of Cicatih watershed, Sukabumi in 1999..………..………...11

6. Predicted flow directions using PC Raster …….……….12

7. Predicted runoff accumulation in January using PC Raster and their stream orders…….……..12

8. Stream orders of Cicatih watershed, Sukabumi………..……….13

9. Calculated monthly spatial runoff distributions in January-April……….……….…………..…14

10.Calculated monthly spatial runoff distributions in May-August………15

11. Calculated monthly spatial runoff distributions in September-December…………...……....16

List of Appendices

1. Map of Soil Types in Cicatih watershed ………...21

2. Mean of monthly temperature during 1988-1999 periods………22

3. Monthly rainfall of 1999 in Cicatih watershed………. ………...23

4. Area rainfall of Cicatih watershed estimated using Thiesen Polygon ………..…………...24

5. Digital Elevation Model (DEM) (m)….………...25

6. Map of 34 disturbed soil sampling points in Cicatih watershed …..…….………..25

7. Map of water holding capacity (WHC) in Cicatih watershed ……….………26

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I. INTRODUCTION

1.1 Background

1.2 Objective

The objective of the study is to calculate and calibrate the monthly spatial runoff from the root zone using simple water balance method in Cicatih watershed, Sukabumi, West Java.

II. LITERATURE REVIEW

2.1 Rainfall-runoff methods

2.2 Total runoff

2.3 Relationships between rainfall and runoff

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Table 1. Rainfall-runoff relationships in the Western Ghats in South India

Source: Putty and Prasad 2000

2. 4 Relationships between runoff and land covers

2. 5 Relationships between runoff and soil characteristic

2. 6 Calibration criteria

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before applying such a criterion and many more. Another criterion in the rainfall-runoff study is the Xiong and Guo (1999) relative error, which describe relative error of the volumetric fit between the observed runoff series and the calculated series.

III. MATERIALS AND METHODS

3. 1 Study Area

The Cicatih watershed is located between latitude 6o 42’ 54’’ - 7o 00’ 43’’ south and longitude 106o_{39’ 8’’ – 106}o_{57’ 30’’ east the} Sukabumi district of west Java province, covering an area of 464.45 km2. Altitude varies from 200 m a.s.l in downstream areas to 3000 m a.s.l in mountain Pangrango. Mean annual rainfall exceeds 2000 mm. Maximum rainfall occurs in the month of November. Mean, maximum and minimum monthly temperatures of 25.5, 24.0, and 28.2 0C respectively, characterized tropical areas. Maximum temperature occurs in May during the dry period in the summer. Brown Latosol is the most common soil type of the Cicatih watershed (Appendix 1). The soil parent materials, which covered 60% of total areas, are tuf volkan intermediers (Kurnianto 2004).

Cicatih watershed area includes five subwatersheds: Cicatih hulu subwatershed (99.17 km2), Cipalasari subwatershed (92.68 km2), Cileuleuy subwatershed (92.24 km2), Ciheulang subwatershed (158.94 km2), and Cikembar subwatershed (23.98 km2). The study before (Kurnianto 2004) shown that

forest located at upper area around the mountainous region (Salak mountain and Pangrango mountain). Only a small area of forest located at center of watershed which exactly placed inside the Walat mountain area. General information about vegetation characteristic of each subwatershed is presented in Figure 1 and Table 2.

3. 2 Software and Data requirements

3. 2. 1 Software: Microsoft office, Arc/View 3.3, PC Raster.

3. 2. 2 Data requirements:

Time series data: mean of monthly temperature during 1988-1999 periods (Appendix 2) and monthly rainfall of 1999 (Appendix 3). Thiesen polygon is applied to compute monthly areal rainfall (Appendix 4). Rainfall missing data is filled by using the inverse distance weighted (IDW) interpolation.

Spatial data: Composite map of 1999 at 1:25.000 scale, Rainfall stations map (Figure 2), Soil observation map at 1:250.000 scale, and Digital Elevation Model (DEM) with 100 m resolution (Appendix 5).

Field data: Disturbed soil sample from 34 sampling locations in Cicatih watershed (Appendix 6). At each location disturbed soil sample is taken at 10-30 cm. Disturbed soil sample is used to find the water holding capacity (WHC) (Appendix 7).

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Figure 1. The study area.

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Table 2. Land cover types of each subwatershed Land-Cover Cicatih Hulu (%) Cipalasari (%) Cileuleuy (%) Ciheulang (%) Cikembar (%) Forest Shrub Cropland Grass Garden Ricefield Settlement Waterbody 15.34 7.08 15.36 0.11 18.33 28.52 15.22 0.04 13.1 7.52 11.27 0.14 44.89 11.72 11.35 - 12.7 9.6 38.08 0.34 22.19 7.03 10.06 - 25.69 12.89 8.04 0.19 12.47 27.88 12.84 - - 1.74 16.63 0.6 58.62 6.77 14.50 - Source: Modified from Pawitan (2005).

3. 3 Methods

The monthly spatial runoff was developed by using PC Raster based on the equation 1 to 12 (Appendix 8). The Ascii file which was imported from Arc/View 3.3 was used as PC Raster input maps. Finally, the result was calibrated based on equation 13 to 17 by using Microsoft Excel.

3. 3. 1 Method description

The method which was applied in the root zone has only one soil water storage: Soil water content (SWC) as show in schematic diagram present in Figure 3. When rainfall (P)

fall reaching the ground, actual evapotranspiration (AET) takes place and the rest part fill the soil water content (SWC). The maximum capacity of soil moisture storage is the water holding capacity (WHC). Rainfall in excess of this capacity results in soil moisture surplus (SMS) then SWC have similar water content with WHC.

As described before, the only input is rainfall. Several processes convert rainfall into actual evapotranspiration (AET), soil water content (SWC), and soil moisture surplus

(SMS). Finally, runoff (Ro) flows as the output.

AET P

SMS

SWC Ro

WHC

Figure 3. Conceptual of water balance method.

3. 3. 2 Actual Evapotranspiration (AET) and Potential Evapotranspiration (PET)

When SWC larger than WHC, AET is assumsed same as the potential evapotranspiration (PET):

AET = PET, if SWC

≥

WHC (1) and

AET = PET

×

SWC/WHC

If SWC<WHC (Arnell 1999) (2)

Where: WHC is water holding capacity, which is derived from the texture by using the table of provosional water holding capasities with different combinations of soil and vegetation in Thornthwaite and Mather (1957).

To calculate PET, Thornthwaite method (1948) in Burt and Shahgedanova (1998) which only need temperature data was used:

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a=0,49+(17,9

×

10-3)I–(77,1

×

10-6)I2+ (67,5

×

10-8)I3 (4)

I =

∑

Des

Jan

T/5)1.516

( (5)

Where: T is temperature, i (Subscript) is monthly time step, and I is heat index. Thus,

PET is used to calculate efective rainfall (Pef):

Pef = Pn – PET (6)

Where: Pn is nett rainfall which is counted as follow:

Pn = P * Ic (7)

Where: Ic is rainfall proportion after interception occurred (%). The Ic values is showed in Table 3.

3. 3. 3 Soil water content (SWC), Soil moisture defist (SMD), and Soil moisture surplus (SMS)

When SWC<WHC the soil water content is counted by using formula:

SWC= SWCi + Pef (8)

If Pn is smaller than PET (Pef = 0), the formula of SWC is present below:

WHC Pef ie

SWC

SWC= (9) Where: WHC is maximum capacity of SWC,

and SWCi is initial soil water content.

and soil moisture defisit (SMD) occurs as:

SMD = PET – AET (10)

(Thornthwaite and Mather 1957). When SWC larger than WHC, the excess of water is called the soil moisture surplus

(SMS) and SWC is similar to WHC. SMS is counted as follow:

SMS = SWC - WHC (11)

(Thornthwaite and Mather 1957).

3. 3. 4 Runoff (Ro)

The calculation of the monthly runoff described by Xiong and Guo (1999) was used:

Ro= SWC

×

tanh(c

×

(SWC/WHC)) (12) Where: c is the coeficient.

Based on description 3.3.1 to 3.3.3, there were two parameters: WHC with the unit of millimeter, and c which is calibrated using observed discharge data. Whole steps of the montlhy spatial runoff calculation is showed in flowchart (Figure 4).

3. 3. 5 Calibration

The Nash-Sucliffe criterion (Nash and Sutcliffe 1970) in Xiong and Guo (1999) was used as the first criterion to judge the calculation result on the basis of comparison between the calculated and historical runoff data, below: 100% F F F R o o

2₌ − _×

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(

)

c i

o Q Q

F =

∑

− (14)

(

)

∑

− = i 2 i i Q Q

F ˆ (15)

/Nc Q Q Nc 1 i i

c ⎟⎟

⎠ ⎞ ⎜ ⎜ ⎝ ⎛ =

∑

= (16)

Where: R2 (%) is used to justify the calculation result. Qi, Q_c, Fo, F are observed runoff, the mean value of the observed runoff, sum of squared deviations, and F is the sum of squared discrepancies, respectively. The Value of R2 is always expected to approach unity for a good calculation.

The second criterion used was the Xiong and Guo relative error (RE). The relative error of the volumetric fit between the observed runoff series and the calculated series, which is defined by:

RE=

∑

(Qi–Q^i)/

∑

×

100%

(17) The value of RE (%) is expected to be close to zero for a good calculation of the total volume of the observed runoff series.

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3. 3. 6 Parameters optimization

In order to optimize the parameters, Xiong and Guo (1999) procedures were adjusted. The procedures of consists of two steps. Firstly, optimize the parameters c and

WHC according to the criterion RE, to achieve a good calculation of total runoff volume. Secondly, optimize the parameter WHC again

according to the criterion R2, with the value of

c obtained in the first step remaining fixed, to further achieve the good fit of shape of runoff hydrograph. The two-step optimization procedure can help to reduce the effects of the inter-relationship between the two parameters on the calibration (Xiong and Guo 1999).

Table. 3 Percent of land covers interception in various locations

Land cover Location P (mm)

Interception (%)

Year Source

Hardwood Canada 213.8 19.3 1995

Caryle-Moses & Price (1999)

Agroforestry Kenya 1583 10.4 1994 Jacson

(2000) Corn, Rice,

casava West Java 1577 18 1995

Corn, Casava West Java 1642 8 1999

Dirk & Bruijnzeel (2001) Nature Forest Kalimantan 2199 11.4 1999

Afforestation

area Kalimantan 3563 6.2 1993-1994

Asdak (1998)

Wheat - - 7 1994-1995 Lull (1964)

Nature Forest West Java - 21 1980-1981 Calder (1986) Source: Modified from Kurnianto (2004).

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Start

P[t,nrow,ncol];PET[t,nrow,ncol] WHC[nrow,ncol]

m=m+1

y=y+1

x=x+1

Pn(m,y,x) = R(m,y,x) * Ic

Pef(m,y,x)=Pn(m,y,x)-PET(m,y,x)

SWCi(m,y,x)=SWC(m-1)

no yes

Pef(m,y,x)>0

SWC(m,y,x)=SWCi(m,y,x)exp(Pef(m,y,x)/WHC(m,y,x)) SWC(m,y,x)=SWCi(m,y,x)+Pef(m,y,x)

AET(m,y,x)= PET(m,y,x)*SWC/WHC(m,y,x) AET(m,y,x)=PET(m,y,x)

SMS(m,y,x)=0 SMS(m,y,x)=SWC(m,y,x)-WHC(y,x)

SMD(m,y,x)=PET(m,y,x)-AET(m,y,x) SMD(m,y,x)=0

Ro(m,y,x)=SWC(m,y,x)tanh(c*SWC(m,y,x)/WHC(m,y,x))

SWCi+1(m,y,x)=SWC(m,y,x)-SMS(m,y,x)

x=ncol

y=nrow

m=t

SWC[t,nrow,ncol];SMS[t,nrow,ncol]; SMD[t,nrow,ncol];Ro[t,nrow,ncol];

End

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IV. RESULTS AND DISCUSSIONS

To fully describe the performance of monthly spatial runoff, the result had been calibrated with the observation data using the Nash-Sucliffe criterion (R2) and the Xiong and Guo relative error (RE). The value of R2 for Cicatih watershed was 66.15 % and the RE

was 1.4 %.

The result was capable of describing the monthly spatial runoff. So it is possible to utilize the result for learning the runoff processes in the Cicatih watershed.

4. 1 Water balance components

The water balance components of the Cicatih are summarized as follows: Rainfall ranged between 77 mm in July and 378 mm in January. Peak of rainfall was 378 mm in January. Maximum AET was 113 mm in May due to the highest PET occurance. Minimum

AET was 65 mm in September due to the lowest SWC occurance. PET varied from 96 mm in February to 113 mm in May. PET

increased as the increased of temperature (T). Mean values of SWC was 291 mm. SWC

varied from 152 mm in September to 437 mm in January depended on the rainfall. SMS

occurred during the high rainfall period between Oktober and June. SMS ranged from 19 mm in June and 241 mm in January. SMS

increased as the increased of rainfall. SMD

occurred during the low rainfall period between July and September. SMD had a small ranged from 19 mm in July to 38 mm in September due to small difference between

PET and AET. Mean, maximum, and minimum runoff are 135 mm, 261 mm, and 36mm, respectively. Maximum runoff was 260 mm occurred in January and minimum runoff was 35 mm occurred in September.

Rainfall, AET, PET, and runoff of each subwatersheds are summarized in Table 4.

AET varied from 59 mm in Cicatih hulu subwatersheds to 130 mm in Cikembar subwatershed. Maximum PET was 130 mm found in Cikembar subwatershed and minimum PET was 88 mm found in Ciheulang subwatershed. SWC varied from 120 mm in Cikembar subwatershed to 453 mm in Ciheulang subwatershed. SMS ranged from 3 mm in Ciheulang subwatershed 274 mm in Cikembar subwatershed. SMD ranged from 18 mm in Cipalasari, Cileuleuy, and Ciheulang subwatershed to 46 mm in

Cikembar subwatershed. The highest and lowest values of mean rainfall were 244 mm occurred in Cipalasari subwatershed and 220 mm occurred in Cikembar subwatershed. Maximum runoff was 263 mm found in Ciheulang subwatershed in January. Minimum runoff was 26 mm found in Cikembar subwatershed during the lowest rainfall occurance in September.

4. 1. 1 Cicatih Hulu subwatershed

Mean AET, PET, rainfall, and runoff were 91 mm, 99 mm, 228 mm, and 133 mm, respectively. Maximum AET was 109 mm occured in May. Maximum PET was 109 mm occured in May. SWC varied from 144 mm in September to 428 mm in January. Peak of rainfall took places in January was 456 mm.

SMS ranged from 28 mm in June to 250 mm in January. SMD ranged from 21 mm in July to 40 mm in September. Runoff varied from 33 mm in September to 260 mm in January.

4.1. 2 Cipalasari subwatershed

Maximum AET was 115 mm occured in May and minimum AET was 69 mm occured in September. Mean values of AET was 98 mm. PET had its maximum value (115 mm) in May. Maximum SWC was 438 mm occurred in January and minimum SWC was 152 mm occurred in September. Maximum rainfall, which was the highest rainfall occurance among the subwatersheds, occured in October with the value of 503 mm. Mean values of rainfall was 244 mm. SMS ranged from 17 mm in June to 239 mm in January. SMD

ranged from 18 mm in July to 37 mm in September. Mean values of runoff was 133 mm. Maximum runoff was 259 mm in January, followed by February 231 mm.

4. 1. 3 Cileuleuy subwatershed

AET varied from 76 mm in September to 126 mm in May. Mean values of AET was 107 mm. Maximum PET was 126 mm occured in May. SWC varied from 141 mm in September to 427 mm in January. Mean value of rainfall was 231 mm. Mean value of SMS was 109 mm. SMS ranged from 28 mm in June to 250 mm in January. Mean Value of SMD was 7 mm. SMD ranged from 18 mm in July to 41 mm in September. Mean values of runoff was 132 mm. Runoff was well varied. Maximum runoff was 259 mm occured in January.

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Table 4. Water balance of each subwatershed (mm)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Cicatih Hulu P AET PET SWC SMS SMD Ro 456 94 94 428 250 0 260 402 93 93 399 221 0 232 239 99 99 330 152 0 167 284 106 106 303 126 0 143 189 109 109 252 75 0 101 160 101 101 206 28 0 66 90 75 96 174 0 21 48 82 64 96 157 0 32 39 97 59 100 144 0 40 33 336 101 101 328 150 0 166 199 99 99 332 155 0 169 207 95 95 331 154 0 168 Cipalasari P AET PET SWC SMS SMD Ro 395 100 100 438 239 0 259 398 99 99 409 210 0 231 270 105 105 340 141 0 166 215 113 113 314 115 0 144 155 115 115 263 64 0 103 184 107 107 216 17 0 69 86 85 102 185 0 18 51 123 74 102 167 0 28 42 107 69 106 152 0 37 35 503 107 107 337 139 0 164 235 105 105 343 144 0 169 260 101 101 342 143 0 168 Cileuleuy P AET PET SWC SMS SMD Ro 449 109 109 427 250 0 259 389 108 108 398 222 0 230 261 115 115 329 153 0 164 323 123 123 303 126 0 141 178 126 126 252 75 0 100 147 117 117 205 28 0 66 80 94 112 173 0 18 47 74 82 112 156 0 30 38 107 76 116 141 0 41 32 281 117 117 326 150 0 162 242 115 115 332 155 0 167 241 111 111 331 154 0 166 Ciheulang P AET PET SWC SMS SMD Ro 267 89 89 453 225 0 263 253 88 88 424 196 0 234 323 93 93 355 127 0 171 217 101 101 329 100 0 148 235 103 103 278 49 0 108 94 96 96 231 3 0 74 65 73 91 199 0 18 55 81 64 91 182 0 27 46 85 60 95 167 0 35 39 255 96 96 352 124 0 169 379 93 93 358 129 0 173 347 90 90 357 129 0 172 Cikembar P AET PET SWC SMS SMD Ro 464 113 113 403 274 0 255 337 112 112 374 245 0 225 215 119 119 305 176 0 160 284 127 127 279 150 0 136 277 130 130 228 99 0 94 140 122 122 181 52 0 59 45 92 116 150 0 24 41 74 80 116 133 0 36 32 49 74 120 120 0 46 26 229 122 122 304 174 0 159 276 119 119 308 179 0 162 249 115 115 307 178 0 161

4. 1. 4 Ciheulang subwatershed

AET of each months had a small range. Mean values of AET was 87 mm. Maximum values of PET was 103 mm occurred in Mei and minimum value of PET was 88 mm occurred in February. SWC varied from 167 mm in September to 453 mm in January. The rainfall was well varied. Mean values of rainfall was 217 mm. Peak of rainfall was 379 mm occured in November. SMS ranged from

3 mm in June to 225 mm in January. SMD

ranged from 18 mm in July to 35 mm in September. Mean values of runoff was 138 mm. Maximum runoff was 263 mm occured in January.

4. 1. 5 Cikembar subwatershed

Mean value of AET was 110 mm. Maximum AET was 130 mm occured in May.

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and the lowest value of PET was 112 mm in February. Maximum SWC was 403 mm occurred in January and minimum SWC was 120 mm occurred in September. Mean values of rainfall was 220 mm. Rainfall peak of 464 mm took places in January. SMS ranged from 52 mm in June to 274 mm in January. SMD

ranged from 24 mm in July to 46 mm in September. Mean values of runoff was 126 mm. During the low rainfall period runoff values were less of than 50 mm.

4. 2 Runoff distributions of Cicatih watershed

Figure 5 shows the comparison between the observed and calculated monthly runoff hydrograph in 1999 at the outlet of the Cicatih watershed. Mean values of observed runoff and calculated runoff were 1157 mm and 1140 mm, respectively. The error of calculated runoff varied from its maximum in January to the minimum in September. The highest amount of observed runoff was 1892 mm occurred in March. Different from the observed runoff, the highest amount of calculated runoff was 2296 mm occured in January.

Flow directions (Figure 6) affected the runoff accumulation. Flow directions was estimated using PC Raster. DEM data was used as the only input. It was generated by considering the 8 point pour algorithm with flow directions from each cell to its steepest downslope neighbour. Moreover, runoff accumulation was generated using the flow directions. Runoff accumulation calculated the amount of runoff that flowed out of the cell into its neighbouring downstream cell. The

runoff accumulation amount was the amount of runoff in the cell itself plus the amount of runoff in upstream cells of the cell. In Cicatih watershed, runoff accumulation had its maximum at the outlet.

Flow directions to west and southwest were common directions from the right side of the Cicatih watershed. On the other side, the flow directions to southeast was common direction from the left side of Cicatih watershed. Kurnianto (2004) described that the flow directions was affected by the slope directions of Salak mountain in left side and Pangrango mountain in right side of the Cicatih watershed. It caused the runoff accumulation from left and righ side met at the midle part of Cicatih watershed. Finally, the runoff accumulation flowed toward the watershed outlet.

Runoff accumulation varied in the watershed. It led to higher accumulation in the most center part, and to lower accumulation in the mountain and at high altitudes. Maximum runoff accumulation was 400000 mm occured in the center part of Cicatih watershed bottom area because of their low altitude. Areas with 0 mm accumulation indicated that all of runoff from that areas flowed out into its neighbouring downstream areas.

The result of the first stream order from the estimation using PC Raster (Figure 7) was similar with the observed first stream order (Figure 8). In addition, some of second, third, and fourth stream orders from the estimation using PC Raster were also similar with the observed stream orders. However, runoff accumulation of the first stream order did not appear in the estimation result.

0 500 1000 1500 2000 2500

jan feb mar may jun jul aug sep oct dec

Month

3/s)

Observed Ro Calculated Ro

Figure 5. The observed and calculated monthly runoff hydrograph of Cicatih watershed, Sukabumi in 1999.

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Figure 6. Predicted flow directions using PC Raster.

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Source: Bakosurtanal (1999)

Figure 8. Stream orders of Cicatih watershed, Sukabumi. The results obtained from the

calculation using the input 1999 data field were monthly spatial variability of runoff distribution. Spatial distribution of runoff was affected by the rainfall, land cover types, and

WHC. However, monthly runoff distribution was only affected by the rainfall.

The monthly runoff distributions showed that minimum runoff occurred between May and September. September (35 mm) was the month of minimum runoff. And maximum runoff period occured in the period of October until April. January (260 mm) was the maximum runoff month because of the occurance of maximum rainfall in January. The pattern of rainfall-runoff relationship was in agreement with result report by Xu (1997) in six watersheds from the humid region in Southern China and one catchment from the semi-arid and semi-humid region in Nothern China. Putty and Prasad (2002) showed that runoff increased as the significant increased of rainfall. Furthermore, The areaaverage values of rainfall distributions and runoff distributions in Cicatih watershed described the rainfall-runoff relationship as well (see Table. 5).

The spatial distribution of runoff from the images (see: Figure 9, Figure 10, and Figure 11) reflect that the contributions from the garden areas was the highest, because this was the most common land cover in the Cicatih watershed. And the lowest contiribution of runoff portion was obtained from the grass areas because of the their small areas. The pattern of major runoff portion from the major land cover areas was also found by Karvonen

(1999) in the Lestijoki watershed, Finland but with the different major land cover contribution. The most common land cover in the Lestijoki watershed, Finland was forest.

During the high rainfall period, maximum runoff could be found in the forest areas (286 mm), followed by cropland areas (269 mm). And minimum runoff was 251 mm occurred in settlement areas. In the low rainfall period, maximum runoff (109 mm) was found in forest areas. And minimum runoff was 0 mm occured in the settlement areas, followed by cropland areas (5 mm) around the mountain Salak and mountain Pangrango. It concluded that the land use types-runoff relationship was widely affected by the rainfall. The high runoff occurred in forest areas due to their high rainfall. Runoff increased with significant incresing rainfall, following a positive linear function.

Table 5. Monthly runoff distributions in Cicatih watershed, Sukabumi

Month Rainfall (mm) Runoff (mm) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 378 345 277 255 200 139 77 87 94 325 280 274 260 232 167 144 103 69 50 42 35 166 169 169

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V. CONCLUSIONS AND

SUGGESTION

5. 1 Conclusions

The calibration procedures consist of two steps parameters optimization. Firstly, optimize the parameters c and WHC

according to the criterion RE. Secondly, optimize the parameter WHC again according to the criterion R2, with the value of c obtained in the first step.

The results of monthly spatial runoff presented in the article had proved to be quite efficient of describing the monthly runoff with R2 value of 66.15 % and relative error (RE) of 1.4 %. The method can easily be incorporated in water resources planning program to estimate monthly runoff in the Cicatih watershed because of their simplicity and efficiency of performance. The implication of the study is to describe the comparison between monthly spatial runoff of the 1999 land uses pattern and the recent year land uses pattern.

The result of spatially distributed runoff clearly indicated the influence of rainfall, land cover types, and water holding capacity

(WHC). However, the monthly distibuted runoff was only affected by the rainfall. The runoff distributions of subwaterheds showed that runoff varied from 263 mm in Ciheulang subwatershed to 26 mm in Cikembar subwatershed. The monthly runoff distribution of Cicatih watershed showed that the lowest runoff was 35 mm occurred in September and the highest runoff was 260 mm occurred in January. The spatial runoff distribution in Cicatih watershed reflected that during the high rainfall period in Cicatih, maximum runoff could be found in the forest areas (286 mm) and followed by cropland areas (269 mm). And minimum runoff was 251 mm occurred in settlement areas. In the low rainfall period, maximum runoff (109 mm) was found in forest areas. Minimum runoff was 0 mm occured in the settlement areas, followed by cropland areas (5 mm) around the mountain Salak and mountain Pangrango. It was found that runoff increased with significant incresing rainfall, following a positive linear function.

5. 2 Suggestion

For future applications, it is suggested to consider the rainfall-runoff pattern in water resources planning program Cicatih Watershed, Sukabumi, West Java.

VI. REFERENCES

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Calder IR. 2002. Forest and Hydrological Services: Reconciling public and science perceptions. Land Use and Water Resources Research. 2: 2.1-2.12.

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age-induced changes in evapotranspiration and water yield in

a eucalypt forest. J. Hydrol. 242: 43-63.

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Fahey B and Jackson R. 1997. Hydrological impact of converting native forest and grasslands to pine plantations, South

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Rodriguez-Iturbe I. 2001. The ecohydrological role of soil texture in a water-limited ecosystem. Water Resources Research. 37: 2863-2872. Indonesia. 1999. Composite map

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Jacson NA. 2000. Measured and modeled rainfall interception loss from an agroforestry system in Kenya. J. Hydro. 100: 323-336.

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S, Askari M. 2005. Biophysical indicators of watershed functions: case study of Cicatih Basin-Sukabumi. Hydrometeorology Laboratory, Departement of Geophysics and Meteorology, FMIPA-IPB.

Putty MRY and Prasad R. 2000. Understanding runoff processes using a watershed model – a case study in the Western Ghats in South India. J. Hydrol. 228: 215-227.

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Appendix 2. Mean of monthly temperature during 1988-1999 periods

Year Month

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 Average

Jan 25.5 24.9 24.0 25.0 25.0 25.0 25.1 25.1 24.5 25.2 26.9 25.2 25.1

feb 25.5 24.5 25.5 24.5 25.0 24.5 24.9 24.9 25.0 25.0 25.9 24.9 25.0

Mar 26.0 25.0 25.0 25.5 25.5 24.4 25.5 25.5 25.6 25.8 26.8 25.2 25.5

Apr 26.0 25.0 26.0 25.5 25.8 26.2 26.1 26.1 27.6 26.0 26.8 25.8 26.1

May 26.5 24.5 26.0 26.0 26.0 26.2 26.3 26.3 28.2 26.3 27.1 26.0 26.3

Jun 25.4 25.0 25.5 25.5 25.5 25.8 25.7 25.7 26.0 25.7 26.6 25.7 25.7

Jul 25.4 25.5 25.5 24.5 25.0 25.5 25.3 25.3 25.7 24.9 26.0 25.2 25.3

Aug 26.0 25.0 25.0 24.5 24.5 25.0 25.3 25.3 25.5 25.6 26.4 25.5 25.3

Sep 25.5 25.0 25.5 25.5 25.5 25.0 25.6 25.6 25.6 26.1 26.0 25.9 25.6

Oct 25.5 25.5 25.5 26.5 24.5 26.0 25.7 25.7 25.6 26.8 25.9 25.7 25.7

Nov 25.1 25.0 25.0 25.5 25.0 25.5 25.5 25.5 25.9 26.6 25.4 25.5 25.5

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Appendix 3. Monthly rainfall of 1999 in Cicatih watershed

Rainfall Stations Month

Cicurug Sekarwangi Sinagar Cibunar Cipendeuy Cipetir Cikembang Pakuwon Selabintana

Jan 478 441 482 108 514 507 453 368 304

Feb 397 358 426 180 322 361 317 406 272

Mar 233 244 253 263 233 402 147 250 481

Apr 293 255 371 31 343 247 275 201 392

May 215 223 138 193 366 267 281 131 256

Jun 150 132 160 15 164 139 131 196 157

Jul 91 56 83 31 30 60 40 93 130

Aug 71 83 65 40 55 131 77 127 153

Sep 91 80 117 20 20 131 24 104 205

Okt 278 278 285 244 198 303 176 562 287

Nov 187 245 221 325 335 271 271 229 538

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Appendix 5. Digital Elevation Model (DEM) (m)

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Appendix 7. Map of water holding capacity (WHC) in Cicatih watershed

Appendix 8. Calculation of monthly spatial runoff using PC Raster

binding

# Input Map

altitude=topomodi.map; area=boundary.map; thiesen=thiesen.map; lu=lu.map;

initsoilwater=initsw.map; maxSWC=whc.map;

subwatershed=Subwatershed.map; lust=nomlust.map;

ldd0=ldd.map;

# Timeseries Data tmpkw = pkw.tss; precip=NewRain.tss; volrain=volrain.tss; volrunoff=volRo.tss; # Output

Tcct= Tcit; Tavetss=Tcit.tss; Tave=Tave; raintotal=total; raintotaltss=rainttl.tss; raintotalcct=totalcit;

raintotalareatss=rainttlarea.tss; raintotalsub=totalsub;

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raintotalsubtss=rainttlsub.tss; volrainttltss=volrainttl.tss; rainnet=net;

rainnettss=rainnnet.tss; rainnetcct=netcit;

rainnetccttss=rainnetcct.tss; rainnetsub=netsub;

rainnetsubtss=rainnetsub.tss; rainnetthis=netthies;

PET=PET; PETsub=PETsub; PETsubtss=PETsub.tss; PETcct=PETcit; PETccttss=PETcit.tss; PETthis=PETthies; PETthistss=PETthies.tss; itss=i.tss;

Pef=Pef;

Pefccttss=Pefcit.tss; AET=AET; AETcct=AETcit; AETccttss=AETcit.tss; AETsub=AETSub; AETsubtss=AETsub.tss; AETthis=AETthies; AETthistss=AETthies.tss; SWC=SWC;

SWCtss=SWC.tss; SWCcct=SWCcit; SWCccttss=SWCcit.tss; SWCsubtss=SWCsub.tss; SWClcst=SWClust; SWClcsttss=SWClust.tss; SMS=SMS;

SMScct=SMScit; SMSccttss=SMScit.tss; SMSsub=SMSsub; SMSsubtss=SMSsub.tss; SMSlcst=SMSlust; SMSlcsttss=SMSlust.tss; SMD=SMD;

SMDcct=SMDcit; SMDccttss=SMDcit.tss; SMDsub=SMDsub; SMDsubtss=SMDsub.tss; SMDlcst=SMDlust; SMDlcsttss=SMDlust.tss; Ro=runoff;

Rocct=Rocit; Roccttss=Rocit.tss; Rolcst=Rolust; Rolcsttss=Rolust.tss; Rosub=Rosub; Rosubtss=Rosub.tss; volRo=volRo; volRotss=volRo.tss;

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acc=acc;

accoutlettss=accoutlet.tss; Volacc=Volacc;

# Tabel Data

portion=inter.tbl;

areamap

cicatih.map;

timer

1 12 1;

initial

I=129;

report koefportion=lookupscalar(portion, lu); SWC=initsoilwater;

WHC=maxSWC;

dynamic

# Temperature

report Tpkw=timeinputscalar(tmpkw,area); report Tcct=Tpkw+2.745-(0.0061 * altitude); report Tave=areaaverage(Tcct,area); report Tavetss=timeoutput(thiesen,Tave); report tratabulan=timeoutput(area,Tave); # Potential Evapotranspiration(PET)

i = (Tave/5) ** 1.516; report itss=timeoutput(area,i); #I = sum of i

a = 0.49 + (0.0179*I) - (0.0000771*(I**2)) + (0.000000675*(I**3)); report PET=16*(10*Tcct/I)**a;

report PETcct=areaaverage(PET,area); report PETccttss=timeoutput(area,PET); report PETsub=areaaverage(PET,subwatershed); report PETsubtss=timeoutput(subwatershed,PET); report PETthis=areaaverage(PET,thiesen); # Total Rainfall

report raintotal=timeinputscalar(precip, thiesen); report raintotaltss=timeoutput(thiesen,raintotal); report raintotalcct=areaaverage(raintotal,area); report raintotalccttss=timeoutput(area,raintotal); report raintotalsub=areaaverage(raintotal,subwatershed); report rainbrutsubtss=timeoutput(subwatershed,raintotal); report volrainttltss=maptotal(raintotal)*cellarea()/(2628*20000); # Nett Rainfall

report rainnet= raintotal * koefportion; report rainettss=timeoutput(area,rainnet); report rainnetcct=areaaverage(rainnet,area); report rainnetccttss=timeoutput(area,rainnet); report rainnetsub=areaaverage(rainnet,subwatershed); report rainnetsubtss=timeoutput(subwatershed,rainnet);

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# Effective Rainfall(Pef)

report Pef= max(rainnetcct - PETcct,0); report Pefccttss=timeoutput(area,Pef); # Soil Water Content(SWC)

report SWC=max(if(Pef gt 0 then if(SWC ge WHC then WHC+Pef else SWC+Pef) else SWC*exp((rainnetcct-PETcct)/WHC)),0);

report SWCcct=areaaverage(SWC,area); report SWCccttss=timeoutput(area,SWC);

report SWCsubtss=timeoutput(subwatershed,SWC); report SWClcst=areaaverage(SWC,lust);

report SWClcsttss=timeoutput(lust,SWC); # Actual Evapotranspiration(AET)

report AET=if(SWC ge WHC then PET else PET*(SWC/WHC)); report AETcct=areaaverage(AET,area);

report AETccttss=timeoutput(area,AET); report AETsub=areaaverage(AET,subwatershed); report AETsubtss=timeoutput(subwatershed,AET); # Soil Moisture Surplus(SMS)

report SMS= if(Pef gt 0 then SWCcct-WHC else 0); report SMScct=areaaverage(SMS,area);

report SMSccttss=timeoutput(area,SMS); report SMSsub=areaaverage(SMS,subwatershed); report SMSsubtss=timeoutput(subwatershed,SMS); report SMSlcst=areaaverage(SMS,lust);

report SMSlcsttss=timeoutput(lust,SMS); # Soil Moisture Defisit (SMD)

report SMD=if(SMS gt 0 then 0 else PET-AET); report SMDcct=areaaverage(SMD,area); report SMDccttss=timeoutput(area,SMD); report SMDsub=areaaverage(SMD,subwatershed); report SMDsubtss=timeoutput(subwatershed,SMD); report SMDlcst=areaaverage(SMD,lust);

report SMDlcsttss=timeoutput(lust,SMD); # Runoff (Ro)

report

Ro=SWC*((exp(0.3*(SWC/WHC))-exp(-(0.3*(SWC/WHC))))/(exp(0.3*(SWC/WHC))+exp(-(0.3*(SWC/WHC))))); report Rocct=areaaverage(Ro,area);

report Roccttss=timeoutput(area,Ro); report Rosub=areaaverage(Ro,subwatershed); report Rosubtss=timeoutput(subwatershed,Ro); report Rolcst=areaaverage(Ro,lust);

report Rolcsttss=timeoutput(lust,Ro);

report volRotss=maptotal(Ro)*cellarea()/(2628*20000); report volRo=timeinputscalar(volrunoff,area);

# Runoff accumulation

report acc= accuflux(ldd0,Ro); accoutlet=mapmaximum(acc);

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CALIBRATION OF MONTHLY SPATIAL RUNOFF FROM THE ROOT

ZONE USING WATER BALANCE METHOD (A Case Study in Cicatih

Watershed, Sukabumi, West Java)

TEUKU ACHMAD IQBAL

DEPARTMENT OF GEOPHYSICS AND METEOROLOGY

FACULTY OF MATHEMATICS AND NATURAL SCIENCES

BOGOR AGRICULTURAL UNIVERSITY

2006

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ABSTRACT

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CALIBRATION OF MONTHLY SPATIAL RUNOFF FROM THE ROOT

ZONE USING WATER BALANCE METHOD (A Case Study in Cicatih

Watershed, Sukabumi, West Java)

TEUKU ACHMAD IQBAL

(G 24101023)

Research Report

To fulfill the requirement for a Bachelor Degree in Science

At the Department of Geophysics and Meteorology

Faculty of Mathematics and Natural Sciences

DEPARTMENT OF GEOPHYSICS AND METEOROLOGY

FACULTY OF MATHEMATICS AND NATURAL SCIENCES

BOGOR AGRICULTURAL UNIVERSITY

2006

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Title : CALIBRATION OF MONTHLY SPATIAL RUNOFF FROM THE

ROOT ZONE USING WATER BALANCE METHOD (A Case Study

in Cicatih Watershed, Sukabumi, West Java)

Name : Teuku Achmad Iqbal

Nrp : G 24101023

Approved by:

Supervisor

Prof. Dr. Daniel Murdiyarso

NIP. 130804892

Dean of Faculty of Mathematics and Natural Sciences

Bogor Agricultural University

Dr. Ir. Yonny Koesmaryono, M.Si

NIP. 131473999

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BIOGRAPHY

Teuku Achmad Iqbal was born in Jakarta at August 30, 1983 with parents name Teuku Syarif and Kemala Sari. He has two brothers.

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V. CONCLUSIONS AND

SUGGESTION

5. 1 Conclusions

The calibration procedures consist of two steps parameters optimization. Firstly, optimize the parameters c and WHC according to the criterion RE. Secondly, optimize the parameter WHC again according to the criterion R2, with the value of c obtained in the first step.

The results of monthly spatial runoff presented in the article had proved to be quite efficient of describing the monthly runoff with R2 value of 66.15 % and relative error (RE) of 1.4 %. The method can easily be incorporated in water resources planning program to estimate monthly runoff in the Cicatih watershed because of their simplicity and efficiency of performance. The implication of the study is to describe the comparison between monthly spatial runoff of the 1999 land uses pattern and the recent year land uses pattern.

The result of spatially distributed runoff clearly indicated the influence of rainfall, land cover types, and water holding capacity (WHC). However, the monthly distibuted runoff was only affected by the rainfall. The runoff distributions of subwaterheds showed that runoff varied from 263 mm in Ciheulang subwatershed to 26 mm in Cikembar subwatershed. The monthly runoff distribution of Cicatih watershed showed that the lowest runoff was 35 mm occurred in September and the highest runoff was 260 mm occurred in January. The spatial runoff distribution in Cicatih watershed reflected that during the high rainfall period in Cicatih, maximum runoff could be found in the forest areas (286 mm) and followed by cropland areas (269 mm). And minimum runoff was 251 mm occurred in settlement areas. In the low rainfall period, maximum runoff (109 mm) was found in forest areas. Minimum runoff was 0 mm occured in the settlement areas, followed by cropland areas (5 mm) around the mountain Salak and mountain Pangrango. It was found that runoff increased with significant incresing rainfall, following a positive linear function. 5. 2 Suggestion

For future applications, it is suggested to consider the rainfall-runoff pattern in water resources planning program Cicatih Watershed, Sukabumi, West Java.

VI. REFERENCES

Abulohom MS, Shah SMS, Ghumman AR. 2001. Development of a Rainfall-Runoff Model, its Calibration and Validation. Water Resour Manage: 15: 149-163.

Arnell NW. 1999. A simple water balance model for the simulation of streamflow over a large geographic domain. J. Hydrol. 217: 314-335. Asdak C, Jarvis PG, Gardingen P van,

Fraser A. 1998. Rainfall interception loss in unlogged and logged forest areas of Central Kalimantan, Indonesia. J. Hydrol. 206: 237-244. Adhikari. 2003. A GIS-Remote sensing

compatible rainfall-surface runoff model for regional level planning. Consulting Engineering Services (India) Private Limited, DD-6, Salt Lake, Kolkata-64, West Bengal, India.

A Study of evaporation from tropical rain forest-West Java. J. Hydrol. 89: 13-31.

Calder IR. 2002. Forest and Hydrological Services: Reconciling public and science perceptions. Land Use and Water Resources Research. 2: 2.1-2.12.

Carlyle-Moses DE, Price AG. 1999. An Evaluation of Gash interception model in northern hardwood stand. J. Hydrol. 210: 103-110.

Cornish PM and Vertessy RA. Forest

age-induced changes in evapotranspiration and water yield in

a eucalypt forest. J. Hydrol. 242: 43-63.