Background Land Cover Changes and Potential Hydrological Responses in Palu Catchment, Central Sulawesi Province.
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to available rainfall Dean Snider, 1972. General form of total runoff volume estimation is expressed by:
= − 0.2
+ 0.8 … … … … … … … … … … … … … … … … … … … … … … … … … 3
Where V
Q
is the runoff volume uniformly distributed over the drainage basin, P is the mean precipitation, and S is the retention of the water. The retention parameter
S is depending on characteristic of soil, vegetation, land use, and soil moisture condition in a watershed, where condition of those parameters are expressed by
the curve number. The relation between retention and curve number is expressing as:
= 1000
− 10 … … … … … … … … … … … … … … … … … … … … … … … … … … … 4
Where CN is curve number. The value of curve number is range from 20 to 100. The lower numbers indicate low runoff potential, while larger numbers are for
increasing runoff potential. The curve number values are determined also by the soil types, where each soil type has their own of infiltration characteristics
presented in Table 2.1. The relationship between runoff and curve number are shows in Figure 2.2, while the value of curve number for different land use and
land cover type are shows in list of appendix of this proposal.
Figure 2.2 Volume of direct runoff as a function rainfall and curve number Singh, V.J. 1992
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Table 2.1 Hydrological soil group classifications
Group Soil Characteristics
Minimum Infiltration Rate inh
A Deep sand, deep loess, and aggregate silts
0.3 - 0.45 B
Shallow loess and sandy loam 0.15 - 0.30
C Clay loams, shallow sandy loam, soils in organic
content, and soil usually high in clay 0.05 - 0.15
D Soil that swell upon wetting, heavy plastic clay, and
certain saline soils 0 - 0.05