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Estimation of runoff for agricultural watershed using SCS curve number and geographic information system
The land use/ land cover map and soil map were intersected in command tools of ARC/Info. The areas of different land use class and soil combinations were obtained in the attributes selection menu by using logical expression and accordingly different CN (Curve-Number) values were assigned. Thus weighted value of CN for the whole watershed was worked out. The CN values for AMC II condition can be converted in to CN values for AMC I and AMC III condition by using available conversion factors as suggested by Suresh, 1997. Putting the value of Curve Number in formula (1), the recharge capacity 'S' was calculated. The direct runoff of the watershed was calculated using formula (2) .
The daily rainfall data for the years 1993 of the study area and the values of maximum potential retention, S obtained from the weighted CN for the watershed area were used for the estimation of runoff from SCS (model). The estimated runoff was then validated by comparing it with the four selected events of monsoon season.
Results and Discussion
Based on the hydrological soil group, the maximum area of Karso watershed was observed to be under hydrological soil group B (84.32%) followed by (15.23 %) C and (0.45 %) group A. Similarly, the study area was identified in the five major land use classes namely agricultural land (42.98%), dense forest (34.74 %), wasteland (19.64 %), settlement (2.05%), and hard surface (0.59%). The major area of the watershed was under agricultural land. The agricultural land was divided into three categories i.e. area under paddy cultivation (19.35%), straight row crops (12.27%) and poor contoured (11.36%) crops. The USDA curve number table 2 (Tripathi, 1999) modified for Indian condition was used for the determination of the curve number for the watershed. By intersecting the land use map and soil map the curve number was assigned to the each combination of land use and soil type. Weighted value of CN were found out to be 71.42 52.75 and 85.7 for AMC II, AMC I and AMC III conditions respectively. The daily rainfall data for the year 1993 were collected and the weighted curve number of the watershed was used for the estimation of runoff. The calculated runoff was found out to be 244.40 mm for monsoon season of the year 1993 which is approximately 35.52 per cent of the total rainfall.
Table: 2. Status of different soil group presents in the study area
| Sl. No. |
Soil Group |
Area (ha) |
Area (%) |
| 1 |
A |
13.09 |
0.47 |
| 2 |
B |
2354.72 |
84.30 |
| 3 |
C |
425.19 |
15.23 |
| |
|
2793.00 |
|
In order to validate the SCS model output, estimated runoff was compared with measured runoff for four selected events of the monsoon season(Table 3). The maximum and minimum deviation were observed to be 28.33 and 3.27 per cent respectively, which are within the permissible limit.
Table: 3. Comparison of estimated runoff with the observed runoff
| Storm Date |
Rainfall(mm) |
AMC Condition |
Runoff Observed (mm) |
Estimated Runoff (mm) |
Percent deviation |
| 11-07-1993 |
43.00 |
II |
1.54 |
1.37 |
11.03 |
| 25-07-1993 |
21.1 |
I |
17.18 |
12.33 |
28.33 |
| 21-08-93 |
105.6 |
III |
85.92 |
63.78 |
25.76 |
| 13-10-1993 |
72.2 |
III |
34.37 |
34.73 |
1.04 |
Conclusions
In the present study the methodology for determination of Runoff for Karso watershed using GIS and SCS model was described. This approach could be applied in other Indian watersheds for planning of various conservation measures.
Acknowledgement
The facilities and technical supports provided by the Regional Remote Sensing Service Centre (RRSSC), Department of Space, Govt. of India, Kharagpur(W.B.) is here by gratefully acknowledged.
References
- Chandrmohan, T. and Durbude , D.G. (2001). Estimation of runoff usings small watershed models, Hydrology Journal. 24 (2):45-53.
- Handbook of Hydrology( 1972). Soil Conservation Department, Ministry of Agriculture, New Delhi
- Rao, K.V., Bhattacharya, A.K. and Mishra, K. ( 1996). Runoff estimation by curve number method- case studies, Journal of Soil and Water Conservation. 40 :1-7
- Sharma, T., Satya Kiran, P.V., Singh, T.P., Trivedi, A.V. and Navalgund, R.R.( 2001). Hydrologic response of a watershed to landuse changes: A remote sensing and GIS approach. Int .J. of Remote Sensing: 22 (11): 2095-2108
- Sharma, D. and Kumar, V. 2002. Application of SCS model with GIS data base for estimation of runoff in an arid watershed. Journal of Soil and Water Conservation: 30 (2) :141-145
- Suresh, R. (1997). Soil and Water Conservation Engineering. Standard Publishers Distr., Delhi. pp 48-51.
- Tripathi, M.P.(1999). Hydrological modeling of small watershed, Unpublished Ph.D. Thesis, Department of Agricultural and Food Engineering, Indian Institute of Technology, Kharagpur.
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