Determination of Surface Drainage Coefficient Through Rainfall Analysis

The drainage coefficient for agricultural watershed at Central Research Station of PDKV Akola (CRS) was estimated. For this purpose 25 years daily rainfall data was used for its depth- duration- frequency analysis to get one to four consecutive days rainfall values for 2, 5, 10 and 20 years recurrence interval (R.I.) Computed drainage coefficients (DC) indicates that the soils at CRS having basic infiltration rate above 3, 5, 7 and 8 mm/hour may not need surface drainage system for one day period rainfall of 2, 5, 10 and 20 years R.I. respectively. The corresponding values in case of two consecutive days rainfall are 2, 3, 3 and 4 mm/hr. For three consecutive days rainfall these values are 1, 2, 2 and 3 mm/hr respectively and for four consecutive days rainfall values are 1,1,2 and 2 mm/hr. In case of one day period the estimated drainage coefficient varies between 64.14 mm/day to 112.14 mm/day for 5 years RI. and between 102.06 to 150.06 mm/day for 10 years RI. in clayey soils at CRS having basic infiltration rate 1 to 3 mm/hr. However, in case of two consecutive days maximum rainfall the estimated values of drainage coefficient (DC) varies between 7.81 to 55.81 mm/day for 5 years R.I. and 22.58 to 70.58 mm/day for 10 years RI. having same type of black cotton soil. In case of three consecutive days maximum rainfall the corresponding values of DC are 8.55 to 32.55 mm/day for 5 years R.I. and 17.11 to 41.11 mm/day for 10 years RI. having basic infiltration rate 1 to 2 mm/hr. Study further revels that soils at CRS having predominantly clayey soils with basic infiltration rate between 1 to 3 mm/hr may necessarily have to be provided with agricultural land drainage for its major existing crops.