ainfallof 780, 870, 930, 1,060, 1,050 and 1,370 mm is recorded at rain-gauge stations of A, B, C, D, E and F in a river basin. Estimate the average areal depth of rainfall over the river basin, using (a) arithmetic average method, (b) Thiessen polygon method and (c) isohyetal method, with neat sketches, wherever necessary.

Using a rainfall of 386 mm for rain gauge Station D, determine the average depth of rainfall that fell for the watershed using the arithmetic average, and Thiessen polygon method. The areas for the Thiessen polygon method are given in the table above for each station. Determine the average depth of rainfall for a watershed using the isohyetal method given the data below. Isohyet (mm) Area Associated (km²) 30 - 40 20 20 - 30 45 10 - 20 35 under 10