Section 4: Soil and Water Conservation Engineering
Hydrology
Subtopic: Analysis of precipitation data
Question Statement:
The normal annual rainfall for 5 rain gauge stations A, B, C, D, E were 112.7, 120.4, 118.3, 125.2 and 110.6 cm respectively. In a particular year station C failed; A, B, D, E recorded 114.9, 118.3, 122.6 and 114.5 cm. The estimated rainfall at station C in cm was ______
Official Answer Key:
118.5 to 119.0
Step-by-Step Solution & Explanation
Using the Normal Ratio Method (since normal annual rainfall values of the stations differ by more than 10% from each other): P_C = (N_C/M)×Σ(P_i/N_i) for the M=4 index stations, where N is normal annual rainfall and P is the recorded rainfall in the deficient year. P_C = (118.3/4)×[(114.9/112.7)+(118.3/120.4)+(122.6/125.2)+(114.5/110.6)] = 29.575×[1.0195+0.9826+0.9792+1.0353] = 29.575×4.0166 = 118.79 cm, within the accepted band 118.5–119.0.
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