In a river reach, the rate of inflow at any time is 350 cfs and the rate of outflow is 285 cfs. after 90 min, the inflow and outflow are 250 cfs and 200 cfs, respectively, and storage of 10.8 acre-ft has been observed. determine the change in storage in 90 min and the initial storage volume.

change in storage =  -310,500 ft^3

intital storage= 3.67 acre ft

Explanation:

Given data:

Rate of inflow = 350 cfs

Rate of outflow = 285 cfs

After 90 min,  rate of inflow = 250 cfs

Rate of outflow = 200 cfs

final storage = 10.8 acre-ft

calculating the average inflow and outflow

average inflow  

average outlow  

total amount of water drain during the period of one hour

= (average outflow - average inflow) *60*90

= (242.5 - 300)*60*90 = -310,500

change in storage is calculate as

= -310,500 ft^3

in cubic meter

= -310500/35.315 = 8792.30 cm^3

in acre-ft

= -310,500/43560 = 7.13 acre ft

initial storage = 10.8 - 7.13 = 3.67 acre ft