1. The Ogallala Aquifer is a major aquifer underlying parts of eight states in t
ID: 152566 • Letter: 1
Question
1. The Ogallala Aquifer is a major aquifer underlying parts of eight states in the high plains of US. Extensive pumping of groundwater from that aquifer during 1960-1980 has led groundwater level declines. Assume the pumping was at the rate of 830 million ft Iday the natural discharge from the aquifer was 10 million ft /day, and the recharge (including irrigation return flow) to the aquifer was 510 million ft3/day. 3o-10+ 5t0 a) What was the rate at which the aquifer was depleted (i.e. difference between recharge and SD WY 30kim tmda Omcha b) Over a 20-year period, how much groundwater did the aquifer lose? NE 133 34 420 KS chita co NM Northern Hgh Plains OK ral Plal TxExplanation / Answer
a.
Rate of pumping = 830 million ft3/day
natural discharge from the aquifer = 10 million ft3/day
Total recharge into the aquifer = 510 million ft3/day
These are the values given in the question. We are asked to find out the rate at which the aquifer was depleted. From the above numbers it is clear that the ground water flow out of the aquifer - which is the sum of natural discharge and pumping - is greater than the groundwater flow into the aquifer - the recharge.
So, total discharge = sum of natural discharge and pumping = 830 + 10 = 840 million ft3/day
Total recharge = 510 million ft3/day (given)
The depletion rate is the difference between these two values.
Depletion Rate = 510 - 840 = -330 million ft3/day
The minus sign means that the change is negatie, ie. the ground water is decreasing at a rate of 330 million ft3 per day.
b.
The rate of depletion = 330 million ft3/day
Total time period = 20 years = 20 x 365 days (one year has 365 days)
= 7300 days
Total ground water lost by the aquifer = rate of depletion x Total time period
= 330 x 7300 = 2,409,000 million ft3
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