residents have been utilizing their shallow aquifer fordecades.Prior to developm

Question

residents have been utilizing their shallow aquifer fordecades.Prior to development,the sandand gravel aquifer had anaverage saturated thickness of about 100feet.The average porosity of the
Group is about 22%.The average precipitationin Mountains is about10-25 inches per
year,but on average,only a small percentage(10to30%)of this precipitation recharges
the aquifer.assume that thewater level in the aquifer is about 3 feet lower than the river water level,onaverage.the agricultural drains are 8 feet lower than thewater table,so that the aquifer is losing water to the drains.Assuming upstream subsurface aquifer inflows are balanced bydownstream outflows we can write the water budget for the Group of aquifers of the Basin asfollows:

ATh

t

= QMR +QRS +QIR QDR QET QPUMP

whereQMR ismountainfrontrechargeinft^3/year,QDR is drain seepage losses inft^3/year,
QRS is river seepage inflows in ft3/year, QIR isirrigation see page that recharges the aquifer
in ft^3/year, QPUMP is groundwater pumping inft^3/year, QET is riparian zone forest
evapotranspiration losses in ft^3/year, AT is area ofthe Basinaquifer system in
ft^2, is aquiferporosity,h is average aquifer water levelin feet,and t is time in years.One
acre-foot equals 43,560ft^3.

There are about 50,000 acres of irrigated farmland in the basin. Most of this is alfalfa. In a typical growing season, well-watered and healthy alfalfa will transpire about 3 feet of water. However the farmers, in order to keep them well watered, flood the fields with a total of 5.5 feet of water (cumulative over the irrigation season). The difference between these values infiltrates through the soil and recharges the aquifer. What is the total volume of water delivered to the aquifer each year in this manner?

Explanation / Answer

Ans- the volume of water goes to aquifer will the overloaded water of the whole farmland. As there is 2.5 feet more water which infiltrate through the soil so the total volume of water will be-

1acre= 43560 square feet

50000 acre = 43560× 50000=

As 2.feet water iltertingniltertis infiltrating

43560×50000×2.5= 5445000000 cubic feet.

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