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 24,000 acres of riparian bosque forest in the basin. These
cottonwood dominated lands typically transpire about 3.5 feet of water (3.5 ft3 of water for
every ft2 of forest land area) over the course of each growing season (assume that this
effectively represents total annual ET). What is the annual volume of water removed from
the aquifer by the bosque vegetation?

Explanation / Answer

One acre = 43560 square feet

Therefore, 24000 acres of riparian bosque forests= 10454400000 square feet

Every square feet of the forest land area loses3.5 cubic feet of water through evapotranspiration over the course of each growing season (which is considered to be the total annual ET in the above question).

So, annual volume of water lost/removed from the aquifer by the bosque vegetation= 10454400000* 3.5 = 3,659,040,000 cubic feet

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