A small $2,000$ acre watershed in Iowa receives $36$ inches of rain a year. Runoff is $25\%$ of total

rainfall, on average. Evapotranspiration of precipitation by crops and other plants in the

watershed is $22$ inches per year. During dry spells, the equivalent of $2$ inches of water from the

shallow groundwater are used by crops and other plants. The rest of the water in this watershed

leaves as base flow from the groundwater to the creek that flows through the watershed.

Through the vagaries of glacial geology the vast majority of the watershed is underlain by a

sandy aquifer that does not substantially connect to other watersheds or aquifers.

a$.$ Draw a control volume for the watershed and aquifer system.

b$.$ Write the water budget for the watershed under steady state conditions.

c$.$ What is the base flow of the creek in cubic feet per second?

$2.$ A combined light industrial, commercial, and housing development is proposed for this $2,000$

acre tract of land. The developer has discussed water supply with the local well driller and

shallow groundwater is deemed to be of sufficient yield and quality to supply water for the

proposed development. It is estimated that total use will be about $200$ gallons per day per

person. For water use purposes, the developer estimates that the usage will be the equivalent

of $1,000$ people. Wastewater will be treated near the watershed outlet and discharged.

Using a water budget, how much does the stream baseflow decrease in cubic feet per second

and in percentage of pre$-$development flow with the new groundwater use? $($Assume no other

changes to the water budget.$)$

$3.$ After development, changes to surface cover from roads, houses, etc. increase the runoff to $30\%$

of total precipitation. Rainfall, evapotranspiration, and steady state conditions are maintained.

a$.$ Does the stream dry up$?$

b$.$ Is the groundwater source a long$-$term sustainable option for the development? Why or

why not?