Response to the following problem:
An unconfined alluvial aquifer is found to occupy an area of approximately 30 km east-west and 10 km north-south. On average, the aquifer contains a volume of water equal to about 1,500 GL. The aquifer is subject to sustainable management practices, and every year the water table rises and falls by an unknown volume. The average outflow rates for the system have been estimated as follows: 22,000 ML/yr is extracted for irrigation, 45,000 ML/yr discharges to the sea and 18,000 ML/yr discharges as base flow to streams.
In the same area, a circular dam has a diameter of 150 m and an average depth of 9 m.
Each year an unknown volume flows in and raises the water level; however the average evaporation rate is 700 mm/yr and 23 ML is pumped out each year for water supplies.