An area consists of a permeable well-sorted sands (white area in the map and cross-section) and impermeable granite (grey area). A river is flowing through the sands. Small streams flow in the granite and their water is captured and conveyed to three irrigated areas by pipes. Abstraction wells also supply water to the irrigated areas.

A. Where do we have the open space in the sands and how do we refer to this type of porosity?

B. Give a hydrogeological classification for the sands and the granite. Under which conditions could the granite rock be considered to constitute an aquitard?

In the area of the sand aquifer, covering 20 km2, we have:

• rainfall which is expected to cause recharge to the amount of 35 mm/year,
• water losses reaching the water table in the irrigated areas, estimated at 100,000 m3/year
• groundwater outflow into the river (base flow) to the amount of 500,000 m3/year

C. Compile the equilibrium groundwater balance for the sand aquifer.

D. Calculate the sustainable yield for the wells in the area considering a maximum allowable reduction of 50% of base flow. Assume that by abstracting more water the losses from the irrigated areas will not change.