An aquifer was located at a certain place, and the area of the zone 900km² is bounded by a confined aquifer of 20m thickness. The average minimum and maximum piezometric levels variations range between 4m to 10m. Hence, compute the annual rechargeable groundwater storage from this area and the average well yields if the area consists of 40 wells, each pumping water for irrigation for about 200 days in a year.
Answer (2)
To compute the annual rechargeable groundwater storage and average well yields, we need to determine the volume of water available in the aquifer and how much is being extracted by the wells.
Step 1: Calculate the Rechargeable Groundwater Storage
The volume of groundwater storage can be computed by using the formula:
Volume of Storage = Area × Thickness × Δ h
Where:
Area = 900 km 2
Thickness = 20 m
Δ h = change in piezometric level = maximum − minimum = 10 m − 4 m = 6 m
Convert area from km 2 to m 2 :
900 km 2 = 900 × 1 0 6 m 2
Now substitute the values into the formula:
Volume of Storage = 900 × 1 0 6 m 2 × 20 m × 6 m
Volume of Storage = 108 × 1 0 9 m 3
This represents the total rechargeable groundwater storage.
Step 2: Calculate Average Well Yields
Now, we'll calculate the average well yield if there are 40 wells, each pumping water for 200 days in a year.
Average Daily Yield per Well = Number of Wells × Days of Operation Total Volume of Storage
Average Daily Yield per Well = 40 × 200 108 × 1 0 9 m 3
Average Daily Yield per Well = 8000 108 × 1 0 9 m 3
Average Daily Yield per Well = 13.5 × 1 0 6 m 3
Thus, each well can potentially yield approximately 13.5 × 1 0 6 m 3 of water per day. However, this is a simplified calculation, and real-world factors such as distribution efficiency, evapotranspiration losses, and actual pumping capacity need to be considered to refine this estimate.
The total rechargeable groundwater storage from a 900 km² area with a 20 m thick aquifer is 108 billion cubic meters. Each of the 40 wells, operating for 200 days a year, can yield around 13.5 million cubic meters of water daily. These calculations provide important insights into groundwater availability for irrigation purposes.
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