- Identify the change in the water table level. The initial water table level is 3 m, and it drops to 7 m. Therefore, the change is \(7 - 3 = 4\) m.
- Calculate the volume of the aquifer that corresponds to this change in water table over the given area. The area of the aquifer is 1.0 ha, which is equivalent to 10,000 m². So, the volume change is \(10{,}000 \, \text{m}^2 \times 4 \, \text{m} = 40{,}000 \, \text{m}^3\).
- Determine the specific yield. The aquifer released 6000 m³ of water. The specific yield \(Y_s\) is given by:\(\displaystyle Y_s = \left(\frac{\text{volume of water released}}{\text{volume change of aquifer}}\right) \times 100\%\)\(\displaystyle Y_s = \left(\frac{6000}{40{,}000}\right) \times 100\% = 15\%\)
- Verify that the calculated specific yield falls within the given range of 15 to 15. Since the computed specific yield is exactly 15%, it fits within the specified range.
Important Questions from Groundwater Occurrence
An unconfined aquifer of areal extent $20 \text{ km} \times 20 \text{ km}$ has hydraulic conductivity of $4 \text{ m/day}$, porosity of $0.32$, and storage coefficient (specific yield) of $0.18$. If the initial saturated thickness of the aquifer is $30 \text{ m}$, and $4\times10^8 \text{ m}^3$ of water is extracted from the aquifer, then the decline in the saturated thickness is _____________ (rounded off to two decimal places) m.
An unconfined aquifer extends over an area of $1 \text{ km}^2$ and has hydraulic conductivity, total porosity and specific retention of $20 \text{ m per day}, 30\%$ and $10\%$, respectively. After pumping some groundwater from this aquifer, the water table dropped to a depth of $20 \text{ m}$ from the ground level. If the water table was initially at $14.5 \text{ m}$ below the ground level, the change in groundwater storage in million cubic meters would be_______
Match the following items between Column I and Column II with the most appropriate combinations:
Column I Column II P Properties of confined and semi- confined aquifers 1 Perched aquifer Q Property of an unconfined aquifer 2 Coefficient of storage R Property of semi-confined aquifer 3 Specific yield S A special case of an unconfined aquifer 4 Leakage factor A fully penetrating well is installed in a homogenous and isotropic confined aquifer. The aquifer has uniform thickness of 16 m and hydraulic conductivity of 25 m/d. Water is being pumped out from the well at a constant rate of $0.1 \text{ } m^3/s$ till steady state condition is reached. If a drawdown of 3.5 m is observed at a distance of 75 m from the well then the drawdown at a distance of 150 m from the well will be________ (in m, rounded off to two decimal places).
- One of the key assumptions made by Dupuit-Forchheimer about the flow behavior in the porous medium towards subsurface drains is
