Understanding the Piezometric Surface
The question asks to identify the imaginary surface formed by connecting the water levels observed in wells drilled into a confined aquifer. This surface represents the hydraulic head of the groundwater within that aquifer.
Identifying the Correct Term
Let's analyze the options:
- Phreatic surface: This term generally refers to the upper limit of the saturated zone, often synonymous with the water table in unconfined aquifers.
- Piezometric surface: This is the correct term for the imaginary surface representing the hydraulic head (potential energy) of groundwater in a confined aquifer. It's the level to which water would rise in a tightly cased well penetrating the aquifer.
- Capillary fringe: This is a thin zone above the water table where groundwater is drawn upward by capillary action, but it's not the surface connecting well levels in a confined system.
- Water table: This specifically refers to the upper surface of the saturated zone in an unconfined aquifer, where the pressure is atmospheric.
Since the question specifies a confined aquifer, the surface connecting the water levels in observation wells is the piezometric surface.
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
