Question
Which one of these is NOT a source of sufficient water supply but can transmit certain quantity of water on a regional scale due to leakage?
The correct answer is
Aquitard
Groundwater Transmission: Identifying Aquitards
The question asks for a geological formation that is not a primary source of sufficient water but can transmit some water regionally through leakage.
Understanding Groundwater Layers
- Aquifer: A saturated layer of rock or sediment that can store and transmit groundwater in significant quantities. It is a major source of water supply.
- Aquitard: A layer with low hydraulic conductivity (permeability). It restricts groundwater flow but does not prevent it entirely. Aquitards can transmit some water slowly through leakage, acting as confining layers between aquifers.
- Aquiclude: An impermeable layer that significantly hinders or prevents the movement of groundwater. It effectively blocks water flow.
- Aquifuge: A layer that is completely impermeable and cannot store or transmit water.
Analysis of Options
Based on the definitions:
- Aquifers provide sufficient water supply, so they are not the answer.
- Aquicludes and Aquifuges are essentially impermeable and do not transmit water regionally, making them unsuitable.
- An Aquitard fits the description perfectly: it's not a source of *sufficient* supply due to its low permeability, but it allows slow transmission or leakage of water on a regional scale.
Therefore, the formation that fits the description is an Aquitard.
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Important Questions from Aquifer Properties
- An aquifer has a surface area of 100 km$^2$. With no recharge, assume that pumping out 2 $\times$ 10$^7$ m$^3$ of ground water resulted in a drop of the water table by 6 m. If the aquifer has a specific retention of 15 %, then the porosity of the aquifer is _____ % (rounded off to one decimal place).
- A well penetrates an unconfined aquifer. The water level (i.e., head) in the well prior to pumping is 25 m. After a long period of pumping at a constant rate of 0.05 m$^3$/s, the drawdowns at distances of 50 m and 150 m from the well are observed to be 3 m and 1.2 m, respectively.
The hydraulic conductivity of the unconfined aquifer is ______ $\times 10^{-4}$ m/s (rounded off to two decimal places).
Consider $\pi$ = 3.14. - A confined aquifer with a uniform saturated thickness of 10 m has hydraulic conductivity of $10^{-2}$ cm/s. Considering a steady flow, the transmissivity of the aquifer in $m^2/day$ is _______ (rounded off to one decimal place).
- A stratified confined aquifer consists of three parallel homogeneous and isotropic horizontal layers with thickness of 10 m, 5 m and 5 m. The layers have the same width. The hydraulic conductivities of the strata are 15 m/day, 20 m/day and 30 m/day, respectively. The water flow follows Darcy's law and is parallel to the strata. Considering the same hydraulic gradient for all the layers, the effective hydraulic conductivity of the aquifer is ________ m/day. [in integer]
If $d$ is the depth of an aquifer through which water is flowing, then the relationship between permeability $K$ and transmissibility (also known as transmissivity) $T$ is given by ________.
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