Aquifer Properties: Understanding Transmissivity
The question asks for the term that represents the product of hydraulic conductivity and aquifer thickness in a saturated condition, specifically for horizontal flow.
Defining Transmissivity
Transmissivity (often denoted by T) is a key property of aquifers. It quantizes the ability of an aquifer to transmit water horizontally. It is mathematically defined as the product of the aquifer's hydraulic conductivity (K) and its saturated thickness (b).
The formula is:
$ T = K \times b $
Where:
- T = Transmissivity
- K = Hydraulic conductivity
- b = Saturated thickness of the aquifer
This value is crucial for calculating flow rates in aquifers using Darcy's Law for regional flow.
Evaluating Other Options
- Specific Yield: This represents the volume of water drained by gravity per unit volume of aquifer material. It relates to water released from storage during drainage, not horizontal flow capacity.
- Coefficient of Storage (Storativity): This relates to the volume of water released from or gained into storage per unit surface area per unit change in hydraulic head. It's important for understanding how water levels change with pumping, particularly in confined aquifers.
- Seepage Force: This is a force exerted by flowing groundwater on the aquifer solids. It's relevant in scenarios like slope stability or filter design, not the overall transmissivity.
Therefore, the product of hydraulic conductivity and thickness directly defines transmissivity.
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 ________.
