What is a Theis curve?
A log-log plot of the well function, W(u), versus the argument u, in which u describes for a confined aquifer the theoretical relationships among observation-well distance, time since pumping began, and the aquifer storativity coefficient and transmissivity .
What does unconfined aquifer mean?
A confined aquifer is an aquifer below the land surface that is saturated with water. A water-table–or unconfined–aquifer is an aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is able to rise and fall.
What is theis method?
The Theis (1935) solution is useful for determining the transmissivity of nonleaky confined aquifers from recovery tests. Analysis involves matching a straight line to residual drawdown data collected after the termination of a pumping test.
What is Theis well function?
The exponential integral is easily calculated with u defined as above and is known as the Well Function, W(u). The calculation of the cone of depression for different pumping rates for various periods of time is just one small part of a many faceted and detailed evaluation of a potential well site.
What is unconfined and confined aquifer?
Unconfined aquifers are those into which water seeps from the ground surface directly above the aquifer. Confined aquifers are those in which an impermeable dirt/rock layer exists that prevents water from seeping into the aquifer from the ground surface located directly above.
What is an unconfined aquifer made of?
Confined aquifers have a layer of impenetrable rock or clay above them, while unconfined aquifers lie below a permeable layer of soil. Many different types of sediments and rocks can form aquifers, including gravel, sandstone, conglomerates, and fractured limestone.
What are the assumptions in the Theis equation?
This implementation is based on the text “Hydraulics of Groundwater” by Jacob Bear (2007) and makes the following assumptions: the aquifer is infinite, confined, homogeneous, and isotropic; the aquifer is horizontal and groundwater flow is horizontal; and. the well diameter is negligible.
What is theis recovery?
The Theis recovery method considers the late-time residual drawdowns with the Cooper and Jacob formulations and it estimates the transmissivity and the ratio of storativity values during pumping and recovery periods.
What is U in theis equation?
Numerical Approximation W(u) is the exponential integral and is tabulated in many places (Abramowitz and Stegun, 1968). For specific values of u, table interpolation may be used to obtain the drawdown.
What is hydraulic conductivity of an aquifer?
Aquifer hydraulic conductivity (A) is the measure of the rate of flow of water in the aquifer. By definition, aquifer hydraulic conductivity is the ability of the aquifer to transmit water under the effect of a hydraulic gradient (Lobo Ferreira et al., 2005).
What’s the difference between a confined and an unconfined aquifer?
A water-table–or unconfined–aquifer is an aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is able to rise and fall. Water-table aquifers are usually closer to the Earth’s surface than confined aquifers are, and as such are impacted by drought conditions sooner than confined aquifers.
What is the cone of depression in an aquifer?
The cone of depression associated with a pumping well in a homogeneous aquifer. The large differences in drawdowns and related volumes of the cone of depression in the two types of aquifers relate directly to how the two types of aquifers respond to pumping.
How is Theis solution used in pumping tests?
The Theis (1935)solution may be used for the interpretation of pumping tests in unconfined aquifers through the application of the following simple correction to drawdown data measured during a test (Kruseman and de Ridder 1994): s′=s-s2/2b(1) where bis saturated thickness [L]
How are uncertainties in aquifer parameters are treated?
Uncertainties in aquifer parameters such as the storativity and transmissivity, saturation and unsaturated thickness are treated by probabilistic and statistical procedures leading to fundamentals of strategic groundwater storage calculation.