Ground-water Flow to Wells
Wells used to extract ground water (or inject)
Cone of depression - area around a discharging well where the hydraulic head
in the aquifer is lowered by pumping.
Want to compute drawdown and T and S.
Unsteady flow - flow in which head changes with time.
|(1.) Bottom confining layer|
|(2.) All geologic units are horizontal and of infinite extent.|
|(3.) Potentiometric surface is horizontal prior to the start of pumping.|
|(4.) Potentiometric surface is not changing with time prior to the start of pumping.|
|(5.) All changes in potentiometric surface position are due to the effect of the pumping well.|
|(6.) Aquifer is homogeneous and isotropic.|
|(7.) All flow is radial toward the well.|
|(8.) Ground-water flow is horizontal.|
|(9.) Darcys Law is valid.|
|(10.) Ground-water has constant density and viscosity.|
|(11.) Pumping well and observation wells are fully penetrating.|
|(12.) Well has an infinitesimal diameter and is 100% efficient.|
Unsteady Radial Flow
|Assume that the aquifer has a radial symmetry .|
|Radial flow toward well.|
|Plan view||Cross Section|
Use polar coordinates to describe flow.
Therefore, can express flow with-
|(1) q value of angle|
|(2) r Radial distance|
If Aquifer is isotropic in horizontal plane. Then ® Flow is radial.
Equation for confined (radial) -Hantush 1964
|r = radial distance from pumping well.|
If recharge- leakage through a confining layer
|e = rate of vertical leakage (L/T)|
Solutions to the equations are extremely useful
Use these equations to determine drawdown around a pumping well.
Aquifer test in a confined aquifer.
Aquifer test in an unconfined aquifer.
ENV 302 - Lectures