Computing Flow through Well Screens Using an Embedded Well Technique.

摘要

PURPOSE: The purpose of this Coastal and Hydraulics Engineering Technical Note (CHETN) is to document a computational technique developed to compute the flow rates through the screens of groundwater pumping wells or relief wells. The technique was developed for the three-dimensional (3D) groundwater (GW) flow simulation using the finite element (FE) method. BACKGROUND: Accurate estimation of flow rates through well screens is essential in groundwater modeling and may impact decisions based on the simulation results associated with various project alternatives. In reality, the flow rate through a well screen can vary both spatially and temporally due to heterogeneity and variability present in the surrounding subsurface environment. The location of the pump within a pumping well may also impact the flow rate distribution. However, a uniform distribution of flow throughout the screen length, resulting from the total pumping rate divided by the screen length, has been often assumed and employed to characterize groundwater withdrawal in groundwater modeling due to its simplicity. This may cause inaccurate model calibration and lead to poor decisions as a result. For relief wells used to protect earthen levees, accurate estimates of flow rate through well screens under various hydrologic conditions is essential to the design of both the relief well system and the associated surface conveyance system so that excess groundwater coming out of relief wells shall be diverted efficiently, effectively, and economically. In this CHETN, a computational technique, hereafter called the embedded well technique, developed to compute flow rates through well screens is described. This technique is applicable for groundwater flow model simulations using the finite element method.