Lecture 30 : Dewatering [ Section 30.3 : Design steps for dewatering systems ]
Distance of well points from the source of seepage
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If the radius of influence R is large compared to the radius of the well, only an approximate estimation of R may be sufficient since the discharge is not much sensitive to the value of R
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An accurate estimation of the distance L from the well to the river should be made for a particular dewatering system, since the discharge is inversely proportional to the value of L.
Effective Wall Radius ru
The effective wall radius is decided based on the installation of the wells with or without filter. If a well is installed without gravel or a sand filter the effective radius can be taken as one half the outer diameter of the well screen. If a filter is used, the well radius is taken as one half the outside diameter of the filter.
Discharge computations
The discharge Q of the well is then calculated using the formula given below:
where Q is the discharge, k is the permeability, H is the depth of strata, h is the height of water in the well, r is the radius of well, R is the radius of influence.
