TM 5-815-5/AFM 88-5, Chap 6/NAVFAC P-418
(Modified from "Foundation Engineering, " G. A. Leonards, ed., 1962, McGraw-Hill
Book Company. Used with permission of McGraw-Hill Book Company.)
Figure 4-23. Approximate radius of influence R.
(1) Line drainage slots. Equations presented in
(b) Head losses in the screened section of a well
figures 4-1 through 4-5 can be used to compute flow
Hs are calculated from figure 4-24b. This head loss is
and head produced by pumping either a single or a
based on equal inflow per unit of screen surface and
double continuous slot of infinite length. These equa-
turbulent flow inside the well and is equivalent to the
tions assume that the source of seepage and the drain-
entire well flow passing through one-half the screen
age slot are infinite in length and parallel and that
length. Other head losses can be determined directly
seepage enters the pervious stratum from a vertical
from figure 4-24. Hydraulic head loss within a well-
line source. In actuality, the slot will be of finite
point system can be estimated from figure 4-25. As
length, the flow at the ends of the slot for a distance of
stated in a(4) above, flow into a well can be impeded by
about L/2 (where L equals distance between slot and
the lack of "wetted screen length," in addition to hy-
source) will be greater, and the drawdown will be less
draulic head losses in the filter or through the screens
than for the central portion of the slot. Flow to the
and/or chemical or mechanical clogging of the aquifer
ends of a fully penetrating slot can be estimated, if
and filter.
necessary, from flow-net analyses subsequently pre-
sented.
b. Flow to a drainage slot.
4-24
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