ETL 1110-1-162
30 Sep 01
Figure B-3. Head build -up in drainage layer.
(a) Manual Methods. To calculate infiltration through the topsoil and select fill and into the
drainage layer, one may assume that Darcy's formula applies for saturated systems under laminar flow.
A worst-case scenario is assumed to determine Q IN. The assumptions are as follows: 1) the cover soils
are saturated prior to a storm event; 2) evapotranspiration effects are negligible; and 3) there is no
percolation through the barrier layer. As precipitation falls onto the cover, water will flow into the
drainage layer at a rate generally limited by the permeability of the cover soils. This method, depicted in
Figure B-3 and summarized below, is further described by Thiel and Stewart (1993).
QIN = KCS I A1
where
QIN =
flow into the drainage layer
KCS =
hydraulic conductivity of cover soils
I
=
gradient (1 for this case)
(unit width) (slope length, L).
A1 =
Similarly, for planar flow through the drainage layer:
QOUT= KD I A2
where:
B-13
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