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Physical hydrogeology 61

BO X
Continued
2.9

Fig. 4 Definition sketch of steady flow to
two parallel streams from a homogeneous
unconfined aquifer with constant
recharge.

the aquifer. Adopting the Dupuit assumptions, the flow per unit From symmetry and continuity, the baseflow entering each stream
width is given by equation 15 and from continuity: per unit width of channel is equal to 2aW. If h is known at any point,
then the baseflow or recharge rate can be computed provided the
Q = Wx eq. 18
hydraulic conductivity is known. This type of analysis has been
By combining equations 15 and 18, then integrating and setting applied to the design of parallel drains on agricultural soils to calcu-
the boundary condition x = a, h = h , the following specific solution late the necessary spacing for specified soil, crop and irrigation con-
a
is obtained: ditions. A reappraisal of techniques used to analyse the horizontal
flow of water to tile drains that also separate the external boundary
h = h + W ( a − x 2 ) eq. 19 of the water table from the internal boundary of the tile drain is
2
2
2
a
K given by Khan and Rushton (1996).

Fig. 2.25 Groundwater flow net for a
two-dimensional vertical cross-section
through a homogeneous, isotropic aquifer
with a symmetrical valley topography.