The impact of urban groundwater upon surface water - eTheses ...

MONITORING NETWORKS AND METHODS
Q = total discharge to the river from the aquifer per metre length of river (m 3 d -1 m -1 )
k = conductivity of the aquifer (m d -1 )
Hs = head in the river (m.a.o.d)
Ha = head in the aquifer (m.a.o.d)
L = distance from the river bank to Ha (m)
r = the hydraulic radius of the river (m)
A = the cross sectional area of the river (m 2 )
P = the wetted perimeter of the river (m)
The calculation assumes perfect radial flow perpendicular to the section and an isotropic value
of k for the aquifer which at this scale is unlikely. A k value of 2 md -1 was used as a combined
estimate for vertical and horizontal conductivity. There is also an assumption that the river
bed sediments do not produce a significant drop in the values of Hs across the bed which
would introduce error.
An Excel spreadsheet was used to calculate flow at all points where data were available from
piezometers on the riverbank within the zone of radial flow (Appendix 18). The value of Ha
was taken from the piezometer and Hs from the river level perpendicular to the piezometer at
distance L. Values for P and A were based on survey data from agency flood defence profiles.
4.9.4 River Bed Sediment Controlled Darcy Flow Analytical Solution
The data derived from river bed piezometers may be used to calculate a flux through the river
bed (Figure 4.9) using the one dimensional Darcy flow equation :
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