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

GROUNDWATER FLOW MODELLING
into grid cells; and particle tracking function allows the visualisation of flow paths and the
calculation of travel times.
6.3.2.1 Boundaries and grid layout
A uniform 50 x 50 grid, of cell size 36m, (Figure 6.3) was used with a single layer of 50m
thickness of a uniform media type. The desired transmissivity was then obtained by varying
the hydraulic conductivity. The grid was aligned approximately north-south with its centre at
OS grid reference SP 0750091500 The ground elevation of the layer was set 1 m above the
maximum fixed head values. No ground surface effects are therefore included in the model.
The boundaries set for the model are as follows:
1. Fixed head boundaries around the perimeter of the model. Head levels were assigned on
an individual cell basis using contour values obtained from mean head levels from
piezometers and monitoring wells.
2. No flow at the base of the model.
3. River cells are assigned a fixed river stage and a conductance relating to the river surface
area in the cell, the bed thickness and the bed hydraulic conductivity.
6.3.2.2 Model Parameters
Hydraulic parameters
Transmissivities in the range 10-320 m 2 d -1 have been obtained from pumping tests within the
Birmingham Aquifer (Jenkins, 1995). The sandstone underlying the model area comprises
part of the Kidderminster formation with a geometric mean value for bulk permeability of
4.95 md -1 (Allen et al., 1997). The thickness of the unit above the underlying coal measures
160