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

MONITORING NETWORKS AND METHODS
al. (1995) consider the characterisation of downward flow velocities by the temperature
response of shallowly buried (5-15 cm) thermistors to variable forcing temperatures applied at
the surface of the riverbed. Silliman et al (1993) discuss the three extremes of flow that may
occur within the river bed sediments.
1. The river is strongly gaining groundwater and sediment temperature will remain constant
dominated by groundwater advection.
2. There is zero flux through the sediments and temperature will be dominated by conduction
of the daily fluctuations of the surface temperature of the sediments.
3. There is downflow from the river to the subsurface, and sediment temperatures will reflect
surface variations with a phase lag and a reduced amplitude which may be characterised
by the advection and dispersion (conductance) equation.
These solutions consider only one dimensional flow and ignore other sources of thermal
energy such as biological activity or chemical reactions within the sediments. The solution of
Bredehoeft et al. (1965) was used to calculate a vertical flux from temperature measurements
taken from a series of multilevel piezometers within the riverbed (Appendix 16).
The one dimensional equation for vertical heat and fluid flow may be written as follows:
∂
∂z
2
TZ z
= − ( c
2
0 ρ 0v
z
∂T
/ k)(
) = 0
∂z
C0 is the specific heat of water = 1.0 cal.g -1 , (4.18 J.g -1 )
P0 is the density of water = 1g.cm -3
Vz is the vertical flow rate cms -1
K is the thermal conductivity of the saturated sediments
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