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

MONITORING NETWORKS AND METHODS
previous workers (Cey et al, 1998, Lee et al,1980 and Carr et al,1980) to quantify localised
groundwater discharge through lake and river beds. The two methods were given field trials to
assess their suitability to the local conditions and the data requirements. The riverbed mini
drive point piezometers were selected as the primary tool for the investigation.
4.5.1.1 Construction of Riverbed Mini Drive Point Piezometers (MDPs)
Piezometers were constructed of flexible 13mm OD (10mm ID) high density polyetheylene
(HDPE) tubing with a drivepoint screwed into the open tube (Figure 4.4) using 3.5 cm of
stainless steel studding thread (10mm dia) capped with a washer and nut. Located behind the
head was a 10cm open section of drilled holes screened with nylon mesh (100 microns)
secured by stainless steel wire. The piezometers were inserted inside a 2 m length (20mm ID)
steel tube and driven by hand into the riverbed using a fence post driver to depths of up to 2
m. The driving tube was removed leaving the MDP firmly in place. The MDP was sealed with
a rubber cork to prevent the growth of algae within the tube and to prevent artesian flow
which would disturb the natural system. The MDPs are firmly anchored within the riverbed
making them impossible to remove by hand (reducing the likelihood of theft) and this
combined with the MDP’s flexible nature prevented damage occurring during the three year
study period despite several large flood events.
A total of 96 MDPs were emplaced as a series of lateral and vertical profiles across the
channel at 18 different locations along the study reach (Figure 4.2, Appendix 11). High
chloride concentrations exist in the surface water owing to sewage treatment work discharges
and generally low concentrations were recorded in the MDPs. This implies that it was
primarily groundwater being sampled at depths of greater than 20 cm. Installation depths for
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