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

STUDY SETTING
Ordnance Datum (maod) occurs to the south west at Romsley Hill and the lowest point of 70
maod is at Kingsbury, north of the Lea Marston Lakes (Figure 3.1).
The river has been extensively modified from its original form as a meandering braided river
system on a broad flood plain. More than 50% of the study reach has undergone engineering
works for flood defence purposes, including strengthening bank sides and straightening some
sections of the river. The channel bottom remains natural and unlined over most of its length,
apart from some concrete-lined sections beneath the M6 motorway (Figure 3.3). Some of the
tributaries have been brick lined (River Rea) or culverted (Hockley Brook). Bed materials
range from sub angular cobbles through gravel, sand and silt and include many artefacts.
Weed growth within the channel is limited during the winter months but is abundant during
the summer and is thought to have an effect on the hydrological regime by reducing flow
velocities (Clay, 1999).
Aside from groundwater discharge, sewage effluent is a major component of dry weather flow
in the river, with 55% of flow at the Lea Marston Lakes (Figure 3.1) attributed to sewage
discharge. Efforts to improve the surface water quality have led to the closure of some of the
smaller sewage treatment works (STWs) and the centralisation of treatment at larger plants.
Several STWs discharge upstream of the study area and one within it, at Rayhall (Figure
3.1a), which is intended to operate at a constant discharge of 30 Mld -1 . Sewage in excess of
this capacity is transported from Rayhall to Minworth STW, by the recently constructed Black
Country Trunk sewer, and discharged downstream of Water Orton. The STWs are a major
control on the surface water flow balance and the water quality within the river and introduce
a significant temporal variability to both. The daily fluctuation in surface water flows related
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