|
|
|
|
|
|
|
|
The town of Hemel Hempstead and the surrounding area are supplied by three groundwater pumping
stations that take water from the chalk aquifer. During times of high demand water can also be
imported from elsewhere through our network. The licences for the abstractions at the pumping
stations are governed by the Environment Agency.
Through the National Environment Programme investigations were undertaken during AMP3
(Asset Management Period 2000 to 2005) by the Environment Agency into the cause of low
flows in the River Gade. This work was combined with the development of a groundwater
model of the Colne catchment and was undertaken by consultants Jacobs Gibb. This work
identified that flow in the rural reach of the River (Gadebridge Park upstream) is reduced
by public water supply abstraction, exacerbated by historical channel modifications.
The project concluded that it was not financially viable to move the public water supply
to another location. Funding was secured in AMP4 (Asset Management Period 2005 to 2010)
to assess the current hydro geological situation in the catchment and come up with various
options for improving low flows in the river.
Project:
The River Gade is an ephemeral chalk stream which in its natural state would exist as a small
and shallow gravel-bed channel for most of its length. Throughout history human intervention
has significantly altered the river's development. The Environment Agency found that the
Upper River Gade suffers from low flows as a result of public water abstraction at Piccotts End
and Marlowes. During AMP3 (2000 to 2005) a study concluded that it would be uneconomic
to move the pumping stations to a different catchment and funding was secured for investigation
into other sustainable options for improving flow conditions in the Upper Gade.
An extensive monitoring program has enabled the collation of ground and surface water data.
A main point to note is the reduction in flow downstream of Bury Mill diversion weir even
during times of low flow as shown in the spot flow gauging results.
A working group, established in autumn 2006, has enabled the involvement of interested parties
with the detail of the project and has aided the development of the project with vital local
knowledge.
HEC-RAS (1D computer flow simulation) modelling has shown that the Bury Mill diversion weir
can be raised by 0.15m without causing major flooding whilst keeping flow within the main
channel at other times.
The options appraisal and cost benefit assessment concluded that option 7 is the best option.
Option 7 involves removing the Environment Agency gauging weir, re-grading the river and
diverting groundwater to the existing channel.
Three Valleys Water have now completed the full options appraisal for the Upper River Gade
Sustainability Study and have passed management of the implementation of these options onto
the Environment Agency. Three Valleys Water will remain involved with the project and hope
that in the course of time this work brings a phase in the future of the Upper River Gade.
We are currently writing the final Water Resources Plan for AMP5 (Asset Management Period
2010 to 2015) which can be found in draft form on our website;
http://www.veoliawater.co.uk/central
In order to help keep the river in good health you can help by reducing you water consumption.
See our water efficiency page on our website for ways to do this;
http://www.3valleys.co.uk/water_efficiency/index.shtml
Alex Back, Hydrogeologist, Three Valleys Water
|
|
