Study hard to secure a licence to abstract
Developing new abstraction facilities demands careful planning to avoid a host of pitfalls. Water adviser Simon Bamford, of Southern Water, examines the issues involved
DEMAND on water resources has become so intense that it is even becoming difficult to obtain a reliable winter supply.
So examining potential sources and their reliability at an early stage is vital. Not only will this avoid a waste of time and money in inadequate systems, it will also ensure the best chance of a new abstraction licence succeeding.
In most places direct summer abstraction licences are now hard to obtain. In some instances, as in Suffolk, even the lower reaches of big rivers are unavailable. The fear is wading birds will suffer if too much fresh water is removed.
The same is also becoming true of winter abstraction in some areas.
To obtain an abstraction licence and to be confident of a supply, hydrological feasibility studies are becoming more common.
A popular approach is to produce flow duration curves, which show how long a given flow rate is exceeded. That provides an estimate of the amount of water potentially available. Details of current abstraction licences can then be added to determine the available resource.
A switch in licence conditions is adding to the pressure for early planning. Minimum residual flows, which indicate natural base flow, are increasingly being replaced by minimum acceptable flows, which take account of environmental interests. More and more applications need an environmental statement, even for winter abstraction.
Hydrological studies also help with implementing an abstraction scheme. Surface water schemes may involve constructing control weirs and pumping chambers. Data from the hydrological study will help determine the correct weir levels and sizes and pumping regime. Bigger pumps may be needed to abstract quickly during brief, high flows, for example.
If a winter supply is desired the hydrological feasibility study may incorporate a reservoir study. This can help optimise location and minimise construction cost. Factors to consider are shown alongside.
Having established that a reservoir is both technically and financially feasible an investigation of the preferred sites is important.
The investigation, undertaken by excavator or drilling rig, should consider the factors shown in the box. There are plenty of examples of poor site investigation, including one client who obtained a winter fill licence for a below ground, clay-lined reservoir.
During construction ground-water flooded in, blowing off a clay lining and filling the reservoir. But the client could not use the water, as it was not licensed.
Lengthy discussions followed with the then National Rivers Authority. After 12 months of monitoring, submission of a new licence application, redesign and reconstruction the client was finally able to abstract.
Groundwater sources should be treated to the same planning investigations as surface water sources. Given that site geology cannot be seen, a phased approach will reduce financial risk and increase the chances of success.
The first stage of a borehole prognosis would involve an assessment of the geology, identifying any aquifers, an assessment of water quality, possible borehole yield, filling depth and chances of obtaining the required yield.
If the prognosis is positive a feasibility study should be undertaken. This would be broadly similar to that undertaken for a surface water source, except that the optimum borehole location would also be identified, and the borehole/pit depth and diameter determined.
Should the borehole or catch pit appear to be feasible, the next stage involves applying to the Environmental Agency for a consent to construct a groundwater supply and to test pump it (Sect 32 Consent). When giving consent the EA will specify details of any survey of water features it requires.
The water features survey should at this stage identify all springs, wetlands, wells, boreholes and pits in the same aquifer which may be affected by the development. This is usually between 500m (1640ft) and 2km (1.2 miles) of the proposed development.
Details of location and description of pumps and depths should also be supplied. The EA will then process the application and, hopefully, grant consent to drill and test, together with specifying water features which must be monitored during test pumping.
Tests can vary in length from 24 hours to several days. During that time water levels/flows in the specified area must also be monitored. The results must then be analysed and submitted to the EA, with the licence application, after advertising in the local Press and London Gazette. *
Securing a new abstraction facility to provide much needed irrigation water demands a rigorous approach to ensure success.
• Permeability of soils.
• Embankment materials.
• Water table.
• Ground stability.
• Construction materials.
• End use.
• Cost effectiveness.
• 1975 Reservoirs Act.
Other options available
It is increasingly apparent that more innovative water resource schemes are needed to overcome the difficulties of obtaining new or additional supplies. Some examples are:
lWater Transfer Ltd Lincolnshire farmers and the NFU obtained consent to construct a sluice and short culvert to transfer water from the River Witham into the West Fen drain system east of Coningsby. About 70 farmers have access to summer water which would not otherwise be available.
lLark Abstractors Farmers decided to co-operate on abstraction after having a total ban imposed in 1990. The group agrees to cut abstraction by a certain percentage, in exchange for a no-ban guarantee from the EA, allowing planned use of a limited supply.
lShared Reservoirs Growers group together to build a reservoir on the best site in terms of geology and/or water supply and then distribute the water via pipelines or watercourses. Now more feasible because it is no longer necessary to specify the land on which the reservoir water is to be used.
lConjunctive Use A low yielding borehole could be used with a surface water abstraction or reservoir to achieve the total quantity of water required. Alternatively, surface water abstraction in the early part of the season can then switch to a reservoir supply as river levels drop, so reducing the volume of storage required.
• Water supply, including discussions with EA.
• Distribution system.
• Electricity supply.
• Geology and groundwater.
• Cost benefit.