Abstraction, Impoundment, Regulation and Entrainment
Abstraction is the term for the controlled removal of water from rivers, lakes etc. Both our rivers arise in high rainfall areas and there are a series of man made reservoirs (Impoundments) - the Elan on the Wye and the reservoirs at Crai, Usk, Talybont, Grynne Fawr and Llandegfedd on the Usk. These fill during high rainfall periods and the water so held can be used for supplies, either by releases down the rivers or by piping it away.
Abstraction points reduce river flows downstream and also cause the problem of Entrainment. This is the inadvertent taking of anything 'unwanted' - in this case the concern is for fish eggs, young fish etc. Screens to prevent this are in themselves problematical particularly for small fish eggs and juveniles.
On the Wye, the huge series of dams across the Elan allow water to be piped directly to Birmingham by a gravity feed. The current abstraction arrangement allows for a very small, continuous compensation flow to the Elan and this flow is augmented if the dams overflow. There is an arrangement that allows for an increase of water released if the lower Wye drops below a certain level at Redbrook (below Monmouth). This Regulation flow is used to support continued abstraction at Monmouth and the water is transferred to South Wales. Additional abstractions are made along the Wye's length for agricultural, industrial and domestic use.
While Usk, Crai and Grynne reservoirs provide water storage and release into the river, the Usk is abstracted at various points: Talybont reservoir is piped to supply south east Wales while water is pumped into Llandegfedd from the lower Usk via Court farm, and thence onwards for supply, again via the South East Wales circuit. The Brecon and Monmouthshire canal has its main abstraction at Newton weir, Brecon, but there are additional off takes from the Crawnon at Llangynidr and from several other tributaries downstream.
So what are the problems associated with the management of a catchment and its water resources in this way?
If managed efficiently, regulation of flow allows for:
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The extreme peaks and troughs of flow can be minimised, though some high flows are essential to good ecological status.
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Water can be provided at reasonable cost, effluent damage can be minimised.
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Some carbon free hydropower is generated.
However, the downsides include:
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Downstream of the various dams, the compensation flow has an abnormal temperature (high in winter, low in summer) and is far from ideal for hatching fish.
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The absence of spate flows can cause gravel compaction causing problems for spawning fish.
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The failure to renew sediment and gravel causes long term loss of spawning territory.
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Above the dams, valuable spawning territory is lost and often not compensated by opening other streams.
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Fish are lost due to problems with screening (Entrainment).
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However well managed, the benefits of water saved for low flows does not fully compensate the loss, particularly if water is piped to other catchments.
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It is impossible to manage appropriate abstraction in the face of unrestricted abstraction as in the case of abstractions of right such as the Brecon and Monmouthshire canal.
Underpinning the abstraction regimen is the so-called CAMS process. Whatever CAMS may achieve, it is not obliged to take account of the particular needs of the migratory, Annex 2 species (Salmon, Lamprey, and Shad) for which the rivers are given their EU protected status. It is therefore quite possible for the two rivers to be managed in accordance to the abstraction regulations required by CAMS but to fall well short of their Favourable Conservation Status or Good Ecological Status as required by the Habitats and Water Framework Directives.
These needs are assessed in a separate process, which unlike CAMS does not involve any stakeholder representation. Of particular concern is the additional abstraction from the Usk to support the leaks from the Brecon and Monmouthshire canal. Under current regulations, an ancient abstraction of right ensures that more than adequate amounts of water may be drawn off at several points from the Usk without any reference to the needs of the river or any particular requirement to conserve water.
The Foundation is as well placed as anyone to argue the case for a regimen that allows a more natural flow and is fortunate to be advised in respect of Water Resources by John Lawson, FREng, FICE, a recently retired consultant in water resource management and a keen angler with long knowledge of both the Wye and the Usk.
We expect significant developments in 2008 and will be actively engaged with the Environment Agency and abstractors to press for changes in abstraction to benefit the rivers.
