LLYN BRIANNE RESERVOIR

Llyn Brianne  is situated on the headwaters of the river Towy, near its source in the Cambrian Mountains. Described as a regulatory reservoir, its purpose is to supplement flows in the main river Towy during low flows, as compensation for potable water supplies abstracted some 40 miles downstream at Nantgaredig, near Carmarthen.

The Scheme attracted many objections, from its inception, and remains controversial  to the present day. This paper seeks to explain  its background, development and discuss its perceived dominance over the Towy since 1972.
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A brief lay-overview of the Report on the Public Inquiry into Building Llyn Brianne and the performance of the Towy during the 38 years since the plugging of the Dam, in February 1972.

1. Pre-Brianne

1.1.1. The Inspector, A S R Mutch AMICE, AMIME, Engineering Directorate, Welsh Office, held a public local inquiry in Llandovery, during December/January, 1966/7, 'into applications from The West Glamorgan Water Board relative to the Llyn Brianne Regulating Reservoir and associated works under the Water Acts 1945 and 1948, the Town and Country Planning Act 1962 and the Water Resources Act 1963' (Mutch 1967). The West Glamorgan Water Board (Llyn Brianne) Order 1968, came into operation on the 3rd July 1968. Licences to impound and abstract were issued on the 26th July 1968.

1.1.2. The Towy scheme was designed to meet the estimated demands of West Glamorgan, and parts of Carmarthenshire until the year 2001, when the average daily abstraction deficiency would reach 391 thousand cubic metres per day (TCMD), 391 Megalitres (Ml/d), or 86 million gallons per day (mgd). The 91 m high dam would hold back 61,000 Ml (13,400 mg), covering an area of 215 Ha (530 acres). It was claimed that the dam would top-off flood surges and reduce gravel migration in the middle river. Autumnal lowering of water level could reduce the incidence of winter floods.

1.1.3. Provision was made in the design for raising the height of the dam, if necessary, to almost double its capacity. Fisheries would be protected by a 'trapping and trucking' scheme, which in turn would be protected by financial settlements. Dead water would be kept to a minimum 2200 Ml (500 mg) by draw-off at a depth of 79M (250ft); oxygen deficiency would be alleviated by a spray flume on the outlet. Flow could be varied between 68 Ml/d (15 mgd) and 2200 Ml/d (500 mgd). Water would be abstracted 40 miles downstream at Nantgaredig, pumped 16.5 miles to Velindre near Swansea for treatment and supply.

1.1.4. River flows would be protected by Compensation, Prescribed , and Minimum flow regimes.

1.1.5. A total of 40 objections and 17 representations had originally been made regarding the proposals. The Inspector's report dealt with sustained objections and representations. Although MAFF had declared an interest in the fishery aspects, no further comment was received.

1.1.6. Cray (31 Ml/d - 7mgd) and Usk (36 Ml/d - 8mgd) direct supply reservoirs featured largely in the discussions. West Glamorgan Water Board (WGWB) claimed that these were being seriously considered for transfer to use as regulating reservoirs for the river Usk where abstraction demand was also expected to increase at a similar rate. Usk Water Board appeared noncommittal and they were excluded from the Order.

1.1.7. Consent had previously been given in 1965 by the Secretary of State for a temporary (10 years) abstraction point on the Towy, at Manorafon. Water abstraction was to be at a normal rate of 18 Ml/d (4mgd), but no more than 36 Ml/d (8mgd), to supplement supplies from slow-filling Usk during the summer months, and treatment at Bryngwyn WTW. The Welsh Office Consent issued in April 1966 anticipated, and was conditional on supersedure, by a Towy scheme.

1.1.8. No reference to this abstraction was made, under the pre-Brianne existing abstractions, by WGWB and the Capel Dewi abstraction (27 Ml/d - 6.1mgd) was wrongly described as being 18 Ml/d (4mgd). No reference was made to the impoundment and abstraction, by direct supply, of 8.2 Ml/d (2 mgd) from the Sawdde, at Llyn-y-fan Fach.

1.1.9. Of the estimated 391 Ml/d (86mgd) deficiency, 68 Ml/d (15mgd) would be required to meet an increased demand in East Carmarthenshire. The pipeline to Velindre was designed to take a maximum flow load relating to 323 Ml/d (71mgd).

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