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4. 38 Years of Llyn Brianne 4.1. Demand deficiency Cray and Usk remain on direct supply, although in 1972, an early change in the use of Usk was anticipated. Extra demand in East Carmarthenshire seems not to have arisen, or is included in present abstractions at Nantgaredig. Overall demand has also been less than estimated, with some 227Ml/d (50mgd) being distributed as far afield as East Glamorgan. 4.1.1. Usk water is fed by gravity to Bryngwyn WTW on the hill overlooking Llandeilo, before onward transmission as potable supplies to West Glamorgan. During treatment a certain proportion of this water is used for ’washwater’ and discharged into Nant Cib - hence the Towy receives several thousand gallons of good quality Usk water every day - unless Manorafon water is being used instead. 4.2. Potential abstraction at Manorafon continues and Consent was increased in 1985 to 36 Ml/d (8mgd). Very rarely used, it is confined to dry weather, normally in the summer, but was brought into operation early in 1992. Compensatory flows (377 Ml/d - 83mgd) relating to the abstraction do not have to conform with the requirements of the Prescribed Flow, because of allowances made for catchment input. 4.3. Compensation, Prescribed and Minimum Flows Apart from the duration of the tracking and trucking scheme, the specified minimum compensation outflow from the dam appears to have been satisfactory. Exceptions occurred during the 80's when short term flow fluctuations were caused by valve control problems, and an occasion when the flow stopped completely for a couple of hours. Bailiffs happened to be near by and the incident was opportunely employed to examine otherwise inaccessible parts of the river bed. 4.4. The Inspector interpreted SWWRA's meaning of the 'comparatively small proposed abstraction' as referring to 86mgd being a small proportion of the ADF. Whereas the description actually appears to refer only to the initial abstraction rate. This was confirmed by comments made by WRC. 4.5. Following the Water Act (1973), overall management became the responsibility of WWA until privatisation in September 1988. 4.6. During this period, the abstraction regime was changed. In 1977, the Consent was amended from specified hourly and daily amounts to average daily amounts. Abstraction, confined to night time, thus taking advantage of cheaper electricity, was achieved by higher hourly abstraction rates. This involved setting flows in excess of the Prescribed requirement. The effect was to cause a greater residual flow through the river whenever there was no abstraction taking place. Although this is beneficial in many respects, there are disadvantages. Sudden changes in river level certainly caused and are still causing some consternation among local anglers below Nantgaredig. At present, abstraction periods vary but take place, on average, for some 14 hours out of 24. The pre-WWA status quo has been reinstated with EA monitoring Dwr Cymru's operations. |
