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1. Pre-Brianne (cont)
1.2. Flow regimes
The scheme provided for a minimum (compensation) flow out of the dam, to protect the upper river, together with a water bank for regulation losses and provision of fisheries freshets; a prescribed flow to protect main river flow, and a minimum flow below the abstraction point. WGWB stated that :- ' Abstraction would chiefly affect that stretch of the river between the point of abstraction and the salt part of the estuary. The whole stretch of the river above the point of abstraction would benefit from the regulation releases and in the lower parts of the estuary tidal flow would tend to dominate the river flows in drought conditions'. Maximum hourly, daily and yearly abstraction rates were specified in the terms of the Licence.
1.2.1. Compensation flow - minimum 68 Ml/d (15mgd)
The terms of the Licence specified a discharge in a uniform continuous flow of not less than 15mgd (68 Ml/d). The terms were described by WGWB as 'agreed in principle' with SWWRA. The Water Resources Board (WRB) considered that 'the proposed regulation and abstraction conditions might require adjustment either way in the light of experience so that the best use was made of the water resources of the River Towy. Provision for a review of this kind was available in sections 42 and 43 of the Water Resources Act 1963'.
1.2.2. Matters which 'might might merit review' were :- (a) the proposed minimum release of 15mgd at all times because such releases might be excessive during medium and high flow conditions; natural flows under present conditions were less than 15mgd for about 20% of the time; the dry weather flow from the catchment above the reservoir was about 3mgd, and (b) the prescribed flows at the point of abstraction.
1.2.3. SWWRA described the flow as 'barely sufficient' to attract ascending fish into the lower fish trap and otherwise unacceptable. The average daily flow (ADF) was 40mgd and additional freshets of 15 - 35mgd would be required. 50% of the water bank would be used. 15mgd also represented the minimum flow to maintain the amenity-related visible presence of the river between the dam and the Doethie confluence.
1.2.4. WRB's DWF of 3mgd was accepted but occurred on only five days in 1947 and 49 in a related catchment. The long term average flow of the Upper Towy was estimated to be 60mgd. SWWRA concluded that 'the 15mgd compensation water should be looked at in the light of these matters'.
1.2.5. Prescribed flow - 682 Ml/d (150mgd)
The licence specified that when the flow per day measured at Ty-Castell, differed from the flow measured below the dam was, (a) by 150mgd (682 Ml/d) or less, discharge must be augmented by an amount equivalent to the abstraction, and (b) exceeds 150mgd, abstraction shall not cause the flow to fall below 150mgd, less the quantity abstracted at Capel Dewi.
1.2.6. SWWRA did not know what flows were required to attract fish (salmon) into the river from the estuary. It appeared that little fish movement took place below 300mgd, and best catches occurred in flows of 800 - 900mgd. The poorest catches occurred in flows less than 100 and more than 1600mgd. The Prescribed Flow of 150mgd should apply only to the very limited proposed (initial) abstraction. The 150mgd was less than 25% of the mean average flow over a 6 year period. Any Minimum Acceptable Flow ultimately determined should be considerably higher than the proposed prescribed flow.
Ty Castell gauging station was not sensitive enough nor suitable for the purpose in hand. It was planned to build a measuring weir near Nantgaredig and include a gauge.
1.2.7. Minimum flow - 135 Ml/d (30mgd)
At no time was the flow below Nantgaredig to fall below 30mgd. WGWB acknowledged that the condition of sewage and effluent discharges into the river at Carmarthen 'was unsatisfactory'. Discharges then amounted to about 1mgd of untreated sewage (excluding 'considerable infiltration') and milk effluent (5day BOD 600 -700 mg/l).
1.2.8. The proposed flow appeared to SWWRA 'to have little or no significance for fisheries conservation or the disposal of sewage effluent'. Such flows were very rare. WGWB had been told that SWWRA would not accept 30mgd as an MAF. 'From all points of view this was too low a figure'. After proposed improvements to sewage and effluent treatment, a flow of 130 - 140mgd (591 - 636 Ml/d) would still be required for dilution. Even then, a theoretical 4mg/l BOD would be exceeded during increased morning discharges.
1.2.9. Stage 1 of Carmarthen Borough's sewage treatment comprised of partial treatment of just 37%, plus an allowance for infiltration, of the then total discharge of 3000 M3d (645,000 gd) DWF (plus infiltration). Scheme completion was due in early 1967. Stage 2 was expected in 1971 and would include the remainder. Secondary treatment was to be operational in 1983.
Milk effluents from 2 creameries were to be treated by high rate filtration in a joint STW, together with sewage from Llangunnor. A consent had been issued for a discharge of 2200 M3d (500,000 gd) at a 5day BOD of less than 120 mg/l.
1.3. Scheme Management
1.3.1. SWWRA considered that overall responsibility should be vested in the Authority which would be responsible for flow regimes. Telemetry at the Llanelli HQ would facilitate instructions to be sent to Velindre for control valve variations.
1.3.2. The terms of the licences for discharge and abstraction were to be agreed between WGWB and SWWRA. Secretary of State was to determine where necessary.