Hodder Water Treatment Works Stocks Reservoir
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An investigation into the potential losses of fish on the filter plates at the Hodder Water Treatment Works Stocks Reservoir Item Type monograph Publisher North West Water, Fisheries Section Download date 06/10/2021 15:27:20 Link to Item http://hdl.handle.net/1834/24800 HODDER WATER TREATMENT WORKS STOCKS RESERVOIR. FISHERIES SECTION RIVERS DIVISION NOVEMBER 1984 AN INVESTIGATION INTO THE POTENTIAL LOSSES OF FISH ON THE FILTER PLATES AT THE HODDER WATER TREATMENT WORKS, STOCKS RESERVOIR. Stocks Reservoir is situated amidst the Forest of Bowland in the upper reaches of the old river valley of the Hodder. Located about 10 miles due North of Clitheroe its altitude is only 100 metres higher than that of this Lancashire market town. The water levels altitude of 180 metres is not unduly high compared with other Pennine Reservoirs but the upland catchment of moorland, reaching to over 500 m gives the reservoir truly oligotrophic characteristics. 1. CONTENTS Page Introduction 1 Investigative Procedures 5 Fish Stocking 5 Anglers Returns 6 Treatment Plant Fish Plates 6 Plant Operational Alternatives 8 Valve Tower Specifications 9 Investigative Findings 11 Fish Stocking 11 Anglers Returns 12 Treatment Plant Fish Plates 14 Physical and Environmental factors affecting fish ingress 15 Plant Operations Analysis 17 Discussions 22 Fish Stocking 22 Anglers Returns 22 Treatment Plant Fish Plates 24 Physical and Environmental factors affecting fish ingress 26 Plant Operations Analysis 27 Summary 31 Recommendations 32 Appendices 1 ,1>V<^VJ .bou w_ 19 73 - 1^X1+. 2 Stocks A.C. circular 3 Fish return form 5 Wind speed and direction 6 Anglers Returns 1983 and 1984 7 Population estimate 8 Fish densities 9 Stocks A.C. fish stocking record 10 Raw and compensation water quality 11 Fish stomach analysis References The reservoir was built in 1927 for the Fylde Water Board who primarily supplied water to Blackpool. The catchment of 9283 acres was initially controlled by the board, and more recently by the Water Authority, the practices of which will not have unduly altered the water chemistry of the reservoir. Moorland sheep grazing predominates, the peaty land producing a pH of around neutral whilst the peaty colour of the water shows the humic acid presence, readily seen in the fairly high hazen readings. The upland catchment is characteristically nutrient poor giving the reservoir it's oligotrophic status with fish food organisms in the static waters of the reservoir rather limited. However, prior to the construction of the earthen dam the River Hodder's upper reaches were annually populated with salmon and sea trout spawning on the riffles. The quality of the riverine salmonid production, upstream of the reservoir, was of such value that when the dam was proposed, compensation for loss of fish spawning was made by way of constructing Dunsop Fish Farm for the Board of Conservators. Natural trout spawning still exists in the Hodder headwaters and the extent of this will be seen in this report, reflecting the quality of wild brown trout in the reservoir. Additionally, the innate migration of trout still possibly exists in the native stock because a number of sea trout must have been land locked by the construction of the dam. There is believed to be a smolt migration downstream from the reservoir in the spring of each year and a behavioural characteristic of brown trout, as opposed to rainbow trout, causes the treatment plant to catch fish on their intake screens throughout the year. The water treatment plant situated below Stocks Dam can filter and treat 115 Ml of water per day. Water is taken from the reservoir by way of a draw off tower (Diagram 1) situated 200 feet out from the top level on the dam wall. The draw off tower has three 24" draw off ports each controlled by 2 X 21" valves. At any one time one or more, usually two, of these ports are open, allowing water and whatever is carried in suspension, through the 24" apertures into a 33" collecting main that delivers the water to the filter house. The supply is then divided into 3, flowing under pressure to three groups of batteries of filters, but prior to the water entering the rapid sand filters each supply goes through a screen called a fish plate. These fish plates are an original design structure (to be described later) a that the treatment plant design correctly allowed for the ingress of fish into the works. As opposed to other water intake structures that have screens to prevent initial ingress of any foreign body, or off line low pressure screens, Stocks has these on line pressurised screens called fish plates. 2. Appropriately'; named, these plates have collected fish regularly, the worst occasion in recent memory being back in 1959. Records did not exist for the numbers of fish lost to the plates prior to 1977 when the present superintendent thought it relevant to keep an unofficial record. This was no doubt, initiated due to the drought of 1976 and the records have been regularly entered up since, and form the basis for this study. Stocks Reservoir has been fished by Stocks Angling Club since the 1960's, the unproductive nature of the water only providing a marginal fishery. Since the 1970's diagnostic fishing has been carried out by the club members with the intention of monitoring the quality and type of fishing that the reservoir can produce. The more recent intention has been to make the reservoir available to the public to fish on a day ticket basis and plans to utilise the whole catchment have been in hand since the late 70's. In September of 1983 the Water Management Committee approved a plan for a public fishery on Stocks Reservoir and this was subsequently passed by the board in January 1984. The proposal was to put the fishery out to tender with a closing date in April, 1984 for the start of fishing in March of 1985. The Authority proposed to provide necessary basic facilities for access and fishing such as car parks, tracks, sewerage, cabin accommodation and electricity. This degree of development and provision of facilities required a lease of 7 years and an option available for two further 7 year periods. In addition to providing this infrastructure the Authority proposed to help initially stock the reservoir with a reasonable head of fish to provide a good "put and take" fishery. A heavy stocking of 100 lbs. per acre was stated with the reservoir at a standing summer level of 210 acres. Therefore, 21,000 lbs. of fish is to be introduced, half of which will be provided by the Authority on a long lease basis, the tenant replacing this stock on termination of the lease. The lease also stipulated that at least 30 day tickets will be available to the public and that the tenant will also provide boats for fishing. With a development of this nature the intention to make it succeed is clearly stated in the ample stocking density of 100 lbs./acre. Although this density decreases to about 601bs/acre when the reservoir is full there is a possibility that there could be substantial fish losses onto the fish plates at such densities. Excessive fish loss would not only mean a loss to the fishery but also an operational problem for the water treatment works in maintaining supply. 3. The objective of this study is to assess the degree and likelihood of fish ingress onto the fish plates at the present and proposed stocking densities. Also to evaluate the operational implications, and if necessary suggest methods of alleviating the problem. Three spheres of study have been undertaken to achieve these objectives, these being:- 1. To selectively stock the reservoir and monitor the angling club catches in order to assess the total population, relating it to fish plate losses and proposed stocking densities. 2. To monitor the fish taken from the fish plates and assess the reasons for their ingress. 3. To study the draw off tower and fish plates, and suggest ways of ameliorating or halting the loss of fish and consequent operational problems. 4. INVESTIGATIVE PROCEDURES Fish Stocking Stocks Reservoir, being a water supply impoundment is prone to severe seasonal fluctuations in water level, (see graph 1 and appendix 1). At top water level of 30.328 metres and 343 acres the density of fish will be at its normal winter biomass and as the area decreases in the dryer summer weather the density of fish will increase. An area of 210 acres was calculated to be a good average summer level for the reservoir. At 5 metres draw down this existed for half of the time between April and October. Consequently it was decided to stock fish, under the tenancy agreement, at this average water level with 100 lbs./acre. Subsequently as the reservoir level increased or decreased so would the density of fish, approximately in inverse proportion to the area. In order to simulate the anticipated heavy density of fish stocking it was proposed to stock the reservoir in 1984, for this study, twice. The initial stocking took place in March, when the reservoir was 2.5 metres down and covered 280 acres. The stocking of 1,000 rainbow trout took place in the neck of the reservoir near the dam, see map 1, thereby concentrating the fish to a partially confined area of the reservoir, near the draw off tower for the first few days. The relatively early date for this stocking was to enable a complete season for the study of angler catch population analysis.