Mr and Mrs R. Holmes
Private hydro-power generation scheme and associated
River Wey in Surrey
– Coir Rolls. Pre-vegetated
– Coir Rolls. Unplanted.
– Turf Reinforcement Mat
– Vertical revetment
– Welded mesh gabions
– Rock rolls
– Hardwood fagots
– Hard wood stakes
– Oak decking
– Oak fencing
– Bridge structures and Steel fabrications
– Artificial plastic reeds fish brushes
– Hydraulic sluice gates and control system
– Geo-thermal heating system
– Hydro-power Archimedes turbine generator
– In-stream structures
– Brickwork form work
– Reinforced concrete structures
Mill House is situated bankside on the River Wey in Surrey. Originally part of a flour mill built c.1768, rebuilt 1876, and demolished in 1922. The wheelhouse, which is still part of Mill House, initially held a 15 ft. breast shot water wheel. The river is once again being put to use producing energy. This all-encompassing project required the disciplines that brought together sound engineering practices while at the same time ensuring wherever possible, that the work carried out would protect, maintain and improve the environment.
Priority had to be given to conform to EU directives and environment agency regulations. Planning permission for hydro generation also required careful consideration catering for migratory habitats of fish and eels. The installation of the hydro-power generator will deliver electricity to the client while surplus supplies are sold on to the national grid. Incorporated into the scheme is a geothermal heating system installed within the structure for the Achilles screw turbine. The heat pump transfers hot water to the domestic quarter’s central heating system.
Initial work required the excavation and construction of a channel designed to house the Archimedes screw driven generator and geo-thermal heating system. Emanating from the main water course, outflow from the screw discharged into the mill pond via a bypass stream. The old wheelhouse was reinforced and refurbished to accommodate the new hydraulic sluice gate housing and the controls to regulate water levels and flow rates to the turbine channel. The existing iron frame foot bridge to the front of the wheelhouse structure was removed and refurbished, The footway adjacent to the wheelhouse and turbine channel was completed with the fitting of oak decking
boards following its reinstatement.
To protect migratory and course fish populations a fish pass has been construction 200m upstream clear of the turbine channel. One of the key elements to the successful operation of the fish pass channel is the installation of artificial plastic reeds referred to as “fish brushes”. These fish brushes slow the water flow down and create eddies and back currents to enable fish to swim up the pass. Remedial aquatic bio-engineering has been carried out to reinstate and protect eroded banks along the property, new habitat has been created, water meadows restored, and the biodiversity of the project site totally enhanced.
To provide access to adjacent banks of the property for both pedestrians and garden machinery two 2m wide bridges were placed across the channels. These units were pre-fabricated in A.G.A.’s workshop at Merton and shipped to site for ease of installation.
The old wheelhouse was completely refurbished and is used to house the hydraulic sluice and control system enabling smoother flow management and reducing flood risk. The Achilles screw speeds are adjusted to maintain defined upstream river level. During peak flows, once the screw reaches maximum speed, sluice gates open to maintain water levels.
The iron footbridge accessing the wheelhouse was removed and renovated. The old foot boards were replaced with oak planks and the walkway replaced across the channel and spillway.
Excavation of the turbine channel from the main river to a bypass stream was constructed to accommodate both the hydro-electric generator and the heat pump system. Sited to the left of the wheelhouse from where water flow and discharge are controlled.
Shuttering and form work for pumped pre-mix concrete used to create the turbine channel. The steelwork frame located within the turbine channel to hold the stainless steel geo-thermal heat panels. Ready for installation the generator is hoisted onto the site with a high lift crane and located into the channel. Discharge water from the generator empties via the bypass stream into the mill pond. A steel trash screen built into the mouth of the channel excludes heavy debris. Oak decking covers the area forming a new path to the footbridge.
The reinforced concrete structure ensures unrestricted movement
and protection of the migratory and coarse fish populations.
A range of bioengineering systems were used to prevent erosion and undercutting of the banks along 200m of the client’s bank. Products included unplanted and pre-vegetated coir rolls, A.G.A. Span vertical revetment, rock rolls and hardwood fagots, each used according to the dictates of the site conditions and habitat creation required.
TRM’s (turf reinforcement mat) were used for soil stabilisation during recovery and naturalisation of the bank. TRM’s will keep the soil in situ during the establishment of under sown grass and wildflower seeds while providing a microclimate for successful germination.
Two 2m wide bridges have been installed across the River Wey for machinery access to wildflower meadows. Both bridges were pre-fabricated at A.G.A. Group Merton workshops and then installed on site over presited steel box sections spanning the river.
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