Welcome to Durham's Archimedes screw - a pretty cool piece of engineering!
The Freemans Reach Hydro Generator uses an Archimedean Screw turbine to convert the hydraulic energy of the River Wear into electrical energy.
Power generation has taken place on the River Wear in Durham City for over 800 years since the medieval Bishop's Mill. This modern generation scheme is one of the first of its type in the UK that generates electricity using a main river in a city centre.
Located on the large diagonal Framwellgate Weir, the 100 kW Archimedes screw measures 13 metres in length and weighs in at 20 tonnes. The turbine exploits a net head of 2.83 metres and can use up to 6 cubic metres of the total mean flow in the river of 14 cubic metres of water per second (m3/s). This will generate an estimated 496, 000 kWh of electricity per year, enough to power the equivalent of roughly 113 UK homes, and will create a CO2 emissions saving of 248,000 kg/CO2/yr.
The River Wear is an important Salmonid River, with salmon and sea trout passing both upstream and downstream of the site. Therefore, as well as generating clean power, the hydro scheme is designed to improve the ecology of the River Wear by allowing fish and elvers to travel upstream more easily in order to access the upper reaches of the river. This involved the installation of a new Larinier fish pass in close vicinity to the screw turbine, as well as upgrading the existing pass located on the main weir.
For fish heading upstream towards the hydro scheme, the entrance to the Larinier fish pass is located close to the turbine discharge point. The Larinier fish pass will accommodate a wide range of fish, is relatively resistant to blockages, and is appropriate for locations like Freemans Reach where the upstream water level is relatively stable.
Heading further upstream, the exit of the fish pass is located sufficiently upstream of the turbine intake. This ensures that fish exiting the pass will be a safe distance from the stronger currents in the intake channel, thus preventing them from being swept back through the turbine.
The Archimedes screw turbine used at Freemans Reach is suitable for use as a fish by wash. Therefore, a fish screen upstream of the turbine is not required, as fish can safely pass downstream through the turbine.
The Freemans Reach hydro scheme is now completed, although the development of the surrounding area is still proceeding.
The coordinates for the cache require reading some of the information above and information at GZ. The cache is located at N 54 46.X W001 34.Y where
X = [(no. of blades of the screw) x (no. of photos at bottom of display board) x 37)] + (length of the screw)
Y = [(no. of 100 kWH per day power generation) x (total mean flow in the river of cubic metres of water per second)] - (no. of equivalent Olympic size swimming pools, litres per hour pass through the Archimedes screw)
Check summation of all the individual 6 missing digits = 25.