The Main Trench
Work on the Main Trench of the dam commenced in April 1923, but the work was limited until the River Hodder could be controlled and diverted through the tunnel or culvert in the hillside beneath the eastern end of the proposed embankment site. The diversion of the River Hodder through the culvert was first carried out on 27th August 1926 which then allowed work on the main trench to begin in earnest.
Dam trench marked out across the valley. Various buildings including loco shed, fitters workshop, works office etc. can be seen in the background.
Photograph from the late May Jackson collection, used by kind permission of Mrs. J. Cowking
The main trench across the valley at the dam site was 1,877 ft. long with a maximum depth of 75 ft. and an average depth of 54 ft. The width of the trench varied from 6 ft. to 24 ft.. It was excavated through 30 to 60 ft. of boulder clay and through calcareous shales until an impervious layer of bedrock was reached.
The main trench from the east bank
The main trench from the east bank in winter
Photograph used by kind permission of Mrs. M. Silverwood
Four electric cranes on gantries built out from the hillside, two on each side of the dam site, were used to lift the spoil excavated from the trench. Two steam cranes were used at the lower levels in the centre of the valley. The spoil was then emptied into railway wagons and carted away to form the base of the dam embankment.
The west section of the main trench
Large baulks of timber in huge quantities were required to shore up the sides of the trench. This meant a constant supply was needed to be brought in by road and rail from the Fylde Water Board sidings on the L.M.S. main line at Long Preston.
The east section of the main trench
Portable steam boilers and pumps were needed to keep the water which was constantly seeping into the trench from inundating the workings.
Bottom of the main trench - bedrock in the foreground
The more detailed information of the geology made available by the work on the Stocks Reservoir site, and in particular in the Main Trench, enabled the Board to decide that the authorised top water level of Stocks Reservoir could safely be raised, thereby increasing its capacity up to the total required for the whole watershed. This rendered the construction of the Hesbert and Greet Reservoirs authorised by the 1912 Fylde Water Board Act unnecessary and resulted in a substantial reduction in expenditure. This was given the necessary authority in the "Fylde Water Board Act, 1925".