Source/Archive record SCH7968 - Chester Tidal Weir Inspection Report

Hughes Sub Surface Engineering Ltd was commissioned by Cheshire West and Chester Council in July 2015 to undertake a diving and surface inspection on the Chester Weir located on the River Dee to check its overall condition, including any defects, scouring and undermining. The inspection occurred between 29th and 31st July 2015. A walkover survey was made to assess the general environment surrounding the weir in advance of the diving inspection. Additionally a walkover inspection was made to check the visible/shallow water elements of the upstream weir structure and crest. The current weir was originally the site of a causeway across the River Dee (remenants of which exist immediately downstream of the current weir toe. The weir is believed to have been first constructed in sandstone in 1093. The weir continues to provide three essential roles in maintaining the very substantial water abstractions from the River Dee. It prevents tidal water ingress up-river for all but the highest tides; it provides the water head for an abstraction immediately behind the weir and it holds back what is a long linear lake which enables the largest abstraction to be taken at Huntington for the United Utilities supply to the Wirral and surrounding area. The weir structure was found to be in overall good condition with no obvious signs of gross defect. Its back face was intact although its profile varied along its length. The masonry blockwork setts were found to be intact, secure and well jointed. The upstream silt river bed meets the back face of the weir approximately 7m back from the weir crest. Some localised debris overlay the back face. The crest was found to be intact and functioning, with flow rates over its top regular and without any obvious interruption. The sloping weir appeared to be in good condition. Minor scour was observed along the length of the toe blocks to weir slope; the blocks were complete but had an irregular alignment. More significant scour was noted at CH10 at toe level and it is recommended that areas of scour should be monitored. Also recommended was survey by high resolution multi beam echo sounder at mean high water springs to produce a 3D digital image of the entire weir structure.