Towards safer, more sustainable debris and security screens

Abstract

The UK has over 35,000 primary, debris and security screens, intended to prevent internal blockage of culverts by debris and/or entry to a hazardous culvert. Historically some screens were constructed with insufficient justification, insufficient area or poor detailing, leading to increased flood risk and unnecessary safety risks to operatives, especially during high river levels. In 2019, CIRIA's Culvert, screen and outfall manual (C786) replaced the Environment Agency Trash and security screen guide and CIRIA Culvert design and operation manual. The manual encourages assessment of the ongoing need for screens and where they cannot be removed, to take a systems approach that considers the wider watercourse and catchment. This paper presents findings from early experience of using the manual on an Environment Agency programme to assess the continuing need for 92 screens in England. Early indications are that avoiding unnecessary screens and removing or modifying existing screens can improve safety, help natural sediment and debris movement along a watercourse, reduce operational expenditure, and support the net zero carbon target and UN SDG 13 (Climate action). It is recognized that every screen is unique and not every situation is covered by guidance. A novel design that reduces flood and/or safety risk can be justified with documented rational analysis.