Spillways are essential to redistribute excess water from large reservoirs and artificially created or enlarged lakes and avoid potentially dangerous pressure on dam walls. Under the 1975 Reservoirs Act, water companies are duty-bound to maintain them.
Silt, debris and vegetation can prevent spillways from functioning and obscure structural damage. Maintenance is critical to ensure the reservoir continues to work, therefore spillways should be inspected every five years.
Stonbury’s maintenance programmes include a clean and inspection, followed by necessary repairs.
Preparation and clean
Assessments are conducted prior to all spillway maintenance work, and special planning is occasionally required to avoid damage to habitats during certain species’ breeding seasons.
Site set-up includes installing straw bales and debris netting at the bottom of the spillway to avoid contaminating the river. Eye bolts are fixed to spillway floors to attach fall-arrest blocks and safety winches, which allows operatives to walk safely on steeper parts.
Cleaning is completed by jet washing – using water pumped directly from the reservoir – to remove silt and debris from the floor, walls and joints. Shrubbery and grass is removed, and if necessary, vegetation near the edge of the spillway is reduced to avoid future growth into the spillway.
Organic waste material is often removed from the site for disposal, but where possible, it is spread on the grounds of the reservoir to reduce environmental impact.
Inspection and repair
Following completion of the clean, Stonbury carries out an accurate joint inspection with the client to identify areas requiring repair.
Specialist repairs to stone-set spillways include stone lifting, replacement, rebedding and repointing. Concrete spillways are repaired with rapid-set, environmentally-friendly and Water Regulations Advisory Scheme (WRAS)-approved mortars.