Catchment Based Solutions for Reducing Trash Screen Blockages, Kirklees Council

Using nature-based solutions to reduce the amount of debris in watercourses in Kirklees, West Yorkshire.

iCASP and Kirklees Council are working on a project to come up with a solution to reduce the amount of debris in water courses. This is line in line with Environment Agency’s ‘Working With Natural Processes’ report (WWNP). The project uses nature based solutions to reduce blockages downstream, this helps the council to keep trash screens on waterways clear.

The primary focus of the project has been flood risk reduction, however, many of the methods offer multiple benefits such as improvements to habitat, biodiversity and water quality. A resource fact sheet has been produced to inform owners of watercourses of their responsibilities.

Watercourse Blockages

The Blocking Triangle – For a blockage to occur all three of these elements must be present.

Vegetation is the key component of debris loads in urban settings accounting for

  • 85% in residential environments
  • 36% in industrial environments

Trash Screens and Culverts

Trash screens and culverts are usually found in urban areas, many have are modern screens are designed to follow best practice guides although other screens pre-date such guidance.

For instance, water has been a driving force behind historic industrial processes – culverts, mill gates, weirs and manmade watercourses are commonplace in traditional mill towns across Yorkshire and Lancashire.  However, historic trash screens and culverts are not up to date with current best practice.

Debris screens have been retrospectively added to many of these features to prevent blockages as the time in between maintenance has increased.

In many of these locations, the nature of the channel and culvert alongside limited financial resources, means redesigning culverts and trash screen is not a practical solution and regular clearance of trash screens is costly.An alternative approach is required that attempts to reduce the load reaching the trash screen.

An alternative approach is required that attempts to reduce the load reaching the trash screen.

How to Manage the Source of Blockages

Removing material before it becomes debris and routine clearance of material from both the watercourse and floodplain can reduce the debris load. However, this is unfavourable from an environmental perspective and requires negotiations with local landowners. Removing debris can cause ecological harm as some debris is needed for watercourses to function naturally. Debris and vegetation can slow the flow of water by increasing channel roughness – removing either can speed up flows with the ability to transport material and increase flood risk.

Changing the dominant species to one that produces less debris to minimise the amount of material entering channels is likely to have a negative impact on biodiversity both within the channel and the riparian zone. Changes to shading created by differing species and canopy densities can have a significant impact on stream temperatures which then has an impact on ecology. Riparian woodlands can play a key role in helping water courses adapt to climate change by helping to regulate stream temperatures – a diverse native broadleaf riparian woodland is most preferable (Keeping Rivers Cool, 2016).

Good land management can also reduce the amount of sediment within a watercourse, through a reduction in erosion potential and the interception of suspended sediments. Riparian buffer strips can help intercept and reduce sediment from reaching the water course. Fencing water courses help to reduce ‘poaching’ from animals and can encourage vegetation growth. Re-meandering and reconnecting the channel with its floodplain can also help reduce sediment loads and increase overall capacity.


Education is an important part of the project as many land owners and residents are unaware of their responsibilities to keep culverts, river beds and banks clear of any matter that could cause an obstruction and to keep trash screens and other structures clear from the build-up of excessive debris or sediment.

Owners of water-courses have the following responsibilities:

  • Allow water to flow naturally by removing blockages, fallen trees or overhanging branches from their watercourse. Trees and shrubs on the banks of a water course should be cut back.
  • Prevent water pollution by removing litter from the banks and not allowing garden waste (including grass cuttings) to be disposed of in water.

Owners of culverts, screens and outfalls are responsible for:

  • Passing on flow without obstruction, pollution or diversion, without affecting the rights of others
  • Keeping the bed and banks clear of any matter that could cause an obstruction
  • Keeping structures clear from the build-up of excessive debris or sediment

To help to protect water quality please DO NOT:
·      Throw anything which could cause pollution on the banks or in the water
·      Use riverbanks to dispose of garden including grass cuttings or other waste, where it could be washed into watercourses or wetlands. Vegetation cuttings which do not contain any invasive species can be left to compost at a suitable area on-site at least 10m away from any watercourses or surface water drains.