Nature-based Solutions for Catchment Management

Nature-based Solutions for Catchment Management (NbS-CM) work by storing or attenuating water in the environment, allowing it to be released slowly either as run-off to rivers and streams or by soakage to the water-table, or by slowing the flow of water along watercourses. By slowing or reducing runoff, flood flows downstream can be reduced.

This is typically achieved by changing land-use practices in the catchment so that soils have a greater capacity to store water or by constructing new storage such as retention ponds or by rehabilitating wetlands. In-channel works and restoring river meanders can also be used to slow the flow.

As well as the potential for flood reduction, the principal advantage of NbS-CM is their ability to achieve ‘co-benefits’. Some of these co-benefits are listed below:

• Many of the measures will improve water quality and create or enhance existing habitats.

• Afforestation and peatland restoration provides carbon storage.

• Some measures can filtrate pollution from runoff.

• Measures that improve soil structure can increase agricultural productivity by reducing the loss of valuable topsoil.

• Improvements to the environment can improve quality of life e.g. river restoration in an urban environment creates a more attractive public amenity.

While pilot and demonstration projects have shown that NbS-CM can provide benefits in reducing flood flows in small catchments, there is very limited evidence that they would provide significant benefits in large scale catchments. These projects have also demonstrated that NbS-CM can reduce the hazard of more frequent, low intensity floods. However, the OPW target standard of protection for flood relief schemes against river flooding is for more extreme floods, such as the 100-year flood, and the benefit of NbS-CM during more extreme floods would typically be reduced.

NbS-CM have not been widely implemented to date in Ireland, but the OPW is active in pursuing this approach for future application. Current work in this area includes:

• The OPW is co-funding the SLOWATERS research project to examine the effectiveness of soft engineering measures in agricultural lands.

• The OPW has provided funding to the Inishowen Rivers Trust in Donegal to investigate the use of such measures to reduce flood risk and provide co-benefits.

• The development of capital flood relief schemes now involves a specific requirement to assess the potential for NbS-CM as part of the potential solutions to managing flood risk for a particular community.

• The OPW is working with the EPA and others to identify approaches that could be used to develop integrated catchment management measures to provide benefits to multiple sectors.