Natural water retention measures – a nature-based solution

What are Natural Water Retention Measures (NWRM)?

Natural Water Retention Measures (NWRM) are multi-functional measures that aim to protect water resources and address water-related challenges by restoring or maintaining ecosystems as well as natural features and characteristics of water bodies using natural means and processes (EU, 2014).

The main functions of NWRM are to reduce flood risk, improve water quality, and create habitats. In carrying out these functions these measures can also provide multiple co-benefits such as climate regulation, climate change adaptation, improved soil management, and the creation of amenities.

NWRM are a broad range of measures in terms of physical scale, cost of implementation, and level of required intervention. The measures exist on a spectrum from those that restore natural processes to those that use ‘green-engineering’ to mimic a natural process to provide a desired function. It should be noted that there are many different terms used internationally to classify and describe the measures included here, including Nature Based Solutions, Working with Natural Processes, Natural Flood Management, and Engineering with Nature.

NWRM are not new; many measures that could be classified as NWRM already exist and are being implemented across different sectors plans and policies.

How they work

As the name suggests, these measures increase the retention time of water in catchments, for a period before it is passed downstream.

These measures can retain water in soils, aquifers, and ecosystems and the retention time can vary from sub-hour to a permanent increase in a catchment’s water retention. By holding water in catchments for longer, these measures facilitate a number of beneficial ecological processes that can improve multiple environmental outcomes, such as creation of new habitat, increases in biodiversity, interception and attenuation of pollutants, improvements in water quality, and where the soils are carbon rich, reduction in greenhouse gas emissions.

NWRM improve water quality by reducing pollutants before they become entrained in run-off and/or by intercepting pollutants once they are already entrained in run-off e.g. via wetlands.

NWRM can also play a role in flood risk management by reducing and delaying the onset of peak flow rates downstream.

They have been shown to be effective at reducing flooding in small catchments for frequent floods.

NWRM – measures with multiple benefits for climate mitigation and adaptation

NWRM can play a dual role with respect to climate change, providing both mitigation and adaptation functions. Several NWRM, and in particular restored peatlands, act as sinks for carbon dioxide, mitigating against climate change.

The predicted impacts of Climate Change scenarios for Ireland include more intense storms and rainfall events, drought, increased likelihood and magnitude of river and coastal flooding, adverse impacts on water quality, and changes in distribution of plant and animal species (Desmond M. et al 2017). NWRM can mitigate against these impacts by creating new habitats, reducing peak flows in our watercourses, and storing water in catchments to mitigate drought conditions. In this way, NWRM can assist us in adapting our catchments to this future.

EU policy document on natural water retention measures

A European NWRM study highlighted that all measures will achieve multiple benefits from implementation and given that these measures are typically aimed at re-naturalising the water environment, the benefits for habitats and biodiversity straddle all sectors and the vast majority of identified measures (EU NWRM, 2015).

Flood prevention and alleviation is also a benefit common to many measures, although the general view at present is that these measures alone are not the sole solution for flooding in Ireland. However, it is recognised that such measures will play a vital role in integrating flood risk management with other catchment management functions.

EU policy document on natural water retention measures (2015)

NWRM in Ireland

The WFD National Technical Implementation Group (NTIG) established a working group to look at the potential for NWRM in Ireland.

The working group determined that the best approach was to categorise NWRM in Ireland into the following five categories:

• Agriculture
• Forest
• Urban
• River Restoration
• Peat

The river restoration category is similar to the hydromorphology group referenced in the EU project, plus an additional category has been added to reflect the unique Irish conditions relating to peat.

Natural Water Retention Measures – overview and recommendations for use in Ireland

A report looking at the potential of NWRM across these five categories and multiple sectors was published in 2021 and is available here: https://stg.catchments.ie/download/wfd-natural-water-retention-measures/

Nature-based solutions and Sustainable Urban Drainage Systems

You can find our more about the implementation of Nature Based Solutions and Sustainable Urban Drainage Systems (SUDS) on the LA Waters Website: https://lawaters.ie/nature-based-suds/