- 8th April 2021
- Posted by: Miranda Pont
- Category: Blog
In the first of two blogs about the NERC Natural Flood Management Research Programme, Steve Rose, Technical Director explores the LANDWISE-NFM research project, looking at the role of two dimensional (2D) hydraulic models in evaluating the effectiveness of scalable and realistic land-based NFM measures.
We are working on two of the three NERC NFM Research Programme projects: LANDWISE-NFM and Q-NFM. The scope of the research programme has been co-designed with project partners, Defra, the Environment Agency, Scottish Environmental Protection Agency, the Welsh Government and Natural Resources Wales to improve our understanding of the potential effectiveness of various NFM measures in differing catchments across a range of flood risk scenarios.
LANDWISE-NFM will evaluate the effectiveness of realistic and scalable land-based NFM measures to reduce the risk from flooding from surface runoff, rivers and groundwater in groundwater-fed lowland catchments. As part of this research programme, we are developing two dimensional (2D) hydraulic models of three groundwater-fed lowland catchments of the River Thames, namely the River Pang, Loddon and Coln. These two dimensional (2D) hydraulic models are usually designed to focus on surface water flow paths through the associated catchments and examine how NFM interventions can contribute to reducing these fast-acting flood peaks at downstream receptors.
However, within lowland more mixed permeability catchments including chalk and limestone geologies, groundwater is a significant part of the water cycle which is not usually directly accounted for within NFM modelling projects. Working with our project partners Reading University and British Geological Survey, we are examining how these two dimensional (2D) hydraulic models can represent the groundwater proportion of the flood hydrograph and how NFM interventions may effect not only surface water but also groundwater flood risk. For a better representation of the hydrological processes and pathways within these lowland catchments, different models have been developed and coupled together, including surface water models, land surface models and groundwater models.
A significant challenge will be constraining the model uncertainties, at the full catchment scale as well as extended timescales involved with groundwater flood events. For the Chalk dominated Pang catchment, we have developed a coupled JFlow® (surface water) and a ZOOMQ3D (groundwater) model. This model has been used to simulate groundwater emergence throughout the catchment where the groundwater is forced onto the ground surface as the water table rises. In addition, we have tested specific rainfall events where precipitation is landing on a much higher groundwater water table and therefore further increase flood risk. The simulation showed good matches with gauged data at Frilsham and Bucklebury.
The modelling will test how different land-based NFM measures, together with some in-channel features, will affect the hydrological processes, flow pathways and flood risk within these catchments. We will consider measures like crop choice, tillage practices, tree planting and leaky barriers, that have been identified by local catchment stakeholders to have the greatest realisable potential.
The NFM measures will be evaluated for their ability to increase infiltration, evaporative losses and/or below-ground water storage, thereby helping to store incident precipitation, reduce surface runoff and slow down the movement of water to lower peak flood levels in groundwater and rivers. However, we need to carefully examine the balance between increased infiltration, soil water storage, deeper percolation/recharge and evaporative losses under different types of NFM measures, because long-term increases in recharge could actually increase groundwater and river flood risk in certain circumstances if there is limited available capacity within the aquifer and in rivers to store any excess precipitation from storm events.
Want to know more?
You can read the second of our two blogs about the NERC Natural Flood Management Research Programme exploring the Q-NFM project and how natural flood management measures can reduce flooding at larger scales here.
The NERC Natural Flood Management Research Programme will be hosting a webinar about the LANDWISE-NFM project. This is part of an ongoing series of monthly webinars run by the NERC Natural Flood Management Research Programme to allow NFM researchers and practitioners to share knowledge and experience and are open to all.
Modelling NFM in lowland catchments
Date: 29 July 2021
Speakers: Steve Rose, Technical Director, JBA Consulting. Dr Maleki Badjana and Professor Anne Verhoef, University of Reading. Dr David MacDonald, British Geological Survey.
You can sign up for your free place via Eventbrite here.
JBA Consulting has over 10 years’ experience in NFM and have led the consortium that delivered the Environment Agency’s Working with Natural Processes Evidence Base, published in 2017. We also have extensive experience in modelling multiple distributed natural flood management (NFM) measures within whole catchments. If you would like more information, please contact Steve Maslen, Head of Environment. You can also find out more on our NFM webpages.