Project Groundwater: Enhancing Community Resilience, England
- Alastair Sheppard
- Nov 22, 2024
- 4 min read
What our customers say:
“Communities nationwide lack effective support due to insufficient monitoring and modelling of groundwater flood risk. These new groundwater hazard maps represent a significant step forward for groundwater flood management. This is long overdue, and Project Groundwater will advocate for this level of mapping to be produced and made freely available on a national scale, as these will be.”
Jed Ramsay Project Leader Project Groundwater, Buckinghamshire Council
Project Groundwater is dedicated to helping communities become more resilient to groundwater flooding. Led by Buckinghamshire Council, the project collaborates with communities in nine high-risk flood areas of the Chiltern Hills and Berkshire Downs, spanning six local authority areas. Funded by Defra as part of the £150 million Flood and Coastal Resilience Innovation programme, the project is managed by the Environment Agency to develop and test innovative, community-tailored resilience approaches.
Significant progress has already been made in groundwater flood modelling, with innovative solutions developed to issue timely alerts and design resilience and place-making activities specifically for managing groundwater flooding.
While flood hazard mapping is widely available for rivers, the sea, surface water, and reservoirs, groundwater flood maps have not reached the same standard, leading to under-representation of its impact and limited risk management.
Initially, MODFLOW was used to estimate the rate of groundwater emergence. Flood Modeller was then employed to route (2D) the groundwater fluxes and produce flood depth results. The downstream limits of the Flood Modeller 2D domains were aligned with river gauging stations, facilitating model calibration. These stations were verified to have reliable daily flow records for the dates of maximum groundwater levels represented.
Six separate hydraulic models were set up, covering both the Chilterns Chalk and Permeable Superficial Deposits areas. For the Chalk areas, the resolution of the 2D domain was 4m for the smaller models (Pang and Kimpton) and 6m for the larger ones (Chalfont St Peter). The domains utilised resampled Integrated Height Model (IHM) data from the Environment Agency, with a horizontal resolution of 2m. Model roughness for each model was derived from Ordnance Survey MasterMap data.
To streamline the modelling process, GIS analysis was first conducted to identify groundwater emergence points. Inflows of less than 0.005 m³/s were aggregated and applied as a single direct inflow boundary. Downstream boundaries assumed free flow conditions based on the slope of the local watercourses.
Preliminary Simulations and Optimisation
Preliminary simulations were conducted to verify the flow paths identified in the GIS analysis and rectify any false obstructions in the IHM data caused by structures such as bridges or improperly defined watercourses. These needed to be 'burnt' into the 2D domain for accurate representation.
Flood Modeller was run until a steady state between inflow and outflow was achieved. In longer, narrower catchments like the Misbourne, the travel time of emerged groundwater to reach this steady state at the downstream boundary was extended. These long travel times were further exacerbated by numerous small emergence values filling and spilling over topographic features, resulting in lengthy run times when using the CPU processor.
To optimise run times, small topographic voids were artificially filled. While this did not significantly change CPU run times, filling larger bodies of water present in the IHM data as depressions resulted in substantial time savings to reach steady state.
Real-world run times depend on the model size, cell size, and number of groundwater inflow points. By using Flood Modeller’s GPU-enabled 2D solver, run times could be reduced by up to 80% compared to the CPU. For example, the Kimpton model, which took 62 hours on the CPU (Intel(R) Xeon(R) CPU E5-1620 v3), ran in just 3.8 hours on the GPU (GeForce RTX 2080 Ti). It is anticipated that run times would be less than an hour using an NVIDIA A100 GPU card.
To fully understand and manage flood risk, groundwater flood mapping should be considered with the same importance as other sources of flooding. Combining subsurface and surface hazards provides the most comprehensive picture of flood risk.
Key Facts
Enhanced community resilience: Groundwater flood hazard maps developed to improve community resilience to groundwater flooding.
Advanced modelling: Flood Modeller utilised to route (2D) groundwater emergence flow over the ground surface.
Optimised performance: Flood Modeller’s GPU-enabled 2D solver reduced runtimes by 80%, with further significant speed improvements expected using NVIDIA A40 and A100 cards.
Innovative warning Service: Creation of a web-based groundwater flood warning service.
Empowering Communities
Project Groundwater aims to provide actionable information to communities through the development of a new web-based groundwater flood warning service using a groundwater map ‘library’. By working closely with communities to achieve local buy-in, raise awareness, and build resilience, the mapping will also provide evidence and confidence to Risk Management Authorities. This will enable them to undertake flood risk assessments, develop business cases for management actions, and design effective schemes. Project Groundwater’s vision “to forever transform how communities prepare and respond to groundwater flooding” relies heavily on robust, freely available, and relatable mapping.
