Problem Addressed

This solution was sourced in response to UKGBC’s Innovation Challenge: “How can communities and local authorities implement, maintain, and assess the impact of nature-based solutions to enhance climate resilience?”

Ecosystem services can be split into two distinct categories: place-based services and water-flow services. Place-based services can be assessed adequately using GIS data overlays and rules, as such benefits accrue where the habitats are located. Water-flow services deliver benefits downstream from the habitats that provide them, so GIS must be blended with hydrological modelling to identify optimal solutions.

Solution Overview

See how HydroloGIS works in under 5 minutes by watching this video!

Standard ‘opportunity mapping’ using GIS will give inefficient and misleading outputs. HydroloGIS identifies, ranks and prioritises all potential solutions to water-related problems across urban and/or rural landscapes. HydroloGIS mathematically models interactions across entire landscape systems to identify ‘best bang for buck’ NBS. Areas with good potential to provide services (high opportunity) are often not where interventions will make the most difference (high impact); HydroloGIS models this and incorporates it into solution design.

The solution:

  1. Shows which parts of the landscape are working hardest to provide the specific benefits in their current state;
  2. Identifies where the largest increases in service provision can be achieved; and
  3. Decides on an optimal NBS type to place in these gaps to maximise benefits delivered.

HydroloGIS identifies the most effective actions to take in the most efficient locations, as well as ranking all alternative options for how well they will reduce local problems. It is unique in mathematically calculating the current and future ability of every ‘pixel’ across a region to mitigate problems such as surface flooding, sewer flooding, water quality, erosion and infrastructure damage. It does this at 0.5m to 25m resolution, depending on the area being modelled. It also looks to maximise the delivery of multiple benefits and its numerical basis aids the quantification of service delivery. The value of a whole range of benefits – such flood damages avoided or carbon captured – can be calculated in statistical, physical or financial terms.

HydroloGIS results cannot be created using standard GIS or hydrological methods because these cannot identify what type of interventions to create; they cannot prioritise or rank solutions; and they often suggest spending resources in inefficient locations. HydroloGIS’ outputs are easy to understand and the ranking system gives stakeholders lots of informed choice during participatory design.

The tool also adds-in multiple other benefits, such as carbon capture, biodiversity or air quality. The delivery of multiple ecosystem services by each intervention helps gain support and funding for projects, including through commercial trading of benefits. Once the NBS have been agreed, their benefits and trade-offs can be calculated using a variety of methods to suit budgets and funding/trading requirements.

Use of the tool is charged at £10/km2 applied, with costs reducing for larger areas. There is no maximum or minimum scale that a project must meet in order for this tool to be used. Independent modelling has suggested that creating only 70ha of HydroloGIS’s priority NBS across 150sqkm of river catchment would return a benefit to cost ration of 15:1.

Verification & Case Study

Viridian have been using HydroloGIS since 2017 for projects commissioned by government, corporates, charities and farmers. They have had results verified by independent flood modelling from Ambiental, nutrient modelling by APEM and full project review by FloodRE. Results for groundwater flooding have been checked by West Sussex County Council engineers and found to be robust; and results for groundwater recharge verified by the hydrogeologist of a major water utility. These verifications have all shown that HydroloGIS’ optimised locations will deliver substantially better results than those suggested by standard ‘opportunity mapping’.

Viridian are currently involved with a Defra pilot around innovation in flood resilience (the Community SUDS Innovation Accelerator), which will improve the current best practice in monitoring the multiple benefits of NbS. They will apply this learning to other projects.

Case Study – H2O:Source2Sea Interreg, Kent Wildlife Trust, 2021:
This covered 2,400km2 of the Stour catchment in Kent and the Authie catchment in northern France. Viridian first sourced all the open-source data needed to run HydroloGIS in both these territories, then modelled the most efficient and effective solutions to a variety of local problems. These included:

  • Flooding of local towns and agriculture from pluvial and fluvial sources;
  • Diffuse nitrate and phosphate pollution in the rivers;
  • Soil being washed into the rivers to cause siltation;
  • Potential to capture and store irrigation water;
  • Recreation provision and potential; and
  • Carbon sequestration.

The client wished all these problems to be solved through natural catchment management, so that they would benefit wildlife and be robust to climate change. Viridian therefore modelled the most effective interventions from the following options:

  • Woodland & hedgerow planting;
  • Creating meadows (semi-natural grassland);
  • Constructing reservoirs or ponds;
  • Constructing leaky dams, mid-field swales, and bunds;
  • Creating or re-instating wetland;
  • Increasing soil infiltration; and
  • Reconnecting flood plains.

Viridian used available imagery, maps and modelling to create outline designs for the optimal 10% area covering all of these nature-based solutions. Finally, Viridian calculated a comprehensive range of natural capital metrics, such as volumes of water stored and tonnes of carbon captured. Viridian quantified the associated ecosystem service flows for 40 sub-regions of these two catchments.

Facts and Figures


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