Quantitative Analysis

Demonstrating the benefits of Natural Flood Management

Natural Flood Management (NFM) can be an effective method of reducing flood risk for local communities. It’s low-cost, negative carbon footprint and potential local amenity value make it an obvious choice for small schemes, but the difficulty of proving the flood risk benefits, the long lead times and issues obtaining support for NFM measures from national bodies mean that many schemes struggle to get off the ground.

Edenvale Young Associates have developed methods that make it possible to quantify the beneficial effects of many natural flood risk management measures as well as provide support to target those measures to the most effective parts of the catchment. We can provide advice at any stage of your flood risk management project, from inception to delivery.

Distributed Hydrology

How we model natural flood management

We simulate the effects of natural flood risk management interventions using a distributed hydrological approach. Our models incorporate:-

  • Rainfall that varies across the catchment, including orographic and rain-shadow effects
  • Overland flow routing using best-of-breed models capturing the effects of the terrain and different land uses at sub-metre resolution
  • Dynamic infiltration losses into the soil capturing the spatial variation in soils across the catchment as well as the effects of trees on the soil wetness
  • Detailed modelling of base-flows, making the approach well-suited for very permeable chalk catchments where other methods struggle.

Our models enable effectiveness mapping of NFM measures, showing where in the catchment a measure produces the biggest changes to peak flow and where measures might results in unintended increases in peak flow.

What NFM measures can we simulate?

Our models allow us to simulate the effects of every common natural flood risk management measure both singly and in combination. We can investigate combinations of natural and hard engineering measures and, in the case of measures such as afforestation, which take many years to become fully effective, we can show how the benefits of the measures increase over time and how these increases can be used of offset projected increases in rainfall and flood flows due to climate change.

Our models represent the effects of NFM measures through their impact on the physical properties of the land.

Detailed NFM Assessment

Do I need it?

While NFM measures can significantly influence flood risk downstream it is important to be aware that such influences are not always guaranteed to be positive. Measures to “slow the flow” are often effective at attenuating and reducing the peak flow from a watercourse, but will also delay the time of that peak flow. There is potential for this to lead to an increase in flooding as this delayed peak coincides with other flood peaks from other tributaries. Afforestation or other interventions to increase infiltration can also affect groundwater and base flows, particularly on permeable, chalk catchments. Large-scale NFM interventions are likely to require detailed assessment to demonstrate positive impact.

If you need an NFM assessment or want to discuss how distributed hydrological modelling could be used to benefit your proposed scheme, contact us to discuss your requirements.

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