Practical Guide to Lowland Natural Flood Management Measures
Floods are nothing new. Humans have lived with extreme weather for thousands of years. However, climate change science predicts an increase in occurrence and severity of high rainfall events. Subsequent increases in extreme flooding will follow suit.
Within the UK, our flood defence system includes large-scale, hard engineered solutions in and around major cities, flood banks and small scale engineered solutions for rural communities and farmland, and coastal engineering. There is increasing political and public interest in how the management of the wider countryside can contribute to the country’s flood defence system, with reference made to natural flood management (NFM) sometimes called Working with Natural Processes (WwNP).
The conundrum faced by landowners and managers is associated with pressure to increase crop yield related to market forces, to achieve the same level of farm income. This guide aims to provide information to landowners to allow them to decide on which NFM measures that will match their farm business.
Natural flood management aims to reduce the downstream maximum water height of a flood (the flood peak) or to delay the arrival of the flood peak downstream, increasing the time available to prepare for floods. This is achieved by restricting the progress of water through a catchment using a range of techniques. These techniques work with the natural features of the catchment to slow down or store flood waters. They rely on one, or a combination, of the following underlying mechanisms:
- Increasing soil infiltration: an open soil structure that will make saturation less likely, potentially reducing surface runoff.
- Evaporation from vegetation and soil can also make space for water.
- Slowing water: by increasing resistance to its flow – for example, by planting floodplain or riverside woods, or blocking grips on moorland.
- Storing water by using, and maintaining the capacity of, ponds, ditches, embanked reservoirs, channels or land.
- Reducing water flow connectivity by interrupting surface flows of water – for example, by having buffer strips of grass, hedges or trees.
Natural flood management measures have been designed so that they do not significantly impact on farming. They are typically small in size and can be considered an extension to the farm’s land drainage or as part of an Internal Drainage Boards maintained network.
Each structure or technique performs a small amount of runoff storage or attenuation, gradually releasing flood water over 12 to 24 hours. It is the collective network, rather than individual features, that aims to provide flood mitigation in the immediate vicinity and further downstream.
In lowland Yorkshire, good management of soil is critical to productivity and natural flood management. This includes practices which are beneficial for soil and water health, including increasing organic matter, contour ploughing and appropriate drainage as well as sensitive ditch management, employing buffer strips and rainwater harvesting.
Natural flood management is not the complete solution to flooding but is one of many tools needed to manage flood events and water levels by taking a total catchment management approach. These tools are proven to be effective at reducing the frequency of flooding for high probability fluvial events (for example, less than a one in twenty-year return period) rather than extreme events (for example, a one in 200-year return period). Used in conjunction with other flood management solutions like hard engineering, natural flood management will have a beneficial impact on slowing the flow of flood water downstream. Research at several small-scale catchments has shown this to be the case.
This guide has been developed to provide the advice and key information needed to aid decision-making, should you wish to install flood management features on your farm. We have included funding sources to support the work you may want to undertake.
The various measures have been grouped into three different levels of intervention:
- Level 1 – Measures requiring minimum or no consultation with authorities such as the Local Authority or local Internal Drainage Board consent or Environment Agency (EA), local Internal Drainage Board consent. These measures are usually low cost and simple to install, but extremely effective.
- Level 2 – Measures requiring a certain level of consultation and possibly consent of authorities (see summary of consents section). These measures are a mix of low to medium cost and may need contractors’ help to install them.
- Level 3 – Measures involving a level of design that is targeted to certain locations within the catchment, requiring planning permission and consents from authorities, and, in most cases, involving professional water management consultant advice. These measures are usually high cost and need contractors to install them.
Each measure is described in terms of its flood management effectiveness, its benefit to agricultural production, and its overall cost. Set up and maintenance costs have been colour-coded, with the definition provided here. This guidance document has been produced so that it is freely available to download as a PDF and if you wish to alter it to fit your situation, please contact the Dales to Vales River Network.