Are Upstream Storage and Natural Flood Management the Same Thing?

Written By: European Sales Director, Hydro International

Upstream flood storage area holding excess water to prevent downstream flooding.

Upstream storage is a vastly underestimated tool for catchment-wide flood prevention that is already well proven.

The White Cart Flood Prevention Scheme, for example, is an upland storage solution that has now been operating successfully for more than six years with the cooperation of the farming community.  It forms an important part of the wider Metropolitan Glasgow Strategic Drainage Partnership to deliver catchment-wide protection.

Thorough Inquiry

 The UK parliamentary Environment Food and Rural Affairs (EFRA) committee’s Future Flood Prevention report makes far-reaching demands for more joined-up governance of flood management.  It identifies upstream flood storage as low hanging fruit to speed progress on better flood management.  After a thorough inquiry, the MPs called on the Government to begin a large-catchment trial of Natural Flood Risk Management (NFM) by July 2017, and called on the National Farmers Union (NFU) to work with the Department for Environment, Food & Rural Affairs (Defra) to develop storage approaches “with low impact on farm productivity and appropriate incentives to recompense farmers”.

In this context, the White Cart project might be perceived as a hard-engineered solution, but it would be difficult to imagine how the huge scale of its protection (the scheme can hold back more than 571 million gallons of flood water) could have been achieved with ‘natural’ measures alone.  Nevertheless, wetlands and biodiversity are important benefits.

Some of the expert stakeholder responses to EFRA’s inquiry emphasise the need to deploy a range of measures:

Total Catchment Management

The Association of Drainage Authorities refers to the need for “Total Catchment Management from source to sea”, including more storage in upper parts of the catchment, as well as further down, to retain water during times of high rainfall.  A mix of other techniques, including SuDS in urban locations, is also needed.

The NFU, in its response to the report, stresses that farmers want to work closely with the Government on NFM.  It also points to the ‘limitations’ that natural measures could have by themselves.  In its written evidence to the committee the NFU said:

“Natural Flood Management (NFM) is not a new concept and sharing examples from different regions is important to raise awareness and encourage innovation; however a scheme’s limitations must also be highlighted.”

The evidence continues:

“The ‘Slowing the Flow’ scheme in Pickering in North Yorkshire is often heralded as a good example of the benefits which NFM schemes can provide.  However, a significant proportion of the flood mitigation is provided by the reservoir dam installed to store water during peak flow conditions.  This emphasises how NFM is not a panacea option to reducing flood extremity and frequency in downstream communities, and flood management needs to be carefully designed for each catchment, considering solutions such as engineered flood defences and maintenance of watercourses.”

‘Basket of Measures’

The NFU cites the Centre for Ecology and Hydrology’s (CEH) briefing “What difference could natural flood management techniques make?”  This is a highly recommended read and supports the need for more scientific evidence of the effectiveness of NFM.  On the subject of the need for a wide range of measures, it says:

 “Flood management is about a basket of measures.  Some of them about engineering, such as the flood defences we have in towns, and so on.  But they work as absolute defences, and upland management schemes will contribute to those.  So we think if you have a basket of measures you’ll protect against some events, and you’ll protect against others using high-class engineering.  So we’re not saying one thing will solve it.  We’re not about flood defence, we’re about flood management, so it’s a whole range of things that will contribute to managing it.”

The National Trust, in its response to the EFRA Future Flood Prevention report, also broadly welcomed the recommendations.  On the subject of NFM, the Trust also points to the need for a mix of techniques to be used across a catchment.

“By slowing flows and allowing natural features to absorb and delay the peak flow of water we can both reduce the overall size of the flood and potentially buy time to prepare defences or evacuate from areas of highest risk.  When combined with traditional engineered flood defences these natural flood management measures can provide an additional level of protection and may enable the protection of homes and infrastructure that would otherwise not justify an expensive engineering solution.”

Just as well-engineered SuDS need more than just swales and ponds to work effectively, so catchment approaches, including flood storage, are going to need more than log dams, tree planting, and even the help of beavers to be effective – although they may well be part of an overall solution.

Beguiled by Nature?

 In our enthusiasm to embrace low-impact and Green Infrastructure solutions it is sometimes easy to  be beguiled by ‘nature’ and overlook the need for sound engineering and measurement.  NFM is not necessarily the same thing as upland or mid-catchment flood storage, although both may work together.

Gathering more data about the performance of all types of approaches can only be a good thing.  I hope that MPs and policymakers alike will continue to encourage and fund more monitoring and data collection in reaching the right conclusions for a total catchment approach.

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Chris Uttley says:

Hi,
As a rural SuDs officer, implementing NFM on a catchment scale I agree with almost all of this, but what is missing is the relative cost of different measures. In Stroud we have demonstrated that NFM measures can be implemented far wider than had been done previously and at a very small cost. Whilst I would support better research and the collection of more data, the fact is that we can deploy many small attenuation measures across the upper part of catchment at a very low cost. The country is spending a fraction of what could actually be achieved with wider implementation. also, a great deal of our measures have very little measurable impact on a farms productivity, as they are sited away from productive areas or impinge only for a short amount of time.

Payments to farmers, as cited by the NFU, are really only relevant where large areas of land will be inundated to the point of significantly impacting an owners ability to farm it, which is likely to be lower down the catchment as part of larger storage schemes.

With more investment across the country, I agree completely with the low hanging fruit scenario. There is a great deal that can be done to slow flows and attenuate peak flows without the need for large amounts of money.

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