2Catchment measures to reduce flood risk
Why does it flood?
4.Flood risk is determined by rainfall duration and intensity, combined with what happens to that rainwater once it hits the ground. Unless evaporated or intercepted by vegetation, rainwater will move downstream under the force of gravity, ultimately to the sea. This can happen by water flowing over ground or by percolating much more slowly down through soil and rocks. The geology and geography of river basins—including the type of soil and rock and the steepness of slopes and land use—determine how much water is absorbed and how much flows off and at what speed. Over millions of years, run-off creates natural stream and river channels: these can overflow during large storms, creating natural flood plains. Flood plains are important for storing and conveying the additional flow. In exceptional, extreme rain events, water will progress beyond the extent of the natural flood plain.
5.Over the centuries, human activities have altered these natural processes and increased flood risk in many instances. Artificial land drainage, deforestation and urban development have increased the amount of water that runs off the land into rivers. Urban development has encroached upon flood plains, and river channels have been narrowed and straightened. Farming methods have had particular impact: currently around 70% of UK land is used for agriculture,7 and some farming practices can reduce soils’ ability to store and drain water. Changing land management practices combined with increased rainfall mean that the likelihood of flooding is now at an all-time high and will continue to increase.
Holistic flood risk reduction
Figure 1: Catchment measures
Source: Dr Paul Quinn
6.As the graphic above shows, a range of natural measures can be can be used to reduce the risk of flooding across a river catchment: from sites upstream close to the source of run-off, through to defences and river flood storage schemes installed along river channel pathways, down to measures in settlements to make communities more flood resilient.
7.Flood management has evolved in recent years to include examples of such ‘catchment scale’ management, in many instances driven by other imperatives such as the needs: to protect water quality for drinking, to lower agricultural pollution, to improve habitat, or to restore landscapes that store carbon. Initiatives by Natural England and the catchment sensitive farming project in areas across the UK have played a key role in improving farming practices in order to deliver such multiple benefits. The Environment Agency (EA) has also encouraged this holistic concept of addressing water flows: its Working with Natural Processes project is one example.8 The Agency is identifying opportunities to use a variety of natural measures such as tree planting and ‘soft engineering’ measures including bunds and dykes. These are deployed alongside more traditional hard engineering approaches, such as construction of concrete flood defences. The EA, Natural England and numerous Non-Governmental Organisations (NGOs) highlighted the benefits of catchment partnership work. Other flood risk management bodies such as Regional Flood and Coastal Committees (RFCCs) are also promoting holistic approaches: the Chair of the Thames RFCC considered both the RFCCs and the EA to be “well placed” to support a catchment approach.9
Trialling catchment scale management
8.In response to Sir Michael Pitt’s report into the 2007 floods, agencies have set up projects to investigate how catchment scale approaches might reduce flood risk. Numerous small scale studies have shown the positive impacts from these types of natural flood management (NFM) measures. Examples include the Pickering ‘Slowing the Flow’ and the Pennines/Peak District Moors for the Future project and schemes in Stroud, Holnicote and Belford. The Department for Environment, Food and Rural Affairs (Defra) has also stepped up its trials of catchment approaches in the wake of the 2015–16 floods as part of its Cumbrian Flood Action Plan, in order to improve understanding of the best approaches and to highlight any constraints.10
9.These trials have focussed on a key type of flooding which has significant consequences for settlements—so called ‘muddy floods’ which happen when sudden storms cause large volumes of water to flow rapidly down rivers to pinch-points where the river might overflow and inundate local properties and land. Slowing down the rate of water flow, including by storing it in fields or reservoirs or using natural measures such as bunds and leaky dams, can reduce this type of flood risk. Natural downstream measures (sustainable drainage schemes (SUDs) and green infrastructure) can be effective across catchments, including in urban areas where installing ponds and swales for example can soak away water to prevent surface water flooding.
10.For this inquiry we visited two of the key projects which provide examples of upstream natural flood management:
- the ‘Moors for the Future’ project in the Pennines which is improving the moorland by, for example, restoring peat areas so that they can absorb more rainfall and reduce run-off; and
- the Slowing the Flow project which also uses a range of natural catchment measures to reduce peak river flows and protect the communities of Pickering and Sinnington in Yorkshire.
Both projects demonstrate the effective catchment partnerships of a range of local organisations and land managers in developing NFM approaches to help cut flood risk and deliver other environmental improvements. The Slowing the Flow project told us that the chance of Pickering flooding in any one year has been reduced. Jeremy Walker, project co-ordinator, told us that the success of the project had led to a number of national initiatives to extend the approaches to other places.11
Figure 2
|
PICKERING: ‘SLOWING THE FLOW’ This partnership project set up in 2008 seeks to demonstrate how better land management can help tackle the flooding problem faced by Pickering in North Yorkshire. It is funded by Defra and led by the Forestry Commission, supported by many bodies including the Environment Agency, the North York Moors National Park, Durham University, Natural England and local communities. The project demonstrates how water flows can be slowed by using natural measures such as:
The project leaders consider it has clearly demonstrated how a strong partnership approach can succeed in delivering an integrated set of land management measures to reduce flood risk at the catchment scale, as well as provide wider multiple benefits for local communities. |
Expanding catchment approaches
11.Despite the current trials, some witnesses still considered that the EA relied too much on constructing defences at the point a flood impacts such as town centres: the Agency did not give adequate consideration to preventing flood waters building up at source and along the river path.12 We have published on our website evidence from a range of bodies holding this view. They include the Wildfowl and Wetlands Trust, the Blueprint for Water Coalition, Rewilding Britain and the National Trust. The Blueprint for Water Coalition considered the UK lacked “ambition for large scale natural flood management which could deliver huge benefits”.13 The Government’s own advisory bodies, the Adaptation Sub-Committee of the Committee on Climate Change (CCC) and Natural England, also told us that downstream flood prevention and resilience measures must be accompanied by action upstream.14 Natural England considered this needed to form part of a “larger toolkit of engineered flood defence and resilience measures”.15
12.However, other witnesses while broadly endorsing the logic of catchment approaches urged caution over interpreting limited evidence as to the effectiveness of these measures. The National Farmers’ Union (NFU) considered natural flood management measures were not a “panacea”: they could not mitigate against extreme rainfall events, such as those of winter 2015–16.16 The Centre for Ecology and Hydrology cautioned that evidence was limited that natural flood management measures would mitigate flooding from “very extreme events” on a large catchment scale.17 Defra itself had reservations, conceding there were opportunities to “make more use of natural flood measures in the context of whole catchment planning”,18 but as long as such approaches also provided “other benefits”.19
Developing an evidence base
13.The EA welcomed innovative NFM proposals which, if “properly accounted for” could provide a cost-effective solution.20 However, it is difficult to quantify the benefits of NFM approaches since these have been trialled only across small-scale catchments. There are as yet no plans to trial approaches on a larger, city scale. Whilst many witnesses claim that studies on small-scale catchments have yielded positive results, a number of others told us that more definitive data was needed, both on the contribution made by specific measures and on the potential to expand the models to large-scale catchments:
- Natural England noted that evidence could be “difficult to collect” and other factors might “confound direct cause and effect analyses”;21
- The Pickering ‘Slowing the Flow’ project considered that monitoring needed to continue to compile a longer run of data on the impact of measures;22
- Rewilding Britain told us that although the Belford catchment scheme in Northumberland cost only £200,000 compared to an estimated £2.5 million for a ‘conventional’ scheme, the evidence as to its impact was not definitive.23 The Belford scheme itself reported that it was extremely difficult to quantify the impact of adding a dense network of leaky ponds to the catchment: although it believed that the approach had been shown to work, with each pond adding storage capacity and slowing flows across the catchment.
14.Defra said it was important to have an effective framework for deciding on the optimal deployment of measures and the funding packages required to implement them. The Department told us:
The challenge is being able to identify where in catchments land management measures can reduce the risk and impact of floods—normally in conjunction with traditional flood defences—and the extent of land management change that is required to have a worthwhile effect.
15.The Pickering project told us that there was an “urgent need for a user-friendly” model to help quantify the potential contribution of a wide range of upstream measures to flood risk management. In the view of witnesses such as the Blueprint for Water Coalition, frameworks needed to be improved to incorporate “the full range” of wider environmental and social benefits from approaches such as ‘slow the flow’ and SUDs.24 This is to some extent now being addressed by the recent publication of documents such as the NFM Handbook by the Scottish Environmental Protection Agency (SEPA),25 and resources published online by the EA and other bodies.26 Natural England considered that although planning tools to deploy such measures were “relatively immature”, this should not delay the adoption of approaches.27 The EA concluded that although the evidence of outcomes was not there for every scheme, there was “enough to say that this is the direction of travel we should continue with”,28 and whilst “not everything now on for us is about natural flood management”, NFM needed to be a “core part of our armoury”.29
16.In September, after we concluded evidence gathering, the Government published its National Flood Resilience Review (NFRR) report.30 This referred to the benefits of natural flood management in places such as Pickering and acknowledged that engineered hard flood defences could “only ever be part of the solution”. The NFRR said that the Government’s 25-year plan for the environment would look at bringing together local partners to integrate flood management with water planning at catchment level. Catchment leaders would coordinate planning, with natural flood management valued as part of natural capital accounting. Furthermore, the Government would continue to base its funding for flood management on “reduction in risk rather than type of intervention” to ensure that new approaches, such as land management to slow the flow, could compete on an equal value for money basis with conventional engineered defences.31 But this aspect of flood management is not the focus of the NFRR. There are only brief references to it in the 140 page document. We are still awaiting publication of the 25-year plan: in its absence we cannot comment on whether Defra will translate these good intentions into effective action.
17.Managing water flows from the top to bottom of river catchments helps to reduce flood risk, in many cases more cost-effectively than simply building flood defences in cities, towns and villages. Early results of trials are encouraging for smaller river catchments: there is sufficient evidence to roll-out ‘catchment scale’ approaches for a far greater number of small river basins. Agencies need more evidence, however, on how effective these measures might be at a larger scale. The Environment Agency must work with academics and with other flood risk management bodies including Internal Drainage Boards and local catchment partnerships to fill this evidence gap: we recommend that Defra commission by July 2017 a trial on a large catchment of 100–200 km². Defra should also set out clearly the auxillary benefits it requires when adopting catchment approaches.
Storing water and land management
18.As part of our consideration of wider catchment approaches, we took evidence on the potential for storing water on land, including farmland, either upstream or lower down on flood plains. This can be a cost-effective approach: the CCC told us that, per hectare, the costs incurred from a flood which affected urban land were £2.5 million higher than one affecting agricultural land.32 Countries such as the Netherlands adopt storage on a widespread scale: during our June visit to see Dutch flood risk management projects, we discussed with a farmer from Boxtell how he allows a river across his land to flood in order to save built-up local land. His water charges were reduced to reflect the cost savings to his local community. In urban and peri-urban areas water can be stored temporarily in green spaces such as parkland and recreation areas, enabling the capacity of a catchment to be increased as more such land is used for this purpose. Tree planting in these areas can enhance storage capacity in these areas.
19.Some English schemes, such as those in Pickering, Morpeth and Clifton Ings in York, incorporate large-scale flood water storage, which has helped reduce flood risk to communities. But several witnesses considered that far more was required. The CCC said that further steps were needed to manage the flooding of agricultural land in recognition that some of the most productive farmland is, in practice, a functional floodplain: “how such land is managed can either heighten downstream flood impacts or can help alleviate problems by temporarily storing flood water where it can do least damage”. However, the Government’s response to the CCC in 2015 was that “enough is being done in this area”.33
20.Other witnesses, such as the National Trust, told us of their reservations about the long-term appropriateness of incentives. The Trust welcomed efforts to compensate farmers for their “short-term, uninsured recovery costs” but in the long-term it was important to manage land more sustainably.34 A number of other witnesses also highlighted the need for land managers to use sustainable practices as a matter of course.35
21.We were particularly interested to hear the views of farmer and land manager representatives, given the impact on their members’ livelihoods. The NFU expressed general support for the concept of storing water on farmland, provided schemes worked well financially with the farming system. But the NFU was not able to provide any detailed views on the potential structure of any incentive scheme. Minette Batters, NFU Deputy President, referred to challenges in developing schemes, including a “lack of recognition of the value of agricultural land”.36 If these matters could be resolved then the role of farmers in flood prevention could be expanded.
22.The NFU later told us of a farm flood storage scheme in Wales, the Dyffryn Conwy Flood Alleviation Scheme, which had delivered tangible benefits for the community. Paul Williams, a farmer participating in the scheme, told us that its success was attributable to close working between scheme organisers and farmers. Farmers’ initial scepticism was overcome by legally binding easements with significant incentives attached. However, farmers had borne costs beyond the level of these incentives from flooding in recent years. Mr Williams recommended that a more accurate system for calculating costs be adopted, including index-linking payments over the 20-year period of any agreement.37 We note that developing a robust payment scheme requires an accurate assessment of both the costs to farmers of submerging their land, whether for long or short periods, and the value of benefits from reduced damage to downstream land and property.
23.We took oral evidence before the European Union referendum on 23 June. We therefore considered incentive schemes within the context of the EU rules on Common Agricultural Policy (CAP) payments and their impact on the construction of English agri-environment schemes (Countryside Stewardship Schemes). Defra told us its policy was to target agri-environment payments on activities where there were “also flood reduction benefits”.38 Witnesses noted constraints in the use of such funds to support flood management measures: a scheme that relies on voluntary uptake by farmers makes it hard to coordinate across a catchment; the short-term nature of CAP funding rules normally limits schemes to five years;39 and incentives cannot be provided beyond the income foregone from farming. Since the referendum Defra has said it will examine how to provide support for farmers in general terms after 2020, with current support applying until then and environmental agreements honoured for their duration if signed before the Autumn Statement.40
24.Storing water on farmland can provide a cost-effective means of reducing flood risk, but farmers are naturally wary of allowing their land to be out of production for long periods. Defra should put flood risk management at the centre of any new support schemes for farmers which replace the Common Agricultural Policy (CAP) framework. The Department must consult by July 2017 on an incentive scheme to pay farmers to allow short-term or long-term storage of flood water on appropriate land. As a precursor to this, the National Farmers’ Union should work with farmers to develop by the end of 2016 a detailed model for calculating the value to communities of land management that reduces flood risk. This model must demonstrate how storage methods can be used which have a low impact on farm productivity
25.As part of work to develop farming policies outside the European Union, Defra must link support to sustainable land management practices, including in regard to flood management.
Sustainable drainage systems (SUDs)
26.SUDs can be used as part of integrated catchment management to reduce surface water flooding. Spatial plans can include SUDs schemes for individual or small developments, or more widely within green infrastructure areas which can be designed to include ponds and swales. [See resilience chapter below for how SUDs can form part of improved community resilience to extreme weather.]
27.Witnesses expressed strong concerns about problems with planning requirements for SUDs in new developments: in their view current regulatory approaches lack teeth. The Woodland Trust told us that fewer than 15% of planning applications in flood risk areas included SUDs measures.41 The CCC and a number of other witnesses recommended that provisions in the Flood and Water Management Act (FWMA) 2010 be commenced as this would strengthen policy.42 The Royal Town Planning Institute (RTPI) noted that the failure to commence these provisions meant that there was no clear pathway for SUDs to be adopted by an appropriate body.43 Witnesses noted that arrangements in Scotland and Wales were tougher: in Scotland SUDs had been a statutory requirement since 2005.44
28.A requirement for developers to use sustainable drainage rather than require their developments to connect to hard infrastructure, was supported by a number of Water and Sewerage Companies since new buildings can strain their drainage systems and, in some instances, lead to flooding. Currently, water companies are not statutory consultees in new development planning applications, but are legally obliged to accept new connections to their sewerage infrastructure. Many supported the ending of this right. Anglian Water told us that there was no statutory provision to allow water and sewerage companies to suggest alternative options for the location of developments based on infrastructure capacity and flood risk.45
29.However, developer representatives considered that the current English approach to waste water connections and SUDs was correct. Steve Wielebski from the Home Builders Federation noted that the industry had used SUDs for some decades but that site characteristics and scheme type determined whether hard or soft engineering was used.46 Home building company, Barratt Developments Ltd, told us that SUDs use was in effect already mandatory as only developments which did not increase pre-development run-off levels were permitted.47 Developer representatives also told us that companies paid significant charges—some £2.6 billion since 1989—for investment in waste water infrastructure but that this money was not ring-fenced to require water companies to make these investments.48
30.Defra noted that in April 2015 requirements were strengthened so that the installation of SUDs must be considered for all new developments of more than 10 dwellings and for all major commercial developments.49 During the passage of the Housing and Planning Act 2016, the Government rejected amendments which would have further strengthened SUDs provisions, instead committing to conduct a review. This is despite Defra and the Department for Communities and Local Government stating that SUDS are generally cheaper to build and “maintaining them will be cheaper than traditional pipework”.50
31.All flood risk management bodies must understand better the contribution that sustainable drainage systems (SUDs) and green infrastructure such as ponds and swales can make to protecting communities from flooding. We recommend that, in its response to this report, Defra set out how the Government’s review of sustainable drainage regulations will ensure that SUDs are deployed to maximum effect in all new English developments. We make recommendations below on changes which would enable water and sewerage companies to take a wider role in local drainage, including responsibility for adopting SUDs: the Government’s review should assess how this might incentivise the more effective use of sustainable drainage. The review must also set out, if measures in the Flood and Water Management Act 2010 on SUDs are not to be commenced, what alternative measures at least equal in strength will be adopted.
Maintenance and dredging
32.The Government has committed a budget of over £1 billion for flood maintenance work this Parliament.51 Maintaining river channels effectively requires clearance of vegetation, debris and rocks as well as management of silt build-up. Those managing water flows, including the EA and Internal Drainage Boards (IDBs) must take decisions on when and where it is appropriate to dredge river channels. A balance needs to be struck: dredging can clear channels to prevent rivers being over-topped and lower local flood risk in some instances. We received evidence from those such as the Flood Prevention Society who criticised the Environment Agency for giving inadequate consideration to dredging.52 However, flood risk can be increased in some places when water is moved more quickly downstream. Further, in some circumstances dredging may not be effective in speeding up water flows: for example, Aviva told us that dredging generally had “little or no benefit” for flood risk.53 Our Special Advisers also cautioned that dredging natural rivers is unlikely to prove beneficial as a river will return to its natural state over time: however, it can be effective in artificial rivers such as the Tone and Parrett in Somerset.
33.The current permitting system is seen by some witnesses as creating a barrier to dredging, even where it would be the most effective option. For example, the classification of dredged material as waste adds to the complexity of gaining permission. The Somerset Drainage Boards Consortium told us that systems needed to be streamlined to allow the more efficient permitting of dredging.54 Channel maintenance such as cutting back vegetation and removal of material deposited in rivers during flood events, such as large boulders and stones, is also important to maintain river channel capacity.
34.The Environment Agency, Internal Drainage Boards and local authorities must ensure that their operational plans include adequate provision for river channel maintenance. Plans must also evaluate where dredging can provide an effective solution in reducing flood risk, taking account of impacts both near to the dredged site and downstream. The Environment Agency must by July 2017 streamline its permit system to allow those who need to dredge to gain the appropriate permissions quickly without requiring multiple applications.
7 Defra, Department of Agriculture and Rural Development Northern Ireland, Scottish Government, Welsh Assembly Government, Agriculture in the United Kingdom, 2012
8 See Environment Agency Working with Natural Processes to Reduce Flood Risk webpages [accessed 10 October 2016]
10 Environment Agency, Reducing Flood Risk from Source to Sea, June 2016
18 Department for Environment, Food and Rural Affairs and Department for Communities and Local Government (FFP 129) para 35
19 Department for Environment, Food and Rural Affairs and Department for Communities and Local Government (FFP 129) paras 34 & 35
25 Scottish Environment Protection Agency, Natural Flood Management Handbook
26 See for example Natural Water Retention Measures webpages [accessed 10 October 2016] and the Environment Agency/Defra report, How to model and map catchment processes, March 2016
28 Q79
29 Q90
30 HM Government, National Flood Resilience Review, September 2016
31 As above
32 Q23
36 Q190
38 Department for Environment, Food and Rural Affairs and Department for Communities and Local Government (FFP 129)
40 Andrea Leadsom, Secretary of State for Environment, Food and Rural Affairs, speech to Conservative Party Conference, September 2016
42 Schedule 3 of the Flood and Water Management Act provides for the establishment of a SUDS Approving Body (SAB) within lead local flood authorities (LLFAs). The Act requires SAB approval of all new drainage systems for new and redeveloped sites and highways to be obtained before construction can commence. It also requires that the proposed drainage system meets new National Standards for Sustainable Drainage, concerned with the design, construction, operation and maintenance of SUDS.
44 Q532, Dr Pirie
46 Q236
47 Q238
48 Q265
49 Department for Environment, Food and Rural Affairs and Department for Communities and Local Government (FFP 129)
50 Department for Environment, Food and Rural Affairs and Department for Communities and Local Government, Delivering Sustainable Drainage Systems, September 2014
51 HM Government, National Flood Resilience Review, September 2016
28 October 2016