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Select Committee on Environment, Food and Rural Affairs Written Evidence


Memorandum submitted by the British Ecological Society (FL 66)

INTRODUCTION

  1.  The British Ecological Society is the learned society for ecology in the UK. Founded in 1913 its mission is to promote the science of ecology worldwide. This response was produced with input from Professor Alan Hildrew, the BES's Climate Change Advisory Group and its Public and Policy Committee.

  2.  The BES response focuses on the potential for land-use management to help mitigate flooding. The BES supports an integrated approach to flood risk, in which land-use practices maximize a range of ecosystem services, such as flood control.

THE ROLE OF ECOLOGY IN MITIGATING FLOODING

  3.  Flooding is the episodic flow of rivers over their channel banks and is a natural occurrence and a key aspect of landscape ecology. While there are many important beneficial ecological effects of flooding, for instance on fish and other wildlife, the ecology of river catchments could be managed to minimise the costs of flooding. Natural ecosystem processes in catchments can ameliorate the intensity of run-off generated by any particular rainfall event, and thus reduce the extent of flooding downstream, where it causes most nuisance and economic damage.

  4.  The careful management of land-use in river catchments can help to mitigate, at reasonable economic costs, the increased occurrence and severity of rainfall that is expected to result from climate change. The uplands receive much of the rainfall and generate much of the runoff to flood-prone rivers—such as the Severn and Wye. The restoration of upland land-use to native deciduous woodland, would help to:

    —  increase the interception of rainfall by vegetation;

    —  increase water infiltration into the soil and groundwater;

    —  increase transpiration to the atmosphere;

    —  reduce peak flow due to surface runoff.

  5.  The economic cost of managing land-use in this way would be modest in the uplands. In addition, this would have additional benefits for conservation objectives and increased carbon storage. Increasing natural flood mitigation measures in the uplands will still require both natural and conventional flood mitigation measures in the lowlands, since once upland ecosystems are saturated their ability to reduce flooding events is limited.

  6.  Giving streams and headwaters more space next to their channels would encourage the development of lateral vegetation and wetlands and increase the retention of flood flows in the upper reaches of rivers. Water would be released more slowly to downstream areas, where most economic damage from flooding occurs. River flow would also help to be sustained during dry periods. Again, there would be some economic cost due to restrictions on agriculture near streams, which would need to be set against reductions in flooding downstream and in benefits to water supply and conservation.

  7.  The intensification of farming practices has tended to reduce the infiltration capacity of soil and decrease water storage in agricultural areas. This can cause higher peak flows in watercourses. Soil with a good natural structure can, depending on soil type, can retain large amounts of water. Certain arable land management practices can lead to soil compaction, puddling, capping and plough pans, all of which reduce infiltration and increase surface runoff. Cultivation techniques including soil management, surface crop cover and headwater management can all be used to increase water storage capacity. The Soil Framework Directive and the Water Framework Directive provide the opportunity to improve the structural health of our soils and could contribute to reducing flood risk.

  8.  The best way to manage water flow through catchments will be to base risk estimates on they dynamics of land use and hydrology in the catchment. Of course lowland flooding results on some occasions from combination of events in more than one catchment.

  9.  Other land management practices which could be used to mitigate flooding include, restoring upland bogs, putting meanders back in rivers and creating new "washlands." Sustainable urban drainage systems would also help by enabling rainfall to infiltrate the ground rather than run-off to urban drains. Such ecological responses would obviously not ameliorate the risk of flooding, but are part of the solution for reducing flooding. Projects to reduce flood events should look at both the effectiveness of the conventional flood management and the opportunities provided by emerging techniques of restoring natural functionality in the landscape. There is evidence that such approaches deliver effective flood management together with social and economic benefits.

  10.  The majority of the experimental information on the effects of forests on runoff in the UK has focused on uplands. Only a few studies have been carried out on lowland broad-leaved woodland. More research on how to best to manage ecosystems to reduce flood events is needed.

IMPACTS OF FLOODING ON ECOLOGICAL FACTORS

  11.  Biological, physical and chemical water quality are impacted by flooding events. Flooding also has localized direct impacts on many species. For example, the nests of many waterbirds are known to have been swept away during this years floods and ground nesting species in areas that flooded are also likely to have failed in their nesting attempts this year. However, assuming the frequency of flooding remains low this is unlikely to have any long term impact on species abundance and distribution.

  12.  Summer flooding is not a typical feature of flood-plain systems in the UK and the long-term impacts of more frequent summer flooding are almost unknown and more research is needed in this area. Species living in wet meadows and washes are typically adapted to winter flooding. In one recent paper detailing the impacts of summer flooding on the Ouse Washes the authors conclude that declines in a population of Black-tailed Godwit are related to the rate of flooding. The generality of such findings are often unknown.

The British Ecological Society

August 2007





 
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