Natural Flood Management. Measures & Multiple Benefits. Steve Rose (JBA)

Transcription

1 Natural Flood Management Measures & Multiple Benefits Steve Rose (JBA)

2 Definitions Natural Flood Management - NFM (SEPA): A range of techniques that aim to reduce flooding by working with natural features and characteristics to store or slow down flood waters. Working with Natural Processes - WwNP (EA): Taking action to manage flood and coastal erosion risk by protecting, restoring and emulating the natural regulating function of catchments, rivers, floodplains and coasts. National Water Retention Measures - NWRM (EC): Measures that aim to safeguard natural storage capacities by restoring or enhancing natural features and characteristics of wetlands, rivers and floodplains, and by increasing soil and landscape water retention and groundwater recharge.

3 Expectations for NFM measures Can contribute to reducing flood risk for smaller, more prevalent events Cannot protect communities during major flood events Can act as complimentary flood risk reduction measures to schemes that include hard engineering FRM measures Can help to reduce the need for raising existing flood defences due to climate change effects Can increase the resilience of communities and businesses to withstand more extreme events Can provide a wide range of additional benefits to the environment and society

4 Conceptual model - hierarchy of FRM interventions [Adapted from RSPB (2009)]

5 Group Exercise Catchment schematic - 10 mins Split into 2 groups Question 1 - What NFM measures might be appropriate across the different parts of the catchment area where and why? Question 2 - What additional benefits to the environment and society would each NFM measure bring? Group feedback (through a nominated Group rapporteur) 10 mins General open discussion

6 Diagram adapted from: Working with natural processes techniques, draft report. Environment Agency, Black and Veatch (April, 2014).

7 Conceptual model - hierarchy of FRM interventions [Adapted from RSPB (2009)]

8 NWRM list

9 NFM Measures generic groupings Woodland creation and management Land management and land drainage Working within and on the banks of the river/stream channel Runoff (pathway) management Coastal measures

10 Woodland creation and management Upland woodlands Historic planting, felling and drainage practices increased flood risk Design of new plantings far better at slowing the flow Benefits: carbon storage, biodiversity, social wellbeing, recreation On-going policy and funds to increase woodland coverage

11 Woodland creation and management Gully woodlands Steep bare uplands gullies provide rapid flow pathways New gully plantings can stabilise the soil Generate woody debris for slowing the flow Benefits: carbon storage, biodiversity, works alongside farming

12 Woodland creation and management Cross slope woodlands Used to interrupt surface flow pathways Encourages infiltration of water into soil and provides shelterbelt Benefits: carbon storage, biodiversity, works alongside farming

13 Woodland creation and management Floodplain and riparian woodlands Used to slow the flow and enhance flood storage opportunities Generates woody debris into channel and on floodplain Benefits: carbon storage, biodiversity, works alongside farming, water quality (inc. sediment)

14 Land & soil management practices Greatly influences water flow pathways to watercourses Good management minimises rapid surface runoff Inappropriate / untimely management can generate more and faster runoff Certain soils in certain circumstance more prone to capping and compaction Certain cropping and harvesting practices can increase flood risk Benefits: water quality (inc. sediment), soil quality

15 Agricultural and upland drainage activities Installed to control water levels to increase crop yield (arable, grass, moor) Increased drainage density and connectivity increases flood risk Measures designed to block / slow flow pathways, elevate watertable level Moorland grip blocking and drainage interventions Benefits: carbon storage, biodiversity, social wellbeing, recreation

16 Working within and on the banks of the channel Bank restoration Aims to reduce erosion and stabilise river channels and banks Planting of live or inert vegetation Riparian fencing to exclude livestock Benefits: channel morphology, sediment capture, works alongside agriculture

17 Working within and on the banks of the channel Reach and floodplain restoration Aims to create more naturally functioning and connected river and floodplain Re-meandering, restoration of channel and floodplain features Set back, partial or full removal of flood embankments Benefits: channel morphology, biodiversity, recreation

18 Working within and on the banks of the channel In-stream structure Aims to slow the flow and force floodwater to spill onto wider floodplain Includes large woody debris dams and soft engineered features Needs to retain low/base flow conditions for biodiversity Benefits: channel morphology, biodiversity, recreation

19 Runoff (pathway) management Overland flow barriers Aims to disconnect flow pathways and temporarily store floodwater Includes earth bunds, stone walls, hedgerows Needs to drain out after flood event has passed Benefits: sediment capture, works alongside farming

20 Runoff (pathway) management Offline storage areas Aims to temporarily store floodwater on floodplain In-stream leaky weirs and/or lowered bank tops promote flood spilling Needs to drain out after flood event has passed Benefits: sediment capture, works alongside modified farming system

21 Runoff (pathway) management Non-floodplain wetlands Restoration and creation of wetlands that remain wet for biodiversity Might include a more formal outfall structure to allow some seasonal flexibility in water level and for maintenance operations Benefits: water quality, biodiversity

22 Coastal NFM Beach management Widening of beach to reduce erosion and absorb wave energy Artificial replenishing of beach with gravel, shingle or sand Benefits: morphology, social well being, recreation

23 Coastal NFM measures Restoration of intertidal areas (inc. managed re-alignment) Mudflats and salt marshes absorb wave energy and reduce wave height Managed re-alignments involves loss of land, but creates room for intertidal habitats being squeezed by climate change induced sea level rise Benefits: biodiversity, morphology, social well being, recreation The 28m Medmerry scheme in West Sussex included the building of 7km (four miles) of new sea walls up to 2km inland.