CPRE NW Earthy Event. Cumbria s floods and their impact on soils

Transcription

1 CPRE NW Earthy Event Cumbria s floods and their impact on soils

2 Storm Desmond 5 th December 2015 Storm Desmond established new UK rainfall records over both a 24-hour (341.4mm at Honister Pass, Cumbria) and 48-hour (405.0mm at Thirlmere, Cumbria) timeframe. The Honister rainfall has a 1 in 1300 year chance of happening. (Centre for Ecology and Hydrology figures) Heavy rain like that from Desmond is about 50-75% more likely now than it was in the past due to climate change. (Dr Peter Uhe, Oxford University Climate Research group)

3 Storm Desmond and Storm Frank came on top of weeks of above average rainfall in the north

4 Record breaking river flow Following record rainfall associated with Desmond, a new peak flow maximum of 1700 cubic metres of water per second was recorded on the Eden River. The Eden s average flow is 53 cumecs. The flow in the River Eden was 32 times greater than normal. During December most rivers in Cumbria and Lancashire recorded record breaking flows

5 Impacts of the floods Properties in a number of towns which have never been flooded before were badly flooded Critical infrastructure including roads, railways, bridges, electricity, gas, telecoms and water networks were damaged or destroyed. In many places, farmland was damaged badly by erosion and gravel deposition and stock lost This accumulated damage is continuing to have severe effects on the lives and livelihoods of people in Cumbria

6 River Eden

7 River Kent and tributaries Kent Sprint Mint Victoria Bridge Sedgewick

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10 Flooding and Soils

11 Flooding and Soils Flooding and exceptionally high water runoff comes with the additional hazard of soil erosion Soil and underlying loose rock is transported during high flows both by flood water and landslides The pictures in this presentation show brown, highly turbid water which is full of soil The soil is eroded from farmland and fells where it is needed and deposited where it is not wanted on roads and in rivers and lost to the sea

12 Soils, floods and drinking water Thirlmere normally has a turbidity (cloudiness) rating of 0.2 NTU (Nephelometric Turbidity Units) After the flooding the turbidity rating was over 30 NTU This is because of the soil and sediment washed into the reservoir during the flooding

13 Soils and agriculture Both arable and livestock farming need soil whether to grow crops or grass to feed stock Large quantities of soil were lost during the floods, and landslides dumped thousands of tonnes of rubble on once productive land

14 Some causes of upland erosion Overuse of fragile upland paths by walkers, mountain bikers and 4x4 drivers Overgrazing and poaching of soils by livestock Loss of species richness Heather burning on grouse moors

15 Causes of increased runoff Increasing numbers of extreme rainfall events Compacted soil Poor soil structure Poor habitat diversity reducing the surface roughness of fellsides leading to faster runoff and lower levels of rainfall interception Ditches and grips in peat Inappropriate land management and crops Inappropriate development e.g. on floodplains, hard paving of gardens

16 Protecting soils and reducing flood risk Improving the quality and structure of soils is very important Soil is less likely to be eroded and more likely to hold water if it has a more robust structure, e.g. contains more organic matter Soil should not be left bare during the winter

17 Protecting soils and reducing flood risk Appropriate upland tree planting Blocking grips in peat Reduction of soil compaction by stock and machinery Cessation of heather burning on peat Heathland restoration Sub-soiling

18 Slow the Flow - Pickering Pickering in Yorkshire has used a whole catchment approach to retention of water and soils This has involved slowing the flow of water through the catchment using: leaky debris dams, grip blocking, tree planting catchment sensitive farming techniques All these reduce the peak height of flood water

19 The future Climate change is moving the goalposts Warm air holds more moisture (5% more for every 1*C of warming) so extreme rainfall events are more likely Flooding will therefore become more common We need a total rethink about the way we manage catchments as we are losing one of our most valuable resources, soil

20 This was a meadow next to Ullswater until 5 th December Video of Kendal flood Video of A591 damage