Case study

• Drainage

  The River Seven reaches peak discharge then recedes approximately 6 hours after rainfall ceases
• Drainage

  The River Rye peaks 1/2 a day to 2 days later
• Drainage

  The Derwent peaks 3 days after the Seven
• Drainage

  Thawing snow on the high moors can cause rapid surface runoff
• Vale of Pickering

  • Largest inland lake at the end of the last ice age which drained away leaving an enclosed area of wetland filling the centre of the valley
  • Characterized by flat, open pasture, areas of intensive animal production with some woodland at Wykeham, Ayton and Hovingham
  • Mixture of hamlets, villages and market towns
• Vale of Pickering

  • Significant river courses include Derwent, Rye, Dove, Seven, Costa Beck
  • Land drainage and groundwater movement along the spring line also make it susceptible to flooding
• Vale of Pickering

  The vale is surrounded by upland areas

  • River Derwent is a source of portable water
  • The wetland deposits in the vale are significant for carbon capture & storage
• Human

  • The market town of Pickering has a population of 7000
  • Pickering Beck flooded in 1999, 2000, 2007
  • 2007 floods flooded 89 properties and main A170 through road restricting access
• Physical

  Pickering Beck (a tributary of the Derwent) runs through Pickering. Catchment of Pickering Beck is 68km²

  Catchment landuse/character:

  • Geology - Gritstone and limestone
  • North Yorkshire Moorland
  • Arable farming in lower catchment
  • Coniferous woodland on surrounding slopes
• Flood risk- hydrological cycle and factors affecting it

  • Large flat moorland receives a lot of precipitation
  • Land management such as overgrazing, cultivation, forestry and moorland drainage reduce the river's catchment natural water storage capacity
• Slowing the flow (soft): no burn zones

  • Heather burning - traditional moorland management that removes vegetation and speeds up runoff
  • No burn buffer zones created along river in upper catchment
• Slowing the flow (soft): plant riparian woodland along banks of river

  • This is a hydrophilic plant that like water e.g. willow, alder
  • Plant 50ha of native woodland in 30m wide strips either side of channel
  • This improves soil structure which reduces erosion, increase water absorption into ground, increase interception, increase evapotranspiration
• Slowing the flow (soft): education

  • talking to farmers to move cattle feeders and plough against the hillslope
• Slowing the flow (soft): natural gullies/dams

  • Manmade and natural gullies drain water off the moors and forests in the North York Moors (moorland gripping).
  • Many natural dams accumulate in these.
  • By constructing more small permeable dams across the gullies which allows normal flow to pass through but slow down water entering into the channel in times of high discharge.
  • Over time the dams will become more effective by trapping more debris (positive feedback).
  • An example is in Cropton Forest where there is a high density of artificial gullies to drain and improve soil for tree growth
• Slowing the flow (soft): debris dam

  • Debris dams or leaky dams are small dams constructed in the streams in the upper catchment from twigs and sticks
  • They allow normal flow to pass through but slow water down in times of high discharge
  • 100 dams were constructed on the Pickering Beck and 50 on the river Seven in 2010
  • Will increase wetland habitats above the dam
  • Beavers have been released into the area to make the dam
• Slowing the flow (soft):

  • A water storage area has been constructed upstream of Pickering in 2015
  • Before no water overspilled onto the flood plain upstream of Pickering
  • Water surged off the moors but stayed in the river channel towards Pickering
  • If water used the flood plain it would spread out and slow down.
  • The river has been narrowed into a culvert which holds back the water at times of flood, forcing it onto the flood plain and slowing it getting to Pickering
  • It holds 120,000 cubic metres
• What is the Slowing the Flow scheme:

  • National pilot project
  • Aims to reduce peak discharge through Pickering and Sinnington using land management
  • Led by Forestry Research (Forestry Commission) and the Environment Agency
  • DEFRA funded a third of the £750,000 cost.
  • Other benefits include: improved water quality, increased biodiversity and community involvement.
  • Durham university developed a computer simulation model to see how the tributaries react to rainfall events before and after the intervention
• Slowing the Flow main principles

  • store water in the middle of the catchment
  • slow the water at the top of the catchment
  • improve water flow through the bottom of the catchment
• Slowing the flow (soft): monitoring

  Monitoring gauges installed in catchments will generate data on flows enabling evaluation e.g. Ropery Bridge
• The Slowing the Flow scheme has slowed peak discharge between 15%-20%
• Pickering doesn't use hard engineering or else Malton downhill may flood
• Over 40,000 trees planted in Pickering
• 180 grips in moorland
• 4% - 25% of decrease in risk of flooding
• 167 debris dams made
• Link to hydrological cycle

  • Has high drainage density so lots of tributaries (Pickering Beck is tributary of river Derwent)
  • Lots of fields and arable land (capable of producing crops) encourage infiltration and interception, leads to evapotranspiration
  • Ploughing is towards the river (instead of parallel) which create gullies to channel water to the river
• Link to hydrological cycle

  
  

  • NYM moorland receives lots of precipitation so high saturation levels, no infiltration
  • Overgrazing creates impermeable surface causing surface runoff
  • Urbanisation creates impermeable surfaces and drainage systems
  • Dalby forest is coniferous which has leaves all year round and intercepts 22% of rain