river exe

• locational context

  located in Exeter , south-west of England

  • source is south of Bristol Channel
  • mouth - english channel at Exmouth
• climate characteristics

  • has orographic rainfall
  • Exmoor rises to 520m - annual average rainfall is over 2,000mm (UK average - 920mm)
  • prevailing westerly winds from the Atlantic bring higher than average precipitation
• geology characteristics

  80% of rocks in basin are impermable

  • geology of catchment spans 400million years
• soil characteristics

  • dominant soils are permable and loamy soils (48% of land area)
  • soils have iron pan - means water can't infiltrate through them
  • reducing percolation and increasing river discharge
• land use characteristics

  • main areas of urban development are south of catchment due to flatter land
  • urban areas include Tiverton (not at risk of flooding)
• agriculture grassland use

  67% - sheep and cattle compact soil , reducing infiltration
• woodland land use

  13%
• peat bogs land use

  3%
• hydrography for the river exe

  • flashy hydrograph
  • high runoff
  • rainfall high in rainfall season - winter

  
• river regime

  the annual variation of flow of a river
• water balance for the river exe

  precipitation = 1295mm

  evaporation + soil water storage = 451

  runoff = 844
• reasons for 65% water balance

  • impermable nature of bedrock reduces percolation and base flow
  • drainage ditches is on Exmoor reduced the amount of soil water storage
• plant water availability

  evapotranspiration rates exceed rainfall inputs in lowland Devon during April - September

  • this can lead to periods of water stress on less water retentive loamy soil e.g heathlands of East Devon
• what is peat?

  Decomposed plant material. Accumlates faster than it decomposes due to lack of oxygen in waterlogged plants
• what is Peatland restoration?

  • drainage ditches have been dug in peat bogs of Exmoor to make it more sustainable for farming - increases speed of water flow to River Exe , potential water surplus
• what is the Exmoor Mires Project?

  the project works to restore peat bogs by blocking drainage ditches with peatbogs or moorland bales.
• aims of the Exmoor Mires Project

  to restore 2000ha of Exmoor to boggy conditions that would be naturally present in order to help retain carbon within the peat.
• pros of the Exmoor Mires Project

  • more water storage in upper catchment - ensures steady supply of water all year round
  • improved water quality - slower throughflow means that less sediment is carried back to river. Reduce channel storage , increased groundwater store
  • improved biodiversity - 31% has been restored to OG ecohydrological function
  • carbon storage , research (Uni of Exeter) , Bogstacle course
• cost of Exmoor Mires Project

  cost £4.5 million
• 2015 - 1000ha of Peat Moorland had been restored
• reduction in daily surface runoff due to peatland restoration

  66%
• what is Wimbleball Reservoir?

  in 1979 , an upland tributary of the River Exe (the River Haddeo) was dammed to create Wimbleball reservoir
• surface area of Wimbleball reservoir

  150ha
• a reservoir is an artificial lake
• pros of Wimbleball reservoir

  • important water store - reduces water stress in summer months
  • crucial impact on this part of catchment - regulates flow
  • reduces likelyhood of flooding - 1960 , 2500 homes flooded and in 1992 - 2,000 flooded
• cons of wimbleball reservoir

  in 2022 after extreme heatwaves - reservoir was 45% full

  • could have resulted in increased water stress and the water flow would be disrupted - risk of drought