Case study - The Rive Exe

Question 1

Locational context

Answer 1

• River flows for 82.7km from source in hills of Exmoore through riverton and exetr to the sea at exmouth
• It has an extensive network of tributaries
• A high drainage density

Question 2

Characteristics of the upper coure ( catchment)

Answer 2

• Physical: The area of the upper catchment is 601km^2 max elevation approx of 514km is in the north, land is much flatter in the south-west elevation 26m
• Geology: Estimated 84.4% of catchment is underlain by impermable rocks, devonian sand stones, accounts for extensive drainage networks
• Land use: Most of land is agricultural grassland 67% woodland 15% and arable farmland on high ground of exmoor moors and peatbogs 3%

Question 3

Water balance equation for the river exe

Answer 3

Precipitation (1295mm) = eveaporation +/- soil water storage (451mm) + runoff (844mm)

Question 4

Background information about the water balance and drainage basin

Answer 4

• High rainfall - absorbed by peaty moorland soils
• Runoff accounts of 65% of the water balance due to impermable nature of the most of the bedrock reduces percolation and base flow
• Drainage ditches on exmoor reduce the amount of soil water storage

Question 5

Human intervention - The construction of Wimblehall Reservoir

Answer 5

• In 1979 the River Haaddeo an upland tributary of river exe was dammed to create the resevior
• Has a surface area of 150 hectares
• Supplies water to exeter and parts of east devon
• Regulates water flow regime during the year - prevents peaks and troughs of water discharge that make flooding or droughts more lilley

Question 6

Human intervention - The restoration of peatland on exmoor

Answer 6

• Drainage basins dug in peat bogs to make suitable for farming
• Inceased water flow to the EXE - reduces water quality as more silt is carried down stream
• The exmoor mires project works to restore the peat bogs by blocking drainage dithces with peatblocks or moorland bales
• This increases water content and returns the ground to saturated boggy conditions - that normally occur in moorland which helps to retain carbon stored in the bog

Question 7

The Exmoor Mires Project

Answer 7

The exmoor mires project aims to restore the 2000ha of exmoor to the boggy conditions that would naturally be present by blocking drainage ditches with peat and moorland bales
* More water storage in upper catchments water transfer is lower in creaseing storage capacity and ensuring a steady supply of water throughout the year
* Improved water quality- slower throughflow which means less sediment is carried into the river, cleaner less ecpensive to treat amd good for wildlife (salmon)
* More carbin storage - peat is carbon and therefore an important carbon store. Dry peat releases co2 through oxidation by encouraging the rewetting of peat and active peat growth
* Co2 is naturally absorbed from the atmposphere
* Improved opportunities for education, leisure and recreation have many species of birds and plants
* Improved grazing and water supply for animals - animals benefit from having year round drinking water as well as improved grazing during the drier parts of the year
* By 2015 over 1000ha of peat moorland had been restored and nearly 100km of ditches blockedm rasing the water table by 2.65cm
* Reduced the amount of water that draisms from montoring the area by two rhirds

Question 8

Collecting data from the moors to stdy the impact of peat restoration - methodolgy

Answer 8

• To measure the effects of the project on the warer tables and water transfers - scientists have established three experimental stations (pools) installation of dipwell transects across newly blocked ditches
• An electic contact dipmeter records the depth of the water table

Question 9

Collecting data from tthe moors to study the impact of peat restoration - results and conclusion

Answer 9

The results indicatre that:
* Water tables have started to rise, meaning that more moisture is being retained within the soil
* Storm flow and flood peaks have been reduced and baseflow has increased

Conclusion: South west water reporr 2012 the increases in water tables seen relfect the increase stroage of water in the peat mass following the restoration and it is consistnet with similar changes recorded in other rewetted peatlands the UK and Ireland