River exe case study

Question 1

where is the source of the river

Answer 1

exmoor national park

Question 2

where is the mouth of the river

Answer 2

exmouth

Question 3

what is the length of the river

Answer 3

96km

Question 4

what is the annual rainfall of the lower catchment

Answer 4

800 - 1000mm

Question 5

what is the annual rainfall of upper catchment

Answer 5

upto 2000mm

Question 6

what is the geogology of the surrounding area like

Answer 6

84% is underlain by impermiable rock causing high surface runoff, and lower catchment is more permiable

Question 7

what is the relif of the land like in surrounding areas

Answer 7

• maximum elevation = 514m
• lowest elevation = 26m
• land is significantly more flat in the south

Question 8

what is the % of grassland and woodland in the surrounding area

Answer 8

• 67% is agricultural land
• 15% woodland

Question 9

what is the water balance

Answer 9

precipitation (1295mm) = evaporation +/- soilwater storage (451mm) + runoff (844mm)

Question 10

what percentage of the water balance is runoff accounted for and what are the reasons for this

Answer 10

65%
- impermiable nature, bedrock reduces perculation and baseflow
- drainage ditches on exmorr reduce soil water storage
- lots of the rainfall is absorbed by peaty moorland soils when this hecomes saturated runoff increases

Question 11

where is the wimbleball resevior located and when was it constructed

Answer 11

• loacated on the river haddeo, a tributary off the upper catchment
• constructed in 1979

Question 12

how big is the area of the wimball reseviour

Answer 12

150, hectacares one of largest in england

Question 13

what is the role of the wimball resevoiur

Answer 13

• supplies waterto exeter and parts of east devon
• acts as a major water store holding approx 21 million m3
• ensures a steady flow and prevents peaks + troughs of discharge

Question 14

how does the wimbelball reseviour alter the natrual waterbalance

Answer 14

• in the winter when rainfall exceeds evapotransipiration it stores surplus water
• in the summer when evapotranspiration exceeds rainfall it releases stored water

Question 15

what are the posotives of the wimball resevior

Answer 15

• maintains river flow during a potential drought
• acts as a store to reduce the risk of flooding
• supports aquatic ecosystems during low flow periods

Question 16

what are the negatives of the wimball resevior

Answer 16

• flooding of farmland and habitats during the construction
• changes in sediment transport + river ecology
• extreme rainfall can exceed storage capacity

Question 17

when did the exmoor mires project begin and who led it

Answer 17

began in 2010

was lead by the exmoor national park authority

Question 18

what are the aims of the exmoor mires project

Answer 18

• aims to restore 2000 heactacres of exmoor back to boggy conditions by blocking drainage ditches with peat bogs and moorland bails

Question 19

why are drainage ditches bad

Answer 19

the lower water table + omcrease surface runoff, increase downstream flood risks, cause drying of peat and carbon loss

Question 20

why are boggy conditions with more peat bogs better

Answer 20

peat acts like a sponge increasing water storage
- it reduces surface runoff and increases lag time
- improves water balance with more water retained in soils
- major stores of carbon and prevent release of co2 if not dried out

Question 21

what are the benefits of the exmoor mires project

Answer 21

• increase storage in upper catchment
• transfers are slowed + more steady throughout the year
• improved water quality, slower throughflow means less sediment in rivers
• increased carbon storage
• improved opportunity for education, leisure and recreation
• improved grazing and increased water supply for animals

Question 22

what are the limmitations of the exmoor mires project

Answer 22

• limmited effect during extreme rainfall
• only affects part of the river catchment - small spatial scale
• requires ongoing maintenance
• dry peat releases co2 through oxidation