River Exe Case Study Water And Carbon

Question 1

Background information:

Answer 1

A river located in South-West England

Starts in Moorland of Exmoor and travels 80km southwards through towns of Tiverton and Exeter to reach the sea at Exmouth on the south Devon coast

Question 2

What are the catchment characteristics?

Answer 2

Area of catchment - 601km2
Shape - long and narrow
River source - Exmoor, an upland area of moorland and peat bogs used for sheep farming and shooting.
Largely underlain by impermeable Devonian sandstones (84.4%) - leading to high drainage density.
Majority of catchment is rural - grassland accounts for 67% land use, with some woodland (15%) and arable farmland.

Question 3

Impact of nature of the drainage basin on the hydrology - relief

Answer 3

Ranges from 514m above sea level in north to 26m in south, Hilly in the north and flatter in the south.

Means surface runoff is higher and discharge is high.
Steep slopes in upper course means more runoff - shorter lag time, flashy hydrograph

Question 4

Impact of nature of the drainage basin on hydrology - area

Answer 4

601km2 - relatively small drainage basin

Small catchments catch less precipitation so peak discharge is lower.
Lag time shorter, precipitation has less to travel.

Question 5

Impact of nature of the drainage basin on hydrology - geology

Answer 5

84% basin is underlain by impermeable rocks, mainly sandstone

Lead to high runoff and low infiltration.
Leads to flooding and steep rising limb.
Percolation low, shorter lag times.

Question 6

Impact of nature of the drainage basin on hydrology - land use

Answer 6

67% grassland
15% woodland
10% arable land
3% moors and peat bogs (Exmoor)
Grassland will allow interception but not dense so won’t hold as much, woodland will intercept majority. Transpiration reduces discharge

Question 7

What is the rainfall for the catchment

Answer 7

rainfall is high for the catchment as it lies in wet south west of uk, 1295mm annually

Question 8

Why is the reignite not as flashy as expected?

Answer 8

Rural nature of catchment - 82% woodland or grassland
Wimbleball reservoir on the River Haddeo (tributary of river exe). Supplies water to Exeter and elsewhere in east devon and regulates flow of river, smoothing out flashy peaks otherwise expected.
Water is abstracted at a couple of locations and used for agriculture

Question 9

What is the water balance equation?

Answer 9

Precipitation = runoff + evapotranspiration (+/- changes in storage)