River Culm: Drainage basin case study

Where is the River Culm?

flows through the 'Redlands' of Mid and East Devon.

Describe significance of River Culm to River Exe

is the longest tributary of the River Exe

The Culm drains an area of?

280 square km

Describe the catchment area of the river Culm

predominantly rural, comprising mixed woodland and agriculture (mostly pasture).

How many people does the catchment area of the River Culm contain?

around 30,000

What % of the area is used in agriculture?

87% (62% grassland and 25% arable)

What % of the area is woodland?

9%

What % of the area is urban?

4%

Topography - Max altitude?

276m at top of tributaries in Blackdown Hills

Topography - Min altitude?

20m (almost sea level) further downstream near main channel

What does the high range in altitude cause?

Rapid runoff

What are diamicton deposits?

Impermeable clay caps that increase surface runoff and increase flood risk.

How does the presence of diamicton in the upper catchment increase flood risk downstream?

Promotes rapid runoff

What type of hydrograph does the Culm have?

Flashy

Why does the river culm have a flashy hydrograph?

- Quickly saturated shallow soil

- Heavier clay soils compacted in agriculture (reduces infiltration)

- Steep slopes in Blackdown hills

- Urban areas with impermeable surfaces

Importance of managing flooding on the Culm?

•release of water from land and into rivers can pose a threat to people living in the catchment and cause community disruption.

- Floods could cut off two key transport arteries

What are the physical factors impacting the Culm Catchment?

- Climate Change

- Soil saturation

- Topography

- Levels of vegetation

What are the human factors affecting the Culm Catchment?

- Land use

- Deforestation

Storm event on Culm

Nov 2022, 71mm rainfall, 15hr lag time