Exe Flashcards
(19 cards)
Which part of the River Exe forms the case study area?
The upper catchment - which lies above the gauging station at Thoverton.
What is the total annual precipitation input?
1295mm - this is relatively high, particularly over Exmoor.
What proportion of the precipitation input leaves the catchment area as discharge?
Approximately 2/3s or 65%.
What is the water balance for the River Exe? Give figures.
Precipitation (1295mm) = evaporation +/ - storage (451mm) + runoff (844mm).
What does a Spearman rank correlation coefficient of 0.36 suggest?
A weak positive correlation.
What is the significance of the confidence level being well below 5%?
Indicating that the result wasn’t statistically significant and could have occurred by chance.
Identify and explain a physical factor that accounts for the relatively high runoff.
Geology - most (85%) of the upper catchment is underlain by impermeable bedrock (Devonian sandstones).
Describe the main land use in the upper catchment (include percentages).
• 67% agricultural grazing - grassland
• 15% woodland
• 3% moors and peat bog
How does the low percentage of woodland affect the water balance?
Less interception and less evapotranspiration so more runoff.
How does grassland management impact runoff?
Grassland transpires and intercepts less than woodland and is kept short by grazing sheep and cattle.
How many houses in the Exe catchment are at risk of a 1 in 100-year flood?
11,000, or approximately 10%.
Where are the houses at risk of flooding located?
Mostly in towns in the lower catchment e.g., Exeter and Exmouth.
What is meant by the regime of a river?
The pattern of a river’s discharge over the course of a year.
Describe the regime of the River Exe.
Flashy but less flashy than might be expected; clear response to rainfall events.
What contributes to the relative flashiness of the regime of the River Exe?
• Geology - upper catchment underlain by impermeable rock (85% Devonian sandstone)
• High drainage density with an extensive network of tributaries.
What is the impact of the rural nature of the upper catchment on the water regime?
Vegetation intercepts and slows transfer of water to rivers, encouraging infiltration and soil moisture storage.
What human activity has affected the drainage of the upper catchment?
Drainage ditches dug in the peat on Exmoor to make the land easier to use for grazing.
