River Exe Case Study Flashcards
Describe the location of the River Exe Catchment - River Exe
The River Exe catchment is based in South-West England, starting in the moorlands of Exmoor and ending at Exmouth on the South Coast. It flows through Exeter and Tiverton.
How long is the River Exe? - River Exe
The River Exe is 82.7 km long, a relatively short river.
What is the annual rainfall in the catchment of the Exe? How does this compare to the UK average? - River Exe
The annual rainfall in the Exe catchment is 1295 mm annually, compared to 750 mm of annual rainfall across the UK.
What is the maximum elevation of the River Exe? What is the minimum elevation? - River Exe
The maximum elevation of the Exe is 514 m, compared to 26 m at its lowest.
Describe the relief of the River Exe. What impact does this have on its hydrology? - River Exe
The river is hilly in the North but flattens out significantly in the South. This can lead to increased runoff and therefore speed of river discharge in the North, whereas downstream the discharge flow is much slower and more sedate.
What is the size of the area of the River Exe? What impact does this have on its hydrology? - River Exe
The size of the Exe basin is 601 km^2, a relatively small basin. This can increase flood risk as water entering the basin takes little time to reach the channel and therefore has a shorter lag time.
What % of the Exe basin is impermeable rock? What impact does this have on its hydrology? - River Exe
84% of the Exe basin is under lain with impermeable rocks, causing flashier hydrographs, increased overland flow and reduced percolation. This creates more runoff.
What percentage of the Exe basin is grassland/woodland? What impact does this have on its hydrology?
The Exe basin is 67% grassland and 15% woodland. The grassland has a high field capacity and therefore stores large amounts of water, whilst the woodland increases interception. This combines to reduce the flashiness of floods.
What happens to the type of erosion as the River Exe shifts from its upper to middle and lower courses? - River Exe
As the River Exe moves further downstream, the type of erosion shifts from vertical erosion to lateral erosion due to the change in the relief of the land and the shape of the river channel.
Why is the Exe not as flashy as would be expected, given its impermeable geology and small catchment? - River Exe
The rural nature (grassland/woodland accounting for 82%) regulates runoff and decreases flashiness, Wimbleball Reservoir regulates the discharge of the river and reduces flood risk, water is often abstracted from the river and used for agriculture.
What is a hypothesis? What is a null hypothesis and why is it needed? - River Exe
A hypothesis is a statement which should be proved or disproved through an experiment. A null hypothesis is needed as it is difficult to accept an individual hypothesis, therefore a null hypothesis allows us to disprove one thing to prove another.
What should a null hypothesis prove? - River Exe
A null hypothesis should prove that there is no relationship between variables, allowing you to determine that there is a relationship as part of your original hypothesis.
What is the purpose of Spearman’s Rank? - River Exe
Spearman’s Rank aims to prove the strength of a positive or negative correlation between variables. The closer a number is to 1, the more positive. The closer to -1, the more negative. The closer to 0, the weaker any correlation.
Why is the relationship between rainfall and discharge at Thoverton weak? - River Exe
Wimblewall Reservoir abstracts water and regulates discharge, rural nature of catchment increases interception and field capacity, agricultural abstraction of water reduces discharge. This weakens the impact of rainfall on discharge.
What do the mean, median and mode respectively show about pieces of data? - River Exe
Mean: calculates the average in large data sets, using all data.
Median: shows the middle value and disregards potential anomalies.
Mode: calculates the most common value to show a trend.
What does the Interquartile Range show? - River Exe
The IQR shows the middle 50% of all data, removing the skewing effect of some anomalous results at extremes of a dataset.
What percentage of houses within the Exe catchment are at risk of a 1 in 100 year flood event? - River Exe
10% of houses in the Exe Catchment are at risk of a 1 in 100 year flood event.
What benefits are there of proportional symbols being used to show flood risk? - River Exe
Proportional symbols are easy to read and interpret, provide a basic understanding of flood risk and the severity of that risk in given areas.
What disadvantages are there of proportional symbols being used to show flood risk? - River Exe
Proportional symbols can be used to show the proportion of houses at risk of flooding rather than the number meaning urban areas have bias towards them. They also make assumptions and generalisations.
Why were drainage ditches dug in the Exe catchment? What were the impacts of this in terms of water and carbon? - River Exe
Drainage ditches were dug to increase agricultural productivity of the land. This meant that lots of carbon is released from sequestration in cold, damp conditions. Furthermore, lag time decreases as runoff increases, therefore increasing flood risk.
What benefits are there of blocking drainage ditches? - River Exe
By blocking up drainage ditches, boggy, peat rich conditions are restored. This increases water storage and carbon storage available in peat bogs. Improves water quality as less sediment is in the water, increases biodiversity.
What is the Exmoor Mires project? How many hectares is it aiming to restore? - River Exe
The Exmoor Mires project is a project aiming to restore 2000 ha of Exmoor to its previous boggy conditions which had been lost through the digging of drainage ditches.
How much did the Exmoor Mires project cost? How many miles of ditches have been blocked? - River Exe
The Exmoor Mires project cost £2.2 million, with 60 miles of ditches being blocked up.
