The Water and Carbon Cycle - (The River Evenlode)

Question 1

What is the name of the river and where is it located?

Answer 1

River Evenlode, located in Oxfordshire, England, and is a tributary of the River Thames.

Question 2

What is the size of the River Evenlode’s catchment area?

Answer 2

Approximately 340 km².

Question 3

What is the length of the River Evenlode?

Answer 3

Around 80 km long.

Question 4

What are the flow characteristics of the River Evenlode?

Answer 4

The river has a relatively low gradient in its upper reaches and becomes more meandering as it flows towards its confluence with the River Thames. The river is generally a lowland river, which means its discharge can fluctuate depending on seasonal rainfall.

Question 5

What type of rock is located in the River?

Answer 5

Oolitic Limestone, clay and sandstone.

Question 6

What is the importance of Oolitic limestone in the Evenlode?

Answer 6

Oolitic Limestone: This type of limestone, made of small spherical grains called ooids, is relatively resistant to weathering. It forms prominent features like cliffs and hills, which influence the river’s flow by creating natural barriers and controlling the shape of the river valley. Its presence affects local hydrology by limiting the amount of groundwater infiltration and contributing to surface runoff.

Infiltration is high in the River Evenlode catchment because the limestone geology allows water to easily seep through the soil and bedrock. Limestone is permeable, meaning it has small pores or cracks through which water can infiltrate, rather than running off the surface. This characteristic helps store water in the ground, contributing to baseflow in the river, especially during dry periods.

Question 7

What is the importance of the clay in the Evenlode?

Answer 7

Clay: Clay, on the other hand, is more easily eroded and can hold moisture, creating more fertile soil in the region. It is often found in valley floors and plays a role in river sediment transport. When the river overflows, clay can be deposited, altering the floodplain and influencing sedimentation patterns.

Question 8

Where does the River Evenlode flow to?

Answer 8

It flows eastwards and joins the River Thames near Eynsham.

Question 9

What types of land use are present in the catchment area?

Answer 9

Primarily rural, including agricultural land (pastoral farming), woodland, and some urban areas like Woodstock and Eynsham.

Question 10

What is the average annual precipitation in the River Evenlode’s catchment?

Answer 10

600-800 mm, with fairly evenly distributed rainfall throughout the year.

Question 11

What is overland flow and how does it affect the river?

Answer 11

Overland flow occurs when heavy rainfall leads to surface runoff, particularly in areas with clay soils or when the ground is saturated.

Question 12

What is throughflow and how does it affect the river?

Answer 12

Throughflow is lateral water movement through soil, contributing to flow in the river.

Question 13

What human activities influence the River Evenlode catchment?

Answer 13

Agriculture (livestock farming, arable farming), urbanization (towns like Woodstock and Eynsham), infrastructure development and River Straightening.

Question 14

How does agriculture impact the river processes?

Answer 14

Agricultural runoff (pesticides, fertilizers) can increase nutrients and pollutants in the river, especially during rainfall.

Question 15

How does urbanization affect the river?

Answer 15

Increased impermeable surfaces lead to higher surface runoff, raising flood risks, especially in urban areas like Woodstock and Eynsham.

Question 16

How has river straightening affect the river?

Answer 16

Often done to improve drainage, reduce flooding risk, and increase land for agriculture.

Disrupts natural meanders, which can increase water speed and cause erosion downstream.

Alters habitats for aquatic life, reducing biodiversity.

Changes sediment deposition patterns, leading to changes in river morphology.

Question 17

Where does erosion occur along the River Evenlode?

Answer 17

Erosion occurs in areas with higher flow, especially on riverbanks during periods of high discharge.

Question 18

What types of sediment are transported by the River Evenlode?

Answer 18

A mix of sand, silt, and pebbles.

Question 19

How does deposition occur in the river?

Answer 19

Deposition occurs in slower-flowing areas, leading to the formation of small gravel bars and features on the floodplain.

Question 20

What river features are present in the Evenlode?

Answer 20

Meanders, floodplains, and occasional ox-bow lakes.

Question 21

What is the water quality in the River Evenlode affected by?

Answer 21

Agricultural runoff (nitrates, pesticides) and urban sewage discharges can degrade water quality.

Question 22

How is water quality managed in the River Evenlode?

Answer 22

The Environment Agency monitors water quality and promotes sustainable farming practices, like buffer zones to reduce runoff.

Question 23

How is water availability in the River Evenlode managed?

Answer 23

The river has relatively stable flow due to groundwater contribution, but droughts can lower baseflow during summer months.

Question 24

What is the flood risk in the River Evenlode catchment?

Answer 24

Flooding risk increases in urban areas due to impermeable surfaces. Flood management strategies include land use zoning and flood defences.

Question 25

When did a significant flood event occur in the River Evenlode catchment?

Answer 25

In 2007, the River Evenlode flooded areas near Woodstock and Eynsham due to heavy rainfall and urban runoff.

Question 26

What flood management strategies are in place in the catchment?

Answer 26

Floodplain zoning, land management, flood monitoring and flood defences are used to mitigate flood risks. Re-meandering, corner bunds, linked series of ponds, planting trees in floodable areas, leaky dams.

Question 27

How might climate change impact the River Evenlode?

Answer 27

Climate change could lead to more extreme rainfall events, increasing flood risk, or more frequent dry periods leading to lower river levels.

Question 28

The river Evenlode had been straightened for agricultural purposes. Why is it being re-meandered?

Answer 28

Re-meandering a river can decrease the chances of flooding. By restoring natural meanders, the river flow slows down, allowing more time for water to be absorbed into the landscape (increasing infiltration) and reducing the risk of rapid downstream flooding. Meanders also help in reducing the volume of water flowing at high speed, which can minimize erosion and flood damage.

Question 29

What challenges might arise regarding the sustainability of water resources?

Answer 29

Higher demand for water, particularly from urban areas like Oxford, could strain resources during dry periods.

Question 30

How does reconnecting the river with the floodplain reduce risk?

Answer 30

Allows water to spread naturally across a larger area, reducing flood intensity and the chances of flood further down stream.

Question 31

What shape does the river Evenlode have?

Answer 31

Undulating, more susceptible to flooding.

Question 32

How does the rock type play a part in the Evenlode's flashiness?

Answer 32

Whilst limestone is permeable and would decrease chances during heavy rainfall if the ground is already saturated the water can still flow quickly into the river contributing to high levels of flooding. Clay is impermeable, meaning it does not allow water to easily infiltrate. When there’s heavy rainfall, water will run off the surface rather than soaking into the ground. This increases the likelihood of flooding, especially in areas with large amounts of clay-rich soil, because it creates more surface runoff that quickly reaches the river.

Question 33

What has been done to mitigate against flooding in the Evenlode?

Answer 33

River management systems e.g. leaky dams, planting of 30,000 trees, 14 hectares of woodland, reconnecting flood plane.

Question 34

Where along the Evenlode provides a valuable habitat for birds, small mammals, and plants from small aquatic species to mature trees?

Answer 34

The Water Meadows.

Question 35

What is Stage 0?

Answer 35

Stage Zero is a partnership between the Environment Agency, the Evenlode Catchment Partnership, Thames Water and Blenheim, to recreate the impact that beavers would have on a flood plain.