The Water and Carbon Cycle - (The River Evenlode) Flashcards
What is the name of the river and where is it located?
River Evenlode, located in Oxfordshire, England, and is a tributary of the River Thames.
What is the size of the River Evenlode’s catchment area?
Approximately 340 km².
What is the length of the River Evenlode?
Around 80 km long.
What are the flow characteristics of the River Evenlode?
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.
What type of rock is located in the River?
Oolitic Limestone, clay and sandstone.
What is the importance of Oolitic limestone in the Evenlode?
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.
What is the importance of the clay in the Evenlode?
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.
Where does the River Evenlode flow to?
It flows eastwards and joins the River Thames near Eynsham.
What types of land use are present in the catchment area?
Primarily rural, including agricultural land (pastoral farming), woodland, and some urban areas like Woodstock and Eynsham.
What is the average annual precipitation in the River Evenlode’s catchment?
600-800 mm, with fairly evenly distributed rainfall throughout the year.
What is overland flow and how does it affect the river?
Overland flow occurs when heavy rainfall leads to surface runoff, particularly in areas with clay soils or when the ground is saturated.
What is throughflow and how does it affect the river?
Throughflow is lateral water movement through soil, contributing to flow in the river.
What human activities influence the River Evenlode catchment?
Agriculture (livestock farming, arable farming), urbanization (towns like Woodstock and Eynsham), infrastructure development and River Straightening.
How does agriculture impact the river processes?
Agricultural runoff (pesticides, fertilizers) can increase nutrients and pollutants in the river, especially during rainfall.
How does urbanization affect the river?
Increased impermeable surfaces lead to higher surface runoff, raising flood risks, especially in urban areas like Woodstock and Eynsham.
How has river straightening affect the river?
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.
Where does erosion occur along the River Evenlode?
Erosion occurs in areas with higher flow, especially on riverbanks during periods of high discharge.
What types of sediment are transported by the River Evenlode?
A mix of sand, silt, and pebbles.
How does deposition occur in the river?
Deposition occurs in slower-flowing areas, leading to the formation of small gravel bars and features on the floodplain.
What river features are present in the Evenlode?
Meanders, floodplains, and occasional ox-bow lakes.
What is the water quality in the River Evenlode affected by?
Agricultural runoff (nitrates, pesticides) and urban sewage discharges can degrade water quality.
How is water quality managed in the River Evenlode?
The Environment Agency monitors water quality and promotes sustainable farming practices, like buffer zones to reduce runoff.
How is water availability in the River Evenlode managed?
The river has relatively stable flow due to groundwater contribution, but droughts can lower baseflow during summer months.
What is the flood risk in the River Evenlode catchment?
Flooding risk increases in urban areas due to impermeable surfaces. Flood management strategies include land use zoning and flood defences.
When did a significant flood event occur in the River Evenlode catchment?
In 2007, the River Evenlode flooded areas near Woodstock and Eynsham due to heavy rainfall and urban runoff.
What flood management strategies are in place in the catchment?
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.
How might climate change impact the River Evenlode?
Climate change could lead to more extreme rainfall events, increasing flood risk, or more frequent dry periods leading to lower river levels.
The river Evenlode had been straightened for agricultural purposes. Why is it being re-meandered?
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.
What challenges might arise regarding the sustainability of water resources?
Higher demand for water, particularly from urban areas like Oxford, could strain resources during dry periods.
How does reconnecting the river with the floodplain reduce risk?
Allows water to spread naturally across a larger area, reducing flood intensity and the chances of flood further down stream.
What shape does the river Evenlode have?
Undulating, more susceptible to flooding.
How does the rock type play a part in the Evenlode’s flashiness?
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.
What has been done to mitigate against flooding in the Evenlode?
River management systems e.g. leaky dams, planting of 30,000 trees, 14 hectares of woodland, reconnecting flood plane.
Where along the Evenlode provides a valuable habitat for birds, small mammals, and plants from small aquatic species to mature trees?
The Water Meadows.
What is Stage 0?
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.
