River Management Flashcards
What factors influence river landscapes in the UK?
Climate, geology, and human activity
Define porosity in the context of rocks.
Porosity is a measure of how much water can be stored in pore spaces between grains of rock
Porous rocks like sandstones can hold significant amounts of water.
What type of rocks are known to be permeable?
Sandstone and limestone
These rocks allow water to pass through due to their vertical and horizontal joints and cracks.
What is permeability?
Permeability is a measure of how easily water can travel through a rock
What are impermeable rocks?
Rocks that have few pore spaces or joints, causing water to flow over them on the surface
Examples include most igneous rocks like granite and metamorphic rocks like slate.
Name a type of sedimentary rock that is impermeable.
Clay
Where can water be stored in regions with impermeable geology?
At the surface
This leads to the formation of lakes and rivers as natural surface stores of water.
What is the purpose of damming rivers?
To control flooding and create reservoirs for water supply
How many large dams are there in the UK?
168 large dams
What is a drainage basin?
The area of land from which a river collects its water
Water is stored in rivers, vegetation, soil, and rocks within a drainage basin.
What is surface run-off?
Water that flows over the ground
This occurs when precipitation falls and does not infiltrate the soil.
What is infiltration?
The process of water flowing into the soil
What happens to water after it infiltrates the soil?
It moves slowly downhill as throughflow
What is groundwater flow?
Water that percolates deeper into the ground and enters the bedrock
List factors that affect rates of infiltration, throughflow, and groundwater flow.
- Size and shape of the drainage basin
- Steepness of its slopes
- Amount of rainfall throughout the year
- Intensity of rain storms
- Amount and type of vegetation cover
- Permeability and porosity of the soil and rocks
What is the influence of geology on water flow and storage?
Geology affects how quickly water flows through a drainage basin and the amount of water it can store.
What is discharge in the context of rivers?
The amount of water in a river, measured in cubic metres per second, or cumecs.
Define annual regime in relation to rivers.
The pattern of discharge in a river over one year, typically shown in a hydrograph.
What are aquifers?
Bands of porous rock that can hold huge quantities of water. These groundwater stores are also known as aquifers.
Examples are chalk and some types of sandstone
What is recharge in the context of aquifers?
Water that enters an aquifer.
What is discharge in the context of aquifers?
Water that leaves an aquifer.
What does it mean to abstract water?
To take water from either a surface or groundwater store.
What is over-abstraction?
Taking water from a store faster than it can be recharged.
When was the last significant drought in the UK?
In 2005 and 2006.
What are flash floods?
Floods caused by high volumes of rainfall in a very short period, leading to a sudden rise in river levels.
What conditions can lead to flash floods in the UK?
Hard, baked dry ground that prevents rainfall from soaking in quickly.
What are seasonal floods?
Floods that occur due to seasonal variations in rainfall, often after prolonged rain when the ground is saturated.
What can cause flooding when snow melts?
Frozen ground preventing water from infiltrating the soil.
How do human actions increase flood risk?
Paving over soil creates impermeable surfaces, reducing infiltration and increasing flood risk.
So, growth of urban areas increases the risk of flooding.
What is the effect of vegetation on water flow?
Vegetation slows water flow and can store water through interception.
What is interception?
The process where some water is caught and stored on leaves.
What is transpiration?
The process of water being returned to the atmosphere through the pores of leaves.
How does deforestation affect flood risk?
Cutting down trees or leaving fields bare can reduce interception, increasing flood risk.
What is one way to reduce flood risk downstream?
Planting trees in upland areas.
What type of rocks are mainly found in the drainage basin of the River Valency?
Slates
These rocks are impermeable.
What is the gradient of the River Valency due to its high source and short length?
Steep
What natural feature helps to remove some water from the soil before it reaches the river?
Trees, via interception
What happens to tree branches during flood events?
They can break off and restrict the flow of water
Define mouth in the context of rivers
where the river meets the sea/lake
Define watershed
where the water falls into two different drainage basins
Define confluence
where two rivers meet
Define tributary
a small stream that joins the main river
Define source in the context of rivers
where the river starts
Define catchment area
the drainage basin
What changes were made to the river channel downstream of Boscastle?
Widened, deepened, and straightened
Why was the river widened?
The wider, deeper channel has a greater capacity so it holds more water.
Why was the river straightened?
Water moves quickly through a straight channel.
By straightening the channel it means that flood water would flow away from the town much more quickly.
Why was the river bed deepened?
As it allows for a greater capacity of water
What type of engineering uses natural features of a river to reduce flood risk?
Soft engineering
What would happen to the Somerset Levels without flood defences?
They would be flooded twice a month by high spring tides
How have people managed this landscape?
People have managed this landscape by dredging the rivers - removing silt and mud so the river channel can carry more water.
What caused the 2014 floods in the Somerset Levels?
High rainfall that saturated soils
Rivers backing up at high tide
What is land use zoning?
When low-value land uses are not protected by flood walls
These zones provide safe areas for water to be stored during a flood event so that water is kept away from more valuable land uses such as homes.
What was the purpose of the demountable flood barriers in Shrewsbury?
To hold back flood water during flood events
