Flashcards in Glossary for Water on the Land Deck (83):
Where a river begins
Where a river enters the sea (may be an estuary or a delta)
Smaller riers that join a larger river channel
Where a tributary joins a larger river channel
The area of land drained by a single river system
The edge of the drainage basin (usually a high ridge of land)
The entire length of the river from source to mouth
A cut-through or cross-section of the river at any one point. In the upper course the cross profile is a steep side v shaped valley, with a small narrow river. In the middle course it is less steep sided, with a wider floodplain and a wider river channel. In the lower course the cross profile is a very flat floodplain with a very wide river channel.
The volume of water being carried in the river channel (measure in cumecs - m3/s
The breakdown of rock and sediment by moving forces
The downward erosion of the river channel caused by the downward pull of gravity on the river water. This occurs in the upper course and creates a steep sided cross profile.
The sideways erosion of the river channel. This occurs in the middle and lower course and creates a very wide, flat cross profile.
The river's flow throws sand and sediment against the river bed and banks
The river's flow erodes the bed and banks
Particles carried in the river rub against each other and are worn down
The action of acids and salts in the river water corroding the bed and banks
The movement of sediment from one place to another
The rolling of larger boulders on the river bed
The bouncing of smaller boulders on the river bed
When sediment is carried in the body of water
When sediment is dissolved in the water
The dumping of the sediment load carried in the waves. Encouraged by a reduction in flow, a fall in discharge or an obstruction in flow.
The sediment that is too large to be carried in the water and is found on the river bed (moved by traction and saltation at times of high flow).
The bedload that is still very jagged - has not been smoothed via erosion (found in the upper course).
The sediment that is carried in the water (moved by suspension and solution).
Landforms of erosion
Landforms created by the erosive power of the river (eg V shaped valleys, interlocking spurs, waterfalls, gorges). Usually found in the upper course of the river.
V shaped valley
Vertical erosion in the supper course creates these steep sided, narrow valleys. The river cuts down, and weathering and mass movement work on the valley sides. Over time steep sides form.
Areas of hard, resistant rock that the river flows around - found in the upper course (not to be confused with meanders which are found in the flat lower course).
A steep drop in the river's course. Formed where a band of resistant rock overlays a band of less resistant rock. The softer rock is eroded by more, causing the undercutting of the harder rock. Abrasion and hydraulic power create a plunge pool, which over time undermines the harder rock. The hard cap rock eventually collapses and the waterfalls retreats back forming a gorge.
A retreating waterfall creates a steep sided gorge - a extremely steep sided cutting.
Landforms of erosion and deposition
Landforms created by erosion and deposition (e.g. meanders and oxbow lakes). Usually found in the middle to lower course of the river.
Bends in the river's course. On the outside of the meander bend the water is deeper and the current flows faster (higher velocity). The force of the water erodes and creates a river cliff. On the inside of the bend the water is shallower and flows slower, which encourages deposition. Sediment is deposited which creates a slip-off slope. An underwater current spirals down the river and carries the eroded material from the river cliff to the slip-off slope (known as helicodial flow).
A steep cliff, found on the outside of a meander and created by erosion (abrasion and hyraulic power).
A beach or bank found on the inside of the meander bend, created by deposition.
An underwater current spirals down the river and carries the eroded material from the river cliff to the slip-off slope.
A highly bendy river.
The meander becomes even more sinuous in the lower course. Continued erosion of the outside of the meander bend and deposition on the inside eventually leads to a very narrow neck. During times of high flow the neck may be broken, creating a new straight channel. The cut off bend becomes an oxbow lake. It may eventually completely silt up due to deposition. If an oxbow lake dries up entirely it becomes a meander scar.
A dried up, old oxbow lake found on the floodplain.
Landforms of deposition (or flooding)
Landforms created by flooding and the deposition of the river (e.g. floodplains, levees and deltas).
A wide, flat area of land either side of the river in the lower course. In the lower course. In the lower course the river carries large volumes of suspended sediment. When the river floods this sediment is deposited on the surrounding land - this sediment is known as silt or alluvium. It is highly fertile.
Natural embankments of alluvium either of the river in the lower course. When a river floods onto the floodplain the coarser, heavier sediment is deposited ffirst creating large banks.
When a river enters the sea it may form a delta. If the sea current is extremely weak the river deposits sediment which then builds up out of the sea. The river then fans out across this deposited sediment creating distributaries (smaller river channels that enter the sea).
Small river channels that fan out across a delta.
Factors affecting discharge
Physical and human factors that affect how much water flows in a river channel (e.g. prolonged rainfall, heavy rain, snowmelt, urbanisation, deforestation, relief and rock type).
Long steady periods of rainfall can lead to high discharge, even flooding.
A short burst of heavy rain that leads to high discharge, and even flooding (e.g. Boscastle 2004).
Rapidly melting snow can increase discharge, leading to flooding.
Steep V shaped valleys increase the amount of surface runoff entering the river channel leading to flooding (e.g. Boscastle 2004).
Rock types affects the rate of infiltration - how quickly the rain water soaks into the ground (rocks can be permeable, impermeable, porous and non-porous).
When water is allowed to pass through a rock (e.g. limestone).
When water is not allowed to pass through a rock (e.g. granite).
When a rock has pores, through which water can pass (e.g. chalk).
When a rock does not have pores, and so water cannot pass through (e.g. slate).
How the land is used affects the rate of surface runoff. Woodland absorbs more water and has less runoff than an urban area for example.
The cutting down of trees and forest - this reduces interception and increases surface runoff.
When trees and their leaves intercept rain water and stop it from hitting the ground. This reduces the likelihood of flooding.
The increase in towns and cities increases surface runoff. Water cannot absorb into concrete and tarmac.
The movement of water across the land's surface.
When water absorbs into the land.
When something is completely full of water.
A graph that shows how a river's discharge responds to a rainfall event. The rainfall is always shown as bars and the discharge as a line. The time between peak rainfall (the tallest bar) and peak discharge (the highest point of the line) is known as the lag time. The shorter lag time the more chance there is of flooding.
The highest level of discharge, shown as the highest point on the line.
The highest level of rainfall, shown as the tallest bar.
The time between peak rainfall and peak discharge. The shorter lag time the more chance there is of flooding.
The first part of the line that climbs towards the peak discharge. This is the river responding to rainfall event.
The second part of the line that falls after peak discharge. This is the river level falling back down after the rain has stopped.
A hydrograph with a short lag time and a very high peak discharge. Flashy hydrographs show flash floods.
Frequency and location of UK flood events
Since 2000, flooding in the UK has become nearly a yearly occurrence. Climate change has brought milder, wetter weather - particularly over the summer. Many of the UK floods now occur in August - and mostly in the West of the Uk (e.g. Cumbria 2009, Tewkesbury 2008 & 2007, Boscastle 2004). All in the west - remember west is wet!
Flash flood event
A burst of short, heavy rain that leads to an intense, rapid flood. Shown by a short lag time, and a high peak discharge (e.g. Boscastle 2004).
The artifiical use of hard structures to prevent flooding.
The use of sustainable measures to lessen the impact of flooding.
Dams and reservoirs (Hard)
The use of a dam to control the rivers discharge. A reservoir provides a sustainable supply of water. Socio-economic and environmental impacts are caused by building dams (e.g. Three Gorges, Chind and Kielder Water, UK).
Straightening meanders (Hard)
Meanders are straightened to increase the flow f water away from a risk zone (e.g. Mississippi River, USA). Can lead to further flooding downstream.
Raising levees (Hard)
Natural levees can be heightening to increase the capacity of the river to hold water (e.g. Mississippi River, USA). Increases the level of water in the river so any flooding is even worse if it does occur.
Warn people (Soft)
People can be warned by TV, radio, phone, text and social media. Can be too late, people may not be listening/watching.
The planting of trees to increase interception and reduce runoff (e.g. Yellow River, China). Does not prevent flooding only lessens the change of heavy flooding.
Flood plain zoning (Soft)
When building on the floodplain is zoned according to risk. Land close to the river is farmland and woodland, then minor roads and playing fields, and then furthest away major roads, homes and hospitals.
Water meadows (Soft)
Areas directly next to the river that are allowed to flood to absorb excess water (e.g. Rhine River, Germany). Takes land out of economic use.
People buy sandbags and waterproof their homes/belongings to prevent major damage. Some people won't do this.
The demand society has for consuming water. It is increasing in the UK and across the globe.
Areas of deficit
Areas that don't receive enough rain fall and have a large population that consumes a lot of water (e.g. south east of the UK).
Areas of surplus
Areas that receive too much rain fall and have a small population that consumes little water (e.g. north west of the UK).