Section C - River Landscape Flashcards
What are the inputs and outputs in a Hydrological Cycle?
Inputs- Precipitation
Outputs- Evaporation, Transpiration, River Flow to the Sea
What are the flows in a Hydrological Cycle?
Flows- Infiltration, Percolation, Through Flow, Groundwater Flow, Surface Runoff
What are the stores in a Hydrological Cycle?
Stores- Interception, Surface Storage, Soil Moisture, Ground Water
Name and explain the 4 types of river erosion processes.
Hydraulic Action- The force of the river water colliding with rocks breaks rock particles away from the river channel.
Abrasion- Eroded rocks picked up by the river scrape and rub against the channel, wearing it away. Most erosion happens by abrasion.
Attrition- Eroded rocks picked up by the river crash into each other and break into smaller fragments. Their edges also get rounded as they rub together. The further material travels, the more it is eroded - attrition causes particle size to decrease from a river’s source to its mouth.
Solution- River water dissolves some types of rock, e.g. chalk and limestone.
Name and explain the 4 types of river transportation processes.
Traction- Large particles like boulders are pushed along the river bed by the force of the water.
Saltation- Pebble sized particles are bounced along the river bed by the force of the water.
Suspension- Small particles like silts and clay are carried along by the water.
Solution- Soluble materials (e.g. limestone) dissolve in the water and are carried along.
What are the two upper course features?
Waterfall/Gorge and V-shaped Valleys/Interlocking Spurs
Explain how waterfalls and gorges are formed.
Waterfall / Gorge- Waterfalls form where a river flows over an area of hard rock followed by an area of soft rock and since soft rock erodes quicker it creates a plunge pool. As the waterfall retreats, this leaves back a gorge.
Explain how V-shaped Valleys and Interlocking Spurs formed
V-shaped Valleys / Interlocking Spurs- In the upper course of a river most of the erosion is vertically downwards, this creates steep v-shaped valleys. The river lacks the energy to erode laterally, so it winds around the high hillsides.
What are the two middle course features?
Meanders and Ox-bow lake
Explain how Meanders are formed
Meanders-Rivers develop large bends called meanders in their middle and lower courses, in areas where the channel has both shallow and deep sections.
Explain how Ox-bow lakes are formed
Ox-bow Lakes- Erosion causes the outside bends to get closer until it forms a small piece of land left called a neck then the river breaks through the land during a flood and flows along the shortest course causing deposition to eventually cut off the meander forming an ox-bow lake like the ones in River Calder
What are the three lower course features?
Levees, Floodplain, Estuaries
Explain how Levees are formed.
Levees- are natural embankments found along a channel edge where heavy material is deposited during a flood on the edges and this process repeats until forming Levees
Explain how floodplains are formed
Floodplains- are wide flat areas of land that flood
Explain how estuaries are formed
Estuaries- found at the river mouth where the river meets the sea. At high tides, silt and sand are carried onto the valley floors and at low tides, it reveals the mudflats
River Jubilee Case Study- Location?
The Jubilee River is a relief channel for the River Thames in southeast England. The relief channel runs through Berkshire and Buckinghamshire, flowing roughly parallel to the River Thames.
River Jubilee Case Study- Purpose?
This area of the Thames flood plain is low-lying and prone to flooding. The impermeable surfaces of the built-up areas have historically resulted in flooding following high rainfall events. Given the high-value property in this area, the EA decided to increase the level of flood protection.
River Jubilee Case Study- Explain this strategy of the flood relief channel.
The Jubilee River was created to take overflow water from the River Thames in times of high discharge following heavy rainfall.
River Jubilee Case Study- Economic Benefits and Issues
The weirs in the river were damaged after 1 year and had to be repaired for £680,000. At a projected cost of £330 million, the Jubilee River was one of four flood-relief channels planned for the lower course of the Thames. However, the EA ran short of funds. If further engineering is to alleviate flooding downstream, local councils and businesses will have to make up a £110 million shortfall. Is this fair, when Windsor and Eton residents did not have to pay? Until a solution is found, small businesses such as shops stand to lose money, as they cannot open when their premises are flooded. Insurance costs are high.
River Jubilee Case Study- Environmental Benefits and Issues
In 2014, there was extensive flooding immediately downstream from where the flood-relief channel rejoined the Thames. The built environment suffered from flooded roads and buildings. Fields were inundated and habitats were disturbed. The concrete weirs are rather ugly, especially under normal flow conditions, when more concrete is exposed. Ongoing repair work has made the matter worse, such as at Manor Farm Weir. There is also the problem of algae collecting behind the weirs. This disrupts the natural ecosystem.
River Jubilee Case Study- Social Benefits and Issues
3000 Wealthy houses protected. The Thames at Old Windsor now suffers from a much higher discharge due to the merging of the two channels just upstream. 2014 flood showed this.
What are the 4 Hard Engineering and the 4 Soft Engineering methods in River Management?
Hard- Dams and Reserviour, Channel Straightening, Embankments, Flood-relief channels
Soft- Flood Warnings and Preparations, Flood plain Zoning, Planting Trees, River Restoration.
Explain Dams and Reserviour and mention the Benefits and Disadvantages
What is it- Dams are barriers built usually in the upper course. A reservoir is an artificial lake behind the dam
Benefits- Reserviours store water, control water flow and prevent floods downstream. Also used for hydroelectric power HEP
Disadvantage- Is Expensive and reservoirs can flood existing settlements. Materials are deposited in reservoirs so farmland downstream can become less fertile.
Explain Channel Straightening and mention the Benefits and Disadvantages
What is it- Meanders are removed to build straighter channels
Benefits- Water leaves more quickly rather than building up so flood risk is lower
Disadvantage- Flooding may happen downstream and fast-moving water increases erosion downstream
Explain Embankments and mention the Benefits and Disadvantages
What is it- raised walls are built along river banks
Benefits- river can hold more water so flooding is less frequent
Disadvantage- Quite expensive and there is a risk of severe flooding if water rises over embankments or it breaks
Explain Flood-relief Channels and mention the Benefits and Disadvantages
What is it- Channels built to divert water away from built-up areas or divert excess water
Benefits- Gates on the channel mean the release of water flow can be controlled, reducing flood risk
Disadvantage- Increase discharged where rivers connect causing flooding in that area
Explain Flood Warnings and Preparations and mention the Benefits and Disadvantages
What is it- EA issues flood warnings, Buildings are modified to minimise flood damage, Residents can prepare sandbags and flood boards prior to the flood
Benefits- WArnings give people time to move valuables and evacuate reducing the impact of flooding
Disadvantages- WArnings don’t prevent floods, People may not have access to warnings, Modifying buildings is expensive, Preparations don’t guarantee safety from floods and it could give people a false sense of security
Explain Flood plain Zoning and mention the Benefits and Disadvantages
What is it- Restrictions prevent buildings on part of floodplains likely to flood
Benefits- fewer impermeable surfaces reducing flood risk and the impact of flooding is reduced as with no buildings there will be no damage
Disadvantage- Expansion of urban areas is limited. It can’t help areas with buildings already.
Explain Planting Trees and mention the Benefits and Disadvantages
What is it- Planting trees in valley increases interception of water and lag time
Benefits- Discharge and flood risk decrease. Vegetation reduces soil erosion and provides habitats for wildlife
Disadvantage- Less land available for farming
Explain River Restoration and mention the Benefits and Disadvantages
What is it- making the river more natural so the flood plain can flood naturally
Benefits- Discharge is reduced so there is less risk of flooding downstream, little maintenance and better habitats for wildlife
Disadvantage- Local flood risk increases especially if nothing is done to prevent major flooding
Name and explain the four factors that affect flood risk.
Heavy Rainfall - Water arrives too quickly to infiltrate the ground.
Prolonged rainfall - Prolonged rainfall saturates the soil
Geology - Clay soil and some rocks such as granite are impermeable.
Relief - If a river is in steep-sided valley water will reach the river quicker.
What is a Hydrograph?
A hydrograph shows how a river’s discharge changes in response to a precipitation event. The vertical axis measures precipitation (usually rainfall) in millimetres and discharges in cubic metres per second (cumecs). The horizontal axis measures time, usually in hours or days. The bars represent rainfall and the line graph shows discharge.
What are the 7 main features of a Hydrograph?
Peak Rainfall, Rising Limb, Peak Discharge, Lag time, Falling Limb, Base Flow, Bankfull Discharge.
What is a Peak Rainfall of a Hydrograph?
Peak rainfall: the highest amount of rainfall per time
unit (the highest bar)
What is a Rising Limb of a Hydrograph?
Rising limb: shows how quickly the discharge rises
after a rainstorm (the first part of the line graph)
What is a Peak Discharge of a Hydrograph?
Peak discharge: the highest recorded discharge
following a rainfall event (the top of the line graph)
What is a Lag Time of a Hydrograph?
Lag time: the time difference between peak rainfall
and peak discharge (measure the horizontal distance
between the top of the highest rainfall bar to the top
of the discharge line and note the difference in hours)
What is a Falling Limb of a Hydrograph?
Falling limb: shows the reduced discharge once the
main effect of runoff has passed (the last part of the
line graph which is going down)
What is a Base Flow of a Hydrograph?
Base flow: the normal flow of a river when its water
level is being sustained by groundwater flow (usually
shown on the hydrograph as a separate line)
What is a Bankfull Discharge of a Hydrograph?
Bankfull discharge: (does not always appear on
hydrographs) will be drawn as a horizontal line
marking the level of discharge above which flooding
will occur as the river will burst its banks
