1
Q
Describe the water cycle
A
- Evaporation of water from the sea
- Condensation into clouds which are carried inland
- Precipitation of the water vapour in form of rain, sleet, snow etc.
- Interception of rain by trees which store the water
- Evapotranspiration of water back into the air
- Surface Storage of water
- Infiltration of water into soil
- Throughflow, the horizontal movement of water through sturated soil to rivers, lakes or seas
- Percolation through porous rock layers
- Groundwater Stored in soil or aquifers
- Baseflow, the horizontal movement of water beneath rock layers to rivers, lakes or seas
2
Q
Def. Interception
A
When water is taken in by plants
3
Q
Def. Percolation
A
When water sinks from the soil into the groundwater store
4
Q
Def. Overland flow
A
When water flows over the land e.g. in a river
5
Q
Def. Throughflow
A
When water flows through the soil
6
Q
Def. Groundwater flow
A
When water flows through the groundwater layer (water bearing rocks)
7
Q
Def. Transpiration/Evapotranspiration
A
When water is evaporated from plants
8
Q
Def. Evaporation
A
When water is heated and turns from a liquid to a gas
9
Q
Def. Condensation
A
When water turns from a gas to a liquid
10
Q
Def. Precipitation
A
Rain, snow, sleet or hail
11
Q
What is a drainage basin?
A
- A drainage basin is an area of land that is drained by a river and its tributaries.
- The highest land forms a natural dividing line between drainage basins.
- Watersheds separate drainage basins
12
Q
Def. Drainage basin
A
The area drained by a river and its tributaries
13
Q
Def. Watershed
A
Marks the edge of a drainage basin (it is the highest point of land)
14
Q
Def. Source
A
The starting point of a river
15
Q
Def. Mouth
A
Point at which a river enters the sea or a lake
16
Q
Def. Tributary
A
A small stream which will join the main channel of a river
17
Q
Def. Confluence
A
The point at which a smaller river (tributary) joins the main river
18
Q
Def. Discharge
A
Discharge of a river is the volume of water which flows through it in a given time. It is usually measured in cubic meters per second.
19
Q
Def. Wetted Perimeter
A
The part of the cross-section – bed and bank – that is in contact with the water).
20
Q
Def. Hydraulic Radius
A
The ratio of the river channel’s cross-sectional area to its wetted perimeter. Hydraulic Radius is a measure of how easy it is for water to move having to overcome friction. It is a measure of the channel’s efficiency.
21
Q
How do river characteristics vary as you go down them, from the upper to the lower course?
A
- Discharge increase
- Occupied channel width increase
- Channel depth increase
- Velocity increase
- Load quanitity increase
- Load particle size decrease
- Channel bed roughness decrease
- Slope angle/gradient decrease
22
Q
What are the main characteristics and landforms of the upper course?
A
Main process is erosion. However, the water is not very plentiful or powerful.
This may form:
- V-shaped valleys and interlocking spurs
- Waterfalls
- Rapids
- Potholes
23
Q
Describe the formation of V-Shaped Valleys and Interlocking Spurs
A
- The river in the upper course erodes vertically and carves a path into the ground
- The soil on the sides of the river becomes unstble and crumbles
- A V-Shape is formed
- Interlocking spurs are projections of high land that alternate from either side of a V-shaped valley.
- The river is not powerful enough to cut through the spurs of hard land and so has to flow around them.
24
Q
Describe the formation of potholes
A
- Water is swirled around in irregularities of the riverbed, creeating vertical eddies
- Rocks are swept into these small depressions and the river does not have enough energy to get them out again, an these rocs are called grinders
- The grinder swirls around the pothole, and drills it down through abrasion, causing the pothole to deepen and widen
25
Describe the formation of a waterfall
1. Waterfalls are landforms found in the upper course of a river.
2. They occur where a band of hard rock (e.g. granite) overlies soft rock (e.g. sandstone).
3. The softer rock is eroded more quickly than the harder rock, through processes such as hydraulic action (the sheer force of the water eroding the soft rock).
4. Water is swirled around at the base of the falls (hydraulic action) creating a plunge pool. Rocks and debris are swept into the plunge pool, they are swirled around and rub against the bed and banks of the plunge pool (abrasion), deepening it further.
5. Over time, the softer rock is eroded further creating an overhang of hard rock. This overhang is unstable as it's weight is unsupported.
6. Eventually, this hard rock collapses and the waterfall moves back upstream (retreats).
7. This process repeats, with the location of the waterfall continually retreating upstream. This creates a gorge, which is a steep sided deep river valley.
26
Def. Gorge
A gorge is a vertical narrow steep sided valley that is usually found immediately downstream of a waterfall.
It is formed by the gradual retreat of waterfalls over hundreds, sometimes thousands of years.
27
Explain how meanders form on a river?
- In a river’s middle course it flows over flatter land and lateral erosion increases.
- Bends in the river start to form, for example when a river meets an outcrop of harder rock and starts to bend around it.
- Water is forced to the outside of the bend, leading to erosion and further widening of the bend by hydraulic action and abrasion.
- The power of the water undercuts the bank on the outer bend leading to the formation of a steep sided bank known as a river cliff.
- Water is shallower on the inside of the bend, increasing friction with the bed and banks and leading to deposition. This forms a gently sloping inner bank called a slip-off slope.
28
Describe the formation of oxbow lakes
- The loops of meanders increase is size as erosion continues on the outside bank and deposition continues on the inside bank.
- As meanders grow, they migrate over the floodplain.
- As they migrate they may start to erode towards each other.
- Gradually the neck of the meander narrows until it is completely broken through (usually during a flood) to form a new straighter channel.
- The old meander loop is cut off by deposition from to form an oxbow lake.
29
Def. Levee
Levees are naturally raised riverbanks (ridges of sediment) found on either or both sides of a river channel, that is prone to flooding. They are found in a river’s lower course. It is formed by flooding over many years and composed of gravel, stones and alluvium (silt).
30
Def. Floodplain
A flood plain is wide, flat area on marshy land on either side of a river, and found in the middle and lower courses. Flood plains are made from alluvium which is deposited when a river floods. Flood plains are used for farming as the soil is very fertile.
31
Describe the formation of levees
- When a river bursts its banks, friction with the land reduces velocity (speed of river) and causes deposition. Heavy sediment is deposited closest to the river, forming levees.
- The size of sediment then becomes progressively smaller with distance from the river.
- This sediment, alluvium, is very fine and increases th efertility of the soil
- With each successive flood, the banks are built up higher.
- Although it may seem that make it more difficult for the river to flood next time, this is not the case as overtime the bed of the river deposits a thicker layer of sediment, which raises the river in its channel. In addition, the banks are eroded and weathered, allowing the river to burst over them again and repeat the cycle
32
Descrie the formation of floodplains
- Meanders migrate across the flood plain due to lateral erosion.
- When they reach the edge of the floodplain they erode the valley side (bluff line). Eventually this cuts a wider valley. This explains why flood plains are very wide.
- When the river floods it deposits silt, creating a very flat flood plain.
- Layer upon layer builds up over many years to form a thick deposit of fertile alluvium.
33
What are the opportunities of rivers?
- Fertile land (thanks to natural irrigation and alluvium deposits)
- Flat land
- Transport
- Fishing, especially in deltas
- Freshwater supplies - for drinking and cooling machinery
34
What are the hazards of rivers?
- Meanders that change their course
- Flooding
35
Causes of floods
- Heavy rainfall events
- Dam burst
- Antecedent rainfall where soil is already saturated with water
- Non-porous/impermeable rocks
36
Which factors encourage flooding?
- Steep sided channel - A river channel surrounded by steep slopes causes
- Lack of vegetation/woodland
- Drainage basin
- Drainage basin in urban area
37
What factors affect the lag time between peak rainfall and river discharge?
- **Geology discharge** - if the rocks under the ground are impermeable and water cannot drain
through the rock layer resulting in rapid overland flow and a shorter lag time. Permeable
rocks encourage a slow transfer by groundwater flow, hence a longer lag time.
- **Soil type** – clay soils do not drain easily and become saturated very quickly. This results in
rapid overland flow and shorter lag times. Dry soils slow down water transfer leading to longer
lag times.
- **Slope** - steep slopes lead to rapid water transfer and shorter lag times. Gentle slopes slow
down water transfer making the lag time longer.
- **Drainage basin shape** - a high density basin has more streams and rivers which speed up
water transfer and shorten lag time. A low density basin has less streams and rivers leading to
a slower transfer and longer lag time.
- **Antecedent conditions** - wet conditions before a storm cause the ground to become saturated.
This speeds up overland flow and shortens lag time. Drier conditions mean the rainfall can
infiltrate into the soil slowing down lag time.
- **Vegetation** - if there is no vegetation in an area, the water runs off into the river quicker,
therefore it would have a short lag time. Alternatively, if there is plenty of vegetation in the
area, the lag time would be longer as the plants would intercept the rainfall.
38
What are the key features of hydrographs?
- **Peak discharge** - maximum amount of water held in the channel.
- **Peak rainfall** – maximum amount of rainfall (millimetres).
- **Lag time** - the time taken between peak rainfall and peak discharge.
- **Rising limb** - shows the increase in discharge on a hydrograph.
- **Falling limb** - shows the return of discharge to normal/base flow on a hydrograph.
- **Base flow** - the normal discharge of the river.
39
When does flooding occur and what does it entail?
- Flooding occurs when a river gets more water than its channel can hold.
- A flood occurs when a river bursts its banks and the water spills onto the floodplain.
- Flooding tends to be caused by heavy rain: the faster the rainwater reaches the river channel, the more
likely it is to flood.
- The nature of the landscape around a river will influence how quickly rainwater reaches the channel.
40
Def. Delta
A large mass of sediment deposited at the mouth of a river
They are deposited when a river enters a standing body of water such as a lake, a lagoon, a sea or an ocean. They are features of river deposition, not marine deposition.
41
What are the three types of delta?
- **Arcuate** - The land around the river mouth arches into the sea, and the river splits multiple times on its way to the sea, creating a fan effect.
- **Cuspate** - These form as a resut of stronger waves, and the land around the mouth juts out arrow-like into the sea
- **Bird-foot** - The rver splits on it's way to the sea, and each part juts out into the sea, like a bird's foot
42
What are the necessary conditions for a delta to form?
- A river with a **high sediment load**
- When a river deposits this sediment faster thsan the sea can remove it
- Usually a **large river**. Otherwise, the action of the sea might disperse the sediment.
- Reasonably **shallow water offshore**. Very deep water inhibits delta building.
- A coast on which the **wave energy is low** though here again how low will depend on other factors such as sediment supply and tidal range.
43
Describe the formation of a delta
1. The river carries a significant quantity of sediment from upstream sources
2. The water velocity solows down due to the flattening of the landscape
3. This causes the river to deposit sediemmt, starting with the largest pieces near to the mouth and finer sediment carried further away
4. As sediment accumulates, it blocks the river mouth, causing it to split into distributaries
5. Sediment builds up over time, gradually creating a delta. The deposition rate icreases s there are now multiple distributaries. However, the highest rate of deposition remaisn at the river mouth
6. Tides, waves, river discharge and ocean currentds giev the delta a particular shape
7. Vegetation such a smangroves colonises the delta and stabilises it, contributing to the delat formation
8. The features of deltas change constantly due to factrs such as sediment supply, sea level rise and human activity
44
What conditions led to the formation of the mississipi delta
- The Mississippi is a major river that is capable of transporting a lot of sediment
- Its flow slows as it enters the Gulf of Mexico
- Sediment is deposited faster than the tides can remove it
- River flow is blocked by so much deposition that the river splits up into distributaries
- Distributaries deposit sediment over a wide area, extending new land into the sea
- The Mississippi River delta has widely spaced distributaries, making it look like a bird's foot.
45
What ae the advantages created by the Mississipi delta?
- The **fertile soils** deposited by the Mississippi River make the delta an ideal area for agriculture. The region is known for its production of crops such as cotton, soybeans, rice, and corn.
- **Biodiversity**: The delta supports diverse ecosystems, including wetlands, marshes, and swamps, which provide habitats for a wide variety of plant and animal species.
- **Economic opportunities**: The Mississippi Delta is home to cities and towns that support various industries, including agriculture, fishing, shipping, and tourism.
46
What problems occur in the Mississipi delta
- **Flooding**: The delta is prone to flooding, especially during hurricanes and heavy rainfall events. This damages to infrastructure, homes, and crops, leading to economic losses.
- **Land subsidence**: The extraction of groundwater and oil and gas from beneath the delta has contributed to land subsidence, or sinking. This increases the risk of flooding and can cause damage to infrastructure and property.
- **Coastal erosion**: The Mississippi Delta is experiencing significant coastal erosion, partly due to natural processes and partly due to human activities such as the construction of levees and canals. Coastal erosion threatens communities, infrastructure, and ecosystems along the coast, leading to loss of land and habitat.
- **Environmental degradation**: Human activities such as pollution, habitat destruction, and drainage of wetlands have contributed to environmental degradation in the delta, including loss of biodiversity and degradation of water quality.
47
Give a brief introduction of the Mississipi river
- The Mississippi is the 4th longest river in the world, 3800km, and flows through ten states - the entire length of the USA, from the boundary waters in Minnesota all the way to the Gulf of Mexico in Louisiana.
- Has over 100 tributaries and its drainage basin covers ⅓ of the USA.
- Despite many attempts of humans to tame this great river, the Mississippi is subject to periodic flooding.
- The largest disaster in history was the 1927 river flood, which was the most destructive flood event in US history.
48
What are the causes of river flooding in the Mississippi?
- **Urbanisation**: Because rivers provide many opportunities for people, many settlements have been built along the banks of the Mississippi e.g. cities such as St Louis and New Orleans. Urbanisation reduces permeability in the river basin and increases the flood risk. Prior to urbanisation there would have been more floodplain available for water to occupy during times of flood.
- **Risks from tropical storm** systems can also lead to flooding in the lower Mississippi valley, for example Hurricane Camille in 1969 and Hurricane Katrina in 2005 both led to significant flood events.
49
What were the specific causes of the 1993 Mississipi flood
- A volcanic winter is thought to have started with the 1991 eruption of Mount Pinatubo. It has been suggested that excess cloud condensation nuclei from the eruption were responsible for the Great Flood of 1993 in the Midwestern United States.
- Like many floods this flood was caused by large amounts of precipitation over a long period of time, in June and July of 1993 much of the area experienced over 150% of normal rainfall and some areas e.g., parts of North Dakota, - Kansas and Iowa experienced more than double their normal rainfall.
- On top of this, the ground was already saturated, not only by the previous rainfalls, but during the previous year the weather conditions were considerably cooler which meant less evaporation.
- Human causes included the development on the floodplain, including the draining of wetlands which could have absorbed water. Continued urbanisation of the river valley has reduced permeable surfaces, leaving fewer areas for water to go. In addition, the levees were poorly built and not federally made.
50
What were the impacts of the 1993 Mississipi flood?
- 43 deaths
- 50,000 people evacuated
- 26,000km of land flooded
- $2.46 billion crop losses
- River traffic stopped for several months
- $15 billion in damages
- Contents of and the buildings themselves destroyed
- Threat of disease from sewage
- Insurance claims high
- Stagnant water attracted mosquitoes and rats
51
Describe the hard engineering flood management techniques on the Mississippi
- 6 huge **dams** and 105 **reservoirs** - Built on tributaries to regulate flow, store water, and generate hydroelectric power. They can help mitigate flood peaks by storing excess water during periods of heavy rainfall and releasing it gradually downstream. However, dams can also alter river ecosystems and impede the natural flow of sediment, nutrients, and fish migration.
- **Strengthening the levees** - Concrete mattresses which were constructed extensively along the Mississippi River and its tributaries' reliance on levees can sometimes increase the risk of catastrophic flooding if they fail or are overtopped.
- **Channelization** - Channelization involves modifying the natural course of the river by straightening and deepening its channel to improve navigation, reduce sediment deposition, and control flooding. While channelization can enhance navigation and flood control, it can also disrupt natural habitats and increase erosion downstream.
- **Diversionary spillways** - overflow channels - Built into which water can be diverted during times of high flow. An example is the Morganza spillway, a flood channel on the Mississippi.
52
Describe the soft engineering flood management techniques on the Mississippi
- **Floodplain Management** - Floodplain management involves zoning regulations and land-use planning to restrict development in flood-prone areas and minimise exposure to flood hazards e.g. St Louis
- **Wetland Restoration** - Wetlands play a crucial role in flood mitigation by absorbing and storing floodwaters, reducing peak flows, and providing natural flood protection. Wetland restoration projects aim to restore degraded wetlands, enhance flood storage capacity, and improve ecosystem health along the Mississippi River corridor.
- **Afforestation**: Planting trees reduces the risk of flooding by increasing interception which slows & delays surface run-off.
53
What are the typical hard engineering flood management techniques?
- **Dams and Reservoirs** - To control discharge downstream
- **Embankments and levées** - To increase river capacity
- **Straightened channels** - To make rivers pass faster through vulnerable areas to reduce the risk of flooding
- **Flood relief channels** - To allow some water to flow out of the main channel to reduce discharge
- **Spillways/Overflow channels** - To take excess water away from the main channel
54
What are the typical soft engineering flood management techniques?
- **River Restoration** - Restores river back to its original form, putting meanders back in, stabilising banks and connecting to floodplains
- **Wetland conservation** - These areas provide somewhere for excess water to go and slow the flow of water
- **Catchment management plan** - To assess the risk of flooding in an area and outline how they will be managed
- **Floodplain zoning** - Only certain land uses are allowed on a floodplain, reducing the risk of damage or casualties
- **Afforestation** - Planting vegetation and trees to increase interception and infiltration
55
What are the opportunities/benefits of living close to the Mississippi River?
- **Settlements** - in the lower course of the river the land is flat and easy to build on.
- **Tourism** - Recreational hobbies like canoeing, swimming, boating, fishing etc are popular.
- **Industry** - Water from the river is used for cooling in factories and power stations.
- **Transportation** - Waterways are useful and important for transportation. Often this is for cargo boats. The total cargo of 2004 was around 31.5 million short tons consisting of 72% imported cargo and 28% exported cargo.
- **Commercial fishing** - (and shrimping in the delta) are important to the people of the Mississippi drainage basin economically and for a food supply. They rely on a healthy river and delta.
- **Farming** - The floodplain in particular is rich in nutrients and the soils are used for agriculture.
56
What were the impacts of the Mississippi River flood in 1993?
- **Economic Damage** - Losses ranging from $15 billion to $20 billion. This included damage to agricultural land, infrastructure, homes, businesses, and transportation networks.
- **Agricultural Losses** - The floods submerged millions of acres of farmland, particularly in the Midwest, destroying crops and livestock, causing significant losses for farmers and impacting the region's agricultural economy.
- **Displacement of Residents** - Thousands of people were forced to evacuate their homes as floodwaters inundated residential areas along the Mississippi River and its tributaries. Many communities were submerged under several feet of water.
- **Environmental Impact** - Contamination of water sources, damage to wildlife habitats, and disruption of ecosystems and chemical spills leading to contamination from flooded industrial sites
- **Infrastructure Damage** - Floodwaters damaged roads, bridges, levees, and other critical infrastructure, hindering transportation and emergency response efforts.
- **Health and Safety Concerns** - Risks of waterborne illnesses, contamination of drinking water supplies, and the spread of infectious diseases. Emergency response teams had to address these concerns while assisting affected communities.
- **Long-Term Recovery** - Extensive long-term recovery efforts, including rebuilding infrastructure, restoring agricultural land, and providing assistance to affected residents and businesses. The floods highlighted the need for improved flood management strategies and infrastructure to mitigate the impact of future flood events.
57
Which places were affected by the 1993 Mississippi river flood?
- **St. Louis, Missouri** - Experienced major flooding along the Mississippi River, leading to evacuations and damage to infrastructure.
- **Davenport, Iowa** - Saw significant flooding along the Mississippi River, with floodwaters inundating downtown areas and causing widespread damage.
- **Quincy, Illinois** - Experienced severe flooding along the Mississippi River, leading to evacuations and damage to homes and businesses.
- **Des Moines, Iowa** - Experienced flooding along the Des Moines River and other tributaries, resulting in evacuations and damage to homes and businesses.
58
What are the problems of living next to the Mississippi River?
* Water Pollution is problematic - Poor farm management results in an inch of topsoil being lost every 12 years and this will flow into the river.
* Farmers spray herbicide and insecticide chemicals on the soil and this too will flow into the river causing algal blooms (eutrophication).
* Poor quality drinking water - Many cities along rivers take their drinking water from the river. The chemicals inside the water cannot be removed by present purification methods.
* Fish in streams have been observed with cancer, fin rot, deformed bones and skin diseases.
* Fish-eating birds such as the Bald Eagle and Peregrine Falcon, were, until recently, on the verge of becoming extinct due to problems in the food chain.
* Hurricanes strike the delta of the Mississippi which can cause flooding, storm surges and problems for the people of places like St. Louis.
* Flooding – see 1993 info
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