River Basin Management

Question 1

Physical Characteristics of the Colorado

Answer 1

Positive
1. Underlying geology of impermeable rock in some areas. eg. Lake Mead. - Dams can be built, less water lost through infiltration/percolation, hard durable volcanic rocks provide a secure base.
2. Steep Valley Sides - good for runoff and water collection, building dams.
3. High precipitation in the Rocky Mountains and winter snow melt - high discharge and large flow.
4. Very little techtonic activity - secure dam building and water storage.
Negative
1. Low rainfall in lower basinas it lies in the rain-shadow of the Sierra Nevada mountains to the West - less discharge in the river.
2. Highly variable seasonal rainfall with thunderstorms and maximum around May time Snow melt only feeds river for part of year - can lead to flash flooding.
3. Hot climate with temps in desert areas regularly over 40° means high evaporation rates - 95% of rainfall in lower basin is lost to this.
4. Climate Change - less precipitation, shorter/warmer winters mean less snow, increased evaporation due to increased temperatures.
5. Sedimentary rocks in area around Lake Powell - seepage/water loss.
Other Factors
1. Poor dry soils mean limited plant growth within the region - high surface runoff/flash floods, very little interception so rain hits soil eroding it, few roots holding soil together so soil is eroded further.
2. Hard dry ground and steep slopes - little infiltration so rapid transfer cause flooding.
3. Thin soils - very little capacity for storage for more surface runoff.

Question 2

Need for Water Management

Answer 2

Human Factors
1. Electricity generation - Is required to power homes, industry and farms.
2. Drinking and domestic water for cities such as Phoenix, Las Vegas and Los Angeles - This is used for domestic appliances, golf courses, swimming pools etc. Mediterranean climate means warm, dry summer season.
3. Irrigation water for agriculture - eg. Imperial valley. Increased need for food production to feed expanding population.
4. Tourism - This boosts the economy with over one million visitors at the Hoover Dam each year and over 6 million to general Lake Mead area.
5. Political Tensions - 7 states and 2 countries is hard to balance. Generally, power lies with the upstream countries who control flow but by time the river reaches Mexico 90% of its water has been removed.
Physical
1. Flooding - Due to seasonal summer rains and build up of sediment.
2. Drought - Due to low rainfall in much of the lower basin. Also, snowmelt is variable and unpredictable.
3. Limited Vegetation - Leads to high surface run-off and low levels of interception which leads to more soil erosion which can silt up lakes.

Question 3

Physical Factors Affecting the Site of Dams

Answer 3

1. Permeability - Impermeable rock is preferred. This would reduce water loss through percolation. Eg. an igneous rock like granite rather than sedimentary rocks. Lake Powell for example loses around 300km2 per year through this.
2. Valley Shape - A v-shaped valley is ideal. This would reduce the construction costs of the dam as less materials are required. It would also mean a smaller surface area so less water would be lost through evaporation. Shorter dams across the valley. High level of flow to catch water.
3. Rock Type - It is important that the rock is strong. This means that it can support the weight of the dam as well as any water contained within it. Eg. granites and other igneous rocks.
4. Volcanic/Earthquake Activity - An area where there is not much of this, which is geologically stable, is preferrable. Earthquakes may de-stabilise the dam and cause subsidence. If it collapses or is damaged it could lead to mass flooding.
5. Climate - A milder climate with moderate rainfall is preferrable. This would mean that less rainfall is lost through evaporation. Plentiful rainfall would also ensure that there was plenty water to supply the river but not so much it floods.
6. Size of drainage basin/catchment area - A larger drainage basin is preferrable. This would mean that there is more oppurtunity for lots of water to be collected. High snowmelt and a large number of tributaries would ensure that lots of water gets straight into the river rather than infiltrating and going into groundwater storage.

Question 4

Human Factors Affecting the Sites of Dams

Answer 4

1. Having Settlements Nearby - This is a positive factor as it can provide a workforce or accomodation during construction and may also make the cost of pipelines/aqueducts/cabling for transporting water cheaper. It also means new settlements won’t need to be built. Eg. Boulder City, Nevada was built for workers on the Hoover Dam, 1933 onwards.
2. Places of Historical and Cultural Importance - These should be avoided such as Native American burial grounds and sites to show sensitivity to native cultures. (Eg. Navajo sacred sites under Lake Powell in the Grand Canyon). This could lead to tensions and unrest and could damage tourist attractions losing money.
3. Sites where settlements already exist - These should be avoided as high costs are involved in rehoming people on land which is to be flooded. Compensation will need to be paid adding to the expense.
4. High Value Farmland - These should be avoided due to loss of income/profit for the farmer. However close proximity would reduce the cost of transporting water for irrigation.
5. Construction Materials - These should be close by where possible. This will reduce the economic and environmental costof transporting materials long distances.

Question 5

Consequences of Water Control Projects

Answer 5

Environmental Consequences
1. Changes in river regime (flow) has led to loss of animal habitats eg. less birdlife around Colorado Delta.
2. Greater evaporation rates from large areas of water which can also change the hydrological cycle.
3. There has been high water loss at Lake Powell due to water seepage through the permeable sandstone rocks.
4. Reliable seasonal flow for animal and plant life. Resevoirs provide sanctuaries for wildlife eg. blue heron.
5. Hydroelectric Power (HEP) is a renewable energy so less fossil fuels are burned, thus reducing climate change.
Socio-Economic Consequences
1. Loss of native American burial sites and other areas sacred to Navajo.
2. High levels of evaporation can mean that the river and farmland become more saline so farmers downstream have had to switch to salt tolerant crops.
3. Disagreement between states over water allocation. Eg. only around 10% of the Colorado reaches Mexico.
4. Construction costs of a dam are high (Hoover Dam $49 million)
5. Displacement of people from the site of the dam and resevoir eg St Thomas which was covered by Lake Mead.
6. Improved flood control as the amount of water in sections of the river can be controlled.
7. Fresh water supply for growing cities eg Phoenix. Increased standard of living in hot, dry climate eg swimming pools, landcaping.
8. More industries attracted to area due to cheap, reliable HEP supply. Eg. electronics in Silicon Valley, California.
9. Expansion of irrigated land due to more water available allows increased agricultural output & higher yields eg Imperial Valley.
10. Areas such as Lake Mead provide places for watersports and recreation. Tourists can visit which then boosts the economy, creates jobs etc.
11. Construction and maintenance of energy plants creates jobs.
12. As floods are now controlled, less silt is deposited on flood plains. This effects the fertility of the soil so yields are reduced.