River Basin Management

Question 1

Positive physical characteristics of the Colorado river

Answer 1

• underlying geology of impermeable rocks, allows for dams to be build (hard durable rock provides secure base), also means less water loss through infiltration and percolation, eg lake mead
• steep valley sides, good for surface run off and collection of water
• high precipitation in Rocky Mountains and winter snowmelt, high discharge levels in river and large flow, however this is only for part of the year
• very little tectonic plate activity, secure for building dams and good for storing water

Question 2

Negative physical characteristics of the Colorado river

Answer 2

• low rainfall in lower basin as it lies in rain shadow of Sierra Nevada mountains to west, less discharge in the river
• highly variable seasonal rainfall with thunderstorms around may time and snowmelt only feeds river for half of the year, this can lead to flash flooding
• hot climate with temperatures in desert regularly over 40°C, high evaporation rates, 95% of the rainfall in the lower basin is lost to this
• climate change has meant less precipitation in the last 50 years, shorter and warmer winters means less snow and snow melt, increased evaporation due to increased temperatures
• sedimentary rock in area around Lake Powell, lots of seepage and water loss

Question 3

Other physical characteristics of the Colorado river

Answer 3

• poor dry soil means limited plant growth within the region, leading to high surface run off and flash flooding, very little interception so rain hits soil eroding it, few roots holding soil together means soil is further eroded
• hard dry ground and steep slopes, means little infiltration leading to rapid transfer of water
• thin soils means little capacity for water storage, leading to more surface run off

Question 4

Need for water management of the Colorado river - human factors

Answer 4

• electricity generation (HEP), this is required to power homes, industry and farms
• drinking and domestic water for cities such as Las Vegas where there is over 50million people, used for domestic appliances, golf courses, swimming pools and Mediterranean climate means warm dry summer so lots of water needed
• irrigation in agriculture, increased need for food production due to increasing population
• tourism, helps to boost economy with more than 1million visitors coming to visit hoover dam each year and over 6million people in the wider lake mead area
• political tensions, with the Colorado flowing through multiple sets and 2 countries it can be hard to balance politically, generally power lies with upstream countries who control flow but then by the time river reaches Mexico 90% of its water has been removed

Question 5

Need for water management of the Colorado river - physical factors

Answer 5

• flooding, due to seasonal summer rains
• drought, due to low rain in much of the lower basin, drought can occur because snowmelt is variable and unpredictable
• limited vegetation, leads to high surface run off and low levels of interception, increases soil erosion which can silt up lakes

Question 6

Physical factors affecting the site of dams

Answer 6

• permeability of the rock, impermeable rock is preferable. Reduces water loss through percolation eg using igneous rocks like granite rather than sedimentary rocks. Lake Powell loses around 300km2 of water per year due to this
• valley shape, v-shape valley is ideal. Reduces construction costs of dam as it requires less materials so has a shorter distance to cross, also smaller surface area so less water lost through evaporation
• rock type, important that rock is strong. Can support the weight of the dam as well as any water contained within it eg granites and other igneous rocks
• volcanic earthquake activity, area with not much of this which is geologically stable is preferable. Earthquakes may de-stabilise the dam and cause subsidence, if it collapses or is damaged it could lead to mass flooding
• climate, a milder climate with moderate rainfall is preferable. Less rainfall lost through evaporation, plentiful rainfall also ensures there is plenty of water to supply river but not so much it floods
• side of drainage basin/catchment area, larger drainage basin is preferable. There is more opportunity for lots of water to be collected, high snowmelt and large number of tributaries would ensure lots of water gets straight into the river rather than infiltrating and going into ground water storage

Question 7

Human factors affecting the site of dams

Answer 7

• having settlements nearby, positive factor as can provide workforce or accommodation during construction, may also reduce costs of pipelines and cabling for transporting water, new settlements won’t have to be built eg Boulder City, Nevada was build for workers on the hoover dam in 1933
• places of historical and cultural importance, should be avoided eg Native American burial grounds, to show sensitivity to native cultures
• sites where settlements already exist, should be avoided as high costs are involved in reforming people on land which is to be flooded, compensation will also need to be paid adding to the expense
• high value farmland should be avoided, due to loss of income/profit for farmer, however close proximity would reduce cost of transporting water for irrigation
• construction materials should be close by where possible, this will reduce the economic and environmental cost of transporting materials long distances

Question 8

Environmental consequences of water control projects

Answer 8

• greater evaporation rates from large areas of water can change the hydrological cycle
• as floods are now controlled, less alluvium is deposited on flood plains, this can effect fertility of soil meaning yield will be reduced
• reliable seasonal flow for animal and plant life and reservoirs provide sanctuaries for wildlife such as blue herons
• hydroelectric power (HEP) is a renewable energy source so less fossil fuels are burned, thus helping to reduce climate change
• changes in river flow has lead to loss of animal habits for example less bird life around the Colorado
• there has been high water loss at lake Powell due to water seepage through permeable sandstone rocks
• improved flood control as the amount of water in sections of the river can be controlled

Question 9

Socio-economic consequences of water control projects

Answer 9

• disagreement between states over water allocation for example only around 10% of the Colorados flow reaches Mexico
• 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
• areas such as lake mead provide water sports and recreation, tourists can visit which then boosts economy and creates job opportunities
• displacement of people, from the site of the dam and reservoirs p for example St. Thomas was covered by Lake Mead
• expansion of irrigated land due to more water available allows an increased agricultural output and higher yields
• loss of Native American burial sites and other areas crafted to Navajo
• construction costs of dams are high for example hoover dam cost around $40million
• contraction and maintenance of energy plants creates jobs
• more industries attracted to area due to cheap and reliable HEP supply
• fresh water supple for growing cities. Increased standard of living in hot, dry climate eg swimming pools and landscaping