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One area can illustrate that the supply of & demand for Water Varies over Time & Space

One area can illustrate that the supply of & demand for Water Varies over Time & Space. A case study of the Colorado drainage basin SW USA. PHYSICAL Geology Relief Climate. Factors affecting SUPPLY are…. POLITICAL. TECHNOLOGICAL.

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One area can illustrate that the supply of & demand for Water Varies over Time & Space

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  1. One area can illustrate that the supply of & demand for Water Varies over Time & Space A case study of the Colorado drainage basin SW USA

  2. PHYSICAL • Geology • Relief • Climate Factors affecting SUPPLY are… POLITICAL TECHNOLOGICAL

  3. At Yuma – after flooding there was a localised rise in water table… … Possible sewage contamination from septic tanks Permeable rocks – Absorb water - Give groundwater supplies Over extraction from aquifers e.g. Phoenix Water table becoming too deep PHYSICAL SUPPLY: GEOLOGY Aquifer sources are important in this arid area – over 25% of supply Loss of water by percolation through bed of reservoirs e.g. Lake Powell

  4. C.A.P. = ? Central Arizona Project North Phoenix - The purpose of CAP is to help Arizona conserve groundwater by importing a fresh, renewable supply of surface water from the Colorado River.

  5. The Lower Basin depends almost entirely on the Upper Basin for its supplies Many deep canyons Suitable for dams & reservoir sites PHYSICAL SUPPLY: RELIEF Sierra Nevada – relief rainfall Rain shadow to east in desert Upper catchment (Rockies) much snowfall & melt into the Colorado in Spring Flows SW to Mexico

  6. Boulder Dam – relief advantages?

  7. High evaporation from reservoir surfaces Extremely arid Low input of rainfall Especially in the Lower Basin Much seasonal supply from snow melt PHYSICAL SUPPLY: CLIMATE Seasonal rainfall Violent thunderstorms Flash flood run-off Not easily stored Rain Shadow of Sierra Nevada Range Much water loss by evaporation (95%) high temperature and low humidity

  8. Relief rainfall Sierra Nevada Rain Shadow Nevada and Arizona

  9. Very little Vegetation so transpiration loss is low in natural systems Main supply is the Colorado river Secondary source is groundwater / aquifers PHYSICAL SUPPLY: Other Soils – friable and absorbent so Groundwater supplies are adequate. Rainwater drains quickly. Soil eroded easily – puts sediment in river and silts up reservoirs quickly

  10. Fieldwork in Arizona – a vegetation stop!

  11. California first to construct canals to take water to the Imperial Valley in late 19th C. Irrigation for agriculture - 80% of use Colorado - a River or A Giant Plumbing System? 800,000 hectares of farmland is irrigated Supply factor TECHNOLOGICAL 20 major dams and reservoirs 33% of Southern California water supplied via Colorado river aqueduct Denver and towns in Rockies supplied across the Great Divide (watershed) by the Big Thompson Project

  12. The main reason for technological interference was flood control. The Colorado was very ‘flashy’ and dangerous Bureau of Reclamation set up in Depression (1930s) to plan and construct major engineering projects With national funding Supply factor TECHNOLOGICAL No overall Drainage Basin Management Central Arizona Project - 540 km canal across desert from Parker dam to Phoenix and Tucson. Lifts water 900 metres uphill Problems of water quality and colour. Supplies 25% of Phoenix water

  13. High Technology allows wasteful use of water in lakes, swimming pools, golf courses, gardens and ordinary domestic use. 40 million people supplied with water & increasing HEP – produces 120 million KW of electricity. Environmentalists oppose any further dam construction Problem of salinisation in water supplied to Lower Basin… Supply factor TECHNOLOGICAL Flood Control – 1983 – disastrous floods below Parker and Davis dams – if the area is so controlled how did this happen? … Surplus water drains from upper farmland with fertiliser and is reused downriver

  14. Colorado Compact 1922 –water allocation – based on population figures of Basin states then. Growing environmental concern and lobby group. N.A.W.A.P.A. scheme suggested but far fetched? Different users have political clout to protect own interests e.g. Dole Supply factor – POLITICAL Also shared with Mexico California dominates then and now. Southern states tend to be non-interventionist – let business decide. Some states would like to renegotiate as things have changed! No interstate transfers have been agreed

  15. Native American population groups still exist in area and have some water rights. Will use the law now to protect their interests. Compact agreed when area had low population – only California had a sizeable population. Now 35 million – more than total of all the other Basin states Demand factor DEMOGRAPHIC Mostly URBAN population – they expect and need water for swimming pools in such a hot environment. Tend to use water wastefully – e.g. golf courses and lakes but have ability to pay. ‘Sunrise’ states with rapid population growth. Much in-migration in 1980s. Nevada 37% growth, Arizona 22% 1990 – 1998.

  16. Agriculture uses 80% of the supply. Uses water wastefully e.g. furrow / flood irrigation. Grows specialist crops e.g Lettuce in Yuma. This demands regular irrigation – may not be SUSTAINABLE Rising price of water – litre for litre now costs more than petrol. Agriculture is least able to afford the rising prices. Some farmers have sold water rights to cities Demand factor ECONOMIC Industrial – ‘Sunrise’ States – have a growing hi-tech industrial base. Many companies have landscaped grounds wit lakes and gardens watered by sprinklers. Business executives expect facilities like golf courses. Domestic / Urban – a growing number of big cities like Phoenix. Demand water for homes and pools. Phoenix has built the 500 km Central Arizona Project to use Colorado water. Groundwater supplies already nearly exhausted

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