River Basin Management Why do we need water management schemes? Ecosystem approach to RBM Multi-purpose RBM Colorado case study.

Why do we need RBM? “…water is among the most essential requisite that nature provides to sustain life for plants, animals and humans. The total quantity of fresh water on Earth could satisfy all the needs of the human population if it were evenly distributed and accessible…” (W. Stumm, 1986)

Ecosystem approach to RBM Possible environmental effects on drainage basin. The effect on local people. The full economic cost of improved agriculture. Possible effects on public health. Possible alternative power production. Long-term feasibility taking into account silting up of the reservoir.

Multi-purpose RBM Multi purpose schemes have been seen as an answer to basic water problems such as: Water supply: The provision of drinking water, irrigation and domestic use. A continual decline in stable run-off due to increased population and per capita use. All management schemes should aim to provide water appropriate to the needs of the population being served. Flood control: Flooding is the moist significant of all natural hazards, it accounts for 2% of global deaths per year. Flood damage increases despite massive investment. Many sites subject to flooding are preferred for industry, commerce or housing. - Engineering response: Using upstream storage, building levees and bypass channels to speed up flow. - Ecological response: Establish natural plant cover, minimise flow from natural land phase.

Multi-purpose RBM (cont) Hydro-electric power: Valuable by-product of integrated schemes. Often incompatible with flood control as reservoirs kept bankfull. Navigation: Water depth has to be kept at a certain level. Economically difficult to justify. During periods of low rainfall, more important to store water for other uses. Recreation: Recreation facilities are often created and bring in important revenue for the area, e.g lakes for fishing, water sports, holiday homes.

Colorado

The Colorado environment Extremely dry, some areas receive <25mm rainfall per year. 95% of rainfall lost to evaporation. Day time temps of >40degrees. Rock fissures caused by summer heat and winter cold make desert surfaces friable. (Friability is the ability of a solid substance to be reduced to smaller pieces with little effort.)solid Little vegetation, therefore soils susceptible to erosion. Rainfall seasonal, often causing flash floods. Colorado river fed by snowmelt, making it unpredictable. Colorado climate: “Why is the SW of USA most needful of water control schemes?” Questions 1,2,5,8,9,16 p.18/21/23

The Colorado’s river basin

Water allocation 7 states with varying agricultural, industrial and public needs. “prior appropriation” – first come first served. Worked well for California who had financial means and growing population to exploit regular water supply from the Colorado.

Colorado Compact Basin divided into upper and lower. Lower basin receives a set amount rather than a %.

Water availability California received the greatest share of the water due to its greater population and political influence, despite 83% of water originates in upper basin. Unreliability of water and decrease in water in river since 1920s. Upper basin is legally bound to supply 92.5km/3 every 10yrs to lower basin, if river is below average, then lower basin is entitled to bigger share of less water. (questions 18,19,21 pg.25)

Greater flood control? Dams filled to extract as much revenue from HEP as possible to offset huge construction costs. Look at “Desert Floods”: 1. Where did the floods of 1993 occur? 2. Why did the flooding occur? 3. What damage limitation was employed? 4. What were the consequences of the floods?

Physical factors affecting dam location Valley shape: deep and narrow = small surface area Climate: High temp= >evap. Precip must be enough to make dam viable Rock type: metamorphic rock= impermeable. Some sandstone, permeable= seepage High drainage density = >efficiency of water collection. Vegetation: stabilises sides & forms barrier Tectonic activity: Close to San Andrea Fault, relatively “new” mountains. Siting Colorado dam

Human factors affecting dam location Siting Colorado dam Infrastructure: Can it be easily connected? Political conflict: Interstate/international Labour supply: accommodation/food etc Location: proximity to large populated areas. Longer distance more evaporation if water in canal. Political – kudos for politicians Relocation of population Demand: is it needed? Is there industrial demand for elect/water? Irrigation: Gain in farm land Loss of farmland Cost: relocation Historical