CSU HaywardDept. Geography and Environmental StudiesGEOG 4350 Fall 2001 Class 9 Environment versus people - dams and development versus free-flowing rivers and nature. Colorado River case study.
Large dams-resource benefits • Worldwide, large dam projects have been extremely popular elements in national development. • Dams are used for hydroelectric power production. • Dams provide flood protection in frequently inundated lowlands. • Dams store and carryover water supply, largely for non-riparian uses (principally urban and irrigation). • Dams can provide a new local fishing industry or water-based recreation opportunities.
Schematic of Hydropower Dam http://www.tva.gov/power/hydro.htm
The excitor sends an electric current to the rotor, a large electromagnet, charging it with a magnetic field. The rotor spins inside the stator, a tightly wound coil of wire. The moving magnetic field causes an electric current to move through the stator. This current, at 10-20,000 volts, leaves the generator and is then carried to the transformers where it is 'stepped up' to 230,000 volts for transmission. The rotor is propelled by a shaft connected to turbines. Water falling through penstocks connected to the reservoir supplies the energy to spin the turbines. HEP Power Principles
Large dams-flow benefits • Dams yield many downstream benefits because of the way they can control diurnal, seasonal and multi-year flow volumes: • Dams can reduce peak flows and the risk of flooding downstream from overbank conditions. • Dams can enhance flood flow forecasting and predictability by timing releases, especially on multi-dam river networks and when operated in series. • Dams enhance dry season flows by their delayed release effect – important for navigation, recreation, irrigation and so forth. • Dams provide drought mitigation through carryover storage.
Flood Prevention • Downstream communities depend on dam operators to manage dams to retain space for peak retention. • Failure to do so can lead to catastrophic damage, flooding of homes, water plants, sewage facilities, hazardous materials sites and so forth. • However, flooding is also a natural phenomena for flood plains, important for soil and aquatic ecosystem health.
Large dams-inundation effects • The construction of any dam will have profound effects on upstream areas due to inundation of previously dry land – large dams have the greatest impacts, often flooding thousands of km2. • Results in a loss of land and productive potential. • Causes loss of existing infrastructure (roads, energy lines, etc.). • Creates social dislocation (flooded villages) and barriers to communication. • Results in habitat loss, especially wetlands. • Frequently may result in heritage loss (archaeology) and the loss of traditional ways of life. • Results in aesthetic and recreational losses (lost canyon views, hiking, camping, etc.)
China’s Three Gorges • Will dam the Yangtze River and be the largest hydroelectric dam in the world. • Its reservoir would stretch over 350 miles upstream and force the displacement of close to 1.9 million people. • International financing has been withdrawn and international protests have been mounted. • Other dams are protest too – Narmada (India), Hidrovia (Paraguay).
Large dams-downstream effects • Dams can have major negative effects downstream as well as upstream. • Dams create hungry waters, producing a sediment deficit and creating a scouring effect. • Dams withhold nutrient flows and by eliminating seasonal flooding prevent floodplain enrichment • Dams smooth out extreme events which are of critical importance in creating and maintaining habitat – riparian vegetation, riffles and pools, sand banks, etc. • Dams tame rivers, eliminating their wild and scenic nature.
Large dams-migratory fish impacts • A key impact of dams has been in the area of migratory fish endangerment (e.g. CA chinook) but also in changes to downstream fish populations due to temperature and sediment changes (e.g. Colorado R.) • Dams prevent fish movement to spawning grounds. • Dams destroy spawning grounds. • Dams change environmental conditions – especially temperature, DO and turbidity. • Dams change food supply dynamics, predation, etc. • Dams change downstream vegetation, shade, cross-channel morphology and long-profile, salinity balances, flow directions and timing in estuaries, etc.
Large dams-sustainability issues • Many critics argue that the true lifetime costs of dams are much higher than they seem, if all the costs + & - are included. • This is especially true in developing countries where soil erosion can reduce the useful life of dams by sedimentation. • True returns returns to capital will be lower due to reservoir sedimentation (water and energy production is less over time). • There are frequently losses of downstream sand and gravel industry productivity. • Commercial fisheries are usually damaged. • We must account for farming revenues upstream and downstream. • The social costs of dislocated communities and lost livelihoods are seldom factored in. • The value of lost ecosystems and species, particularly in the tropics, is hard to quantify. • Dam construction affects indirectly global warming, being one of the largest causes of deforestation in Latin America (but offsets fossil fuels too!).
Large dams-other interesting issues • There are a number of other issues that can be considered with respect to dams which include: • Catastrophic risks fromdam collapse (more common than you think and perhaps more possible too?) • Equity Issues related tolocal losses (usually rural, poor) versus distant benefits (often urban, elite) • Transboundary issues creating conflicts between nations e.g. India/Bangladesh, Turkey/Iraq, Egypt/Sudan, Syria/Israel. • Disease exacerbation in areas of dam development – biharzia (Schistosomiasis), dengue, malaria, encephalitis.
Lake Chabot would flood the homes of around 60,000 people, two freeways and parts of Oakland airport – in minutes!(see Kramer 2001 thesis or Kramer & Lee 2001 articles) Are we safe in our own back yard?
Teton Dam Failure, 1976, Idaho June 5, 1976: the failure in the Teton Dam led to flooding in the cities of Sugar City and Reburg in Idaho. The dam failure killed 14 people and caused over $1 billion in property damages. Water was seen flowing down the downstream face of the dam, an earthfill embankment dam 300 ft. high, early on the day of the failure. Just a few hours later a crack in the dam had grown to a large hole, which soon led to the breach of the dam.