the impact of flood control measures on river processes

example of how flood control measures can impact a river process

The three Gorges Dam on the River Yangtze in China

about the Three Gorges Dam

It cost over $28.6 billion and took nearly two decades to build.

It required the uprooting of more than a million young people along the Yangtze river.

The construction

the building of the dam involves the construction of a wall across a river - this allows the water flow to be regulated by channeling water through pipes or passageways controlled by flood gates.

Why was it built

• was built to generate hydroelectric power

• control flooding on the Yangtze river

The dams reservoir

• stretches up to 600km and has a storage capacity of 22 cubic kilometres and handles inflows of about 98.8m liters a second.

positive about the dam

• it has helped reduce the frequency of major downstream flooding from once every 100 years.

  .

effects before the dam

• before its construction, floods on the Yangtze river killed more than 300,000 people in the 20th century.

• Many people also died from starvation of crop failure due to flooding on the floodplain.

flood in 1998

• the most serious flood - made 14 million people homeless and $20 billion worth of damage was caused.

the benefits of the dam

• The dam has saved lives by interfering with the river’s natural process of flooding its floodplain

• crops are now free from the risk of flooding.

• water from the river irrigates crops and provides fresh water supply to millions of people

consequence of interfering with the rivers natural process

means alluvium is now being deposited in the reservoir (depriving the land further downstream )which reduces soil fertility.

dam interference with the natural flow

• saltwater creeps up the river, killing freshwater fish.

• leads to a loss of biodiversity - many species of aquatic life are unable to migrate up or downstream.

waste water and pollution

• over one billion tons of wastewater are released each year into the year.

• The pollution gets trapped behind the resovoir dam and causes serious environmental problems

Increased erosion in the reservoir

it is caused by the rising water levels and has resulted in 70% more landslides and bank collapses

Artificial levees

another example of human interaction with surface processes: building of artificial levees along a river’s course in order to prevent flooding.

mississippi river in America

thousand miles of levees and floodgates are in place to control the flow of the river

the levees significantly alter

flooding across its floodplain.

downside to artificial levees

disrupts the natural depostition of sediments which is necessary for

• maintaining fertile soils

• supporting diverse ecosystems.

the levees - migration of fish

The levees interfere with the natural migration patterns of fish