DEFINITION OF A DAM

A dam is a barrier constructed to hold back water and raise its level creating a reservoir which is an enlarged natural or artificial lake, storage pond or impoundment (water control) created using a dam to store water.

CATEGORY OF DAMS

Dams in kenya are categorised into three:-

1. Category I (Greater than 50M height)
2. Category II (15-50M height)
3. Category III (Less than 15M height)

ROLE OF DAMS

IRRIGATION

The vast quantities of water in reservoirs allow dams to act as effective and steady sources of water for irrigation with minimal seasonal fluctuations. 30 to 40 percent of the 271 million hectares that are irrigated worldwide rely on irrigation dams.

With the large population growth expected for the next decades, irrigation must be expanded to increase the food capacity production. It is estimated that 80% of additional food production by the year 2025 will need to come from irrigated land. Even with the widespread measures to conserve water by improvements in irrigation technology, the construction of more reservoir projects will be required.

FLOOD CONTROL

Dams and reservoirs can be effectively used to regulate river levels and flooding downstream of the dam by temporarily storing the flood volume and releasing it later. The most effective method of flood control is accomplished by an integrated water management plan for regulating the storage and discharges of each of the main dams located in a river basin. Each dam is operated by a specific water control plan for routing floods through the basin without damage. This means lowering of the reservoir level to create more storage before the rainy season. This strategy eliminates flooding. The number of dams and their water control management plans are established by comprehensive planning for economic development and with public involvement. Flood control is a significant purpose for many of the existing dams and continues as a main purpose for some of the major dams of the world currently under construction.

HYDROPOWER

Hydroelectric power plants generally range in size from several hundred kilowatts to several hundred megawatts, but a few enormous plants have capacities near 10,000 megawatts in order to supply electricity to millions of people. World hydroelectric power plants have a combined capacity of 675,000 megawatts that produces over 2.3 trillion kilowatt-hours of electricity each year; supplying 24 percent of the world’s electricity.

In many countries, hydroelectric power provides nearly all of the electrical power. In 1998, the hydroelectric plants of Norway and the Democratic Republic of the Congo (formerly Zaire) provided 99 percent of each country’s power; and hydroelectric plants in Brazil provided 91 percent of total used electricity.

Electricity generated from dams is by very far the largest renewable energy source in the world. More than 90% of the world’s renewable electricity comes from dams. Hydropower also offers unique possibilities to manage the power network by its ability to quickly respond to peak demands. Pumping-storage plants, using power produced during the night, while the demand is low, is used to pump water up to the higher reservoir. That water is then used during the peak demand period to produce electricity. This system today constitute the only economic mass storage available for electricity.

INLAND NAVIGATION

Natural river conditions, such as changes in the flow rate and river level and changing river channels due to erosion and sedimentation, create major problems and obstacles for inland navigation. The advantages of inland navigation, however, when compared with highway and rail are the large load carrying capacity of each barge, the ability to handle cargo with large-dimensions and fuel savings. Enhanced inland navigation is a result of comprehensive basin planning and development utilizing dams, locks and reservoirs which are regulated to provide a vital role in realizing regional and national economic benefits. In addition to the economic benefits, a river that has been developed with dams and reservoirs for navigation may also provide additional benefits of flood control, reduced erosion, stabilized groundwater levels throughout the system and recreation.