Al Wahda Dam (Morocco)
Encyclopedia
Al Wahda Dam, formerly known as M'Jaara Dam, is an embankment dam
on the Ouergha River
near M´Jaara in Sidi Kacem Province, Morocco
. It was constructed for flood control
, irrigation
, water supply
and hydroelectric power production. It is the second largest dam in Africa and the largest in Morocco. It was described by Land Ocean Interactions in the Coastal Zone (LOICZ) as "the second most important dam in Africa after the High Aswan dam
."
, in its center is controlled by six floodgate
s and has a discharge capacity in excess of 13000 m3/s.
The power plant, at the dam's toe and adjacent to the spillway is supplied with water via a 10.8 m (35.4 ft) diameter and 247 m (810.4 ft) long pipe which in turn transfers the water into three penstocks. Each of which is 5.7 m (18.7 ft) in diameter 60 m (196.9 ft) in length. This scheme provides 62 m (203.4 ft) of hydraulic head
and up to 450 m3/s to the Francis turbine
s. Each turbine powers an 80 MW generator for a total installed capacity of 240 MW.
. In addition, it has helped reduce floods in the Gharb region along the Ouergha and Sebou River
s by 90%. It provides water for the potential irrigation of over 110000 ha (271,815.7 acre). Electricity produced by the dam's hydroelectric power station also alleviates the burning of 140,000 metric tons of fossil fuels a year along with serving peak energy demand. The dam's reservoir though has a high rate of siltation
and it is estimated to lose 60000000 cubic metre of storage each year. The silt trapped in the reservoir also doesn't reach the coastal estuary which increases erosion along the coast.
Embankment dam
An embankment dam is a massive artificial water barrier. It is typically created by the emplacement and compaction of a complex semi-plastic mound of various compositions of soil, sand, clay and/or rock. It has a semi-permanent waterproof natural covering for its surface, and a dense, waterproof...
on the Ouergha River
Ouergha River
The Ouergha River is a watercourse in Morocco that is tributary to the Sebou River.-History:The Ouergha River was a key battle site in the French invasion of Morocco in the year 1924...
near M´Jaara in Sidi Kacem Province, Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...
. It was constructed for flood control
Flood control
In communications, flood control is a feature of many communication protocols designed to prevent overwhelming of a destination receiver. Such controls can be implemented either in software or in hardware, and will often request that the message be resent after the receiver has finished...
, irrigation
Irrigation
Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...
, water supply
Water supply
Water supply is the provision of water by public utilities, commercial organisations, community endeavours or by individuals, usually via a system of pumps and pipes...
and hydroelectric power production. It is the second largest dam in Africa and the largest in Morocco. It was described by Land Ocean Interactions in the Coastal Zone (LOICZ) as "the second most important dam in Africa after the High Aswan dam
Aswan Dam
The Aswan Dam is an embankment dam situated across the Nile River in Aswan, Egypt. Since the 1950s, the name commonly refers to the High Dam, which is larger and newer than the Aswan Low Dam, which was first completed in 1902...
."
Background
In 1988, the Board of Water and Climate considered the dam and eventually it was recommended for development. Construction began in 1991, the dam began to create its reservoir in 1996 and was inaugurated on March 20, 1997 by King Hassan II. A total of 14000000 cubic metre of material were excavated during construction.Specifications
The dam is an earthen embankment type made of 28000000 cubic metre of material and 720000 cubic metre of concrete. It is 88 m (288.7 ft) tall at its highest point and the main portion of the dam is 1600 m (5,249.3 ft) long. Directly to the north and adjacent to the spillway is a saddle dam that is 1000 m (3,280.8 ft) long and 30 m (98.4 ft) high. The dam's spillwaySpillway
A spillway is a structure used to provide the controlled release of flows from a dam or levee into a downstream area, typically being the river that was dammed. In the UK they may be known as overflow channels. Spillways release floods so that the water does not overtop and damage or even destroy...
, in its center is controlled by six floodgate
Floodgate
Floodgates are adjustable gates used to control water flow in flood barriers, reservoir, river, stream, or levee systems. They may be designed to set spillway crest heights in dams, to adjust flow rates in sluices and canals, or they may be designed to stop water flow entirely as part of a levee or...
s and has a discharge capacity in excess of 13000 m3/s.
The power plant, at the dam's toe and adjacent to the spillway is supplied with water via a 10.8 m (35.4 ft) diameter and 247 m (810.4 ft) long pipe which in turn transfers the water into three penstocks. Each of which is 5.7 m (18.7 ft) in diameter 60 m (196.9 ft) in length. This scheme provides 62 m (203.4 ft) of hydraulic head
Hydraulic head
Hydraulic head or piezometric head is a specific measurement of water pressure above a geodetic datum. It is usually measured as a water surface elevation, expressed in units of length, at the entrance of a piezometer...
and up to 450 m3/s to the Francis turbine
Francis turbine
The Francis turbine is a type of water turbine that was developed by James B. Francis in Lowell, Massachusetts. It is an inward-flow reaction turbine that combines radial and axial flow concepts....
s. Each turbine powers an 80 MW generator for a total installed capacity of 240 MW.
Positive and negative impacts
The dam has had a positive impact downstream by supplying water for drinking and irrigationIrrigation
Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...
. In addition, it has helped reduce floods in the Gharb region along the Ouergha and Sebou River
Sebou River
Sebou is a river in northern Morocco. The river is 458 kilometres long and has an average water flow of 137 m3/s, which makes it the largest North African river by volume. The source is in the Middle Atlas mountains. It passes near the city of Fes and discharges to the Atlantic Ocean in Mehdia...
s by 90%. It provides water for the potential irrigation of over 110000 ha (271,815.7 acre). Electricity produced by the dam's hydroelectric power station also alleviates the burning of 140,000 metric tons of fossil fuels a year along with serving peak energy demand. The dam's reservoir though has a high rate of siltation
Siltation
Siltation is the pollution of water by fine particulate terrestrial clastic material, with a particle size dominated by silt or clay. It refers both to the increased concentration of suspended sediments, and to the increased accumulation of fine sediments on bottoms where they are undesirable...
and it is estimated to lose 60000000 cubic metre of storage each year. The silt trapped in the reservoir also doesn't reach the coastal estuary which increases erosion along the coast.