ABSTRACT

Choosing a suitable site for dam is a crucial phase in dam construction. A successful outcome of this effort is initiated by taking into consideration some watershed properties and characteristics. This study aimed to investigate hydrological information for dam site selection by integrating GIS with AHP Multi-Criteria Decision Analysis to establish hydrologic characteristics of the region suitable for a dam construction. The method used was based on consideration of seven criteria which included topographic factors (slope), geological factors, soil type, catchment size, land cover, proximity to river and proximity to roads

CHAPTER ONE

1.0            INTRODUCTION

1.1 Background of study

Dam, structure built across a stream, a river, or an estuary to retain water Dams are built to provide water for human consumption, for irrigating arid and semiarid lands, or for use in industrial processes. They are used to increase the amount of water available for generating hydroelectric power, to reduce peak discharge of floodwater created by large storms or heavy snowmelt, or to increase the depth of water in a river in order to improve navigation and allow barges and ships to travel more easily. Dams can also provide a lake for recreational activities such as swimming, boating, and fishing. Many dams are built for more than one purpose; for example, water in a single reservoir can be used for fishing, to generate hydroelectric power, and to support an irrigation system. Water-control structures of this type are often designated multipurpose damsm .Abushandi E. and Alatawl (2015)

Auxiliary works that can help a dam function properly include spillways, movable gates, and valves  that control the release of surplus water downstream from the dam. Dams can also include intake structures that deliver water to a power station or to canals, or pipelines designed to convey the water stored by the dam to far-distant places. Other auxiliary works are systems for evacuating or flushing out silt that accumulates in the reservoir, locks for permitting the passage of ships through or around the dam site, and fish ladders (graduated steps) and other devices to assist fish seeking to swim past or around a dam. Thanoon A.A (2013)

A dam can be a central structure in a multipurpose scheme designed to conserve water resources on a regional basis. Multipurpose dams can hold special importance in developing countries, where a single dam may bring significant benefits related to hydroelectric power production, agricultural development, and industrial growth. However, dams have become a focus of environmental concern because of their impact on migrating fish and riparian ecosystems. Salman S.R (2015)

The oldest known dam in the world is a masonry and earthen embankment at Jawa in the Black Desert of modern Jordan. The Jawa Dam was built in the 4th millennium BCE to hold back the waters of a small stream and allow increased irrigation production on arable land downstream. Evidence exists of another masonry-faced earthen dam built about 2700 BCE at Sadd el-Kafara, about 30 km (19 miles) south of Cairo, Egypt. The Sadd el-Kafara failed shortly after completion when, in the absence of a spillway that could resist erosion, it was overtopped by a flood and washed away. The oldest dam still in use is a rock fill embankment about 6 metres (20 feet) high on the Orontes river in Syria, built about 1300 BCE for local irrigation use. Patel (2015)

The Assyrians, Babylonians, and Persians built dams between 700 and 250 BCE for water supply and irrigation. Contemporary with these was the earthen Ma’rib dam in the southern Arabian peninsula, which was more than 15 meters (50 feet) high and nearly 600 meters (1,970 feet) long. Flanked by spillways, this dam delivered water to a system of irrigation canals for more than 1,000 years. Remains of the Maʾrib Dam are still evident in present-day ma’rib, Yemen. Other dams were built in this period in Sri Lanka, India, and china.Ghoraba S.M (2017)

The Romans

Despite their skill as civil engineers, the Romans’ role in the evolution of dams is not particularly remarkable in terms of number of structures built or advances in height. Their skill lay in the comprehensive collection and storage of water and in its transport and distribution by aqueducts. At least two Roman dams in southwestern Spain, Proserpina and Cornalbo, are still in use, while the reservoirs of others have filled with silt. The Proserpina Dam, 12 meters (40 feet) high, features a masonry-faced core wall of concrete backed by earth that is strengthened by buttresses supporting the downstream face. The Cornalbo Dam features masonry walls that form cells; these cells are filled with stones or clay and faced with mortar. The merit of curving a dam upstream was appreciated by at least some Roman engineers, and the forerunner of the modern curved gravity dam was built by byzatine engineers in 550 CE at a site near the present Turkish-Syrian border.BO,A (2014)

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