Silting and Desilting of Reservoirs

Dan G. Batuca, J.M. Jordaan Jr

• Publisher: CRC Press
• Year: 2021
• ISBN:
  9781000446517
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

The creation of river dams and the storage of water have been a strategy for survival for many centuries. Reservoirs have diverse functions, providing irrigation, water supply, storage of water, flood control, navigation and power generation. The silting of a reservoir is an unavoidable process. Although it cannot be halted, silting can be slowed down and controlled by a variety of soil conservation practices and by modifying agricultural practices in the catchment area. Other methods ofreducing silting include the placing of certain engineering structures in the river system and the introduction of adequate strategies of reservoir operation. Silting and Desilting of Reservoirs includes aspects such as hydraulics, sediment transport, silting, sediment distribution, calculation and prediction of silting and solutions to reservoir silting.

CHAPTER 1

Introduction

Reservoirs are prevalent man-made works, since time immemorial they have been mentioned by many and various historical sources, written or not written, some older than 5000 years (Jansen 1980).

In Antiquity, reservoirs for irrigation, water supply and flood protection were built in Egypt (the Kosheis reservoir, 2900 BC and the Moeris reservoir, 2300 BC), in Mesopotamia (700 BC) and Persia (500 BC), in China (year 600 BC), in Sri Lanka (the Basawakkulam reservoir, 430 BC and the Tissa reservoir, 300 BC), in India (the Girnar reservoir, 300 BC), as well as in some Asian and European provinces of the Roman Empire (the Cornalbo and Proserpina reservoirs in Spain, 100 AD).

In the Middle Ages, in spite of the general decline of human creative activities, reservoirs were still built in some Asian provinces of the Byzantine Empire (years 500–600), in India (the Moti Talev and Cuddalore reservoirs, the XI-th century) and in Spain (the Almonacid reservoir, the XI-th century) as well.

In the Modern Ages, the XV-XVIII-th centuries, a sudden surge was recorded in the field of dam and reservoir construction, with their use being made extensively for many purposes: irrigation, domestic water supply and later, hydropower production. Such reservoirs were built in Spain (the Tibbi reservoir), in France (more than 60 reservoirs), in the Ottoman Empire and in Japan (540 reservoirs). In the year 1800 there were some 500 reservoirs in the world, of which only 41 reservoirs had a capacity greater than 0.1 km³ (14 km³ volume in total).

In the present times, the XIX-XX-th centuries, the most significant evolution in construction and use of reservoirs was recorded. The capacity of the reservoirs and the height of the dams continuously increased; giant and super-giant reservoirs of 100–200 km³ capacity were realised by dams higher than 300 m. The concept of multipurpose use of the reservoirs was introduced as well.

During this time, the most important rivers of the world were fitted out with complex, multipurpose reservoirs (the Danube, Volga, Don, Missouri, Colorado, Zambezi, Euphrates, Nile, Indus, Yellow and other rivers). During the first half of the XX-th century, especially between the First and the Second World War, a number of 539 reservoirs (528 km³ volumetric capacity in total) was realised.

During the period 1950 to 1985 an important growth in the number of reservoirs was recorded, from 5268 in 1950 to 36,226 (17,406 excluding China) in 1986; the annual growth rate in their number was 5.5% (ICOLD 1988, as shown in Figure 1.1).

Between the years 1960 and 1970, the existing reservoirs all over the world had a total storage capacity of 4000–5000 km³ and occupied a total surface area of 400,000 km²; a number of 320 very large reservoirs (with surface areas greater than 100 km²) and 32 giant reservoirs (with surface areas greater than 1000 km²) were recorded.

Between the years 1975 and 1980, more than 30,000 large dams were registered by ICOLD in the world, but their real number is much larger (in China alone there were probably more than 13,500 and in the former Soviet Union more than 25,000 large dams).

In the year 1985, there were 2357 large reservoirs (with storage capacity greater than 0.1 km³) in the world, having a total volume of 5552 km³, from which 697 were in the USA, 237 in the former USSR, 152 in India, 142 in China, 133 in Canada, 84 in Brazil and 82 in Spain, as shown in Figure 1.2. The 1991 ICOLD statistics of the greatest reservoirs in the world are given in Figure 1.3.

The Owen Falls Reservoir in Uganda (1954) is the largest reservoir in the world (205 km³ volume and 68,000 km² surface area), but includes the big natural Lake Victoria. The Akosombo Reservoir realised in the year 1965 on the Volta River in Ghana is the most extended man made reservoir in the world (8482 km² surface area). The Rogeonski and Nurek Reservoirs realised in the year 1985 on the Vaksh River in Russia are the deepest in the world (dam heights over than 310 m).

Figure 1.1. The 1988 statistics of large reservoirs in the world (after ICOLD 1988).

Figure 1.2. The 1985 statistics of reservoirs with capacity greater than 0.1 km³ (after ICOLD 1988).

Figure 1.3. The 1991 statistics of reservoirs with capacity greater than 1 km³ (after ICOLD 1988).

Romanian reservoirs

In Romania, small reservoirs for fishing, milling and water supply were mentioned for the first time in some historical written documents in the XII-th and XIII-th centuries (the Ioanits Diploma, the Descriptio Moldaviae and the Cantacuzino Stolnic Map).

The first dams for hydropower generation were built at the end of the last century in Bucharest, the Capital City (1890) and Sibiu City (1896).

Before the First World War, the Sadu (1907), the Breazova (1909) and the Cugir (1912) small reservoirs were built for power generation, and in the year 1930 the Scropoasa Dam was realized on the Ialomita River for the same purpose.

Due to the great need of energy in Romania after the Second World War, the Gozna (1952), Moroeni (1953) and Astileu (1956) reservoirs were built, as well as the big cascades of reservoirs on the Arges, Bistrita and Olt Rivers.

In the year 1978 there were registered a number of 92 large dams for multiple purposes and in the year 1985 there were 8 large reservoirs with storage capacity greater than 0.1 km³. In the year 1990 there were ICOLD registered a number of 133 large dams (some statistical data are given in Table 1.1).

Table 1.1. Statistical data for some of the largest reservoirs in Romania (based on the TCH data, 1990).

Reservoir	River	Dam wall height (m)	Reservoir capacity (10^6 m^3)	Year of completion
Iron Gates 1	Danube	60.6	2900	1971
Stanca Costesti	Prut	45.0	1400	1978
Izvoru Muntelui/Bicaz	Bistrita	127.0	1230	1961
Vidraru	Arges	166.6	465	1966
Vidra	Lotru	121.0	340	1974
Fantanele	Somes Cald	95.5	220	1978
Gura Apelor	Raul Mare	173.0	220	1990
Valea Iovan	Cema	110.5	130	1981
Siriu	Buzau	122.0	125	1980
Beresti	Siret	27.0	120	1986
Dragan	Dragan	120.0	112	1987
Ipotesti	Olt	34.0	110	1988
Poiana Uzului	Uz	80.5	100	1973

The evolution of storage capacity of reservoirs in Romania up to the year 1982 in Romania is shown in Figure 1.4.

Figure 1.4. Time evolution of the water storage volumes in Romanian reservoirs (based on the ISPH data, 1984).

The largest and the most important reservoirs in Romania are the Iron Gates 1 on the Danube River (2.9 km³ volume and 320 km² surface area) and the Izvoru Muntelui on the Bistrita River (1.23 km³ volume and 32.6 km² surface area).

In the prospect of the first decade of the XXI-st century, the design and construction of 1400 new small and large reservoirs (34 km³ volume) for various single, dual or multipurpose are t...