Geography
Sand Dams
Sand dams are structures built in dryland regions to capture and store rainwater in sand layers. They are typically constructed across seasonal rivers and streams, allowing water to seep through the sand and be stored for use during dry periods. This sustainable water management technique helps to provide a reliable source of water for communities in arid environments.
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8 Key excerpts on "Sand Dams"
- Christopher J. Barrow(Author)
- 2016(Publication Date)
- Routledge(Publisher)
Such techniques have been used in Botswana, Namibia, Ethiopia, Mexico, southern USA and many other countries. Pereira (1977: 193) describes the successful use of check-dams to create venetian cisterns in Ethiopia for watering high-value export vegetable crops. It is possible without too great an expenditure to improve the most basic sand-filled reservoir to increase its storage and reduce water losses between fillings. Figure 6.10a, b illustrates an intermediate technology approach which could achieve such objectives. Where there are springs with inadequate flow to meet daily needs of livestock or cultivators, or if they run dry for part of the year, sand-filled reservoirs may offer a suitable means of uprating them (sand or gravel may have to be transported to the spring to form the storage layer). Percolation dams are check-dams designed to retain water and wet sediments from spates long enough for it to infiltrate and recharge groundwater. Between 1967 and 1970 in a drought-stricken part of Maharashtra State (India), USAID grain was used to pay labourers on a work-for-food basis to build forty percolation dams to recharge floodplain aquifers which could then be tapped by shallow wells in the dry season. The programme was a success. Wells dug before infiltration was improved ran dry in most dry seasons; after the percolation dams were built, wells continued to provide water even during droughts (Pacey et al. 1977). Although there is often abundant labour in rural regions which could theoretically be used on construction to improve water supplies, it may be very difficult to make use of it in practice
eBook - ePub- Alan C. Twort, Don D. Ratnayaka, Malcolm J. Brandt(Authors)
- 2000(Publication Date)
- Butterworth-Heinemann(Publisher)
CHAPTER 5 Dams, Reservoirs and River Intakes5.1 IntroductionReservoirs are provided to regulate supply and may be required to store rainfall in wet periods for use in dry periods. Such storage typically requires an impounding dam across a natural river valley. Service reservoirs provide a similar function but related to treated water (Chapter 18 ). A dam across a natural river valley is sometimes called an impounding dam, as it impounds a natural watercourse.The earliest dam Smith was able to report in his book. A history of dams (Smith, 1971 ) was the 37 feet high Sadd el-Kafara dam, built between 2950 and 2750 BC, the remains of which lie 20 miles south of Cairo. It had upstream and downstream walls of rubble masonry each 24 m thick at the base, with a 36 m wide, gravel-filled space between; it appeared to have had a short life because it suffered from the two principal defects that continued to plague many dams for the next 4500 years—it leaked and was probably overtopped. However, the nearby Ma'la dam, located in Giza, operated successfully for over 3000 years. The remains of the dam can still be seen today. The dam was constructed using a greater volume of material than that contained in the Great Pyramid at Giza; the irrigation water storage that it provided was one of the keys to Egypt's prosperity.There are many materials of which a dam can be made—earth, concrete, masonry or rockfill. The choice depends on the geology of the dam site and what construction materials are nearest to hand. Concrete and masonry dams require hard rock foundations; rockfill dams are normally built on rock, but have been built on alluvial deposits; earth dams can be built on rock and also on softer, weaker formations such as firm clays or shales.Masonry dams are still built in developing countries where labour costs are low. Where labour costs are high, masonry has generally been replaced by mass concrete compacted by using immersion vibrators or, in recent years, by roller compaction. It was not until the middle of the nineteenth century that concrete and masonry dams began to be designed according to mathematical analysis of the internal and external forces coming upon them; nor until the first quarter of the twentieth century was the behaviour of earth dams sufficiently understood for mathematical design procedures to be applied to them also. Recent advances in dam design are such that only the salient principles involved can be given here.
eBook - PDFFlooding and Management of Large Fluvial Lowlands
A Global Environmental Perspective
- Paul F. Hudson(Author)
- 2021(Publication Date)
- Cambridge University Press(Publisher)
4 Dams, Rivers, and the Environment . . . their effects far exceed any effects likely to occur from global climate change over a period of several centuries. —W. L. Graf (2003) As noted earlier, a variety of conditions will control the response on different rivers. —Williams and Wolman (1984, p. 14) 4.1 HYDRAULIC INFRASTRUCTURE AND SOCIETY 4.1.1 Context and Focus Many rivers are substantially degraded because of human reli- ance upon water resources to support intensive agriculture, industry, and settlement. This includes emplacement of “hard engineering” structures that modify landscapes and water supplies, such as dams, dikes (levees), groynes, river bank pro- tection, and irrigation networks, among other forms. Dams and reservoirs are a specific type of hydraulic infrastruc- ture constructed to meet a variety of societal demands and provide stable water supplies for irrigation, navigation, industry, flood control, enabling agricultural activities and human settlement to expand upon marginal lands (Williams and Wolman, 1984; Graf, 2006). Dams and reservoirs, however, have many unintended adverse consequences. These include altered hydrologic regimes and sediment trapping that impact downstream environments, and in some cases increase human vulnerability to global environmen- tal change. Additionally, constructing dams to reduce flood risk is a false justification. This is because flood control results in reduced downstream flow variability for the purpose of promoting floodplain development for settlement and agriculture within a predictable physical environment, which is the actual justification. This chapter singularly focuses on dams, the major form of hydraulic infrastructure in the upper and middle reaches of drainage basins, and which impact downstream fluvial lowlands and deltas. The chapter begins by examining the motivation for dam construction and establishes their near ubiquitous presence upon the global riparian landscape.
eBook - PDFPrinciples of Water Resources
History, Development, Management, and Policy
- Thomas V. Cech(Author)
- 2018(Publication Date)
- Wiley(Publisher)
DAM BASICS PURPOSES OF DAMS Dams have been used to regulate the flow of rivers for centuries. The ancient civilizations constructed dams made of earth, rocks, logs, and other simple materials to redirect rivers for flood control and irrigation. Dam projects of the 20th century were generally built for multiple purposes, including flood control, irrigation, recreation, navigation, and hydroelectric power generation. Dams and reservoirs have enhanced the health and economic prosperity of citizens around the world. However, dam construction comes with a price: altered natural and human environments. Reduced streamflows, degraded water quality, and impacts on migrating fish are among the serious problems caused by dams throughout the United States and the world for centuries. Why do we need to understand the basic principles of dams? Very few major rivers in the world do not have a dam crossing their course. Dams are a basic, fundamental water management tool used to control, regulate, and deliver water for a variety of purposes (see Table 7.1). Many people are fascinated by dams, whereas others abhor these monolithic structures. Regardless of one’s personal opinions, it is important to understand the basic features of dams when study- ing the topic of water. How are dam sites selected? In some locations, a flood-control dam is built upstream of a city or developed area in order to protect downstream property and human life from flood devastation. Dam designers (usually experts in civil engineering) determine the size of such a flood-control structure on the basis of a probable maximum flood (PMF) event, perhaps a Q500 flood, discussed in Chapter 3. Dams for irrigation projects are generally constructed at an elevation high enough to deliver irrigation water to cropland entirely by gravity. Dams for hydroelec- tric power generation are located at a site where the DAMS
eBook - ePubA Water Story
Learning from the Past, Planning for the Future
- Geoff Beeson(Author)
- 2020(Publication Date)
- CSIRO PUBLISHING(Publisher)
A dam is a barrier that holds back water to form a reservoir or lake, usually by obstructing the flow of a stream. (In general usage the term ‘dam’ is often taken to refer to the reservoir formed by the dam.) Dams are typically made of earth, rock or concrete. Their purpose can be for water storage, irrigation, the production of hydroelectricity or flood control. The reservoirs formed are also often significant sites of recreation – swimming, fishing, boating, water skiing and sailing. They therefore have great economic and social benefits. Most dams in Australia have been built to store water when it is plentiful for use at times when it is most needed. There are four main types of dam structure in Australia:• Embankment dams are made of rock, gravel and sand, with the finest materials placed in the centre to form a waterproof core. Embankment dams are heavy enough to resist the force of the water that builds up behind the wall.• Gravity dams are thick, massive structures that can hold back huge quantities of water by their own weight. They are made of stone masonry or concrete and may be tied to their foundations by steel cables within them.• Arch dams are concrete dams that are curved in plan with the convex side facing the reservoir (upstream side). The arch transfers the load of the water to the sides (abutments). Arch dams are suitable for use in narrow canyons with strong abutments capable of resisting the thrust produced by the arch.• Buttress dams are another form of concrete dam in which buttresses on the downstream side transfer the load to the base (foundation) of the dam.Dams are designed to incorporate a method of releasing water from the reservoir, and a means of letting excess water go. Outlet pipes are usually built through the bottom of the dam during construction. These allow water to be supplied from the reservoir for downstream use, and for the reservoir to be emptied if necessary. A spillway is a channel cut lower than the top of a dam and is made of concrete in a large dam. Spillways are designed to allow water to flow out of a full dam rather than flowing over the top of the dam and causing damage. Some dams have gates in the spillways which can be used to increase the amount of water stored as well as to control downstream flooding.4
eBook - PDF- L S Blake(Author)
- 1994(Publication Date)
- CRC Press(Publisher)
Dams Dams ADM Penman OSC. CEng. FICE Geotechnical Engineering Consultant Contents 18.1 Definition 18/3 18.1.1 Types of dam 18/3 18.2 Briefhistory 18/3 18.3 Embankment dams 18/4 18.3.1 Introdueti01l 18/4 18.3.2 Rockfi11 dan with \lpstIeam reiDfol'Cllld CODCI'de membrane 18/4 18.3.3 Rockfi11 dam with upstream upbaltic: membrane 1815 18.3.4 Rockfi1l dam with <:eDtral asphaltic core 18/5 18.3.5 Rock.fill dam with llCIltral clay core 18/11 18.3.6 Earthfill dam - homogeDCOUSIeCbOD 18/11 18.3.7 Earthfi1l dam WIth <:eDtraI clay core 18/13 18.4 Concrete dams 18/13 18.4.1 Introduction 18/13 18.4.2 Gravity dams 18/13 18.4.3 Ro1lcrete dams 18/14 18.4.4 Buttre8ll dams 18117 18.4.5 Arch dams 18/23 18.5 Design concepts 18/29 18 5.1 Embankment dams homopDeOus sec:ti01l 18/29 18.5.2 Embankment dams with central day coni 18/29 18.5.3 RoDer-compaclCld coucrete 18/33 18.6 LqisIatioD 18136 18.7 Further readinI Ia 36 R.dcreDca 18/36 Biblioarapby 11/37 18.1 Definition In the UK, the name 'dam' is given to a civil engineering structure built across a valley to form an artificial lake as a reservoir of water. There are numerous variants. Some reser- voirs are formed on relatively flat land by building long dams to encircle the required areas. Others are built to store materials other than water. In South Africa and some other countries the word 'dam' is used for the reservoir which is retained by a 'wall' or 'dam wall'. 18.1.1 Types of dam Dams are separated into two main types by the choice of material used for their construction: (1) embankment; and (2) concrete dams. (1) Embankment dams are made from nonorganic particulate material excavated from the Earth's surface local to the dam site and used more or less as excavated. They are subdivided into earthfill and rockfill dams, although many embankment dams contain both types of fill. Further subdivisions can be made, according to the material used, to make the water- proof element, e.g.
- Karrie Lynn Pennington, Thomas V. Cech(Authors)
- 2021(Publication Date)
- Cambridge University Press(Publisher)
Dams represent human power and ingenuity in changing the Earth to suit our needs. Dam construction and operations can also represent a lack of understanding and empathy for the environmental and human needs of the people, rivers, wildlife, wetlands, and floodplains most directly influenced by such projects. In addition, it can represent a willingness to ignore the consequences of our actions in favor of economic and personal gain. The challenge for you, who are student’ s today and the planners of tomorrow, is to recognize that development and environ- mental health do not have to be mutually exclusive. There are sustainable solutions that require cooperation and a willingness to change our mindsets. You can do this. In 1950, there were 5,700 large dams in the world (defined as being at least 15 meters (50 feet) in height or storing more than 2.8 million cubic meters (2,300 acre-feet, or 750 million gallons). Today, there are 60,000 [3]. Eighty percent of these large dams are located in just five countries – China, Spain, India, Japan, and the United States [4]. The US has approximately 6,000 large dams and 73,000 smaller dams but has slowed its construction pace significantly in the past two decades. China, on the other hand, had fewer than 100 large dams in 1949, but today has over 22,000 large and 80,000 smaller dams [5]. Among these is the world’ s largest dam, China’ s Three Gorges dam (see Figure 10.1). Brazil, India, Turkey, and Africa have all built dams with varying degrees of success in terms of energy production, human welfare, and environmental concerns. Dams can be vital to civilization. However, onstream dams – whether large or small – are an obstacle across the natural course of a river and disrupt its normal functions. Onstream dams not only capture the flow of a river, but also its contents. Nutrient-rich silt and sediments are restrained behind such a dam and accumulate at the bottom of the reservoir.
eBook - PDF- L S Blake(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
Dams A DM Penman φsc, CEng, RCE Geotechnical Engineering Consultant Contents 18.1 Definition 18/3 18,1.1 Types of dam 18/3 18.2 Brief history 18/3 ' 18.3 Embankment dams 18/4 18.3.1 Introduction 18/4 183.2 Rockfill dam with upstream reinforced concrete, membrane 18/4 183.3 Rockfill dam with upstream asphaltic membrane 18/5 18.3.4 Rockfill dam with central asphaltic core 18/5 183.5 Rockfill dam with central clay core 18/11 183.6 Earthfifl dam -homogeneous section 18/11 183.7 Earthfill dam with central clay core 18/13 18.4 Concrete dams 18/13 18.4.1 Introduction 18/13 18.4.2 Gravity dams 18/13 18.43* Rollcrete dams 18/14 18A4 Buttress dams 18/17 18.45 Arch dams 18/23 18.5 Design concepts 18/29 18.5.1 Embankment dams ~ homogeneous section 18/29 18.5.2 Embankment dams with central clay cores 18/29 18,53 Roller-compacced concrete 18/33 18.6 Legislation 18/36 18.7 . Further reading 18/36 References 18/36 Bibliography 18/37 This page intentionally left blank Brief history 18/3 18.1 Definition In the UK, the name 'dam' is given to a civil engineering structure built across a valley to form an artificial lake as a reservoir of water. There are numerous variants. Some reser-voirs are formed on relatively flat land by building long dams to encircle the required areas. Others are built to store materials other than water. In South Africa and some other countries the word 'dam' is used for the reservoir which is retained by a 'wall' or 'dam wall'. 18.1.1 Types of dam Dams are separated into two main types by the choice of material used for their construction: (1) embankment; and (2) concrete dams. (1) Embankment dams are made from nonorganic particulate material excavated from the Earth's surface local to the dam site and used more or less as excavated. They are subdivided into earthfill and rockfill dams, although many embankment dams contain both types of fill. Further subdivisions can be made, according to the material used, to make the water-proof element, e.g.
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