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Small Dams Planning, Construction, and Maintenance by Barry Lewis | PDF Free Download.
Farmers are well aware of the need to boost productivity. In the face of greater competition for domestic and overseas markets, the farmer who wants to succeed has to take a business person’s approach to increase efficiency, reducing costs, and improving output.
In this environment, water becomes an economic factor, and its provision a matter for careful deliberation.
This book is designed as a guide for small dam owners, engineering students, Government agencies, developers, and earthmoving contractors who are responsible for designing, building, and using the majority of water storage constructed.
It is also designed for engineers who have not specialized in small earth dam design for agricultural hydrology, but who may be called upon, from time to time, to design small water storage schemes.
It is not intended to replace standard procedures currently used by those specialized engineers who are engaged in farm water design, although many of the design methods described herein are based on their procedures.
It does, however, attempt to provide such engineers with a comprehensive array of design data and a concise reference to basic design techniques that are not otherwise readily available. To cover all aspects of water conservation and use in detail is not possible in a book of this size.
However, it will give the landowner an insight into those aspects of planning which must precede the establishment of a feasible and economic water supply project.
The information for this book has come from a number of sources. One is a series of small dam pamphlets (which I wrote for the Rural Water Authorities in Australia over a number of years), another is data from papers that I have read and presented at conferences around the world.
People have always gathered water during wet seasons so as to have enough for themselves, their animals, and their crops in dry spells. The earliest known dams were in China in the sixth century BC. The ruins of ancient dams also exist in the Tigris and the Nile River Valleys.
Some Roman dams built in Italy, Spain, and North Africa are still being used today. Today, dams are built to allow the storage of water to give a controlled supply for domestic or industrial consumption, for irrigation, to generate hydro-electric power, or to prevent flooding.
Large dams are built of earth, rock, concrete, or a combination of these materials (for example, earth and rockfill).
They are built as gravity dams, where the stability is due entirely to the great weight of material; arch dams, where abutments at either side support the structure; or, arch-gravity dams, which are a combination of the two.
Those who plan, design, construct, maintain, use, and administer significant infrastructure developments that have a real potential to harm people and property if something goes wrong, are potentially subject to significant legal liabilities.
These liabilities need to be taken into account when decisions are made in relation to such developments.
It is well known that Australia is a dry continent characterized by variable rainfall. It is less well known that, in response to widespread harvesting of water on the small and large scale, Australia has the highest water storage per capita in the world (Lewis and Perera, 1997; Lewis, 2001b).
Small dam development has occurred in response to agricultural expansion, and to the need for a reliable source of water for stock, domestic and irrigation use, particularly during periods of drought.
However, there is a growing belief in the community that small dams are impacting on water resources in many major catchments by reducing stream flow and flow duration.
Potential and actual impacts of such reductions on the conflicting needs of the environment, agriculture, and industry are cause for concern.
These concerns are set against a background of changes including increased areas of intensive land uses such as viticulture and horticulture, and the development of farmland into rural residential subdivisions in commuter belts surrounding major cities and rural centers.
These changes are associated with increased small dam development. In a significant proportion of cases, particularly where intensive land-use changes have occurred, small dams are constructed that exceed the available water resource.
Where this occurs, downstream impacts on streamflow will be the cause of conflict between users (including the environment).
In addition, landowners may experience financial losses by constructing dams of a size inappropriate for the catchment. In most countries around the world and in the Australian States, provisions of the relevant Water Act(s) require that environmental consideration be taken into account in relation to new and renewed licenses.
These requirements apply to both regulated and unregulated waterway systems. Since unregulated waterways may not have large storage capacities from which environmental releases can be made, flow needs to be specified as a proportion of daily streamflow, or as a minimum daily flow.
Many factors such as in-stream habitat requirements need to be considered when allocating an entitlement to environmental flows. In the case of regulated waterways, environmental flows can be released as part of the normal operating procedure.
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