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24-25 May 2017
 
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More on dams and dam lakes

Dams are hydraulic structures used for creating and maintaining backwater effect and water pressure. Generally, they are built in the beds of bonds and rivers.

Water retaining dams are built for creation of dam lakes. Pressure water dams are built for raising and controlling of water level in the river. Generally, one dam serves for both tasks being water retaining and pressure water structure at the same time.

Water reservoirs created by water retaining dams are used for accumulation of water resources for various applications and industries. Industrial facilities, housing and utilities, agricultural melioration systems extract water from the water reservoirs. For navigation of water transport, the waterway network created in such a manner is used. Fish-farm industry extensively uses artificial water bodies.

Depending on method of water passage through the dam site, the dams can be spillway and non-overflow ones. In the first case, water in rather extended front passes through the body of the dam. In the second case, spillway structures are located aside from the dam or, if they are relatively small, in the body of the dam.

By water head height, the dams can be:

  • low-head dams with the head less than 25 m,
  • middle-head dams with the head 25-75 m,
  • high-head dams with the head over 75 m.

The structure of the dam depends on the method reallocation of water loads. Gravity dams neutralize water pressure energy by foundation soil viscous forces of construction materials or structural units. In the foundation of the gravity dam, there lies gravel and sludge dump or concrete element. Arched dams redistribute water energy to the bed banks. Its foundation is represented by a reinforced concrete element.

Features of Dam Design

Water management design defining necessary volumes and ceiling levels of the reservoir is the source information for the dam design. The next step is selection of dam construction depending on topographic and geotechnical conditions at the dam foundations and river banks or on their geotechnical conditions only. Also, hydrological and climatic conditions of the development area, availability of construction materials, seismic activity, general organizational chart for construction and performance of works, characteristics of the passage of diversion water flows, timing of introduction into service, and dam operation conditions should not be overlooked.

Type and construction of the dam should be selected basing on engineering and economical comparison of options considering building and construction work technology and general layout of the hydro system. Only options with equal level of elaboration and reliability can be compared.

As a result of the examination, optimal characteristics and dimensions of the dam and its structural components will be specified.

Features of Dam Construction

The dam construction process differs in need for multiple comprehensive works in complex natural conditions. Water surface variability, flood periods, ice drifts and other factors require the complex of preparatory actions based on the elaborated project. When constructing dams in the bed, it is necessary to dam out the water flow and dewater for the construction period.

Dirt dams are built as follows:

  • By dumping with the further earth compaction, planning and decking of the dam top and slopes;
  • By hydraulicking according to the hydraulic fill method;
  • By land fill into the water without mechanical seal;
  • By massive directed hade fault blasts.

Dirt dams are built in accordance with the following manufacturing sequence:
  • Soil surface preparation in the development area, earthworks in the foundation pit for cutoff and apron, soil filling and compaction;
  • Dam body formation by means of layer-by-layer land fill, leveling, watering, and compaction;
  • Slope and crest leveling and lining.
  • Concrete dams are built in accordance with the following manufacturing sequence:
  • Soil surface preparation in the development area, earthworks in the foundation pit for cutoff and apron, soil filling and compaction (for foundation soils);
  • Excavation of pit (for foundation soils);
  • Installation of reinforcement, civil, and assembly works.

Dam Lakes

The main specification figures of artificial dam lakes are characteristic water levels and volumes. Generally, three water levels can be specified: the dead storage (DSL), normal headwater (NHL), and highest water level (HWL); HWL differs from NHL by the height of headwater level overload. These levels allow allocation of three pools of the dam lake. The first is the dead storage capacity, the second is useful capacity, and the third is the flood-control storage.

The dead storage capacity is a spare capacity for gradual filling with alluviation appearing in the course of reservoir sedimentation, and for other needs (fish hibernation, provision of regular sanitary conditions, fire fighting, etc.).

The useful capacity is designated for various household purposes (irrigation output, flow augmentation and downstream water level raising in low-flow period, flood accumulation for flood control, etc.). The necessary useful capacity and top of conservation storage are defined in the course of water-management design.

The highest water level is the level at which the maximum design water flow passes fully opened dam spillways and available coast spillways. The value of HWL is defined in the course of technical-economic calculation considering the losses from temporary head-water land flood over a period when the water level surpasses NHL, and the cost of any construction of dam spillovers ensuring passage of the maximum design water flow.

Actual Situation

Construction of dams and creation of artificial reservoirs entails area flowage, alteration of hydrogeological conditions of adjacent areas, deterioration of the sanitary state of the water reservoir, and variation of flora and fauna. However, this is an integral part of modern economical, social, home- and foreign-policy life of the society.

The fresh approach primarily based on elimination of negative influence and conservation of environment is to be elaborated with keeping in mind the economical aspects.

 
 
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