Remedies for maintaining water management system (dam)
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Dams and reservoirs
Dams and reservoirs
Sustainable management of a river as a resource requires that water is delivered at the time of need for human use and that the supply is reliable. At the same time, water should be available for the survival of the riverine ecosystems. Dams are constructed across valleys or rivers to store, regulate and divert water for various purposes such as agricultural production, hydropower generation, human and industrial use and flood peak attenuation. Most dams serve multiple purposes. Large areas along the river stream are submerged by the reservoir created behind the dam. Instream regulating devices, such as weirs and locks, result in areas of permanent inundation within the main channel, thereby negating the normal ecological functions associated with flood events.
Flood control dams store all or a portion of the flood waters in the reservoir, particularly during peak floods, and then release the water slowly. Typically, the principal use of such dams is to store a portion of the flood volume, in order to delay and attenuate flood peaks downstream. Space within a reservoir is generally reserved to store impending floods. Based on hydrological forecasts, the reservoir is regulated in a way to minimize the chances of coincident peaks from floods in different tributaries synchronizing in the main stem of the river downstream. Small to medium floods generated from the catchment are fully captured by the reservoirs. However, extreme flood events are only attenuated partially and their transformation downstream is delayed. The extent of attenuation depends on the available storage capacity vis-à-vis the magnitude of the flood event. The main performance parameter in assessing the flood control benefits of a reservoir is, therefore, the extent of the flood peak reduction during extreme events.
Many dams have multiple purposes and flood management may be required only for a few days or weeks in any particular year. Potential conflicts between flood management objectives (where storage space in the reservoir is required) and hydropower and irrigation (where it is desirable to keep the storage capacity as filled as possible) make it difficult to operate a multiple purpose reservoir. While allocating water for various uses, the need to maintain environmental flows should also be addressed. This should not only be guided by the percentage of the total flows released, but also by the need for variability of outflows in the downstream of a storage reservoir to be mimicked in order to maintain near-pristine conditions. (WMO 2006a, Dyson et al.