The Natural Flow Regime Of A River Is Dependent On Various Factors Including

The natural flow regime of a river is dependent on various factors including rainfall, temperature and evaporation when considered in a broader geographic scale or macro-scale and is also influenced by the physical characteristics of a catchment at the catchment level or micro-scale (Resh et al, 1988). As mentioned earlier, river flow regimes are also affected directly and indirectly by human activities. Such human interventions disrupting natural flow of a river through construction and operation of reservoirs and dams have the potential of triggering a series of undesirable consequences like extensive ecological degradation, loss of biological diversity, water quality deterioration, groundwater depletion, and also more frequent and intense flooding (Poff et al, 1997). Reservoir are built to store water to compensate for fluctuations in river flow, thereby providing a measure of human control of water resources, or to raise the level of water upstream to either increase hydraulic head or enable diversion of water into a canal. The creation of storage and head allows reservoirs to generate electricity, to supply water for agriculture, industries, and municipalities, to mitigate flooding and to assist river navigation (Resh et al. 1988).
The biological effects of hydrologic alterations are often difficult to disentangle from those of other environmental perturbations in heavily developed catchments as identified by Rosenberg et al. (Environmental Reviews 5: 2754, 1997). The impacts of large-scale hydrological alteration include habitat fragmentation within rivers (Dynesius and Nilsson 1994), downstream habitat changes, such as loss of floodplains, riparian zones,and adjacent wetlands and deterioration and loss of river deltas and ocean estuaries (Rosenberg et al. 1997)36, deterioration of irrigated terrestrial environments and associated surface waters (McCully 1996). Hydrological alterations also bring in other indirect or secondary impacts on the genetic, ecosystem and global levels. They can cause genetic isolation through habitat fragmentation (Pringle 1997), changes in processes such as nutrient cycling and primary productivity (Pringle 1997, Rosenberg et al. 1997), etc.
With the realization of the importance of natural flow regime and the possible dangers posed by human alterations, there emerged a relatively new and promising water and ecology management paradigm. Many researchers started seeing this as a very comprehensive and sound management option and on many occasions stressed regarding the urgency of protecting or restoring "natural" hydrologic regimes (Sparks 1992; National Research Council, Doppelt et al. 1993; and Dynesius & Nilsson 1994).