Action Area Number Five: River Flow health
River flow health or environmental flow health is the flow of river water that is essential for sustaining a healthy riverine ecosystem.The variation in the water flows is termed a flow regime and it may severely affect the water quality.The discharge of water in a channel is the volume of flow passing through a channel at a given time.
Optimum River Flow
Changesin the regular flow of stream water can cause biological, chemical, and physical differences in the environment. Nutrient cycling, oxygen and carbon cycling, sediment transport, water purification, waste assimilation, etc. are the numbers of biological processes that contribute only when the river has a healthy flowing environment. Mobilization of various elements by the low-flow water can lead to change in the chemistry by acidifying and lowering oxygen content which can lead to eutrophication in the area. The high flow of water and turbidity can cause biological depletion by threatening the reproduction capacity of river biota in the instream areas. The floodplains, catchment areas, river channels, vegetation cover, and the other physical features of the river ecosystem have a great influence on the water flow. The flow regime of the river causes a great change in the normal structure of the riverine physical environment and can adversely affect the environment.
In a natural river channel, the discharge of water can be changed by both spatial and temporal variations. The frequency, duration, and size of hydrological events (flood and drought), range of precipitation, seasonal discharge, etc. are the climatic conditions that lead to flow regimes. Other than the climatic characteristics, the change in the physical features of drainage basins by the regulation in the flow of river water by the construction of dams, weirs, land use, trapping, and utilization of large amounts of water has led to stress in the river ecosystem and evenly cause degradation of the environment.
Groundwater
Groundwater contributes a considerable amount of water flowing into the river and such gaining of water by the river from the groundwateris called base flow. The major contribution of water in the stream by the precipitation runoff and glacier melts, along with, the groundwater having a vital role in the hydrological setting of the river. In all climatic conditions, a sufficient amount of water will come from the seepage of groundwater into the streambed, in summer stabiles the environmental flow toa certain extent. The longitudinal connectivity of stream and groundwatertakes place in three main ways. Some are gaining streams that gain water from the inflow of groundwater, some are losing streamsthat lose water by the outflow and some are gaining and losing streamsthat gain and lose water in some reaches.
Pumping of water can disturb the level of the water table, it has a great influence on the water level below ground. The groundwater may naturally vary according to seasonal change, climatic conditions, and other hydrological events, the utilization of groundwater beyond the replenishing capacity of an aquifer causes a lower water table and leads to depression in the area especially the area near exploitation. Thus, the over-exploitation of groundwater alters the exchange between the surface and groundwater, and it rigorously affects the flow health of the stream.