Downstream Impact
4.3 Nature of Losses in Hydroelectric Projects
4.3.1 Productivity of Land and Agricultural Yield
The operations of hydroelectric projects induce obvious changes in the daily and hourly flow accompanied by depth, duration and extent of flow downstream. At the same time, the sediment coming from upstream generally gets interrupted behind the dam and water released from the dam is sediment deficit water, in other terms it is starved water having tendency to erode the downstream channel as well as the floodplain. All these processes ultimately reduce the fertility of land and lead to reduction in crop yield. Some of the study conducted on sample villages related to downstream impact of dam operation by Adams (1985) shows that significant fall i.e. 82 percent to 53 percent was observed on downstream agriculture in a village, while in other village the fall was about 60 percent to 40 per cent where as dry season cultivation fell from 100 percent to 27 percent. The changes in downstream flow may lead to change in ground water table and most of the time it was observed that it goes on decreasing. In such situation, excess burden of capital investment
will increase on those farmers who depend on the ground water for the agriculture. Farmers dependent on the river flow get badly affected by the reduced flow condition.
4.3.2 Fishery
Due to operation of hydropower project there will be diurnal variations of flow which affect the downstream ecology up to several hundreds of kilometers. Fish production is main source of financial as well as nutritional aspects for many inhabitants downstream. Dam can affect fishery in many way like;
Natural flooding pattern: due to power scheduling huge discharge flowing the downstream during operational hours whereas meager amount of discharge flow downstream in non- operating hours. This significantly affects the fish production.
Degradation of river bed: Diurnal variation of flow will affect the physical stability of channel and induce degradation of channel downstream lead to loss of spawning ground for some kind of species.
Water Quality: Water released from turbine is comparatively cold that may be deoxygenate or may contain some harmful chemical, adversely affecting the fishes and other river biota.
4.3.3 Loss of Forest
During the construction of dam massive area of forest goes in submergence upstream, whereas construction of access road will reduce the forest cover and will increase the human interference.
The upstream population is forced to relocate; more land will be created and occupied downstream for the purpose of agriculture by the displaced. As a result deforestation will
increase downstream which lead to destruction of habitat for many forest species putting them at risk. Furthermore, the downstream populations who depend on the forest as a primary source of food, building materials, medicine etc., their food security and livelihoods become vulnerable.
4.3.4 Loss of Riparian Zone
The operation of hydro power dams bring high fluctuations of flow in a day as the reservoir is to be operated to meet the peaking power demand. Riparian zone is the transition zone between land and channel stream. The magnitude of floods can hold different consequences for riparian ecosystems, as high-magnitude floods may create new geomorphic features and affect the entire landscape while smaller magnitude floods will influence ecosystems characteristics such as plant community structure or may only have impacts at the plant species level (Hughes 1997). The intensity and rate of the discharge downstream may affect the plant cover in riparian zone. Frequent diurnal variations caused in any hydro power projects may pose a sudden draw down condition on the river bank on an average repeatedly.
Such situation may cause significant loss to herbaceous plants as those species are more likely to get damaged by the fluctuations of water levels as compared to woody trees. The processes of erosion and sedimentation will create temporary islands and sandbanks in the river bed and the growth of vegetation on such land forms will form a mosaic patches provide the habitats for colonization.
4.3.5 Reduction of Water for Domestic Use
Dams, particularly hydroelectric project, release large volume of water downstream for a few hours while turbine is in operation, whereas release becomes negligible during the non operating hours. Such a critical situation may cause the hydrological and hydraulic
imbalance leading to dry river bed in conjunction of decline in water table in the vicinity. The human settlement or township residing downstream having their dependence on river for day to day work will drastically suffer and may result in shortage of water to fulfill their daily domestic demand.
4.3.6 Poor Nutrition and Hygienic Conditions
It has been found from the socio economic study that large number of rural population exist downstream of LSHE project. The habitants of this area are mainly dependent on various agriculture practices, fish production and forest downstream of dam for their livelihood. These means of livelihood greatly depends on the availability of water in stream and aquifers. Dam induced flow regime may be insufficient to meet agriculture, fishery or domestic need of the downstream population. These results in deficit crop yield, decline in fish production and reduction in forest cover ultimately affecting the food security and livelihood of the downstream dwellers. As these aspects have direct connection with health and nutrition it influences the life of inhabitants. The change in flow scenario seriously affects the recharging process of the aquifers downstream. As a result the water table keeps on going down and continuous depletion of ground water may lead to a situation that it may become difficult for the people to extract ground water from the aquifers in an economically viable way. On the other hand reduction in flow downstream may always pose shortage of domestic water. All these leads to poor nutrition and hygienic condition.
4.3.7 Loss of Employment /Livelihood and Uncertainty of Income, Poverty and Debt
Dam operation will change downstream flow scenario which ultimately causes different losses enumerated in preceding sections. These situations will be more significant, imposing uncertain income and migration in search of new employment for the rural
downstream population whose livelihood is having direct or indirect connection with river.
Reduction in flow downstream leads to decrease in many job opportunities for those who work in the agricultural farms, associated with fishing activity or having dependence on forest. Continuous happening of such phenomenon may push those farmers and fishermen towards poverty and debt.
4.3.8 Increase in Mental Stress
The families who are facing above mentioned situation will always be passing
through mental stress. Women and children of those families will be most vulnerable because of migration and debt etc.