Effects of Mini Hydropower Plant and Their Solutions

Introduction:

Non renewable energy sources including fossil fuel, nuclear energy and coal have been used to generate electricity around the world. Depletion of non-renewable energy sources, environmental pollution associated with fossil fuel burning and disposal of nuclear waste, energy crisis and increasing demand are recognized as arising problems associated with the energy generation from non-renewable energy sources.

Recently mini hydropower plants are being promoted as renewable energy. Hydropower projects below 10 MW capacity are defined as mini hydropower projects. The hydropower generated within the mini hydropower plants can be used in two different way. Generated hydropower plant can be sold to national grid. The generated hydropower can be distributed to use within the local area.

Although hydropower is often marketed as green energy, there are still social and environmental impacts which usually varies with the size of the power plant. Impacts associated with mini hydropower plants are mostly restricted to local environment and public attention dose not drawn towards these impacts. Further, such impacts could vary with the locations.

 Impacts associated with mini hydropower plants     

Mini hydropower plants effects the environment at different stages.

Impact on air at project zone - Heavy vehicles used for excavation and material transporting such as tractors and loaders emits polluted air due to fuel combustion during the construction phase of MHP (Cara et al. 2010). Dust is also emitted through the unloading sand, cement and explosive material. Further, emissions from chemicals such as paints, fuel and lubricants available at the site affect negatively to the sensitive biodiversity around the project (Gvakharia 2010).

 Impact due to noise - Project noise can affect during both construction and operation phases. Concrete vibrators, diesel motors, trash rack cleaner, the trash conveyor, heavy vehicles and explosions generators disturbing noise at the construction phase while turbines, the gearbox, the turbine, the transformer, the hydroelectric unit and the speed increaser can generate continuous noise in the operation phase of hydropower plants (Cara et al 2010). Noise generated from construction effects temporary on forest fauna. It may scare birds, reptiles and other animals. Fauna near to the power plant are effected by the noise generated from turbines throughout the operation stage.

Impact to the riverine environment –Water storage or diverting flow in the upstream of a stream effects proceeding the downstream.

Trees damaging earth structure as well as vegetation in upper catchment area have to be removed to provide easy access construction of infrastructure for mini hydropower plant. Those deforestation activities negatively affect the sensitive aquatic structure of the area, destroy the food and habitats of animals, disturb the food chain and cause soil erosion, remove top soil, finally leads to slope instability in the impact area. Water sources dry up due to deforesting and affect the domestic water supplies of the area. Felling economic crops and trees with timber value affects the economy of the society of the particular area (Thoradeniya et al. 2007). The topography of the area is changed by the constructing concrete structure and felling trees. Those topographic changes can decrease the esthetic beauty and land value of the area. Such deteriorations in catchment increase the soil erosion potential of channel beds and banks and ultimately leads to landslide.

Explosive materials have to be used for explosion of rocky substrates during constructions phase of the mini hydropower plants. Those explosions effect health and safety of employees and neighbors.

It the hydropower generation is involved with the upstream areas of main rivers, it affects the water body all over the country. Water diversions for power generation causes either complete eliminating or significant reduction of downstream flow during dry season. It increases the risk of salt intrusion towards the fresh water rivers.

 This flow variation with time negatively effects the structure of aquatic ecosystem structure and fishing migration in between intake and outlet of the power plant. Allocation of water from stream for hydropower plant generation leads to water shortages for other water users including irrigation, agriculture and other traditional usage of the stream.

Chemicals used in construction and operation stages cause sudden leakage or spills and mix with stream. It reduces water quality and affects the whole biodiversity of the area.

 Construction activities of mini hydropower plants leads to heavy sedimentation at the reservoir base. It reduces the capacity of the catchment bed. Thereby it increases the potential of flood during heavy rains. Deposition of sediment on the breeding ground effects the reproduction of the aquatic animals.

Birds and other human activities are obstructed by transmission lines through sensitive ecosystem. It causes bird strikes and electrocutions. Further, health and safety issues like cancer and headache for human are also caused by high voltage transmission lines.

Storage of water in a same place for long time provide ideal breeding habitats for mosquitoes. Thereby it indirectly increases the transmission of vector borne disease to surrounding areas.

Water shortage of stream results in declined landscape values and tourism activities and cause disturbance to other leisure activities related to the stream.

The construction of dam across stream disturb the migrations of fish species for different needs including reproduction and searching of food. These movements are always essential to ensure the fish survival. One of best example is the migration of eel that, after growing in the river, moves into sea across the downstream in order to reproduce. It also separates the populations of aquatic organisms. Continuous rotation of turbine kill or injures the fishes which pass through it. Thereby mini hydropower reduce the population density of aquatic animals and decline the biodiversity of the aquatic body.

Mini hydropower plants are not totally emission free. Small run-of-the-river plants will typically emit between 0.01 and 0.03 pounds of CO2 per kWh.

Migratory measures:

The Environmental Impact Assessment (EIA) is the best methods to evaluate the socioeconomic and environmental impacts linked with mini hydropower throughout the to the project life cycle before the construction of them and suggests the most suitable mitigation measures. Cost benefit analysis can be carried out to select the best place for construction of mini hydropower including the environmental impacts as cost.

Careful design and rational operation can mitigate these effects effectively and enhance the integration of the plant within the natural environment in which it is built as following.

A minimum flow must be released for hydro power generation in order to maintain adequate environmental flow to preserve the hydrological continuity of the river and the conserve the natural habitat and ecological life.

The impacts of noise can be unacceptable when the mini hydropower plant is located near to houses or in a sensitive natural area. Small tolerances in gear manufacturing, application of sound insulating blankets over the turbine casing, use of water cooling instead of air cooling of the generator and acoustic insulation of the building can be taken to minimize the noise around the mini hydropower plants.

 Hydraulic wheels with a fixed barrage inside of them can be installed rather than conventional turbine.  The rotation velocity of the vanes is 10 times slower than the conventional ones. So Fish can go through the turbines without any damage.

The construction of fish ladder, dissipate the energy providing a low-velocity flow through which the fish can easily ascend.

The mini hydro power plants can be constructed with minimum damage to the catchment vegetation. Trees can be grown around the catchment of existing plants to enhance the esthetic value of the environment, preserve the biodiversity and trap the water during heavy rainfall.

Timber and stone wall or brush mattress can be applied to protect the stream bank from the erosion.

The power house can be constructed by using natural features including use of local stones, ground, and vegetation for the building and, non-contrasting colors and textures for painting to reduce contrast with the background to minimize visual impact.

Small-scale weirs can be built to trap the sands and the particles and later it can be manually removed. The accumulation of sediment can be reduced through the mechanically removing the sediments by periodic dredging (Bergkamp et al., 2000). Sediments can be removed through periodic flushing of the reservoir by releasing large volumes of water through outlets in the dam. In the case of run of rivers, flow diversion is helped to reduce the sedimentation.

The renewable energy label can be given for both of new and existing hydropower plants. Highest standard can be only achieved by following the strict environmental conditions including improving environmental flows, sediment flushing, fish ladders and protective measures for wetland. In addition to those protective measures, operators have to allocate a part of their income for environmental improvement measures, including habitat restoration and rehabilitation. Consumers can choose to purchase ‘green’ electricity at a higher price.