INTRODUCTION

Integrated planning and management based on a comprehensive ecosystem assessment is necessary for environmentally sound, sustainable management of natural resources.  In the development of the power sector in a country, the role of hydropower generation stands well recognised. However, in the interest of sustainable development, it is necessary that environmental concerns are identified and duly addressed as early as possible in the project. Planned development with an integrated approach is necessary to raise the living standards of the people, revive economy and alleviate poverty. Poorly planned projects can result in disastrous impacts on basic life-support systems such as clean air and water, productive soil and rich biotic diversity. Development of water resource projects such as dams and reservoirs, canalisation and dredging activities, irrigation schemes and others such as the creation of new lands via filling operations can represent large scale engineering works which can cause significant impact on physico-chemical, biological, cultural, sustainable development and socio-economic components of the environment. Development of river valley projects involves change in land use pattern and corresponding hydrological regimes. These developmental projects often result in unanticipated and undesirable consequences, which may be drastic so as to reduce or even nullify the socio-economic benefits for which the projects were planned.

Large dams in India and elsewhere have been accompanied by significant alterations in the upstream and downstream physical and biological environment. In India, there is no comprehensive audit of these impacts, but some available facts and figures indicate the magnitude and severity of such developments. They are:

• The creation of reservoirs in more than 1,500 major river valley projects has flooded over 500,000 ha. (5,000 sq. km.) of forest land;
• Water logging and/or salinisation perhaps affect half of the canal irrigated land in the country, with varying degrees of severity;
• Malaria has seen a resurgence in the last decade or so, especially in the command areas of irrigation projects and around reservoirs;
• Several species of wild animals and plants (such as the River dolphin Platanista gangetica and the fish Hilsa ilisha) have been threatened by dams and their associated impacts;
• Salt-water ingress in the coastal areas of states with a major dam-building history (in the states of Kerala and Karnataka) is severely affecting drinking water and agricultural lands for several kilometres inland.

The associated environmental problems of water related projects are erosion, flooding, sedimentation, landslide, torrents, roadside erosion and shifting cultivation areas. In order to minimise these impacts, there is a need to adopt comprehensive, integrated watershed approach in the development of hydro-projects for electricity generation and irrigation. Water and soil ecosystems play a vital role in sustaining all life forms performing useful functions in the maintenance of the overall balance of nature.

1.    Characterisation of Water, Soil and Sediments

Water, soil and sediment have their own significance in regulating the biotic system of the universe. Slight alterations in the quality of these will adversely affect the ecosystem. Dam construction uses a large area of land and the mass gathering of labour causes water and soil quality deterioration, and clearing of forest for shelter causes soil erosion, which further results in sedimentation in the river or near-by waterbodies.

Water is essential for life and plays a vital role in the proper functioning of the earth's ecosystem. The pollution of water has serious impact on living creatures and can negatively affect the use of water for drinking, household need, recreation, fishing, transportation and commerce. Many factors affect the chemical, physical and biological characteristics of a waterbody. They may be either natural like geology/ weather or anthropogenic, which contribute to the point and non-point source of pollution. Developmental projects like construction of dams may change the quality of water as it involves blocking the natural flow. It impacts aquatic organisms and changes the nature of the stream itself. As water slows down and backs up behind a dam, various changes in its physico-chemical and biological characteristics take place. Water quality monitoring involves recording data about these various characteristics and usually involves analysing and interpreting these data. Monitoring helps to ensure that a particular waterbody is suitable for its determined use.  

Soils are considered natural bodies, covering part of the earth surface that support plant growth and that have properties due to the integrated effect of climate and organisms acting upon the parent materials conditioned by relief over a period of time. This definition of soil shows the dependency of soil on several environmental factors. Hence, soil could be characterised by the formula

                     S = f (cl, o, p, r, t)

where,  s = soil, f = function of, cl = climate, o = organisms, p = parent materials, r=relief and t = time. Any change in these variables will result in change in soil quality.  Nevertheless, the developmental activities in the catchment would certainly change variables and ultimately the fate of soil.

Rivers in the world carry as much as three billion tonnes of material in solution and ten billion tonnes of sediment every year. The characterisation of sediments reflects the quality of the catchment area, through which the rivers flow. Sedimentation of a river, lake or reservoir is associated with its flow and also disturbs the water quality and aquatic ecosystem. Runoff from different sources result in different qualities of sediment and ultimately various changes take place. The sediment content may also vary from month to month depending on the season, while it may be negligible during the winter and summer months, it is greatest during the monsoon months.

Higher sediment delivery ratio (ratio between the amount of sediment yield and the gross erosion in watershed) is associated with smaller catchments. As one moves upstream, the drainage basin area decreases and the topographic factors that promote sediment delivery becomes more intensified resulting in higher sediment - delivery ratio. The actual rate of silting of a reservoir depends on many other factors, in addition to the rate of sediment production in the catchment area. They are, trap efficiency of the reservoir, ratio of reservoir capacity to total runoff, gradation of silt, method of reservoir operation, etc. The trap efficiency of a reservoir is defined as the ratio of sediment retained in the reservoir and sediment brought by the stream. Damming the water also deposits the sediments that they carry. This causes sediment build up behind the dam, often changing the composition of the river.

The following factors affect sedimentation -

1. Extent of catchment area and the friable nature of the different zones.
2. Amount of sediment load in the rivers.
3. Type of rainfall and snowfall in each zone.
4. Mean monthly and annual run-off from catchment or sub-catchment.
5. Slope of each zone of catchment.
6. Vegetation in each zone of catchment.
7. Geological formation of each zone, estimated relative weathering and erosion with due regard to climatic conditions.
8. Presence of upstream reservoirs and extent of trapping of sediment therein.
9. Amount of sediment flushed out through sluices.
10. Degree of consolidation of accumulated sediment depending upon the extent of exposure to air, sun and wind.
11. Operation schedule of reservoir.

2.    Complexities of Environmental Impacts of River Valley Projects

Assessment of environmental impacts of river valley projects must be taken up with the following considerations:

1. It is important to identify the positive impacts of a developmental project as well as the negative ones and the constraints they may impose.
2. Most of the environmental factors involved in dam construction are interrelated; people displaced from the inundated area of the reservoir, or whose movement is facilitated by the reservoir and dam construction activities may move upstream in the watershed. Use of forests for agricultural activities by them may create additional erosion, leading to increased sedimentation in the reservoirs, thereby reducing storage capacity. Sediment, in turn affect the water quality and may reduce the capacity for power generation. In general, the dam affects downstream river flow, water quality, associated cultivation, and fisheries. The dam can also affect conditions elsewhere in the river basin through changes in subsurface water levels, resettlement of displaced people and landuse pattern.
3. A dam may affect the development of a region and may lead to newer settlements and industrial activity. This impairs the functioning of the ecosystem due to anthropogenic pressure on forest and aquatic ecosystems for land. This facilitates the need to measure cumulative impacts of the projects.
4. It is very essential to quantify all the significant impacts of water resource projects through Environmental Impact Assessment (EIA) at different phases of the project.

Thus it is necessary to monitor the impacts of the projects, in order to restore / rehabilitate the ecosystem.

Environmental Assessment is a process used to identify the impacts of a project or activity on the environment. The negative and positive consequences of development projects are assessed to provide decision-makers with a holistic and informed opinion based on sound and objective research and analysis.
Thus Environmental assessments -

• are necessary to guide development, both at the strategic level and at the project level;
• can serve as early warning systems;
• help to identify alternative approaches;
• identify cross-sectoral impacts and enable managers to view project proposals in a local, regional and global perspective; and
• involve dialogue and interaction between various ministries, NGOs, local authorities, municipalities and the private sector.

Cumulative impacts are the additive environmental impacts of a persistent causal agent over time. The term Cumulative Impact Assessment refers to accumulation of human induced changes in valued environmental components including human beings, fauna and flora; soil, water, air, climate and the landscape; the interaction of these factors; and on material assets, and the cultural heritage across space and over time. It reveals the identification, description and assessment of the direct and indirect long-term combined effects of a project.
Cumulative Impacts of river valley projects can be classified into two classes:

1. Cumulative Impacts on environment due to water storage and
2. Cumulative Impacts on ecosystem within and across the reservoir catchment.

Reservoir function is also affected due to these additive impacts, which in turn decreases its actual life. The main impacts are eutrophication, siltation or sedimentation, toxic chemical accumulation, acidification and extinction of natural biota. These are the key effects that start in very acute level and reach to maximum, responsible for quality degradation, reduced recreation and aesthetic values, degraded biodiversity, changes in culture, etc.

On the other hand, the cumulative impacts on surrounding ecosystem include extinction of endemic flora and fauna, succession by alien species, water related diseases affecting both humans and animals, instability of agricultural production, water logging and salinity, etc. The main diseases related to water are malaria, diarrhoea, filariasis, trachoma, bilharzia, etc. As some of these are additive, it can result in severe damage to the ecosystem and the environment.              

This section discusses the water, soil and sediment quality characteristics in the Sharavathi River Basin, by analysing qualitative impacts on water, sediment and soil.

3.    River Systems and Water Resources of Karnataka

The state has very good water resources in its numerous rivers, lakes and streams and to a certain extent groundwater. Seven river basins drain the whole state (The names and the areas drained are given in Table 1).

Table 1. River basins of Karnataka State

The total catchment area of these rivers is 1,91,773 sq. km. and the estimated average flow is 97,800 million m³ (M cum). The Krishna and Cauvery river basins drain about 77% of geographical area of the state. Sharavathi, Netravathi, Varahi, Bedti (Gangavathi) and Aghanashini are the more important rivers, all of which have considerable hydroelectric potential. They arise in the west of the Ghats and flow into the Arabian Sea. The area of forests and hills has a rugged topography, characterised by deep ravines and steep hills rising to heights of 1,250 to 1,890 m, which are the source of all the east and west-flowing rivers of the state.