Contents preface (VII) introduction 1—37

14.4. ENVIRONMENTAL EFFECTS
A well-planned water resource project should be desirable from economic, social as well as environmental considerations. It should, however, be noted that some of the project components, notably dams and reservoirs, cause adverse environmental effects in the regions of their direct influence. While trying to achieve major project objectives of a water resource project, the planner must examine alternative plans of dams and reservoirs to minimise adverse environmental effects.
Environment is best defined as all external conditions which affect the existence of all living beings. Different living beings affect one another, and the environmental requirements of different living beings are interrelated.
Besides, it is generally not possible to evaluate environmental effects in economic terms. In case of pollution of water and air, however, it is possible to estimate economic loss to some degree. In addition, it is difficult to assign a degree of importance to various environment conditions likely to be judged differently by different persons depending upon their own viewpoint. For example, the people of a hilly region will have a different viewpoint regarding the siting of a dam from those living in the plains where land is inundated during floods and wells go dry during drought.
The environmental effects which directly affect the livelihood and well-being of people are of prime concern. Other environmental effects on various other living beings are also of concern to man but only to the extent to which the existence of the living beings is important to man’s living conditions. The beneficial environmental effects include land use improvements by irrigation, flood protection, improved water supplies for domestic and municipal uses, power supplies without consumption of fuel, water quality improvement, fishery improvement, recreational improvement, and health improvement. Various adverse environmental effects may be caused due to construction and operation of dams and reservoirs. Some of these can be mitigated by taking suitable steps while others are unavoidable. These have been tabulated in Table 14.1. The environmental check-list (Table 1.14) provides a comprehensive guide to the areas of environmental concern which should be considered in the planning, design, operation, and management of water resource projects.