 |
| ||||||||||||||||||||||||||||||||||||
The anticipated ecological impact of a proposed irrigation project is now a primary factor in the evaluation by international development agencies. In World Bank practice, an Environmental Assessment report is in fact a prerequisite to further examination of a project. A number of ecological issues which should receive attention are discussed in the following notes, including riparian factors, which have determined the fate of a number of prospective projects. Relevant Operational Directives and Guidelines issued by international agencies should be referred to for further detail.
An important issue is the effect of a proposed development on existing groundwater use in the area, particularly on the watertable regime and the operation of existing small wells and dugwells, including those providing village water supply. Provision of alternative supply may become necessary. The substitution of good quality water from deeper project wells in place of contaminated water from shallow open village wells can be a positive factor. Quality of groundwater and its long-term effects on soils in the irrigated area can be an important ecological consideration, particularly where water quality is marginal.
The introduction of canal irrigation usually leads to a change to two-seasonal or three-seasonal irrigated cropping, which can have an important effect on the incidence of water-related diseases in the project area. Exclusion of irrigation from the immediate vicinity of villages may be necessary.
As discussed earlier, canal irrigation can cause a rise in watertable and increased surface runoff, both of which can cause a deterioration in drainage conditions unless adequate drainage measures are designed into the project. Some of the historic ecological disasters resulting from irrigation have been due to the rise in watertable bringing saline groundwater near the surface. Soil salinization over extensive areas has resulted and large scale tube drainage installation has subsequently been necessary to remedy this situation. Where there is risk of such occurrence in a new irrigation area, the subject should be addressed and control measures specified.
Ecological problems arising from reservoir construction have been much in the public eye in recent years. The prospective reservoir basin is frequently an inhabited, cultivated, area. The increased agricultural production resulting from irrigation of downstream areas, using the stored water, will usually exceed the existing current production within the basin by a factor of several times. However, the benefit to the downstream cultivators comes at the cost of those within the reservoir basin, who are displaced by the project. Token cash compensation to the reservoir "oustees" is no longer considered an acceptable solution. They must be re-located elsewhere, in an area offering means of livelihood.
However, in a country in which all available land is already occupied, or under forests, finding a suitable area for re-location can be difficult. Relocation into the downstream irrigation area can be a partial solution where there are a sufficient number of large holdings which can be subdivided under land reform provisions. It is not, however, a generally applicable solution. Furthermore "oustees" may resist being relocated to an area distant from their original home. Establishing new settlement areas by clearing of forest lands, preferably near to the reservoir area, is a possible solution technically, but may run counter to national policies regarding preservation of forests. One trade-off can be afforestation of an equal area of marginal lands elsewhere, at project cost. However, resettlement of reservoir oustees remains a problems. Preservation of endangered species of wild-life and flora within the reservoir basin may also be a factor.
Where a reservoir is, in fact, included in the project plan, and where the reservoir basin includes areas under forest, the question of clearing of vegetation before initial filling must be considered. Trees left standing, and submerged, can inhibit the use of the reservoir for fish culture, particularly the use of nets, apart from being most unsightly. The decomposition of smaller vegetation under submerged conditions can, in some situations, generate highly toxic outflow unusable for irrigation for a period of several years.
Where irrigation headworks including dams, intakes, and the upper reaches of the supply canal are in hilly terrain, erosion resulting from canal and road construction on steep unstable slopes can also be a major ecological factor in project evaluation.
Any new consumptive diversion from a river reduces downstream flows and may adversely affect existing or prospective downstream users. Conversely a proposed project may be adversely affected by future upstream diversions or storage. Such circumstances may be the cause of serious disputes. They may occur between neighboring projects within the same state, or between states, or across international boundaries. There is no universally-accepted legal framework for settling such disputes, particularly at the international level. Development agencies consequently endeavor to avoid becoming involved in such problems by requiring, in principle, that riparian issues be addressed, and agreement between the riparian parties be reached, before a project is accepted for appraisal. However, there may be little incentive for the riparian parties, other than the one desiring the new development, to reach such an agreement. A downstream riparian can almost always find some disadvantage, and withhold consent on that account. Thus, the prospective financing agency, while seeking to avoid involvement, may nevertheless have to inject some judgement as to the relative merits of a case, to avoid needed development being held up indefinitely on insignificant grounds. In exercising that judgement, the agency can provide a forum for airing the positions of the parties concerned and for technical fact-finding.
Not only consumptive diversions but also flood protection works can be the subject of riparian dispute. For instance, embankment construction to prevent a river from flooding across adjacent agricultural lands reduces the flood storage in that reach of the river and correspondingly increases the downstream flood-flow. Where the river crosses an international boundary between the upper and lower areas, a riparian dispute may result, requiring evaluation of respective upstream and downstream effects.
An international financing agency can have an important role in riparian disputes concerning major international rivers by funding the works required to provide a mutually acceptable solution. Division of the waters of the Indus River following partition of India, involving extensive works funded by the World Bank, is a notable example. However, decades of negotiation and the prospect of major Bank financing have failed to result in a solution elsewhere.
Turning to very much smaller works, riparian issues may be encountered in the improvement of village-constructed diversions from a small stream. There are frequently a number of diversions down the length of the stream, each having its own primitive brush-wood weir. The weirs frequently fail, passing on the flow to downstream diversions. An informal system of priorities of water rights has been established by tradition, based largely on the nature of the weirs. Any effort to improve the most upstream weir to provide more security to the diversions at that point reduces diversions at downstream weirs, upsetting the traditional balance of water use. It may be necessary, in these circumstances, to supply the downstream areas by canal, from the upstream improved diversion weir. However, the formal division of the water between upper and lower areas, taking the place of the traditional informal division, may involve protracted village-level negotiation.
 |
 |
