Collecting data on water

The need for a better and more comprehensive information base cannot be exaggerated. It goes without saying that planning major investments in water resources development needs to be based on a thorough understanding of the natural resources available and the forces that are harnessed and controlled. This cannot be done without a good information base containing historical and current data on such factors as variability of rainfall, evaporation, underground water, floods and droughts.

Hydrological forecasting, which is of enormous economic and social importance, relies on prior knowledge of how river basins and river channels would respond to precipitation of varying intensities and durations. This calls for a study of past records of rainfall, snowfall and river flows and for the determination of relationships among the various factors. More accurate hydrological forecasting can save substantial amounts of resources, while inaccurate forecasts can cause both loss of lives and waste of resources.

To build sound storm-drain and sewer systems, culverts and bridges, data on the frequency and intensity of rainfall and the flow of rivers are needed. Engineers designing a major dam must know the extent of spill-over that must be built into it so that the structure will not be endangered by large floods. They must also have accurate knowledge of water loss by evaporation so that water is available during dry periods, but the height and therefore the cost of the dam are not excessive. To avoid disastrous effects of changes in land use, it is important to assess the possible effects on stream flows and the water balance of a particular drainage basin. In designing irrigation systems, it is essential to know the amount of water needed to keep the soil moisture at the optimum level and to estimate the amount of water required during the irrigation season to prevent crop failure. Greater economies can be achieved in the use of water if reliable forecasts of rainfall can be made available in advance etc.

Better data are also needed on ground-water recharge. In humid zones where ample amounts of water are generally available, the main problem in ground-water development is to determine where to construct a well in order to tap the water needed. In dry climates, the rate Of recharge of an aquifer has to be estimated first so as not to over-exploit its potentials for ground-water delivery. Without this information, one runs the risk of quickly depleting the resource.

Gathering information on water resources is not a once-and-for-all effort, since climatic variables are subject to fluctuation. Internationally, variability tends to be much larger in dry regions where precipitation is scarce than in better endowed humid id regions. Furthermore, fluctuations in run-off tend to be a multiple of fluctuations in precipitation. Consequently, arid and semi-arid regions are extremely sensitive to climatic variability. This sensitivity poses serious problems to decision makers who lack adequate empirical data.

Data on completed projects also need to be collected so that the various economic, social and environmental effects can be continuously monitored and evaluated. In that way, mistakes in other projects may be avoided. Site-specific information-gathering on various aspects of water resources must be supplemented through improved exchange of information, particularly between similar climatic regions. Certain problems - the continuing incidence of salinization and waterlogging, for instance - have arisen in many parts of the world and are still occurring because knowledge that already exists is insufficiently exchanged. In many cases, the knowledge has simply failed to reach the decision makers. Much the same can be said of methods for controlling specific environmental hazards, like floods, droughts, desertification and deforestation.