Cover Image
close this book Local Experience With Micro-Hydro Technology
View the document Preface and Acknowledgment
View the document Foreword to the 3rd edition
View the document Abstract
close this folder A. Introduction
View the document 1. THE NEED TO EXPAND DOMESTIC ENERGY PRODUCTION
View the document 2. TRADITIONAL ENERGY RESOURCES IN RURAL AREAS
View the document 3. NEW SOLUTIONS ARE NECESSARY
close this folder B. Development of hydropower resources
View the document 1. THE UNUSED HYDROPOWER POTENTIAL
View the document 2. DISTRIBUTION OF RESOURCE AVAILABILITY OVER TIME AND GEOGRAPHICAL AREA
View the document 3. CHARACTERISTICS OF HYDROPOWER RESOURCES
View the document 4. BIG OR SMALL HYDRO?
close this folder C. Small hydropower in the rural situation
View the document 1. PAST AND RECENT HISTORY
View the document 2. RURAL ELECTRIFICATION IN DEVELOPING COUNTRIES
close this folder D. A practicable approach
View the document 1. CONSTRAINTS AND PROBLEMS
View the document 2. TECHNOLOGY
close this folder E. PROJECT EXAMPLES
View the document 1. SALLERI-CHIALSA MICRO HYDEL PROJECT, NEPAL
View the document 2. BHORLETAR TURBINE IRRIGATION PROJECT, NEPAL
View the document 3. NAM DANG HYDRO-ELECTRIC PROJECT, THAILAND
close this folder F. ECONOMIC CONSIDERATIONS
View the document 1. BASIC APPROACH a) Cost-Benefit-Approach for Socio-Economic Selection
View the document 2. MICRO-HYDROPOWER AND LARGER HYDROPOWER PLANTS
View the document 3. MICRO-HYDRO PLANTS AND OTHER ALTERNATIVES
close this folder G. ASPECTS OF TECHNOLOGY TRANSFER AND DISSEMINATION
View the document 1. POLICIES AND INSTITUTIONS
View the document 2. FINANCE
close this folder ANNEXES
View the document ANNEXE I :ALPHABETICAL INDEX OF BIBLIOGRAPHY
View the document ANNEXE II GLOSSARY OF ABBREVIATIONS USED
View the document ANNEXE III ALPHABETICAL MANUFACTURER'S LIST (updated 1985)
View the document ANNEXE IV ALPHABETICAL LIST OF INSTITUTIONS AND ORGANISATIONS INVOLVED IN HYDRO DEVELOPMENT
View the document ANNEXE V STANDARD ENERGY CONVERSIONS

2. DISTRIBUTION OF RESOURCE AVAILABILITY OVER TIME AND GEOGRAPHICAL AREA

The graphical presentation of continent-wise potentials in fig. 2 does of course not show how distribution is within the regions and over time. There are two main factors that determine the generating potential at any specific site: the amount of water flow per time unit and the vertical height that water can be made to fall (head). Head may be natural due to the topographical situation or may be created artificially by means of dams. Once developed, it remains fairly constant. Water flow on the other hand is a direct result of the intensity, distribution and duration of rainfall, but is also a function of direct evaporation, transpiration, infiltration into the ground, the area of the particular drainage basin, and the field-moisture capacity of the soil. Runoff in rivers is a part of the hydrologic cycle in which -powered by the sun - water evaporates from the sea and moves through the atmosphere to land were it precipates, and thence returns back to the sea by overland and subterranean routes.


Fig. 3: World Distribution of River Runfoff in mm/year

Source: AMBIO, Vol. 3, No. 3-4, 1974: The Global Freshwater Circulation

Area-wise distribution of river runoff (in mm/year) in fig. 3 gives an indication of the geographical situation of hydro resources in the various parts of the world. It appears that regions around the aequator, Central America and parts of South-East Asia, northern Europe and North America have higher than average runoffs. In large parts of northern Africa (Sahel, Sahara), Arabia, Central Asia, Australia and western North America, as well as southern Africa and America, runoff is far below average. These areas are of little or no interest in the context of hydropower potential. For areas with average and higher runoff, the short-, medium-and long-term variations of flow are of prime interest. It is this local pattern that determines the availability of water to generate power in relation to time and duration. Such variations are subject to the weather regime, i.e. seasons, and a multitude of other factors such as those already mentioned. Generally speaking, perennial rivers with slight flow variations are the most suitable for hydropower development. High runoff variations, on the other hand, make harnessing more difficult, and extremes such as only seasonal runoff and floods impose serious economic and technical constraints on possible utilisation.