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close this bookForests, Climate, and Hydrology: Regional Impacts (UNU, 1988, 217 pages)
close this folder3. Effects of tropical forest on water yield
View the document(introduction...)
View the documentAbstract
View the documentThe tropical forest regions
View the documentHydrological processes in tropical forests
View the documentWater yield characteristics
View the documentMethods of detecting the effects of forests on water yield
View the documentEffects of tropical forests on water yield
View the documentConclusion
View the documentAppendix
View the documentSymbols and abbreviations
View the documentReferences
View the documentAssessment
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Water yield characteristics

Water yield is defined as the discharge of a stream at a particular cross section as calculated over a specified period of time: a day, a month, a season, or a year; or over a number of such intervals. The average yield is a measure of the volume of runoff, the quantity of water available for utilization and development (Benham 1974). The yield is often used to describe the regime of flow of the river empirically and stochastically. It is usually measured in a well-defined watershed to ensure that no significant leakage occurs.

Colman (1953) argues, however, that yield should not be considered in terms of the total amount of runoff alone but should include rate of flow and its temporal variations as well as water quality (incorporating sediment load). He submits that all are important aspects of water yield, and control over all of them is required if proper management of water yield is to be achieved. In this report, however, only streamflow aspects of water yield are included. The total water yield has several components that should be considered separately in order to detect the effect of forests. These include:

  1. total discharge for hours, days, months, seasons, years;
  2. overland flow and interflow (= direct runoff) for similar periods;
  3. baseflow discharge for similar periods;
  4. stormflow discharge for individual storms;
  5. discharge duration and retardation.