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Home The River Basin People and the River Governance Resource Management
The River Basin
 Introduction
Geography
Climate and Weather
Hydrology
 Principles of Hydrology
 Water Cycle
 Surface Water
 Groundwater
 SW/GW Interactions
Water Balance
 Hydrology of Southern Africa
 Hydrology of the Kunene Basin
Water Quality
Ecology & Biodiversity
Watersheds
 References

 



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Water Balance  

Water balance is a concept used to understand the availability and the overall 'state' of water resources in a hydrological system. A hydrological system is usually a standard surface water unit such as a quaternary catchment or, in the case of the Kunene River, the river basin. This concept is also sometimes referred to as a Water Budget.

Annotated Hydrologic Cycle with abbreviations inserted.
Source: FISRWG 1998
( click to enlarge )

This holistic approach to assessing the availability of water resources takes into account all of the water inputs into, and all the extractions out of the system or circulation.

Inputs can include:

  • Precipitation - rain;
  • Groundwater influx from an adjacent aquifer or a transboundary (trans-river basin) aquifer;
  • Snow melt; and
  • Inter-basin transfer -(water transferred into the basin from an adjacent river basin).

Extractions include:

  • Evaporation;
  • Transpiration;
  • Extraction for consumptive use from streams and rivers - water for industrial or domestic use and irrigation;
  • Extraction for consumptive use from groundwater aquifers; and
  • Inter-basin transfer (water transferred out of the basin to adjacent river basin).

A simple approach to a water balance equation could be considered as (Wanielista et al. 1997):

P + R + B - F - E -T = ΔS

Abbreviations:

P = Precipitation
R = Runoff or excess rainfall
B = Subsurface flow
F = Infiltration
E = Evapotranspiration
T = Transpiration
S = Change in storage in the saturated zone - soil or groundwater

 

 



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