1.8 Water Balance

Water balance - gives an overview of how much water is used for which process

summary: water balance is a mass balance set up over a certain period and over a certain area (usually a catchment). the most important terms: precipitation, evapotranspiration, discharge, and storage change. Allows us to identify important processes and compare catchments

• useful for comparing catachmetns

• water balance is based on the mass balance equation

• inflow - outflow = storage change

• what flows into a certain volume at a certain time than what flows out then at the end of the period there is more water than at the start

  • catchment has the same working

    • identify which fluxes are relevant

    • flux - something flowing into or out of the catchment

      • inflowing: precipitation

      • outflow - evapotranspiration and discharge at the outlet

• if you set up a water balance for a whole year: you sum all precipitation that fell during that year

• do the same for evaporation and discharge

  • then compare for the difference between the end and the start of the year

  • HAVE TO CONVERT DISCHARGE BY CATCHMENT AREA = dischage is in volume/time then to conver it is —- (volume/time)/area —— end up with then length per time

Complex catachemnts

• i.e in lowland areas

  • surface water flowing into the catchmetn

  • groundwater exchange - either vertically (seepage) or horizontally

Groundwater storage

• need the change in the amount of groundwater

  • multiply the groundwater change with distortivity to get the storage change

    • less than the groundwater level change because most of the soil volume is taken up by soil particles and immobile water

Storage change

• increases and decreases over the year

• the end is about the same at the start of the year - can be negelected

• storage change cannot be neglected if you set it up over a part of the year