WC8 - water balance
water balance
balance between the inputs and outputs, it can be calculated for any unit area
inputs precipitation
outputs - overland flow/stem flow, evapotranspiration and water storage
water balance is expressed as: P=O+E+/-S
p: Precipitation
O (or Q): Runoff (including river regime)
E: Evapotranspiration
S: Storage
what causes runoff?
Amount of soil water storage
Types of Precipitation
Geology
Reservois/damming of rivers
Intensity of precipitation
land use change
Type of climate
Urbanisation
impermeable = increase runoff
Increase of people living in urban areas
more managed infrastructure
conversion of a peice of land used by humans from one purpose to another
landcover = impermeable surfaces = decrease in soil = high runoff
change in gradient of an area can decrease runoff
Large natural or articial lake used as a water supply source
Impermeable rock = high runoff
high intensity = more water = high runoff
low intensity = low runoff
Total amount of rain falling during a given time period
Long term pattern of weather in a particular area
wet climate = high runoff
dry climate = low runoff
high runoff: rainfall will pass quickly through soil or overland
low runoff: snowfall will delay runoff, if it melts quickly runoff will increase
rain, snow etc
high runoff: if the rate of rainfall exceeds the infiltration rate then runoff will begin
low soil water = low runoff
amount of water that can be stored in the soil
can increase runoff due to change to soil and vegetation
can shorten runoff time into streams
permeable and porous rock = low runoff
The distinguishing characteristics of a rock
precipitation (biological, channel) = Runoff (durface runoff & channel flow) + Evapotranspiration +/- storage (groundwater & soil moisture & surface channel)
river regime
changes in a rivers dischange throughout the year