Unit 2 - Water Blanace

Water balance

a way of keeping track of how much water enters, leaves, and is stored within a defined area or system

basic idea: water in - water out = change in storage

Control Volume

The specific area or system that you choose to keep track of water within when doing a water balance

Storage

The amount of water that is held within a system at a given time

surface storage → streams, snow

subsurface storage → unsaturated and saturated zones

Flux

The rate at which water moves into or out of a system

a.k.a how much water is moving and how quickly

Residence time

The average amount of time a water molecule spends in a pool or reservoir. “how long does water stay here before it leaves?”

Equation:

RT = Reservoir volume/Inflow or outflow rate

T= V/Q

Steady State

A condition where the amount of water entering a system equals the amount of water leaving it.

Inputs = Outputs

Change in storage (ΔS)

the change in the amount of water stored in a system over a period of time.

Change in storage = water entering - water leaving

Water balance

a way of accounting for all water entering, leaving, and being stored within a system

Surface Storage vs. Subsurface Storage

Surface: water stored at earths surface, such as streams and snow

Subsurface: water stored below the surface, including unsaturated zone and saturated zone

influx vs. outflux

influx: water entering a system

outflux: water leaving a system

Surface water vs. groundwater storage

Surface: water stored on earth surface, including water in streams and snow

subsurface (groundwater is a apart of this): water stored below the surface

water balance equatiuon

ΔS = influxes - outfluxes

• more in than out: positive change

• more out than in: negative change

• in = out: no change

catchment scale water balance

a water balance that accounts for water entering, leaving, and being stored with a catchment.

at long-term average conditions, the catchment can often be treated as being steady state