Hydrograph Analysis

Components of river flowLatrobe River Gauging Station Flows - 226204

0

200

400

600

800

1000

1200

09/11/2004 17/02/2005 28/05/2005 05/09/2005 14/12/2005 24/03/2006 02/07/2006 10/10/2006 18/01/2007 28/04/2007

Date

Flow

(ML/

d)

Contributions into a river/stream• Overland flow

– Flow over land surface due to precipitation (runoff)• Interflow

– Lateral movement of soil water during & immediately after precipitation

– Discharges directly into stream• Return flow

– Flow across land when soil-water throughflow discharges prior to entering stream

• Baseflow– Discharge from groundwater into stream

• Direct rainfall

Baseflow• Streamflow contributed by groundwater• If no rainfall occurs, hydrograph often follows an

exponential decay called a base flow recession• The base flow recession is a function of

topography, drainage pattern, soils and geology

Gaining stream receives groundwater baseflow into the stream

Losing stream leaks surface water into the groundwater storage

Rivers

2

6

4

8

Rain

fall

(mm

)

time

Disc

harg

e m

3 /hr

50

100

Risin

g lim

bFalling limb

Peak discharge

Lag time

Groundwater baseflow

Stormflow

Varying flow conditionsA stream may switch from a gaining stream during low flow conditions to a losing stream during flood conditions

Storm Hydrograph

Storm flow component

Baseflow component

Precipitation component

Bank storage

Bank Storage

Bank storage component is the water entering the stream bank as the stream height rises. As the stream height subsides, the water drains from the bank to be added back to the stream.Is bank storage greater for a stream with steep banks? Or gently sloping banks?

Hydrograph developmentdepends on the:• Rainfall intensity• Infiltration rate• Volume of water infiltrated• Soil moisture deficiency

Environmental flows

End of surface water

Fin

Einde