Hydrograph Analysis

Components of river flow

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

Rainfall (mm) time Discharge m 3 /hr Rising limb Falling limb Peak discharge Lag time Groundwater baseflow Storm flow

Varying flow conditions A 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 development depends on the: Rainfall intensity Infiltration rate Volume of water infiltrated Soil moisture deficiency

Environmental flows

End of surface water Fin Einde