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Sources of streamflow from hillslopes. Baseflow streamflow maintained by groundwater contributions Stormflow Augmented by direct precipitation on saturated area Overland flow R eturn flow Shallow subsurface stormflow. Streamflow Components. Terms

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sources of streamflow from hillslopes
Sources of streamflow from hillslopes

Baseflow

streamflow maintained by

groundwater contributions

Stormflow

Augmented by direct precipitation on saturated area

Overland flow

Return flow

Shallow subsurface stormflow

streamflow components
Streamflow Components

Terms

Event water- water that enters the stream network during a storm event

  • Stormwater: typically surface runoff
  • Throughflow: typically shallow soil water flow

Pre-Event water- any water that resided in the catchment prior to event

Base-flow – Subsurface water discharging into streams from groundwater source

runoff mechanisms
Runoff mechanisms

Various mechanisms of Streamflow Generation

Urban sources Rural sources

runoff production terms
Runoff production terms
  • Overland flow
    • Infiltration-excess overland flow- runoff generated where infiltration capacity is exceeded by rainfall intensity
    • Saturation-excess overland flow- runoff generated where shallow water table intersects ground surface
  • Return flow- groundwater reemerges from the soil at a saturated area and flows downslope as overland flow
  • Variable source areas as saturated areas expand and contract
dominant runoff processes
Dominant Runoff Processes

Thin Soils

Gentle slopes

Wide Valley Bottoms

Direct Precipitation &Return Flow Dominate

Horton Overland Flow Dominates

Subsurface flow less important

Variable Source Area

Topography and Soils

Subsurface stormflow dominates

Peaks produced by return flow &

Direct precipitation

Steep straight slopes

Narrow Valley Bottoms

Humid Climate

Dense Vegetation

Arid to Semi-Arid

Sparse Vegetation

Urbanizing

Climate, Vegetation,

& Land Use

topmodel
TOPMODEL
  • Numerical model for routing water through a catchmentto predict hydrographs
  • Based on catchment characteristics
  • Fundamental streamflow generation mechanism- saturation excess overland flow
hillslope water balance
Hillslope Water Balance

et

R recharge from unsaturated to saturated zone

Water conservation equation for saturation zone – quantified as saturation deficit

_ _

S(t) = S(t-1) - R+ qsubsurface+ qreturn+ evap from saturated zone

topographic wetness index
Topographic (Wetness) Index

TI= ln( a/ Tan B)

Where:

a= upslope contributing area

B= local slope

flux and water conservation equations and saturation deficit redistribution
Flux and water conservation equations and saturation deficit redistribution

Saturation deficit=s

Water equivalent depth to water table

S catchment mean saturation deficit

m model parameter representing depth decline of soil conductivity and redistribution of saturation zone water

λ mean wetness index

β topographic slope

_

=

for each time step
For each time step:
  • For each wetness index interval:
    • Calculate infiltration to unsat zone, et from root zone, recharge to sat zone, return flow, overland flow from direct precipitation
  • For whole catchment (or hillslope)
    • Compute subsurface drainage
    • Update catchment mean saturation deficit
    • Redistribute local saturation deficit