Chapter 8 Runoff Discharge Flashcards
Rain and snowmelt water take various paths to streams. Each path contributes differently to;
- peak and timing of storm runoff
- erosion
- transport of chemicals into streams
Planners need to understand runoff processes to;
- identify the area contributing to runoff generation
- assess the impact of deforestation, road construction, and other landuse change on runoff characteristics
- evaluate the risk of stream pollution
Path 1:

Horton overland flow
Path 2:

groundwater flow
Path 3

shallow subsurface storm flow
Path 4:

Saturation overland flow
Infiltration capacity decreases as
the soil gets wet
Overland flow occurs when
rainfall intensity exceeds infiltration capacity
Infiltration capacity …………………considerably within a ………………depending on ………………………… and ………………………………
varies
catchment
soil types and vegetation cover
Horton overland flow may occur in
localized areas within the catchment; partial-area concept.
Horton overland flow is rare in
vegetated humid region
. Horton overland flow is rare in vegetated humid region. It is common in areas
devoid of vegetation such as;
- semi-arid rangelands
- compacted soil, e.g. logging roads
- paved urban area, e.g. parking lots
subsurface storm flow (SSSF)
During the storm, the water table near the stream rises rapidly and increases the volume of groundwater flow.
If a low permeability layer exists at some depth,
water accumulates above this layer and flows horizontally toward the stream
Subsurface storm flow generates …………………….. than ………………………..
lower volume of runoff than Horton overland flow
Runoff to rainfall ratio is usually
less than 20%
Most of the rain is stored in ……………………and is …………………..to ……………………………..
the sediments
released slowly
supply steady base flow
If the rainstorm is large enough, the water table near the stream
rises to the ground surface
return flow (RF).
Groundwater seeps out from the ground surface and generates overland flow.
This Groundwater seeps ………..from the ground surface and generates …………………………is called return flow (RF)
out
overland flow
The rain falling on the saturated area cannot infiltrate because
groundwater flow direction is upward under the area.
Direct precipitation onto ………………………..also generates overland flow.
saturated areas (DPS)
The combination of RF and DPS is called
saturation overland flow.
Before a storm, saturated areas are limited to
the close vicinity of the stream.