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.
Before a storm, saturated areas are limited to the close vicinity of the stream. They …………….during the storm resulting in ……………………………………….
expand
larger rate of runoff generation
Before a storm, saturated areas are limited to the close vicinity of the stream. They expand during the storm resulting in larger rate of runoff generation
some areas also ……………. and ………………………………
expand and contract seasonally
In arid and semi-arid regions with ………………………and those disturbed by ……………………………
scarce vegetation
humans (urbanization, logging, etc.)
In arid and semi-arid regions with scarce vegetation and those disturbed by humans (urbanization, logging, etc.), infiltration capacity is ………………………. and ………………………… is a dominant process
a limiting factor
Horton overland flow
infiltration capacity is a limiting factor and Horton overland flow is a dominant process. This also happens when the top soil is
frozen
In most humid regions, ………………………………. and …………………………………are dominant processes.
subsurface storm flow and saturation overland flow
Where the soils are ………………, ……………and …………………………., the water table is deep and the saturated zone is confined to the………………………
well-drained
deep
very permeable
valley floor
Where the soils are well-drained, deep and very permeable, the water table is deep and the saturated zone is confined to the valley floor. …………………………….is less important than ……………………………in this situation.
Saturation overland flow
subsurface storm flow
Where the soils ………………………………………………………….., and slope is ………………………………………………………….,the water table is shallow and the saturated zone expand readily.
are thin and only moderately permeable
gentle and concave shaped
Where the soils are thin and only moderately permeable, and slope is gentle and concave shaped, the water table is shallow and the saturated zone expand readily. ………………………………….dominates in this situation.
Saturation overland flow
Modification of the land surface during urbanization changes
the type and magnitude of runoff processes.
Modification of the land surface during urbanization changes the type and magnitude of runoff processes. Covering parts of……………………………. increase …………………………………………………
the catchment with impervious roofs and concrete lots increases the volume and rate of Horton overland flow.
Planners have to design……………………….to accommodate increased runoff.
detention ponds
…………………….. and…………………….convey runoff rapidly to stream channels.
Gutters and storm sewers
The channels are …………………………and……………………. to increase the efficiency, so that they transmit the flood wave ………………………..more quickly.
straightened
lined with concrete
downstream
