Soil Lec (2.2 & 2.3) Flashcards
the portion of rainfall that makes its way toward stream channels, lakes, or oceans as surface or subsurface flow
The Runoff Process
The Runoff Process usually refers to ____
overland or surface flow
Factors (demands) to be satisfied before run-off can occur
- evaporation
- infiltration
- interception
- surface storage
- surface detention
- channel
includes rainfall its characteristic duration, intensity, and distribution
precipitation
Factors Affecting Runoff
- precipitation
- watershed
- topographic features
- vegetation and management practices
- other factors (structures like dams, levees, bridges)
what does AWS stand for
automatic weather station
decrease with time thus, a storm of short duration may produce no runoff
Infiltration
directly related to the duration of a storm for a given intensity
Total runoff
True or False
Intensity influences both the rate and volume of runoff
True
slopes of upland areas, the degree of development and gradient of channels, and the extent and number of depressed areas also affect the rate and volume of runoff
Topographic Features
True or False
Watershed size is directly related to the volume and rate of runoff, but rate and volume per unit area of watershed decrease as runoff area increases
True
Dense covers of forests or shrubs could intercept up to ____
25% of annual precipitation
a function of vegetation
Rainfall interception
True or False
Vegetation tends to delay overland flow and increases surface detention to reduce peak runoff rates
True
interception also has a ____, which delays rainfall from reaching the soil only after running down the plant or dropping from the leaves
detention storage effect
Methods of monitoring, measurement and run-off prediction
- Rational Method
- Soil Conservation Service Method
- Flood Frequency Analysis Method
- Computer Prediction of Run-off
the time required for water to flow from the most remote (in time of flow) point of the area to the outlet once the soil has become saturated and minor depressions are filled
time of concentration
general equation for predicting a peak runoff rate
Q = 0.0028 CiA
Time of concentration (TC) can also be estimated by ____ by ____ to obtain travel time
dividing the length of flow ; an estimated velocity of flow
the ratio of the peak runoff of the rainfall intensity and is dimensionless
run-off coefficient (C)
True or False
The rational method assumes that rainfall and run-off frequencies are similar
True
This method depends mainly on the presence of records from the basin being studied
Flood Frequency Analysis Method
This method is widely used in more advanced countries, particularly in the US
Computer Prediction of Run-off
The method emphasized in predicting the total volume of run-off coming from a watershed during a design flood is
Soil Conservation Service Method
