Lecture 7 - Rainfall Runoff Flashcards
simply that area of land that contributes surface runoff to a single outlet and is separated from other watersheds by a drainage divide.
watershed
Rainfall that falls in a watershed will generate ——to that watershed outlet.
Runoff
One of the principal objectives in hydrology is to transform rainfall that has fallen over a watershed area into flows to be expected in the receiving stream.
Hydrologic Theory
The total input into a watershed associated with a particular storm event can be represented graphically through a plot of rainfall versus time
Rainfall Hyetograph
The total output from a watershed in response to a particular input (precipitation) can be represented graphically through a plot of flow vs time
Runoff Hydrograph
The storm hydrograph is divided into:
Direct runoff and Baseflow
It is the groundwater contribution to a stream
Baseflow
Watershed Characteristics
Size Slope Shape Soil Type Storage Capacity
Runoff is generated when the rainfall rate exceeds the infiltration capacity and then overland flows occur in portions of the watershed (Sometimes run in small rivulets or channels before reaching the larger streams)
Surface Runoff/Direct Runoff
Some portion of water that infiltrates moves rapidly downslope through the unsaturated zone to stream channels
Subsurface flow/ Interflow
Water infiltrates the ground and percolates the saturated zone, then groundwater flow in the saturated zone discharges into the stream
Baseflow
Sometimes runoff is generated when the water table reaches the ground surface as in the case of spring
Saturation Excess runoff
It is the simplest rainfall-runoff formula, which allows the prediction of peak flow
RAtional Method
Provides design discharge for design of hydraulic structures
Peak Discharge Design method
A design method does not have to be accurate as an evaluation method since some factor of safety is always incorporated into design
Peak Discharge Design Method
