Lesson 8 - Hydrograph Analysis Flashcards
It is a continuous plot of instantaneous discharge vs time
Hydrograph
Detailed analysis of hydrographs is usually important in flood damage mitigation, flood forecasting or establishing design flows for structures that convey floodwaters.
Hydrograph Analysis
Components of Runoff:
- Overland flow or Surface Runoff
- Interflow or Subsurface Storm Flow
- Groundwater Flow or Base Flow
The water that travels over the ground surface to a channel.
Overland Flow or Surface Runoff
The precipitation that infiltrates the soil surface and move laterally though the upper soil layers until it enters a stream channel
Interflow or Subsurface Storm Flow
The portion of precipitation that percolates downward until it reaches the water table.
Groundwater flow or Base Flow
It has been customary to consider the total flow to be divided into two parts:
Direct runoff and the base flow
Presumed to consist of surface runoff and substantial portion of the interflow
Direct runoff
Considered to be largely groundwater
Base Flow
The time from the center of mass of the rainfall excess to the peak of the hydrograph
Lag Time
The time from the start of rainfall excess to the peak of the hydrograph
Time of rise or peak
One estimate is the time from the end of the rainfall excess to the inflection point of the hydrograph
Time of Concetration
The total duration of the Direct runoff hydrograph
Time base
A typical hydrograph resulting from an isolated period of rainfall consists of a rising limb, crest segment and falling limb and recession
Recession and Base flow separation
Baseflow Separation Techniques
- Straight-line method
- Fixed Base Method
- Variable Slope Method
