Time of Concentration
The time required for runoff to flow from the most remote point of the watershed to the outlet
Remote point dependent upon flow travel time, not topographical distance
Factors that affect Time of Concentration
Slope: steepness changes water speed
Steeper landscape creates higher speed
Surface Roughness: size and shape of particles
Smaller, smoother particles allow water to travel faster
Channel Shape/Flow Patterns: type of flow affects how fast water moves
Above surface water generally moves faster than below surface
3 Methods of Calculation
Kirpich Method
Used if data about Watershed is limited
Usually has a short time of concentration
Travel Time Method
Add the different times of water movement based on flow patterns
Sheet Flow, Shallow Concentrated Flow, Open Channel Flow
Curve Number Method
Divide larger watersheds into smaller units
Best if land is < 2000 acres