1. NRCS DIMENSIONLESS UNIT HYDROGRAPH

2. NRCS DIMENSIONLESS UNIT HYDROGRAPH
Time/Tpeak
q/qpeak or Qa/Q
1.0 1 5
q = Discharge at time 1
q p = Peak Discharge
Qa = Accumulated Volume at time 1
Q = Total Volume
= A Selected Time
To = Time from Beginning of the rise of the peak
3/8
5/8 tl

3. PEAK FLOW

4. Timing Considerations
Lag Equation (Regression)
Segmental Method (Physically Based)

5. Lag Equation

6. Segmental Method Sheet Flow – Overland Flow
Shallow Concentrated Flow (Rills and Gullies
Open Channel or Pipe Flow (Conveyance System

7. Sheet Flow
Precipitation
Sheet Flow
Sheet flow
Infiltration

8. Sheet Flow
Sheet Flow
Sheet flow
Infiltration L
???

9. Sheet Flow Where: 0 < L < 100 ft S = slope ft/ft
P = 2-year 24-hour Precipitation

10. Shallow Concentrated Flow

11. Shallow Concentrated Flow
Velocity in fps
Slope in ft/ft
Land Use Curves

12. Open Channel Flow
n = 0.06
n = 0.07
n = 0.035

13. Topen channel flow = Length/Velocity

14. Time of Travel Tt = t1 + t2 + t3 Sheet Flow Shallow Concentrated Flow
Open Channel or Pipe Flow