1. CRWR-PrePro Calculation of Hydrologic Parameters
Francisco Olivera, Ph.D.
Center for Research in Water Resources
University of Texas at Austin

2. Hydrologic Parameters
Watershed
Abstractions and routing method
Parameters
Stream
Routing method

3. Watershed Abstractions and Routing Method
Abstractions: rainfall/runoff transformation
SCS curve number method
Initial loss + constant rate loss
Routing: runoff/flow transformation
Soil Conservation Service (SCS) synthetic unit hydrograph

4. Watershed Abstractions
Precipitation (mm/hr)
Runoff (mm/hr)
Soil properties
Runoff = f(precipitation, land use, soil properties, moisture conditions, temperature, wind)

5. Watershed Routing
Runoff (mm/hr)
Watershed
Flow (m3/s)

6. Watershed Routing Time Runoff (mm/hr) Runoff and Flow Flow (m3/s) Time
Flow = f(runoff, watershed hydrologic properties)

7. Hydrologic Parameters
Watershed
Abstractions and routing method
Parameters
Stream
Routing method

8. Watershed Abstractions
Average Curve Number
Initial Loss (mm) Constant Loss (mm/hr)
SCS Method
Initial + Constant Method

9. Watershed Routing SCS Unit Hydrograph Area (Km2) Area (Km2)
Average Curve Number
Length of longest flow path (m)
Slope of longest flow path (m/m)
Lag time
Area (Km2)
Length of longest flow path (m)
Average flow velocity (m/s)
Lag time
SCS Unit Hydrograph

10. Hydrologic Parameters
Sub-basin lag-time according to the SCS formula:
tp: sub-basin lag-time (min)
LW: length of sub-basin longest flow-path (ft)
CN: average Curve Number in sub-basin
S: slope of the sub-basin longest flow-path (%)
t: analysis time step (min)

11. Watershed Lag-Time (SCS)
Flow length upstream and downstream
Average Curve Number
Identification of the longest flow-path
Length and slope of the longest flow-path
Lag-time

12. Hydrologic Parameters
Sub-basin lag-time according to 0.6 L/v formula:
tp: sub-basin lag-time (min)
Lw: length of sub-basin longest flow-path (ft)
Vw: average velocity sub-basin longest flow-path (m/s)
t: analysis time step (min)

13. Watershed Lag-Time (L/V)
Flow length upstream and downstream
Longest flow-path average velocity
Identification of the longest flow-path
Length of the longest flow-path
Lag-time

14. Elevation Grid

15. Flow Length Downstream

16. Flow Length Upstream

17. Longest Flow-Path

18. Flow Length Downstream to the Watershed Outlet

19. Hydrologic Parameters
Flow length downstream to the sub-basin outlet.

20. Flow Length Upstream to the Watershed Divide

21. Hydrologic Parameters
Flow length upstream to the sub-basin divide.
A NODATA cell is defined at the sub-basin outlets before running the flow length function.

22. Watershed Longest Flow-Path

23. Hydrologic Parameters
Sub-basin longest flow-path.
The longest flow-path is the geometric locus of the points for which the sum of both flow lengths is a maximum.

24. Slope of Watershed Longest Flow Path

25. Hydrologic Parameters
Sub-basin parameters: Grid code, area (Km2), unit hydrograph model (SCS), length of longest flow path (m), slope of longest flow path (m/m), average curve number, lag-time (min), baseflow (none).

26. Hydrologic Parameters
Watershed
Abstractions and routing method
Parameters
Stream
Routing method

27. Routing Method

28. Pure-Lag Method tlag: flow time in the reach I: inflow to the reach
Q: outflow from the reach
Flow is delayed a fixed amount of time tlag.

29. Muskingum Method S: storage in the reach
K: flow time in the reach (Dt < K < Dt/2X)
X: storage parameter
I: inflow to the reach
Q: outflow from the reach
Dt: analysis time step
Flow is delayed a fixed amount of time K, and redistributed around its centroid.

30. Routing Method Flow time (Ls/Vs) Ls/Vs < Dt Ls/Vs > Dt
Pure Lag Routing
Muskingum Routing
Ls: length of the stream
Vs: flow velocity in the stream
Dt: analysis time step

31. Hydrologic Parameters
Watershed
Abstractions and routing method
Parameters
Stream
Routing method

32. Hydrologic Parameters
Reach lag-time for Pure Lag routing:
tlag: reach lag-time (min)
Ls: length of reach (m)
Vs: reach average velocity (m/s)

33. Hydrologic Parameters
Reach lag-time and number of sub-reaches for Muskingum routing:
K: Muskingum parameter K (hr)
X: Muskingum parameter X
Ls: reach length (m)
Vs: reach average velocity (m/s)
n: number of sub-reaches

34. Hydrologic Parameters
Reach parameters: Grid code, sub-basin code, length(m), velocity (m/s), routing method (Lag or Muskingum), Muskingum X, Muskingum K (hr), number of sub-reaches, lag time (min).