1. HEC-HMS Simulation 3 Different Loss Models
Example 3
HEC-HMS Simulation
3 Different Loss Models

2. Purpose
Illustrate different loss models in a HEC-HMS precipitation-runoff simulation
The example is “minimal” in the sense that only a small set of HEC-HMS capabilities are employed
Realistic parameter values are employed from public-domain references, but the example is fabricated for pedagogical simplicity.

3. Learning Objectives
Learn how to copy a “project” so can modify without damage to original files.
Reinforce the concepts of “Projects” as a data-storage paradigm.
Learn how to import observations.
Use of measured rainfall and discharge. Where available can use to “calibrate” a watershed model.
Learn how to parameterize different loss models
Initial loss and constant rate loss model
NRCS CN runoff generation (loss)
Green-Ampt loss model

4. Problem Statement
Simulate the response of the Ash Creek watershed at Highland Road for a the XXXX historical conditions.
Use Example 2 as the base “model”, modify by substitution of the real rainfall time series and the observed runoff time series.
Treat the entire watershed as a single sub-basin.

5. Background and Data Watershed Outlet
Highland Road and Ash Creek, Dallas, TX.
Area is residential subdivisions, light industrial parks, and some open parkland.
White Rock Lake is water body to the North-West

6. Physical Properties Watershed Properties AREA=6.92 mi2 MCL=5.416 mi
MCS=
CN=86
R=0
This was used in IaCl specification
-- will examine source of number
-- will also need GA values

7. Historical Data Precipitation and Runoff May 20, 1978
Total depth about 3-inches, close to Example 2 depth (much different time scale)

8. Historical Data
Precipitation
Note start time
Runoff
Note start time

9. Start Time Start time is important
The start time of rainfall time series and runoff time series should be same
A common error is time mismatch, usually obvious in the simulation but not always.

10. Using “Real” Data Need to prepare the data
Uniform time steps (no 17 hour gap)
Rainfall and runoff data should have same start times, use zero-padding to make happen
Data become “time-series” elements
Rainfall => With a “rain-gage” in HEC-HMS
Runoff => With a “discharge-gage” in HEC-HMS

11. Building The Model – Create a New Project
Use Example 2 as the base model
Start Example 2
Select “Save-As”
Save to a new project name and file

12. Building The Model – Create a New Project
Use Example 2 as the base model
Start Example 2
Select “Save-As”
Save to a new project name and file
Name
Path
Check these to create duplicate files

13. Building The Model Verify the copy
Run a simulation
Convince self that have a working copy

14. Data Preparation
Now prepare the external hyetograph from the historical data
Use Excel to prepare the time series
Specify a long enough time window in the time-series manager
Use HEC-HMS “fill” to fill in the 17 hours

15. Data Preparation: Rainfall
Use Excel to prepare the time series
Specify a long enough time window in the time-series manager
to should cover the rainfall and allow an entire day for runoff
Can refine if needed

16. Data Preparation:Rainfall
Specify a long enough time window in the time-series manager
to should cover the rainfall and allow an entire day for runoff

17. Data Preparation: Rainfall
Use Excel to prepare the time series
Identify non-uniform time step sections
line up with input table in HEC-HMS
One-time only is easiest to enter blocks, then use HMS tools to fill in values
Many storms, worth writing code to interpolate (external to HMS)
Not every 15 minutes here

18. Data Preparation: Rainfall
Use Excel to prepare the time series
Identify non-uniform time step sections
line up with input table in HEC-HMS
One-time only is easiest to enter blocks, then use HMS tools to fill in values
Many storms, worth writing code to interpolate (external to HMS)

19. Data Preparation: Rainfall
One-time only is easiest to enter blocks, then use HMS tools to fill in values
Enter value first line (not displayed)
Highlight fill block
Right-click block and select fill method

20. Data Preparation: Rainfall
One-time only is easiest to enter blocks, then use HMS tools to fill in values
Enter value first line (not displayed)
Highlight fill block
Right-click block and select fill method
Completed data fill (zero padding in this case)

21. Data Preparation: Rainfall
Continue for remaining non-uniform spaced blocks.
When complete, plot the time-series and Excel and HEC-HMS; should look the same (padded the Excel file to start/end same elapsed time)
This plot is QA/QC only, once data are entered, won’t need further Excel plots.

22. Loss Model Parameters
IaCl model in TxDOT

23. Data Preparation: Runoff
Use Excel to prepare the time series
Specify a same time window as rainfall
Copy, paste, fill by same process.

24. Data Preparation: Runoff
Create discharge gage
Time series manager.

25. Data Preparation: Runoff
Specify time window

26. Data Preparation: Runoff
Use same process as for rainfall
Insert blocks
Use fill tool to insert missing values
Plot results to compare

27. Data Preparation: Runoff
Continue for remaining non-uniform spaced blocks.
When complete, plot the time-series and Excel and HEC-HMS; should look the same (padded the Excel file to start/end same elapsed time)
This plot is QA/QC only, once data are entered, won’t need further Excel plots.

28. Example 3: IaCl Loss Model
Leave remainder of model unchanged
Represents the IaCl model
Represents the NRCS DUH transformation model
Run the simulation using the real rainfall (in contrast to a hypothetical input)
Compare simulation output with discharge gage
Assess how well the estimation methods worked
Try different loss models (Run 2 and Run 3)

29. Example 3: IaCl Loss Model
Instruct the program to plot the observed gage with the simulation gage.
Basin/Options

30. Example 3: IaCl Loss Model
Dotted curve is observed runoff, solid is simulation
Timing ~ 70 minutes late
Peak ~ 50% low
Volume ~ 20% high
One could “calibrate” but that is for a later module.
Stipulate that simulation is a bit off, and explore different loss models.

31. Example 3B : Green-Ampt
Requires some added knowledge about the Ash Creek locale
Soil types and tables of values
Prior study (if lucky – in this example available)

32. Example 3B : Green-Ampt Soil Types Texas available from TAMU
Nationwide from NRCS
This example will download the NRCS map, it is more assessable to hydrologists, the TAMU database is specialized for soil scientists.

33. Example 3B : Green-Ampt NRCS Soil Map Zoom to this area
Read description

34. Example 3B : Green-Ampt
NRCS Soil Map : Type 2

35. Example 3B : Green-Ampt
NRCS Soil Map : Type 2
Loamy and clayey soils

36. Example 3B : Green-Ampt
Compare description with published soil behavior
Use middle description.
Other arrows indicate reasonable bounding ranges

37. Loss Model: Green-Ampt
Parameter estimation
Initial water content
Saturated water content: 0.464
Saturated hydraulic conductivity: 0.04 in/hr
Soil suction: 8.27 inches

38. Example 3B: Green-Ampt Results Timing ~ 70 minutes late Peak ~ 50% low
Volume ~ 9% high (good!)

39. Example 3A : NRCS Loss Model
Example 3A will substitute the NRCS Loss Model for the IaCl model
Clone the project again (Save As …) to preserve structure and reduce chance of a data specification error
Change the loss model specification, enter curve number and re-simulate.

40. Example 3A : NRCS Loss Model
Curve number selection
Determine hydrologic soil classification
Uses same soil map as in Green-Ampt
Soil Group C or D appropriate based on saturated hydraulic conductivity.

41. Example 3A : NRCS Loss Model
Make an assessment of “open space”, residential, and commercial industrial.
Then decide fraction impervious for a composite number.
Subjective, but most analysts will be within +/- 10.

42. Example 3A : NRCS Loss Model
Look up CN for the different parts, I choose lowest value in C group soil.
10% of area is the stream drainage, essentially open space CN ~ 79, %IC=0
30% of area is commercial-business (note the general aviation airport is included) CN ~ 91, %IC ~ 85
60% of area is some kind of residential, CN ~ 83, %IC~40
Composite these to a value of CN=90 for the watershed, IC is already considered.

43. Example 3A : NRCS Loss Model
Clone the project again (Save As …) to preserve structure and reduce chance of a data specification error
Change the loss model specification, enter curve number and re-simulate.

44. Example 3A : NRCS Loss Model
Results with different loss model.
Timing ~ 70 minutes late
Peak ~ 50% low
Volume ~ 50% high

45. HEC-HMS Example 3 Learning Points
Copy entire projects to keep different models organized.
Used Excel to prepare data for import into Time-Series-Manager; allows use of measured values where available.
IaCl, Green-Ampt, NRCS CN perform differently but require similar data preparatory effort.

46. HEC-HMS Example 3 Learning Points Used external data sources
NRCS soil maps (internet)
Texas A&M Soil Database (didn’t use, but know available)
Used a Green-Ampt soil property correlation in SWMM (but from the soils literature)
Used TxDOT hydraulic design manual for CN estimation. NEH 630 Chapter 9-10 would have produced similar values.

47. HEC-HMS Example 3 Learning Points
Assembly of external data sources is vital to the hydrologist
Most practicing hydrologist’s offices are a mess of old reports – that’s where they find the data.
Many useful external data sources are available in PDF reports from a variety of sources, need to get in the habit of citing the data source should one need to defend input value choices.

48. HEC-HMS Example 3 Learn more Next example HEC HMS user manual
FHWA-NHI Highway Hydrology
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Calibration tools