Example 6B

1. Example 6B HEC-HMS Simulation 3 Different Loss Models

2. Purpose • Illustrate different loss models in a HEC-HMS precipitation-runoff simulation

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 20 May 1978 historical conditions. • Use Example 6A 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=0.005595 • 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 ModelVerify 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 • 5-20-1978 to 5-22-1978 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 • 5-20-1978 to 5-22-1978 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 0-4193-7

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. 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. IaCl Loss Model • Instruct the program to plot the observed gage with the simulation gage. • Basin/Options

30. 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. 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. 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 4B : Green-Ampt • NRCS Soil Map Zoom to this area Read description

34. Green-Ampt • NRCS Soil Map : Type 2

35. Green-Ampt • NRCS Soil Map : Type 2 • Loamy and clayey soils

36. Green-Ampt • Compare description with published soil behavior • Use middle description. • Other arrows indicate reasonable bounding ranges

37. Green-Ampt • Parameter estimation • Initial water content. 0.187 • Saturated water content: 0.464 • Saturated hydraulic conductivity: 0.04 in/hr • Soil suction: 8.27 inches

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

39. NRCS Loss Model • 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. 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. ]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. 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. 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. NRCS Loss Model • Results with different loss model. • Timing ~ 70 minutes late • Peak ~ 50% low • Volume ~ 50% high

45. HEC-HMS Example • 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 • 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 • 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 • Learn more • HEC HMS user manual • FHWA-NHI-02-001 Highway Hydrology • Next example • Calibration tools • SWMM • Nothing special here, would need similar data preparation. Again scale issue is challenge.