DES 606: Watershed Modeling with HEC-HMS

1. DES 606: Watershed Modeling with HEC-HMS Baseflow and Diversion Theodore G. Cleveland, Ph.D., P.E. 16 OCT 11

2. Baseflow • The hydrograph is comprised of two principal parts • The storm flow component is called the direct runoff hydrograph • The base flow (background) component.

3. Baseflow • The hydrograph is comprised of two principal parts: a base flow (background) component and a storm flow component. The storm flow component is called the direct runoff hydrograph • (DRH). The DRH is the hydrograph resulting from excess precipitation over the watershed • after the losses (abstractions) are removed. It is believed that the lag time from beginning of • precipitation to the peak of the DRH, the shape of the DRH) and the decay pattern of the • DRH are related to the characteristics of the basin as well as the rainfall pattern. Various • approaches to model such relations are in common use.

4. Incomplete Specifications • Parts of HMS model are not connected • Sub-basins not connected to other elements • Data missing • Rainfall gages missing • Record lengths inconsistent • Troubleshooting these kinds of problems is really learning how to interpret the HMS message log

5. Incomplete Specifications

6. Incomplete Specifications

7. Incomplete Specifications The warning seems to be associated with missing data. We will need to import data into the project.

8. Incomplete Specifications Repair the data files, then re-run

9. Incomplete Specifications Fix again, and re-run – this run has no warnings.

10. Clobbered HMS-DSS files • As analyst changes components and re-runs sometimes the DSS database gets clobbered. • This situation will usually throw errors that prevent the run form completing. • Easiest solution is to stop and restart HMS • Hopefully you have been saving files so recovery is possible.

11. Previous model, attempted to save with new filename. • Did not save, however HMS does not report failed save outside of log file

12. Previous model, attempted to save with new filename. • Attempted re-run of project (using new name) throws errors shown. • Solution is to import data from prior model, or start over.

13. How to Fix – Restart HMS

14. Import Prior Project

15. Select Prior Run 1

16. Select Run 1 The restart clears the computer memory And resets HEC-HMS paths There may be other ways to reset – this one is known to work

17. Poor Conceptualization • Hardest to detect and repair • If have data, then can use to guide repairs • Without data • use rules-of-thumb appropriate for locale • 3cfs/acre/in-hr • Tlag(hrs) = SQRT(AREA(sq.mi.) • use check-sums • Is loss what was anticipated? • Do flow peaks seem about correct?

18. Summary • Troubleshooting HEC-HMS projects needed to make simulation model what analyst thinks is modeling • Three modes of trouble • Incomplete specifications • Clobbered DSS file paths • Poor Conceptualization

19. Summary • Hints to help make troubleshooting easier • Name projects and components; avoid default naming • I didn’t follow for the course, but some examples show named components. • Maintain Excel data files as project • Use external (to HMS) preparation as a backup device. • Use HMS backup feature. • If recovery is needed, can use these files and cut-and-paste to recover work. • Maintain separate projects for substantial changes • This is my personal preference, the ANALYSIS tools in HMS are intended to perform such tracking for you

20. Summary • These hints should handle the bulk of the incomplete specification and DSS clobbering failure modes. • Conceptualization is harder

21. Summary • Conceptualization hints • Sketch (on paper) the watershed and components; keep a copy handy as build the project. • Parameter estimate external to HMS as much as practical; note estimates on the sketch. • Keep a simulation log (on paper) as you make minor changes; major changes should be separate project (my preference) or separate ANALYSIS (HMS tracking scheme)