Module 3: HEC-HMS Elementary Model Theodore G. Cleveland, Ph.D., P.E, M. ASCE, F. EWRI August 2015 Module 3 1

 Applications  Overview of HEC-HMS  Example 3 – A elementary HEC-HMS model. Module 3 2

 HEC-HMS is a Hydrologic Model  Peak Flows  Hydrographs  Hydrograph Routing ▪Stream reaches ▪Reservoirs and detention basins ▪Hydrograph lagging and attenuation ▪Sub-basin modeling (if appropriate) Module 3 3

“ … models are like maps; never final, never complete until they grow as large and complex as the reality they are supposed to represent.” Paraphrased from James Gleick “Genius: The Life and Science of Richard Feynman” Module 3 4

A model is a simplification of reality – should capture the excitation-response of the system under study but only as complex as needed. Module 3 5

 Require engineering judgment  Experience helps  Results can be difficult to interpret  Require accurate input data  Judgment here too, some data have marginal influence on results, other data are vital.  Require quality control procedures Module 3 6

 Separate (individual) programs in 1967 (L. R. Beard)  Unified into a single program in 1973  Revised in 1981: kinematic wave  PC full version in 1988  Revised 1991: Extended memory support  Final release 1998  32 years development until final release Module 3 7

 Evolved from HEC-1  Project begun in 1990  HEC-HMS “released” in 1998  Current version is 3.5  21 years of development to date.  Include the HEC-1 period and have nearly 50 years of development – The program “engine” is mature! Module 3 8

 Purpose  Replacement for HEC-1 ▪Foundation for future hydrologic software  Improved interface (GUI), graphics, and reporting.  Newer hydrologic computation methods imbedded  Integration of hydrologic capabilities Module 3 9

Watershed –Losses –Transformation –Storage –Routing Precipitation –Meterology, Climate  Runoff  Fraction of precipitation signal remaining after losses 10 Module 3 10

 Hydrologic Cycle Components in HEC- HMS (circa 2008) Land Surface and Vegetation ChannelsReservoirs Infiltration Loss Snowpack Rainfall, P(t) Snowfall Snowmelt Runoff Percolation Loss Evapo- transpiration Discharge, Q(t) Module 3 11

 Precipitation  Abstractions  Fraction of precipitation that does not contribute to runoff (and ultimately discharge)  Routing  Watershed routing  Stream (Channel) routing  Reservoir (Storage) routing Module 3 12

 Data management  Graphical User Interface (GUI)  Multiple input files  Multiple output files  Time-series in HEC-DSS  All files arranged in a “Project”  Paths to individual files  Can entire project folders and have them run elsewhere Module 3 13

 project-name.hms  List of models, descriptions, project default methods  basin-model-name.basin  Basin model data, including connectivity  meterologic-model-name.met  Meterologic model data Module 3 14

 control-specifications-name.control  Control specifications  run-name.log  Run log; messages, warnings, etc. during a run.  project-name.run  List of runs, includes recent execution time. Module 3 15

 Example 3 – A minimal HEC-HMS model  Ash Creek Watershed  Use TxDOT research reports to generate certain data elements  Exercise 3 – A minimal HEC-HMS model  Rocky Run near College Station, TX  Use TxDOT research reports to generate certain data elements Module 3 16

 HEC-HMS is a computer program for rainfall-runoff modeling  A minimal model is a non-trivial exercise, requires considerable thought to generate data. Module 3 17