Introduction to HEC-GeoHMS. Watershed boundary delineation. Assembling Hydrologic Modeling System

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2 Introduction to HEC-GeoHMS Watershed boundary delineation Assembling Hydrologic Modeling System

3 HEC-GeoHMS GIS tool set supporting HEC-HMS modeling S Developed by USACE S ArcView 3.x extension v1.1 supported and widely used S Version 4.2 for ArcGIS 9.X available through ESRI not officially released by HEC S Requires Spatial analyst

4 About GeoHMS HEC-GeoHMS companion product to HMS ArcGIS version (ESRI for HEC under CRADA) I/O support through HMS (ASCII, XML) History HEC-PrePro (UT, 1997), CRWR-PrePro, PrePro 2003, Watershed Delineator (ESRI, 1997) ArcView 3.* versions (ESRI for HEC, ) Development philosophy Build on top of Arc Hydro tools Automate GIS feasible functionality

5 HEC-GeoHMS GeoHMS Functionality DEM preprocessing definition (main view) Watershed delineation on models (project view) Topographic characteristics extraction Hydrologic parameter computations Model schematization Model input preparation (ASCII) Other GIS processing Rainfall distribution/interpolation LU/soils :runoff coefficient mapping

6 GeoHMS Functionality (cont.) HEC-GeoHMS and Arc Hydro tools are tightly linked GeoHMS computes as many Arc Hydro attributes as possible (e.g. NextDownID, JunctionID, DrainID) DEM preprocessing (main view) is done using ArcHydro tools Topographic characteristics extraction is based on Arc Hydro tools Arc Hydro tools operate on both main and project views

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8 DEM Preprocessing (parent definition) Hydrologically correct DEM Flow direction (D8 method) Flow accumulation Stream definition and segmentation Watershed pre-delineation Project ( baby ) data extraction

9 Hydrological corrected DEM Sinks Some sinks are real Streams in the correct place: To burn or not to burn Watershed boundaries in the correct place To fence or not to fence

10 SRTM-DEM Topo -DEM of Klang river basin. SRTM-DEM

11 Stream definition and segmentation Threshold (performance) Watershed pre-pelineation At stream confluences DEM Preprocessing (cont.)

12 Flow direction processing Coding direction Elevation Flow direction

13 Flow accumulation processing Flow direction Coding direction Flow accumulation

14 Watershed Delineation Flexible addition and removal of basin outlets Merge existing basins Split basin anywhere on the stream Add an outlet anywhere (trace the outlet stream to an existing stream) Profile Interactive or batch processing Understanding of basin character

15 Watershed delineation Delineate the contribution area to the cell or group of cell

16 Batch Subbasin Delineation Rule - The point should be located within the grid cell that has an existing stream. Import Batch Points Places all selected points in the map into the batch point file. Id source feature classes have Name and Description attributes, they area assigned to the batch points Delineate Batch Points Takes points from batch point feature class and uses them to do basin subdivision. BatchDone and SnapOn attributes to control snapping

17 Bach processing Topo-DEM Batu Dam Klang Gate Dam

18 Bach processing SRTM-DEM

19 Bach processing SRTM-DEM

20 Improvement of Derived basin binderies based on the Bach processing using two sources of DEMs Delineated boundaries from SRTM-DEM Delineated boundaries from Topo-DEM Main rivers Diversions VIPs

21 Extracting sub-basin database for KRB

22 Comparison o of some basic parameters a e r from two sourceso u r c e s Topo-DEM30 SRTM-DEM30 Name Perimeter km Elevation m Slope Perimeter % Area km 2 km Elevation m Slope % Area km 2 s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s Min Max Avg STDEV Sum * * * * * * 4

23 Nash-Sutcliff Efficiency (NSE) coefficient (Nash and Sutcliffe, 1970) Where : Elevation, Area, Perimeter or slope derived from SRTM-DEM : Elevation, Area, Perimeter or slope derived from Topo-DEM : Mean Elevation, Area, Perimeter or slope derived from Topo-DEM NSE efficiency coefficient for elevation, area, slope and perimeter Elevation Area slope Perimeter

24 Conclusions: Nash-Sutcliff Efficiency (NSE) coefficients indicate similarity about 97%, 84%, 72% and 99% for basin area, perimeter, slope and centroid elevation respectively, when considering Topo-DEM as reference. From the analogy of two source of elevation dataset, this is drawn that SRTM-DEM can explain the Topo-DEM by 88 percent, which is reasonable estimation for such a large watershed. As can see in figure 3, delineated basin boundary using SRTM- DEM in flat urban areas are not as good as no urbanized areas. In particular, sub-basin s19, s23, s26, s27, s28, s31, s32 and s33 that are all situated in highly developed urban area, illustrate the largest discrepancy compared to the sub-basin boundary delineated by Topo-DEM. Good agreement is found for the area with high relief mostly in mountainous areas.

25 u Develop HMS inputs from GeoHMS u HMS Schematic u Basin Model u Background Map File u Grid Cell Parameter File

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27 5-10 July 2009, Kyoto University, Kyoto, Japan Assemble an HMS model

28 Running HEC-HMS

29 Showing the results

30 Thank you