1. From GIS to HMS
U.S. Army Corps of Engineers Hydrologic Engineering Center
University of Texas at Austin Center for Research in Water Resources
Francisco Olivera Aubrey Dugger David Maidment Edward Holley

2. Overview Digital Elevation Model (DEM) Hydrologic Parameters
Precipitation Data
GIS to HMS
HMS
Hydrograph

3. Digital Elevation Model (DEM)
DEM of the Upper Cedar River in Iowa.
Cell size: 500 m

4. Flow Direction
Water flows to one of its neighbor cells according to the direction of the steepest descent.
Flow direction takes one out eight possible values.

5. Flow Accumulation
Flow accumulation is an indirect way of measuring drainage areas (in units of grid cells).

6. Stream Definition
All grid cells draining more than 250 cells (62.5 Km2) are part of the stream network.

7. Stream Segmentation
Stream segments (links) are the sections of a stream channel connecting two successive junctions, a junction and the outlet, or a junction and the drainage divide.

8. Watershed Delineation
All grid cells flowing towards a specific stream segment (link) constitute its watershed or drainage area.
The watershed grid is then converted from raster into vector.

9. Dissolving Watershed Polygons
Dangling polygons should be dissolved into any of its adjacent (through the side) polygons.

10. Watershed Parameters Length of main channel L (ft)
Slope of main channel s (%)
Average curve number
Lag time tc (min) (SCS 1973):

11. Watershed Parameters

12. Stream Parameters
Muskingum steps
Muskingum K
Muskingum X

13. Stream Parameters

14. HMS Basin File
The output of HECPREPRO is a text file that serves as the HMS Basin File (input).

15. Hydrologic Elements Structure
Hydrologic elements structure showing subbasins, reaches, junctions and sinks.

16. Hydrologic Elements Structure
Detail of the hydrologic element structure.

17. Theissen Polygons
A Theissen polygon is defined for each precipitation station.

18. Theissen and Subbasin Polygons
Theissen polygons intersected with subbasin polygons.
Each polygon of the resulting coverage belongs to only one Theissen polygon and only one subbasin polygon.

19. Theissen and Subbasin Polygons
Attributes of the subbasins are attached to the resulting coverage by joining the attribute tables.

20. Watershed Precipitation
The watershed precipitation is the weighted average (according to the Theissen polygons) of the precipitation recorded at the neighbor stations.

21. GageWts.precip file for HMS

22. Precipitation Input File for HMS in DSS Format

23. HMS - Basin Hydrograph

24. HMS - Reach Hydrograph

25. Observed vs. Compared

26. Observed vs. Compared

27. Conclusions The connection between GIS and HMS has been developed.
Sub-basin attributes can be transferred.
Problems transferring reach attributes.
Model calibration necessary to estimate hydrologic parameters.