Rick Faber CE 513 Watershed and Streamwork Delineation Lab # 3 4/24/2006
1. Objective & Discussion: 2 To learn to use the ArcHydro tools to produce hydrologically descriptive data sets starting from a DEM. Some of these data sets include: drainage lines, catchment extent, stream definition, and watershed delineation. 2. Major Steps Utilized in this Lab 1. DEM Reconditioning impose linear features on DEM, (burning/fencing) 2. Fill Sinks remove sinkholes (what if there really is one?) 3. Flow Direction calculate the steepest slope & direction 4. Flow Accumulation How many pixels flow into this pixel, i.e. how many upstream pixels. 5. Stream Definition threshold for defining area that would typically represent a stream 7. Catchment Grid Delineation - which stream segment this pixel drains to 8. Catchment Polygon Processing convert catchment grid into a catchment polygon feature 9. Drainage Line Processing Convert stream link raster into Drainage line vectors feature 10. Adjoint Catchment Processing Catchments for all outlet points i.e. the aggregated upstream catchments 11. Drainage Point Processing drainage point feature class for all catchments. I.e. the outlet of each catchment 12. Drainage Density Evaluation Streams per area calculations & comparisons. Watershed Processing 1. Batch Watershed Delineation Delineate watersheds from a point feature class. 2. Interactive Point Delineation Delineate watershed from a single interactive point. 3. Batch Subwatershed Delineation Calculate subwatersheds for a point feature class. 4. Flow Path Tracing trace the path water would flow from any given direction. 3. Flow Chart of Major Steps The ArcHydro tools flow just down the Terrain Processing Menu:
3 4. Lab Questions: 1. Cell size, Number of rows and columns of smdem, maximum and minimum elevation values in smdem. 1 pt Cell 100m, 1300 columns, 818 rows. Elevation ranges from 70 to 618m
2. Layout with a depiction of topography either with contours or hillshade in nice colors. Include the streams from NHD. Mark your point of highest elevation and indicate its elevation. 5pts 4 San Marcos Watershed This map shows the general features of the San Marcos watershed. The point of highest elevation in the watershed is indicated, and the district topography differences between the eastern & western portions of the watershed are very noticeable.
3. Make a screen capture of the attribute table of Fdr and give an interpretation for the values in the Value field using a sketch.2 pst 5 Screen shot showing the Attribute Table of Flow Direction Table shows direction values 1,2,4,8,16,32,64,128 and the count. As the basin flows generally southeast, you notice the small number of NE (32) direction pixels. For a given cell, the flow directions are coded as: I.e. if the flow direction from one cell is to the cell just below it, it is given a value of 4. 32 64 128 16 1 8 4 2 4. Report the drainage area of the San Marcos basin in both number of 100 m grid cells and km2 as estimated by flow accumulation. 353180 100m 2 grid cells = 3531.8 km 2 Report the omitted drainage area assumed due to imprecise delineation at the location indicated on the southern edge, in both number of 100 m grid cells and km2. 2pts 754 100m 2 grid cells = 7.54km 2
6 5. A layout with a comparison of the generated DrainageLine and the NHD river network for San Marcos. Make comments on this comparison and suggest ways to improve the match between them.5pts 59
6. How many DrainagePoints, DrainageLines and Catchments are there? 7 116,116,116 What is the ID field in each feature class that associates the appropriate DrainagePoint with its DrainageLine and Catchment? GRIDID Make a graphic showing how one associated DrainagePoint, DrainageLine and Catchment are related.3pts DrainagePoint, DrainageLine & Catchment Associations This plot shows the GridID of the indicated features. The Drainage point relationship to the catchment and the Drainageline become obvious 7. Report the drainage area of the San Marcos basin in km2 estimated from both the DEM flow accumulation and subbasin HUC. 3531.8 km 2 vs. 3538 km 2 respectively. (3520 from the Adjoint catchment calculation) Report the length of streams in the San Marcos basin in km from both the DEM delineated drainage lines and NHD flowlines. 567 km vs. 1892 km respectively Calculate the drainage density (length/area) in km/km2 for both the DEM delineated drainage lines and NHD flowlines. Use the area that you feel is most appropriate. Comment on reasons for the differences in drainage density.5pts DEM: 567 km / 3531.8 km 2 = 0.30 km/ km 2 NHD(HUC): 1892 km / 3538 km 2 = 0.53 km/ km 2 The NHD flowlines are much denser. We chose a Stream definition area that was larger during the calculation of streams and all the subsequent calculations. Fewer streams for the same area. Again a tradeoff of accuracy vs. calculation performance.
8. Layout showing the delineated watershed for your selected outlet. Report the Drainage Area of the watershed you delineated in km2. 5pts (area in Map Text) 8
9 9. Layout showing the delineated watershed for each USGS Gauging Station. Label each watershed outlet with its contributing Drainage Area obtained from the Watershed Feature class. Prepare a table using Excel giving Name, USGS gage number, Watershed point HydroID, Watershed HydroID, Drainage area from ArcGIS (converted km2). 5pts Table of Watershed Info for the USGS gauging stations Gauge Name USGS guage # Watershed point HydroID Watershed HydroID Drainage Area from ArcGIS km^2 Blanco River At Wimberley Tx 08171000 520 519 921 Blanco River Nr Kyle Tx 08171300 522 521 1070 Plum Creek At Lockhart Tx 08172400 524 523 290 San Marcos R At San Marcos Tx 08170500 526 525 126 San Marcos River At Luling Tx 08172000 528 527 2178 This Table shows the Watersheds defined by the different USGS gauging stations in the study area. Note that the watersheds are not exclusive, that is the watershed for the point lowest on the river includes all of the watersheds above it. The table also shows the difference in HydroID s for the two feature classes. See page 10 for layout 10. Layout showing the delineated watershed for your point including the DrainageLine and Catchments See page 11 11. Layout showing the delineated subwatersheds the San Marcos stream gages and basin outlet point. Include the DrainageLine and the Catchments feature classes. See Page 12 Prepare a table giving Name, USGS gage number, and subwatershed area (converted km2) for each subwatershed. Show that the total area is the sum of subwatershed areas.5pts Table of Subwatershed Name,USGS ID & Area Name USGS Gauge # Subwatershed Area (km^2) Blanco River At Wimberley Tx 08171000 921 Blanco River Nr Kyle Tx 08171300 149 Plum Creek At Lockhart Tx 08172400 290 San Marcos R At San Marcos Tx 08170500 126 Outlet Point na 1063 San Marcos River At Luling Tx 08172000 980 Total Area of all Subbasins 3529 This table shows the gauging stations identities & corresponding subbasin area. The sum of the subwatershed areas are nearly identical to the area of the entire watershed as opposed to the watershed table above. 12. Layout showing the flow path for your selected point including the DrainageLine and the Catchments. See Page 13
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