Elaine B. Darby GIS – Fall 2005 Bull Creek Watershed Elaine B. Darby GIS – Fall 2005 Direction Provided by Dan Yates, Lower Colorado River Authority (LCRA)

Lake Travis Bull Creek Watershed ERSI Imagery with NHD Streams

ArcGIS generated Hillshade Layer

Data Gathering & Processing 10 m & 30 m DEM’s Downloaded from USGS Seamless server 10 m DEM clipped for Bull Creek Watershed 30 m DEM extent masked to 10 m DEM NHD Streams & Waterbodies (1:24,000) LCRA Hydromet Gauging Stations NEXRAD Data – Nov, 2004

Bull Creek Watershed Agree DEM based on 10 m DEM & NHD Streams LCRA Hydromet Gauges Define how this map was generated – 10 m DEM using surface terrain – Agree DEM, fill sinks, etc….

Watershed Delineation 30 m DEM on the left has 51 catchments; 10 m DEM has 53 catchments Delineation differences from thresholds – default values = 1% of maximum flow accumulation for 10 m DEM = .81 km^2 vs 0.83 km^2 for 30 m DEM Area = 4.553 km^2 Area = 4.475 km^2 30 m DEM 51 Catchments 10 m DEM 52 Catchments

Bull Creek Watershed Analysis Bull Creek Watershed Analysis Area Analysis by DEM Bull Creek Watershed Analysis DEM Catchment (km^2) Drainline (km) 30 m 82.57 70.513 10 m 82.26 71.541 Bull Creek Watershed Analysis DEM FAC Cells Cell Size Area (km^2) 30 m 116,119 26.7 X 26.7 82.78 10 m 798,236 10.1 X 10.1 81.43 1.7% Difference

Drainlines vs NHD Streamlines NHD Streamlines - Blue Default Threshold = 0.81 km2 Threshold = 0.3 km2 Threshold = 0.2 km2

Bull Creek Watershed Analysis Total Area of Catchments (km^2) Stream Threshold Analysis based on 10 m DEM Threshold (km^2): No. of Catchments Total Area of Catchments (km^2) 0.81 52 82.26 0.3 142 82.27 0.2 205 82.51 0.1 396 83.28

Rainfall Event in November, 2004

NEXRAD Data Provided by Dan Yates, LCRA Data Source – National Weather Service – West Gulf River Forecast Center NWS archive – http://dipper.nws.noaa.gov/hdsb/data/nexrad/wgrfc_stageiii.php NCDC Java NEXRAD Tools – http://www.ncdc.noaa.gov/oa/radar/jnx

Old Spicewood Springs Road NEXRAD Data in GIS Old Spicewood Springs Road Loaded NEXRAD vector files into GIS and added county boundaries – Travis County is highlighted Photos are taken from Bull Creek Watershed Photos from Bull Creek Foundation - www.bullcreek.net

Nexrad Grid – Nov. 14 – 17, 2004 Bull Creek Watershed 0 – 0.37 0.37 – 1.02 1.02-1.70 1.70 – 2.35 5.7 inches 2.35 – 2.94 2.94 – 3.53 3.53 – 4.12 4.12 – 4.70 4.70 – 5.29 5.29 – 5.99 5.99 – 6.84 6.84 – 7.91 7.91 – 9.14 9.14 – 10.6 10.6 – 13.6 6.0 inches

LCRA Hydromet Gauges Jollyville SW2 Bull Creek at 360 November 14 – 17 ,2005 Jollyville SW 2 5.80 inches Bull Creek at 360 6.12 inches

NEXRAD Stage III Data Stage III – based on reflectivity measurements merged with surface rain gauge observations Hourly precipitation – mm/hr – 4 km2 Grid based data Hydrologic Rainfall Analysis Project (HRAP) projection

NEXRAD Projections Polar Stereographic map projection Spherical Earth vs. Ellipsoidal East-West distances distorted relative to North-South distances Ref. CRWR Online Report 95-3 A GIS Procedure for Merging NEXRAD Precipitation Data and Digital Elevation Models to Determine Rainfall-Runoff Modeling Parameters (1995) By Seann M Reed and David R. Maidment

Large data sets – use algorithms NEXRAD  GIS Reed, Maidment (1999) & Xie, Zhou, et. al. (2005) Algorithms to perform coordinate transformations to mesh NEXRAD and DEM NCDC Java NEXRAD Tools Vector and Raster Grid Export Options Programs: Two simple programs are available that can be used to generate an Arc/Info polygon coverage of HRAP cells for any user defined region of the country. In Netscape, clicking on any of the filenames below will allow you to view the text. You can also save these text files to your local disk by choosing: "File", "Save As." GENHRAP.F : FORTRAN 77 source code that writes a file of coordinate values used to create a polygon coverage of NEXRAD cells in geographic coordinates given a user specified geographic extent. This code has been compiled and executed using an F77 compiler on a Sun UNIX system. Compatibility with other compilers is unknown. "Genhrap.f" creates four output files: "hrap.xxx","geoc.xxx","hrap.xxx.dat", and "inputgc.xxx." Only the files "hrap.xxx.dat" and "inputgc.xxx" are needed as input to the program "genhrap.aml." GENHRAP.AML : An Arc/Info script written in Arc Macro Language (AML) that creates a polygon coverage of HRAP cells in geographic coordinates given the output from genhrap.f, projects these cells using a user specified projection file, and attaches the appropriate HRAP-ID values to the projected coverage. "Genhrap.aml" uses the file "inputgc.xxx" to generate a polygon coverage and "hrap.xxx.dat" to add HRAP coordinates as attributes to this coverage. "Genhrap.aml" produces a coverage of HRAP Cells in your chosen projection called "xxxgeoccprj." "xxx" refers to a user specified suffix. View a Sample Session Using these Programs In this session, user input is presented in bold text. An image of the results from this sample session may be viewed by clicking here. Large data sets – use algorithms

CONCLUSIONS 10 m vs 30 m DEM – Catchment Areas NEXRAD data Very small difference for Bull Creek Watershed No substantial difference in drainage area using 1% default threshold and ¼ % threshold NEXRAD data Integration into GIS can be done using transformation programs