1. 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)

2. Lake Travis
Bull Creek Watershed
ERSI Imagery with NHD Streams

3. ArcGIS generated Hillshade Layer

4. 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

5. 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….

6. 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 = km^2
Area = km^2
30 m DEM
51 Catchments
10 m DEM
52 Catchments

7. 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

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

9. 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

10. Rainfall Event in November, 2004

11. NEXRAD Data Provided by Dan Yates, LCRA
Data Source – National Weather Service – West Gulf River Forecast Center
NWS archive –
NCDC Java NEXRAD Tools –

12. 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 -

13. Nexrad Grid – Nov. 14 – 17, 2004 Bull Creek Watershed
0 – 0.37
0.37 – 1.02
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

14. 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

15. 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

16. 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

17. 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

18. 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