Urbanization factors in the Gilleland Creek watershed, Travis County, Texas Michael Kanarek GEO386G Final Project Dec. 2, 2011 1
Introduction The watershed of Gilleland Creek, which flows through eastern Travis County, Texas, contains a number of urbanized environments, including residential and industrial areas, and high-traffic roadways. Given these features, the stream is almost certainly influenced by urban recharge, including leaking water and wastewater lines, as well as potential contamination from these sources and surface runoff. Since Gilleland Creek is a tributary of the Colorado River, an important source of municipal water and recreation in Texas, maintaining its quality is of paramount importance. Hypothesis In order to protect the water quality in Gilleland Creek, it is important to understand the potential impacts of urbanization on the watershed. To this end, data on land development, hydrographic features, streets, and water and wastewater from local governments will be used to quantify what parts of the watershed are most urbanized and what locations are likely sites for future manmade development. 2
Data Collection Data for this project was obtained from the Capital Area Council of Governments Information Clearinghouse (www.capcog.org/information-clearinghouse/geospatial-data) (Figure 1) and the City of Austin s GIS Data Sets (ftp://ftp.ci.austin.tx.us/gis-data/regional/coa_gis.html) (Figure 2). Geodatabases containing data on city limit boundaries, hydrography, and the Land Fragmentation Analysis 2008 (detailing information on vacant and non-vacant land) was obtained from CAPCOG. The City of Austin provided shapefiles on streets and watersheds at the ftp site listed above. Shapefiles detailing water and wastewater lines were obtained by accessing the city water utility s secure ftp site. Figure 1: The website for the Capital Area Council of Governments Information Clearinghouse provides a wide variety of data on Bastrop, Blanco, Burnet, Caldwell, Fayette, Hays, Lee, Llano, Travis, and Williamson counties. Figure 2: The City of Austin GIS Data Sets website provides data on Austin and parts of Travis County. 3
ArcGIS Processing Using the Batch Project script of ArcToolbox within ArcCatalog, the data for city limits, hydrography, the 2008 Land Fragmentation Analysis, streets, watersheds, water lines, and wastewater lines were projected from NAD83 Texas Central State Plane Feet to NAD83 UTM Zone 14N into a new geodatabase. (Figure 3) Figure 3: The Batch Project tool within ArcToolbox allows for the quick processing of multiple data sets into a new, unified projection system. 4
The projected data was then loaded into a new map in ArcMap. The maps for Travis, Williamson and Bastrop counties from the Land Fragmentation Analysis 2008 were added and symbolized to indicate vacant and non-vacant land. (Figure 4) This data was then further simplified (in order to reduce the many small polygons representing densely packed housing developments) using the Dissolve tool from Data Management Tools in ArcToolbox. Figure 4: Within the Land Fragmentation Analysis 2008 data set, parcels were symbolized to indicate vacant ( Y ) and non vacant ( N ). The color scheme was later changed for the final map. 5
Lake and river data were then added and symbolized appropriately. The same was done for Austin/Travis County streets, water and wastewater lines, and city boundaries (current as of January 2011). The Watersheds data was then added to the map, with Gilleland Creek singled out and emphasized. (Figure 5) Figure 5: From the watersheds data set, Gilleland Creek was the only one displayed and highlighted to emphasize the area. 6
Watershed Analysis The shape area was calculated using the attribute table for the watersheds layer, indicating that the Gilleland Creek watershed is 89154171 m2 (~89 km2) in size. To determine the total length of Gilleland Creek and all contributing streams within the watershed, the Select By Location function within ArcMap was used. (Figure 6) Streams within the boundaries of the watershed were selected using Target layer(s) features are within the Source layer feature as the Spatial selection method. Figure 6: The Select By Location function was used to isolate streams within the watershed. 7
Then by using the Statistics function for the selected features within the river layer attribute table, the total length of streams was determined to be 174088 m. (Figure 7) The same procedure was used to determine the amount of streets within the watershed, with a total of 355213 m. Again, this procedure was repeated to determine the amount of water and wastewater lines within the watershed. By this method, there are 141909 m of water lines and 101914 m of wastewater lines. Figure 7: The statistical summary within the data table revealed the total length of the selected streams, the ones within the watershed. 8
To determine what parts of the watershed are classified as vacant land vs. non-vacant land, first the Select by Location function within ArcMap was used to select all parcels that fall at least partly within the watershed. (Figure 8) Figure 8: Select By Location was used to highlight all parcels that exist at least partly within the watershed. Here they are highlighted in blue. 9
Then, using the Clip tool within the Analysis Tools of ArcToolbox, these parcels were clipped to the portions that only fall within the watershed. The Select by Attributes function of ArcMap was then used to find the areas within the watershed that are vacant or non-vacant land. (Figure 9) Figure 9: The Clip tool was used to narrow land parcels to just what exists within the watershed. Data Summary Category Streams Roads Water lines Wastewater lines Category Total watershed area Vacant land Non-vacant land Total length (m) 174088 355213 141909 101914 Area (m2) 89154171 57594348 31559823 Percent of total 64.6 35.4 10
Results and Conclusions By analyzing the data provided, trends begin to emerge. The headwaters of the Gilleland Creek watershed are much more heavily urbanized than the southern reaches. (Figure 10) And with the 2007 opening of Highway 130 right through the middle of the watershed, further urbanization is all but guaranteed near this new roadway. Figure 10: The more heavily urbanized northern portion of the Gilleland Creek watershed. 11
However, the limitations of this data must also be realized. While road data is consistent throughout the county, the only available data for water and wastewater lines was through the City of Austin utility, neglecting the communities of Round Rock, Pflugerville, and Manor. Portions of all of these municipalities exist within the watershed, but they did not have any readily available data. (Figure 11) Figure 11: The blue highlighted areas are segments of wastewater lines within the watershed contained in the data set. But the pink and black areas are urbanized (and sometimes heavily urbanized) areas that do not get their wastewater service from the City of Austin and are thus not represented in the data. Conclusion Gilleland Creek is only moderately urbanized at the present time; however, the potential exists for continued urbanization within the watershed. Further work on this watershed is recommended to identify potential hot spots for contamination, etc., and monitor how urbanization is impacting the area. A finalized map can be found on the next page. 12
624000 Gilleland Creek Watershed, Travis County, Texas 628000 632000 636000 640000 644000 3372000 3372000 ROUND ROCK PFLUGERVILLE Watershed boundary Roads Wastewater lines 3366000 3366000 35 Gilleland Creek Water lines Gilleland Creek (emphasis added) Other rivers/streams V U 130 MANOR 35 3360000 3360000 Lakes Non-vacant land Vacant land 290 Area shown 290 624000 3354000 V U 130 Gilleland Creek 628000 632000 636000 640000 3348000 AUSTIN 3348000 3354000 644000 ± 1:150,000 Datum: NAD83, UTM Zone 14N