A Land Suitability Analysis for Williamson County, Texas
Prepared by the GeoLand Services Company
December 9, 2004
ABSTRACT
A land suitability analysis is a prerequisite for good sustainable land management practices. It involves the evaluations of several criteria ranging from soils, current land use, roads, population, rivers, slope and floodplains. In the fast growing pace of Williamson County Texas there was a need for a new suitability study. The primary focus of this project was to try to identify the best areas in Williamson County suitable for urban development, agriculture and recreation. ArcGIS 8.3 and spatial analyst extension were used to match the suitability of these land uses. Social and economic factors were excluded from the study. The study findings indicate that the western half part of the county is mainly suitable for urban development and the eastern half of the county is well suited for agricultural practices. Suitable recreation areas were found throughout the county.
Keywords
Land suitability, soil, land use land cover, urban development, agriculture, recreation ,GIS, spatial analyst, vector, projections, merge and clip, buffer, raster, cells reclassify, raster calculator.
Assessing the suitability of an area for a particular land use requires a considerable effort in terms of information collection that presents both opportunities and limitations to decision-makers (Ghaffari, Cook, Lee). Land use is a form of change that can be managed properly. For this reason GeoLand Services Company was asked by Dr. Lawrence Estaville of Texas State University to acquire data and do a GIS land suitability analysis management study. The region under study is Williamson County, which is located in east-central Texas. Irregular in shape, this county covers 426 square miles, about 720,640 acres (Werchan, Coker). Williamson County falls into a pilot study area along the Interstate Highway 35 (IH-35) corridor from the greater San Antonio area, served by the Alamo Area Council of Governments (ACOG) and the greater Austin area served by the Capitol Area Council (CAPCO).
Williamson County was selected for this study because it is one of the fastest growing counties in Texas and in the country. According to the Texas Water Development Board, the population of Williamson County will increase from approximately 200,000 in 1999 to an estimated 750,000 in 2050 (Volente). Because of this enormous population growth, there is an urgent need to classify the land into preferred urban development, agriculture and recreational uses.
Recently, voters approved more than 100 million dollars in bonds for green space acquisition in the Austin-San Antonio Corridor (Wender). This approval is directly linked to the new State Highway 130 that serves portions of Williamson County. It is obvious that local citizens wish to incorporate green space and avoid creating another I-35. Clearly, major development would target Williamson County where the new road construction has already started. Now is the time to give some thought as to how Williamson County should develop in the next decade while preserving the beauty of Central Texas.
A Geographic Information System (GIS) has been used to match the suitability for urban development, agriculture, and recreation areas based on particular criteria. GIS is an organized activity by which people measure and represent geographic phenomena, then transform these representations into other forms while interacting with social structures (Chrisman, 2003). ArcGIS is a vital tool for finding suitable areas for urban development, agriculture and recreation in Williamson County. The Spatial Analyst extension was necessary in order to do a raster analysis.
The goal of Geoland Services Company is to develop a spatial model in land evaluation for urban development, agriculture and recreation areas in Williamson County using GIS and other methods.
2. LITERATURE REVIEW
2.1 Urban Development
In the fast growing Williamson County, urban development is the citizens and business’ major interest. In order to identify the recommended agricultural and recreational land use areas effectively and realistically, it is necessary to predict the areas where the development might spread in the future first. Soils, floodplain and roads were the three criteria used in order to find the best suitable areas for urban development.
Soil is a very important component for development. In fact, soil analysis is necessary to determine whether a proposed building or house can be supported adequately (Building). One of the problems faced in building houses in Texas is the high percentage of clay in the soil composition. Clay is well known for the high shrink and swells potential in wet and dry conditions. Swelling soils are a major geologic hazard, and expansive clays and clay-shale cause extensive damage world-wide every year (Cires). In order to locate the best areas for development it was necessary to identify all the soil units of Williamson County. Therefore, the soil survey book of Williamson county Texas was used. This soil survey is an inventory and evaluation of the soils in the survey area. It can be used to adjust land uses to the limitations and potentials of natural resources and the environment. It can also help avoid soil-related failures in land use (Coker, Werchan). Furthermore, soil units can be used to determine the suitability and potential of a soil for specific uses, and can also be used to plan the management needed for those uses.
We also focused on Roads and Existing Urban Development in the research in order to observe where the future development might occur. Hoyt's Sector Model and Harris and Ullman Multiple Nuclei Model are two generalized urban structure patterns in America. Based on their models, a city would grow around already populated areas because of the existing infrastructure service or grow along roads for convenience ( Campbell).
Floodplain is another important component to be considered for urban development. Floods are the most common and widespread of all natural disasters--except fire. Most communities in the United States have experienced some kind of flooding after spring rains, heavy thunderstorms or winter snow thaws. According to the Federal Emergency Management Agency, a flood is: "A general and temporary condition of partial or complete inundation of two or more acres of normally dry land area or of two or more properties (at least one of which is your property) from:
Geoland Services Company decided to use floodplain as a component for the research in order to make the urban suitability more efficient. We did not want to find most suitable areas on top of a floodplain.
2.2 Agriculture
Most of the literature review used for this project came from the Soil Survey of Williamson County, Texas. This book was so comprehensive and specific to the area of our project, that other sources were virtually unnecessary. The information provided by this book was specific to every subject of concern to our project. There was not only information specific to the soils present in Williamson County, but also discussion of the soils’ relationship to land use. This book even stated issues concerning land use in Williamson County. The particular subjects I reviewed and used for the analysis of agriculture included Detailed Soil Map Units, Prime Farmland, Use and Management of the Soils, and Soil Properties. Two tables were used directly in the analysis:
Some research was also done on the Negative Population Growth Organization’s website. Their website provided some statistics on population growth in Texas and the occurrence of land use change. The website may be viewed at http://www.npg.org/states/tx.htm.
2.3 Recreation
Recreation land use in Williamson County is currently managed by many different administrators including the Lower Colorado River Authority, Texas Parks and Wildlife Department, Williamson County, the cities of Round Rock, Austin, Georgetown, Cedar Park, Pflugerville and Leander, the Cedar County United Soccer League and the Williamson County Park Federation. All of these agencies, municipalities and federations have a common goal, to provide for and make best use of recreation areas in Williamson County, Texas.
Recreation categories came from the United States Department of Agriculture publication Soil Survey of Williamson County, Texas. Information on soil stabilization comes from Enviroseal, a manufacturer of soil amendments and stabilizers, at www.enviroseal.com.