Updated Land Cover Information for Water and Environmental Management in Urban Areas

Abstract

The continuing trend of urban growth and development creates the need for updated ground cover information for a wide range of applications. Some applications relate to models used in hydrologic, water quality control, and watershed management while other applications respond to specific needs of urban managers. The results presented here are the outcome of work carried out during the last two years for the cities of Springfield and Columbia, Missouri using high spatial resolution satellite data. The challenge that had to be met was to determine the usefulness and limitations of these data sets to enhance or effectively replace conventional data sources. Panchromatic air photos are the most common source of spatial information by urban managers. In some cases photos acquired by federal agencies are inexpensive information sources, however, in many cases municipalities have to contract new air photo coverage or use the new generation of satellite images to satisfy their needs. Airphotos have been replaced by satellite image data for large area (regional scale) mapping because of the multispectral characteristics, digital format and low cost per area of the latter. New satellite image data with spatial resolutions ranging from 5 to 1 meter provide a new data option for selected applications. The subject discussed in this paper is the application of this type of satellite image data for mapping impervious and bare ground surfaces, and for determining runoff curve numbers (CNs) required by hydrologic and environmental computer models. The area covered by impervious surfaces in urban regions does not remain constant in urban centers. Whenever a new development takes place, the total impervious surface increases with a direct impact on the amount of runoff into stormwater systems and urban watersheds. High spatial resolution images can provide mapping of impervious surfaces (parking lots, rooftops, roads, etc) with an estimated accuracy of approximately 80% that is satisfactory for planning and monitoring purposes. Mapping areas where the soil is exposed is another capability desired by urban managers. Exposed soil can indicate construction sites with implications for the control of building permits, changes in the municipal tax base and identification of potential sources of sediments runoff to water bodies, an environmental issue. The accuracy of construction site determinations in Columbia is more than 90%.