Impervious surfaces generate runoff that creates increased flooding, erosion, and water pollution issues for urban communities and their surrounding environments. Further, combined sanitary and storm water sewer systems currently used in many older cities result in greater pollution and environmental degradation. Knowing the extent of a community’s impervious surfaces can help to locate areas that may benefit from Best Management Practices. As communities grow, they are confronted with the challenges of building and maintaining infrastructure to store and treat excess volumes of storm water. In metropolitan areas across the United States, construction costs for storm water management facilities developed during the last 20 years have been estimated at over $1.4 billion.
In many communities an accurate assessment of impervious surfaces is the baseline measure of landscape impacts on water quality. Governments and Utilities interested in preventing and / or mitigating negative impacts of urbanization on water resources need to know the location and extent of impervious surfaces, their relationships to the water cycle, their impacts on waterways, and the ways that this relationship can be understood to better manage storm water plans and costs. Many municipalities have developed storm water utility billing systems that assess a fee based on the amount of impervious surface per parcel or customer to help optimize revenue and offset the increasing costs of storm water management. Such fees and other best management practices (BMPs) are also designed to offer incentives to reduce at the source the volume of storm water entering the ecosystem.
Applications For Impervious Surface Calculation
- Hydraulic and hydrologic modeling
- Modeling storm water
- Predicting non-point source water pollution loads
- Developing storm water remediation plans
- Assessing storm water utility fees
- Measuring urban development/build-out analysis
- Assessing and monitoring watershed health
- Watershed modeling
- Urban planning and land use planning
- Implementing an array of strategies and best management practices for reduction of stormwater apart from centralized structural solutions.
Sanborn Impervious Surface Calculation Products
Sanborn offers two primary products designed to provide the baseline data needed to meet any impervious surface mapping challenge. Our products have been proven in planning and land management applications in communities across the United States.
This manual approach is the traditional way of creating impervious surface maps and typically involves compilation of planimetric features such as roads, building, parking lots, driveways, sidewalks etc., using 2D or stereo heads-up digitizing techniques. This approach is suitable for smaller geographies such as a City or a County. However, it tends to be cost prohibitive at the regional scale. It can also be expensive if frequent updates are required.
This approach leverages software techniques to recognize impervious surfaces based on color, texture, size, shape and pattern. Analysts “train” the software to recognize different types of impervious surfaces and then to find areas in the data that have similar characteristics or properties. After impervious areas have been identified automatically, an analyst manually reviews / edits areas that appear to be impervious surfaces but are not (i.e. baseball diamonds, agricultural fields with high reflectance, etc.). This approach is more cost effective than the planimetric approach, more time-efficient, and lends itself better to general change detection (i.e., identification of new impervious areas). The product derived using this approach is primarily a raster product and results in a somewhat different appearance than if using traditional planimetric methods. The remote sensing process produces an impervious layer for a community’s GIS that quantifies impervious surfaces for the entire community’s area of interest. This data layer can then be summarized by any set of GIS polygons.
The manual approach can be implemented using analog or digital imagery, while the automated approach can be implemented with 3-band digital imagery (either color infrared or true color). For best implementation results for semi-automated products (which require less manual editing), 4-band imagery, which includes the color infrared band, is preferred. In addition, imagery must be orthorectified and should be acquired during “leaf-off” conditions.