From Greenscapes to Hardscapes

A study of tree canopy and impervious surface in the Metro Atlanta area Study Reveals Alarming Trend
Upper Chattahoochee Riverkeeper partnered with the University of Georgia in a study to create the firstever data set of tree cover and impervious surface in the 16-county Atlanta metro area. The study mapped change over a ten year period, using satellite images taken in 1992 and 2001.

The results of this study showed a startling trend. The 16-county metro region is losing 54 acres of tree canopy, and building more than 28 acres of hard surfaces, every single day. Over this ten year period, daily loss has resulted in the cumulative destruction of at least 197,000 acres of trees and an increase of 103,000 acres of hard (impervious) surfaces.

Geographic Information Systems (GIS) Data
A grant from the Georgia Forestry Commission funded the creation of the GIS database by Dr. Elizabeth Kramer, Director, Natural Resources Spatial Analysis Laboratory (NARSAL) at the University of Georgia. The data generated by NARSAL is derived from Landsat TM and ETM+ imagery and maps both the percentage of impervious surface and forest canopy in 30 meter pixels (or 30 meter by 30 meter segments in each satellite scene). This new data is free and available to anyone on the Georgia GIS Clearinghouse and USGS websites. The data will allow local officials and planners to visualize trends in their regions and help municipalities make wise land use decisions as they confront growing development pressures.

To access this data visit: gis1.state.ga.us and seamless.usgs.gov

What does this mean for our watershed’s future?
Roads, parking lots and building rooftops all add to the hard, or impervious, surface that exists in our area. The land (or watershed) loses much of its ability to absorb rain when trees and plants are removed and hard surfaces are built. When this happens, rain collects oil, bacteria, sediment, grease and other pollutants and then washes into our rivers and streams, contaminating drinking water sources.

The amount of impervious surface in a watershed is directly related to the health of that watershed, and whether or not it will be able to continue to supply clean water to communities.  Generally when 10-15 percent of a watershed is covered by impervious surfaces, the increased sediment and chemical pollutants in runoff have a measurable affect on water quality.

What can we do?
In 2003, a Watershed Management Plan was approved for the Metro Water Planning District which requires local governments to adopt ordinances that control erosion from construction sites, stormwater runoff from paved areas, and protect stream buffers, and also allow conservation subdivisions that encourage protection of greenspace.

While some District counties have passed these ordinances, others still have not. Of course, passage of these regulations is just the first step; only enforcement will ensure clean water supplies.Talk to your local officials and urge them to take steps now, by adopting ordinances and incentive programs that protect clean water and, most importantly, by enforcing all clean water laws. Future generations depend on the actions that we take today.