News Subscribe  to Our Newsletter Sign  up for Email Updates CGF  In the News Press  Inquiries Past  Articles Calendar			Cumulative impacts: when the whole is greater than the sum of its parts CGF receives grant to study impervious surfaces by Kathy Switky Some of the most challenging environmental problems  are known as "cumulative impacts," whose effects creep up on  us through the accumulation of small, often relatively insignificant impacts.  CGF has recently received funding to help manage some of these problems  locally by tracking and managing the accumulated impacts of impervious  surfaces in Santa Clara County. Waterways particularly vulnerable to cumulative  impacts  Cumulative impacts are among the most significant environmental problems  for watersheds, which by definition collect water - as well as pollutants,  erosion, physical barriers and other problems - from wide areas. The  accumulation of impervious surfaces is one of the cumulative impacts most  threatening to watersheds. Pavement, buildings and other changes to the  landscape that prevent water from entering the ground can lead to dramatic  changes in water flow patterns both above and below ground. The challenge  is that the effects of cumulative impacts are not immediately apparent  to decision-makers reviewing individual projects, each of which constitute  only a small part of a larger problem. For example, when a small house is replaced with a much larger home, its driveway is typically expanded to accommodate firefighter access. The permitting process might limit the increase in impervious surfaces only to keep that individual project from having a significant impact on its own, while ignoring the cumulative impacts created by the sum of many projects that add pavement to the watershed.  Paving paradise?  Scientific evidence indicates that high levels of impervious surfaces  in a watershed can have serious consequences, including accelerated erosion,  accentuated flooding and damage to biological systems and physical habitat. Given the pattern of increasing development in Santa  Clara County, we can expect that most or all watersheds in the county  are affected by increasing amounts of impervious surfaces.  But according to CGF's research, local governments  do not currently track the net change in impervious surfaces caused by  development, even though the data are readily available. Not a single  jurisdiction tracks countywide changes in impervious surfaces to see if,  when combined with changes from other projects, the cumulative impact  of paving over county watersheds is significant. CGF to develop methods for tracking cumulative  impacts In September, Committee for Green Foothills received funding from the Santa Clara Valley  Water District under its Watershed Stewardship Grant Program, which  awarded nearly $400,000 in grant funds to 19 local organizations to improve  ecosystem health, water supply and water quality. The $7,600 grant will allow CGF to study the usefulness  of tracking cumulative changes in impervious surfaces and develop methods  for managing them. With a policy report and follow-up workshops, we expect  to help local agencies develop planning processes that account for and  - when possible - mitigate the cumulative impacts from changes in impervious  surfaces. Published November 2004 in Green  Footnotes. Page last updated November 8, 2004 .

	Photo by Kathy Switky.