12/19/2001 Env Bd Packet - Laserfiche WebLink

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Figure 5. A "planted wooded vegetative filter strip" by Pohiig Builders, Inc., Malvem, Pennsylvania. The gravel filled trench in the foreground acts as a level spreader. rain and phosphorus contained in dust, both accumulating through "atmospheric deposi- tion." Furthermore, there are automobile re- lated deposits: copper from brake linings, zinc from tire wear, lead, and other pollu- tants that, upon decomposition, consume oxygen. Runoff pollution has been found to be largely unaffected by frequent street cleaning activities and occurs in both down- town areas and in suburban settings (13). Runoff pollutants are most effectively con- trolled through the use of vegetation that can be planted to act as filter strips to slow down flows, induce sedimentation, convert nitrogen and phosphorus into plant tissue, and encourage infiltration and the related cleansing actions. Figur 5 shows a planted vegetative filter strip with woody vegetation, as advocated by the U.S. Department of Agriculture. Its root zone acts as a filtering device for below -ground lateral flows of nu- trient enriched groundwater (12). Much re- search on vegetative filters in the past has concentrated on grassy filter strips, but exist- ing woodlands are also reported to have a high trap efficiency for surface filtration (15). In residential areas filter strips can be seeded with a grass and wildflower mix to become an attractive wildflower meadow. Cori 11111fTherrnal pollution. Directly related to water quality is stream warming through urban runoff and the resulting re- duction of the water's oxygen-carrying ca- pacity. Drainage improvements often lead to the removal of riparian vegetation and result in a loss of shade. A study by the Metropoli- tan Washington Council of Governments 18 JOURNAL OF SOIL AND WATER CONSERVATION concludes that there is an average tempera- ture increase of 1.5 °F in headwater streams for every 30 m (100 ft) of flow through poorly shaded or open reaches of a stream (4). A 23 m (75 ft) buffer of vegetation on both sides of the stream can offset this prob- lem and offer the additional benefit of stormwater runoff filtration when used in conjunction with level spreading devices (Figure 6). Many management devices, such as impoundments that cause stream warm- ing, need to be shaded through planting. Stormwater management planning Proximity to open space, woodlands, fields, clean streams, and scenic views are among the reasons people give for moving to the suburbs. In a tragic way, urbanization tends to destroy many of these characteris- tics. As an example, the 2.6 million new resi- dents in the Chesapeake Bay Basin by the year 2020 are projected to be living mostly in low - density, large -lot developments with inefficient infrastructure and extensive im- permeable surfaces, all leading to an aggra- vation of current runoff problems (16). Stormwater management planning at the urban fringe, the area where most land use decisions are being made today, offers an opportunity to influence the pattern of new development in the suburbs by stitching to- gether linear open space systems that follow stream valleys to protect natural processes. This can be accomplished most productively on the municipal level through the formula- tion of a stormwater management plan re- flecting a three step process that starts with (1) an analysis of issues, (2) leading to the setting of standards, and (3) the passage of an ordinance containing a procedure to apply standards to development sites. Following the above steps, a stormwater management plan is currently being pre- pared for London Grove Township, Pennsyl- vania (10). Realization and analysis of issues On the local level, land use decisions are being made by elected officials. These are often laymen representing their constituen- cy, relying on the advice of the municipal engineer, the solicitor, and those serving on the planning commission. Stewardship for comprehensive water resource management is only possible when there are knowledge- able community leaders and an informed constituency. This can be accomplished through the preparation of a stormwater management plan, containing a survey of existing conditions and an analysis of prob- lems and opportunities, presented in a docu- ment that people can read to obtain back-