03/04/1996 Park Board Packet - Laserfiche WebLink

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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 t r s z �� ;•i. ? as impoundments that cause stream warm- ing,4 a need to be shaded through lantin 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- ", +'•' �- r .^ ,�'i. ,, tics. As an example, the 2.6 million new resi- dents in the Chesapeake Bay Basin by the Figure 5.A"planted wooded vegetative filter strip"by Pohlig Builders, year 2020 are projected to be living mostly Inc.,Malvern,Pennsylvania.The gravel filled trench In the foreground in low-density, large-lot developments with acts as a level spreader, inefficient infrastructure and extensive im- permeable surfaces, all leading to an aggra- vation of current runoff problems (16). rain and phosphorus contained in dust, both Stormwater management planning at the accumulating through "atmospheric deposi- urban fringe, the area where most land use tion." Furthermore, there are automobile re- decisions are being made today, offers an lated deposits: copper from brake linings, opportunity to influence the pattern of new n zinc from tire wear, lead, and other pollu- development in the suburbs by stitching to- tants that, upon decomposition, consume gether linear open space systems that follow oxygen. Runoff pollution has been found to stream valleys to protect natural processes. be largely unaffected by frequent street This can be accomplished most productively cleaning activities and occurs in both down- on the municipal level through the formula- town areas and in suburban settings (13). tion of a stormwater management plan re- Runoff pollutants are most effectively con- flecting a three step process that starts with trolled through the use of vegetation that (1) an analysis of issues, (2) leading to the can be planted to act as filter strips to slow setting of standards, and (3) the passage of down flows, induce sedimentation, convert an ordinance containing a procedure to nitrogen and phosphorus into plant tissue, apply standards to development sites. and encourage infiltration and the related Following the above steps, a stormwater cleansing actions. Figure 5 shows a planted management plan is currently being pre- vegetative filter strip with woody vegetation, pared for London Grove Township, Pennsyl- as advocated by the U.S. Department of vania (10). Agriculture. Its root zone acts as a filtering device for below-ground lateral flows of nu- Realization and analysis of issues trient enriched groundwater (12). Much re- search on vegetative filters in the past has On the local level, land use decisions are concentrated on grassy filter strips, but exist- being made by elected officials. These are ing woodlands are also reported to have a often laymen representing their constituent- high trap efficiency or sur ace i tration cy, relying on the advice of the municipal (15). In residential areas filter strips can be (engineer, the solicitor, and those serving on seeded with a grass and wildflower mix to the planning commission. Stewardship for become an attractive wildflower meadow. comprehensive water resource management Co amUftbermal pollution. Directly is only possible when there are knowledge- related to water quality is stream warming able community leaders and an informed through urban runoff and the resulting re- constituency. This can be accomplished duction of the water's oxygen-carrying ca- through the preparation of a stormwater pacity. Drainage improvements often lead to management plan, containing a survey of the removal of riparian vegetation and result existing conditions and an analysis of prob- in a loss of shade. A study by the Metropoli- term and opportunities, presented in a docu- tan Washington Council of Governments ment that people can read to obtain back- . 1a JOURNAL OF SOIL AND WATER CONSERVATION