In performance-based zoning, developers are allowed flexibility in planning and designing the development as long as they meet minimum requirements set by the local government. These minimum requirements vary based on the particular resource protection objectives of the
community but might include limiting the amount of impervious surfaces or preserving sensitive features such as wetlands or steep slopes with high erosion potential. Developers can choose lot sizes, building types, site layouts, and other development characteristics as long as they meet the minimum criteria. Performance-based zoning offers protection of natural resources for the
community and increased flexibility for the developer. It requires greater effort on the part of the local government, however, to carefully tailor the language of the ordinance to ensure that
resources are adequately protected, and to carefully review development proposals to ensure that performance criteria are met.
Officials in Columbia, Missouri, were interested in developing a uniform policy to deal with
storm water pollution (Tritto, 2000). This effort was initiated in response to a recent back-and-forth battle between a developer and the Columbia City Council. Officials are reviewing a report
developed by Missouri University researchers that evaluated the environmental sensitivity of 13 watersheds in the Columbia area using 12 criteria focused on human health and
environmental protection. The report recommended limits on the percentage of impervious surfaces for developments based on categories of watershed sensitivity. Developers would be allowed to exceed these limits only by taking additional steps to control storm water pollution through the use of management practices. The approach recommended in the report would
provide a financial incentive for developers to direct high-density developments to less-sensitive watersheds because tougher standards on impervious areas and the costs of storm water controls would make it more expensive to develop in environmentally sensitive watersheds. City officials are also reviewing storm water management policies in other cities to develop uniform guidelines so that developers are better-informed about what is expected of them.
3.3.3.3.1 基于性能的分区
以性能为基础的分区是指只要符合当地政府规定的要求，开发人员可以灵活地规划和设计发展。这些最低要求根据不同的特定资源保护目标,但可能包括限制数量的不透水表面或保持敏感高的特性,比如湿地或陡峭的斜坡侵蚀潜力。开发人员可以选择很多种类、建筑类型、网站布局等发展特点,只要他们满足最低标准。绩效分区提供了自然资源的保护开发者社区和提高灵活性。基于性能的分区提供了自然资源的保护开发，并提高灵活性。它需要更大的努力，因此,当地政府仔细调整条例,以确保的语言资源被充分保护,仔细检查以确保发展建议符合性能标准。
密苏里州哥伦比亚官员致力于制定一个统一的政策处理雨水污染。(Tritto, 2000)这一努力是为了应对最近的开发人员和哥伦比亚市议会之间的拉锯战。官员正在评估报告由密苏里州大学的研究人员开发的评估13处水域的环境敏感性在哥伦比亚地区使用和关注人类健康和环境保护标准。报告建议限制不透水表面的百分比为提高基于类别的分水岭敏感度。开发人员将只允许超过这些限制通过采取额外的步骤来控制雨水污染通过使用管理实践。该报告中推荐的方法提供财务激励直接高密度发展敏感度低的水域,因为严格的标准不受地区和雨水的成本控制将使它更昂贵的开发环境敏感水域。城市官员也回顾在其他城市雨水管理政策发展统一指南,开发人员会对预期目标有更好的信息来源。
3.3.3.3.2 Overlay zones
Overlay zones superimpose additional restrictions on existing zoning categories to provide extra protection for a particular natural resource. For example, if a wetland or endangered species habitat crosses the boundaries of several development zones, an overlay zone can be established to limit development in areas that affect the wetland. Overlay zones can also be used to limit development in areas with highly permeable soils to protect an underground drinking water source from contamination. The overlay zones would maintain the general land use category, such as residential or commercial, but would require additional protection, such as greater limits on impervious area or special vegetation protection requirements.
3.3.3.3.2 覆盖区域
现有覆盖区域分区类别提供额外附加的限制保护自然资源。例如,如果一个湿地或濒危物种栖息地跨越几个开发区的边界,可以建立一个覆盖区限制开发区域。覆盖区域也可以用来限制发展地区的高度渗透性土壤保护地下饮用水源免受污染。覆盖区域将保持土地利用总体类别,如住宅或商业,但需要额外的保护,如更大的限制在不透水区域或特殊的植被保护的要求。
3.3.3.3.3 Bonus or incentive zoning
Bonus or incentive zoning is another method to allow developers greater flexibility in return for preservation of open space and sensitive or environmentally significant features. With incentive zoning, a developer might be allowed to develop at a higher density than normally allowed if in return he or she preserves additional open space, creates a wetland, or reduces the site’s overall impervious area with underground parking, transportation modifications, or innovative site layouts. The success of bonus or incentive zoning is highly dependent on an individual
developer’s perception of the economic benefits of additional density credits; therefore, this type of zoning cannot be relied upon to protect natural resources. However, bonus or incentive zoning can encourage voluntary and economically beneficial protection for open space and sensitive features.
3.3.3.3.3奖金或奖励分区
奖励或激励分区是激励开发人员更大的灵活性的另一个方法,以换取保存的开放空间和敏感或与激励环境显著特性。分区是开发人员可能被允许开发比通常允许如果在更高的密度返回他或她保留更多的开放空间,创建一个湿地,或降低了网站的整体不透水面积与地下停车场,交通修改或创新的网站布局。成功的奖励或激励分区是高度依赖于一个独立的个体开发者的经济效益的看法更多的密度学分;因此,这种类型的分区不能依靠保护自然资源。然而，奖金或奖励分区可以鼓励开放空间和敏感自愿和有经济效益的保护功能。
3.3.3.3.4 Large-lot zoning
Large-lot zoning establishes a very low density of development; individual dwellings are built on lots of 5 acres or more. Large-lot zoning is most effective when lots are very large (5 to 20 acres) (Caraco et al., 1998). The purpose of large-lot zoning is to spread development thinly, thereby conserving a large proportion of open space on each lot and reducing impacts on water resources.
This method can produce undesirable results, however, including — Promoting sprawl;
— Fragmenting habitats with more extensive infrastructure and lawns; — Increasing reliance on automobile transportation;
— Excluding lower-income residents who cannot afford to purchase large parcels of land. One approach to minimizing the negative impacts of large-lot zoning is to combine it with cluster zoning. In this way, a large area of open space can be protected, while accommodating new development in a more concentrated manner. Although used in many areas, large-lot zoning is not considered to be any more protective than other zoning tools.
3.3.3.3.4 大类分区
大类分区建立了一个非常低密度发展;个人住房是建立在大量的5亩以上。大批分区是最有效的,当许多非常大(5到20英亩)。大批分区的目的是传播发展,从而保护大部分开放空间在每个很多,减少对水资源的影响。该方法可以产生不良的结果,包括：
—促进扩展;
—大量的草林等基础栖息地遭到破坏 —对汽车运输越来越依赖
—低收入居民买不起大块的土地
最小化的负面影响大批分区的方法是把它与集群分区。通过这种方式,可以保护大面积的开放空间,而适应新开发一个更集中的方式。尽管在许多领域使用,大批分区不再被认为是比其他分区更好的保护工具。
3.3.3.3.5 Farmland preservation zoning
Farmland preservation ordinances are another type of measure to provide open space retention, habitat protection, and watershed protection. Farmland protection may be a less-costly means of controlling pollutant loadings than the implementation of urban runoff structural control
practices. Much of the farmland currently being converted has soils that are stable and not highly erodible. Conversion of these farmlands often displaces farming activities to less-productive, more-erodible areas that may require increased nutrient and pesticide applications.
Many communities consider both agriculture and forestry to be an integral part of rural heritage and strive to preserve these industries and the open space associated with them. According to the 1997 National Resources Inventory, nearly 16 million acres of forest, cropland, and open space were converted to urban and other uses from 1992 to 1997. The average rate for those five years—3.2 million acres per year—is more than twice the conversion rate of 1.4 million acres per year recorded from 1982 to 1992 (USDA-NRCS, 2000).
Agricultural lands can be protected by implementing a modified large-lot zoning ordinance that makes residential development less economically attractive. Alternatively, a cluster development ordinance can be established that specifies a density for an agricultural development and also requires that dwellings be built on small lots, leaving the remainder of the site as agricultural open space. The ordinance can also specify that development must occur on the least-productive part of the lot so the richest soils can be reserved for cultivation.
Agricultural zoning ordinances can be combined with other initiatives to promote farming and forestry and to protect rural areas from being overtaken by urban sprawl (Sims, 2000b). The
King County, Washington, executive official has undertaken several initiatives to promote
diversity in lifestyle choices, encourage the continuation of farming and forestry, protect environmental quality and wildlife habitat, and maintain a link to the county’s heritage by preserving rural areas. So far the county has reduced its development rate in rural areas from 15 percent in 1980 to 6 percent at present. The target is to further reduce the development rate to 4 percent. The county issued orders to close loopholes in subdivision and land segregation regulations, and it tightened subdivision requirements for rural lands. These efforts will ensure that new development is consistent with current environmental and development standards.
3.3.3.3.5农田保护分区
农田保护条例是另一种类型的衡量提供开放空间保留,栖息地保护、农田和流域保护。保护可能是较为便宜的控制污染物载荷比城市径流结构控制的实现实践。大部分的农田正在转换的土壤,是稳定和不高易受侵蚀的。这些农田经常转换取代农业活动低效生产转移到高效生产,可能需要增加营养和农药的应用。
许多社区都考虑农业和林业农村文化遗产不可或缺的组成部分,努力保护这些产业和与它们相关的开放空间,根据1997年全国资源库存,近1600万英亩的森林,农田和开放空间被转换为城市和其他用途的平均利率从1992年到1997年。这五个吗年——3.2英亩的转化率的两倍多(中国每年140万英亩从1982年到1992年每年记录(USDA-NRCS,2000)。 可以保护农田实现修改大批分区条例会降低住宅开发经济吸引力。另外,集群发展
条例可以建立,农业发展也指定了一个密度要求建在住宅小很多,离开网站的其余部分是农业开放空间,条例还可以指定发展必须发生很多的一部分所以最富有的土壤可以预留给种植。
农业分区条例可以结合其他措施促进农业和林业和保护农村地区被城市扩张超越(西姆斯,2000 b)。金县、华盛顿、行政官员已经采取一些措施来促进多样性的生活方式,鼓励农业和林业的延续,保护环境质量和野生动物栖息地,并维持一个链接到县的遗产保持农村地区。到目前为止,县减少了其在农村地区的发展速度从目前1980年的15%降至6%。目标是进一步降低发展速度4%。县发行订单关闭漏洞细分和土地隔法规,加强农村土地细分要求。这些努力将确保新开发符合当前环境和开发标准。
3.3.3.3.6 Watershed-based zoning
Historically, zoning has been used to establish limits on building density and to separate uses believed to be inherently incompatible (Arendt, 1997). Watershed-based zoning, in contrast, uses watershed and subwatershed boundaries as the basis for making land use decisions. Typically, zoning objectives focus on maintaining or reducing impervious cover in sensitive subwatersheds and redirecting development to subwatersheds that are better able to absorb their influence (Caraco et al., 1998).
Local, state, and federal officials recently approved the Riverside County (California) Plan, which involved multi-agency cooperation in identifying where development may occur and where land should be preserved (Verden, 2000). Over the next 50 years, the Riverside County Plan will serve as a blueprint for building new roads, shopping centers, and homes, while also preserving rapidly disappearing habitat. The plan is designed to avoid costly delays and confrontations between regulators and developers. With the population of Riverside County
expected to double in 20 years, the plan will help developers accommodate growth while it also protects rare plants and animals. State and federal land, transportation, and wildlife managers hope the Riverside County Plan will be a model for other communities struggling to balance development and preservation. − Sensitive areas are protected.
− In rural areas, growth is directed to existing population centers and resource areas are protected.
− Stewardship of the Chesapeake Bay and the land is a universal ethic.
− Conservation of resources, including a reduction in resource consumption, is practiced. − To assure the achievement of the above, economic growth is encouraged and regulatory mechanisms are streamlined.
− Funding mechanisms are addressed to achieve these visions
3.3.3.3.6 以流域为主的分区
从历史上看,分区已被用于建立限制建筑密度和单独的使用认为是固有的不兼容(阿伦特,1997)。相比之下,使用流域和集水区边界作为土地利用决策的基础。通常情况下,
分区目标专注于维持或减少不透水覆盖次集水区和重定向开发,能更好地吸收他们的影响力。
当地州和联邦官员最近批准了河滨县(加利福尼亚州)计划,涉及多部门合作识别发展可能发生在哪里土地应该保存(面向北海,2000)。在接下来的50年,河滨县吗计划将作为蓝图建设新的道路,购物中心,和家庭,同时保持迅速消失的栖息地。该计划旨在避免昂贵的延迟和监管机构和开发商之间的对抗与河滨县的人口.20年来将增加一倍,该计划将帮助开发人员适应增长,同时它也保护珍贵的植物和动物。州和联邦土地、交通、和野生动物管理人员希望河滨县计划将是一个模型,其他社区努力平衡开发和保护。包括：
—敏感地区的保护。
—在农村地区,针对现有人口增长中心和资源领域保护。 —切萨皮克湾的管理和土地是一个普遍伦理。 —保护资源,包括减少资源消耗,是习惯。
—为了保证上述的成就,鼓励经济增长和监管流线型的机制。 —融资机制来实现这些愿景。
3.3.3.3.7 Urban growth boundaries
Urban growth boundaries are lines drawn around metropolitan areas to delineate where urban development can take place (inside the boundary) and where it may not (outside the boundary). Outside of urban growth boundaries, land use is restricted to agriculture, forestry, and open space (Nelson and Moore, 1993). The boundaries encourage more compact (i.e., infill) development, control urban sprawl, and help protect rural heritage. The approval process for new development can be streamlined within the growth boundary to further encourage development in these areas. The duration or lifespan of growth boundaries is normally related to planning periods or cycles, typically 10 to 20 years. Boundaries should be examined at regular planning intervals, however, to assess whether conditions have changed since they were established.
Establishing the location of urban growth boundaries sometimes requires complex decisionmaking. Officials should be reasonably sure that there is sufficient land within the boundary to
meet projected growth over the planning period and that public facilities and services can be provided at reasonable cost in a timely fashion. The potential impact of growth within the
boundary on existing natural resources also needs to be determined. In the context of watershed planning, it is advantageous to use watershed boundaries or other natural features as urban growth boundaries. In this manner, key or sensitive watersheds can be protected from the impacts of development.
In Arizona, the 1998 Growing Smarter Act and its 2000 addendum, Growing Smarter Plus, were signed into law by Governor Jane Hull (Morrison, 2000). This legislation addresses the issue of development by strengthening the ability of communities in Arizona to plan for growth and to acquire and preserve open space. The Growing Smarter legislation requires communities to address growth and growth-related pressures by mandating general plans that identify growth areas, establish policies and strategies for new growth, identify open space needs, regionally plan for interconnected open space, and analyze the environmental impacts of the development anticipated by the general plan (City of Tucson, no date).
3.3.3.3.7 城市增长边界
大城市周围城市增长边界线条描绘城市的地方开发可以发生(在边界),它可能不是(外边界)。以外的城市增长边界,土地使用仅限于农业、林业和开放空间(纳尔逊和摩尔,1993)。鼓励更多的界限(即加密)开发紧凑,控制城市扩张,帮助保护农村文化遗产。新开发的审批流程可以简化在增长边界内进一步鼓励这些领域的发展。的持续时间或寿命增长边界通常是相关的计划时间或周期,一般10到20年。边界应该在定期检查计划的间隔,然而,评估条件改变了因为他们建立了。
建立城市增长边界的位置有时需要复杂的决策。官员应该相当确信有足够的土地的边界内满足预计增长在规划期间,公共设施和服务以合理的成本提供及时,内经济增长的潜在影响边界在现有自然资源也需要确定。上下文中的分水岭规划,有利于使用流域边界城市或其他自然特性增长边界。通过这种方式,可以保护的关键或敏感水域发展的影响。 在亚利桑那州,1998年的增长法案》和2000年的齿顶聪明,聪明加上增长,州长签署成为法律简船体(莫里森,2000)。这项立法地址的问题通过加强社区在亚利桑那州的能力发展计划和增长获取和保持开放空间。越来越多的聪明的立法要求社区解决增长和成长相关压力总体规划要求,确定增长领域,建立新的增长政策和策略,确定开放空间需求,区域计划相互关联的开放空间,并分析发展的环境影响预期的总体规划(图森市,没有日期)。
3.3.3.4 Establish limits on impervious surfaces, encourage open space, and promote cluster development
As described earlier, urban runoff contains high concentrations of pollutants washed off
impervious surfaces (roadways, parking lots, loading docks, etc.). By retaining the greatest area of pervious surface and maximizing open space, nonpoint source pollution due to runoff from impervious surfaces can be kept to a minimum. Refer to section 4.3.2 for a detailed discussion of site design practices to reduce impervious surfaces in new developments.
The following are examples of successful implementation of open space requirements and cluster development:
− Brunswick, Maine, recently adopted an allowable impervious area threshold of 5 percent of any site to be developed in the defined coastal protection zone. The remaining
95 percent is required to be left natural or landscaped. The threshold was developed and adopted using a $28,000 grant.
− Virginia provides general guidance with regard to minimum open space and maximum impervious areas to local governments within the Chesapeake Bay watershed. While specific requirements are not associated with the guidance, local plans are required to contain criteria and must be approved by the Chesapeake Bay Local Assistance Board. − Carroll County, Maryland, is a community with substantial farmland and open space. Because it is located close to both Baltimore and Washington, DC, the county amended its zoning ordinance to encourage cluster development and preserve open space. This and land protection efforts by Carroll County have resulted in protection of 33,000 acres by agricultural easements (Maryland Environmental Trust Land Conservation Center, 2002) − Broward County, Florida, has an open space program and encourages cluster development to reduce impervious surface area, protect water quality, and enhance aquifer recharge (Broward County, Florida, 1990).
− New Hampshire has a model shoreland protection ordinance that encourages grouping of residential units, provided a minimum of 50 percent of the total parcel remains as open space.
3.3.3.4 建立不透水表面的限制,鼓励开放的空间,并促进集群发展
如前所述,城市径流含有高浓度的污染物被洗掉不透水表面(道路、停车场、装货码头、等等),通过保留最大的区域透水表面和开放空间最大化,由于径流从非点源污染不透水表面可以维持在最低限度。请参考4.3.2节详细讨论网站设计实践来减少不透水表面的新发展。 以下是成功实现开放空间和集群发展需求的例子:
− 不伦瑞克,缅因州,最近采取了许用不透水面积阈值的5%定义的任何网站开发沿海保护区。剩下的95%是需要离开自然或景观。阈值是发达国家和通过使用一个28000美元的赠款。
− 维吉尼亚提供一般指导关于最小和最大的开放空间不透水区域地方政府在切萨皮克湾的分水岭。而具体要求不与指导,当地计划要求包含标准和切萨皮克湾当地援助委员会必须批准。
− 马里兰卡罗尔县,是一个社区,大量农田和开放空间。因为它靠近巴尔的摩和华盛顿特区县修改其分区条例鼓励集群发展和保持开放空间。这一点,土地保护的努力罗郡导致保护的33000英亩农业地役权(马里兰州环境信任土地保护中心,2002)。
− 佛罗里达州布劳瓦郡有一个开放的太空计划,鼓励集群发展以减少不透水面积,保护水质,提高含水层补给(布劳沃德县,佛罗里达州,1990)。
− 新罕布什尔州的模型滨岸保护条例,鼓励分组住宅单位,提供至少50%的总补贴仍然是开放的政策。
3.3.3.5 Revitalize existing developed areas
Redeveloping existing areas can alleviate water quality impacts by reducing the strain of
development on open space land and minimizing the amount of impervious surface added to the watershed. Existing impervious surfaces, such as declining shopping malls and retail centers, can provide large tracts of developable land and are a prime opportunity for mixed-use infill
development. For additional discussion of options for revitalizing urban areas, see Management Measure 10—Existing Development.
3.3.3.5振兴现有发达地区
重建现有的地区可以通过减少的压力缓解水质的影响开发开放空间土地和减少不透水表面的数量增加了分水岭。现有不透水表面,如购物中心和零售中心,下降提供可开发土地的大片和多用途加密是一个绝佳的机会发展。为额外的讨论选项振兴城市地区,看到管理衡量发展。
3.3.3.6 Establish setback (buffer zone) standards
In coastal areas, setbacks or buffer zones adjacent to surface water bodies, such as rivers,
estuaries, or wetlands, provide a transition between upland development and these water bodies. The use of setbacks or buffer zones may prevent direct flow of urban runoff from impervious areas into adjoining surface waters and provide pollutant removal, sediment attenuation, and infiltration. Riparian forest buffers function as filters to remove sediment and attached pollutants, as transformers that alter the chemical composition of compounds, as sinks that store nutrients for an extended period of time, and as a source of energy for aquatic life (USEPA, 1992).
Setbacks or buffer zones are commonly used to protect coastal vegetation and wildlife corridors, reduce exposure to flood hazards, and protect surface waters by reducing and cleansing urban runoff (Mantel et al., 1990). The types of development allowed in these areas are usually limited to non-habitable structures and those necessary to allow reasonable use of the property, such as docks and unenclosed gazebos.
Factors for delineating setbacks and buffer zones vary with location and environment and include:
− Seasonal water levels;
− Nature and extent of wetlands and floodplains; − Steepness of adjacent topography; − Type of riparian vegetation;
− Quantity and velocity of runoff entering the buffer; − Soil types and infiltration capacity;
− Density of development adjacent to the riparian corridor; and − Wildlife values.
Overall, aquatic buffers are highly effective at removing particulate pollutants, but less effective in removing soluble pollutants (such as nitrogen, for which documented removal rates range from -15 to 99 percent). Proper siting and design and regular maintenance enhance removal efficiency.
3.3.3.6 建立缓冲区标准
在沿海地区,挫折或缓冲区附近地表水体,如河流,河口或湿地,旱地发展之间提供一个过渡,这些水体。使用挫折或缓冲区可能防止城市径流直接流不透水区域相邻表面水域并提供污染物去除,沉积物衰减,渗透。河岸森林缓冲区函数作为过滤器去除泥沙和污染物,变形金刚,改变化合物的化学成分,水槽,储存营养物质一段时间,作为水生生物能源(构成,1992)。挫折或缓冲区通常用来保护海岸植被和野生动物走廊,减少洪水灾害风险,保护地表水减少和清洁的城市径流(曼特尔et al .,1990)。在这些领域发展的类型允许通常是有限的结构和那些需要允许合理使用的属性,如码头和没围起来的凉亭。 因素描述挫折和缓冲区随位置和环境，包括:
—季节性水位;
−湿地和泛滥平原的性质和范围; −相邻地形险峻; −河岸植被的类型;
−径流进入缓冲区的数量和速度; −土壤类型和渗透能力; −密度发展毗邻河岸走廊; −野生动物的价值。
总的来说,水生缓冲区是高度有效的去除水中的微粒污染物、但不那么有效在去除水中的可溶性污染物(如氮、记录删除率范围从-15年99%)。适当的选址和设计和定期维护增强去除效率。
3.3.3.6.1 Buffer ordinance
Buffer ordinances provide guidelines for buffer creation and maintenance. They should include the following provisions:
— Buffer boundaries to be clearly marked on local planning maps; — Maintenance language that restricts vegetation and soil disturbance;
— Tables that illustrate buffer width adjustment by percent slope and type of stream; and — Direction on allowable uses and public education.
The following are examples of setback or buffer requirements:
− Town commissioners in Apex and Cary, North Carolina, have agreed to set wider buffers between development and streams (Price, 2000). Under the new ordinance, buffers must be at least 50 feet wide along intermittent streams and must average 100 feet wide along perennial streams. The towns chose to use an average rather than a strict 100-foot
minimum to allow landowners flexibility. In addition to the buffer ordinance, Apex and Cary halved the limit of impervious surfaces on a given tract of land over which retention ponds are required to control runoff (from 24 percent to 12 percent). Town officials will hold a public hearing to vote on the new regulations.
− Monroe County, Florida, requires a setback of 20 feet from high water on man-made or lawfully altered shorelines for all enclosed structures and 50 feet from the landward extent of mangroves or mean high tide line for natural water bodies with unaltered
shorelines (Monroe County, Florida, Code, Section 9.5-286).
− Brunswick, Maine requires a buffer of 125 to 300 feet from mean high water within the Coastal Protection Zone (Section 315 of the Brunswick Zoning Ordinance), depending on the slope of the buffer, as designated on the town's land use map.
− Queen Anne's County, Maryland, established a standard shore buffer of 300 feet from the edge of tidal water or wetland, 50 percent of which must be forested.
− Maryland’s Critical Area Act requires the establishment of a minimum buffer of 100 feet of natural vegetation landward from the mean high-water line of tidal waters or the edge of tidal wetlands and tributary streams. Unless a property owner can demonstrate unwarranted hardship and prove no negative impact to water quality, plant, fish or wildlife habitat, the local jurisdiction will not permit disturbance or new development within the buffer except for access or water-dependent facilities. Any clearing that occurs
for access or water-dependent facilities must be mitigated through a buffer management plan approved by the local jurisdiction (Critical Area Commission for the Chesapeake and Atlantic Coastal Bays, no date).
3.3.3.6.1缓冲条例
缓冲条例为缓冲区创建和维护提供指导。他们应该包括下列规定: ——缓冲区边界清楚地标明其内地方规划地图; ——维护语言制约植被和土壤扰动;
——表说明缓冲区宽度调整斜坡和类型的流百分比;和 ——允许使用和公共教育的方向。 以下是挫折或缓冲需求的例子:
---镇委员在先端和卡里的镇委员,北卡罗莱纳同意设置更大的缓冲开发和流之间(价格,2000)。在新条例下,缓冲区必至少50英尺宽以及间歇流,必须平均宽100英尺常年流。城镇平均选择使用,而不是一个严格的100英尺
最低允许地主灵活性。除了缓冲条例,先端卡里减半的极限不透水表面的一个给定的大片土地上,这里保留
池塘被要求控制径流(从24%到24%)。小镇官员将举行公开听证会新规定进行投票表决。 ----门罗县,佛罗里达州,需要挫折的20英尺在人为或高水位依法改变所有封闭的结构和50英尺的海岸线向陆地红树林的程度或说高潮线自然水体和一成不变的 海岸线9.5节(门罗县,佛罗里达州,代码,-286)。
−不伦瑞克,缅因州需要125到300英尺的缓冲区内平均高水位沿海保护区(第315节不伦瑞克的分区条例》),根据指定缓冲区的斜坡,在城镇土地利用图。马里兰−安妮女王的县,设立了一个标准的岸缓冲的300英尺潮汐水或湿地边缘,其中50%必须森林。
----马里兰州的临界面积法案要求建立一个最低100英尺的缓冲区自然植被向陆地从平均高水位的行潮汐水域或边缘潮汐湿地和支流流。除非业主可以证明不必要的困难,证明没有负面影响水质,植物、鱼或野生动物栖息地,当地管辖范围内不允许干扰或新开发缓冲区内除了访问或顾问团设施。任何发生的清算访问或顾问团设施必须通过一个缓冲减轻管理计划批准的当地管辖(切萨皮克的关键区域委员会和大西洋沿海海湾,没有日期)。
3.3.3.6.2 Vegetative and use strategies within management zones
Buffers can be divided into three zones—the streamside, middle, and upland zones (HersonJones et al., 1995). Dense vegetation in the streamside zone (recommended to be approximately
25 feet wide) prevents excessive activity in this sensitive area, maintains the physical integrity of the stream, and provides shade, litter, debris, and erosion protection. The width of a grassed or mostly forested middle zone (minimum of 50 feet) depends on the size of the stream and its floodplain and the location of protected areas such as wetlands or steep slopes. The upland zone, typically 25 feet wide, is an additional setback from the buffer and usually consists of lawn or turf. Zones in the buffer should be delineated to determine the types of vegetation that should be maintained or established.
Allowable land uses in the three zones vary. The streamside zone is limited to footpaths, runoff channels, and utility or roadway crossings. The middle zone may be used for recreation and runoff control practices. The upland zone may be used for many purposes, with the exception of septic systems, permanent structures, or impervious covers. A depression incorporated into the design of the upland zone can detain runoff during storms. This runoff is released slowly to the middle zone as sheet flow, which is then transferred to the dense streamside zone, designed to have minimal to no discharge of surface water to the stream.
3.3.3.6.2营养管理区域内和使用策略
缓冲区可以分为三个zones-the溪,中间,和陆地区(HersonJones et al .,1995)。浓密的植被在河边地带区(建议约25英尺宽)防止过度活动在这一敏感地区,维护的物理完整性流,并提供了阴影,垃圾,碎片,和侵蚀保护。植草或的宽度大部分森林中间区域(至少50英尺)取决于流和它的大小泛滥平原和湿地保护区等的位置或陡峭的山坡。高地区域,通常25英尺宽,是一个额外的缓冲,通常由草坪或挫折应该划定地盘。在缓冲区域确定的植被类型保持或建立。
允许三个地区不同土地用途。溪区是有限的小路,决选渠道,效用或公路口岸。可以用于娱乐和中间区域径流控制措施。高地区域可以用于许多目的,除了败血性系统,永久结构,或不透水覆盖,萧条纳入设计的高地区域可以拘留期间径流风暴。这径流缓慢释放中间区域为层流,然后转移到密集的河边地带区,设计最小的,没有地表水排放到流中。
3.3.3.6.3 Provisions for buffer crossings
Stream crossings should minimize impacts on buffer integrity while providing crossing points for linear forms of development such as roads, bridges, golf course fairways, underground utilities, enclosed storm drains, and outfall channels (Schueler, 1995). They should also be designed to provide fish passage and to withstand overbank flows from the 100-year storm event. Design considerations for buffer crossings include: minimizing the width of the crossing; orienting the crossing at a right angle to the stream; limiting the total number of crossings; ensuring that outfalls discharge at the invert elevation of the stream channel; and burying utility crossings at least 3 feet below the channel’s invert elevation. An outfall should not be placed directly in the main channel. Energy-dissipating devices can be installed in outfalls to protect the streambed and adjacent banks.
3.3.3.6.3规定缓冲口岸
流道口应减少对缓冲区的完整性的影响,同时提供过境点线性形式的发展,如道路、桥梁、高尔夫球场球道,地下公用事业、封闭的雨水渠和排水口通道(Schueler,1995)。他们还应该设计提供鱼类通道和承受漫滩流从100年风暴事件。设计考虑缓冲过境点包括:减少跨越的宽度;定向在直角交叉流;限制过境点的总数;确保排放口排放的底拱高程河道;和埋葬效用口岸至少3英尺以下频道的底拱高程。不应该直接放置在一个排水口主要通道。耗能设备可以安装在保护河床和利弊附近的银行。
3.3.3.6.4 Integration of structural runoff management practices where appropriate
Depressions can be incorporated into the upland part of a stream buffer to provide runoff detention during storms and to promote sheet flow over the middle zone of the buffer. A flat, grassed area or level spreader can also be used in the upland part of the buffer to create sheet flow and to promote infiltration over the rest of the buffer.
Storm water ponds and wetlands can be located inside or outside the buffer. According to Schueler (1995), ponds inside the buffer should be used only for runoff quantity control.
Although ponds in the buffer treat the greatest possible drainage area, are more likely to maintain their water level during dry periods, provide a diversity of aquatic habitats, and can increase the total width of the buffer, they displace vegetation and might cause barriers to fish migration, modification of existing wetlands, and stream warming.
3.3.3.6.5 Development of buffer education and awareness programs
Buffer education efforts should foster community awareness and encourage stewardship. These objectives can be met by posting signs along the buffer boundaries that describe allowable activities in different parts of the buffer. Buffer owners can be educated by distributing
pamphlets, hosting stream walks, and holding meetings. New owners should be made aware of buffer limits and allowable uses when the property is transferred. Buffer stewardship can be
encouraged through reforestation and “bufferscaping” programs. Annual inspections can be done with “buffer walks” to determine the extent of encroachment, devegetation, erosion, or excessive sediment deposition.
3.3.3.6.4集成结构径流管理实践 凹陷可以被并入到流缓存器，留在风暴和片流缓冲区的中间地带。一个平面,植草面积或水平分布也可以用于旱地缓冲区创建表的一部分流,促进渗透在其余的缓冲区。 雨水池塘和湿地可以位于内部或外部的缓冲区。池塘内缓冲应该只用于径流数量控制。虽然在缓冲池将最大可能排水区域,更容易维护水位在干燥期间,提供水生栖息地的多样性,可以增加总宽度的缓冲,他们取代植被和可能导致鱼类洄游的门槛,修改现有的湿地。 3.3.3.6.5缓冲教育和意识计划的发展
缓冲教育应该培育社区意识,鼓励管理。这些目标可以达到通过发布描述允许沿缓冲区边界的迹象活动的不同部分缓冲区。缓冲所有者可以通过分配教育小册子,举办流散步,并召开会议,新老板应该意识到缓冲区的限制时,允许使用财产转移。缓冲区管理鼓励通过植树造林和绿化项目。年度检查可以做到的“缓冲行走”来确定侵犯的程度,侵蚀,或过度沉积物沉积。
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