Protecting Natural Wetlands - A Guide to Stormwater Best Management Practices

Although a number of manuals describe best management practices to be used to address stormwater runoff, this manual is a first attempt at addressing the specific water quality concerns related to wetlands. It is intended for use by anyone addressing potential impacts to wetlands from stormwater runoff, and it presents a wide range of planning approaches as well as specific BMPs that can be employed in a variety of situations. Regardless of what type of approach is taken, and at what level, this manual should be used as a starting point in a process to identify and evaluate appropriate BMPs to protect wetland resources. The information in this document is presented in four sections. Section 2 describes the factors (wetland and stormwater characteristics) that should be considered when developing BMPs to protect wetlands and their natural functions from the potential impacts of stormwater discharges and other diffuse sources of runoff. Wetland factors to consider include wetland type, hydrology, climate, and site specific conditions. Stormwater functions to consider include the quantity and quality of runoff and the frequency of runoff events. Although they are described separately, the wetland factors and stormwater factors are closely related. For example, climate influences the frequency and intensity of storm events; the wetland type affects the capacity of the wetland to handle a given quantity or quality of stormwater runoff; and the functional attributes of a particular wetland can be severely affected by the introduction of even small amounts of certain contaminants. When deciding what BMPs may be appropriate for a particular situation, both sets of variables - wetland factors and stormwater factors - should be considered individually and in combination. Helpful tables that detail thse factors (for example, wetland types or typical pollutants found in stormwater runoff) are provided in Section 2 to assist managers in considering the factors in depth. A third set of factors - the characteristics of potential BMPs - should also be considered in combination with the wetland and stormwater factors. An overview of BMPs for controlling the effects of stormwater on the functions of natural wetlands is provided in Section 2; details are provided in the BMP fact sheets in Section 4. Section 3 of this document presents several case studies that describe examples of situations where BMPs were used to protect natural wetland functions from the impacts of runoff and to restore the functional quality of degraded wetlands. Case studies were selected from both arid and nonarid climates, as well as from temperature and colder climates. Some of the case studies include an in-depth overview of a particular experience using BMPs to protect wetlands, whereas others present only anecdotal information. Since states have only recently had stormwater management programs in place, or will begin implementation of such programs within the next decade, only a limited number of well-documented case studies show the effectiveness of stormwater management BMPs and natural wetlands. Section 4 presents fact sheets describing specific BMPs and their potential relationship to natural wetlands. For each BMP, a fact sheet is provided with the following information: definition and purpose of the BMP, its scope and applicability, design criteria considerations, potential effects on wetlands (i.e., benefits and limitation for use), cost-effectiveness (where applicable), maintenance, and sources of additional information. BMPs included in this document represent examples of some of the more commonly used practices. Numerous BMP manuals from state and local governments throughout the country were used to gather the information presented in the fact sheets.