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Tr protection

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 Establish trout waters (Tr) protection measures (for programs
 with development or redevelopment draining to Tr waters)

"Develop, adopt and implement an ordinance (or similar regulatory mechanism) to sure that the best management practices selected do not result in a sustained increase in water quality temperature."

At the present time, the new DWQ Stormwater BMP Manual does not contain specific guidance about which types of BMPs are most appropriate for use in trout waters watersheds. However, EPA’s Post Construction Stormwater Management web site contains fact sheets on ten commonly used structural BMPs. One of the items covered in the fact sheet for each BMP is its impact on receiving stream temperature.

The tables below summarize the information from EPA’s fact sheets for the various BMPs. It is important to note that these tables do not include all of the BMPs available. One of the best options in trout waters is to use nonstructural BMPs such as minimizing impervious surfaces and controlling soil erosion.

Structural BMPs that are Appropriate for Trout Waters:

Infiltration basins

An excellent option for cold water streams because they encourage infiltration of stormwater and maintain dry weather flow. Because stormwater travels underground to the stream, it has little opportunity to increase in temperature.
Sand filters

Can be a good treatment option for cold water streams. Surface sand filters are typically not designed with a permanent pool, although there is ponding in the sedimentation chamber and above the sand filter. Designers may consider shortening the detention time in cold water watersheds. Underground and perimeter sand filter designs have little potential for warming because these practices are not exposed to the sun.

Bioretention

A good option in cold water streams because water ponds in them for only a short time, decreasing the potential for stream warming.
Grassed channels

These practices do not pond water for a long period of time and often induce infiltration. As a result, standing water will not typically be subjected to warming by the sun in these practices.

Porous pavement

Can help to reduce the increased temperature commonly associated with increased impervious cover. Stormwater ponds on the surface of conventional pavement, and is subsequently heated by the sun and hot pavement surface. By rapidly infiltrating rainfall, porous pavement reduces the time that stormwater is exposed to the sun and heat.

Structural BMPs that are NOT Appropriate for Trout Waters:

Dry extended retention basins

Can increase stream temperatures (Galli, 1990). Overall, dry extended detention ponds increased temperature by about 5°F. In cold water streams, dry ponds should be designed to detain storm water for a relatively short time (i.e., less than 12 hours) to minimize the amount of warming that occurs in the practice.
Wet detention ponds

Pose a risk to cold water systems because of their potential for stream warming. When water remains in the permanent pool, it is heated by the sun. A study in Prince George's County, Maryland, found that storm water wet ponds heat storm water by about 9°F from the inlet to the outlet (Galli, 1990).

Wetlands

Pose a risk to cold water systems because of their potential for stream warming. When water remains in the permanent pool, it is heated by the sun. A study in Prince George's County, Maryland, investigated the thermal impacts of a wide range of storm water management practices (Galli, 1990). In this study, only one wetland was investigated, which was an extended detention wetland (see Design Variations). The practice increased the average temperature of storm water runoff that flowed through the practice by about 3°F. As a result, it is likely that wetlands increase water temperature.