4.5.23 PB Packet - Final - Laserfiche WebLink

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196 last for years. 10. a)The culvert must be designed to allow for aquatic life and fish passage. Generally,the culvert or pipe invert should be buried at least 1 foot below the natural streambed(measured from the natural thalweg depth). If multiple barrels are required,barrels other than the base flow barrel(s) should be placed on or near stream bankfull or floodplain bench elevation(similar to Lyonsfield design). These should be reconnected to floodplain benches as appropriate. This may be accomplished by utilizing sills on the upstream and downstream ends to restrict or divert flow to the base flow barrel(s). Silled barrels should be filled with sediment so as not to entrap wildlife or support mosquito breeding conditions. Sufficient water depth should be provided in the base flow barrel(s) during low flows to accommodate fish movement. If culverts are longer than 40-50 linear feet, alternating or notched baffles should be installed in a manner that mimics existing stream pattern. This should enhance aquatic life passage: 1)by depositing sediments in the barrel, 2)by maintaining channel depth and flow regimes, and 3)by providing resting places for fish and other aquatic organisms. In essence,base flow barrel(s) should provide a continuum of water depth and channel width without substantial modifications of velocity. b) If multiple pipes or cells are used, at least one pipe or box should be designed to remain dry during normal flows to allow for wildlife passage. c) Culverts or pipes should be situated along the existing channel alignment whenever possible to avoid channel realignment.Widening the stream channel must be avoided. Stream channel widening at the inlet or outlet end of structures typically decreases water velocity causing sediment deposition that requires increased maintenance and disrupts aquatic life passage. d) Riprap should not be placed in the active thalweg channel or placed in the streambed in a manner that precludes aquatic life passage. Bioengineering boulders or structures should be professionally designed, sized, and installed. The NCWRC encourages the applicant to consider additional measures to protect wildlife species in developing landscapes. More detailed information on each of these measures and supporting literature can be found in NCWRC's Guidance Memorandum to Address and Mitigate Secondary and Cumulative Impacts to Aquatic and Terrestrial Wildlife Resources and Water Quality(August 2002; http://www.ncwildlife.org/Portals/O/Conserving/documents/2002_GuidanceMemorandumforSecondaryan dCumulativelmpacts.pdf). At this time,the information provided is not sufficient for our staff to make definitive recommendations or conclusions concerning this project. Please contact me at(336)269-0074 or olivia.munzerkncwildlife.org if there are any questions about these comments or for free technical guidance.