Protocol 5: Outfall and gully stabilization - ChesapeakeCommons/stream-restoration-model GitHub Wiki

This protocol is also referred to as "Outfall and gully restoration".

Protocol 5 is designed to create a stable channel to dissipate energy that extends from the storm drain outfall to the perennial stream network. The new channel is re-constructed to achieve an equilibrium state where future sediment loss is minimized or eliminated altogether. These projects may only be applied within the headwater transition zone and active headcut areas (Group 2, 2019).

See complete 2019 Protocol 5 guidance and design example.

Inputs

Name Type Description
tss_lbs_reduced float Annual reduction in pounds of total suspended solids.
tn_lbs_reduced float Annual reduction in pounds of total nitrogen.
tp_lbs_reduced float Annual reduction in pounds of total phosphorus.

Outputs

The functional implementation of protocol 5 is a no-op that leaves the inputs unchanged.


Appendix A: Qualifying conditions

  • The channel or gully slope below the source must exhibit predictive indicators for severe erosion or hill-slope failure and must be observed to be actively enlarging or degrading.

  • The project should utilize a comprehensive approach to stream channel design, addressing longterm stability and resiliency of the channel, banks, and floodplain.

  • Each project must comply with all state and federal permitting requirements, including 404 and 401 permits, which usually contain conditions for pre-and post-project assessment and post construction monitoring.

  • Projects need to meet post-construction stability criteria and successfully establish needed vegetation. Projects should maintain or improve existing native riparian vegetation in the headwater stream corridor to the extent possible. Projects should follow regulatory agency guidance regarding compensation for any losses of forest, wetlands and sensitive habitats within project work areas.

  • Projects should avoid the use of pipe extensions or drop structures unless it can be demonstrated that they are needed to sustain channel stability and they do not introduce new aquatic organism passage issues.

  • The project should provide functional lift within the project reach, typically as indicated by improvements of Levels 2 (Hydraulics) and when possible 3 (Geomorphology) of the stream functions pyramid (Harman et al , 2011).

  • The project directly addresses a headcut, with severe vertical incision (progressive bedlowering).

  • The project MUST NOT introduce barriers or challenges to aquatic organism passage or degrade instream habitat. Projects should always seek to improve passage of aquatic organisms and aquatic habitat where possible.

  • Drop structures, extension of an existing storm drain pipes, stormwater collection features, and scour protection or other hard armoring techniques used in OGSPs are not eligible for credit in perennial or intermittent channels.

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