Stream Restoration Crediting to Meet MS4 and TMDL Requirements Webinar

Land use changes have resulted in channel instabilities, which can lead to excessive erosion. Stream restoration crediting can be a solution for mitigating unavoidable impacts, prevent erosion, improve water quality, restore habitat or address resiliency in terms of flooding and wetland functions. This webinar provides a brief background on TMDLs and MS4 permits as regulatory drivers for stream restoration as well as approaches from the Chesapeake Bay Program and Maryland Department of Environment as examples to illustrate how stream restoration credits are used to help meet TMDL and MS4 permit objectives.

Under the Federal Clean Water Act, states are required to identify and report impairments to rivers. The Total Maximum Daily Load must be calculated to determine the maximum amount of a pollutant for a particular waterway to determine a goal for reductions. The EPA’s How’s My Waterway site provides information on the condition of waterways.

NPDES permitting regulates point sources to waters of the U.S. MS4 permits require stormwater controls to illicit discharge detection and elimination, public outreach education, and runoff pollution reduction of water through storm sewer systems.

Nationally 46% of rivers and streams have excess nutrients. The presentation focused on the Chesapeake Bay Program as a case study. A watershed-wide TMDL was set in 2010, and a pollution diet was created including local TMDL plans and deadlines for load reductions allocated to the counties and municipalities. Stream restoration crediting is used as an approach to help meet TMDL targets.

The Chesapeake Bay Program’s Urban Stream Restoration Expert Panel Protocols, recently updated in 2019 and 2020, provide a methodology to determine sediment and nutrient load reduction credits for stream projects.

  • Protocol 1 – Prevented Sediment (most widely applied credit)
  • Protocol 2 – Hyporheic Exchange
  • Protocol 3 – Floodplain Reconnection
  • Protocol 4 – Dry Channel Regenerative Stormwater Conveyance
  • Protocol 5 – Outfall and Gully Restoration (New in 2019)

Presenters provided equations, computation steps, and examples to compute load reductions using Protocols 1 and 5 for preventing future erosion and Protocol 2 for instream denitrification. Presenters also summarized the updates to Protocol 3 for floodplain nutrient and sediment load reductions. Impervious acre credit computations for stream restoration projects was also presented following Maryland Department of Environment’s recent guidance.

Additional resources are provided below.

For more information, feel free to reach out to our presenters:

Shannon Lucas –

Hannah Scholes –