Protocol 1: Prevented sediment - ChesapeakeCommons/stream-restoration-model GitHub Wiki

Protocol 1 provides credit for projects occurring in first- through third-order streams with perennial flow that stabilize banks and prevent sediment erosion in actively degrading channels.

See complete 2019 Protocol 1 Guidance.

View source code.

Inputs

Name Type Description
banks array An array of bank objects (see below).

Bank values

Name Type Description
bulk_density_of_soil float/integer Bulk density of bank soil measured in pounds per cubic foot (lbs/ft3).
bank_erosion_rate float/integer Bank erosion rate measured in pounds per foot per year (lbs/ft/year).
eroding_bank_length float/integer Eroding bank length measured in feet (ft).
eroding_bank_height float/integer Eroding bank height measured in feet (ft).
nitrogen_concentration float/integer Default: 0.
phosphorus_concentration float/integer Default: 0.

Outputs

Name Type Description
tss_lbs_reduced float Annual reduction in pounds of total suspended solids (tss). If multiple banks are provided, this number will be the aggregate of all tss reductions.
tn_lbs_reduced float Annual reduction in pounds of total nitrogen (tn). If multiple banks are provided, this number will be the aggregate of all tn reductions.
tp_lbs_reduced float Annual reduction in pounds of total phosphorus (tp). If multiple banks are provided, this number will be the aggregate of all tp reductions.

Formulas

See design example.

# Calculate sediment load.

tss_lbs_reduced = bulk_density_of_soil * bank_erosion_rate * eroding_bank_length * eroding_bank_height

# Convert erosion rate to nutrient loading rates.
#
# The measured nutrient values of the sediments are:
#  - 1.05 pounds TP/ton sediment
#  - 2.28 pounds TN/ton sediment

tn_lbs_reduced = (tss_lbs_reduced/2000.0) * nitrogen_concentration

tp_lbs_reduced = (tss_lbs_reduced/2000.0) * phosphorus_concentration

# Estimate stream restoration efficiency.
# Assume the efficiency of the restoration practice to be 50%.

tss_lbs_reduced = tss_lbs_reduced * 0.50

tn_lbs_reduced = tn_lbs_reduced * 0.50

tp_lbs_reduced = tp_lbs_reduced * 0.50

Appendix A: Qualifying conditions

  • The stream reach must be greater than 100 feet in length and be still actively enlarging or degrading in response to upstream development or adjustment to previous disturbances in the watershed (e.g., a road crossing and failing dams). Most projects will be located on first- to third-order streams, but if larger fourth and fifth order streams are found to contribute significant and uncontrolled amounts of sediment and nutrients to downstream waters, consideration for this BMP would be appropriate, recognizing that multiple and/or larger scale projects may be needed or warranted to achieve desired watershed treatment goals.

  • The project must utilize a comprehensive approach to stream restoration design, addressing long-term stability of the channel, banks, and floodplain.

  • Special consideration is given to projects that are explicitly designed to reconnect the stream with its floodplain or create wetlands and instream habitat features known to promote nutrient uptake or denitrification.

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

  • Stream restoration is a carefully designed intervention to improve the hydrologic, hydraulic, geomorphic, water quality, and biological condition of degraded urban streams, and must not be implemented for the sole purpose of nutrient or sediment reduction.

  • There may be instances where limited bank stabilization is needed to protect critical public infrastructure, which may need to be mitigated and does not qualify for any sediment or reduction credits.

  • A qualifying project must meet certain presumptive criteria to ensure that high functioning portions of the urban stream corridor are not used for in-stream stormwater treatment (i.e., where existing stream quality is still good). These may include one or more of the following:

    • Geomorphic evidence of active stream degradation (i.e., BEHI score)
    • An IBI of fair or worse
    • Hydrologic evidence of floodplain disconnection
    • Evidence of significant depth of legacy sediment in the project reach
⚠️ **GitHub.com Fallback** ⚠️