CRATER PLANNING DISTRICT COMMISSION

WIP III WORKING GROUP

Outfall & Gully Stabilization Projects (OGSP)April15, 2016

Joseph Battiata, P.E.

City of Hopewell

Stormwater Program Manager

AGENDA

1. Brief overview of pollutant load reduction strategies

2. BMP cost effectiveness3. Stream Restoration4. Outfall & Gully Stabilization Projects

LOCAL AREA PLANNING GOAL BMPS

Structural BMPs• Bioretention

Basins/Raingardens

• Dry Ponds/Wet Ponds

• Infiltration Practices

• Filtering Practices

• Permeable Pavement

• Vegetated Channels

• Shoreline

Non-Structural BMPs• IC Reduction

• Land Conversion

• Urban Tree Canopy

• Forest Buffers

• Street sweeping

• Storm Drain Cleaning

• Nutrient management

• Growth Management

STRUCTURAL BMP CROWD PLEASERS

Permeable PavementBioretentionRain Gardens

Performance (%)

DA

Cost ($$$$)

= Cost/lb

HIGH COST – HIGH PERFORMANCE BMPS

Stream RestorationShoreline ManagementLand Use Conversion

Performance

DA (length, other)

Cost ($$$$)

= Cost/lb

RIVERSIDE PARK STORMWATER GREENWAY

Design & construction:Preliminary Cost/lb = $ 14,615/lb TPFinal Cost/lb = $ 6,096/lb TP

RIVERSIDE PARK STORMWATER GREENWAY

Design & construction:Final Cost/lb ~ $ 50,000/lb TP

Bioretention (L1)- 1.84 acPermeable Pavmnt (L2) – 0.15 ac

STREAM RESTORATION LOAD REDUCTION CALCULATIONS

CBP Expert Panel Report Default Values

OR

CBP Expert Panel Report Protocols 1, 2, & 3

TN TP Sediment

Default Rate (lb/ft/yr) 0.075 0.068 44.88 non-coastal plain

15.13 coastal plain

STREAM RESTORATION LOAD REDUCTION CALCULATIONS

CBP Expert Panel Report Protocols 1, 2, & 3: Protocol 1: Credit for Prevented Sediment during Storm Flow (monitoring, BANCS, or Alt.)Protocol 2: Credit for Instream and Riparian Nutrient Processing during Base Flow (TN only)Protocol 3: Credit for Floodplain Reconnection VolumeProtocol 4: Credit for Dry Channel RSC as an Upland Stormwater Retrofit

Active Headcut

REGENERATIVE STORMWATER CONVEYANCE (RSC)

Sand/Wood chip mix

RIVERSIDE PARK STORMWATER GREENWAY RSC

TN TP Sediment

Pollutant Reductions (lb/yr) 54 11 3,144

Performance (%)

DA

Cost ($$$$)

= Cost/lb

CBP EXPERT PANEL REPORT:

RECOMMENDATIONS FOR CREDITING OUTFALL & GULLY STABILIZATION PROJECTS

Approved October 15, 2019

CBP EXPERT PANEL REPORT:

Protocol 5: Alternative Prevented Sediment for Outfalls

OUTFALL GULLY & STABILIZATION PROJECTS

Headwater Transition Zone = Stormwater Hotspot Erosive force of flows discharged from storm drain

outfalls High channel slopes and energy conditions Exposed and non-cohesive soils Poor vegetative cover Floodplains that are narrow or absent

OUTFALL GULLY & STABILIZATION PROJECTS

Courtesy: MDOT SHA Courtesy: VDOT

OUTFALL & GULLY STABILIZATION PROJECTS

1. Define Existing Channel Conditions;2. Define Equilibrium Channel Conditions;3. Calculate Total Prevented Sediment4. Convert Total Sediment Volume to Annual

Prevented Sediment Load5. Determine Annual Prevented Nutrients

OUTFALL GULLY & STABILIZATION

Very common in coastal zone: • development drainage systems discharge at the edge

of escarpment;• Channels typically hidden in dense overgrowth;• Headcuts migrate upstream and eventually impact

drainage and transportation infrastructure;• Require repair to protect infrastructure – get credit and

possibly funding

Performance

DA (length, other)

Cost ($$$$)

= Cost/lb

QUESTIONS???