Stevens-Rugg Brook:Diversion Structure Improvement

AlternativesSt Albans, Vermont

Background

Flood damage to homes, businesses, rec areas, and ag areas led to need for detention structure between Stevens and Rugg Brooks

Water quality, sediment and erosion concerns

Three proposed initial routes: railroad, power line, trailer park

Many problems existed between the city and landowners leading to the selection and implementation of the power line alternative.

1974 construction began on structure

Stevens Brook diverts water to Rugg Brook

Detention Structure

Map of Jewett Brook and Mill River Watersheds

Two streams are Stevens (N) and Rugg (S)

City of St Albans in orange/teal

Problem

The existing St. Albans diversion structure is not effective at preventing floods during high water flow events and does not produce effluent that meets water quality standards.

Stevens Brook and existing Culvert

Culvert holds 70 cfs when full

Base flow is 2 cfs

When flow exceeds 70 cfs, pooling occurs which leads to diversion structure

Flood Event 1 Year 5 Year 50 YearPeak Flows

(cfs)218.3 800.5 2109.3

Diversion Structure: Sediment Basin

Diversion Structure: Outlet weir

Diversion Structure: Outlet

Diversion Structure: Rugg Brook

Problem: Sedimentation

Problem: Debris Accumulation

Problem: Water Quality

Problem: Erosion-Stevens

Improvement Measures: 1 Construct Sediment Traps in Existing Basin

Excavate permanent deep pools for sediment

revegetation for aquatic habitat

Removal of pollutants bound to sediments

Measure 1: Engineer Drawing

Improvement Measures: 2Construct Detention Basin by Excavating Diversion

Channel

Excavate 2-3 ft deep basin at downstream end

Low flow outlet in existing weir

Sediment forebay at head of basin

Revege for aquatic habitat

Improvement Measures: 3Construct Detention Basin by Raising Outlet

Structure

Low flow outlet at current elevation, raise weir 1-2 feet

Sediment forebay at head of basin

Revege for aquatic habitat

Improvement Measures: 4Construct Enhanced Wetland in Diversion Channel

Enhance habitat

Sinuous low flow channel for settling

Shallow and deep pools

Sediment forebay

Revegetation for aquatic habitat

Alternative Constructed Wetlands

Flood attenuation

Pollutant removal

Aquatic habitat

Extended detention wetland

Pond/wetland system

Pocket wetland

Findings: Multiple Criteria Decision Analysis

Sediment Removal

Pollutant Removal

Flood Detention

Aquatic Habitat

Cost Geomorph.

Aesthetics

Agency of Natural Resources

3 3 1 3 1 2 0

Town Residents

1 3 2 0 3 3 2

City Residents

1 2 3 0 3 3 2

Developers 0 0 3 0 0 3 0

Recreational users downstream (St. Albans bay)

3 3 2 3 0 1 3

Total 8 11 11 6 7 12 7

From MCDA most important criteria are: pollutant removal, flood water detention and stream geomorphology

  Pollutant Removal

Flood Water Detention

Geomorphology of Rugg Brook

Total

Measure 1 3 0 1 4

Measure 2 1 3 3 7

Measure 3 1 1 2 4

Measure 4 3 0 1 4

Recommendations: MCDAMeasure 2: sediment forebay and detention pond

Constructed wetland close to outlet including native plant stock

Reduction and development of effective impervious surfaces in the city of St Albans.

Riparian buffers

Recommendations: Buffer

Stevens BrookBank stability

Reduce sedimentation

Buffer

Along sides of detention pond and constructed wetland

Increase bank stability

Habitat

Aesthetics

Recommendations: Monitoring and Maintenance

Are the improvements functioning as designed?

Future sediment removal and disposal

Testing effluent against water quality standards

Geomorphologic assessment of Rugg

Acknowledgments

Erica Gaddis

Breck Bowden

Dan Lindly: Town administrator

Bonnie Wagner: Northwest Regional planning Commission