sheffield brook floodplain restoration & culvert replacement

Sheffield Brook Floodplain Restoration & Culvert

Replacement

Kristine M. Baker, P.E.Fuss & O’Neill, Inc.

Presentation for

Connecticut Association of Flood Managers Conference

October 25, 2017

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Agenda

• Project Site• Existing Conditions• Project Objective• H&H Modeling• Existing Conditions Results• Proposed Project• Expected Results

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Project Site

Project Site

Watershed Area

Hartford, CT

Old Lyme, CT

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Existing Conditions

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• Problem: Lack of floodplain storage and undersized culvert causing interior flooding in neighborhood

• For example, an inland event in March 2014 created significant flooding from a recorded 4.7-inch storm; approximately a 10-year return period

Interior Flooding Issues

Flooding on Sea Spray Avenue (March 30, 2014)

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1. Restore Floodplain– Improve ability to store and convey and floodwaters

2. Increase Capacity of Culvert Under Beach– Double Capacity of Existing 36” Pipe– Reduce Shoaling of Pipe

3. Tidal Controls for Coastal Events– Reduce potential for storm surge to flood neighborhood

Keys to Reducing Flooding

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Hydrology & Hydraulics ModelingHydrology Model Schematic Hydraulics Model Schematic

(HydroCAD) (HEC-RAS)

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Existing Conditions Model

0 200 400 600 800 1000 1200 1400 1600-2

0

2

4

6

8

10

12

Main Channel Distance (ft)

Ele

vatio

n (ft

)

W

W

2.1

5 6 7 8 9 10 11 12 13 14 15 16

1-YEAR FLOOD

2-YEAR FLOOD

10-YEAR FLOOD

100-YEAR FLOOD

Existing Conditions Maximum Water Surface

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Existing Conditions Model Results1-year Flood 2-year Flood

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Existing Conditions Model Results10-year Flood

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• Major modeling conclusions are: – The 36-inch culvert causes backwater under all the modeled

storm event scenarios– Floodwaters overtop the culvert and flow as overland flow

over the surface to the beach under the 10- and 100-year flood events

– The backwater from the culvert begins to influence the water surface elevations near Maple Avenue

– Flooding north of Maple Avenue is not influenced by the culvert, so will require addition of floodplain storage to reduce water surface levels

EC Modeling Conclusions

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1. Restore Floodplain– Improve ability to store and convey floodwaters

2. Increase Capacity of Culvert Under Beach3. Install Weir Boards to Reduce Tidal Flooding

Proposed Project

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Floodplain Restoration

1. Two-Stage Channel Design2. Meandering Stream through created Floodplain3. Removal of 5,500 CY of previously placed fill4. Bioengineered Stabilization – Root wads and plantings

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Two-Stage Channel Design

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Culvert and Tidal Control Improvements

1. Twin 36” Culverts2. Junction Box for Weir

Boards3. Open Channel with

groins and revetment

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Weir Board Junction Box

PLAN VIEW

FRONT VIEW

SIDE VIEW

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Expected Results1-year Flood Event 2-year Flood Event

PROPOSED

EXISTING

PROPOSED

EXISTING

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Expected Results

PROPOSED

EXISTING

10-year Flood Event 100-year Flood Event

PROPOSED

EXISTING

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• Kris, I need the updated flood modeling results

Expected Results

10-year FloodExisting

Water Surface

Ground Surface

Proposed Water

Surface

Location of Maple Ave

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• Junction Box construction

Construction Photos

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• Groin

• Bilco Doors

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• Upstream Headwall

• View Looking downstream

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Kristine Baker, PESenior Project EngineerFuss & O'Neill, Inc.146 Hartford Road, Manchester, CT 06040860.646.2469 x4436kbaker@fando.com www.fando.com

Contact Information