Gwinnett County
NRCS Watershed
Dam Rehabilitation
Program
Jonathan Semerjian, PE
Dept. of Water Resources
Stormwater Management
Gregg Hudock, PE
Golder Associates
Sam Fleming, PE
Dewberry
Presentation Overview
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Background
Program at a Glance
Program Drivers
Planning and Implementation
Challenges
Yellow River Dams
Other Keys to Program
Summary
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Background
• Gwinnett County, GA
– Metro Atlanta
– 437 Square Miles
– Population 800,000+
• Piedmont Region
– Headwaters Watersheds
• 1/3 Gulf of Mexico
• 2/3 Atlantic Ocean
• 437 Square Miles
• Population
– 805,000
– 80% Unincorp. / 20% Cities (16)
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Background
• Gwinnett County Government
– Dept. of Water Resources
• Stormwater Management
• Stormwater Utility Funded
– Unincorporated Gwinnett & Lilburn
• Implemented in 2006
• $34M Annual Revenues ($2.46/100 sf)
– Aging Stormwater Infrastructure
• ~1,300 Miles County-Maintained Pipe
– ~1,000 Miles Corrugated Steel
– ~500 Miles > 20 Years Old
• ~80,000 Drainage Structures
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Background
• 14 NRCS Watershed Dams
– 357 Statewide
• GASDP Inventoried Dams – 139
– 30 Category I
• 16 County Owned/Operated
– 56 Category II
• 3 County Owned/Operated
– 3 Exempt High Hazard
– 45 Exempt
• 4 County Owned/Operated
– 1 Not a Dam
– 4 Not Classified
• 2 County Owned/Operated
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Program at a Glance
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Initiated NRCS Dam CIP in 1999
– Began Design 1 Dam/year 1999-2001
– Planning stage for remainder 2002-2004
– Construction 2003 - present
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Status
– 9 dams upgrades completed
– 3 dams design completed and ready for
construction
– 2 dams met GASDP standards without
upgrade needs
Total Program $20 million
– $14.8 million County funded
– $5.2 million NRCS Grant funded
• 65 NRCS / 35 Local Match
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Program Drivers
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Public Safety and Regulatory
Compliance
– Signed O&M Agreement
• Responsible Operator
– RC&D & SWCD Co-Sponsors
• Generate Revenues
– State Regulation
• Safe Dams Act (1978)
• Original law exempted NRCS Dams
• Exemption ended in 2000
– Population Growth
• 72,000 (1970)
• 588,000 (2000)
• 805,000 (2010)
– Originally designed to protect agricultural
lands from flooding
– Increased Development in the Breach Zone
• Classification “High Hazard”.
– Inadequate Spillway Capacity and Stability
• Most designed prior to Act
• Stepped Design Criteria
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Program Drivers
• Resource Protection
– Flood Protection
• Up to 98% reduction in 1% annual chance peak
– Recreation
• County Parks
– Fish and Wildlife Habitat
– Water Quality
– Public Infrastructure
• Smaller downstream bridges and culverts
• Roads & utilities
– Property Values
• Increased values around lakes
• Reduced floodplain downstream
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Program Implementation
• CIP Implemented in 1999
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Y15, Y14, N1 under design
6-year program outlook
Funded by General Property Tax
Y16 & Y17 under design by USACE thru
State
• Design Challenges
– Development encroachments
– Existing and Planned Development
– No room to widen earthen auxiliary
spillways
– Leverage dam length for overtopping
chute spillways
– RCC most cost effective
– Floodplain Management – No Rise
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Program Implementation
• NRCS Grant funding availability
– Small Watershed Rehabilitation
Amendments of 2000
– 65/35 Cost share
– Federal Design Criteria plus
GASDP Standards
– Full PMP design (NRCS)
– GASDP design storm based on
size of dam
– ¼ to full PMP
– Refocus Design Strategies
– Enter into MOU with NRCS
– Try to secure Grant Funding
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Program Implementation
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No Business Dam No. 1 (N1)
– Located in a golf course
– Construction impacts to golf course
operations
– Necessary Spillway Width
– Construction Staging
– Loss of Revenue
– 35% Cost Share Fed Stds > 100% County
GASDP Stds
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Grant req’d Spillway designed to full PMP
Greater impacts to adjacent properties
Greater costs to construct
Forwent grant pursuit and fund 100% local
– Widened earthen auxiliary spillway
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Program Implementation
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Planning Strategy
– Planning Studies on Remaining Dams
– Determine most cost effective solution
– 65/35 Cost Share (Fed and GASDP Stds) vs. 100%
Local (GASDP Stds)
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Cost to meet GASDP only as little as 10% of cost to
meet Fed Std
– 5 dams RCC overtopping spillways
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3 with NRCS Grant
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1 Conv. Concrete Labyrinth Weir Chute Spillway over
the top of the dam (Y3 to be constructed)
– 6 dams combination modified earthen aux. spillways
and/or wave walls
– Better planned CIP
– Funding needs for timing of design and const.
– Commence Design for all Structures
– Y14 first to commence construction (2003)
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Challenges
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Design
– Converging Spillways
• Piedmont Region of GA
• Narrow, steep stream valleys
• Convergence beyond tested limits
– Test Studies Conducted
• Y15 USBR Hydraulics Laboratory
– County funded
• H3 USDA ARS HERU Laboratory
– NRCS funded
• Better to converge flow in control section
– Variety of Control Sections
• Arced Ogee, Straight Broad Crested,
Arced Broad Crested, Winged Broad
Crested, Sharp Crested Weirs
• Multi-stage spillways
– Floodplain Management (No Rise)
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Challenges
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Elected Officials and County Administration
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Briefings, memos, briefings, memos, and more
briefings and memos
• “Spillways have never run around.”
• “Do we really need to spend this much money?”
• “What happens if we don’t do anything?”
• “Why did we save those O&M Agreements?”
• “Can we get out of this?”
• “If we fix this once, will we have to go back
again?”
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Communication was the key
• Explain options, benefits, consequences
• Brief and to the point
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Funding
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Initially funded by General Fund
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Stormwater Utility Funding starting in 2006
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BOC final authority on budget
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Securing Grant Funds
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Challenges
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Public Acceptance
– Multiple Public Meetings
• Discussed alternatives and get input on
selected alternative
– Aesthetics
• Exposed RCC not acceptable
• No exposed concrete preferred
– Graffiti
• Vegetative cover on RCC chute steps
after Y14
– Fish
• Drain lakes during construction
• Restock after construction
– Often Contentious
• Threatened lawsuits (Y15 and Y16)
• Assignment of easement offered (Y15)
• Had to find a champion
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Challenges
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Land Rights
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Flowage Easement
• Referenced to an elevation (Top of Dam)
– Some amended to lower elevation
• Flood Flowage, Ingress/Egress, and O&M
• Interpreted to allow Construction Upgrades
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Temp Const/Perm Drainage Esmts where const
activities went beyond Flowage Esmt
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Cost to Cure
Construction
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Contractor Pre-qualification
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On-site RCC pug mills and staging areas
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Construction Traffic
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Water source for RCC
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Minimizing Change Orders
• RCC Mtls, Unsuitables, Stone, etc…
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Complaints by local residents
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Grant administration
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Yellow River Dam No. 14 (Y14)
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In a developed subdivision
– Proposed development in land
between exist. aux. spillway and dam
Grant funded (65/35 Cost Share)
Maintained reservoir levels 3-feet below
normal pool during construction (Fish)
Interceptor sewer along right abutment
GA Power Easement primary access
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Allowable construction activity coordination
Stage RCC Pug Mill, material stockpiles, etc… in
existing earthen aux. spillway
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Maintain 50% width clearance
Provided off-duty patrol for traffic control
Converging spillway with arced ogee weir
Construction 2003-2004 (Golder, Thalle)
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Yellow River Dam No. 14 (Y14)
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Yellow River Dam No. 15 (Y15)
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In a developed subdivision
Active, uncooperative, and litigious HOA
– Threatened lawsuits
– Assignment of easement offered
Half Dam length available for overtopping
spillway control section
Collins Hill Rd d/s and adjacent to dam
Grant funded (65/35 Cost share)
Model test at BOR
Converging spillway with winged broad
crested weir, vegetative cover
Construction 2007-2008 (Golder, ASI)
• Construction bundled with Y16
• Pug mill adjacent to site
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Yellow River Dam No. 15 (Y15)
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Yellow River Dam No. 16 (Y16)
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In a developed subdivision
– HOA coordination
Took over design from GASWCC
Interceptor sewer thru exist. earthen aux.
spillway
20-foot wide dedicated access btwn houses
– Const. access thru lake bed
D/S private lake normal pool elev higher than P/S
outlet pipe and toe drains
100% local funded
Converging spillway with sharp crested weir and
vegetative cover
Construction 2007-2008 (Schnabel, ASI)
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Construction bundled with Y15
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Pug mill off-site (4-miles away)
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Fish kill during pre-const lake draining
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Yellow River Dam No. 16 (Y16)
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Yellow River Dam No. 17 (Y17)
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In County Park
Park used for HS overflow parking
Designed by USACE thru GASWCC
Grant funded (65/35 Cost Share)
Construction procured and
administer by Gwinnett
Significant unsuitables at toe of
dam from original construction
Converging spillway with broad
crested weir and vegetative cover
Construction 2004-2005 (USACE,
Golder, ASI)
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Yellow River Dam No. 17 (Y17)
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Other Keys to Program
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Operation and Maintenance
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Mowed twice per year and removed debris as
needed
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Annual Inspections
• Now quarterly
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No major deficiencies to address other than spillway
capacity
Instrumentation
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Remote monitoring being installed to monitor
reservoir levels
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Plan to install on all NRCS Dams
Emergency Action Plans
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Developed for all 14 NRCS Dams
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Sunny Day and Storm in Progress (PMP) Failure
Events
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Imminent, Potential, and Non-failure Classifications
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Property Owner listing for notifications
• Reverse 911
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Expanding to private dams
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Summary
• Understand Needs/Drivers
– Benefits, Consequences, and Options
• Communication
– Elected Officials
– Management/Administration
– Public
• Planning
– Identify Funding Sources
– Concept Planning before Implementation
– EAPs
• Operation and Maintenance
– Keep O&M and Inspections Up to Date
• Qualified Consultants and Contractors
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Questions
Jonathan Semerjian, P.E.
Section Manager
Gwinnett Co. Dept. of Water Resources
684 Winder Hwy.
Lawrenceville, GA 30045
678.376.6934
[email protected]
Gregg Hudock, P.E.
Golder Associates
770.496.1893
[email protected]
Sam Fleming, P.E.
Dewberry
678.537.8627
[email protected]
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