Natural Channel Restoration after Irene and Lee
a Schoharie County Opportunity
Will VanDeValk, Area Engineer USDA/NRCS
2013 Mohawk Watershed Symposium 1
NRCS Emergency Watershed Protection Program
Several towns approached NRCS in late 2011 seeking technical and financial assistance
State Office staff evaluated sites for EWP eligibility 10 sites (reaches) on 6 Streams were determined eligible Significant Threat to Public Health and Safety 75% NRCS Funding for construction (25% Local Match req’d) NRCS determined that a holistic approach to stream
restoration is critical to long-term success 2
Platter Kill/Flat Creek Road (5,500 LF reach)
Approx. 40-ft high raw bank near upstream end of 5,500 LF reach
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Platter Kill/Flat Creek Road (5,500 LF reach)
Loose, saturated, highly-erodible bank Bed & bank armoring washed away by flood
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Platter Kill/Flat Creek Road (5,500 LF reach)
Approx. 50-ft high near vertical bank Bed & lower bank armoring washed away by flood
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Platter Kill/Flat Creek Road (5,500 LF reach)
Home site destroyed by channel relocation
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Platter Kill/Flat Creek Road (5,500 LF reach)
15-ft wide x 7-ft high box culvert beneath roadway
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Little Schoharie Reach A (9,600 LF reach)
Overwidened channel w/ loose berms
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Little Schoharie Reach B (8,200 LF reach)
40-ft high raw bank below laboratory facility
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Little Schoharie Reach B (8,200 LF reach)
Downcutting of exposed clay/silt material
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Little Schoharie Reach C (6,000 LF reach)
Original meandering channel, abandoned by flood
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Little Schoharie Reach C (6,000 LF reach) Approx. 20-ft high eroding bank near Brooky Hollow Evidence of considerable downcutting
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Little Schoharie Reach D (6,700 LF reach)
Sharp bend @ Huntersland Rd., 10’ – 15’ downcutting
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Little Schoharie Reach D (6,700 LF reach)
Conditions on 1/24/12 (~ 5 mos. after Irene)
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Little Schoharie Reach D (6,700 LF reach)
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Conditions on 3/06/13 (~ 18 mos. after Irene)
Little Schoharie Reach D (6,700 LF reach)
Sloughing of bank near residence as stream downcutsg
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Line Creek/Mill Valley Rd. (10,400 LF reach)
Home site destroyed by channel relocation
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Line Creek/Mill Valley Rd. (10,400 LF reach)
Stream adjacent to road & residences
Some hard-armoring or structural solutions may be required
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Damage Survey Report (DSR) Process Field Procedures (began in Jan. 2012)
GPS-locate features & estimate lengths & heights Office Procedures (Conceptual – Level)
Enter field data into GIS system Preliminary Hydrologic & Hydraulic analyses Conceptual solution (reconnect stream w/ floodplain,
remove berms, restore meander pattern, size channel for 1 to 2 year flows, provide grade-control, revegetate banks, hard-armoring only where necessary)
Quantity estimates Cost Estimating (completed 3/27/12)
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Loss of stream meander Raw Bank Height & Area
estimates ~ 885,000 sq. ft. of raw
bank along 5.6 miles (Reaches A – D)
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Project Finances (NRCS estimates)
10 Project sites on 6 streams covering approximately 47,300 LF (9 miles) of stream
Construction Cost estimated at $21.2M
NRCS share (75%) = $15.9M NYS has agreed to fund Local share (25%) = $5.3M
NRCS will fund up to $1.59M for allowable non-
construction costs (administration, engineering, etc.)
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Project Plan – Schoharie County EWP
County under contract with AECOM to “Provide Assessment, Design and Construction Administration for Support of Natural Stream Restoration Projects”
Assessment & Design in 1st half of 2013 Construction to begin this summer, with completion by
mid-January, 2014 (EWP condition)
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Fluvial Geomorphology
The study of how landforms change with time under the influence of rivers and streams
Frequently takes a “watershed scale approach” Attempts to work with a river’s natural processes
vs. Conventional Channelization
Tends to make the river conform to a preconceived regular shape
Often used in short reaches, to meet very specific criteria (e.g. 100-year flood)
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Conventional Channelization
Wide, trapezoidal channel
Often straight
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• Contain Floods
Conventional Channelization
Wide, trapezoidal channel
Often straight
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• Contain Floods • Levees sometimes
used
Conventional Channelization
Wide, trapezoidal channel
Often straight
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• Contain Floods
• Levees sometimes used
• Low flows wide & shallow
Natural Channel Design
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• Irregular shape w/ low-flow channel
• Meandering
• Channel contains ~ 1.5 year flood (Bankfull Flow)
Natural Channel Design
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• Irregular shape w/ low-flow channel
• Meandering
• Channel contains ~ 1.5 year flood (Bankfull Flow)
• Higher flows use floodplain
Natural Channel Design
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• Irregular shape w/ low-flow channel
• Meandering
• Channel contains ~ 1.5 year flood (Bankfull Flow)
• Higher flows use floodplain • Low flows confined
Side-by-side Comparison
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• Natural Channel Design •Conventional Channelization
Low Flows Low Flows
Side-by-side Comparison
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• Natural Channel Design •Conventional Channelization
Bankfull (~ 1.5 yr Flood)
Design Flood (>>1.5 yr flood)
Side-by-side Comparison
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• Natural Channel Design •Conventional Channelization
Large Floods
Large Floods (if berms are used)
Energy Balance of Streams (Lane, 1955)
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Regional Curves – Flow
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Energy Dissipation in Stable Streams
Bed Roughness Form Resistance - Step Pools (steeper streams) - Riffle/Pool sequences (moderate slope streams) - Meander Pattern (flatter streams) Floodplain acts like an “Energy Relief Valve”
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Rock cross-vanes for energy redirection, grade control & sediment transport
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Man-made approaches
Bed Material is Important!
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Summary – Natural Channel Design
puts the ~ 1.5 year flood in the channel and larger floods out onto a floodplain
Low-Flow conditions, Water Quality, Habitat, Ecosystem Function, and Resilience are all important
In areas w/out an adequate floodplain, other methods (or a combination of methods) may be necessary
Requires extensive data collection & analysis should provide Schoharie County with many stream
corridor benefits
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Slide 40
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