Designing Improved Stream Crossings

Report
Design for Stream Crossing Resiliency
….by accounting for natural stream processes
Design for Stream Crossing Resiliency
More frequent, more intense storms:
Streams convey more
water…
Design for Stream Crossing Resiliency
More frequent, more intense storms:
Streams convey more
water…
…sediment
Design for Stream Crossing Resiliency
More frequent, more intense storms:
Streams convey more
water…
…sediment
Design for Stream Crossing Resiliency
More frequent, more intense storms:
Streams convey more
water…
…sediment
…and debris
Design for Stream Crossing Resiliency
More frequent, more intense storms:
Streams convey more
water…
…sediment
…and debris
Design for Stream Crossing Resiliency…
…streams also convey wildlife
Habitat Connectivity & Flood Resiliency:
A “Win-Win” Design Scenario
River and Stream Continuity Partnership Guidance:
MA River and Stream Crossing Standards
General Standards
1.
Spans (bridges, open-bottom culverts) strongly preferred
(but where these are impractical, well designed culverts may be
appropriate)
2. If culvert, then it should be embedded
3. Span the channel: 1.2 x bankfull width
4. Natural bottom substrate within structure
5. Design with streambed characteristics
6. Openness > 0.82 feet (0.25 meters )
Smart Stream Crossing Design:
1.
Apply the Stream Crossing Standards*
2. Design for Capacity and Stability
3. Provide for Resiliency
*Applicable for non-tidal streams…
For tidal streams: preserve or restore natural tidal
exchange.
Smart Stream Crossing Design:
1.
Apply the Stream Crossing Standards
Convey the “bankfull discharge” through the crossing in a
sustainable, natural channel
(for replacement structures: to the extent practicable)
Smart Stream Crossing Design:
1.
Apply the Stream Crossing Standards
Convey the “bankfull discharge” through the crossing in a
sustainable, natural channel
(for replacement structures: to the extent practicable)
2. Design for Capacity and Stability
Convey a range of greater than bankfull flows, while
sustaining this natural channel and the structure
Smart Stream Crossing Design:
1.
Apply the Stream Crossing Standards
Convey the “bankfull discharge” through the crossing in a
sustainable, natural channel
(for replacement structures: to the extent practicable)
2. Design for Capacity and Stability
Convey a range of greater than bankfull flows, while
sustaining this natural channel and the structure
3. Provide for Resiliency
Withstand extreme events without losing the structure
Smart Stream Crossing Design:
1. Apply the Stream Crossing Standards
Convey the “bankfull discharge” through the crossing in a
sustainable, natural channel
 Cross Section Geometry
 Streambed
 Vertical Alignment
Smart Stream Crossing Design:
1. Apply the Stream Crossing Standards
 Cross Section Geometry
 Streambed
 Vertical Alignment
A brief primer on “Bankfull Width”
Design to the River and Stream Crossing Standards
Design to the River and Stream Crossing Standards
Bankfull Discharge
Bankfull discharge = the water discharged when a stream just
begins to overflow into the active floodplain.
Bankfull stage = the elevation at bankfull discharge
Bankfull width = the width at bankfull stage
Design to the River and Stream Crossing Standards
Bankfull Stage
Bankfull discharge ~ 1.5 Year Frequency Event (varies)
Design to the River and Stream Crossing Standards
Bankfull Stage
Topographic breaks in slope
Flat depositional surface of the floodplain
Depositional features
Changes in vegetation
Undercuts in bank
Changes in bank material particle size
Other erosion features on upper bank (e.g., scour around roots)
Stain lines or lower extent of lichens or mosses on boulders or structures
Design to the River and Stream Crossing Standards
Bankfull Stage
Bankfull Width
Design to the River and Stream Crossing Standards
Bankfull Width
1.2 x Bankfull Width
Span: bridge or open bottom culvert
Bankfull Width
1.2 x Bankfull Width
Bankfull width
Bridge span
Bankfull width
Span: bridge or open bottom culvert
Open Area
Open Area (ft2)
= Openness Ratio (ft)
Structure Length (ft)
Openness Ratio (m) > 0.82 ft for General Standards*
(*Optimum Standards have greater openness and minimum clearance requirements)
Smart Stream Crossing Design:
1. Apply the Stream Crossing Standards
 Cross Section Geometry
 Streambed
 Vertical Alignment
Span: bridge or open bottom culvert
Preserve existing stream bed (preferred);
or if necessary,
Provide for bed material comparable to natural channel
and that results in depths and velocities at a variety of flows.
Streambed
Culvert with Stream Simulation
1.2 x Bankfull Width
Provide for bed material comparable to natural channel and
that results in depths and velocities at a variety of flows.
Design for the Streambed
Requires analysis of
 Streambed material
Design for the Streambed
Requires analysis of
 Streambed material
Design for the Streambed
Requires analysis of
 Streambed material
 Bedform (how the
material is arranged in
the natural channel)
Design for the Streambed
Requires analysis of
 Streambed material
 Bedform (how the
material is arranged in
the natural channel)
Requires an
understanding of
stream morphology
Crossing design for a steep gradient boulder &
cobble dominated stream…
…may differ from the design for a flattergradient stream with a sand & gravel bed.
Smart Stream Crossing Design:
1. Apply the Stream Crossing Standards
 Cross Section Geometry
 Streambed
 Vertical Alignment
Analysis of the “Long Profile”
From Gubernick & Bates, Stream Simulation Design for AOP,
Culvert Summit 2006
Analysis of the “Long Profile”
From Gubernick & Bates, Stream Simulation Design for AOP,
Culvert Summit 2006
Analysis of the “Long Profile”
New Span
From Gubernick & Bates, Stream Simulation Design for AOP,
Culvert Summit 2006
Smart Stream Crossing Design:
2. Design for Capacity and Stability
Convey a range of greater than bankfull flows, while
sustaining this natural channel and the structure
 Capacity for Design Flows
 Stability Considerations
Smart Stream Crossing Design:
2. Design for Capacity and Stability
 Capacity for Design Flows
 Base flows addressed by
bankfull channel design
 Peak flows based on
accepted engineering
standards
Smart Stream Crossing Design:
2. Design for Capacity and Stability
MassDOT Bridge Load and Resistance Factor (LRFD) Manual (June 2013 Update)
Table 1.2 Hydraulic and Scour Design Flood Selection Guidelines
Highway Functional Classification
Interstate, or Numbered State
Highways
Rural Principal Arterial
Rural Minor Arterial
Rural Collector, Major
Rural Collector, Minor
Rural Local Road
Urban Principal Arterial
Urban Minor Arterial Street
Urban Collector Street
Urban Local Street
Hydraulic Design
Flood Return
Frequency (Years)
100
Scour Design Flood
Return Frequency
(Years)
200
Scour Check Flood
Return Frequency
(Years)
500
50
50
25
10
10
50
25
10
10
100
100
50
25
25
100
50
25
25
200
200
100
50
50
200
100
50
50
Engineering Design Standards
Statutory Review Requirements
 MGL Chapter 85
 No bridge on a public highway having a span in excess of
ten feet… shall be constructed or reconstructed by any
county or town except in accordance with plans and
specifications therefor approved by the department.
Said department shall approve or alter to meet its
approval all such plans submitted to it and shall
determine the maximum load which any such bridge
may safely carry…
 Requires review by MassDOT District/Bridge
 Applies to any span >10 ft (including multiple barrels)
Engineering Design Standards
Statutory Review Requirements
 Item 49 – USDOT Recording and Coding Guide for the
Structure Inventory and Appraisal of the Nation’s Bridges
Engineering Design Standards
Statutory Review Requirements
 MGL Chapter 85
 Design to MassDOT/ASHTO bridge standards


2009 MassDOT LRFD Bridge Manual
AASHTO LRFD Bridge Design Specifications
 Submittal Requirements




Hydraulic report
Geotechnical report
Structural design requirements
Scour analysis/scour protection at spans
Smart Stream Crossing Design:
2. Design for Capacity and Stability
Design Flows – what about climate change?
 Precipitation Data
• TP-40 is out of date
• New data options…
 Stream Gage Data
• USGS Regression Equations for Massachusetts are out of date
• New data options…
 Even with updated data, forecasting using historic data
may be problematic
• Provide for resiliency…
Precipitation Data: current option…
www.precip.net
NRRC and NRCS
• Greatly expanded and
recent data base
 Authorized by NRCS
for TR-55 and TR-20
until NWS Atlas 14 is
updated
 Not formally adopted
by MassDEP
2 year
100 year
Rainfall Depth (in)
TP-40
NRCC
Percent
Change
Barnstable
3.5
3.3
-5%
Berkshire North
2.8
2.8
Berkshire south
2.9
Bristol
Rainfall Depth (in)
TP-40
NRCC
Percent
Change
Barnstable
7.1
8.2
16%
0%
Berkshire North
6.2
7.0
13%
2.9
0%
Berkshire south
6.4
7.6
19%
3.4
3.3
-3%
Bristol
7.0
8.6
22%
Dukes
3.6
3.3
-8%
Dukes
7.2
8.3
15%
Essex
3.1
3.2
3%
Essex
6.4
8.8
38%
Franklin
2.8
3.0
5%
Franklin
6.2
7.4
19%
Hampden
3.0
3.1
2%
Hampden
6.5
8.0
23%
Hampshire
2.9
3.0
3%
Hampshire
6.4
7.6
19%
Middlesex North
3.0
3.0
0%
Middlesex North
6.3
8.0
26%
Middlesex Central
3.1
3.1
1%
Middlesex Central
6.4
8.5
33%
Middlesex South
3.1
3.2
4%
Middlesex South
6.5
8.9
36%
Nantucket
3.6
3.2
-11%
Nantucket
7.2
7.9
10%
Norfolk
3.2
3.3
2%
Norfolk
6.7
8.7
30%
Plymouth
3.4
3.4
-1%
Plymouth
6.9
8.7
26%
Suffolk
3.2
3.3
2%
Suffolk
6.6
8.8
33%
Worcester North
2.9
3.0
2%
Worcester North
6.2
7.8
25%
Worcester Central
3.0
3.1
2%
Worcester Central
6.4
8.2
29%
Worcester South
3.1
3.2
3%
Worcester South
6.6
8.6
31%
County
County
Precipitation Data: on the horizon…
NOAA Atlas 14
Precipitation Frequency Estimates
Volume 10: Northeastern States
Projected web-publication: September 2015
Regional Regression Equations
for Peak Discharges
MassDOT/USGS update is
underway.
Scheduled for completion
late 2015
(Published 1983)
Smart Stream Crossing Design:
2. Design for Capacity and Stability
 Stability Considerations
 Stream bed sustainability
 Structure integrity
Smart Stream Crossing Design:
2. Design for Capacity and Stability
Streams are dynamic
Bridges and culverts are static
(or intended to be!)
Streams are dynamic…
…crossing structures are static
Streams are dynamic…
Culverts are rigid horizontally and vertically
Stream bed horizontal and vertical adjustment limited to
material in the culvert
Culvert bottom acts as a
“grade control” structure
Streams are dynamic…
….culverts are rigid
However, “stream
simulation” culvert
design can prevent this
condition
Streams are dynamic…
Bridges and open bottom culverts are rigid
horizontally (unless undermined!)
Stream bed vertical adjustment is not limited by the
bottom of the structure
Future channel?
Streams are dynamic…
…bridges are rigid horizontally
…however, this can (and must) be addressed by design.
Design for stability
Requires analysis of
 Stability of the crossing
structure: protect
(sustain) the bridge!
 Dynamic stability of the
streambed material:
sustain the streambed!
“Critical Conditions” design
 Structure stability under critical conditions:
 MassDOT LRFD Bridge Design Manual (check for latest
revision):
Evaluate bridge foundation scour using flow parameters of the
local flood event that generates the maximum depth of bridge
foundation scour- considering flood return frequencies
(depending on type of road) up to 500 years.
 Apply countermeasures if warranted.
Supplemental Guidance to LRFD
Bridge Manualfor streambed
design for crossings
Design must evaluate stability within the
crossing structure…
Need to address both:
Base flow (habitat continuity)
Extreme flow events
In some cases, design may need to provide
for stability within the crossing structure…
Design to simulate streambed
material and bedform
Design to address foundation scour
and streambed stability
Stream Simulation with Stable Sub-bed
In some cases, design may need to consider stabilizing the channel…
RIPRAP GRADE CONTROL STRUCTURE
Bridge
Bridge
Adapted from: US Army Engineer Research and Development Center
(1999), Channel Rehabilitation: Processes, Design, and Implementation
What about replacements?
Constraints affecting replacement
to provide wildlife passage:
 Flood management concerns
 Conveyance capacity
 Impacts on existing flood profiles
 Potential wetland alteration
 Road impounded wetlands
 Potential “head cut” considerations
 Vertical alignment limitations
Constraints affecting replacement
to provide wildlife passage:
 Historic structures
 Existing utilities
 Construction-phase logistics
 Maintaining road traffic
 Maintaining stream flow
(water handling)
 Site access and weight/size
limits on equipment and
materials
Historic structures
Constraints affecting replacement
to provide wildlife passage:
 Costs and funding priorities
Mitchell Brook – before and during construction
Flood Profile Impacts
Existing elevation of
100-year design flood
Flood Profile Impacts
Altered elevation of
100-year design flood
Caution: Potential downstream
flooding impacts
Flood Profile Impacts
 Federal Executive Order 11988
 Restricts federally funded actions that would
result in raising the 100 year flood elevation
Addressing Flood Profile Impacts:
 Determine if potential for alteration exists
 Determine whether the impact can be addressed
 Alternative design approaches?
 Downstream actions?
 Determine if CLOMR (or other action) is required
 Document and file application
 If no to above, explore other ways to mitigate for
habitat disconnection:
 May require a lesser restoration of habitat connection
Road-Impounded Wetlands
Road-Impounded Wetlands
Flow constriction results in sediment
deposition upstream of culvert
Altered hydrology results in
establishment of wetlands
Road-Impounded Wetlands
More effective conveyance, lowering
invert can lower upstream water surface,
erode accumulated sediment, and alter
wetland hydrology
Addressing Road-Impounded
Wetlands:
 Determine if potential for alteration exists
 Determine whether the “gain” offsets the “loss”
 If yes to above, can it be permitted?
 Consultation with resource agencies
 If no to above, explore other ways to mitigate for
habitat disconnection:
 In-stream mitigation may be warranted:

Application of stream restoration techniques to offset or
correct impacts
Road-Impounded Wetlands
Install counter measure (e.g. rock weir)
to prevent upstream headcutting and
maintain wetland hydrology
New required vertical alignment
Existing vertical alignment
Bridge Deck
Bridge Chord
Required opening height
Required span
Vertical alignment and bridge geometry constraints
Existing Utilities
Urban channel alteration & degradation
Urban channel alteration & degradation
Constraints, constraints…
…Some crossings need to be fixed!
Adapted from Gubernick, Culvert Summit 2006
Some other alternatives
Some other alternatives
Smart Stream Crossing Design:
2. Design for Capacity and Stability
Replacement Crossings
 Analysis for peak flows similar to new crossings
 More analysis required for “passage” flows:
 May need to base on less than bankfull discharge:



Species/life-stage specific (consult with MassDFG), or
10% exceedance quantile, or
25% of Q2-yr
 Need to evaluate culvert bed material stability
relative to nearby channel stability
 Need to assess need for a low flow channel


90% exceedance quantile, or
7Q2
References for designs less than 1.2 x
bankfull width
Concepts
Design analysis
Design methodology for providing stream bed
continuity at road crossings
Examples:
 “No-Slope” design*
 “Stream Simulation” design*
 “Roughened Channel” design*
 Bridge replacement with retained abutments**
*Based on work by: Kozmo (Ken) Bates (formerly with Washington
DFW) and USDA Forest Service
**Based on MassDOT practices
“No Slope” design option
 Applicable only to culverts, not bridges or bottomless
structures
 Suitable for new structures or replacements
 Generally limited to locations with natural gradients
less than 3%
 Most likely applicable to streams with fine-grained,
mobile bed material
“No Slope” design option
1. Culvert installed with
flat invert gradient
2. Culvert width = 1.2 x
bankfull width
3. Downstream countersink
20% of rise, minimum, or
greater depth if required by MA
Standards
5. Bed material = native
material, either
installed or “recruited”
flow
4. Upstream countersink
40% of rise, maximum
Note: Given countersink requirements (#3,#4),
maximum length of culvert will be limited by slope
of stream (L < 0.2*D/s)
Stream Simulation Design
 Applicable to new and replacement culverts
 Applicable to replacements of pipe culverts with




bottomless culverts or bridge spans
Applicable to new clear-span structures where
stream alignment would be altered
Suited to moderate to high channel gradient, and
locations with narrow stream valleys
Greater than 6% gradient may have limitations
Structure cross section size must be sufficient to
permit access for stream bed construction
Stream Simulation Design
Culvert installed with
sloped invert
Bed consists of various materials and bed
forms designed based on geomorphologic
analysis of local stream bed or suitable
“reference” stream
Stream Simulation Design
Alluvial (e.g., cobble/gravel)
Non-alluvial (e.g. step-pool)
Roughened Channel Design
 Applicable to new and replacement culverts, where




not feasible to provide width > 1.2 bankfull width
Suited to moderate to high channel gradient, and
locations with narrow stream valleys
Structure cross section size must be sufficient to
permit access for stream bed construction
May require scour protection (e.g., armoring) of
channel at the culvert outlet
Not recommended for flat-gradient streams with
fine-grained mobile bed material (consider “noslope” design instead.
Roughened Channel Design
Scour protection
at outlet
Bed consists of material designed for
stability under anticipated design flows –
typically requires size of material to be
comparable to the larger material found in
natural channel
Shaped
channel
Before
Before
Winter 2013
Bridge Replacement with Retained Abutments
Smart Stream Crossing Design:
3. Provide for Resiliency
Withstand extreme events without losing the structure
Problematic Design Issues
 Climate Change
 Pressure Flow
 Flood Relief
 Embankment “piping”
 Floatation
 Debris
Source: FHwA
HEC-5
Bankfull condition
τ = γ*d*s
d
Source: FHwA
HEC-5
Critical flood condition
τ = γ*d*s
d
Source: FHwA HEC-5
Potential Countermeasures:
Options: control depth, energy grade, or
size/gradation of channel bed material:
 Wider structure? Valley span?
 Flood plain relief culverts?
 Design section of road as spillway?
 Use larger bed material size in structure?
 Use larger material as a sub-bed to the stream
simulation bed material?
Flood relief culverts, spillway
Source: Forest Service Stream Simulation Working
Group (2008), Stream Simulation
Flood relief culverts, spillway
Source: Forest Service Stream Simulation Working
Group (2008), Stream Simulation
Example of reinforced spillway
Source:
Pressure Flow Issues:
Seepage (piping) through embankment
Free draining material for road
construction is not necessarily designed
for conditions when roadway acts as a dam
Adapted from:
FHwA HEC-5
Pressure Flow Issues:
Floatation of flexible pipe
Buoyant force
Particularly of concern with corrugated
metal or other flexible pipe
Adapted from:
FHwA HEC-5
Debris Issues
During Hurricane Irene
After Hurricane Irene
After Hurricane Irene
Design References
and Guidance
http://wdfw.wa.gov/publications/00049/
http://www.mass.gov/dfwele/der/freshwater/rivercontinuity/guidancedoc.htm
http://www.fs.fed.us/eng/pubs/pdf/StreamSimulation/index.shtml
http://www.mhd.state.ma.us/downloads/projDev/Design_Bridges_Culverts_Wildlife
_Passage_122710.pdf
http://www.fhwa.dot.gov/engineering/hydraulics/pubs/11008/index.cfm
Questions?
[email protected]
Bridge Replacement with Retained Abutments
Culvert Replacement – site with constrained access
After Hurricane Irene
September 2011
Source:
During
Construction
Source:
Source:
November 2012
Questions?
[email protected]

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