Culvert Design in Forested Watersheds That Improve:• Ecological Function,• Infrastructure Protection, and • Public Safety

Marty E. Rye, P.E.Hydrologist

Superior National Forest

Northland Innovative Stormwater Management Conference – Duluth, MN November 2010

3 Main Points Today1) Why a change from traditional culvert

design is warranted

2) What does this approach entail

3) A few examples of designs / installations to consider

What is a Culvert??

Road infrastructure that passes water from a stream or river

Stream infrastructure that passes vehicles

Culvert Design Employing Traditional Engineering Perspective

• Risk-based Social contract

• Machine – type model• Deterministic• Service – Based• Model for Accuracy• Interventionist• Simplifications / Assumptions Clear water design

Engineers are very good at designing infrastructure to work under “design” conditions – design flood, large trucks, etc.

Traditional Culvert Design Does Not Do a Good Job

Considering What Else is in the Stream…..

Traditional Culvert Design Assumptions w/ Riverine Structures Typically Include

• No change over time in:– Hydraulics– Hydrology– Sediment Supply

• No disturbances / debris• Functional design event

How About Just Trapping Sediment and Keeping the Wood Out?

Consequences of Failure are Profound• Human Life• Economic• Ecological• Political / Opportunity

Mpls Tribune 6-05

Characteristics of a Stream• Complex System ‘Chaotic’ (non-linear) Variability Dynamic

• Ecological Management Function-Based Model for Insight Non-interventionist Boundary definition

is difficult Multiple scales

Healthy Natural Systems Are Continually Under Construction

Process of Demolition and Reconstruction is Inherent- Vegetation- Streambanks

Change can be either gradual or due to a sudden disturbance

A Healthy Stream (and Fishery) Requires Connectivity

• Retain connection with floodplain and floodplain wetlands

• Retain longitudinal connection (passage)

• Connectivity/Genetic Diversity/ Recolonization

• Reproduction – seasonal

• Dispersal/Colonization

• Feeding – daily / weekly / seasonal

• Thermal/Chemical Refuge

Fisheries (Aquatic Organism) Passage Include Demands at

Different Temporal and Spatial Scales

Small Streams / Tributaries Are Very Important

• Make up a large percentage of stream miles

• Cumulatively provide more habitat than large rivers

• Support species not found in larger streams and rivers

• Provide important spawning & nursery habitat for fish

From Nick Schmal, USFS

Traditional Analytical Approach to Aquatic Organism Passage

• Single species (fish) management• Single species as a surrogate for all

others

Traditional “Analytical” Approach to Aquatic Organism Passage • Bates, others – maximum swimming speed for

prescribed length• Perform hydrologic / hydraulic analysis to

develop design to meet requirements• Difficult process

– What species do you choose?– What life stage?– What frequency of discharge?– Etc.

However, We Recognize A Need to Pass Numerous Species

• Mussels need passage of a host species

• Sculpin / other non-game fish• Even crayfish move in a

stream• Different requirements for

different life stages

Spawning Migration

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Data from: Scott and CrossmanFrom Nick Schmal, USFS

Longnose Dace

Redside Shiner

Pygmy Whitefish

Spawning Migration; ALL FISH

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Data from: Scott and CrossmanFrom Nick Schmal, USFS

Passage

Passage??

So, Traditional Culvert Design Does Not

Accommodate Debris Flow and Has

Environmental Impacts

We Need an Approach to Account for Stream Characteristics and Process to Protect

People / Infrastructure and

Ecological Functions

Specifically, We Need to:

• Accommodate other entities in the stream (fish, ‘critters’, sediment, wood, ice, etc.)

• Accommodate needs during “all flows at all times” – not just the ‘design event’

Stream Simulation Approach to Crossing Design

Simplistically, if organisms, sediment, and debris can make to the crossing, and the crossing conditions at the crossing are similar – then the crossing should not be a barrier*

Ratio of wood length / channel width is most important factor in what type of debris will move downstream

Eliminates need to perform low flow analysis for multiple species, multiple life stages, etc. (preferred method – though need to try make sure will work if channel changes – downstream avulsion, etc.)

(*) downstream hydraulic conditions also need to be taken into account

Crossing Design Criteria• Prescriptive Standards – Dimensional standards

– Bankfull width– Additional 2 ft for terrestrial

• Performance Standard – Based upon performance– Pass wood, – Provide sediment conveyance– Accommodate aquatic organism passage

not overtop at such a frequency– maximum depth or velocity over road, etc.

Good discussion of performance criteria in:

Miller, D.E., and P.B. Skidmore. 2003. Establishing a standard of practice for natural channel design using design criteria. In: Restoration of Puget Sound Rivers. D.R. Montgomery, S.M. Bolton, D.B. Booth and L. Wall (eds.). UW Press, Seattle, WA

Stream Simulation Approach is Described by a Number of Good

Resources, Including:

• Stream Simulation: An Ecological Approach to Providing Passage for Aquatic Organisms at Road-Stream Crossings, May 2008. USFShttp://www.fs.fed.us/eng/pubs/pdf/StreamSimulation/index.shtml

• MESBOA– Document developed by Sandy Verry for

MnDNR

Make Sure the Crossing Is NeededSTEP 1 – Is always….

IS THE CROSSING NEEDED??• Really – can other crossings be used, etc.?

• Does it need to be permanent – can it be pulled?

• Can the transportation system be designed to minimize crossings?

The More You Can Simulate the Stream – the Better

What Do You Need to Match the Stream Conditions?

Simplistically trying to match velocity at “all flows”:

• Fish that can make it to the crossing should be able to make it through the crossing

• Sediment delivered to the crossing will make it through the crossing (but not too much)

• Result of matching velocity is to match the area and slope - or matching the cross-section dimensions……generally at the ‘bankfull’ elevation

Match the Reach Geometry / Characteristics

Match• Slope• Substrate (roughness /

resistance)• Area

Match substrate by using a ‘bottomless’ arch, bridge, or depressing invert to allow substrate to accumulate in

the culvert

What Do You Get For Additional Expense of Depressing Invert?

• Inexpensive way to accomplish low flow substrate channel requirements

• Manner to potentially avoid / minimize issues if a downstream headcut advances to your structure– Base level lowering– Avulsion (meander cutoff)

Culvert Invert• Should one assume the sediment is scoured

during the design flood event? – i.e. how should I model it?– Professional judgment – depend on type of stream and

the mobility….I would default not to assume scour and available for flow….

• A bottomless crossing becomes even more attractive – more adoptable…– Careful to make sure a scour analysis is done and

ensure footings are sufficiently deep

What Do You Get for Additional Expense of Larger (Taller) Opening?

• Need to thoughtfully consider impact of flow velocities during large events

• Really paying for velocity reduction

• Hydraulically could potentially ‘head-up’ the crossing –but what is the potential impact to development downstream scour hole (and eventual aquatic passage issues, etc.)

• Need to evaluate for each crossing

• Additional capacity for the “erratic” debris tree crown (freeboard)

• Additional capacity if changes in sediment transport or hydraulics:– upstream sediment flux– downstream conveyance due to jam

What Do You Get for Additional Expense of Larger Opening?

Consider making wider to accommodate terrestrial organism passage…….

• Add a couple of feet of dry bank • Used by numerous terrestrial organisms• Also used by fisherman, etc.• MnDOT has used on some crossings

– Contact Peter Leete of MnDNR for some more information (Peter.Leete@state.mn.us)

Terrestrial Passage

Some Quick Thoughts About Floodplain Culverts

• Increase conveyance capacity• Benefit for beaver management??? (stay tuned)• Emergency capacity if main is plugged / frozen• Can maintain some better flowlines

– Don’t concentrate flow (velocity) in channel– Retain energy flow in floodplains– Potentially reduce ineffective flow area

• Evaluate – especially valuable where large floodplain conveyance

Schematic of Flowlines Prior to Crossing

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Single Crossing w/o Floodplain Culverts

Incorporating Floodplain Culverts

Upstream during snowmelt

Other benefits to floodplain culverts:

Downstream during snowmelt

• Ice reduces capacity in main culvert during peak flows

• Floodplain culverts are accessed faster with more flow

Offset Culverts

However, Multiple Barrel Culverts Are Still a Trap for Debris

Large Event in 2008• MnDOT 2008 Almost Lost the Road• Danger to Traveling Public• Potential Loss of Private Property• Maintenance and Repair $$’s

Some Project Examples on the Superior National Forest

• John Olson• Scott Snelson• Jason Butcher• Mike Manlove• Ken Gebhardt• Roger Perkuri • SNF Leadership• Regional staff• Others….

Result of Interdisciplinary Work by Numerous Folks Over the Years!

Tait River, 1935Bridge (19’span)

Bridge (19’span)

Culvert (12’ span)

Tait River, 1955

Tait River, 2001

Bridge (24’span)

Bridge (19’span)

Culvert (12’ span)

1977 project file: “.. Existing culvert (6’) was broken into two sections, washed downstream 200 to 500 feet, and is not salvagable. Survey and design, replace with larger capacity culvert, remove old bridge timbers and existing culvert…

1988 project file: “.. Immediate repair of the damage to the crossing (8’) is important to minimize sediment problems resulting from the existing washouts” replaced w/ 8’ culvert”…

Blind Temperance History

1930’s: Bridge1950’s: Culvert

Photos – John Olson

Blind Temperance 2001

≈$85,000(in 2001)

-Poor road/stream alignment

-Annual maintenance required/replacement schedule.

-Not designed properly for flood flows.

-Upstream pooling/flooding effects – dead trees.

-Important Forest access road to Wilderness Area.

Before

Inga Creek-Perched outlet

-Velocity barrier/RFSS mussel populations and brook trout.

-Frequent road fill erosion and downstream deposition

Inga Creek• Engineering and Fisheries - $51,000.• High profile project as success story.

Before

Inga Creek

Tailwater Control

Kadunce River(2005)≈ $80,000

Little Mississippi Creek (2008)

≈ $55,000

Mark Creek (2008)

≈ $60,000

Mark Creek

Timber Bridges

≈$35,000

(Highly variable)

Treated Deck Crossing

Re-use after 10 years or so…

≈$25,000(Gabion abutments)

Summary• Historically, crossing design has been the

purview of the engineering community designing for flood conveyance. However, others have recognized the ecological impact of crossing installation and have requested / demanded a legitimate voice in the design of crossings.

• In order to have an ecologically functioning system that provides the multiple ecological services and is sustainable, our structures have to be designed with a broad / multi-discipline understanding of riverine processes.

Summary• In addition to the ecological impacts, simply

designing for “clear water” flood hydraulics does not adequately address riverine processes to protect the public’s safety and investment.

• Need recognize the role of:– Sediment– Wood– Disturbance dynamics– Dynamic nature of streams

Summary• As the body of research work and

experience increases, it will be increasingly difficult to justify clear water flood hydraulic design as the standard of practice. This will likely impact liability exposure of designers and owners alike with failures / damages during flood events and long term ecological impacts.

ConclusionsThe result of incorporating ecological engineering principles are:

•Increased protection of the traveling public and roadway infrastructure by better accommodating debris flow (wood, ice)channel dynamicsIncreased hydraulic capacity

•Increased ecological function because of: better longitudinal connectivity ability to accommodate dynamic nature of streamsability to retain important habitat components (wood) in streams

Questionsand

Discussion