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Understanding the Impacts of Culvert Performance on Stream Health
Kristin ThomasAquatic Ecologist
Michigan Trout UnlimitedTransportation and the Environment Conference
12/5/2018
Importance of adequately sized crossings
• Fish and organism passage• Stream morphology• Design considerations• Funding and partnership opportunities
Why is connectivity important?• Biologically
• Block passage of organisms• Fish• Invertebrates• Amphibians• Terrestrial
• Geomorphically • Disrupts normal stream function
• Inhibits transport• Sediment• Wood
• Changes channel shape – changes function
Culvert Problems• Inlet or outlet drop (perch)• Physical barriers• Wood debris accumulation• Excessive velocities• Insufficient water depth• Flow contraction (turbulence)• Absence of bank edge areas• Discontinuity of channel substrate• Behavioral barriers• Riparian fragmentations
How do culverts block AOP?
Perched
Velocity
Velocity/turbulence
Swimming speed
• Burst Speed• Highest speeds attainable • Maintained only for short time <20 seconds
• Prolonged Speed• Speeds fish can maintain for 20 seconds to
200 minutes• Spans speeds between burst and sustained• Often the speed used in culvert design
• Sustained• Speeds fish can maintain for long periods of
time >200 minutes
Why do aquatic organisms need to move?
• Spawning habitat• Nursery habitat• Foraging areas• Deep water refuge• Seasonal habitats• Genetic variability
Dennis Kirkland
Seasonal Movement
• Life stage movement needs• Movement to meet a variety of
needs• Reproduction• Colonization of available habitat• Chemical or thermal refuge• Food
• Can be daily, weekly, seasonally, yearly, or less
Migration Timing
0
100
200
300
400
500
600
700
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
MonthN
umbe
r Mig
ratin
g
0
50
100
150
200
250
300
Dis
char
ge (c
fs)
Design Window
Gullett, Kale. Aquatic Organism Passage. NRCS-ENTSC
Genetic Variability
• Genetic diversity correlated to population’s ability to adapt• Genetic diversity foundation of ecosystem diversity• Sustainability of a population depends on the maintenance of genetic
diversity• Genetic drift and inbreeding depression
• Cannot maintain genetic diversity in small populations• Must be able to move and interbreed with other populations
Not just fish!
Inter-specific Interactions
• Occurrence of some species depends on presence of others
• Freshwater Mussels• Many species depend on fish hosts to
complete lifecycle• Larval mussels, glochidia, attach to fish gills
to complete lifecycle• Many will attach to any available fish• Some are fish species specific
Snuffbox mussel
• Endangered mussel found in MI• Need glochidia to attach to logperch,
darters and sculpin• Female attract logperch with soft mantle• When the fish tries to eat the mussel grabs
its head and shoots her glochidia into the fish’s gills
• https://www.youtube.com/watch?v=-1YcaIN8cRs
Riparian Wildlife• Use river and streams as travel
corridors• Rivers and streams provide link
connecting wetland, aquatic, and terrestrial ecosystems.
• Cross over road when no banks present in structure
• Dry passage opportunities reduce roadkill
Bankfull benches in large culverts
How do culverts disrupt stream function?
Geomorphic importance• River can’t flow efficiently through small culvert• Disrupts sediment and organic material
movement• Upstream
• Slows velocity • Build up of fine sediment• Build up of wood and other debris
• Downstream • Increase in velocity • Scours deep pool• Coarsening of substrate • Increased erosive capacity
Geomorphic importance: Example
• Look at up and downstream characteristics to identify undersized crossings
• Stream width• Substrate composition• Bedform structure
• Compliment to visual data to indicate impact of culvert
Cedar River Example
0102030405060708090
100
Upstream Just Above Just Below Downstream
Perc
ent o
f Str
eam
Bedform Composition Athey Rd.
Pool
Riffle
Run
0
5
10
15
20
25
30
35
Upstream Just Above Just Below Downstream
Wid
th (f
eet)
Stream Width Around Athey Rd.
0102030405060708090
100
Upstream Just Above Just Below Downstream
Perc
ent o
f Str
eam
Bot
tom
Substrate Composition Athey Rd.
Hard
Fine
Another undersized crossing
What are we after?
• Natural dynamic stream channel
• Passage of all aquatic organisms
• Low maintenance, flood-resilient road
Sizing and Placement of Stream Culverts
• Match culvert width to bankfull stream width• Extend culvert length through side slope toe• Set culvert slope same as stream slope• Bury culvert 1/6th bankfull stream width• Offset multiple culverts • Align culvert with stream• Consider headcuts and cut-offs
Dr. Sandy Verry, US Forest Service
MESBOAC Example
MESBOAC Example
MESBOAC Example
Stream Simulation Design
• Simulate the natural streambed• Bed shape• Particle diversity• Roughness• Mobility• Forcing features• Control permeability
Slide courtesy of Kozmo Bates, AquaKoz
Culvert Design—Stream Simulation
Slide courtesy of Kozmo Bates, AquaKoz
AOP and maintained stream function benefit aquatic organisms, streams, and humans
1. Less maintenance cost2. Reduced overall long-term cost3. Ecologically the “right thing to do”4. Cooperative funding opportunities
Prioritization and Funding
• RSX inventory• Identify crossing that are
barriers
• Overlap of priority with partner groups
• Work together to fund optimal design
Funding Opportunities
• USFWS Fish Passage Program• DNR Aquatic Habitat Grant Program • Sustain our Great Lakes
