Culvert instalation

Question 1

What are the main considerations in culvert installation

Answer 1

1. Flooding – Design for peak flows
2. Structurally Sound – must bear weight of traffic (Hwy truck 75 tonnes, off Hwy 160 tonnes)g
3. Protected from stream scour
4. Protected from Debris and bedload movement

Question 2

What are the culvert types?

Answer 2

• Corrugated Metal Pipe - CMP
• Polyvinylchloride Pipe – PVC
• Wood Box Culvert
• Precast Concrete
• Log culvert

Question 3

What determines what type to use?

Answer 3

• Availability of Materials – Isolated Camps must ship everything in by barge so try to use local materials like cedar
• Service Life – cedar lasts +/- 25 years
• Height of Structure – build lower profile with wood

– Shallow rock bed streams are tricky

• Natural streambeds can be preserved with log culverts

Question 4

What wood would you use to build a box culvert?

Answer 4

Cedar. Has the advantage of being low

Question 5

What is “perching” the outlet?

Answer 5

When the outlet of the pipe is not low enough to provide stream connectivity. Blocks fish

Question 6

How can you avoid outlet erosion?

Answer 6

Armor ditches and outlet

Question 7

What is d50

What is the minimum riprap size for armouring?

Answer 7

The average size piece of rip rap in streambed.

D50x 20% is minimum armour size

Question 8

What is stream scour

Answer 8

• Scour is the removal of sediment (soil and rocks) from streambeds caused by moving water.
• Swift moving water has more energy (turbulence and velocity) to lift and transport sediment than slowly moving water.
• Many bridge and culvert failures have been caused by scour

Question 9

What is the skew angle rule?

Answer 9

Skew Angle – 3 degrees for each 1% of road grade over 3%

– Example – 15% road grade

= (15% - 3%)(3°) = 36°

– a skewed culvert is longer!

Question 10

Does Angling a pipe down increase the flow?

Answer 10

No. 2-3% will flush better and allow beadload to move through

Question 11

Does I let shape effect flow?

Answer 11

Beveled end culverts have larger capacity than flat ends (inlet control)

Question 12

What are some typical culvert spacing considerations

Answer 12

• Cross drain spacing decreases with grade of road and erodibility of materials
• Look for spots where grade of road is flatter
• Do not drain water onto large steep fill slopes!
• every stream gets a culvert

Question 13

What’s an important consideration for large pipes

Answer 13

Put in a sand bed for the pipe and bury with sand to create. Sand layer around the pipe.

Question 14

What are some log culvert considerations

Answer 14

• Lash with cable or Drifts to hold logs in place
• Geotextile to prevent soil from entering stream
• Fill spreads the load but adds “dead load”

Question 15

What is the term for logs bridges with a gravel top?

Answer 15

Puncheon

Question 16

Log culvert advantages?

Answer 16

• You can build the exact size you want
• Materials on site
• Build concurrent with sub-grade
• Low profile to prevent ski jumps in road
• Better fish passage (natural bottom)
• inexpensive
• Resist blockages
• Resist damage during maintenance

Question 17

Log culvert disadvantages

Answer 17

• Rot faster than metal pipes
• Burn during a slash burn
• Material falls through into stream

Question 18

What are the lifespans of the common wood in service

Answer 18

• Cedar – 10-15 years
• Fir, Spruce, Pine – 6-8 years
• Hemlock – 2 years

Question 19

What’s a Squamish culvert?

Answer 19

• Putting a low swale in road and armor with rock
• Great for post logging access where low traffic is expected
• Won’t plug with debris

Question 20

What is the standard culvert maintenance procedures?

Answer 20

• Make a comprehensive checklist
• Annual inspections are a legal requirement*****
• Record: inspection date, culvert location

– GPS works great

• Rank the work by priority

– Risk assessment for (safety, environment, cost)

– problems with fish or safety get fixed first

– Fix small problems last

Question 21

Culvert definitions

Answer 21

• Invert – the bottom
• Soffit – the top
• Haunches – lower quarter, between bed and mid-diameter
• Deflection – the flattening of the pipe
• Camber – intentional bend put in a pipe to allow for settling