Culverts Flashcards
What was the flaw in the Rutherford creek disaster?
Bridge was designed for 50 year flood and 100 year flood event took places, destroying a bridge that resulted in loss of life.
What is the most important thing to remember if you need to cross streams?
Maintain natural drainage patterns
What is a common result of the alteration of natural drainage patterns?
When water is redirected by ditches into other streams, those streams are often incapable of containing the large volumes of water being redirected by ditches. This commonly results into debris flows which can do serious structural and ecological damage.
What’s is the solution to altering drainage?
Put a culvert in every single stream you need to cross
What happens when a road is built cross slope?
Groundwater is intercepted by ditches and becomes surface water.
- increased flashiness and water volumes in nearby streams.
How can you reduce surface erosion on roads?
Ensure ditches that create a path of least resistance for water to flow.
Why is sidecast an issue
Fill destabilizes easily when saturated
3 key design objectives
- adhere to natural drainage pattern by strategic placement of culverts
- ensure culverts are properly sized
- redistribute intercepted water back onto the hillside with cross drain culverts.
What defines a stream? What is a go,den rule of steam flow?
- alluvial bed > 100 m long. Less is a NCD which still requires a culvert.
- or any water flowing into a fish stream or water intake.
Golden rule is not to direct streamflow into a ditch.
What are the most significant impacts to fish habitat and water resources in forestry?
Roads cause 80% increase in sedimentation.
Give 4 negative effects of poor culvert design?
- 80% of sedimentation comes from poorly directed runoff
- Poorly designed culverts increase maintenance costs
- Damaged culverts cause lost production
- Improperly drained roads never stabilize leading to grading, ditching and resurfacing.
Why would additional culverts be required even where there is no surface water?
extra culverts reduce the distance water is carried in a ditch and disperse water over a greater area, reducing the potential for debris flows.
What is important to remember about cross ditch spacing and soil type?
slope and soil type are limiting factors.
As the road gets steeper, more cross ditches needed
As soil type gets finer, more cross ditches will be needed.
What is outsloping? when is it acceptable?
when a road is angled so that water runs straight off it and downhill. only acceptable for short term roads that are to be deactivated.
What would you do if you were designing a ditch less road?
combine with coarse materials in order to reduce intercepted water.
What are overland roads?
Roads that are built above natural ground surface from very coarse materials and capped with gravel. Used in very wet conditions and not meant for long term service.
Why would you avoid long continuous road grades?
Putting flat steps in the road creates velocity breaks for ditch water and also gives a good opportunity to put in a culvert.
How would you protect your ditches from erosion?
armour ditches with shot rock. velocity drops with increased roughness and depth.
What is a bridge?
Temporary or permanent structure carrying a road above a stream.
What is a culvert?
transverse drain pipe or long structure covered with soil and lying below the road surface
cross drain?
culvert that carries ditchwater from one side of the road to the other (no stream)
What is a major culvert?
stream culvert with a size of 2m or greater, or a maximum design discharge of 6m3/sec or greater.
stream culvert?
used to carry stream flow in an ephemeral or perennial stream channel from one side of road to the other.
When would you legally need a professional engineer?
Major culverts and long spans
high abutments and complex bridge structures
