1. Bridges Reach analysis Fundamental tool for design
Scalable and can be phased
3 defined levels of analysis

2. Bridges Step-wise sizing method Existing bridge condition and history
Confined channels
Floodplain channels
Floodplain management
Flood control features
Infrastructure

3. Which is best? No Slope short, low slope streams (<75’ , <3%)
simple situations (single lane road, low fill)
confined to moderately confined channels
Stream Simulation
default channels <15 ft
steeper, longer culverts
improved ecological connectivity required
moderately confined channels
Hydraulic Method
retrofits
exceptional circumstances
Bridge
default channels >15 ft
wide, steep, or high energy streams
high potential for vertical or
horizontal instability
high debris or sediment load

4. Survey minimum 40 channel widths
Long Profile
Long profile is necessary to understand reach-level behavior of the channel
identify grade breaks
assess regrade potential and effects
average scour depth of pools
determine channel incision
channel characteristics for stream simulation
In alluvial channels
Survey minimum 40 channel widths
plus culvert length
Chapter 7, P. 40

5. Outlet drop caused by scour pool vs. incised channel
Outlet Scour
Original Channel Grade
Incised Channel
Original Channel Grade
Nick point supported by
culvert
Incised Channel Grade

6. 4 ft

7. Channel profile Scale of Problem = Scale of Solution
Outlet scour – Solution at culvert scale
Short
Incised channel –
Reach solution; regrade
Expected regrade
Long

8. Channel Regrade Options
Grade control
(or fishway)
Maintain upstream
bed elevation to protect
current habitat or
infrastructure
Build up as options

9. Channel Regrade Options
Grade control
(or fishway)
Build up as options
Increased reach gradient leads to
Greater transport capacity
Increased downstream velocity
Decrease in habitat quality

10. Channel Regrade Options
Grade control
impacts
Required to maintain culvert within design criteria (part of culvert design)
Locks-in channel section in a vertically mobile channel system (often leads to more controls downstream).
Requires maintenance for the life of the culvert (obligation of the landowner).
May reduce habitat value of reach.
Build up as options

11. Channel Regrade Options
Grade control
(or fishway)
Min 25
Min. 35-
50 ft
Build up as options
Downstream bed control
to anticipate further channel
incision.
These recommendations are not in the culvert manual.

12. Channel Regrade Options
Allow upstream
bed elevation to lower
and establish a new profile.
Regrade
Build up as options

13. Channel Regrade Options
Build up as options

14. Channel Regrade Options
Regrade impacts
Temporary upstream habitat loss
Possible permanent loss of habitat (exposure of bedrock)
Downstream sediment deposition
Potential lowering of local water table, perching riparian
Build up as options

15. Channel Regrade Options
Regrade benefits
Reestablishment of natural stream profile and processes
Rejuvenation of upstream habitat
Elimination of man-made structure in stream
Build up as options

16. Channel regrade considerations
Extent of regrade expected.
Low channel slopes (fine bed materials) are sensitive.
High channel slopes less so.
Condition of upstream channel and banks
Are they susceptible to bank collapse, riparian dewatering?
Habitat impacts by upstream incision
Is there value of culvert as nick point, preventing further incision?
Is there hard pan or bedrock near the surface?
Culvert and channel capacity reduced by sediment slug released from upstream incision.
Risk to utilities and structures.
Potential passage barriers created upstream by further incision.
Construction access to dig regrade.
Chapter 7, p

17. Incising upstream channel
Slug of regraded material plugging the culvert.

18. Are these “plans” good enough?

19. Complete plans include:
Project Plans
Complete plans include:
Project layout
New and old culvert profiles superimposed
Long channel profile
Bed material specifications and quantities
Care of water (erosion control, diversion plans)
Road runoff treatment

21. Project Plans

22. Project Plans

23. Project Plans

24. Stream Simulation Culvert Effectiveness Study
WDFW and DNR
Bob Barnard
Sheila Yokers
Heather Tschaekosfske
Alex Nagygyor

26. Reference Reach
Culvert

27. 10% (5) culverts with D50 larger than reference
Sites arranged in order of decreasing sediment size →

28. Thalweg Depth survey

29. 10% (5) culverts with deeper mean thalweg depth than reference
Reference reach 95% CI envelope
44% (22) culverts with shallower mean thalweg depth than reference

30. 6% (3) culverts with Q100 velocity greater than reference
11% (5) culverts with Q100 velocity less than reference