1. Bridges

2. Definition
A Bridge is defined in Minnesota as a structure over 10’ in length, sized hydraulically to convey water under a highway, railroad or other embankment
Road grade, geometrics, site-distance, vertical curvature or ecological considerations may also influence the size of the waterway opening

3. Basic Criteria For DNR- no stage increase over 0.5’ for new crossings.
Check flood damage potential upstream
Velocities no more than 8-9 fps
Match the channel width up and down stream

5. Case Studies Br
ADT < 50, minimum flood is 5 year
Design speed: 30 mph
Sag Vertical Curve
Match the natural channel bottom
Used a 100 year design event as road profile drives the design
Used single span structure with deep beam to save on structure size.

7. Case Studies Br 85560 25 year design was used
ADT <50 (Dead End), minimum flood is 5 year
Inplace 4- 36” CMP with Slab
Resident was cut off during floods, township wanted dry crossing
Road design 30 mph, design speed set the road profile
Max velocities between 8-9 fps
Stage increase < 0.5’
Designated trout stream
25 year design was used

9. Case Studies Br 58552 Used a 100 year design event
ADT < 50, minimum flood is 5 year
Sag Vertical Curve, design speed 30 mph
Old bridge was constricting the river
Channel Bottom Upstream and Downstream ~ 80’ wide
High debris stream
Vertical curve drives the design
Used a 100 year design event

11. Case Studies Br 08552 100 year design was used
ADT 510 minimum flood is 25 year event
Road profile is driving the design
Inplace road does not overtop
Stage increase was to be held at a minimum
0.6’ for the inplace
0.5’ for the proposed
100 year design was used

13. Case Studies Br 30515 100 year design was used
ADT 925 minimum flood is 25 year
ARRA Project- Federal Funds were used
55 mph design speed was required as ARRA funds were used
Sag Curve was designed for the design speed
Bridge sized to match natural channel bottom
100 year design was used

15. Case Studies
Br 22605
ADT < 50, 5 year event
Road Profile is driving the design
Matched the waterway opening of inplace bridge
Br 55583
ADT 2200, 50 year minimum event
Velocities are high, 8.5 fps
Match existing bridge lengths
100 year design was used on both bridges

16. Deck Drains
Federal Requirement: Army Corps of Engineers General Permit does not allow bridges with over 500 heavy vehicles per day to drain directly to a trib to a navigable water
No State Regulation, but DNR has conditions in the General Permit that will not allow direct drainage to a stream
When ever possible, keep the deck drainage from being discharged directly to a stream