1. 2016 FHWA National Hydraulic Engineers Conference
Portland, OR
August 9-12, 2016
Hydraulic Design Considerations of a Bridge Crossing a Levee
Edward Foltyn, P.E., Sr. Hydraulic Engineer, ODOT Bridge Engineering Section
David McDonald, P.E., Hydraulic Engineer, Region 1, Oregon DOT

2. Background
The existing bridge is a single-span through-truss. It is historic because of the welded truss
The existing bridge is functionally obsolete and is scour critical. Also, there is damage to some of the truss members from vehicular accidents.
The roadway has poor alignment for the agricultural and truck traffic to-and-from a quarry.
This bridge is at the downstream end of a USACE constructed levee system.
ODOT was asked to design and permit a bridge crossing for Umatilla County.
ODOT was asked to design and permit a bridge crossing the Walla Walla River in Milton-Freewater, OR near the Oregon-Washington border for Umatilla County.
The existing bridge is a single-span through truss. It is historic as it is the only welded truss in the State. The bridge is functionally obsolete and is being replaced for roadway widening and better alignment. The bridge has been damaged from trucks (agricultural and quarry) hitting the superstructure
This bridge is at the downstream end of a USACE constructed levee system. This levee was constructed by the USACE n the 1940s, refurbished in the last few years. It is currently maintained by the Milton-Freewater Water District

4. Typical Bridge Hydraulic Considerations
Flooding Issues
No-Rise Certification
Balanced cut/fill below 100-yr flooding
Fish Passage Issues
Federal Aid Highway Program (FAHP) Programmatic with NOAA NMFS (anadromous species, OR - NMFS)
“…procedures and tools for implementing the Federal Highway Administration (FHWA) statewide programmatic Endangered Species Act (ESA) Section 7 consultation and Magnuson Stevens Act (MSA) consultation with the National Marine Fisheries Service (NMFS) and the U.S. Fish and Wildlife Service (USFWS). “

5. Fish Passage (cont.) Scour Issues Oregon Department of Fish & Wildlife
Local populations and In Water Work Window (IWWW)
Scour Issues
Long term aggradation/degradation
Both occur in this reach (degradation D/S of exiting bridge, aggradation near the proposed bridge). The abutments for the existing bridge are a choke point
Contraction Scour
Pier scour
No piers
Abutment Scour
Existing bridge is experiencing abutment scour, settlement has occurred

6. Levee and Bridge Considerations
Could not find much clear-cut information about bridge construction within a levee (large multispan structures generally stay outside of levee)
Limited information about levee encroachment (mostly stay out)
FHWA could not provide any information
USACE “policies” were to stay away from the landside slope toe, but not written in stone

7. Primary criteria for new design
Roadway alignment needs improvement for agricultural and trucks from quarry
Single span for fish passage, debris, and to eliminate pier scour issues
Had to meet USACE levee criteria
Low chord needs to be above the top of the levee
Any excavation/disturbance is supposed to be behind the landside slope toe

9. Normal Design at a Levee
This would have required a span of 250’ or so

10. Analysis and Design
We obtained a recent FEMA FIS HEC-RAS deck (2010 update of FIS; 100-yr flow 11,000 cfs, 500-yr flow 22,700 cfs)
Modified HEC-RAS data deck to incorporate USACE design flow of 18,600 cfs
The Modified data deck overtopped the levee at the location of the new bridge before the bridge was modeled.

11. Analysis and Design (cont.)
Contacted USACE, Walla Walla District. They modified the deck
The new alignment for the roadway and bridge leads to a significantly longer span
Wanted to maintain a single span bridge to minimize fish passage, debris, and permitting issues

12. Current Design at Levee

13. Preliminary Design Existing Bridge Proposed Bridge Structure Type
Through Truss (not much structure below deck level), historic because of the welded truss configuration
Steel Girder (deep girder below deck level ~8’)
Span length
112’, perpendicular
190’, with the skew
Spans
Single Span
Abutments/foundation
Concrete structure as downstream end of levee
Pile foundation constructed in the levee
Roadwork in the vicinity of the bridge
Poor roadway alignment
Reconstructed several thousand feet of roadway to improve alignment and raise roadway 10’

14. Conceptual Plan

15. Current Status and Issues
This is a County owned structure and will remain so
Currently the project is delayed for R.W. issues
There are still issues with the existing bridge. It is historic, but the county wants it removed
The existing abutments are the downstream anchor for the levee system. When the existing bridge is removed, who is responsible for the maintenance and likely replacement of this portion of the levee?
USACE Review for Milton-Freewater Water District
Final plans due late winter/spring 2017

16. Conclusions
When working near a levee, determine the “standards” early in the project
In our case, the levee standards were more strict than any other criteria that we normally use, this stream will never see the effect of a bridge unless the levee fails