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

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

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). “

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

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

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

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

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.

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

Current Design at Levee

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’

Conceptual Plan

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

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