The Rumsey Bridge is located on County Road 41, and provides the only all-weather access to properties on the east side of Cache Creek near Rumsey (see Attachment A.) The arch portion of the bridge was built in 1930, and after a major flood event damaged the northeastern abutment, the bridge was lengthened in 1949. Highlighting the unpredictable nature of Cache Creek, the southwestern approach was nearly destroyed in the 1995 flood events, and the bridge was out of service until repairs could be made.
Caltrans oversees bridge safety in California and inspects the bridge every two years. Since the 1960s, Caltrans inspection reports have noted problems with concrete spalls and exposed reinforcing steel on the existing arch bridge, attributed to poor concrete quality and construction. The latest inspection report classifies the bridge as structurally deficient, with a ‘sufficiency rating’ of 37.7 out of 100. As a result of this classification, the bridge is eligible for rehabilitation or replacement under the Highway Bridge Program (HBP) administered by Caltrans.
Under current funding rules, approved HBP projects on local roads such as County Road 41 are effectively 100% funded, though this has only been the case since 2010. Before 2010, HBP projects required the County to provide an 11.47% local match. In the 1990’s the local funding match requirement was even higher at 20%. In the early 1990’s the County requested and received HBP funds to repair the Rumsey Bridge, but had to abandon the effort because of insufficient local match funds. The current funding program represents a significant opportunity to address the ongoing risks of maintaining the serviceability of this bridge in the long term.
Quincy Engineering, Inc. was retained by the County to analyze the existing bridge and study alternative solutions. Their modeling has determined that the existing bridge is neither seismically stable, nor is it able to resist scouring events that creek flows could produce. Staff has attended several informational public meetings with local residents about potential repair or replacement options, which are detailed in the attached Feasibility Study (Attachment B.) The community provided feedback on Quincy’s initial work, and there was strong community sentiment that the existing arch bridge is a key part of the community of Rumsey. As a result, additional configurations for a new bridge with arch elements were developed by Quincy to estimate costs and appearance. Six alternatives were circulated in an April 2015 public survey. Surveys were mailed to 108 property owners of record in the Rumsey area, with postage-paid return envelopes. Thirty eight surveys (35% response rate) were returned. 58% of the respondents showed an affinity for one of the arch bridge replacement styles discussed in the Feasibility Study, and 39% favored the more cost effective box girder alternative. The arch-style design alternative with the most support (47%) was replacement of the existing style.
At the July 28, 2015 meeting, Board members expressed concern with the high costs of the arch-style bridge options, and indicated support for the more cost-effective replacement options that would provide safe access across the creek. Considering only construction costs, the lowest cost option involves constructing a box-girder bridge and leaving the existing bridge in place.
The estimated cost to remove the existing bridge as a part of the larger construction project is $600,000, the difference between the estimated costs of Alternatives 2 and 3. Removal is federally funded as part of a bridge replacement project, but would require local funds if done at a later date. Leaving the existing bridge in place would require a minimum level of ongoing maintenance to ensure public safety. At a minimum, periodic inspections would be needed, along with seasonal closures of the bridge to keep pedestrians off the structure during high water events, when the bridge would be most likely to collapse without warning. (During high water flows scour pits may develop during the storm event and undermine the foundation. These cannot be seen during the storm and tend to fill themselves in after the event, so the risk of collapse may not be apparent during or after the event.) The cost of this minimum level of ongoing maintenance, which would not address the continuing deterioration of the structure itself, is estimated to be in the range of $5,000 to $7,500 per year. The more significant future cost, if the existing bridge is left in place, would be the eventual cost to remove and dispose of it, and any damage claims if the bridge were to collapse during a storm event and alter Creek flows in a manner that damages nearby property. While the estimated cost in the feasibility study to remove the bridge is $600,000, it should be noted that as a stand-alone project the removal cost could be higher. The future cost would be dependent on the bidding market, and recent bid results (2013) to remove the slightly longer bridge over Putah Creek for the City of Winters as part of a bridge construction project show how costs can vary: bids ranged from $250,000 to $860,000. The advantages and disadvantages related to the decision to remove or keep the existing bridge are summarized below.
| Advantages and Disadvantages of Leaving Existing Bridge in Place in the Long Term |
| Advantages |
Disadvantages |
| Leaves in place an historical structure that is of value to the community. |
Public safety risk if bridge collapses while in use. |
| Removes pedestrian traffic from new bridge. |
Minimum annual maintenance cost to the County of $5,000-$7,500, to ensure public safety (Assumes no actual bridge repair.) |
| |
Future cost to the County of $600,000 or more to remove and dispose of existing bridge. |
| |
Unknown County liability if bridge were to collapse in creek during a storm event and alter creek flow pattern/direction |
| |
No funding mechanism for future County costs. |
| |
Does not improve hydraulic performance of creek flows under the existing bridge. |
| |
Appearance of existing bridge will be impacted by adjacent new structure, which will have a higher roadway elevation than existing. |
| |
New structure could not be constructed as close to existing structure if existing was to be preserved. More right of way would need to be purchased to utilize existing bridge following construction. |
Aside from the bridge type selection, there is also the question of alignment. Selection of alignment involves considering, among other factors, road approach alignment and safety, how public traffic will be managed during construction, the cost of a temporary bridge if the bridge is replaced on the same alignment, environmental and archeological impacts, historical integrity, and right of way costs. Replacing the bridge on the existing alignment would require the use of a temporary bridge, estimated in the feasibility study to cost $2,000,000. The 2013 bid results for a temporary detour bridge for the previously mentioned Winters bridge replacement project ranged from $1,070,000 to $2,874,000. Acquiring the additional right of way to place the bridge on a new alignment would be more economical than a temporary bridge. An added benefit of a new upstream bridge alignment is that the alignment of the intersection of State Route 16 and County Road 41 can be improved. Absent a desire to replicate the bridge in its existing location, the preferred location for a new bridge is on a new alignment, upstream of the existing bridge. The environmental, archeological, and historic impacts the selected alternative will be fully studied, and may impact the preferred alignment.
Based on the discussion above and previous Board direction, staff recommends that the project move forward with the construction of a new cast-in-place concrete box girder bridge to be placed on a new alignment upstream of the existing bridge, and the demolition of the existing bridge. |