Alhambra Valley Road Washout Repair

Project Information
Updated November 3, 2017


Alhambra Valley Road opened to traffic on Thursday, November 2, 2017



Project No.: 0672-6U6201
Federal Project No.: PR ER-32LO (105)

Project Description: Remove washed-out culvert debris, headwalls, gabion baskets. Construct a single span, pre-cast, prestressed voided slab bridge, approximately 60ft by 40ft. Supported on concrete abutments on driven piles, roadway and channel excavation, imported borrow, rock slope protection, placing new road section with signing and striping. Project will require temporary water diversion.

General Location: El Sobrante/Pinole
Supervisory District: #1
Location: Google Map
Contractor: Flatiron West, Inc.
Resident Engineer: Ramon Montes de Oca, Quincy Engineering
Project Manager: Slava Gospodchikov
Construction Start Date: June 12, 2017
Funding Source: Federal
Working Days:  60 days
Estimated Completion Date:  November 3, 2017

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Additional Project Information

Contra Costa County has worked with Caltrans and resource agencies to obtain authorization from Federal Highway Administration (FHWA) to start emergency repairs of Alhambra Valley Road at Pinole Creek crossing that completely washed out during a January 10, 2017 storm event.

Background

Alhambra Valley Road is a major collector with the Average Daily Trips (ADT) = 2,862 (2008 data) serving as an important commute route, providing access to deliver essential public services to the surrounding rural residential areas, and a scenic highway popular among bicycle riders.

The road is a Federal-aid highway and is eligible for emergency response funds in the event of damage as a direct result of a natural disaster.

The replacement project does not change the function or character of the highway facility from what existed prior to the disaster.

Initial assessment and alternatives analysis

On January 30, 2017, County met at the site with representatives from Caltrans and resource agencies. All agreed that given the high environmental sensitivity of the Pinole Creek watershed, it was not reasonable to construct temporary improvements and perform permanent restoration as separate projects. Such approach would effectively cause the environmental impacts and project costs to double, and extend the impacts on the road users. The Pinole Creek watershed is a known steelhead spawning habitat; therefore, replacement creek crossing must be fish passable and not impede steelhead from moving to spawning habitat upstream.

County hired Balance Hydrologics to perform geomorphic reconnaissance of the stream and hydraulic modeling. Based on the modeling results, a 16'x16' concrete box culvert with its bottom buried 2 feet below the stream flowline was identified as the replacement conveyance system. An alternative double 12’x12’ box culvert and other alternatives have been also evaluated. Ultimately, County prepared a repair plan featuring an 18’x16 box culvert 90 feet long as proposed repair for approval by FHWA on March 8, 2017.

However, County received a letter from National Marine Fisheries Service (NMFS) dated March 22, 2017 recommending a 24-ft wide culvert and urging to engage in selecting an appropriate alternative.

Given the engineer’s estimate for the box culvert upsized to 18-ft width with 20-ft high wingwalls has exceeded $2 million, and being pressed by NMFS for an even bigger culvert, County has chosen a bridge alternative, which is comparable in cost but provides more environmental benefit and reduces potential for facility damage due to floating debris blockage, making it more resilient to damage from future natural disasters.

Proposed repair

The repair scope generally consists of installing temporary water diversion, removing washed-out culvert debris, headwalls, gabion baskets; constructing a single span, pre-cast, pre-stressed voided slab bridge – 60 feet span by 40 feet width, supported on concrete abutments on driven piles, roadway and channel excavation, imported borrow, rock slope protection, aggregate base, Hot Mix Asphalt, fencing, signing and striping. The bridge will accommodate two 12’ lanes and 5-8 ft shoulders for bicycle and pedestrian movement. Channel under the bridge will be protected from erosion with rock slope protection (RSP).

To simplify bridge geometry and constructability, the free right turn from Castro Ranch Road will be eliminated, which as an added benefit would improve safety of the intersection consistent with statewide effort of phasing out free right turns.

Right of Way (RW)

There is a 66-ft wide road RW approximately centered on the road alignment. In addition to the comparative cost of bridge to the oversized culvert, the bridge will be fully contained within County road right-of-way and will not require RW acquisition as was the case with the box culvert option.

Conclusion

Repair design has been delayed by inability to collect field data during stormy weather. County has not been able to conduct surveys and hydraulic analysis until March because of continuous storms. Necessity to meet the goals of NMFS for protection of endangered species dictates the bridge alternative that is attainable and would return the road to service this summer. The state of emergency still exists where no convenient detours are available to the traveling public and debris in the creek obstructs fish movement. The shortest detour is approximately 20 miles.

Alhambra Valley Road Washout Road Repair/Culvert Replacement General Plan