Bank Stabilization at Bridge No. 36-48, Hwy 9, PM 9.3

Bank Stabilization at Bridge No. 36-48, Hwy 9, PM 9.3

This project is the more permanent solution. Work will include repair of the scoured southern bank for approximately 120-feet upstream of the bridge. The emergency work performed this past winter is inadequate as a permanent repair because it can only protect the bank up to moderate flows. The current project will place rock rip rap over filter fabric with a vegetative revetment (willow) that will extend up the southern bank to variable elevations. The total area of rip rap placement will be approximately 120-feet by 15-20 feet tapering to conform to the existing sandstone formation. The existing sack-concrete apron immediately under the south footing of the bridge is undermined and needs stabilization. In order to reduce potential impacts to steelhead, pre-cast concrete jacks will be lowered by crane and hand-placed below and adjacent to the sack- concrete apron. Once in place, the jacks should slow flow under the sack-concrete and facilitate the deposition of sediment within the jacks helping reduce further scour and stabilizing the footing. There is an existing gravel bar on the north side of the river immediately upstream of the Highway 9 Bridge that is believed to be the cause of the bank erosion. This bar was partially removed as part of the emergency work during the winter, and the removal of additional material is necssary to restore parallel flow through this section of the river. A crane operated from the bridge and an excavator on the gravel bar will be used to place the rip rap on the south bank. A front-end loader and crane will remove the material from the gravel bar will be used to place the rip rap on the south bank. A front-end loader and crane will remove the material from the gravel bar. The material will be trucked off-site to an appropriate disposal site.

Santa Cruz