PG& E contracted Global to perform surveys of four concrete chambers at two separate Dams; Rock Creek Dam and Cresta Dam both located on the North Fork of the Feather River in Northern California. The concrete basins are approximately 25 feet wide by 124 feet long. Global divers accessed the structures through a trash rack and 48-inch inlet; which added an additional obstacle. The total penetration through the pipe and into the deeper area was approximately 35 feet,plus the additional 124 feet to the end of the chamber,necessitated an in-water tender for every dive.
A probe and a scanning sonar were utilized to conduct the surveys and determine the depths of the built up sediment. At Rock Creek,a Steel Wire Rope was established inside one of the chambers approximately 5 feet off bottom. This enabled an MS 1000 sonar to be suspended in order to scan images of the chamber every 5 feet for the entire length.
Inside the same trash rack a 24” pipe was inspected utilizing an ROV; two gate valves had been previously discovered by PG & E engineers to be non-functioning. These 24-inch pipes bifurcated about 25 feet inside the center pier and split off to both chambers supplying water to keep the gates afloat. It was suspected that the pipes and the valves were full of sediment deposited from upstream.
A thorough report providing the data obtained from the sonar images and the probe measurement was provided to the client upon completion of the project.
Global supplied divers to hand operate suction dredge hose for the removal of accumulated river sediment from cooling water intakes at the mothballed N Reactor on the Hanford Nuclear Reservation.
Approximately twelve (12) feet of sediment has built up in front of intake structure of the Agrium Finley Pump Station located on the Columbia River in Kennewick,WA. Divers used a suction pump to pump the sediment / water slurry from the forebay area to an upland location for disposal. Divers operated from a dive trailer located on shore adjacent to forebay area. The suction pump was located on the adjacent pump deck; a booster pump was in line to assist in moving the sediment / water slurry the long distance to the disposal location.
In 1929 the City of Portland built Bull Run Dam 1 on Federally protected and restricted land,the Bull Run Watershed. This complex,Bull Run Dam 1 and 2 is a significant source of potable water for the City of Portland and the surrounding area. Due to its location of Federally protected land and fact that we are working in potable water great care has been taken during the project,from complete decontamination of all diving gear and related equipment that enters the water,to complete containment for all mechanical equipment on site. Access to the site is extremely limited,there is no thru access across the top of the dam,all of the equipment had to be staged on top of the dam. The water level has fluctuated over 40 feet during the project,making access to the water extremely difficult.
The dam has seven slide gates mounted to the face of the dam inside a trashrack enclosure. These gates,located at various levels allow the operators the control the flow of water as well as the level (temperature) of the water as it moves through the system. During the project the existing trashracks as well as the supporting beams were found to be severely rusted. They are all being replaced with new galvanized beams and panels. One existing gate,#6 had severely eroded concrete behind the frame where it mounts to the dam wall allowing water to pass even when the gate was closed. Part of the project was the complete removal of the gate,drilling out of the original anchor bolts,repair to the concrete and reattachment of the gate to the dam. This entire process was carried out inside of the trashrack enclosure Tracks were mounted to the underside of the enclosure and the gate was moved to the outside edge where it lifted and set on deck for cleaning and storage while the concrete repairs were being made. The gate was reinstalled and secured with new anchors.
The existing materials were all the original installation,the nuts which secured the stem to the gate were severely corroded and had to be cut off. All of the existing stems were removed and disposed of as well as all of the stem guides and the actuators mounted on the surface. New stems guides were mounted to the face of the dam. New stems were attached to the guides. As stated above,all of the work was carried out inside of the trashrack structure,all of the parts and pieces had to be lowered into the water then cross hauled under the overhead structure and lowered into place. Once installed through the operator floor the stems were attached to new operators and connected to the gate itself. All gates were fully function tested for proper operation.
Part of the project also involved repairs to the spillway. Rolling scaffolding was raised and lowered on the curved spillway surface as needed to access the area to be repaired.
We were contracted by Kiewit to provide diving services to assist with the installation of a wall between Bays 8 and 9 of The Dalles Dam on the Columbia River. The wall is intended to redirect the salmonids that are migrating downstream and increase their survival rate.
The wall is 10 feet wide and over 800 feet long,the last 150 feet of which is at an angle to direct the water flow into a deeper portion of the river. It is constructed of precast concrete segments that were installed in the spillway and onto a leveling slab built on the river bottom. The segments were set in place and leveled using jacking rods. Once level and in place,the next segment was brought in and the process repeated. After several of them were in place,divers tied the segments together with rebar dowels. Forms were then installed on the joints between and around the bottoms. Concrete was then tremied into the segments. This process was repeated across the stilling basin.
Where the wall extends beyond the stilling basin,a 15-foot-wide leveling slab was installed. The river bottom was cleaned of loose debris. An area that ran across the path of the wall was excavated,because the underlying rock was fractured and non-competent. Form work was lowered from the surface and fit to the bottom contour. Rebar doweling was drilled and epoxied into the river bottom where needed. Rebar mats were installed inside the form work. Concrete was again tremied in place.
The wall has been carried over onto the leveling slab in the same manner as on the stilling basin.