will dredge material pile up hydraulically

“Some fish will, when there’s a disturbance, leave the area. “It’s sucking up not only sediments but sucking in water at the same time, and the water has plankton in it, it has fish eggs in it, and it has invertebrates, and fish.”Įnvironmental work windows exist to encourage projects to dredge when special status species are not present, such as during late fall and winter when Pacific herring are not spawning and migrating salmon and steelhead are present. ”Most of the dredging that happens in San Francisco Bay is a mechanical dredge because of entrainment issues,” said Goeden.Įntrainment is the inadvertent removal of organisms during hydraulic dredging suction. Hydraulic dredging is limited in the Bay because of its high impacts. In contrast, hydraulic dredging takes up sediment and water somewhat indiscriminately, “just imagine it’s kind of like a vacuum cleaner underwater,” shares Brenda Goeden, the Sediment Program Manager at San Francisco Bay Conservation and Development Commission (BCDC). Mechanical dredging meticulously lifts sediment up by the bucketful and therefore takes longer and is more expensive.Ĭlamshell dredging project in the Delta. Retrieving the sediment from the Bay’s floor is done by using either mechanical dredge heads, such as a clamshell or excavator, or hydraulic dredge, such as a hopper dredge.

In fact, approximately 3 million cubic yards of materials are dredged annually from the Bay.īecause the Bay is the largest Pacific estuary in the Americas and home to numerous endangered species and delicate habitats, it is certainly worthwhile to explore how dredging is done in the Bay and what kinds of ecological effects there are. While covering a large area, San Francisco Bay is on average less than three meters deep at low tide, so navigation channels, ports, harbors, and marinas are dredged on a regular basis to maintain the Bay as a major maritime hub. As I continued paddling by I also wondered about what kinds of pollutants might be hidden in the growing pile of sediment as the metal claw brought up its next load. My mind boggled as to the kinds of life one would see in the muddy load as it poured out of the claw.

(Photo by Raul Agrait, )Īs I lifted my paddle out of the water near Brooks Island Regional Reserve, I looked up and saw a giant metal claw emerge from the water’s surface and deposit a sizable slurry of slick and shiny mud in a large flat barge. Polychaete worms are part of the benthic macroinvertebrate community that can be affected by dredging activity. Horned Grebe dining on a polychaete worm (Alitta sp.) offshore from the Candlestick Point State Recreation Area.

Will dredge material pile up hydraulically