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<br />San Leandro Marina Dredging <br />Past - Present - Future <br /> <br /> <br />San Leandro City Council <br />Marina Committee <br />May 22, 2007 <br /> <br />Tides - A Boater's Perspective <br /> <br />. Height of ocean and bay waters and their changes are a <br />result of the relationship of the earth with the sun and <br />moon <br />This change in the elevation of the water, referred as the <br />'Ude", also produces water movement or 'currents" in the <br />SF Bay <br />. Maximum and minimum water elevations 'high" or 'low" <br />tides occur twice each day <br />Each high and low tide is different and result in a water <br />elevation difference of as much as 11 feet each 12 hour <br /> <br /> <br />Siltation of the Bay - <br />The need for dredging <br /> <br />Existing material in the bay, bank erosion, silt from storm <br />drains, drainage channels, rivers and atmospheric dust <br />are transported by the currents at the bay floor <br />The bay floor and the dredged channels receive the silt, <br />which requires removal <br /> <br />Marina and the Channel <br /> <br />1970 Channels 1,2,3 <br />& 4 were federalized <br />- 69 acres of water <br />surface <br />1984 Channel 2 was <br />abandoned and 4A <br />established with the <br />relocation of the boat <br />launch ramp <br />Marina Basin (City <br />maintained non- <br />federal channel) <br />- 13Acres <br /> <br /> <br />Tides - A Boater's Perspective <br /> <br />Boats berthed at the Marina typically have 2' to 7' drafts <br /> <br />At design dredge depth (after dredginfij) water depth <br />ranges from 7.5' to 10' at normal low tide, but can be as <br />little as 5' <br /> <br />As of October 2006, when the last sounding was <br />performed by u.s. Army Corps of Engineers (CO E), the <br />average water depth was 5.7', with a minimum of 3' <br /> <br />At extreme low tide, which can happen twice a month, <br />some areas can have little or no water <br /> <br /> <br />Types of Dredging <br /> <br />Mechanical Dredoino <br />- A mechanical excavator supported on a barge (land located <br />equipment can be used near the shoreline) <br />- Excavator may be a bucket on an articulated arm or, more <br />usually, a Clam shell on a winch line <br />- Sediment Is scooped up by the excavator and placed on to the <br />barge for transportation to Its desired destination <br /> <br />;J...r...-.........'...M!...........N......*.'.................... . ....... <br />;(::,:'::(<!~Y;h:,:_, <br /> <br /> <br />1 <br /> <br />