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Mr. Michael Jewell To: operation is expected to increase during wetter water years, and over the life of the project due to sea level rise. For portions of the sheetpile to be installed on land, vegetation will be cleared and grubbed for a 35 -ft -wide footprint. For the portions of the sheetpile to be installed in water, installation will be done in water using a barge and tug boat. The structure will consist of two parallel sheetpile walls 20 ft apart. The space between the walls will be dewatered and filled with granular fill. Installation of the gate structure and its foundation will be done in the dry by constructing a metal sheet cofferdam for a 70 x 70 ft area. This area will be dewatered. Concrete cylinder piles (24 inch) will be driven inside the cofferdam, then concrete walls and floor, and then the metal miter gate. The gate for each structure will be 50 ft long. Equipment will include a barge, tugboat, vibratory hammer, crane, and vehicles for transporting equipment, material, and personnel. Closure Structure This measure will involve construction of structures across Smith Canal and Fourteenmile Slough to prevent flooding from the San Joaquin River and Delta; for Fourteenmile Slough, it also will limit the level and duration of water saturation due to higher tides on private levees to the east to reduce the risk of their failure. Each structure will consist of a fixed sheet pile wall structure with an opening gate structure to allow tidal flows and boats to pass when open. The structure will tie into high ground, either the new beim for the Smith Canal structure or the levee for the Fourteenmile Slough structure. The structures will be routinely closed during any water stage equal to or greater than 8 ft North American Vertical Datum of 1988 (NAVD88) caused by high tides or high tide in combination with rain on snow flood events, as well as during emergency (e.g., failure along Smith Canal and Fourteenmile Slough levees to the east) (see Operation and Maintenance, below). The frequency and duration of gate closure operation is expected to increase during wetter water years, and over the life of the project due to sea level rise. The Smith Canal gate structure will be constructed first by SJAFCA under an Army permit while the Fourteenmile Slough gate structure will be constructed later by the Corps as part of the Federal project. Specifics for the Smith Canal gate are as follows. For portions of the sheetpile to be installed on land, vegetation will be cleared and grubbed for a 35 -ft -wide footprint. For the portions of the sheetpile to be installed in water, installation will be done using a barge and tug boat. Elements of construction within waters of the United States include the gate structure, the fixed wall, riprap placement, protective elements in the forms of a series of steel pipe piles along the ship channel side of the fixed wall, fender piles on both sides of the gate structure, riprap on both ends of the fixed wall, and several fishing platforms. Other improvements on higher ground at Dad's Point will be done to bring areas up to at least 15 feet NAVD to provide flood risk protection. The total footprint of all permanent impacts to waters of the United States, which is also designated critical habitat for the smelt, will be 0.820 acres.