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4/7/20 (P:\TER2001\Delineation\San Leandro Treatment Wetland JD Revised 4‐7‐20.doc) 4 days in the region of the study site) in a year of median rainfall. In most cases, this criterion can only be measured directly by monitoring the site through an entire wet season. Rivers and Harbors Act Jurisdiction The Corps administers Section 10 of the Rivers and Harbors Act, which prohibits "the unauthorized obstruction or alteration of any navigable water of the United States.” Obstruction or alteration includes construction either in or over a navigable water, excavation or deposition of material, or any other work affecting the course, location, condition, or capacity of such waters. Section 10 jurisdiction extends shoreward to the line of Mean High Water (MHW) and includes areas behind dikes that are below the MHW line. Areas that have been filled to elevations above MHW are not subject to Section 10 jurisdiction, provided that the filling was carried out under a Corps permit. FIELD METHODS LSA certified wetland delineator and senior biologist Bernhard Warzecha investigated the site on February 6, 2020, during times of low tide. The high tide line was mapped using a global positioning system (GPS) receiver with sub‐meter accuracy capabilities. The high tide line is the line of intersection of the land with the water’s surface at the maximum height reached by a rising tide. The high tide line was determined by a line of scum, fine shell, and debris deposited in the rip‐rap, and other physical markings and characteristics, including vegetation lines, and interpretation of aerial photography. RESULTS CWA Jurisdiction (Section 404) LSA observed and GPS‐mapped a continuous high tide line along the slough levee, defining the potential upper limit of jurisdictional Other Waters of the United States. Portions of the area below the high tide line support sufficient hydrophytic vegetation cover to meet jurisdictional wetland criteria and are mapped separately from the Other Waters. The potential area of jurisdictional Other Waters within the Project Study Site is approximately 0.09 acre, and the potential area of jurisdictional wetland within the Project Study Site is approximately 0.13 acre. These potential jurisdictional features are mapped on Figure 3, attached. Rivers and Harbors Act Jurisdiction (Section 10) Rivers and Harbors Act Section 10 jurisdiction applies to all areas below the elevation of MHW. Based on the Alameda NOAA tide gauge, the elevation of MHW is 5.98 feet above mean lower‐low water, which is equivalent to 5.75 feet in the NAVD88 datum. This elevation approximately corresponds to the upper limits of the unvegetated mud flats of the tidal slough, as shown on Figure 3. The potential limit of Section 10 jurisdiction within the Project Study Site is approximately 2.2 acres and is mapped on Figure 3.