2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 6
Presentation Time: 2:45 PM


DINGLER, John1, ANIMA, Roberto1, REISS, Thomas1 and PHILLIPS, Eleyne2, (1)Coastal and Marine Geology, U.S. Geol Survey, 345 Middlefield Road, M.S. 999, Menlo Park, CA 94025, (2)U.S. Geol Survey, 345 Middlefield Road, Menlo Park, CA 94025, jdingler@usgs.gov

The National Park Service plans to restore most of the Giacomini Ranch to tidal wetland. The ranch comprises 563 acres of diked lowland at the head of Tomales Bay that is currently being used as pastureland for the grazing of dairy cattle. Prior to the establishment of the ranch about 50 years ago, the area was primarily salt marsh that formed as the delta of Lagunitas Creek expanded into Tomales Bay. As part of reclaiming the salt marsh, levees and tide gates were constructed to prevent tidal incursion and stream flooding. Because the primary goal of the project is to restore natural hydrologic processes within the area to promote the return of ecological functions and processes, the levees will have to be breached or removed. Developing a successful restoration strategy will require knowledge of elevations within the pastureland, and the range of water depths that can be expected from tidal, river, and wind action. Toward that end, we have produced a detailed topographic map of the area, and have measured water level and wind climate in Tomales Bay for over two years. A meteorological tower and water level-gauge are installed on the outer levee adjacent to Lagunitas Creek. Mounted on the 10 m tower are a suite of sensors to measure wind speed at one, two, four, and eight meters above the ground; wind direction; and atmospheric pressure, temperature, and rainfall. The water-level gauge measures changes in level caused by the interaction of tides, creek flow, and wind-driven water setup. Another water level gauge is installed on a National Park Service pier midway between the first Giacomini station and the mouth of Tomales Bay. Data from the water level gauge at the pier show a flood-tide lag of approximately 2¼ hours with respect to the predicted tides at the NOAA site and an ebb-tide lag of approximately 3½ hours. Tidal ranges are approximately equal at the two locations. At the Giacomini site, the lag is approximately 1 hour for the flood tide and 4½ hours for the ebb. Elevations are not equal; the peaks match, but the troughs at the Giacomini gauge are significantly truncated relative to those at the NOAA site. We speculate that the truncation is caused by an increased impact of the flow in Lagunitas Creek during the ebb tide. Most of the winds at the site are from the northwest and southeast. The maximum wind speed measured at the 8 m anemometer is over 14 m/s.