The Washington State Department of Transportation is planning to repair and replace portions of the Hood Canal Bridge. To minimize construction impacts, it is important to spatially evaluate the location of biological resources, such as eelgrass (Zostera marina), geoduck clams (Panopea abrupta), and rockfish (Sebastes spp.), near the bridge, particularly at the eastern and western termini, and associated construction sites.
An underwater mapping effort was conducted during January 2001, during a season noted for dieback of eelgrass and senescence, whereas CASI imagery was collected during the summer of 2000 when eelgrass cover was at a maximum. Although the two methods produced some minor differences in the eelgrass patch margins, the vast majority of the areas overlapped along the eastern terminus where both methods were employed. Hence, the resulting maps for both the eastern and western termini should be considered accurate delineations of eelgrass (cover type and geopositional accuracy). At both the eastern and western termini, close to the bridge, a general lack of eelgrass continuity was noted. However, continuous beds were mapped on both sides at varying distances from the bridge.
The merged intertidal-subtidal eelgrass maps are the result of one of the first integrated mapping efforts of nearshore eelgrass in the Northwest. The spatially referenced data collected on substrate type, fish, and macroinvertebrates will allow examination of habitat usage in the future near the eastern and western termini of the bridge.
May 6, 2007
Dana Woodruff, Amy Borde, Greg Williams, John Southard, Ron Thom, Charles Simenstad, Ralph Garono, Rob Robinson, Jim Norris.
Washington State Transportation Center (TRAC)
- # of Pages: 36 p., 1,658 KB (PDF)
- Subject: Bridges, Construction and maintenance, Environmental impacts, Fishes, Habitat (Ecology), Mapping, Pontoon bridges, Substrates (Waterways)
- Keywords: Eelgrass, underwater video, Hood Canal, CASI, hyperspectral, remote sensing, habitat assessment, GIS, Underwater video mapping.
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This abstract was last modified April 29, 2008