Graduate Thesis Or Dissertation
 

Evaluation of estuarine channel conditions in Coos Bay, Oregon using side-scan sonar

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/v405sd51r

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  • Side-scan sonar records in Oregon's Coos Bay estuary navigation channels were obtained at intervals of two to three months during the November 1974 - October 1975 time period from Coos Bay Channel Mile 11+50 to 15+20, and from a reach in the Marshfield Channel. A limited side-scan survey effort was also accomplished in the South Slough from Channel Mile 1+00 to 2+30 and in the Coos Bay main channel, from Channel Mile 2+40 to 11+50. The latter surveys were considered secondary to the prime research effort, but did provide imagery results of significance which are included in this report. A primary study task was to attempt identification of sediment types on the Coos Bay Estuary bed by side-scan survey. It was determined that objects with a diameter size of 10 centimeters or larger could be directly identifiable from side-scan imagery results. Lesser sized materials, such as sands and small shells were not directly seen on the sonographs but accurate inference through interpretation of tonal response and sonograph imagery patterns was proven to be possible. Another task was to discern deep draft vessel impacts on the estuary bed in the Coos Bay Navigation Channel from Channel Mile 12+00 to 15+20. The annual sediment turnover value attributed to vessels plying the navigation channel as interpreted by side-scan survey has been calculated to be approximately 350,000 cubic yards versus a historical annual removal of 390,000 cubic yards per year by dredging activities. A method using the side-scan equipment to establish bedload transport processes and transport values in marine waters was suggested during the study period. The method has been expanded to include calculation of a rate of sediment turnover resulting from movement of the bedload. Side-scan records were obtained immediately following pipeline maintenance dredging of the navigation channel above Channel Mile 12+00. The dredging signature left along the navigation channel and the relative rate of return of topographic bed conditions to a predredge status has been presented. Little major change in the bed sediments or topography occurred during the course of this study and has been confirmed by side-scan records. Hopper dredge activities in the upper bay were also recorded by side-scan imagery. Suggested future applications of side-scan equipment are also discussed. including the potential for an improved method of classifying estuaries. The basis for classification utilizes side-scan sonar to identify estuarine bed sediment types and the recovery rate of the bed from natural or man-made disturbances.
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