Noyo River and Harbor, California, Design for Harbor Entrance Protection: Coastal Model Investigation

Source: https://erdc-library.erdc.dren.mil/jspui/ A I :75-scale undistorted hydraulic model was used to determine wave conditions at the entrance to Noyo River and Harbor as a result of an offshore breakwater. The impact of the improvements on long-period wave conditions in the harbor as well as wave induced and riverine bed-load sediment patterns was evaluated. The model reproduced the river from its mouth to a point approximately 15,000 ft upstream, both Noyo Harbor and Dolphin Marina located on the south bank, approximately 3,400 ft of the California shoreline on each side of the river mouth, Noyo Cove, and sufficient offshore area in the Pacific Ocean to permit generation of the required test waves. A 45-ft long wave generator, crushed coal sediment tracer material, and an automated data acquisition and control system were utilized in model operation. It was concluded from the model investigation that: (a.) Existing conditions are characterized by rough and turbulent wave conditions in the Noyo River entrance. Maximum wave heights ranged from 8.5 to 13.7 ft in the entrance for operational conditions (incident waves with heights of 14 ft or Jess) and from 12.2 to 15.2 ft for extreme conditions (waves up to 32ft in height) depending on incident wave direction. (b.) The offshore breakwater plan will result in maximum wave heights ranging from 6.3 to 9.3 ft in the entrance for operational wave conditions and 8. 7 to 14.6 ft for extreme conditions depending on incident wave direction. (c.) The offshore breakwater plan will not meet the 6.0-ft wave height criterion in the entrance for all incident waves of 14 ft or less (operational conditions). Based on hindcast data, however, the breakwater plan will result in the criterion being achieved 37 percent more of the time than it currently is for existing conditions when operational waves are present. The magnitude of wave heights also will be decreased by about 27 percent as a result of the offshore breakwater for operational waves. (d.) With no waves present, the offshore breakwater resulted in riverine sediment patterns similar to those obtained for existing conditions except for the 1 00-year (41,000-cfs) discharge. For this condition, the breakwater prevented material from moving as far seaward in the cove as it did for existing conditions. (e.) With waves present from west-northwest and west, the offshore breakwater slightly changes the paths of riverine sediment migration and subsequent deposits for some river discharges and does not for others. In general, considering all test conditions, riverine sediment will deposit in an area in the cove between the existing jettied entrance and the proposed structure location, both with and without the breakwater installed. (f.) The offshore breakwater will not interfere with the migration of wave-induced sediment into the cove for waves from northwest; however, for waves from southwest, the breakwater will prevent some sediment from penetrating as deeply shoreward in the cove as it did under existing conditions. (g.) The offshore breakwater plan will have no adverse impact on surge conditions due to long-period wave energy in Noyo Harbor, Dolphin Marina, and the lower reaches of the river.