MONITORING OF DREDGED UPPER SANTA CRUZ HARBOR MIXED SAND AND MUD SEDIMENT RELEASED INTO THE NEARSHORE AREA OF SANTA CRUZ, CALIFORNIA Report prepared by; Steve G. Watt and H.G. Greene Center for Habitat Studies Moss Landing Marine Laboratories (831) 771-4140 December 19, 2002 Monitoring of dredged upper Santa Cruz Harbor mixed sand and mud sediment released into the nearshore area of Santa Cruz, California Prepared by: Steve Watt and Dr. H.G. Greene Center for Habitat Studies Moss Landing Marine Laboratories 8272 Moss Landing Road Moss Landing, CA 95039 (831) 771-4140 December 19, 2001 Prepared for: the Santa Cruz Harbor Port District 135 Fifth Avenue Santa Cruz, CA 95062 and the California Department of Boating and Waterways Table of Contents List of Figures…………………………………………………………………ii List of Tables…………………………………………………………………iii Executive Summary…………………………………………………………..1 1. Introduction…………………………………………………………………...2 2. Local Geologic and Climatic Setting…………………………………………4 3. Oceanographic Conditions……………………………….……………………7 4. Santa Cruz Littoral Cell……………………………………………………….8 5. Marine Biological Assessment……………………………………………….11 6. Methods………………………………………………………………………12 6.1 Scientific Literature Review……………………………………..………12 6.2 Monitoring Program…………………………………………………….13 6.3 San Lorenzo River……………………………………………………….14 6.4 Santa Cruz Harbor………………………………………………………16 6.5 Oceanographic Data…………………………………………………….17 6.6 Sediment & Water Sampling……………………………………………..19 6.6.1 Onshore Sample Collection……………………………………19 6.6.2 Offshore Sample Collection……………………………..…….23 6.6.3 Sediment and Water Sample Processing………………………23 6.7 Geophysical Surveys……………………………………………………...26 7. Results and Discussion……………………………………………..…….…….28 7.1 Sediment Input over the monitoring program…………………………..28 7.2 San Lorenzo River…………………………………….………………..…30 7.3 Santa Cruz Harbor…………………………………………….………..30 7.4 Marine biological Assessment…………………………………………..33 7.5 Oceanographic Conditions and Littoral Drift……………………….….33 7.6 Onshore Sediment Samples…………………………….……………….39 7.7 Offshore Sediment Samples…………………………………………..…48 7.8 Onshore Water Samples………………………………………………...61 7.9 Offshore Water Samples………………………………………………...66 7.10 Hydrographic Surveys……………………………………………….….67 8. Conclusions………………………………………………………………..…..78 Acknowledgements……………………………………………………………80 Literature cited………………………………………………………………...80 Appendix A. Goldberg et al. (2000) Expected dredge material transport and habitats at risk within the vicinity of The Santa Cruz Small Craft Harbor…………………………….83 Appendix B. Wentworth and other sediment classifications…………………100 Appendix C. Onshore sediment and water sample database tables…………...102 Appendix D. Offshore sediment and water samples………………………….106 Appendix E. Greene et al. (1999) Benthic Habitat Classification…………….110 S.G. Watt and H.G. Greene, 2002 i List of Figures Figure 1. Study area location……………………………….………...3 Figure 2. Study area beaches………………………………………..5-6 Figure 3. Littoral cell………………………………………………....9 Figure 4. Flow chart……………………………………...…………..13 Figure 5. Station locations……………………………………….…...14 Figure 6. Sediment sample locations…………………..….………....20 Figure 7. Water sample locations……………………….……………22 Figure 8. Geophysical survey area…………………………….….….26 Figure 9. San Lorenzo stream flow……………..……………………31 Figure 10. San Lorenzo River flood…………………………….….….32 Figure 11. San Lorenzo River low stream flow………………….…….32 Figure 12. Buoy and Array swell heights and periods…………………34 Figure 13. Wave model and Santa Cruz Array swell heights………….37 Figure 14. Harbor photo………………………………………………..37 Figure 15. Blacks beach in winter profile………………………....…...41 Figure 16. Lagoon flooded beaches………………………………..…..42 Figure 17. Exposed pilings on Twin Lakes Beach…………………….43 Figure 18. Pre-Experiment beach sample mean grain-sizes…………...44 Figure 19. Experiment beach sample mean grain sizes…………..…....45 Figure 20. Post-Experiment beach sample mean grain sizes…………..46 Figure 21. Seabright beach cusps……………………………………....47 Figure 22. Twin Lakes Beach…………………..………………..…….47 Figure 23. Pre-Experiment offshore sample mean grain sizes…..…….50 Figure 24. Experiment offshore sample mean grain sizes……………..51 Figure 25. Post-Experiment offshore sample mean grain sizes………..52 Figure 26. Pre-Experiment offshore pie charts………………………...53 Figure 27. Experiment offshore pie charts……………………..……...54 Figure 28. Post-Experiment offshore pie charts……………………….55 Figure 29. Pre-Experiment silt and clay percentages………………….57 Figure 30. Experiment silt and clay percentages………………………58 Figure 31. Post-Experiment silt and clay percentages…………………59 Figure 32. Locations of >20% silt and clay concentration……….……60 Figure 33. Pre-Experiment swash-zone water sample NTU...….……..63 Figure 34. Experiment swash-zone water sample NTU………..……...64 Figure 35. Post-Experiment swash-zone water sample NTU…..……...65 Figure 36. Pre-Experiment offshore water sample NTU……….……...68 Figure 37. Experiment offshore water sample NTU………….………..69 Figure 38. Post-Experiment offshore water sample NTU…….………..70 Figure 39. Pre-Experiment processed multibeam image……..………...72 Figure 40. Pre-Experiment processed backscatter image……..………..73 Figure 41. Examples of identified benthic habitat types……….………74 Figure 42. Post-Experiment processed multibeam image……..…..…...75 Figure 43. Post-Experiment processed backscatter image…….……….76 Plate 1. Seafloor Interpretation Comparisons………. back cover envelope S.G. Watt and H.G. Greene, 2002 ii List of Tables Table 1. Sediment, sources, sinks, and transport …………..………..11 Table 2. Monitoring Period Timeline……………………………..….21 Table 3. Sediment inputs over the monitoring period…………..……29 Table 4. Littoral drift estimates………………………………………35 Table 5. Onshore sediment sample descriptive statistics…………….40 Table 6. Offshore sediment sample descriptive statistics…………..48-49 Table 7. Swash-zone water sample NTU………………..……………62 Table 8. Offshore water sample NTU………………………………...66 S.G. Watt and H.G. Greene, 2002 iii Executive Summary In late March of 2001 the Santa Cruz Small Craft Harbor was permitted to dredge approximately 3,000 yd3 (2,300 m3) of upper harbor mixed sand, silt and clay sediment into the surf-zone approximately 70 yards (64 m) from the shore of Twin Lakes Beach. A monitoring program was designed and implemented by the authors of this report to determine if sedimentary changes occurred in the beaches and nearshore benthic habitats in the vicinity of the Santa Cruz Harbor due to the retention of the mud rich dredged sediment. In addition to a comprehensive scientific literature review, a variety of data was collected to monitor the experimental dredging event and the natural processes occurring in the study area during the monitoring period from February 18 to April 14, 2001. San Lorenzo River stream flow data were used to calculate sediment discharge estimates. Oceanographic swell information was downloaded to monitor wave conditions and to calculate littoral drift estimates. Over 300 sediment samples were collected and grain-size analyses performed. Over 300 water samples were collected to observe changes in turbidity over time. Two separate ~7 km2 geophysical surveys were executed to describe and quantify benthic habitats and sedimentary changes that may have occurred during the monitoring period. The complete integration and analyses of all the data types collected during the monitoring period leads us to the conclusion that the dredged upper harbor sediment released into the surf-zone during the experimental dredging event (including sediment derived from other nearby sources), did not significantly change, alter, or impact the beaches or nearshore marine benthic habitats in the study area. S.G. Watt and H.G. Greene, 2002 1 1. Introduction On March 28, 29, and 30 2001 the Santa Cruz Small Craft Harbor was permitted to release approximately 3,000 yd3 (2,300 m3) in 500-700 yd3 increments (approximately 380- 540m3) of mixed sand, silt and clay sediment into the surf-zone. The material was excavated near J-Dock in the upper Santa Cruz Harbor and released approximately 70 yards (64 m) from the shore of Twin Lakes Beach (Figure 1) near the east jetty. The mud-rich sediment was dispersed between the hours of 7:00 pm to 12:00 am. The upper harbor sediment was composed of ~60% silt and clay (or mud) and 40% sand (Sullivan & Krcik, 1999). The high concentration of mud present in the material is not allowed for surf-zone disposal according to EPA Region IX standards for grain-size (Foss, 1999). The concern is that the fine-grained material may be retained in the beach and nearshore benthic habitats and change the existing natural environment that was present before the experimental dredging event. The primary goal of the monitoring period was to determine if sedimentary changes occurred in the beach and nearshore benthic marine habitats near the Santa Cruz Harbor due to the retention of fine-grained mud that was released during the experimental dredging event. Sedimentary changes were anticipated that may include, but not limited to, the degradation of the quality of sand on the neighboring beaches, burial of the nearshore marine benthic habitats, and alteration of the natural transport of coastal sediment. Our approach was to monitor the habitats that stand the greatest chance of being impacted by the experimental dredging event rather than focus on tracking the dispersal of the mixed sand and mud sediment as it enters the surf-zone. This study focuses on the sandy beaches from Point Santa Cruz eastward to Soquel Point and the