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Home My WebLink AboutCT 13-03; ROBERTSON RANCH-RANCHO COSTERA; GEOTECHNICAL REVIEW OF EROSION POTENTIAL; 2011-10-18I GEOTECHNICAL REVIEW OF EROSION POTENTIAL RANCHO COSTRA LAND BRIDGE, RANCHO COSTERA PROJECT S (ROBERTSON RANCH WEST VILLAGE) ' CARLSBAD, SAN DIEGO COUNTY, CALIFORNIA FOR •. •1. SHAPELL HOMES • .. 8383 WILSHIRE BOULEVARD, SUITE.700 BEVERLY HILLS, CAUFORNiA90211 . . W.O. 6145-A6-SC OCTOBER 18, 2011 • ..• S ••• ... RECEIED. . . •' •• .• . DEC 092013 :'• LANLI ci..Ur'MENT ENGINEERING I Geotechnical e Geologic. Coastal . Environmental 5741 Palmer Way • Carlsbad, California 92010 • (760) 438-3155 • FAX (760) 931-0915 • www.geosoilsinc.com October 18, 2011 W.O. 6145-A6-SC Shapell Homes 8383 Wilshire Boulevard, Suite 700 Beverly Hills, California 90211 Attention: Ms. Teresa Sousa, Mr. John Buller, and Mr. Erik Pfahler I Subject: Geotechnical Review of Erosion Potential, Rancho Costera Land Bridge, Rancho Costera Project (Robertson Ranch West Village), Carlsbad, San Diego County, California Dear Ms. Sousa, Mr. Buller, and Mr. Pfahler: In accordance with your request and authorization, GeoSoils, Inc. (GSl) has reviewed the potential for erosion in the vicinity of the proposed land bridge (i.e., open bottom arch culvert) at the subject site, for possible application along the bottom of the arch culvert. The evaluation of scour around engineered structures (bridges and culverts) is typically performed by civil engineers that have a specific knowledge of scouring, hydrology, and bridge/culvert construction. The geotechnical review comments and recommendations herein should be incorporated into that type of scour study. Based on our review of the referenced reports and documents (Appendix A), and engineering analysis, the following discussion is provided. USDA SOIL ASSOCIATIONS A site specific custom soil resource report was prepared for Rancho Costera (USDA, 2011). A review of that report, and Bowman, et al. (1973), indicates that surficial site soils in the immediate vicinity of the land bridge are mapped as the Salinas clay loam. However, a textural analysis completed by this office (GSl, 2011 c) indicates that surlicial soils in the vicinity of the land bridge are actually sandy barns to barns, and as such, likely belong to the Visalia sandy loam, which borders the mapped boundaries of the Salinas clay loam (USDA, 2011; Bowman, et al., 1973). SOIL TEXTURE Based on a review of prior field and laboratory testing GSI (2011 c), soils in the vicinity of the land bridge range from sandy barns to barns with approximately 46 to 70 percent Sand, 16 to 33 percent Silt, and 15 to 22 percent Clay. The relative distribution of grain size is shown on the Soil Textural Triangle, Figure 1, in GSI (2011 c). For ease of review, GSI (2011 c) is provided as Appendix B. SOIL EROSION Based on a comparison with similar soil conditions evaluated for the Viaslia sandy loam (USDA, 2011; Bowman, 1973), the soil types evaluated in GSI (2011 c) may also be considered to have the following erosion related soil attributes used by the Revised Universal Soil Loss Equation (RUSLE). Erosion factors include the Kfactor (Kw and K0 and the T factor. Site K Factors - Kf = 0.20 Kw= 0.17 Erosion factor K indicates the susceptibility of a soil to sheet and rill erosion by water. Factor K is one of six factors used in the Universal Soil Loss Equation (USLE) and the RUSLE to predict the average annual rate of soil loss by sheet and nil erosion in tons per acre per year. The estimates are based primarily on percentage of silt, sand, and organic matter and on soil structure and Ksat (saturated hydraulic conductivity). Erosion factorKf indicates the erodibility of the fine-earth fraction, or the material less than 2 millimeters in size. Erosion factor Kw indicates the erodibility of the whole soil. The estimates are modified by the presence of rock fragments. Values of K range from 0.02 to 0.69 in the study area. Other factors being equal, the higher the value, the more susceptible the soil is to sheet and rill erosion by water. Site T Factor - T = 5 Erosion factor T is an estimate of the maximum average annual rate of soil erosion by wind and/or water that can occur over a sustained period without affecting overall plant growth and viability (technically crop productivity). The rate is in tons per acre per year. Soils with K factors of the magnitude discussed above are considered to possess a relatively "low" erodibility (Jones, et al. [undated]). Our review indicates that these soils may start to erode when velocities of water runoff approach approximately 0.65 feet (0.20 meters) persecond (Aquatext, 2011; USGS, 1984), to as much as 2.5 feet (0.76 meters) per second (Amimoto, 1981). Shappell Homes W.O. 6145-A6-SC Rancho Costera Project, Carlsbad October 18, 2011 FiIe:e:\wp12\61006145a6.gro Page 2 GeSoth, bc. To model the erosion and potential scour of soils in the up-gradient channel, around and inside the arch culvert bottom (open bottom), the civil designer should incorporate the geotechnical and soil information herein, as well as evaluate the hydrology and scour potential for this site. Scour protection for the proposed arch culvert should be added as recommended by the civil consultant. The civil designer performing the scour evaluation for the channel should incorporate the sieve analysis data from GSI (2011 C), included herein as Appendix B. If deeper scour will expose soils in the channel that have not been described herein (below 4 to 5 feet), additional investigation may be warranted. Typically, soils are considered erosive if they are classified by the Unified Soil Classification System (USCS) as "SP", "SM", and "SW", U with low density, little or no induration or plasticity (Plasticity Index <5), and low fines content (< 10%). LIMITATIONS I The conclusions presented herein are professional opinions. These opinions have been derived in accordance with current standards of practice, and no warranty, either express I .or implied, is given. Standards of practice are subject to change with time. GSI assumes no responsibility or liability for work or testing performed by others, or their inaction; or work performed when GSI is not requested to be onsite, to evaluate if our I recommendations have been properly implemented. The opportunity to be of service is greatly appreciated. If you have any questions I concerning this report, or if we may be of further assistance, please do not hesitate to contact any of the undersigned. No z co Respectfully submi CH ndrew Guat John P. Frank in 1A Geotechnical En 1 0 ?Engineering eolog)~ RGC/ATG/JPF/jh Attachments: Appendix A - References Appendix B - GSI Report Dated April 22, 2011 Distribution: (3) Addressee 1 (2) O'Day Consultants, Inc., Attention: Mr. George O'Day Shappell Homes Rancho Costera Project, Carlsbad File: e:\wpl 26100\6145a6.gro W.O. 6145-A6-SC October 18, 2011 Page 3 APPENDIX REFERENCES I. I. I. 1. APPENDIX A REFERENCES Aquatext, Scouring Velocity, The Free On-line Aquaculture Dictionary, http://www.aguatext.comltables/scouring.htm. Amimoto, Perry Y., 1981, Erosion and Sediment Control Handbook: Division of Mines and Geology, Department of Conservation, May. Bowman, R.H., Bishop, R.E., Griffen, R.W., and Jones, M.L., 1973, Soil survey, San Diego area, California, Parts I and II, United States Department of Agriculture (USDA). GeoSoils, Inc., 2011 a, Geotechnical review of coastal development permit plans for El Camino Real Rancho Costera Project, Carlsbad, San Diego County, California, I W.O. 6145-A4, dated September 12. 2011 b, Supplement to the updated geotechnical investigation for Rancho Costera (formerly Robertson Ranch West Village), Carlsbad, San Diego County, California, I W.O. 6145-Al-SC, dated June 6. 2011 c, Soil texture and groundwater evaluation, Planning Area 23C (Wetland/Habitat Area), Rancho Costera, Carlsbad, San Diego County, California, W.O. 6145-A2-SC, dated April 22. I , 2010, Updated geotechnical investigation for Robertson Ranch West Village, Carlsbad, San Diego County, California, W.O. 6145-A-SC, dated October 11. I Jones, D.S., Kopwalski, D.G., and Shaw, R.B., undated, Calculating revised universal soil loss equation (RUSLE) estimates on Department of Defense lands: A review of RUSLE factors and U.S. Army land conditions - trend analysis (LCTA) data groups. Morgan, R.P.C., 2005, Soil Erosion and Conservation, Third Edition, Blackwell Publishing Toy, T.J., Foster, G.R., and Renard, K.G., 2002, Soil Erosion, processes, prediction, measurement, and control, John Wiley &Sons, pub. United States Geological Survey (USGS), 1984, Physical basis and potential estimation techniques for soil erosion parameters in the precipitation-runoff modeling system (PRMS), Water-Resources Investigations Report 84-4218. United States Department of Agriculture, 2011, Custom soil resource report for San Diego County area, Rancho Costera, dated October 13. GSoills, bc. APPENDIX GSI REPORT DATED APRIL 22, 2011