Many experts forecast potential El Ni?????o conditions this winter. In 1997 the phenomenon resulted in 200 -300 percent of normal rainfall for much of California and the San Francisco Bay Area causing severe erosion and landslides. Residents in nearby Daly City watched as much of Daly City Drive collapsed down the beautiful but unstable coastal cliffs at Avalon Canyon. Over 120,000 cubic yards of material was lost due to the landslide and erosion. Thirty-thousand cubic yards of this eroded soil was deposited in the sediment basins with the rest lost to the ocean. The collapse endangered many, left the road impassable and resulted in nine homes evacuated. The potential danger and cost of such failures illustrates the need for erosion control planning. One important aspect of erosion control planning is a thorough site assessment. Has the source of the original problem been identified and corrected? All too often landslides are repaired by merely removing or regrading the original slide material. This quick fix will likely result in continued failures. It is important to determine the initial cause of the failure and correct these deficiencies to help prevent a repeat failure. Rebuilding the Canyon Daly City was faced with the problem of how to repair and protect the area before the next winter. Jacobs Associates, an engineering consulting firm, was retained. With the help of FEMA funds, Ford construction began the reconstruction throughout the summer and fall, which included 430,000 cubic yards of cut and fill that was benched, creating shorter slopes and ditches to channel surface flows. In addition, a new canyon storm drainage system was installed using over 1,800 feet of 36- and 28-inch HDPE (High-Density Polyethylene) pipe. A new sediment basin complex was constructed at the base of the canyon to collect runoff before discharging to the ocean. Evaluation and Design It is important that the purpose of the protection is considered. Will this be a temporary treatment that will be removed or redone at a later time? Many times this approach is chosen when conditions will not allow for permanent treatment applications. Temporary controls will include the use of straw, which is pneumatically blown on the site, and either incorporated into the soil by punching or tacked down with the use of a binding agent applied with a hydroseeder. Seeding with quick growing grasses will provide the vegetation and root structure to integrate and stabilize the surface soil. There are additionally many manufactured products that are quick to install and provide immediate protection. These include straw or coconut tubes and silt fence that is placed on the slope surface to create shorter slopes and provide sediment control. The design and installation of permanent measures will include blankets and fixed structures such as gabions or riprap. The vegetation selection will be very important. Keep in mind that you are re-establishing the species that are native to the area. This will include native grasses, forbes, shrubs and trees. On the Avalon Canyon project; Carol Florence from Oasis Associates, the landscape architect for the project, selected a mix of native grasses and groundcover. The planting also included the use of Monterey Pines, Shore Pines and Monterey Cypress trees, along with willow cuttings for wetter locations on the project. Soil composition, access and slope factor must also be evaluated. Is the onsite soil capable of sustaining plant growth? And if so, what is its make-up? Is the area accessible with equipment? How steep and long are the slopes? Will it be necessary to perform all work with hand crews? When designing your erosion treatments you will be using different applications on sandy soils, clay and rock. The use of equipment and related products will help keep labor costs down if they can be used. On the Avalon Canyon project the soils were of a highly erodible, silty nature. Straw was to be applied and incorporated by punching where access allowed. All other areas were to be protected using a BFM (Bonded Fiber Matrix) application. This would be applied using a hydroseeder. Execution / Teamwork Unrelated delays and complications during drainage installation and the reconstruction phase pushed the completion of the dirtwork out until the fall. Ford construction was still completing grading operations during the start of the rainy season; the site was now exposed to potentially devastating erosion. Given the new conditions with access severely limiting the erosion and revegetation efforts, a re-evaluation was necessary. The erosion control professional recommended that the addition of a quick germinating nurse crop be added to the seed mix to provide interim protection before the slower growing grasses began to take hold. While winter storms began arriving, KCI began the application of the seed mix with fertilizer and a MBFM (Mechanically Bonded Fiber Matrix) to the site. The use of Hydro-blanket MBFM allowed the work to go forward even during early light rains where other technologies would have required drying times before protection would be achieved. As work continued the conditions and access continued to deteriorate. The hydroseeder and crews were lowered down to the work while tethered to a D-9 Cat. Long Hose runs were used to access remote areas. First seed mix, fertilizer and MBFM were applied, followed by up to another three applications of MBFM for a total of 3,500 pounds/acre. The MBFM was applied from different directions to provide a "blanket" of protection and eliminate any voids or exposed soil that would allow surface flows to penetrate the matrix and result in surface erosion. During Thanksgiving heavy, rains were pounding down upon the canyon. Areas where no erosion control had been applied experienced very noticeable amounts of erosion and sediment loss. These areas had to be re-graded and cat walked. Where the erosion control had been applied, no appreciable amount of erosion existed. This was before any measurable germination was evident to provide vegetative stabilization. The peak of erosion season had now arrived and approximately 25 percent of the site had been treated. Access was now impossible for the straw blowers and the winch/crimper truck to apply the originally planned straw on previously accessible slopes. With the excellent results of the treated areas evident and time running out, Florence and Ford elected to use the MBFM treatment over the entire site. Over the next several weeks, crews from KCI completed work on the canyon. As winter passed and spring arrived, the team efforts were observable. "It appears as if this site is well protected by the nurse crop and the long-lived native coastal species are becoming established," said Gilpin. During this time, planting crews finished the revegetation work by installing the 2,000 tree seedlings and willow cuttings. The nurse crop had established itself, the native grasses, shrubs and groundcovers were growing and both the short-term emergency erosion control needs and long-term revegetation efforts were successfully achieved. Florence best summed up everyone's feelings when she said, "It was a gut wrenching winter and, although the view from Avalon Canyon is priceless, the multiple adverse environmental and synthetic conditions put all of our combined knowledge to the test! Projects of this magnitude are the product of a team effort. All in all, the city of Daly City believes that the work effort was a success." Naturally occurring erosion, when accelerated by manmade disturbance, is a complex interaction of many factors. In order for erosion control measures to be effective, all of these factors must be taken into account. The many influencing factors must be identified, analyzed, and corrected separately or if possible, in conjunction with others. Landowners, architects and engineers working with the erosion control contractor can all be instrumental in the development of a comprehensive plan to identify and correct these many contributing factors which lead to soil erosion and slope failures. Jim Gorter is a certified professional in erosion and sediment control (CPESC) and a member of the International Erosion Control Association.