A Lake Tahoe bluff restoration

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1 JUNE/JULY 2011 VOLUME 29 NUMBER 3 From eroded to elegant Under the green roof in northern California A Lake Tahoe bluff restoration Reviving the Wrigley Reservoir Geosynthetic applications in the new I-35W Bridge More Q s-&-a s from the GMA Techline SUSTAINABILITY A European perspective The return of In the Lab Case histories examine geomembrane performance Subscribe S at e gazi n.com

2 The project site (completed) was situated on the west shoreline of Lake Tahoe overlooking Rubicon Bay. 18 Geosynthetics June July 2011

3 PROJECT SHOWCASE From eroded to elegant A Lake Tahoe bluff-restoration story By James Chinchiolo 19

4 PROJECT SHOWCASE Lake Tahoe bluff restoration The property is a gently sloping lot that abruptly drops 60 ft. down to a sandy beach on the lakeshore. Introduction This project took place on a scenic high-banked lakefront property in Rubicon, Calif., with a 60-ft-high unstable and badly eroded shoreline bluff facing (Photo 1). The site was originally owned by Scottish immigrant and journalist B.C. Forbes (founder of Forbes magazine), and it is now owned by a London family that splits its time between the U.S. and U.K. Having found and bought such a dream property, the owners first had to deal with the issue of serious bluff erosion (Photo 2). Remediating the bluffside deterioration would become the largest and most complex shoreline stabilization and restoration project ever attempted in Lake Tahoe basin history. The project site is on the western shore of Lake Tahoe on 4.8 acres with a vast 180-degree panorama overlooking Rubicon Bay. The property is a gently sloping lot that abruptly drops 60ft down to a sandy beach on the lakeshore. Photo 1 The story starts with a badly eroded Lake Tahoe shoreline bluff. 20 Geosynthetics June July 2011

5 The entire project involved removing an existing residence and constructing a new single-family home, tennis court, and guesthouse. This required placement of the main house just behind the bluff s edge and into a zone threatened by the unstable bluff face. Bluffside restoration Bluff stabilization was an obvious and immediate objective (Photo 3). Initial concerns and discussions about the stability of the bluff face were prompted by the owner s desire to both protect the new residence and to preserve that landscape with its magnificent view. There was also the requirement to create a safe and stable walking path down to the private beach. Surface erosion and sloughing of the bluff face at first look appeared widespread; furthermore, erosion of the bluff face was likely accelerated by the waves of Lake Tahoe undercutting the toe of the bluff during periods of high water. PROJECT HIGHLIGHTS LAKE TAHOE SHORELINE STABILIZATION AND RESTORATION LOCATION Rubicon, Calif., west shore of Lake Tahoe DESIGN/BUILD PRIMARY CONTRACTOR Landslide Solutions Inc. PROJECT ENGINEER John S. Black Consulting GEOTECHNICAL CONSULTANTS Holdrege & Kull LANDSCAPE DESIGN AND INSTALLATION Native Plant Farms & Tree Movers CIVIL AND ROCK PLACEMENT CONTRACTOR Manchester Enterprises Inc. PERMIT SPECIALIST AND PROJECT CONSULTANT Jan Brisco ARCHITECT Faulkner Architects BLUFF STABILIZATION Soil Nail Launcher Inc. PHOTO 2 Issue #1 serious bluffside erosion. SURFACE TREATMENTS MacMat HDPE open-web mesh TRM Galfan -coated SuperMesh CellScape coconut coir cellular confinement ( CustomCoir ) TIMELINE 10 weeks COST $120/sf PHOTO 3 Bluff stabilization was an obvious and immediate objective. James Chinchiolo is the CEO of Landslide Solutions Inc., based in Elk Grove, Calif. Photos courtesy of Landslide Solutions Inc. 21

6 PROJECT SHOWCASE Lake Tahoe bluff restoration PHOTO 4 About 500 soil nails were launched into the bluffside. PHOTO 5 An area of more than 10,000sf was covered with meshreinforcement materials. 22 Geosynthetics June July 2011

7 In addition to structural considerations required to accommodate the new walking path and main house, the owners envisioned a masterfully restored facade to recapture the much-admired native High Sierra ecology. Their vision paralleled the strict scenic assessment standards set by the Tahoe Regional Planning Agency (TRPA) and aided in smoothly carrying the stabilization project through a rigorous agency review process. Traditional methods of mechanical slope stabilization such as benching, shotcreting, or retaining wall construction would have been effective at stabilizing the bluff face. Those approaches, however, would have substantially altered the appearance of the shoreline bluff facing and would have been rejected by the TRPA. Project obstacles and solutions The sandy silt bluff material coupled with the semi-arid Lake Tahoe environment was not an ideal restoration combination. After considerable thought and discussion with erosion control vendors and consultants, it was decided that a hybrid biotechnical solution was required a smorgasbord of stabilization ingredients: about 500 soil nails launched into the bluffside (Photo 4). more than 10,000ft 2 of turfreinforcement mat and coated mesh materials (Photo 5). more than 10,000ft 2 of customvegetated coconut coir confinement cells (Photo 6). more than 400 tons of 2ft-6ft diameter native granite boulders. The soil nails, installed at up to 200mph with a declassified British air cannon, provided slope stability and anchorageplate points for the ensuing mesh layer. PHOTO 6 A coconut coir cellular containment system was installed over the mesh to accommodate the soil infill and custom vegetation. PROJECT RECOGNITION The Tahoe Regional Planning Agency (TRPA) recognized recipients of the 2010 Best in the Basin Awards during its Feb. 23 meeting at the North Tahoe Event Center in Kings Beach, Calif. This project was recognized with a Best of the Basin award in the Residential Modification/Shorezone category. The 21st annual TRPA Best in the Basin awards program recognized projects demonstrating exceptional planning, design, and compatibility with the Lake Tahoe environment. Local professionals in the fields of landscaping, planning, engineering, water quality, and resource management judged each category. The award description: The Houghton-Berry property is located atop a steep bluff in Rubicon Bay where the shoreline [had sustained] highly eroded banks and severe undercutting. The design challenge was to protect the site from further erosion and loss of pine trees while maintaining the aesthetic character of the area. Rather than proceed with conventional, mechanical erosion control methods, the owners incorporated the latest technology to complete a sustainable restoration project. Soil nails were launched into the hillside, followed by application of a webbing layer. That layer was then covered by jute material where planting pockets were incorporated to ensure revegatation would take hold. The entire bank utilized mostly indigenous boulders from the site and native plantings selected for the Rubicon micro-climate. The result is a model for future bank stabilization and erosion control projects. 23

8 PROJECT SHOWCASE Lake Tahoe bluff restoration PHOTO 7 Indigenous boulders and native plantings covered the rejuvenated bluffside. PHOTO 8 The degradable confinement system cells were hand-packed with a blend of custom soils and native vegetation. 24 Geosynthetics June July 2011

9 The biotechnical surface treatment also included native granite boulders and thousands of plants. Boulders were placed within closely spaced arrays of the soil-nail surface plates at various heights to complement the boulders at the toe of the slope and bordering the pathway (Photo 7), which created a natural appearance. More than 10,000ft 2 of coconut coir cellular confinement was installed and hand-packed with a custom soil blend, then vegetated with plants and seed (Photo 8). A broad range of plant materials from grass and forbs to shrubs and trees, all native to the regional Tahoe Basin watershed, were selected to achieve maximum root anchorage and foliage cover. Lateral low-volume drip lines (Photos 8 & 9) were placed throughout the facing and were required only temporarily to help establish the native plant species. G >> For more, search erosion at PHOTO 9 Drip lines were needed initially to establish the plantings; the new bluffside path leads to the beach. 25