Landscape Architect Articles

Slide Solution: Reconstructing Laguna Beach, Bluebird Canyon11-01-07 | News

Slide Solution: Reconstructing Laguna Beach?EUR??,,????'?????<

By Leslie Dunham, regional marketing manager, Fuscoe Engineering Inc.

When a weak bedding plane more than 60 feet below grade is inundated by almost two and a half times normal rainfall, as Laguna Beach was in the late spring in 2005, a slide was inevitable.

What happens when a hillside with a weak bedding plane lurking more than 60 feet below grade is inundated by almost two and a half times normal rainfall? A landslide of devastating proportions is the inevitable result.

The Laguna Beach-Bluebird Canyon landslide made national news in June 2005 when the entire side of this steep hill slid down, shearing off over 500,000 cubic yards of earth, destroying 12 homes and damaging or threatening many others in what had been an idyllic coastal neighborhood.

The Flamingo Drive ?EUR??,,????'?????<

An unprecedented rainfall and an underlying sloping stratum of clay sediment can be blamed for much of the destruction. The thick clay layer acted like a stopper, essentially trapping the rainwater percolating through the soil above it and groundwater levels rose below.

The wetted earth material then built up over days into a weighty, muddy mass that slid off the surface of the clay table, sending all the earth and homes above it toppling down below.

On June 1, 2005 a massive landslide in Bluebird Canyon in Laguna Beach, Southern California destroyed 12 homes and damaged or threatened another 10 homes. This is Flamingo Drive, or more accurately, Flamingo Dive. At the time, Southern California was experiencing its second wettest winter and rain had saturated the slopes. About 1,000 people were evacuated from 350 other homes on the hillside.

None of the homeowners had insurance to recover their losses?EUR??,,????'?????<

As a crisis project, the design and construction were fast-tracked to reconstruct the slope and expeditiously restore each property. Local civil engineering and landscape architectural firms were immediately contacted to supply professional remediation expertise.

Sand bags, visqueen and piping allow for a winterized slope, reducing mudslide potential. Visqueen is the polyethylene sheeting seen here.

Landscape Architecture

The city of Laguna Beach selected Frederick Thomas Hume, ASLA, to provide landscape architectural services. The assignment entailed collaborating with city staff, project engineers and contractors. ?EUR??,,????'?????<

A retaining wall and earthen fills will be required to stabilize this headscarp.

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Erosion Control?EUR??,,????'?????<Provide plant material and other means to help protect the reconstructed slope from future erosion.

Screening?EUR??,,????'?????<Reintroduce evergreen vegetation at the end of the valley to restore the privacy the homeowners once enjoyed.

Views?EUR??,,????'?????<Limit the height of new plantings to allow views to the ocean from the upper canyon.

Private Properties?EUR??,,????'?????<Recognize that each lot is unique and each homeowner has expectations about the use of their private property.

Plantings?EUR??,,????'?????<Reintroduce fast growing, low maintenance, water thrifty plant material and omit invasive plant species, while complying with the city?EUR??,,????'?????<

Fire Safety?EUR??,,????'?????<Use approved fire retardant plants configured according to the city?EUR??,,????'?????<

Maintenance?EUR??,,????'?????<Provide fencing and service vehicle access along the new swale at the bottom of the restored slope.

Planting Setbacks?EUR??,,????'?????<Comply with setback requirements from the newly constructed watercourse and underground utility lines at the bottom of the slope.

Soil Fertility?EUR??,,????'?????<Because of the nature of the emergency, it was impossible to stockpile topsoil. The sandy-clay soil was graded and compacted to 90%. It was highly alkaline, contained high levels of salts and lacked organic material. Plants needed to be selected that would survive under these conditions.

Timing?EUR??,,????'?????<Provide long and short-term solutions that reflect the individual timelines for rebuilding each home. Some homes were to be rebuilt as soon as the property was reconstructed and other lots would remain vacant for years.

Cost?EUR??,,????'?????<The final solutions needed to be cost effective and prudent.

Two temporary shoring walls reinforced with rail-tie strength lumber are planted 80 feet into the earth with I-beams pumped with concrete placed at intervals to add weight. Sturdy metal tie-backs were added, extending up to 120 feet in length and packed with grout, which hardened into reinforcing anchors.

Solutions began to emerge from the diverse and sometimes conflicting design criteria. Several landscape design alternatives were developed, the concepts were reviewed by city staff and homeowners, then the concepts were publicly presented to the city?EUR??,,????'?????<

The first phase of the Flamingo mass grading project, completed in late December 2006, removed 202,000 cubic yards of material and included the construction of a soil cement key 100 feet below the surface about twice the size of the Hotel Laguna. The second phase involved the removal of approximately 180,000 cubic yards of soil, the permanent placement of approximately 80,000 cubic yards of that material near the top of the landslide and the construction of a second soil cement key?EUR??,,????'?????<

The solutions for the ?EUR??,,????'?????<

The density of the soil required special drains for the larger plants to relieve any water that builds up around the roots. Also, all of the planting pits were enlarged and soil around each plant amended and fertilized to help the plants adapt to the otherwise nearly inert soil conditions.

A ?EUR??,,????'?????<

The new plantings in the ?EUR??,,????'?????<Heteromeles arbutifolia), rhus (skunkbush sumac) and other native plantings. Lower-story groundcover plants underneath the trees offer an attractive foundation that minimizes maintenance by reducing the need to remove leaf litter.

This temporary wall at the bottom of the canyon allows new storm drain and water facilities to be constructed while keeping workers out of harm?EUR??,,????'?????<

Restoring homeowner privacy was a primary concern at the far west end of the valley zone. This area was geographically different from the rest of the site, which afforded an opportunity to plant non-native vegetation. Thirty-six inch evergreen and 72-inch box pepper trees were selected as the primary screening tree from the city?EUR??,,????'?????<

Wind and rain warranted field checks and repair work for winterization efforts to protect the surrounding properties.

Frederick Thomas Hume, ASLA collaborated with Richard Johnson & Associates, Inc. for arboricultural and horticultural consultation, GL Motshagen for irrigation design and Wallace Labs for soil fertility testing. The landscape contractors included Valley Crest Tree Company and Rey Art Landscape, Inc.

In addition to the Bluebird Canyon project, Frederick Thomas Hume, ASLA is also working on several other significant projects in the region. He provided design services for the city?EUR??,,????'?????<

The ?EUR??,,????'?????<

Civil Engineering

Fuscoe Engineering, Inc. was asked to provide emergency civil engineering services, including grading, drainage, sewer and water plans. ?EUR??,,????'?????<

The constructed storm drain and water lines are now installed and backfilled. The pipe for the storm drain goes through the toe of the landslide area and is 600 feet long. The construction company installed 3,500 lineal feet of smaller storm drain pipe?EUR??,,????'?????<

The Fuscoe team went on site to assess the damage. A huge segment of the public access road had been demolished, and both the sewer line and water main beneath it were destroyed, as was a natural storm drainage channel. The steep grade of the slope with loose, tumbling earth complicated access. Regrading, restoring and stabilizing the hillside would be a monumental task. The next phase would entail reconstructing Flamingo Drive, the public roadway and would involve minor road realignments to improve nonstandard conditions. Curb, gutter and asphalt would all need replacement, and underlying electric and gas lines required realignment and reinstallation.

Initially, the entire site needed regrading to recompact the soil and thereby stabilize the site to prevent a mudslide recurrence. To accomplish this, huge amounts of dirt had to be shifted or removed and soil cement keys were placed in a terraced effect to solidify the terrain. The challenge was to grade the project efficiently while minimizing the amount of dirt to export while considering the load of soil to retain on the site and how this would impact the size and cost of the necessary soil cement keys. Removing the dirt proved to be the least expensive strategy and had the residual effect of improving the homeowners?EUR??,,????'?????<

The new plantings in the ?EUR??,,????'?????<

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The high water table posed additional concern, so a dewatering operation was initiated; holes were punched dozens of feet through the ground and the water sucked out and diverted to holding tanks that drained downstream of the site.

Installation of the storm drain and water lines was problematic. Two temporary shoring walls reinforced with rail-tie strength lumber were planted 80 feet into the earth with I-beams pumped with concrete placed at intervals to add weight. Sturdy metal tie-backs were added, extending up to 120 feet in length and packed with grout, which hardened into reinforcing anchors.

These innovative slope stabilization measures, while effective, complicated placement of necessary utilities. Sewer and water lines had to be carefully routed between the grade beams without hitting or destabilizing the I-beams. Additionally, in certain instances, the utility lines required complicated routing around trees slated for salvage. The massive destruction and tricky accessibility made identifying where existing utilities were broken or ripped apart by the slide, and then determining how and where to join the new utility lines to ensure feasible operation, proved arduous.

Evergreen vegetation was reintroduced at the end of the valley to restore the privacy the homeowners once enjoyed.

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The final engineering plans entailed restoration of the hillside to provide a 1.5 factor of safety for all improvements, a significant achievement considering site constraints, difficult access, edge conditions and other troublesome issues. Other site considerations include establishing proper drainage courses for existing and proposed drainage facilities. The concerns of nearby homeowners with homes not affected by the slide continue to be addressed, such as constant construction activity and noise, driving accessibility, anxieties regarding how views will be affected by the new construction, etc. The Fuscoe Engineering GIS Graphics team is producing high-tech view simulations utilizing 3D technology for demonstrating to residents that the new slope design will not adversely impact their ocean views and in several cases, actually enhance them.

Project coordination has been undeniably complicated. Besides satisfying the requirements of multiple agencies from a design perspective, the 12 homeowners whose residences were destroyed by the slide had multiple requests that also require consideration and application. Attempting to bring this project ?EUR??,,????'?????<

As Fuscoe Engineering, Inc. passes into its 15th year, it is honoring its entrepreneurial past, while creating an exciting and rewarding future. One of the biggest gainers in the Orange County Business Journal?EUR??,,????'?????<

Fuscoe Engineering embraces what it calls ?EUR??,,????'?????<