Mudslide More Human Folly Than Act of God

Recent reports have mischaracterized the Niguel Summit catastrophe as an “act of God.” The landslide, which has devastated two residential communities and scores of homeowners, did not occur through divine intervention. It was instead an accident of man’s poor planning.

The fact is that particular area long has been designated as a “high risk” land mass by the state. It was well-known that a great number of landslides regularly occur in the soil formations upon which Niguel Summit and most other South County developments lie.

In particular, the state’s geological map shows that many of the slopes are relatively unstable, and also that the Niguel Summit area was classified in a category of most likely to fail.

When dealing with a hillside, developers should:

1. Adequately assess the geological conditions for stability;

2. Ensure the safety of future residents, and not be driven by the economics of increased density;

3. Properly inspect and supervise construction to ensure no shortcuts are taken or miscalculations made.

Man-made slopes rely on engineering and construction to obtain necessary strength and compaction. In mass grading, the soil’s natural balance can be radically altered and interfere with the integrity of the surrounding area.

Developers are obligated to fully investigate existing conditions, carefully study the soils and ensure that all proper engineering and grading procedures have been completed.

Soil components must also be addressed. Orange County’s native earth contains many of the worst soils for artificial hillsides.

Weak and expansive clays are common throughout the county. Sand and fine silts contribute to poor material commonly used when creating lots for residential construction.

Once slopes soften, the constant rains from a winter season can be the catalyst that compromises the strength of the clay, leading to a mammoth slope failure.

When “100-year rains” occur annually, they are not once-in-a-lifetime events or “acts of God.”

Slope evaluation and construction must also consider the seismic risks. The entire county is within Seismic Zone 4, the highest zone for potential shaking hazard. Two major faults (the Elsinore-Whittier to the north and Newport-Inglewood along the coast) have impact for Orange County.

Does this mean that homes should not be built on man-made slopes in south Orange County? The answer is a qualified “no.”

Geotechnical engineers today can create a man-made slope solid enough to withstand an El Nino drenching. But like everything else in life, there are limits.

For instance, a slope with a 3:1 ratio is about half the incline of a 2:1 slope, and thus is much less likely to give way. This is especially true in areas such as South County, where geologists have known for more than 20 years that underlying soil formations are prone to slippage. The steepness of the slope is a major factor in influencing massive landslides. The Niguel Summit slopes are 2:1.

Perhaps builders should be limited to lower densities or not be allowed to build at all on some slopes where the native soil components cannot maintain the required strength and compaction. Perhaps not every natural canyon should be filled in, but left for drainage. Other measures include:

1. When developing in hillside terrain, require analysis of pressures on slopes;

2. Require sufficient drainage systems that go beyond the “swale,” or slight ditch. The county and cities should require developers to adequately grade each lot and install drain lines and drains;

3. Don’t allow developers to cut steep slopes in unstable areas with weak soil; keep those slopes at a ratio of 3:1 or higher. Homes that are on steeper slopes should be secured by caissons that don’t simply dangle in the fill but are embedded in bedrock. Stronger retaining walls should be designed and built. Better erosion control methods should be implemented.

With the new surge of land development and home building, the county and cities need to bolster building department staffs. Money should be allocated by state and city governments to monitor projects, since the building industry has again proved it won’t or can’t do it alone. On-site supervision by licensed professionals must be mandated from initial planning to addressing problems after the development is completed and sold.

Finally, companies and individuals responsible for creating new communities and building new homes should be held strictly liable for structural and geological failures. Only by doing so can homeowners know they have direct recourse if, in the middle of the night, their beloved home slips down a sodden slope and turns into a headline--misnamed as an “act of God.”