Wednesday, January 13, 2010

Colluvial Soils Cause Wildflower Development Franklin, NC Landslides



Macon County Digitized Soil Hazards Map—
Additional Macon County landslide hazard maps are
available through the NCGS.

Wildflower Development Franklin, NC Landslide —November 17, 2009

It will be months before the North Carolina Geological Survey completes its investigation of the Thompson Road-Wildflower subdivision landslide and related road endangerment areas. State geologists told county officials:
The lowermost portion of the deposit spilled over a steep road cut for a driveway above Thompson Road. Large trees, many with root balls still attached, were pushed over, snapped off, and partially buried by a debris flow in the toe area. Unstable embankment material remains below the eastward and westward extensions of the main scarp. This unstable material will probably continue to move.

The other failure areas along the Wildflower development road network have the potential for continued movement, especially with heavy rainfall events.
Citing safety concerns, the NCGS advised Macon County officials that they should warn down slope property owners of the possibility of future land sliding.

The Wildflower subdivision landslides were set in motion by a developer’s attempt to build a steep slope 30-mile road system on highly-unstable colluvial soils.

As noted in the following histories, these types of slope failures are well-documented in Western North Carolina.

The Cascades Subdivision Landslide

A little over three years ago a road-building crew caused a massive landslide on Eagles Nest Ridge in Haywood County, North Carolina. Luckily, no homes were in the path of what Jeff Schmerker called “A Whopper of a Slide.” The Mountaineer—September 12, 2006



Photo 1-View looking up the track of the August 31, 2006 embankment failure-debris flow from the development road near lot 107.

Photo 2-View looking downslope at the debris deposit and damage to lot 107
Photo 3-View of cracks in embankment extending northeast from the head scarp of the August 31, 2006 embankment failure-debris flow
Photos compliments of the North Carolina Geological Survey

The Cascades Subdivision landslide occurred in a 700-acre development which was being built by Maurice Wilder of Clearwater, Florida.

After the landslide Dennis Franklin, contractor for the project, notified county officials and instituted temporary measures to stabilize the area. Marc Pruett, Haywood County’s erosion control supervisor, said that without notification he probably would not have known about the slide since no homes or residents were in danger.

Maggie Valley engineer Kevin Alford, who investigated the slide for a Cascades property owner, said that the failed section of the road bed occurred because:
The upper road was built out of shot material (from) where they had to blast the roadway in there. It got too heavy. The sliding material acted like a bulldozer, scouring the slope of almost all soil and vegetation. It wiped out a path down to bedrock. It was like an elliptical -shaped bulldozer. It is an amazing thing when you see that kind of material go down the mountain. When you get up in the mountains and start building roads, there are good ways to build roads and bad ways to build roads. In a situation like that I think it would have been reasonable to do subterranean work to find out what was there. When you have a large amount of uncompacted rock fill that gets a lot of water in it, you have potential for slope failures. There is still more material up there, so it could happen
again.
North Carolina Geological Survey’s Findings

Geologists investigating the landslide site found that the collapsed slope embankment was composed of highly unstable woody debris and graphitic-sulfidic bedrock fragments. Rain on this weak, improperly-constructed, roadbed probably precipitated the landslide.

During the course of their survey the geologists determined that the still standing ~ 300 foot long road embankment showed evidence of additional failures. They warned that if the fragile embankment is not properly stabilized, this land mass will pose future threats.

Recommendations to the developer included a professional investigation of the failed site in conjunction with extensive and expensive stabilization measures or removal of the remaining roadbed. It is unknown whether Mr. Wilder followed the safety recommendations outlined by the North Carolina Geological Survey. All developers conducting business in the state are left to their own best judgment on landslide remediation.

In their assessment report the NCGS referenced other Western North Carolina landslides caused by contractors' use of graphitic-sulfidic road fill.

When developers build roads in a subdivision or planned community North Carolina law stipulates that they declare their subdivision roads either private or public. Mr. Wilder's roads were recorded as private. If private, property owners are required to sign the following liability document:

Sample Subdivision Street Disclosure Statement

Pursuant to N. C. G. S. Section 136-102.6 _______, as the Declarant of _______,
issues this statement indicating that all of the roads within_______ are private. It is the obligation of _______ Homeowners' Association, Inc. (hereafter "Association") to maintain and keep in good repairs all of the private roads in _______Subdivision. It is mandatory for all property owners in _______ to be a member of the Association and the property owners, with the exception of the Declarant, have an obligation to pay assessments to maintain the private roads. The Declarant specifically states that the streets have not been constructed in such a manner to allow inclusion on the State highway system for maintenance.

No Escape Clause in the Subdivision Street Disclosure Statement

If the Wilder landslide had occurred after lots had been sold The Cascades property owners, without exception, would have been obliged to repair the damage.

The use of the Subdivision Street Disclosure Statement as a conveyance document for streets in hazardous-land subdivisions has not been legally challenged so property owners remain at uninformed risk. The following material information is omitted on Steep Slope Subdivision Street Disclosure Statements:

—Land in this subdivision is steep slope. Soils above a 15% grade are generally "not suitable” or “poorly suited” for residential development— “Some are too unstable to be used as a foundation for buildings or roads.” References: Western North Carolina Soil Surveys/North Carolina Geological Survey.

Horseshoe Cove Subdivision Landslides

The Horseshoe Cove Subdivision landslides provide an example of the financial consequences of sharing ownership of roads built on unstable soils. Below are some photographs of the damage caused to the subdivision's roads. Engineering evaluations commissioned by the property owners found that their subdivision had been built on colluvial soils.



Post-development hazardous-land determination did not invalidate the terms of the Horseshoe Cove Subdivision Street Disclosure Statement. Collectively the Horseshoe Cove property owners paid $300,000 to repair roads and drainage. The preventive landslide techniques (Costs: $2,868,000-$5,230,000) recommended by McGill engineers were not pursued.

The Federal Emergency Management Agency

Members of various influential groups, such as the North Carolina Association of Realtors and the Home Builders Association have persuaded legislators that Western North Carolina landslides and other regional geologic hazards are immaterial threats to property owners.

Federal officials disagree.

Although the Federal Emergency Management Agency cannot force North Carolina to provide hazardous-land real estate disclosure they are requiring all disaster-designated counties to evaluate and assess real property for landslides, wildfires, and flooding as part of their hazard mitigation plans. These unpublicized real estate risk compilations are under the purview of county planning boards. Ask to see them.

2 comments:

Pam Williams said...

As I set here reading this, it is so hard for me to believe that the North Carolina Association of Realtors and the Home Builders Association continue to support their irresponsible stance that "regional geologic hazards are immaterial threats to property owners."

I believe this is criminal. It is as simple as that to me.

I live in Horseshoe Cove. I live on property built on colluvial soil. The two roads above me are built on colluvial soil. It is a fact...I have proof. The McGill Engineering Firm gave me and other homeowners in Horseshoe Cove proof in an expensive evaluation they did of this Cove.

I remember the day I and other homeowners met with McGill. I knew it would be difficult to hear, as we had had multiple landslide incidents...one of those being a boulder breaking through a neighbor's home. Other neighbors were cut off to their homes due to landslides. The Horseshoe Subdivision had literally turned into hell.

After the report was explained to the group of homeowners, the hell got worse. Millions of dollars was quoted to us as being required to fully FIX unfixable slopes. Sure, the moneies could be spent if homeowners could acquire such sums; however, there would never be a guarantee of FIXING THE UNFIXABLE.

Since that time, some moneies have been spent with some degree of satisfaction. Some homeowners have not given full disclosure,but yet they sold their homes and left. One of those homeowners was a realtor himself. How he did what he did, I will never know. I have to tell the truth about living here, and I will never pass my problem onto another.

I will guard the truth of this hell on earth until the day I die...yet the Association of Realtors and the Home Builders Association continue to say, "regional geologic hazards are immaterial threats to property owners."

Mark said...

For sure, the Wildflower development road network can cause soil settlement. Water continue to seep in, thereby decreasing the volume of the soil. Soil stabilizing is an option with the use of soil stabilization methods. By the way, regional geologic hazards are not immaterial threats to property owners.