It will likely be eight years before better maps of the mountains in the Hiwassee River basin are made by a NC geological team
By Tom Bennett
Special to Hiwassee River Watershed Coalition
Murphy, N.C., August 7, 2007 – Cherokee and Clay counties in the Hiwassee River watershed are NOT among 19 counties scheduled to be mapped by a 2014 target date set by the scientists of the North Carolina Geological Survey.
Therefore, according to a work schedule envisioned by that organization, it could be eight years or more before the science is in place to guide legislators who hopefully will be willing to write greater statutory protection for the Cherokee and Clay County mountains.
It’s a critical environmental issue, since soil erosion and sedimentation moves down the slopes and into the rivers, such as the Hiwassee, Nottely and Valley here in this watershed.
Rick Wooten of the NCGS is one of the scientists given the task of following up on the Hurricane Recovery Act of 2005 and making new maps. The WATR Column sent him questions by e-mail. Wooten has graciously provided answers giving greater detail about the math of the mountains. Here is our interview:
INTERVIEW WITH RICK WOOTEN
1. Will you put in layman’s language the math formula that was in House Bill 1756, the Safe Artificial Slopes Act of 2007, and envisioned an affected area having slopes of 25 percent or more?
Rick Wooten: “The terms 1:1 and 1.5:1 are expressions for the slope ratios (steepness) measured in terms of slope run (horizontal distance) over slope rise (vertical distance). Typically an “H” and “V” are included in the expression like 1H:1V to avoid confusion. For example for a slope of 1H:1V, the rise is equal to the run; this being equivalent to a 45 degree slope. A slope of 1.5H:1V is equivalent to a slope of 34 degrees.”
2. An Asheville Citizen-Times article referred to a 2014 target for completion of mapping of the mountains of western North Carolina. Is that correct?
Rick Wooten: “The Hurricane Recovery Act of 2005 authorized the North Carolina Geological Survey to prepare landslide hazard maps for the 19 counties declared in the act. Although there are steep slopes in Cherokee County, it was not a declared disaster county (nor were Graham and Clay counties) as a result of the hurricanes of 2004. Presumably this was because these counties did not experience the damage from these storms like other counties. The 2014 time frame is our (NCGS) estimate of the time it will take us to complete the 19 counties assuming that the funding for the mapping continues, and the data we need to do the mapping is available… If funding becomes available to map more than the original 19 counties we would plan to map Cherokee County; however, it would be after 2014 unless the N.C. General Assembly changes the mapping priorities.”
3. In the mapping you are doing, are GPS and aerial photos used? Describe this in a layman’s paragraph, please.
Rick Wooten: “We use a variety of tools in our mapping to identify areas of past landslides, and areas prone to future landslides. We use various vintages of aerial photography, geologic and soil survey maps, and LiDAR integrated into a computerized geographic information system (GIS).
“LiDAR, an acronym for Li_ght D_etecting A_nd R_anging, is a form of airborne laser altimetry where high resolution topographic data (latitude, longitude, and elevation) are collected by an aircraft with laser equipment. Data from this method results in a topographic map, or digital elevation model, which has a much higher resolution, and is more accurate, than earlier topographic maps made prior to this technology.
“The LiDAR data was collected for all of North Carolina, initially to prepare up-to-date flood plain maps for all N.C. counties. Our review of the maps and aerial photographs helps us target specific areas for field verification that appear to have had past landslide activity and prehistoric landslide deposits.
“Our field verification process includes identifying and classifying the types of landslides and the different types of soil and rock involved. Future landslides tend to occur in the general areas where landslides have occurred in the past. We also use GPS (global positioning satellite) surveys extensively to help accurately locate features in the field.”
4. What is your job title, please?
Rick Wooten: “Senior Geologist for Geohazards and Engineering Geology, North Carolina Geological Survey.”
Additional information on landslide hazards in North Carolina
Tom Bennett of the Martins Creek community near Murphy, N.C., was a retired newsman, Hiwassee River Watershed Coalition member/volunteer/donor and recipient of the 2015 Holman Water Quality Stewardship Award. Tom died on December 28, 2020.