Tuesday, April 25, 2023

3.21.23 Oakhurst Geological Hazard Abatement District Meeting Summary

Normally I do not separate the summary for the Oakhurst Geological Hazard Abatement District (GHAD) meetings, the meeting we had in March had been a long time coming and there was quite a bit of useful information presented.  What we learned at our 3.21.23 meeting appeared to present a potential serious risk to certain areas within the GHAD.  All of the detail is in the agenda packet (https://claytonca.gov/fc/agendas/council/2023/03212023web.pdf  starting on page 165 of the PDF) and I won't reproduce it here. I wanted to highlight some key takeaways and share my thoughts.
  • The GHAD is distinct from the City of Clayton, though the Clayton City Council serves as the Board of the GHAD.
  • The GHAD assesses a levy on approximately 1,400 parcels within the City of Clayton, with different tiers based on the type of home (single family, multi-family, duet).  The purpose of this assessment is to fund the activities of the GHAD.
  • The total assessment has a Consumer Price Index (CPI) riser so that the assessment may increase each year by an amount correlated with CPI.  The current revenues the GHAD assessments yield is approximately $47K/year.  Most of this amount is consumed by various program administration activities, and less on any actual monitoring or maintenance.
  • The level of assessment was set pre-Prop 218.  Prop 218 made increasing the assessment subject to voter approval.
  • The duties of the GHAD are outlined in the Plan of Control document.  These duties include maintenance of drainage facilities (V-Ditches, etc.), inspection of drainage ditches for cracking, sliding, or other damage, debris removal, repairs, cleanout of drains, measurement of movement and water pressure using inclinometers and piezometers, evaluation of erosion control effectiveness, identification and locating of various geological hazards, etc.
  • The revenues the GHAD receives are substantially lower than what would be required for the GHAD to perform all of its required duties.
  • Over time, many measuring devices that are used to monitor and measure movement have been damaged or are no longer operable.
  • There are several areas where movement is highly likely, however due to lack of monitoring equipment, the GHAD does not have any information as to the magnitude or existence of such movement.
  • If there is significant geological movement, it has the potential to cause severe damage to nearby homes.
  • Our City Engineer, who also serves as the GHAD General Manager, engaged with a Certified Engineering Geologist and Geotechnical Engineer (BSK Associates) to perform evaluation of the area and to make recommendations.
Here is a timeline of the GHAD:

Now onto more detail:

First, this is the area that is covered by the GHAD:

The GHAD area is shaded above.  There are three distinct areas of the GHAD that are surrounded by dotted lines, and each has specific risks associated with those areas.

In the open spaces in the GHAD, there are several drainage facilities, including V-ditches, catch basins, and various ways to collect and route water away.  This is important as build up of water, or water running over the surface in large amounts over time can cause erosion, and can build up underground causing landslides of various magnitudes.

In several areas, the City has installed inclinometers.  These are devices that are bored deep into the ground at various depths.  They are set in place, and by measuring their relative position periodically, we can determine how much the earth is moving at a specific depth.  This is a key detection tool that is available to us.  If there is movement detected, then engineers can determine the best course of action in terms of mitigating slides and reducing risk of slides.

For many years, our Engineers and firms the city has hired to monitor these inclinometers have recommended that we install additional units to replace those that have become inoperable over time.  Many of these devices have not been measured since 2016, though the requirement is to be measured quarterly.  Because of the lack of available funding, replacement or additional measuring devices were not purchased or installed.

BSK examined the areas with the GHAD at different points in time.  First in Oct-22, again in Dec-22, and then again in Mar-23.  They were able to detect movement both before the large storms in December and January, and movement again afterwards.  BSK indicated that if there are heavy rains after periods of drought or lack of rain, that often accelerates movement.

Here are a few examples they found:

In the above picture, water has eroded its own pathway adjacent to the V-Ditch designed to capture that water.  This will be exacerbated over time and will increase risk of further slide activity.

In this picture, damage to a V-Ditch is apparent and repairs should be made. There were many examples of this type of damage.

In this picture, a catch basin was overrun with dirt and debris, possibly exacerbated by clogs in various drains or other debris preventing the flow of water.

There are several areas that need repair, else they will not function as intended and additional water flow has the potential to cause more damage.

This is a diagram of the Pebble Beach Dr. area.  On the left it shows the neighborhood map and a solid line.  The line represents an area that is displayed on the right which would be a cross section of the same area.  The font is small, but it shows locations of previously installed inclinometers, depths where they are no longer functional, and where others are recommended to be installed.  From this, we can see that underneath certain homes there exists the potential for movement, but the GHAD does not have the ability to monitor it.

In addition to the above specific examples, there are several areas where slides are visible at the surface.  It is clear that movement is occurring, but what is not clear is the magnitude.

When I first joined the Council (and the GHAD board), I read through the reports and even back then it was indicated that more work needed to be done.  In 2019, I requested that a detailed scope of work of the GHAD to be discussed, as well as the timing and funding of that work.  This information is the result of the years of requests and the report is thorough.  The above images are only a subset of what is shown in the full report.  There are areas that if there were slides or movement, they could impact many homes in the area.

I've asked staff to come back with answers to several questions, but the main ones are these:
  1. What is the one time costs necessary to bring the GHAD current on anything that was previously deferred?  That includes new inclinometers, piezometers, repairs, etc.
  2. What would be the ongoing operational costs necessary to conduct the required activities including monitoring and maintenance?
  3. What is a healthy reserve amount that the GHAD would need to maintain in order to address emergencies or situations as discovered by such monitoring?
After staff is able to come back with this information, the residents that live within the GHAD will have some decisions to make.  The current level of funding for the GHAD is clearly insufficient to support the activities that the GHAD requires.  If the GHAD funding is not increased, then it will be severely limited in the actions it will be able to make. Simply doing the analysis necessary to produce the report that this post is based on exceeds the funding available for the GHAD in a given year.  

On an ongoing basis, there is insufficient funds to even conduct the monitoring, much less install monitoring devices themselves.  Without knowing if any movement is occurring, it is impossible to craft a plan of action to mitigate impacts of such movement.  I did find this Pioneer article: (https://issuu.com/claytonpioneerinc./docs/may_21_clayton_pioneer_2004) published in May 2004 (page 14) that indicated the GHAD went to the voters three times in an attempt to raise assessments and each of the three times the increase did not pass.  I did a review of all voting records for Clayton from 1997-2004 (oldest date available online) and could find no record of any vote regarding GHAD assessments, however it could have occurred before this time or via some other means.  In any event, if the residents within the GHAD are interested in having the actions of the GHAD performed, they will almost certainly need to agree to fund it via GHAD assessments.  

I will share more as the City gathers information about the above details.  We plan to have the GHAD back on the agenda at our 5.16.23 meeting.