Seasonal variations in vegetation, rainfall, and soil moisture conditions have the potential to impact the slope stability of locally forested coastal bluffs in the Atlantic Highlands of New Jersey. Both the seasonality and rainfall amounts of the two types of storms that induce shallow landslides in the area vary considerably. Most of the documented historical landslides are the result of heavy rainfall caused by late summer-fall tropical cyclones. The majority of the remaining documented landslides are related to spring nor’easters and total storm rainfall amounts for these storms are generally lower than the rainfall amounts for the tropical cyclones. In order to assess how conditions that may affect the potential for shallow landslide initiation vary seasonally, we are monitoring shallow pore-water pressure and soil moisture, precipitation, and slope movement.
Our monitoring is located at two sites of previously documented historical landsliding. The Mount Mitchill Scenic Overlook (MMSO) site is located on a slope interpreted to be the main scarp of a deep-seated, rotational landslide or slump that occurred in April 1782. The scarp slope is covered by a veneer of colluvium that has accumulated over the past few centuries. Shallow landslides have been documented nearby on the bluff and other evidence for shallow landslide movement includes scars on the upper slope and convex lobes lower on the slope. The Ocean Boulevard Bridge (OBB) site has experienced recurrent episodes of shallow landslide movement including in 2007 and May 2012. This data release presents the time series data from instrumentation installed at MMSO and OBB for a monitoring period that began on August 1, 2016, and lasted through December 31, 2018. Monitoring data collected in the time period prior to this data release is available in Fiore and others (2017). The instrumentation includes three observation wells, nine soil moisture probes, two rain gauges, and a cable extension transducer. At MMSO, we monitored shallow pore-water pressure in the lower part of the bluff, rainfall, effective rainfall beneath the deciduous forest canopy, and shallow soil moisture at three locations on the lower and middle parts of the bluff. At OBB, we monitored the shallow pore-water pressure at one location in the upper bluff and another location in the landslide deposit, shallow soil moisture at one location in the middle bluff and another location in the landslide deposit, and movement along the west flank of the May 2012 landslide where a displaced soil block forms the upper part of the landslide deposit.
Soil samples were collected at six locations on September 28, 2017 using a stainless steel core barrel pushed vertically into sediments along leveled ground below the organic horizon. Samples were analyzed in the laboratory for various hydraulic and geotechnical properties.
This data release presents the output for each instrument sensor type as recorded on the datalogger, as well as the laboratory results of the hydraulic and geotechnical properties of the soil samples collected. In some cases the output requires conversion to engineering units and we provide all the necessary factors, values, and equations to facilitate these conversions.
The most significant storm during this monitoring period was a cloudburst on August 7, 2018, that produced numerous shallow slope failures in sandy colluvium across the bluffs. Data included in this release support an interpretive paper published in the Quarterly Journal of Engineering Geology and Hydrogeology regarding this cloudburst.