Landslide Monitoring and Research in the Atlantic Highlands area, New Jersey

Science Center Objects

Recent shallow landslides have occurred on the steep hillslopes of the Atlantic Highlands area during and after large storm events with exceptionally heavy rainfall. These shallow landslides have resulted in extensive damage to residential property and local infrastructure and threatened human safety.The USGS New Jersey Water Science Center (NJWSC) and the USGS Landslide Hazards Program (LHP) are currently monitoring hillslopes within the Atlantic Highlands area of NJ to better understand the hydrologic and meteorological conditions associated with shallow landslide initiation.

 

Relief map of the Atlantic Highlands area

 Shaded relief map of the Atlantic Highlands area, New Jersey showing the location of historical shallow landslides (red circles; locations modified from NJGWS 2016), and the Mount Mitchell Scenic Overlook (MMSO) and Ocean Boulevard Bridge (OBB) monitoring sites. (Public domain.)

Introduction

Landslides on the steep coastal bluffs of the Atlantic Highlands area (Boroughs of the Atlantic Highlands and Highlands) in Monmouth County, NJ have been recurring, punctuated events through recorded and pre-recorded history.  Both shallow and deep-seated landslides have occurred in this area episodically, with the oldest, documented deep-seated landslide occurring in April of 1782 (Minard, 1974). However, the recent landslides have been mostly shallow in nature and have occurred during large storm events with exceptionally heavy rainfall. Landslides of these types can be triggered on unstable slopes by intense and/or sustained rainfall and rapid changes in pore-water pressure.

Landslide in OOB monitoring site

May 2012 Landslide photo from the OBB Monitoring Site in the Atlantic Highlands.  (Credit: Pam Reilly, USGS. Public domain.)

The recent shallow landslides in the area consist primarily of slumps and flows of earth and debris within areas of historic landslides or on slopes modified by human activities (Ashland and others, 2017). Such landslides are typically triggered by increases in shallow soil moisture and pore-water pressure caused by sustained and intense rainfall associated with spring nor’easters and late summer-fall tropical cyclones. However, the critical relationship between rainfall, soil moisture conditions, and land movement has not been fully defined.

 

 

 

Objective

The objective of the USGS landslide research within the Atlantic Highlands area is to continuously monitor hydrological and meteorological conditions to identify conditions that destabilize a hillslope. The hydrologic monitoring data provide insights into the role of antecedent soil moisture on hydrologic storm response and seasonal variations in slope stability in the coastal bluffs.

 

 

 

 

Scientists at the USGS will use the monitoring results to:

  • Evaluate changes in soil moisture and pore-water pressure caused by storms of varying duration, intensity, cumulative rainfall amounts, and seasonality;

  • Identify how seasonal variations in soil moisture and pore-water pressure affect landslide susceptibility; and

  • Quantify the critical rainfall conditions that correspond to shallow landslide occurrence.

2014 landslide in the Atlantic Highlands

Landslide from April 2014, showing the earth and retention wall behind a house being sloughed off.   (Credit: Francis Ashland, USGS. Public domain.)

 

 

Current Landslide Monitoring Sites

USGS monitoring efforts began in August 2015 at two historic landslide locations, below the Ocean Boulevard Bridge (OBB) and below Mount Mitchell Scenic Overlook (MMSO). Continuous monitoring data is collected for the following parameters:

  • Rainfall (MMSO only),
  • Soil moisture,
  • Groundwater conditions (pore-water pressure), and
  • Downslope movement.  

Near real-time data are collected continuously and recorded every 15 to 60 minutes on a datalogger. Site visits are routinely made to download data, perform maintenance, and conduct visual inspections.

 

 

 

 

 

 

 

 

USGS Scientists installing a monitor base station

USGS Geologist Francis Ashland and USGS Hydrologist Alex Fiore installing a base station at the OBB monitoring site.  (Public domain.)

Current Monitoring: Relevance and Benefits

Continuation of the landslide monitoring network is highly relevant to the citizens and community along the north flank of the Atlantic Highlands area. Long-term data from the continuous monitoring will help to refine provisional seasonal rainfall thresholds recently developed for landslides in the Atlantic Highlands area (Ashland et al, 2017). The data can also be used by community members or municipality officials to mitigate landslide hazards. In the future, the data collected on hydrologic response and movement during major storms could be incorporated into a near-real time prototype landslide warning network. Near real-time monitoring systems could be crucial in identifying active or imminent landslide hazards.

On a regional level, this approach may have broad applications to other unstable hillslopes in New Jersey and the northeast. This joint effort by two USGS Mission Area Programs (Hazards and Water) is consistent with USGS goals of advancing knowledge of the regions natural systems, investigating interdisciplinary processes and providing scientific technical support and information to local and federal agencies.  

 

 

Acknowledgements

The study was funded by the Disaster Relief Appropriations Act of 2013 (PL 113–2) and the USGS Landslide Hazards Program.  The USGS would like to thank the Monmouth County Parks System and the Borough of the Atlantic Highlands for their ongoing cooperation and collaboration on the project.

Future Plans

Potential for a Landslide Early Warning System

The primary objective of the USGS National Landslide Hazards Program and the USGS New Jersey Water Science Center is to potentially reduce long-term losses from landslide hazards by improving our understanding of the physical processes that control land movement on the coastal bluffs.

 

USGS Hydrologist downloading data near the rain gauge

Photo of USGS Hydrologist Alex Fiore downloading data from near an open-canopy rain gauge at Mount Mitchill Senic Ovelook
(Public domain.)

As part of our initial research, historical data on rainfall and landslide occurrences were analyzed to identify rainfall conditions that induced shallow land movement. From these results we derived two provisional rainfall thresholds that provide a preliminary assessment of the probability of shallow landslides occurring in the area ( See Ashland and others, 2017 and Fiore and others, 2017 for details).

A future goal of this study is to incorporate data from the current monitoring on precipitation, soil moisture conditions, hydrologic response and land movement with the provisional rainfall thresholds into a prototype landslide early warning system for the area. Prior to developing such a system, the ongoing monitoring must provide further insight into the rainfall and hydrologic conditions that result in shallow landslide initiation. Therefore, continued long-term monitoring at these sites is essential to verify that land movement occurs when critical soil moisture and/or rainfall threshold conditions are exceeded and to ensure the reliability and accuracy of the prototype landslide early warning system.

Development of a landslide early warning system would involve modifying the current monitoring sites so that data is transmitted in near real-time to local officials during storms to alert them of changing conditions in the bluffs and the potential for shallow slope failure.

 

Disclaimer

Monitoring sites are operated as part of a research project. Active data collection may be discontinued at any time in the future.

Data users are cautioned to consider the data limitations and thoroughly read the associated metadata information before using it for decisions that concern personal or public safety or the conduct of business that involves substantial monetary or operational consequences.

Although the data have been subjected to rigorous review and are substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, the data are released on the condition that neither the USGS nor the U.S. Government may be held liable for any damages resulting from authorized or unauthorized use. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and/or contained herein.