Есть что улучшить? Предложите правку.
By Pamela A. Reilly, Francis X. Ashland and Alex R. Fiore, U.S. Geological Survey
A USGS hydrologist downloads data near the open-area rain gage at Mount Mitchell Scenic Overlook. Photo: Pam Reilly, USGS.
The bluffs
The steep coastal bluffs of the Atlantic Highlands area — the Boroughs of Atlantic Highlands and Highlands, New Jersey — have seen landslides, shallow and deep, from time to time.
- The oldest documented deep-seated landslide, in April 1782, changed the bluff's shape significantly (Minard, 1974).
- Recent landslides have been mostly shallow, during large storms with exceptionally heavy rain (Ashland and others, 2017) — damaging homes and infrastructure and threatening people's safety.
Recent shallow landslides (red; NJDEP, 2016) and the Mount Mitchell Scenic Overlook (MMSO) and Ocean Boulevard Bridge (OBB) monitoring sites (white). USGS.
What they are: mostly slumps and flows of earth and debris, in areas of old landslides or on slopes altered by people. They are typically set off when sustained, intense rain — from spring nor'easters and late summer–fall tropical storms — raises soil moisture and pore-water pressure near the surface. But the exact link between rain, soil moisture and movement hasn't been pinned down.
Recent landslides: A, May 2012, at the Ocean Boulevard Bridge site; B, April 2014; C, one of three in the Borough of Highlands during Tropical Storm Irene, August 2011. Photos: A, Pam Reilly; B and C, Francis Ashland; USGS.
What's being measured
Monitoring is on mostly forested slopes where landslides have happened before:
| Site | Instruments |
|---|---|
| Mount Mitchell Scenic Overlook | two rain gages (forested and open); pore-water pressure in shallow wells, from vibrating-wire transducers near each well's bottom; soil-moisture probes at depths chosen by the soil profile |
| Ocean Boulevard Bridge | a cable extension transducer measuring how far a recent landslide moves downslope |
Data are recorded continuously, every 15–60 minutes, on a datalogger; staff visit to download data, maintain equipment and inspect the slopes.
The results will show:
- how soil moisture and pore-water pressure respond to storms of different length, intensity, total rain and season;
- how seasonal changes affect slope stability;
- the critical rainfall that goes with shallow landslides.
Toward an early warning system
The study, by the USGS National Landslide Hazards Program and New Jersey Water Science Center, aims to help local emergency officials reduce landslide hazards.
- So far: historical rainfall and landslide records produced two provisional rainfall thresholds — a first estimate of the chance of shallow landslides (Ashland and others, 2017).
- Next: combine the monitoring data (Fiore and others, 2017) with those thresholds into a prototype early warning system.
- First, more data: continued long-term monitoring must confirm that the ground moves when soil moisture or rainfall thresholds are exceeded, to make the system reliable.
- Then: send data in near real time to local officials during storms, to alert them when the bluffs could fail.
Data: Groundwater levels, soil moisture, precipitation and slope movement, 2015–16.
Sources
Based on Landslide Monitoring in the Atlantic Highlands Area, New Jersey, by Pamela A. Reilly, Francis X. Ashland and Alex R. Fiore, USGS Fact Sheet 2017–3068, U.S. Geological Survey; a work of the United States government in the public domain. The opening, the map and the photographs are taken from the fact sheet's PDF, which the import had left out.
Лицензия: CC0 1.0 (общественное достояние) · По материалам pubs.usgs.gov
1
0
0
0
Комментарии
