SECTION 5.4.5: RISK ASSESSMENT - LANDSLIDE DMA 2000 Hazard Mitigation Plan Update – Burlington County, New Jersey 5.4.5-1 March 2019 5.4.5 LANDSLIDE The following section provides the hazard profile (hazard description, location, extent, previous occurrences and losses, probability of future occurrences, and impact of climate change) and vulnerability assessment for the landslide hazard in Burlington County. 2019 HMP UPDATE CHANGES ➢ The hazard profile has been significantly enhanced to include a detailed hazard description, location, extent, previous occurrences, probability of future occurrence, and potential change in climate and its impacts on the landslide hazard is discussed. Additionally, it includes information regarding sinkholes. ➢ New and updated figures from federal and state agencies are incorporated. U.S. 2010 Census data was incorporated, where appropriate. ➢ Previous occurrences were updated with events that occurred between 2013 and 2017. ➢ A vulnerability assessment was conducted for the geological hazards; it now directly follows the hazard profile. 5.4.5.1 PROFILE Hazard Description Geologic hazards are any geological or hydrological processes that pose a threat to humans and natural properties. Every year, severe natural events destroy infrastructure and cause injuries and deaths. Geologic hazards may include volcanic eruptions and other geothermal related features, earthquakes, landslides and other slope failures, mudflows, sinkhole collapses, snow avalanches, flooding, glacial surges and outburst floods, tsunamis, and shoreline movements. For the purpose of this HMP update, only landslides and land subsidence/sinkholes will be discussed. Landslides According to the U.S. Geological Survey (USGS), the term landslide includes a wide range of ground movement, such as rock falls, deep failure of slopes, and shallow debris flows. Although gravity acting on an over steepened slope is the primary reason for a landslide, there are other contributing factors (NJGWS 2013). Among the contributing factors are: (1) erosion by rivers, glaciers, or ocean waves which create over-steepened slopes; (2) rock and soil slopes weakened through saturation by snowmelt or heavy rains; (3) earthquakes which create stresses making weak slopes fail; and (4) excess weight from rain/snow accumulation, rock/ore stockpiling, waste piles, or man-made structures. Scientists from the USGS also monitor stream flow, noting changes in sediment load in rivers and streams that may result from landslides. All of these types of landslides are considered aggregately in USGS landslide mapping. In New Jersey, there are four main types of landslides: slumps, debris flows, rockfalls, and rockslides. Slumps are coherent masses that move downslope by rotational slip on surfaces that underlie and penetrate the landslide deposit (Briggs et al 1975). A debris flow, also known as a mudslide, is a form of rapid mass movement in which loose soil, rock, organic matter, air, and water mobilize as slurry that flows downslope. Debris flows are often caused by intense surface water from heavy precipitation or rapid snow melt. This precipitation loosens surface matter, thus triggering the slide. Rockfalls are common on roadway cuts and steep cliffs. These landslides are abrupt movements of geological material such as rocks and boulders. Rockfalls happen when these materials become detached. Rockslides are the movement of newly detached segments of bedrock sliding on bedrock, joint, or fault surfaces (Delano and Wilshusen 2001).
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SECTION 5.4.5: RISK ASSESSMENT - LANDSLIDE
DMA 2000 Hazard Mitigation Plan Update – Burlington County, New Jersey 5.4.5-1
March 2019
5.4.5 LANDSLIDE
The following section provides the hazard profile (hazard description, location, extent, previous occurrences and
losses, probability of future occurrences, and impact of climate change) and vulnerability assessment for the
landslide hazard in Burlington County.
2019 HMP UPDATE CHANGES
➢ The hazard profile has been significantly enhanced to include a detailed hazard description, location, extent,
previous occurrences, probability of future occurrence, and potential change in climate and its impacts on
the landslide hazard is discussed. Additionally, it includes information regarding sinkholes.
➢ New and updated figures from federal and state agencies are incorporated. U.S. 2010 Census data was
incorporated, where appropriate.
➢ Previous occurrences were updated with events that occurred between 2013 and 2017.
➢ A vulnerability assessment was conducted for the geological hazards; it now directly follows the hazard
profile.
5.4.5.1 PROFILE
Hazard Description
Geologic hazards are any geological or hydrological processes that pose a threat to humans and natural
properties. Every year, severe natural events destroy infrastructure and cause injuries and deaths. Geologic
hazards may include volcanic eruptions and other geothermal related features, earthquakes, landslides and other
Burlington County 173,044 $165,526,729,867 4,584 2.6% $4,743,744,814 2.9%
Source: Burlington County; NJ Department of Treasury, 2017; NJGS, 2008
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Note: The NJGS Carbonate Formation boundaries were overlaid on the custom general building stock inventory; the structures with their centroids within hazard areas were totaled for each municipality.
Impact on Critical Facilities
In addition to critical facilities, a significant amount of infrastructure can be exposed to mass movements of
geological material:
• Roads—Access to major roads is crucial to life-safety after a disaster event and to response and
recovery operations. Landslides can block egress and ingress on roads, causing isolation for
neighborhoods, traffic problems, and delays for public and private transportation. This can result in
economic losses for businesses.
• Bridges—Landslides can significantly impact road bridges. Mass movements can knock out bridge
abutments or significantly weaken the soil supporting them, making them hazardous for use.
• Power Lines—Power lines are generally elevated above steep slopes; but the towers supporting
them can be subject to landslides. A landslide could trigger failure of the soil underneath a tower,
causing it to collapse and ripping down the lines. Power and communication failures due to
landslides can create problems for vulnerable populations and businesses.
• Rail Lines – Similar to roads, rail lines are important for response and recovery operations after a
disaster. Landslides can block travel along the rail lines, which would become especially
troublesome, because it would not be as easy to detour a rail line as it is on a local road or highway.
Many residents rely on public transport to get to work around the county and into Philadelphia and
New York City, and a landslide event could prevent travel to and from work.
Several other types of infrastructure may also be exposed to landslides, including water and sewer infrastructure.
At this time all critical facilities, infrastructure, and transportation corridors located within the hazard areas are
considered vulnerable until more information becomes available. Figure 5.4.5-3 and Figure 5.4.5-4 display the
critical facilities located on areas of steep slopes and above carbonate formations, respectively. Overall there
are 32 critical facilities located on steep slopes, with dams being the most exposed with 10. There are 68 critical
facilities located above carbonate formations. Senior facilities and dams have the greatest exposure to carbonate
formations with 8 facilities each.
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Figure 5.4.5-3. Critical Facilities Located on Areas of Steep Slopes (Greater than 15%)
Source: Burlington County; USGS 2016
0 2 4 6 8 10 12
Wastewater Pump
Shelter
School
Municipal Hall
Light Rail
Day Care
Dam
County Building
Correctional
Chemical
Bass River Twp Bordentown City Cinnaminson Twp Delran Twp Eastampton Twp Evesham Twp
Florence Twp Mansfield Twp Moorestown Twp Mount Holly Twp New Hanover Twp Pemberton Boro
Pemberton Twp Shamong Twp Springfield Twp Woodland Twp
SECTION 5.4.5: RISK ASSESSMENT - LANDSLIDE
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Figure 5.4.5-4. Critical Facilities Located in the Carbonate Formation Hazard Area
Source: Burlington County; NJGS, 2008
Note: EMS – Emergency Medical Services
EOC – Emergency Operation Center
0 1 2 3 4 5 6 7 8 9
Airport
Chemical
County Building
Dam
Day Care
EMS
EOC
Fire
Historic Site
Library
Medical
Municipal Hall
Police
School
Senior
Shelter
Substation
Water Tower
Well
Waste Water Pump
Waste Water Treatment Plant
Southampton Township Pemberton Borough North Hanover Township New Hanover Township Medford Township Evesham Township
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Impact on the Economy
Geologic hazards can impose direct and indirect impacts on society. Direct costs include the actual damage
sustained by buildings, property and infrastructure. Indirect costs, such as clean-up costs, business interruption,
loss of tax revenues, reduced property values, and loss of productivity are difficult to measure. Additionally,
ground failure threatens transportation corridors, fuel and energy conduits, and communication lines (USGS
2005). Estimated potential damages to general building stock can be quantified as discussed above. For the
purposes of this analysis, general building stock damages are discussed further.
A landslide or sinkhole/subsidence event will alter the landscape. In addition to changes in topography,
vegetation and wildlife habitats may be damaged or destroyed, and soil and sediment runoff will accumulate
downslope potentially blocking waterways and roadways and impacting quality of streams and other water
bodies. Additional environmental impacts include loss of forest productivity. There are 952 buildings located
on steep slopes and account for $796 million, or less than 1-percent of the County’s total building cost; for areas
above carbonate formations, there are 4,584 buildings worth $4.7 billion (2.9% of the County’s total) exposed.
These dollar value losses to Burlington County’s total building inventory replacement cost value would impact
Burlington County’s tax base and the local economy.
The New Jersey Turnpike, I-295, and Route 130 are the major roadways that traverse the western portion of the
county from northeast to southwest. These roads serve as the major thoroughfares of the county and run through
the most densely populated areas of the county; all three of these roadways traverse areas of steep slopes. Other
major roadways that traverse areas of steep slopes include the Garden State Parkway, NJ-38, NJ-413, NJ-70, NJ-
73, NJ-90, US-206, and US-9. Lengths of US-206 and State Route 70 intersect areas underlain by carbonate
formations.
Since the county is substantially developed in the areas adjacent to the Delaware River many of the major utilities
including power generation plants and regional sewerage treatment plants are located with the landslide moderate
susceptibility/low incidence area.
Future Growth and Development
As discussed in Section 4 and Volume II, Section 9, areas targeted for future growth and development have been
identified across Burlington County. It is anticipated that new development within the identified landslide and
subsidence hazard areas will be exposed to such risks. Any developments at or near the base of steep slopes may
be at risk to losses from a landslide. Although areas of steep slopes are most at risk for landslides, landslides are
still possible on lesser slopes, and future developments are not completely free of risk.
There are no recent or proposed developments around the County located on areas of steep slopes. There are 5
new developments located above carbonate formations; three of these developments are located in Medford
Township. Refer to Figure 5.4.5-5 for a map of proposed new development and the landslide susceptibility areas
of Burlington County.
Effect of Climate Change on Vulnerability
A direct impact of climate change on landslides is difficult to determine. Multiple secondary effects of climate
change have the potential to increase the likelihood of landslides. Warming temperatures resulting in wildfires
would reduce vegetative cover along steep slopes and destabilize the soils due to destruction of the root system;
increased intensity of rainfall events would increase saturation of soils on steep slopes. Under these future
conditions, the County’s assets located on or at the base of these steep slopes will have an increased risk to
landslides. Roadways and other transportation infrastructure located in these areas will also be at an increased
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risk of closure, which would impact the County’s risk as described above under Impact on Life, Health, and
Safety, General Building Stock, and Critical Facilities and Impact on Economy.
Higher temperatures and the possibility of more intense, less frequent summer rainfall, may lead to changes in
water resource availability. The projection in the increase of average temperatures may lead to an increase in
the frequency of droughts. Sinkhole activity intensifies in some karst areas increases during periods of drought.
With an increase in drought periods, the number of sinkholes can increase (Linares et al. 2016). Additionally,
changes to the water balance of an area including over-withdrawal of groundwater, diverting surface water from
a large area and concentrating it in a single point, artificially creating ponds of surface water, and drilling new
water wells will cause sinkholes. These actions can also serve to accelerate the natural processes of bedrock
degradation, which can have a direct impact on sinkhole creation.
Change of Vulnerability Since the 2014 HMP
Burlington County and all plan participants continue to be vulnerable to the landslide hazards. Several
differences exist between the 2013 Plan and this update. For this plan update, an updated general building stock
based upon replacement cost value from MODIV tax assessment data and 2018 RS Means, and an updated
critical facility inventory were used to assess the county’s risk to the hazard areas. Additionally, steep slopes
were used to delineate the landslide hazard area for this plan to provide a more detailed assessment of the
County’s risk. The County also requested that the risk to subsidence and sinkholes be assessed for the this HMP
update. Due to differences in data used for the vulnerability assessment, a direct comparison could not be
conducted to determine whether there has been a change in vulnerability since the last HMP.
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Figure 5.4.5-5. Potential New Development and Landslide Hazard Boundaries