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THE COUNTY’S NATURAL ENVIRONMENT
PLANNING ISSUE
Steep slopes can be
environmentally fragile and
must be protected or carefully
developed since they are
subject to increased erosion,
and slope movement such as
rock or mud slides.
What's New
•
One of the county’s most damaging landslides
occurred in Lower Merion Township on January 2,
2007. Though it involved a small amount of mud and
rocks, it caused the derailment of a 54-car freight train.
Fortunately, none of the train cars loaded with fuel oils
leaked and there were no injuries. Similar landslides
have occurred along the Schuylkill Expressway.
•
In 2012, PennDOT initiated a $1.2 million slope
stabilization and drainage project in the landslide
prone areas along the Schuylkill Expressway to
prevent future problems.
Geology
Climate
Hydrology
Floodplains
Air Quality
Steep Slopes
Soils
Wetlands
Woodlands
Wildlife
Natural Areas Inventory
Steep Slopes
Steep slopes create dramatic landscapes that define
community character and limit development. Steep slopes,
which are often easily eroded, are environmentally
sensitive areas. Under certain conditions, they can present
a danger to public health and safety if they are not
protected. Generally, as slope increases, the depth of
topsoil and the ability of the soil to support structures and
vegetation decrease. This makes them susceptible to
erosion and mass movement of soil through landslides and
soil creep. Erosion potential is greater when steep slope
vegetation is removed, often times resulting in
sedimentation in adjoining watercourses. Due to their
unique soil and exposure to natural lighting and weather
conditions, steep slope environments often support unique
plants and wildlife that add to the region's biodiversity.
Slope failure can take many forms resulting in the mass
movement of rock and soil. Generally, rapid landslides
caused by excess moisture are referred to as mudslides or
earth flow. These have occurred in isolated areas of the
county. Slow mass movement caused by water is soil or
rock creep. Rock slides, generally not likely in the county,
occur under dry conditions.
Soil movement on slopes can take many forms such as soil creep.
Various types of structural and vegetative slope
stabilization controls can be employed to further stabilize
slope areas. Recent innovative slope stabilization efforts
have employed cut brush layers in lieu of or in conjunc-
tion with synthetic fabrics or various types of structural
devices. This approach, which is termed biotechnical sta-
bilization or soil bioengineering, entails the use of living
vegetation, primarily cut, woody plant material that is
purposely arranged and imbedded in the ground to prevent
surficial erosion and to arrest shallow mass movement. In
the case of brush layering, the live cut stems and branches
provide immediate reinforcement. Additional long term
stabilization occurs as a result of plant rooting that takes
place along the length of buried stems. Unlike most inert
reinforcements, imbedded brush layers also act as hori-
zontal drains and wicks that can enhance the hydrologic
regime in the slope.
