1. 7.4 Karst Areas
      2. 7.4.1 The Nature of Karst

Pennsylvania Stormwater Best Management Practices Manual
Chapter 7
program is undergoing an aggregate study in Centre County, PA to determine the most
economical and durable stone for gravel roads.
Local Municipalities and state agencies have jurisdiction of over 90% of dirt and gravel roads, and
because the cost of paving these roads is often too high for the road owner, there are several
best maintenance practices that can be employed to maintain an unpaved road in an
environmentally sensitive manner. Recommendations include:
Working with the natural landscape in the design of roads (minimize cut and fill)
Identifying existing drainage patterns and designing to minimize disturbance
Crowning the road to drain the water away from the center
Using graders with scarified blades as preferred equipment to reshape a road
Sizing roadside ditches appropriately and outletting appropriately within an infiltration
Driving Surface Aggregate mix should have increased abrasion resistance, be angular on
the surface with increased fines to provide stability and facilitate compaction (stone quality
Vegetating roadside banks to prevent erosion
Using snowplow shoes when clearing snow and re-shaping the road after snow season
Preserving soil stabilizing vegetation in ditches and observing appropriate roadside
vegetation management practices along road corridors
Limiting driving speeds
Reduced road maintenance costs (grading, regrading, & re-graveling), and reduced
sedimentation in water affecting aquatic life and drinking water reservoirs, should result from the
implementing these measures, and are consistent with the various BMPs discussed in this
manual. A detailed listing of technical bulletins and further information on “Environmentally
Sensitive Maintenance” practices for dirt and gravel roads is available from the Center for Dirt and
Gravel Road Studies at Penn State University (www.dirtandgravelroads.org).
7.4 Karst Areas
7.4.1 The Nature of Karst
Surface-Water Interaction:
Water is a key to sinkhole collapses. Taking water away from where
it was or putting a new, concentrated source of water where it wasn’t before can speed the
development of sinkholes. Examples of new sources of water could be drainage from rain gutters,
pavement, collection ditches and ponds. Treatment basins or lagoons must be diligently lined in
karst to prevent a sudden drainage out of the bottom and into the groundwater. Leaky water and
sewer pipes can cause the soil underneath to wash away and are often the trigger for sinkholes.
However, an existing sinkhole under a pipe can cause the initial leak. The greater the volume of
water and the faster it moves into the karst system, the more soft material is washed from the
voids. Weather events can also trigger sinkholes. In Pennsylvania, sinkholes can “pop” when a
heavy rain event comes after a prolonged drought.
Karst areas present problems to those attempting to work with conventional hydrologic models.
Typically, modeling of a karst site or watershed via SCS or other traditional methods provides
poor representation of runoff rates, with regard to both flooding and over-design of conduits and
stormwater management facilities. This is largely because standard hydrologic modeling methods
lack allowances for losses into sinkholes, fractures, crevices or caves that may exist in the
363-0300-002 / December 30,
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