Flooding
is defined as a general and temporary condition of partial or complete
inundation of normally dry land areas from: the overflow of inland or tidal
waters; the unusual and rapid accumulation or runoff of surface waters from any
source; or mudflows or the sudden collapse of shoreline land. Flooding is arguably the highest priority
natural hazard in Jefferson County. This
is largely due to the physical geography of the county, which includes several
rivers and creeks as well as a varied topography.
Located at the confluence of the Potomac and Shenandoah Rivers, Jefferson County is separated into three major drainage divides by the County’s rolling topography. The Shenandoah River has a drainage area of 247 square miles at the downstream county boundary. Its average channel slope within Jefferson County is approximately 4.6 feet per mile. Between these drainage divides are a network of 22 major streams that feed into the two aforementioned rivers and Opequon Creek. Opequon Creek has a drainage area of 8.0 square miles and an average channel slope of approximately 56 feet per mile. Most streams in the County flow in a northwest-southeast orientation toward the Opequon or Shenandoah. Turkey Run, one of the largest streams, has a total drainage area of 8.0 square miles and its average channel slope within Jefferson County is approximately 50 feet per mile. Evitts Run, another large stream, has a drainage area of 17.91 square miles. Its headwaters are in central Jefferson County and flows eastward to the Shenandoah River. Flowing Springs Run, an additional large stream, has a drainage area of 7.88 square miles. It heads just north of Ranson and flows eastward to the Shenandoah River. Almost all of these streams are spring fed, thus resulting in the intermingling of surface and subsurface waters. Regardless of their origin, all waters ultimately flow into the lower Potomac River and the Chesapeake Bay.
Identification
of floodplain areas within the County and the incorporated municipalities was
based on the most recent Flood Insurance Rate Maps (FIRM) produced by FEMA
(Federal Emergency Management Agency). Map
1, titled, “Flood Hazard Areas” displays the locations of all of the major
water bodies in the county and delineates the 100-year floodplain boundaries
(Zone A). These are areas that have a
one percent chance of equaling or exceeding the recorded base flood elevation
during any year. Based on this map, four
of the five incorporated municipalities have 100-year floodplains within their
jurisdictions. Bolivar is the only
municipality without a designated floodplain within its boundaries. While Bolivar may not have a mapped floodplain
according to FEMA it is not completely without flooding problems. According to the Bolivar Comprehensive Plan,
nuisance flooding impacts many roads due to poorly designed and maintained
drainage systems. Map 1 also
shows several areas in the unincorporated portions of the county where 100-year
floodplains have been identified.