Identification of constraints on regulation of Upper Mississippi River System Lock and Dam 18

This study undertook the identification of constraints on a one
foot pool  raise at Mississippi River Lock and Dam 18.  Pool 18 is
approximately 26.5 miles long with a thalweg gradient of 0.28 foot
per mile.  A pool raise, as measured at the dam, would have
variable spatial effect depending on main stem and tributary
discharge which creates a sloping water surface at all but extreme
low flow conditions.  At low or no flow conditions, a one foot
pool raise at the dam would flood shoreline vegetation throughout
the pool.  At the most probable flow the fall migration period, a
one foot pool raise could flood approximately 300 acres of low
elevation and shoreline vegetation in the lower 16 miles of the
pool.  Constraints identified for water level manipulation in Pool
18 were limited Federal real estate interests, and the structural
capability of Lock and Dam 18 to maintain any pool elevation over
the elevation of the overflow spillway.  The study team concluded
that before any decision is made to implement a water level
control plan, several issues will require additional
investigation.  Those investigations include seepage and
additional pumping requirements for adjacent drainage districts,
detailed design work for structural modifications, coordination
and documentation for National Environmental Policy Act
compliance, sedimentation/degradation immediately below the
overflow spillway, comprehensive topographic survey for habitat
classification and real estate interests, cost sharing
responsibilities, and modification and approval of the Project
Regulation Manual.