Glossary

Bear trap gates consist of two leaves. When in the lowered position, the upstream leaf overlaps the downstream leaf. The gate is raised by applying upper pool pressure to a chamber under the leaves. This pressure, sometimes supplemented with air or hydraulic cylinders, raises the dam gate. These gates generally retain a pool differential of 20 ft or less and are normally about 90 ft wide. They are ingeniously conceived but can prove difficult to maintain. Silt or sand deposits in or under the gates are particularly likely and may make it impossible to fully lower or raise the gates.

An L Wall with a Kicker Pile is similar to a T wall on a pile foundation. In a T-Wall on a pile foundation, the steel sheet piling is a pile acting to control seepage and/or resist any unbalanced forces due to global instability. Whereas, in an L-Wall, the steel sheet piling is a pile acting to control seepage and provide support to the structure.

Clay Levees are embankment sections comprised of clay materials that generally have minimum slopes of 1 V on 2 1/2 H and minimum top widths of 3.05 m (10 ft). For low height levees, side slopes of 1 V on 2 H have occasionally been used.. When clay levees are constructed on pervious foundations, the bottom width may not be adequate to reduce under seepage in pervious foundations beneath the levee.

Without control, underseepage in pervious foundations (such as sand which allows the transmission of water through the soil) beneath levees may result in (a) excessive hydrostatic pressures beneath an impervious top stratum on the landside, (b) sand boils, and (c) piping beneath the levee itself. Underseepage problems are most acute where a pervious substratum underlies a levee and extends both landward and riverward of the levee and where a relatively thin top stratum exists on the landside of the levee. Principal seepage control measures for foundation underseepage are (a) cutoff walls and trenches, (b) riverside impervious blankets, (c) landside seepage berms, (d) pervious toe trenches, and (e) pressure relief wells.

The greatest flood level againstwhich a protective measure is designed to be fullyeffective; often expressed as a recurrence interval(e.g., 100-year level of protection) or as anexceedance frequency (e.g., one-percent chance ofexceedance).

Of or pertaining to a shore.

The sedimentary material moved in the littoral zone under the influence of waves and currents.

The movement of littoral drift in the littoral zone by waves and currents. Includes movement parallel (longshore transport) and perpendicular (on-offshore transport) to the shore.

In beach terminology, an indefinite zone extending seaward from the shoreline to just beyond the breaker zone.

The majority of lock gates are miter gates primarily because they tend to be more economical to construct and operate and call be opened and closed more rapidly than other types of lock gates. Miter gates are categorized by their framing mechanism as either vertically any or horizontally framed. On a vertically framed gate, water pressure from the skin plate is resisted by vertical beam members that are supported at the ends by a horizontal girder at the top and one at the bottom of the leaf. The horizontal girders transmit the loads to the miter and quoin at the top of the leaf and into the sill at the bottom of the leaf. Horizontally framed lock gates include horizontal girders that resist the water loads and transfer the load to the quoin block and into the walls of the lock monolith. Current design guidance as provided by EM 1110-2-2703 recommends that future miter gates be horizontally framed; however, a large percentage of existing miter gates are vertically framed.

Submergible tainter gates are used infrequently as lock gates. This type of gate pivots similar to a spillway tainter gate but is raised to dose the lock chamber, and is lowered into the chamber floor to open it. The load developed by water pressure acting on skin plate is transmitted along horizontal girders to struts that are recessed in the lock wall. The struts are connected to and rotate about trumnions that are anchored to each lock wall.

Parallel to and near the shoreline.