The Corps of Engineers Telescoping Weir for Confined Placement Sites

ERDC TN-DOER-T3

January 2001

The Corps of Engineers

Telescoping Weir for Confined

Placement Sites

PURPOSE: This technical note describes the Corps of Engineers patented invention known as the

telescoping weir.

BACKGROUND: The fundamental objective of the Innovative Technologies Focus Area of the

Dredging Operations and Environmental Research (DOER) program is to identify and catalog inno-

vative dredging operations, processes, or equipment and techniques developed by domestic and in-

ternational dredging entities. A number of technologies developed within the U.S. Army Corps of

Engineers are currently undergoing evaluation for potential demonstration under the DOER pro-

gram. Among these is the telescoping weir, a Corps invention (patent pending) for water manage-

ment in confined placement sites (Francingues et al. 2000).

Confined disposal facilities (CDFs) are engineered structures designed to provide required storage

volume for dredged materials and to meet required effluent solids standards specified in state water

quality certificates. If properly designed, constructed, and operated, the CDF will retain the dredged

material solids within its diked confines while allowing the carrier water to be released from the con-

tainment area with no more sediment in suspension than allowed under the state water quality certifi-

cation. Because in almost all cases the CDF must be used over a period of many years, long-term

storage capacity of the facility must be strictly managed and maximized. Gain in storage capacity

within the CDF is dependent on removal of pore water within the fine-grained fraction of the

dredged material allowing consolidation and desiccation. The dual requirements of short-term ef-

fluent control and long-term storage capacity are directly related to the ability of the operator to man-

age influent and effluent water within the CDF in an effective and efficient manner. The short-term

effluent control requires a specific operational approach during active dredging projects; the

long-term decanting of pore water requires another operational approach. Both approaches use a

weir. The innovation regarding weir design is the subject of this technical note. A more complete

treatment of design, construction, operation, and management of CDFs, including specifics of weir

selection and design, can be found in Headquarters, U.S. Army Corps of Engineers (1987).

DISCUSSION OF THE CONVENTIONAL WEIR: Conventional weirs are engineered struc-

tures of various sizes, shapes, and lengths as dictated by the requirements of the CDF (Figures 1 and

2). The two most critical weir design parameters are ponding depth and weir length. In order to

maintain acceptable effluent quality, the upper layers containing low levels of suspended solids

should be ponded at depths greater than or equal to the minimum depth of the withdrawal zone,

which will prevent scouring settled material. The withdrawal zone is the area through which fluid is

removed for discharge over the weir as shown in Figure 3 (Figure 4-6 of Headquarters, U.S. Army

Corps of Engineers, 1987). Efficient sedimentation is promoted by ponding water to a specified

depth in the placement site. This ponded depth is controlled by the elevation of the weir crest. In

conventional operations, weir boards are raised to obtain the required ponding depth and lowered

periodically as the dredging rate decreases to control the effluent quality and to discharge water