CONSIDERATIONS IN SELECTING TELESCOPING WEIRS

ERDC TN-DOER-T3

January 2001

CONSIDERATIONS IN SELECTING TELESCOPING WEIRS:

Engineer Manual

1110-2-5027 (Headquarters, U.S. Army Corps of Engineers, 1987) provides guidance in design,

construction, operation, and management of CDFs to achieve dredging project goals. A set of the

logical steps in the CDF design procedure is presented to assure adequate settling performance and

initial storage volume.

Presently, selection and design of a telescoping weir are not as clearly understood as those for con-

ventional weirs due to the limited operating information upon which to base an empirical design.

For example, there may be limitations in the fabrication process that will not allow for increases in

the diameter of the stainless steel cylinders. Considerations in shipping overland by truck may limit

the overall width dimensions. At some point there is a practical limitation that would lead one to se-

lect multiple weirs to handle larger flows. For these and other technical and practical reasons, there

is only one telescoping weir size to choose from at this time. (The topic of design of the telescoping

weir will be covered in a future DOER technical note.)

However, this section lists the principal factors deemed critical to properly selecting and installing a

telescoping weir for use in an existing or new site. If the following factors cannot be achieved, then

the telescoping weir may not be the best choice for a water control structure in the confined place-

ment site:

Acceptable site for weir placement.

Acceptable route for weir discharge pipeline.

Acceptable energy gradient for discharge pipeline.

Sufficient freeboard within CDF for efficient operation.

Acceptable bearing capacity for the weir, its superstructure, and foundation pad.

Access road to the site of the weir location.

Access to site for installation of cofferdam (if needed during construction phase).

Access to site for installation of piling (if necessary for increased bearing capacity).

The following are lessons learned that must be taken into consideration when selecting a telescoping

weir:

Safety is the primary consideration under site suitability.

CDF shape and size are factors in determining the best location and size of a telescoping weir.

Projected life of the CDF project needs to be considered as a factor in determining site suitability.

Project sponsor issues must be considered in the planning stage.

401 water quality certification requirements must be considered in all phases of implementation.

Operability (ease of operation) is an essential quality of a telescoping weir.

Economics must be considered in a preliminary fashion during the planning stages but can be

addressed in detail after design is completed in the engineering phase.