12 December 2001
confined by levees or containment dikes, or unconfined. Because of environmental
considerations, confined upland sites are generally preferred unless the dredge spoil is
being used to create wetlands. Selection of an upland site requires consideration of
return of effluent water to the waterway. Unnecessary entrapment of water that may
cause flooding must be avoided. It must be assured that effluent water does not pick
up additional turbidity or toxic chemicals as it returns to the waterway. A more thorough
discussion of these options is contained in the Handbook of Dredging Engineering
(Herbich, 1992), Chapter 8, and in Chapter 5 of Dredging: A Handbook for Engineers
(Bray et al., 1997). Bray also discusses the various types of sites for disposal as well
as various processes of disposal and cleaning of dredged material and the decision
making process for disposal (Bray et al., 1997). The PIANC bulletin, Management of
Dredged Material From Inland Waterways (PIANC, 1990) and USACE EMs 1110-2-
5026 and 1110-2-5027 are also useful and recommended sources of information.
Upland Open Site. This disposal location is generally used for placement
of coarse, cohesionless sediments. Material placement is controlled with small berms
constructed by a bulldozer or similar land-construction equipment.
Upland Diked Site. This type of disposal location is generally used for
the confined placement of fine-grained sediments. Dikes constructed prior to sediment
placement typically have overflow weirs to minimize turbidity in receiving waters. Dikes
may be constructed of existing soil or may be built up with hydraulically placed fill. Soil
embankments should have a maximum slope of 1 vertical to 2 horizontal on the exterior
face and 1 vertical to 3 horizontal on the interior face. Hydraulic fill must be placed at
the natural angle of repose. Care should be taken to provide a cross-sectional area
sufficient to withstand the water depths in the fill. A minimum freeboard of 2 feet is
typical. Placement of dredged material at an upland diked site may cause ground-water
contamination; investigations should be made to determine if this possibility exists.
Certain situations require that the diked site be lined with filter cloth or a layer of clay to
prevent penetration of pollutants into the ground-water system.
Open-Water Site. With this type of disposal location, materials are
generally limited to coarse sediments due to environmental considerations. EPA
regulations and designated disposal areas should be investigated.
Contained-Water Site. For this type of disposal location, earthen dikes
are usually constructed prior to dredging. The use of silt curtains instead of earthen
Downtime Criteria for Projects and Water Level Extremes. An
acceptable method for determining the design basis for water level extremes, such as
the frequency and duration of low and high water levels should be determined from the
historical record and used to define the maximum level of planned and unplanned
downtime with respect to project scheduling.