CONCLUSIONS - doere90011

ERDC TN-DOER-E9

May 2000

CONCLUSIONS: More than 20 years ago, the existing literature did not permit a "neat compila-

tion and analysis" of the ecological consequences of dredging (Morton 1977). Despite continued

concern and research in this area, particularly with respect to effects of suspended sediments,

assessments of potential impacts on aquatic organisms remain highly subjective. Clearly, many

past investigations focused upon detrimental effects induced by dosages well above those likely to

occur at dredging project sites. Also obvious is the fact that appropriately designed studies to address

dredging impacts are very limited in number and breadth of coverage, both with respect to taxa and

life history stage. The lack of relevant data continues to foster controversy in impact assessments.

Extrapolations from responses at inappropriate concentrations or exposure durations are widespread

and engender interpretations rife with opportunities for false conclusions. Likewise, generic

assessments of impacts based on responses across broad taxonomic lines should be viewed with

extreme caution.

Until adequate data are available quantifying biological responses to appropriate concentration/

exposure duration dosages, assessment of potential dredging-induced impacts must unfortunately

remain subjective. The authors endorse the construction of models (e.g., Newcombe and Jensen

1996) to integrate "best available knowledge" and to optimize objectivity in the assessment process.

However, it is strongly recommended that any assessment consider not only the concentration

threshold aspect of the dosage issue, but also realistic estimates of the likelihood and duration of

exposure above that threshold. Tools to assist in this process are currently being developed under

the Dredging Operations and Environmental Research Program, such as SSFATE, a numerical

model customized for simulations of dredging-related suspended-sediment plume dynamics (see

Johnson et al. 2000).

POINTS OF CONTACT: For additional information contact Dr. Douglas Clarke (601-634-3770,

clarked@wes.army.mil), or the Program Manager of the Dredging Operations and Environmental

Research Program, Dr. Robert M. Engler (601-634-3624, englerr@wes.army.mil). This technical

note should be cited as follows:

Clarke, D. G., and Wilber, D. H. (2000). "Assessment of potential impacts of dredging

operations due to sediment resuspension," DOER Technical Notes Collection (ERDC

TN-DOER-E9), U.S. Army Engineer Research and Development Center, Vicksburg, MS.

www.wes.army.mil/el/dots/doer

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