CONCLUSIONS - doern70008

ERDC TN-DOER-N7

August 2000

The time required for the material to completely recover its original hydraulic shear strength is

apparently on the order of months, but appreciable decreases in erodibility occur after a week or so

of standing. Thus, the underflow and deposit are most susceptible to erosion during and shortly

after the disposal operation.

CONCLUSIONS: Presently some generalizations can be made about underflow spreading, but

more definitive information requires site-specific information and analytic procedures. Important

factors include: sediment composition, rheological and erosional characteristics, bed topography,

ambient currents and waves. As mentioned earlier, cohesive underflow can freeze, and thus deposit

en masse. Particle deposition can also occur from an underflow depending on bed shear stress.

Under DOER a work unit "Modeling Dispersion from Pipeline Disposals," methods of analysis for

pipeline discharges are being developed into a numerical model that will include many of the

aforementioned processes. Products from this work unit will combine available process description

for stripping during descent, jet entrainment and trajectory, turbulent and laminar underflow

spreading, entrainment of water into the turbulent underflow, entrainment of the underflow into the

water column, consolidation by settling of the underflow, deposition from the underflow, age, and

grain characteristics of the deposited strata, and consolidation and erosion of the deposited bed. An

important factor is bed slope and it will be described in a spatially- and temporally-varying manner.

Interfaces will be developed between these products and the newly developed SSFATE such that

multiple-grain-class suspended plumes can be predicted.

POINTS OF CONTACT: For additional information, contact Mr. Allen Teeter (601-634-2820,

teeter@hl.wes.army.mil), or the Program Manager of the Dredging Operations Environmental

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

nical note should be cited as follows:

Teeter, A. M. (2000). "Underflow spreading from an open-pipeline disposal," DOER

Technical Notes Collection (ERDC TN-DOER-N7), U.S. Army Engineer Research and

Development Center, Vicksburg, MS. www.wes.army.mil/el/dots/doer

REFERENCES

Chou, L., Cialone, M., Dorth, M., Ebersole, B., Fleming, B., Gailani, J., Gravens, M., Hall, R., Johnson, B., Letter, J.,

Nail, G., Scheffner, N., Smith, J., Teeter, A., Thompson, E., and Vemulakonda, R. (1998). "Dredged Material

Management Plan (DMMP) for the Port of New York and New Jersey - modeling studies to support island CDF

and constructed CAD pit design," Draft Interim Report, U.S. Army Engineer Waterways Experiment Station,

Vicksburg, MS.

Coussot, P., and Proust, S. (1996). "Slow, unconfined spreading of a mudflow," Journal of Geophysical Research,

101(B11), 25, 217-25,229.

JBF Scientific Corp. (1978). "An analysis of the functional capabilities and performance of silt curtains," Technical

Report D-78-39, U.S.Army Engineer Waterways Experiment Station, Vicksburg, MS.

Huang, X., and Garcia, M. H. (1998). "A Herschel-Bulkley model for mud flow down a slope," Journal of Fluid

Mechanics, 374, 305-333.

Johnson, B. H., Teeter, A. M., Wang, H. V., Cerco, C. F., and Moritz, H. R. (1999). "Modeling the fate and water

quality impact of the proposed dredged material placement at Site 104," Technical Report CHL-99-2, U.S.Army

Engineer Waterways Experiment Station, Vicksburg, MS.