Order this information in Print

Order this information on CD-ROM

Download in PDF Format

     

Click here to make tpub.com your Home Page

Page Title: Currents
Back | Up | Next

Click here for a printable version

Google


Web
www.tpub.com

Home


   
Information Categories
.... Administration
Advancement
Aerographer
Automotive
Aviation
Combat
Construction
Diving
Draftsman
Engineering
Electronics
Food and Cooking
Math
Medical
Music
Nuclear Fundamentals
Photography
Religion
USMC
   
Products
  Educational CD-ROM's
Printed Manuals
Downloadable Books
   

 

needs to be taken into account). Further, currents do not appear to affect
the surge phase of the disposal (Bokuniewicz et al. 1978; Truitt 1986a).
However, water column currents and bottom slopes are important in slow
placement of sand caps where the currents and density flows can cause
some waste of capping material.
Long-term effects of currents at a prospective site may still need to be
investigated from the standpoint of potential erosion of the mound and cap
or potential recontamination of the site from adjacent sources. Storm-
induced currents are also of interest in the long-term stability of the site.
However, disposal operations are not conducted during storms, so the de-
signer does not need to consider storm-induced currents during disposal.
Measured current data can be supplemented by estimates for extreme
events using standard techniques; for example, see the Shore Protection
Manual (HQUSACE 1984). Selection of a nondispersive site in a rela-
tively low-energy environment normally results in a site with low bottom-
current velocity and little potential for erosion. However, in some cases,
particularly if the material is hydraulically placed, a thorough analysis of
the potential for resuspension and erosion is necessary. In the analysis of
erosion, the effects of self-armoring due to the winnowing away of finer
particles are a factor that increases erosion resistance over time but is
difficult to quantify.
The same technical approaches used to evaluate erosion potential
and/or magnitude and rate of erosion for purposes of cap design can be
used in screening and/or selecting sites. The process of screening and site
evaluation for erosion potential must consider current and wave conditions
for both ambient and episodic events such as storms. Conventional methods
for analysis of sediment transport can be used to evaluate erosion poten-
tial (Teeter 1988; Dortch et al. 1990). These methods can range from sim-
ple analytical techniques to numerical modeling (Scheffner et al. 1995).
Modeling evaluations will normally result in a varying rate of erosion for
various portions of a site or mounded feature (e.g., erosion would normally
be greater at the crest of a mound or at the corners of a mounded feature).
Erosion criteria for site screening should also be based on both ambient
and episodic events and should account for a varying rate of erosion over
the site. For projects in which no subsequent capping is anticipated for a
long time period (several decades or longer) or for which materials for cap
nourishment are not easily obtained, it is suggested that net cap erosion
over the major portion of the mound or deposit should not exceed 1 ft1 over
a period of 20 years of normal current/wave energies or for a 100-year
extreme event. The recommended criteria of 1 ft of erosion, 20-year ambi-
ent time interval, and 100-year return interval for storms is based on
engineering judgement, a common sense level of conservatism, and field
experience gained to date. One foot is a round number that can be measured
with some precision for most locations. Twenty and one hundred years as
1
The U.S. customary units of measurement are used in lieu of metric (SI) units for
those cases common in dredging practice. Metric (SI) units are used in this report when
consistent with standard usage. A table to convert from non-SI units of measurement to SI
units can be found on page xiv.
23
Chapter 4 Site Selection Considerations for Capping

Privacy Statement - Press Release - Copyright Information. - Contact Us - Support Integrated Publishing

Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business