Appendix G: Procedures for Conducting Frequency-of-Erosion Studies

Appendix G

Procedures for Conducting

Frequency-of-Erosion Studies

Introduction

This appendix describes a procedure for determining frequency-of-occurrence

relationships for vertical erosion (aka erosion frequency) of dredged material

mounds off the Gulf and Atlantic coasts of the United States due to tropical and

extratropical storms. The erosion frequency data can be used as a basis for com-

puting the required thickness of the erosion layer portion of a contaminated

dredged material mound cap. The design cap must be sufficiently thick to

accommodate erosion from storm activity and still provide chemical and biologi-

cal isolation. The primary goal of erosion frequency studies are therefore to

develop information that can be used to determine (a) how thick a cap should be

to provide sufficient protection and/or (b) at what depth must a mound with a

given cap thickness be located to provide the same level of protection. Specific

recommendations for erosion layer thickness design are contained in the body of

this report. To make the erosion frequency discussion more easily understood,

the procedures are illustrated in an example. The example used is an erosion fre-

quency study done for the U.S. Army Engineer District, New York, as part of a

site-capacity study for the Mud Dump disposal site located off Sandy Hook, NJ.

Numerical Models

The ability to effectively conduct erosion frequency studies has been made

possible as a result of advances in modeling made by the Corps' Dredging

Research Program (DRP) (Hales 1995).1 The modeling advances were made in

two areas. The first area was the development of an integrated hydrodynamic,

sediment transport, and bathymetry change model, called Long-Term FATE of

Dredged Material (LTFATE) model. This model is capable of modeling the

References cited in this appendix are listed in the References at the end of the main text.

Appendix G Procedures for Conducting Frequency-of-Erosion Studies