Coastal Engineering Technical Note IV-15
Rev. September 1999
Formulation of Sediment Budgets
at Inlets
by Julie Dean Rosati and Nicholas C. Kraus
PURPOSE: The Coastal Engineering Technical Note (CETN) herein discusses the steps
required for developing a sediment budget in coastal reaches that include inlets. The types of
data sets and analysis procedures useful in formulating sediment budgets are addressed, as well
as a methodology for incorporation of both quantitative and qualitative data. A sediment-budget
methodology for inlets and adjacent beaches is presented, and its application is illustrated
through an example. This (September 1999) revision supercedes the previous CETN and
contains recent developments from the Coastal Inlets Research Program. The revision expands
the methodology for formulating sediment budgets along coasts that include inlets, and
additional notation and terminology are introduced.
BACKGROUND: Sediment budgets for inlets and adjacent beaches provide a conceptual and
quantitative model of sediment-transport magnitudes and pathways for a given time period.
Sediment budgets are a framework for understanding a complex inlet and coastal system,
whether in its natural or engineered condition. Often, the natural condition is studied to gain
background information necessary for evaluating the inlet and adjacent beach response to coastal
engineering projects (see Komar 1996, 1998) for an overview of concepts and applications).
Sediment budgets can enter at any of four stages in project development:
a.
Existing Condition. A sediment budget for the existing condition is the most common type.
This budget forms the basis for evaluating the impacts of planned engineering activities and
the natural evolution of the inlet or coast.
b.
Historical (pre-engineering activity) Condition. This budget is typically constructed for
comparison with the existing-condition budget. A common application of the two budgets
is a Section 111 or similar study, in which the impacts of inlet-related engineering activities
(Federal navigation projects) on the adjacent beaches are estimated.
c.
Forecast Future Condition. Adapting and extrapolating the existing-condition sediment
budget can assess the potential response to future projects or modifications.
d.
Intermediate Condition. Sediment budgets representing other periods create a model of inlet
or coastal evolution through time, which may lend insight to interpreting present or future
evolution. As examples, intermediate-condition sediment budgets may document evolution
of the inlet from initial formation to a quasi-equilibrium state, or they may reveal a picture
of long-term natural bypassing through a cycle of channel migration and welding of a
portion of the ebb-tidal shoal to the adjacent beach.
THEORY: A sediment budget is a tallying of sediment gains and losses, or sources and sinks,
within a specified control volume (or cell), or series of connecting cells, over a given time.
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