CETN IV-15
Rev. September 1999
In one of the earliest works that may be considered a regional sediment budget, Caldwell (1966)
summarizes a study performed in the 1950s by the New York District of the Corps of Engineers
for the north New Jersey coast (U.S. Army Corps of Engineers 1957, 1958). The budget,
formulated by examining changes in shoreline position, served as a "field laboratory of shore
processes" with the objective of examining alternatives to mitigate for erosion. This celebrated
study deduced a regional divergent nodal point in net longshore transport direction at
Mantoloking, located just north of Dover Township. Net longshore transport to the north
increased with distance north from Mantoloking because of the sheltering of waves out of the
north by Long Island, New York. The budget considered net and gross longshore sand transport
for this 190-km reach including 10 inlets over time intervals of 50 to 115 years.
Another example of a regional sediment budget is that of Jarrett (1977, 1991) for the North
Carolina shoreline, including three barrier islands and two inlets. Mann (1993) discussed use of
a "near-field" versus "regional" sediment budget. The near-field sediment budget represents
local (project area) sediment sources, sinks, and pathways. The regional sediment budget
combines the near-field budget with the sediment-transport processes occurring on the adjacent
shorelines. For development of inlet sand management strategies (and estimating the inlet's
littoral impacts), Mann recommends consideration of a regional sediment budget so that
interactions of the inlet (and any proposed modifications) on the adjacent shorelines can be
assessed. Although it may be difficult to define and balance all sources, sinks, and sediment-
transport pathways within a regional context, this comprehensive approach may allow the
practitioner to recognize a source or sink of sediment hundreds of kilometers away that has a
potential significance to the project area (Komar 1998).
Step 2: Develop a Conceptual Budget. Kana and Stevens (1992) introduced a "conceptual
sediment budget," which they recommend developing in the planning stage prior to making
detailed calculations of individual sources and sinks. The conceptual sediment budget is a
qualitative model giving a regional perspective of the inlet interaction with beach processes,
containing the effects of offshore bathymetry (particularly shoals and, therefore, wave-driven
sources and sinks), and incorporating natural morphologic indicators of net (and gross) sand
transport. The conceptual model may be put together in part by adopting sediment budgets
developed for other sites in similar settings and incorporates all sediment sinks, sources, and
pathways. The conceptual model should be developed initially, perhaps based upon a
reconnaissance study at the site as part of the initial data set. Once the conceptual sediment
budget has been completed, data are assimilated to validate the model rather than to develop the
model.
Step 3: Ensure Compatibility of Temporal and Spatial Scales. In a discussion of the
planning process for coastal projects, Kraus (1989) advocated the concept that the temporal and
spatial scales of data used to develop and drive a model (whether a numerical, analytical,
physical, or conceptual model) must be commensurate with these scales of the model itself. For
example, a sediment budget developed based on pre- and post-storm data representing a day-to-
month-length temporal scale within the immediate vicinity of the inlet should not be extrapolated
to forecast to temporal scales of years and decades for a region extending over several barrier
islands. Similarly, a sediment budget developed based on a 50-year period cannot adequately
bracket the seasonal fluctuation observed locally at the project site. Sediment budgets are
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