CETN IV-20
September 1999
Produces report-quality graphics and has all typical Windows operating system features
related to graphics, cut-and-paste operations, and similar actions between software
applications.
Allows images (e.g., aerial photographs of the coast) to be loaded as background wallpaper
with the sediment budget, upon which computational elements are drawn.
Contains a tutorial, example project, and help files with on-line guidance.
The following section reviews sediment budget theory (see CETN-IV-15 (Revised September
1999) for more detail). 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. A sediment budget can be developed in several ways (e.g., Shore Protection Manual 1984;
Jarrett 1991; Bodge 1999). By conservation of mass (volume) of sediment, the difference
between the sediment sources and the sinks in each cell, hence for the entire budget, must equal
the rate of change in sediment volume occurring within that region, accounting for pertinent
engineering activities such as sand placement and dredging. In SBAS, the sediment budget
equation is
∑ Qsource - ∑ Qsink - ∆V + P - R = Residual
(1)
in which all terms are expressed consistently as a volume or as a volumetric change rate; Qsource
and Qsink are the sources and sinks to the control volume, respectively; V i s the net change in
volume within the cell; and P and R are the amounts (volume or volume rate) of material placed
in and removed from the cell, respectively. The Residual represents the degree to which the cell
is balanced. If the budget of an individual cell is balanced, its residual is zero. For a reach of
coast consisting of many contiguous cells, the budget for each cell must balance in achieving a
balanced budget for the entire reach.
SBAS also presents the Residual for a macrobudget, which is the solution of Equation 1 for all
cells. One of the steps in the recommended procedure (see CETN-IV-15 (Revised) for more
detail) is to balance the macrobudget before detailed cell-by-cell calculations commence. If the
macrobudget is not balanced, at least one of the individual cells will be out of balance.
The purpose of this CETN is to highlight the features of SBAS and demonstrate its application
through an example problem. Companion CETNs (CETN-IV-15 (Revised) and CETN-IV-16)
contain background information.
OVERVIEW: SBAS organizes the user's workspace for maximum convenience in all aspects of
sediment budget formulation, visualization, and reporting. Within the right-hand side of the
screen, called the topology window, SBAS formulates a sediment budget by allowing the user to
create a series of cells and arrows representing sources, sinks, and sediment-transport pathways
that characterize the sediment budget. The left-hand side of the screen organizes alternatives
within a particular project (Figure 1). Alternatives may represent various time periods, different
boundary conditions for the same time period, or modifications to assumptions within the budget
reflecting a sensitivity analysis. Once a sediment budget alternative has been defined, and the
user has created sediment budget cells with sources and sinks, values can then be assigned to the
various components of the sediment budget topology. The SBAS indicates by color coding
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