Coastal Engineering Technical Note IV-21
December 1999
Surface-Water Modeling System Tidal
Constituents Toolbox for ADCIRC
by Adele Militello and Alan K. Zundel
PURPOSE: This Coastal Engineering Technical Note provides guidance on specification of
tidal boundary conditions for the ADvanced CIRCulation Multi-dimensional Hydrodynamic
Model (ADCIRC) circulation model (Luettich, Westerink, and Scheffner 1994) within the
Surface-Water Modeling System (SMS). This technical note is one in a series prepared by the
Coastal Inlets Research Program documenting specific features of the SMS developed for
ADCIRC applications.
BACKGROUND: Circulation modeling of open ocean regions applies tidal forcing as an ocean
boundary condition. Tidal forcing consists of one or more tidal constituents, such as the M2
constituent, applied at each boundary point. At tidal boundaries, time- and space-dependent
information is specified that is unique for each tidal constituent. A tidal constituent toolbox was
developed within the ADCIRC module of the SMS to provide a convenient user interface for
specifying tidal forcing for ADCIRC circulation modeling. This technical note describes tidal
constituents and the toolbox, including instruction for tidal boundary condition specification. The
tidal constituents toolbox was implemented in Version 6 of the SMS.
TIDAL CONSTITUENTS: The tidal signal experienced at any location is a composite of
multiple partial tides called tidal constituents. Approximately 390 tidal constituents have been
defined (Doodson 1922), the most significant of which are formed by the gravitational attraction
between the earth and the moon and sun. Table 1 lists the principal constituents and their periods.
Sixteen of the 19 constituents listed are diurnal (one cycle per day) or semidiurnal (two cycles
per day). Diurnal and semidiurnal constituents are denoted by the subscripts "1" and "2,"
respectively, in their symbols. For information on tides, tidal theory, and tidal prediction, see
Doodson (1922), Schureman (1924), and Defant (1961).
In typical modeling applications, eight constituents are specified: K1, O1, P1, Q1, M2, N2, S2, and
K2. Because these constituents make up a significant portion of the tidal signal, they are usually
sufficient for calculation of tidal water level and current. The analyst should verify that these
eight constituents are appropriate for a given model application.
TIDAL CONSTITUENT TOOLBOX: The tidal constituent toolbox within the SMS is a
convenient interface in which tidal forcing can be specified for the ADCIRC model. The toolbox
is housed within a Model Control interface that allows the user to specify control parameters for
ADCIRC. Because control parameters are dependent on the mesh, the Model Control interface
should be entered after the mesh has been developed.
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