EM 1110-2-1100 (Part II)
30 Apr 02
Figure II-8-17. Example of short- and long-term surf zone current data (Leffler et al. 1990)
Currents can vary significantly over short distances, especially around inlets, and some knowledge of the
spatial current field can be useful for design.
(b) Currents are best estimated from measurements, numerical modeling, or physical modeling. A
combination of both measurement and modeling typically yields the best estimates. Measurements provide
boundary conditions and calibration/validation data for the model. The model provides full spatial current
fields and a capability for estimating design conditions well beyond any measured events.
(c) More approximate information on currents can be obtained from several sources. Published
tidal current tables for use by mariners are available for many U.S. areas important to navigation (Part II-8-7).
As with winds, currents at one location can sometimes be transferred to another nearby location, with due
consideration of differences between locations. A short measurement record from the desired location can
be very helpful in estimating transfer relationships. ACES includes a simplified model for inlet hydraulics.
Time-varying inlet currents can be calculated for given time-dependent sea level fluctuation.
i.
Design example.
(1) This section contains a detailed example of estimating hydrodynamic parameters for design. Because
of the complexities and many variations of design environment possible in coastal engineering (for example,
inner surf zone versus outer surf zone versus outside the surf zone), the example is more an illustration than
a blueprint for coastal design. Data used in the example are more extensive than would typically be available.
When measurements are lacking, the information on water levels and waves must be estimated from some
combination of experience, nearby measurements, hindcasts/forecasts, and other physical and numerical
modeling. Information must be properly transformed to the project site.
II-8-34
Hydrodynamic Analysis and Design Conditions
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