EM 1110-2-1100 (Part II)
30 Apr 02
Chapter II-5
Water Levels and Long Waves
II-5-1. Introduction
a. Purpose.
(1) This chapter describes water levels and the various long wave components that contribute to a total
water surface elevation. Vertical datums are also described to define some of the more commonly used
reference datums.
(2) The following sections provide project engineers with sufficient guidance to develop a preliminary
study approach and design procedure to analyze engineering projects that require consideration of water level
elevations. References are provided from existing Engineer Manuals that describe generic design-criteria
formulae for use in preliminary analyses. Additional references and approaches to problem solving are
provided for complex projects that require detailed surface elevation and current input data for design. These
data are generally provided by numerical models.
b. Applicability. Information contained in this chapter is directly applicable to any project requiring
local water levels or currents as a primary design consideration. Applications include the design of coastal
structures intended to provide protection against some pre-defined water surface elevation, specified
according to an appropriate economic analysis and evaluation. Determining acceptable design elevations may
require developing local stage relationships as opposed to frequency-of-occurrence relationships. This
information can be generated through historical records or numerical modeling techniques to simulate the
propagation of historical storm events. Additional examples of water surface and current variability include
circumstances where tidal circulation patterns and surface elevations change as a result of structural or
bathymetric modifications to existing coastal inlets or navigable waterways. These circulation-dominated
problems can be addressed using either numerical or physical models.
c. Scope of manual.
(1) Water wave classification is used to describe the behavior of long waves and to distinguish between
intermediate waves and short waves (described in Part II-2). This allows the reader to select which chapter
of this manual is appropriate for the intended application. If long waves are appropriate, this chapter will
provide a means of approximating basic wave characteristics such as celerity, current magnitudes, and surface
elevation.
(2) The speed of propagation, surface profile, and vertical velocity distribution of long waves are
different from those of short waves described in Part II-2. Because these properties of waves represent
important design criteria, it is important to make a distinction between long and short waves. Therefore,
Part II-5-2 reviews wave classification criteria and summarizes long wave properties.
(3) Tides are the most common and visible example of long wave propagation. Part II-5-3 summarizes
tidal hydrodynamics and describes characteristic tidally induced long wave variability. This section includes
a background description of the forces responsible for generating tides, gives examples of the variability of
tides, and presents a methodology for harmonic reconstruction of tides.
(4) Many of the concepts described by tidal records are used as a basis for defining tidal datums.
Part II-5-4 describes reference elevation datums commonly in use in the United States. Attention is also paid
Water Levels and Long Waves
II-5-1
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