EM 1110-2-1100 (Part V)
31 Jul 2003
(5) Wave and water level climate.
(a) The wave and water level conditions at the project site represent the major forces that shape the
beach, and determine both the longer-term lateral spreading of material comprising the beach nourishment
project and the short-term response of the project to storms. Exposure of the project site to wave energy from
various directions determines the predominant longshore sand transport rate and direction. Offshore islands
or coastal structures, peninsulas, or adjacent land masses may partially or completely shelter the project site
from certain waves. The presence of these features modifies the energy, frequency, and directional
characteristics of the incident waves that approach the site from deeper water. The presence of submerged
offshore shoals, reef outcroppings, shore-attached shoals, or depressions (in general, any irregular
bathymetry), also can have a significant persistent influence on local wave transformation and the longshore
sand transport regime created by the incident breaking waves. It is important to assess the degree in which
the wave climate varies from one end of the project to the other. Persistent variations in wave conditions of
5 to 10 percent can create significant local differences in project performance.
(b) There are several time scales of importance with regard to wave climate. The design life of a beach
nourishment project is usually tens of years. Periodic renourishment is typically done every 3 to 5 years.
There is evidence of cyclical patterns in weather (e.g., El NiZo) that vary on the order of years, which would
tend to produce wave climate patterns having similar multiple-year cycles. Annual changes in weather, and
annual variations in the frequency and intensity of storm activity create a longshore sand transport regime
that can vary considerably from year to year. Definition of the wave climate at these different time scales
helps in assessing long-term beach nourishment project performance, potential variation in performance from
one renourishment cycle to the next, and from year to year.
(c) Wave and water level conditions that accompany extratropical and tropical storms are also an
important aspect of project setting and project design. The time scale of these events is on the order of days.
Since most beach nourishment projects are justified based on storm protection benefits, it is important to
quantify the frequency and severity of storms that can impact the project site during its design life. Lower-
intensity storms typically erode the beach berm. More severe storms, particularly those with higher water
levels, can inundate the berm and focus direct wave attack on dunes and exposed upland property. The most
important storm parameter influencing beach and dune erosion is maximum water level, followed by wave
energy and storm duration.
(d) Hindcast wave and water level information, or data measured nearby, can be used to characterize the
wave and water level climate near the project site at the time scales of importance. Sometimes wave
information is available in deep water, and other methods must be used to "transform" the information to the
project site (e.g., to transform deepwater wave information past islands or very irregular bathymetry).
Part II-2 discusses methods for developing wave climate information, including wave hindcasting. Part II-3
discusses techniques for estimating nearshore waves, including wave transformation methods. Part II-5
discusses methods for estimating water levels due to storms.
(6) Existing structures and infrastructure.
(a) How threatened are commercial and private structures, and infrastructure such as roads and utilities,
by storm waves and water levels? Formulation of a beach nourishment project often involves compiling an
inventory and description of the location of existing infrastructure and commercial and private properties to
assess their vulnerability. The properties are valued to aid in quantifying the benefits that accrue from
construction of a beach nourishment project. Are there structures that protrude beyond the predominant
shoreline position? If so, it may be difficult and not cost-effective to provide a lasting beach having the
design width in front of those structures. Attempting to do so may result in a persistent apparent erosional
"hot-spot" in these locations. Aerial photos provide a good source of information for describing the
Beach Fill Design
V-4-9
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