In this study methods were developed for the prediction of wave
conditions that are hazardous to navigation at river entrances, with
emphasis on applicability to the Columbia River. There are two basic
components to the prediction system: (1) a semi-automated spectral
method for forecasting the significant height and average period of
waves in deep water, and (2) an index of navigation hazard at river
entrances that depends on the significant height and average period in
deep water and on the mean current and water depth at the entrance.
The computerized, deep water forecast method is a hybrid scheme
that combines the spectral principles of the Pierson-Neumann-James
method with the graphical input techniques of Wilson and the fetch
limited spectrum of Liu. The significant heights generated by the
method are well verified by winter wave measurements at Newport,
Oregon.
The hazard index is based on the probability of wave-breaking in
water of arbitrary depth and current. The breaking probability is
derived under the assumption that wave heights and squared periods are
statistically independent and distributed according to a Rayleigh
probability density function. The breaking-wave probability and the
hazard index depend on the wave steepness in deep slack water and on
the depth (relative to the wave period squared) and current (relative
to the period) at the river entrance. The dependence on depth and
current is achieved in two ways: (1) the limiting steepness (breaking
index) k found as a function of relative depth and relative current,
and (2) the wave spectrum in water of arbitrary depth and current is
found by transformation of the spectrum in deep slack water. The
transformation is performed by requiring that the rate of wave energy
propagation remain constant. The hazard index is closely related to
the probability of breaking swell. At water depths that are typical
of river entrances, the hazard index depends strongly on the significant
wave height, mean current and depth, but only weakly on the mean wave
period (since the breaking height of swell at such depths is only weakly
dependent on period).
Hindcasts of deep water significant wave heights and hazard indices
compared reasonably well with measured heights and Columbia River bar
closure periods. Forecasts based on accurate prognostic weather charts
should provide similar results. / Graduation date: 1974
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32516 |
| Date | 25 May 1973 |
| Creators | Enfield, David B. |
| Contributors | Quinn, William H. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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