ESTUARY INLET CHANNEL STABILIZATION STUDY USING A HYDRAULIC MODEL

Theodore T. Lee

Abstract


A hydraulic model study was conducted to determine the most feasible means of reducing shoaling into a coastal inlet channel that had been used by loaded Landing Ship Tank (LST) class vessels serving the port of Tan My near Hue, Republic of Vietnam The ultimate objective was to increase the time during which the channel will be open to navigation by improvements in physical configuration An extensive field data acquisition and analysis program was executed to provide basic information for model prototype correlation This incidentally resulted in the re-evaluation of several empirical formulae being used for prediction of littoral transport and of tidal currents The comprehensive field measurements of shoaling in the channel area also permitted the determination of the scale effects on the quantitative results of sediment deposition in the channel and on the time scale of bottom evolution The experiments were conducted systematically in three phases The three-dimensional studies for Phase I and II were conducted using a rigid bed, sand or walnut shell covered (1/250 horizontal and 1/50 vertical scale) hydraulic model of a 15 sq mi ocean-estuary land area Periodic long-crested waves tides tide/river induced currents were simulated in the model Phase I covered qualitative evaluation of nine improvement plans, from which a BEST PLAN," an upshore jetty to protect the existing channel, was selected Phase II covered qualitative and quantitative evaluation of four variants of the "BEST PLAN,' from which the most effective and economical variant was determined To insure reliability of quantitative results, comprehensive experiments were conducted using three different sediments (D50 = 0 41 mm and 0 90 mm, 7 = 1 35 for two types of ground walnut shells and D50 = 0 22 mm, 7 = 2 65 for sands), and three model scaling criteria (Froude Scaling, "Ideal Velocity" Scaling, and Modified Froude/Ideal Velocity Scaling) Phase HI covered two-dimensional model tests, in a 180 foot flume, of the stability characteristics of the proposed rubble mound type jetty on a movable bed The major conclusions of this study include (1) the jetty, as postulated in the BEST PLAN,' would reduce annual maintenance dredging requirements by 74 to 84 percent, (2) a systematic three phase model study such as used in this investigation is most feasible (from a time-consumption viewpoint, use of light weight materials such as ground walnut shells may be more economical than use of natural sands as model material), and (3) use of theory alone in predicting a tune scale for bottom evolution should be approached with caution especially where field data are not readily available.

Keywords


estuary; inlet stabalization; channel stabalization; hydraulic model

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