Inlet Stability Research Articles

The “Furkert‐Heath” relationship for tidal inlet stability reviewed

Abstract The “Furkert‐Heath” relationship is a commonly used method of assessing the stability of New Zealand inlets. However, the equation published by Heath in 1975 was incorrectly calculated which has led to misinterpretation of data in some cases. Recalculation resulted in a new linear relation, presented here, between the inlet gorge cross‐sectional area A and tidal prism O. Misuses of the “Furkert‐Heath” equation are identified including: extrapolating predictions beyond the data field; neglecting errors inherent in measurement of A and O; method of characterising sedimentation regime; neglecting confidence limits of data; using A‐O relationships as the sole indicator of inlet stability; and applying the relationship to inlets other than barrier‐enclosed inlets.

SEDIMENTATION PATTERNS IN A TIDAL INLET SYSTEM MORICHES INLET, NEW YORK

A detailed study of the historical development of Moriches Inlet, Long Island (New York), was completed to determine the morphodynamic interaction of tidally influenced processes and the effects of man-made alterations on the inlet channel and affiliated flood and ebbtidal deltas. The south shore of Long Island in the vicinity of Moriches Inlet is a microtidal, wave-dominated (mixed-energy) environment. Characteristic of this setting, the inlet bisects a low-lying barrier island backed by an open bay and has a prominent flood-tidal delta. In this study, bathymetric charts of the inlet, bay, and barrier nearshore zones were contoured for analysis. Using a polar planimeter, the areas between isobaths from mean high water to the bottom surface were measured. This information was used to determine the volumetric distribution of sediment and water in the system. In addition, harmonic analysis was applied on digitized bay-tide records to ascertain the relationships of the semidiurnal overtide constituents. From the results, mean rise/fall duration differences, related to the conservation of mass, were calculated. The results of the quantitative spatial analysis indicate that Moriches Inlet was flood-dominant from breach in 1931 until closure in 1951. After reopening in 1953, the inlet became ebb-dominant as a result of inlet stabilization and extensive dredge-and-spoil operations in the inlet and bay. Good correlations exist between net sedimentation in the inlet with (1) bay-surface area change, (2) water storage capabilities of the flood-tidal delta, and (3) the cross-sectional area of the inlet. The relationship among these variables suggests that there is a system-wide response to the change in the hydrodynamics caused by man-made alterations, resulting in ebb dominance.

Closure to “Inlet Stability Solutions for Tributary Inflow”

Closure to “Inlet Stability Solutions for Tributary Inflow”

Discussion of “Inlet Stability Solutions for Tributary Inflow”

Discussion of “Inlet Stability Solutions for Tributary Inflow”

Discussion of “Inlet Stability Solutions for Tributary Inflow”

Discussion of “Inlet Stability Solutions for Tributary Inflow”

Inlet Stability Solutions for Tributary Inflow

Formulas in use relating to the flow of water through tidal inlets do not take into account the joint effects of inertia and tributary inflow that play a significant role in determining the characteristics of many inlets. In a proposed analytical model these two factors are considered where the tributary inflow to the bay causes ebb flow through the inlet to exceed flood flow. The solution method applies to the same type inlets as studied by E.I. Brown and G. H. Keulegan, i.e. inlets that have a bay in which the water rises and falls uniformly over the entire bay area. An additional assumption is that the discharge into and from the inlet is governed by a head loss that is quadratic in velocity.

YF-16 Inlet Design and Performance

The YF 16 inlet design, the integration of airframe and inlet, the design philosophy, development tests, and performance of the inlet throughout the flight and maneuver envelope of the airplane are reviewed. Model data are included which show the airplane forebody effect on the inlet flowfield and the performance of the inlet in terms of pressure recovery, distortion, turbulence, inlet stability, and spillage drag. The data presented verify that the single, fixed-geometry, normal-shock inlet located in the protective flowfield of the fuselage nose provides an integrated inlet/airframe configuration that meets all of the design and performance goals established for the YF -16 air-combat fighter. Indeed, the simple, low-cost, and uncomplicated inlet design optimizes rather than compromises airplane performance in the air-combat arena, and at the same time provides a Mach 2 capability for the airplane.

MEASUREMENT OF BED FRICTION IN TIDAL INLETS

The flow characteristics and the stability of a tidal inlet are governed, among other factors, by the channel bed friction. In order to determine the bed shear stress regime and the frictional characteristics, near-bed velocity profiles were obtained at the throat sections of two inlets, John's Pass and Blind Pass, on the Gulf Coast of Florida. A specially designed steel cage with five current meters in a vertical array was used to obtain the profiles in the bottom one meter of the flow. The profiles were found to be logarithmic but it is noted that, especially near the times of slack water, the effect of inertia becomes significant. However, during the major part of the flood or ebb flow period, frictional effects are dominant. In the fully rough regime of flow, the bed-shear stress - velocity relationship is found to follow the square law, with a constant, characteristic friction factor and Manning's n for each inlet. This friction factor is used in hydraulic formulas, based on uniform, steady open channel flow relationships, to obtain the tidal prism - throat cross-sectional area ratio, which is then compared with that obtained from flow discharge measurements. Agreements and discrepancies in the comparison are discussed. The relationship between the bed shear stress at incipient motion and the grain size at the bed is reviewed, and it is noted that the observed relationship at the two inlets does not agree with the well-known correlation of Shields for uniform sandy beds.

Stability of some New Zealand coastal inlets

Abstract The relation of tidal compartments to entrance cross‐sectional areas is examined for 20 coastal inlets. Sixteen inlets conform to a linear relationship, which is consistent with stable entrances the sizes of which are determined by the ability of the tidal flow to transport sediment. Based on this criterion deposition should be taking place at the entrances of the other four inlets: Wellington, Lyttelton, and Akaroa harbours, and Paterson Inlet. Available data confirm this for Wellington and Lyttelton Harbours.

EVALUATION OF OVERALL ENTRANCE STABILITY OF TIDAL ENTRANCES

This paper is written in continuation of earlier published material (2, 4, 5) dealing with stability of tidal inlets on littoral drift shores. The experience available at that time was responsible for the introduction of two parameters: .vmean max/ defined as the mean max. velocity in the gorge at spring tide and the K/M-tot ratio (tidal prism at spring tide divided by material transport to the entrance from the adjoining shores) as the most pertinent parameters for description of overall stability. A more detailed justification for this choice is given in this paper, based on computation of the relative sediment transport at various tidal phases. Examples of earlier date (4) and twelve new examples from India are given.

PERFORMANCE OF A JETTY-WEIR INLET IMPROVEMENT PLAN

Comprehensive monitoring has been carried out since 1970 to determine the performance and effects of a navigation and inlet stabilization project at Ponce de Leon Inlet, Florida. The improvement plan at the tidal inlet included construction of two jetties, a weir sand by-pass system, and dredging of a navigable channel (Figure 1). An evaluation was made of the general current patterns, the relative refracted wave energy distribution, and the volumetric beach and hydrographic fluctuations associated with the inlet. An analysis of this data was used to interpret the dramatic and unexpected changes which have resulted along the adjacent coastline and within the inlet after the completion of the inlet improvements.

HYDRAULICS AND SEDIMENTARY STABILITY OF COASTAL INLETS

A method is presented for investigating the stability of coastal inlets against closure due to transport and deposition of sand in the inlet cross-section. The method utilizes earlier contributions by: (1) Keulegan representing the hydraulics of inlets, (2) O'Brien which describes an equilibrium relationship between the cross-sectional area of an inlet and the bay tidal prism, and (3) Escoffier which relates to the stability of an inlet under changes in conditions which tend to close or enlarge an inlet. A "stability index" is defined which incorporates the buffer storage area available in the inlet cross-section, prior to the onset of closure and also includes the capability of the inlet to transport excess sand from its cross-section. In order to apply the method, geometric and hydraulic data representing the inlet are necessary; the minimum data required include a survey of the inlet throat cross-section and the lag between high (or low) water in the ocean and the following slack water in the inlet. In addition, it is necessary to conduct measurements or make assumptions concerning the minor and gradual hydraulic loss coefficients. Based on assumed depositional patterns in the inlet, the method is applied to five real inlets and the stability indices are presented.

New Developments in the Field of Tidal Hydraulics

The paper describes the recent advances in tidal hydraulics and the methods of solving tidal hydraulics problems. The problems of inlets, canals, and estuaries (including salt water intrusion) are considered and the bibliography gives a selection of the more recent literature on these subjects. The role of the hydraulic model and the computer is described. The question of the stability of inlets as related to tidal range and inlet cross section is handled. The paper does not attempt to develop the procedures for solving tidal hydraulics problems; rather it points out the recent, meaningful advances in this area of engineering and refers to the literature where more detailed descriptions can be found.

Tidal Inlets Housekeeping

A tidal inlet on an alluvial shore presents a littoral barrier which must be overcome by flushing and bypassing of material. Presumably, the tidal inlet arranges itself in the most practical way by providing the highest flushing ability at the least loss of energy to bottom friction. This, however, is not the only condition for stability of a tidal inlet. There must be enough tidal flow available to accomplish the task of transporting all the littoral material which entered the inlet. This requires a tidal prism and discharge of a certain size compared to the quantity of littoral drift which is carried to the inlet. Part of this material may be transferred across the inlet entrance on a bar or shoal. In the inlet channel, a bottom shear stress which corresponds to a velocity of about 1 m per sec results. At this velocity, sand bottom with 0.15 mm to 0.3 mm sand changes its geometry by flattening the dunes approaching plane bottom. Both tangential and normal forces contribute to the drag of a duned-bed stream. Because the tangential forces contribute directly to sediment transport, the drag force of the bed on the stream is more effectively used to transport sediment with flatter dunes and plane bottom.

The Use and Detection of Fluorescent Sand Tracers: ABSTRACT

Two recent developments, fluorescent tracers and a fluorescent particle counter, hold promise as practical means to the quantitative evaluation of littoral drift and sediment transport in rivers. Unlike radioactive material, luminophores present no health hazard or storage problems, offer a wider range of applicability, can be recovered in samples, and are more economical to use. The fluorescent tracers have been employed in studies of such specific problems of sediment migration as beach erosion, inlet stability, dune processes, and artificial beach nourishment. Fluorescent dyes and thermosetting plastics have been combined to coat sand in a process designed to produce the tracer material, so that the physical properties of tracers and the sediments are nearly identical. Of the several materials and techniques tested, urea-formaldehyde resin, fluorescing organic dyes, and a catalytic procedure imparted the best chemical and physical characteristics to the tracer grains. The application of tracers to sand transport studies became practical only with the invention of the fluorescent particle counter. This instrument provides a rapid and accurate method of frequency determination of tracer particles in sand samples, and therefore affords a much needed statistical treatment of sediment transport. The particle counter has been built on the principles of optics, electronics, and threshold decision logic, to differentiate simultaneously for four tracers, the fluorescent colors of which have been established through spectrophotometric measurements. Tracers in samples with concentrations varying from 10-7 to 10-2 are counted, tabulated, and recorded at the rate of 20,000 particles/second. End_of_Article - Last_Page 360------------

STABILITY OF COASTAL INLETS

This paper is a continuation of papers of earlier date (4) and (5) and is an abstract of (6). Pertinent factors involved in inlet stability are discussed briefly. Results of analysis of existing data are mentioned and a future research program is outlined.
 In order to obtain a stable tidal inlet in alluvial material it appears to be an inevitable assumption that littoral drift material is being supplied continuously to the inlet. Part of this material is deposited on the inlet bottom where the tidal currents will move it forward and back as a kind of "rolling carpet."
 In order to obtain a relatively stable situation this carpet must not move back and forth too rapidly since it thus runs the risk of being lost at both ends (the ocean and the bay). Nor can it be allowed to move too irregularly, changing its velocity and travel time rapidly, since it may soon "get stuck" at one or at both ends in the form of excessive deposits. If - because of insufficient littoral drift supply -- inadequate amount of material is available for building up this carpet the inlet will be constantly "shaved" and will gradually develop non-scouring open bay or perhaps estuary characteristics. Fig. 1 shows longitudinal sections through inlets of different length. In the first case the (unstable) channel is so short that the rolling carpet extends outside the inlet floor, which in turn causes material to be deposited on shoals in the sea and in the bay by the material-loaded ebb and flood currents. In the second case the (also unstable) channel is so long that material is now deposited inside both ends of the inlet channel because it gradually became so long that currents were too slow to carry the material load out in the sea or in the bay for depositing. The third case demonstrates a stable "status quo" situation between inlet length, current velocities, and material load.

Stability Of Coastal Inlets

Existing theories of relationship between tidal range, tidal prism, and inlet cross-section are reviewed and compared; existing data on inlets are introduced into discussion, as well as effect of quantity and type of littoral material on inlet action.

Closure to “Stability of Coastal Inlets”

Closure to “Stability of Coastal Inlets”

Discussion of “Stability of Coastal Inlets”

Discussion of “Stability of Coastal Inlets”

Stability of Coastal Inlets

Existing theories of relationship between tidal range, tidal prism, and inlet cross-section are reviewed and compared; existing data on inlets are introduced into discussion, as well as effect of quantity and type of littoral material on inlet action.