Inlet Geomorph Bibliography-Relationships

Escoffier, F.F. The Stability of Tidal Inlets. Shore and Beach, October 1940, Volume VIII No. 4, pp. 114-115.

This short paper describes the computation of the mean velocity (Vm) with inlet and bay dimension and tidal range as knowns using an equation by Brown (1928). The computation assumes the flood and ebb current velocities are equal and Escoffier discusses a critical mean velocity (Vcr) which is sufficient for sediment entrainment. Escoffier assumes that for most beach sediments the value is 3ft/sec. The Brown equation for mean velocity of peak tidal current may be used to compare Vm to Vcr to determine if the inlet is self-filling, self-eroding or stationary in size. The paper then discusses inlet stability using the Brown equation and graphically represents stable and unstable cases with Vm vs channel size. The paper discusses how the theory can be utilized to determine inlet stability.

Bruun, P., and Gerritsen, F., 1959 Natural By-Passing of Sand at Coastal Inlets. Journal of the Waterways and Harbors Division WW4, pp. 75-107.

Bruun and Gerritsen define the two main principles in bypassing of sand by natural action; bypassing on an offshore bar and bypassing by tidal flow action or a combination of these two methods. The ratio of Mmean/Qmax=r (magnitude of littoral drift) and quantity of flow through the inlet can assist in the identification of these mechanisms. If the ratio is high r>200-300, bar bypassing is predominant. A lower ratio, r<10-20 indicates tidal flow bypassing.

The authors discuss the principle included in bar bypassing and present examples of inlets with bypassing (including structured and improved inlets) and bar bypassing at harbors. They discuss the principals involved in bypassing by tidal flow action at improved and unimproved inlets and provide multiple physical examples of this mechanism, including at harbors. The authors touch on the influence (or lack thereof) of sediment grain size and identify a bypassing factor consisting of multiple constituent factors which influence bypassing. A discussion of the ratio of Mmean/Qmax is included. Littoral drift and Mmean values are presented in table form for multiple inlets.

Jarrett, J.T., 1976. Tidal Prism – Inlet Area Relationships. GITI Report 3, U.S. Army Engineer Waterways Experiment Station, Vicksburg MS. 55 pp.

In this paper Jarrett discussed the works of LeConte (1905), O’Brien (1931), Nayak (1969 and 1971) and Johnson (1972). Jarrett obtained data from 108 inlets on all coasts of the United States and discusses the sources and methods of obtaining this information. Jarrett classified the inlets into three main categories (1) all inlets, (2) unjettied or single jettied inlets, and (3) inlets with jetties. He also classified them by coast. Jarrett identified a relationship between inlet area and tidal prism of the form A=CPn and presents the data in table and graph form within the paper. He also discussed the differences in the relationships between the different groups. This paper also contains referenced tables of tidal prism, cross sectional area, hydraulic radius, and tidal current data for the 108 inlets in his study.

Hughes, S.A., 2002. Equilibrium Cross-sectional Area at Tidal Inlets. Journal of Coastal Research, 18(1). West Palm Beach, FL., pp. 160-174.

The paper begins with a literature review and discussion of the relationship that exist between Hughes discusses the mathematical relationships between the minimum cross sectional area of a stable inlet (A) and tidal prism (P). He then presents a derivation of the A vs P relationships considering an equilibrium depth is associated with maximum discharge per unit width. The equation that is derived is then compared to field data from 102 US tidal inlets with good correspondence with most inlets having equilibrium areas larger than the minimum predicted. Additionally, there is good correspondence found to equilibrium results obtained from eighteen movable bed model experiments. Hughes includes a discussion of scaling in movable bed models and derives a movable-bed modeling relationship suitable for channel scour caused from bedload transport caused by tidal currents. The relationship is not valid for scour caused by waves.

Seabergh, W. C., 2003. Long-Term Coastal Inlet Channel Area Stability. In: Proceedings Coastal Sediments '03. 2003. CD-ROM Published by World Scientific Publishing Corp. and East Meets West Productions, Corpus Christi, Texas, USA. ISBN 981-238-422-7.

Seabergh applies the concept of equilibrium area of tidal inlets (LeConte, 1905 and O’Brien 1931 and 1969) to inlets that are not in equilibrium i.e. inlets with bays that do not fill completely but still exhibit fairly consistent channel flow over many years. Seabergh discusses work by others on inlet equilibrium which do not require complete bay infilling for maintenance of stable channels.

The Kulegan (1967) “K” repletion coefficient is introduced to define the percentage that the bay fills. A number of examples from US inlets with low K values are presented in table form. This is discussed in concert with the Escoffier (1940, 1977) equilibrium curve which requires complete bay filling, whereby the Escoffier analysis of tidal inlet cross-sectional area equilibrium for cases with existing low K values indicates that equilibrium area will be much larger than the existing area. However, the low K inlets may not expand their entrance cross-sectional area in the absence of anthropogenic changes (dredging, structure implementation, etc.).

Shigemura, T., 1981. Tidal Prism – Throat Width Relationships of the Bays of Japan. Shore & Beach, Volume 49, No. 3, pp. 34-39.

Shigemura studied 231 natural bays, to which no artificial works had been added, along the four major coasts of Japan. He defined the throat area as the cross-sectional area at the narrowest section, or throat, of a bay entrance. Previously Shigemura (1980) developed a relationship between the throat area and the tidal prism of the form A=CPn. In this paper he examines ten (10) external variables through a correlation analysis to determine which exerts the most significant influence on throat width. Based on this analysis, Shigemura arrives at basic correlation relationships, separated by coast (Pacific Coast, Japan Sea Coast, Kyushu West Coast, and Inland Sea Coast), of the form Wt=CPn. Because these initial relationships do not account for external variables such as littoral drift, geological or geometrical features, Shigemura refines the relationships based on seven “geometrical parameters.”

In order to evaluate the significance of the parameters, he defines a reliability parameter of the regression equation and performs a correlation analysis between the reliability parameter and the geometric parameters. He found that, of all the Wt-P equations, the parameter rwl (the ratio of the throat width to the shore length of the bay) had a high correlation with the reliability parameter and, based on this information, uses the rwl parameter further refine the correlations by classifying the bays into four groups. Additionally, the paper includes a discussion of equations other researchers have developed and provides the values for the C and n variables throughout the stages of refinement.

FitzGerald, D.M., and FitzGerald, S.A., 1977. Factors Influencing Tidal Inlet Throat Geometry. Proceedings, Coastal Sediments 77 Conference, ASCE, pp. 563-581.

FitzGerald and FitzGerald define and assess the parameters that affect tidal inlet throat geometry. Initially, the work of previous researchers in the area of inlet throat geometry is discussed. FitzGerald and FitzGerald define the inlet throat as the part of the channel which is the narrowest and deepest and has the maximum hydraulic radius. The inlet throat has the minimum cross-sectional area and maximum current velocities. FitzGerald and FitzGerald discuss the size, depth, channel symmetry and sedimentological control of the inlet throat.

In this paper FitzGerald and FitzGerald investigated eight central South Carolina inlets (mesotidal inlets) to determine factors which influence the symmetry of the inlet throat. They discuss that symmetry is a product of (1) meandering of the channel thalweg, (2) inlet shoreline configuration, and (3) dominant longshore transport direction. Temporal variations in throat cross-section are developed. They discuss the variations in throat cross-sectional area and short-term changes at Price Inlet, SC and the long-term changes of Stono Breach, Dewees and Capers Inlets, SC. A table of historical changes in throat geometry is presented. They develop the relationship of cross-sectional area versus tidal range for Price Inlet of the form Y=947+119X. The paper discusses the channel response over a complete tidal cycle at Pierce Inlet in order to evaluate if the inlet throat cross-sectional area responds quickly to changing tidal conditions.

Fitzgerald, D.M., and Nummedal, D, 1983. Response Characteristics of an Ebb-Dominated Tidal Inlet Channel. Journal of Sedimentary Petrology, 53(3), pp. 833-845.

This paper details the study of changes in the main channel of Price Inlet, SC on timescales ranging from hours to years. Price Inlet is a barrier island inlet located on the mixed-energy South Carolina coast north of Charleston Harbor. The field work carried out for this research occurred between 1974 and 1977. Fitzgerald and Nummedal discuss water storage and tidal stage in the Price Inlet drainage basin including a discussion of water surface area in the back barrier and throat cross-sectional area over the tidal cycle. Migration and morphological changes of the tidal channel were also monitored at three cross-sections along the inlet channel. Cross-sectional area was measured on a bi-monthly basis measured at slack water.

It was concluded that the inlet cross-section is highly sensitive to changes in tidal range because of the relationship between tidal range and potential sediment transport. The paper also includes a discussion of channel change during one tidal cycle as it relates to sediment transport. The calculated magnitude of potential inlet sediment transport is high enough at Price Inlet to suggest that significant changes in inlet hydraulic geometry can be expected during a single tidal cycle. This hypothesis is tested over a single cycle on July 29, 1977 through monitoring of the throat cross-section and inlet flow parameters. Throat current velocities and cross-sectional areas were measured each hour and changes of the areas are discussed in the paper. Longer-term changes in the morphology of Price Inlet was found to be controlled by the growth of the ebb-tidal delta shoals and growth of the channel-margin linear bars. The bars reduce transport into the inlet and thus results in a larger channel equilibrium cross-sectional area.

Walton, T.L., and Adams, W.D., 1976. Capacity of Inlet Outer Bars to Store Sand. Proceedings, 1976 Coastal Engineering Conference, ASCE, pp. 1919–1937.

Walton and Adams investigated the equilibrium storage volume of sand in the outer bar/shoal of newly cut inlets. Inlets were classified into highly exposed, moderately exposed and mildly exposed to offshore wave action based on the H2T2 (wave height)2 * (wave period)2 parameter. The paper considers the inlet as a sediment sink to the adjacent shorelines and utilizes the equilibrium shoal volume in their calculations as the point at which the erosional influence to the adjacent shorelines is diminished. Walton and Adams utilized the “no-inlet contour method” of Dean and Walton (1973) to calculate ebb shoal volumes for 44 inlets in assumed equilibrium within the United States. They developed a relationship of the form V=aPb and used liner regression to determine the value for b for inlets separated by exposure and for all inlets together. Walton and Adams also determined that the ebb shoal volume and the inlet channel cross-sectional area relate to one another in the form V=a’Ab’.

Walton and Adams identified that in areas of high wave activity there appears to be a well-defined limiting relationship to the amount stored in the offshore bar as a function of tidal prism. They noted that the volume of sand in an inlets outer bar is strongly correlated to tidal prism and cross sectional inlet throat area. They found that more sand is stored in the outer bar of a low energy coast than is stored in the outer bar of a high energy coast.

The paper also included references to a number of tidal prism and inlet cross-section values and identified that future work in this area should take into consideration longshore energy and size distribution of littoral material and examine inner bay storage.

Hayter, E.J.; Hernandez, D.L., Atz J.C., and Sill, B.L., 1988. Study of Ebb Tidal Delta Dynamics. Proceedings, 1988 Conference on Beach Preservation Technology, Florida Shore and Beach Preservation Association, Tallahassee, FL, pp. 365-374.

This paper discusses ebb shoal mining and the infilling of ebb shoals. The study presents the results of a laboratory scale movable bed tidal inlet model to investigate both the effects of oscillatory flow and waves on ebb shoal formation as well as the effect of shoal mining on the inlet-shoal system. Details of the model are included. Best fit lines for shoal volume and G, a parameter including the effects of sediment size (D50), specific gravity of sand and water (ys, y) and average inlet area (Bh) was determined (G=Bhd50 (ys-y/y). Scale effects of models are discussed. The dimensionless empirical relationships between shoal volume, wave energy and tidal prism V/G=0.00048(P/G)-1340, V/G=0.00069(P/G)-1870, and V/G=0.00476R0.527 where V/G is the normalized shoal volume, P is the tidal prism, R is a dimensionless parameter R=P/GE, and E is dimensionless wave energy density (E=yH2s/8yh2) (Hs is the significant wave height) where h is the mean water depth in the inlet were used to predict prototype shoal volumes in order to test their ability to simulate inlet-shoal conditions. Data from 12 Florida east coast inlets were used for this analysis.

The defined relationships have confirmed that shoal size and shape is generally governed by ebb jet flow. Both the fixed bed and movable bed models utilized in this research confirm this conclusion. This study validates the use of a laboratory scale model in the investigation of ebb shoal mining.

Marino, J.N., and Mehta, A.J., 1987. Inlet Ebb Shoals Related to Coastal Parameters. Proceedings, 1987 Coastal Sediments Conference, American Society of Civil Engineers, pp. 1608-1623.

In this paper, the evolution of ebb tidal shoals is introduced through a discussion of a history of St. Augustine Inlet (opened in 1941) including jetty construction and dredging history. Marino and Mehta examined eighteen inlets on Florida’s east coast, relating their ebb shoal volume to spring tidal prism, inlet cross-sectional area, inlet width, inlet depth and sprig tidal amplitude. Ebb shoal volumes were determined through the Dean and Walton method (1973). Published values, or estimates based on literature, were used for the values of cross-sectional area, width, depth, prism and wave data. A dimensional analysis was utilized to determine functional relationships which may relate to ebb shoal volume. The paper examined the ebb shoal volume vs spring tidal prism relationship of Walton and Adams (1976) to determine which parameters explain the scatter in the Walton and Adams data within the same energy range. The discussion also examines the influence of bed shear stress, current shear stress, wave shear stress and channel depth.

Conclusions of the paper contain estimates of the total amount of material found within the 18 examined ebb shoals and identifies a general trend of decreasing ebb shoal volume from north to south along the East coast of Florida. Marino and Mehta conclude that the ebb shoal volume appear to be a function of spring tidal prism, inlet area, tidal amplitude and the ratio of inlet width to depth (which arises as a result of the effect of wave induced sediment transport at varying depths over the ebb shoal).

Oertel, G.F., 1988. Processes of Sediment Exchange Between Tidal Inlets, Ebb Deltas and Barrier Islands. Lecture notes on Coastal and Estuarine Studies, Volume 29, Springer-Verlag New York, Inc. NY, pp. 297-318.

The introduction of this paper includes a brief discussion of literature as it related to prism area relationships and bypassing of sediment and inlet stability. Hydraulics and sedimentary processes at inlets are then discussed, initially in the absence of sediment transport outside of the channel itself. The paper then turns to a discussion of the processes occurring at the ebb tidal delta. Formation of the delta and the differences between the ebb and flood flow processes. Following is a discussion on equilibrium delta budgets the amount of material stored in an ebb delta. Oertel then introduces the concept that material may originate from the inlet gorge or from the adjacent littoral drift. Focus was placed on the amount of material available from the inlet gorge.

In this study, nine tide-dominated inlets were examined. Their ebb delta volumes were determined through the Dean and Walton method (1975) and tidal prisms were either measured or found in literature. Based upon this data, two equations relating bar volume and prism (mean and spring prisms) were determined. The plots were compared to the Walton and Adams (1976) data for tidal prism. This comparison is discussed within the paper. Diversion of the inlet jet by longshore current is discussed along with the sediment transport implication this diversion created on the inlet channels (i.e. inlet migration). Georgia and North Carolina inlets were used as examples.

Four types of deltas (with varying degrees of longshore versus onshore currents) are discussed with regard to bypassing and channel migration. Illustrations of tidal inlets are included which identify channel orientations caused by different magnitudes of inlet migration and sediment bypassing.

Cobb Island in Virginia is presented as a case study in island sediment budgets and illustrations are included identifying cases where barrier island shorelines change but their budgets remain balanced i.e., stability by rollover, stability by spit growth, stability by migration, and stability with constant shoreline position (complete bypassing).

Mehta, A.J.; Dombrowski, M.R., and Devine, P.T., 1996. Role of Waves in Inlet Ebb Delta Growth and Some Research Needs Related to Site Selection for Delta Mining. Journal of Coastal Research, SI 23, pp. 212-136.

A motive of this paper was to obtain an understanding of the processes occurring at the ebb delta in terms of deposition in order to assess how these processes affect ebb delta mining. The role of waves in modulating the growth of ebb tidal deltas has been examined for four Florida east coast entrances (Jupiter Inlet, South Lake Worth Inlet, Boca Raton Inlet and Bakers Haulover Inlet). Volumes of the ebb deltas were determined using the Dean and Walton method (1973).

A model is presented in this paper to explain delta growth based upon an analysis of bottom shear stress from current and wave influence (Tb) and the critical stress for scour (Tcr) where, when Tb<< Tcr deposition occurs until they are approximately equal. At this point there is no further deposition and there is an equilibrium water depth above the delta and the delta reaches an equilibrium volume. The influence of wave energy would increase the delta volume (increased wave energy) or decrease the delta volume (decreased wave energy) and the shoal would move away from this equilibrium volume. Details regarding these conditions and relating hydraulic and morphodynamic parameters to the delta area are then explained within the paper.

The four Florida entrances examined in this paper have mostly littoral transport components with minimal riverine influences. They are examined by the authors to assess the effects of waves compared with tidal currents as the deltas transition from the no inlet condition to equilibrium. The author’s utilized the O’brien ratio of wave power to tidal prism power and plotted growth rate curves over time based on the high and low values of this ration. The curves were then compared to the measured ebb volumes. The ebb delta volume growth curves grow monotonically, reaching an asymptotic condition (indicating a dynamic equilibrium of the ebb shoal). The equilibrium delta volume condition was also examined in this paper.

The focus of the paper then turned to examples of delta mining with examples from US entrances and a discussion of considerations of in mining site selection criteria.

Powell, M.A., Thieke, R.J., and Mehta, A.J. 2006. Morphodynamic Relationships for ebb and flood delta volumes at Florida’s tidal entrances. Ocean Dynamics, Volume 56, pp. 295-307.

This paper reviews relationships between cross sectional area, ebb delta volume, flood delta volume and tidal prism based on data from 67 sandy entrances in Florida. This paper contains a list of these 67 Atlantic and Gulf Coast inlets which include data of latitude, longitude, tidal range, wave energy, flux, grain size, depth, flow area, tidal prism, and ebb and flood volumes. The paper includes discussion of and multiple references to previous work. Powell, Thieke and Mehta plotted prism versus throat area for all inlets examined and found a best-fit equation of the form Ac=6.25x10-5P1.0. They further discussed ebb delta volume and tidal prism noting that the ebb delta volume is determined by tidal currents and waves. A review of the literature is included as part of the discussion on ebb delta volume and tidal prism. Additionally, the authors applied the previously defined equations to the data from the 67 Florida inlets studied. Further the authors identified relationships between flood delta volume and tidal prism and discussed the initial volume growth of the flood delta and perform a best-fit analysis as was done in the ebb delta case. At the terminus of the paper the authors include a case which identifies the effect of the closure of a storm induced breach near Matanzas Inlet, FL.

Sha, L.P. and Van den Berg, J.H., 1993. Variation in Ebb-Tidal Delta Geometry along the Coast of the Neatherlands and the German Bight., In: Journal of Coastal Research, Volume 9, No. 3 (Summer, 1993), pp. 730-746.

This paper discusses the geometry of ebb tidal deltas and associated hydraulic aspects using examples and data based upon the Dutch-German coastal barrier region. The paper discusses the tidal regime of the North Sea coasts and details the morphology of ebb tidal deltas of the area including historical information. The interaction of offshore and inshore tidal currents at the inlet mouth for ebb tidal deltas of the Wadden Sea and of the South Western Netherlands is discussed as is the importance of the wave versus tidal forces of the inlets in this region as the development of asymmetries and orientation depend upon those two factors. In a figure, the authors then relate the tidal range to the parameter of tidal prism over significant wave height squared (P/Hs)2 and identify a protrusion index which is the ratio of ebb tidal delta protrusion to inlet width and determined that delta protrusion is positively related to the ratio of tidal prism and wave action. This analysis includes data from US inlets, Friesian Island Inlets and Inlets of the SW Netherlands.

Buonaiuto, F.S., and Kraus, N.C., 2003. Limiting Slopes and depths at Ebb-tidal Shoals. Coastal Engineering 48(2003) pp. 51-65.

In this paper bathymetry at 13 small to medium US inlets were investigated using LIDAR and NOS bathymetric data to quantify limiting bottom slopes of ebb shoals at entrance channels. Buonaiuto and Kraus found a regression relationship between the maximum slope observed on the ebb shoal and significant wave height at the inlet. No correlation was found with limiting slope in their study for tidal prism, wave steepness and combined tidal prism and wave height.

At all inlet entrances the steepest slopes were found along shorelines, scour holes, around the seaward margin of the ebb shoals and along lateral walls of navigation channels. Channel slopes ranged from 6 to 8 degrees with stabilized inlets having greater slopes than unstabilized inlets. The authors found that the wave dominated environment has steeper slopes than tidally dominated environments. They also investigated the depth over the crest of the ebb shoal and devised the parameter (HsP)^1/4 relating incident wave height and tidal prism which correlated with the limiting depth over the ebb shoal.

Gaudiano, D.J., and Kana, T.W., 2001. Delta Bypassing in South Carolina Tidal Inlets: Geomorphic Variables and Empirical Predictions for Nine Mesotidal Inlets. Journal of Coastal Research, 17(3), pp. 280-291.

Nine South Carolina (mixed energy coast) tidal inlets (2 stabilized and 7 not stabilized) were examined to determine the relationship between the volume of sand in the ebb-delta and the individual bypassing shoals, the time interval between bypassing events and the tidal prism. A conceptual model of shoal bypassing was validated. The paper includes a literature review of ebb breaching. Aerial photographs over a 53-58 year time period were digitized and examined to identify bypassing events. The inlets included in the evaluation were: Midway, Pawleys, North, Pierce, Capers, Dewees, Breach, Stono and Captain Sams Inlets. The shoal volumes were determined from the aerial photographs by measuring the plan area of the shoals and then multiplying by an estimated thickness of three meters. This method assumed vertical sides on the shoal so, a scaling factor was introduced to account for the missing volume. Following this analysis, the average annual contribution from the delta to the adjacent beaches was computed from which the local annual sediment transport was calculated.

Gaudiano and Kana also included the results of field studies conducted to measure inlet throat cross sections and tidal prisms for seven of the nine inlets. A linear relationship between the average shoal bypassing event interval (I) and the tidal prism (Tp) was found of the form I=0.046Tp+4.56. They were able to identify that larger inlets undergo shoal bypassing events less frequently than smaller inlets and that the variable I is related to the longshore sediment transport rate. Gaudiano and Kana developed a relationship of the form S=6.42Tp+113.4 which describes the relationship between the average bypassing shoal volume (S) and the tidal prism (P). Gaudiano and Kana described qualitatively a point in the quantity of sediment supply to the system which will induce bypassing.

Additionally, Gaudiano and Kana plotted the shoal volume/tidal prism data obtained from the seven inlets they examined onto the Walton and Adams (1976) best fit line. Gaudiano and Kana determined that the seven South Carolina Inlets all plotted above the Walton and Adams best-fit line. They postulated that a greater influence of the tides in South Carolina may be the cause of this difference.

Gaudiano and Kana identified that the shoal bypassing mechanisms identified by FitzGerald (1978) were present with the South Carolina inlets. They identified inlet migration and spit breaching, periodic landward migration of swash bars and ebb-tidal delta breaching. The paper describes the breaching process at each of the inlets examined.

Vincent, C.L., and Corson, W.D., 1981. Geometry of Tidal Inlets: Empirical Equations. Journal of Waterway, Port, Coastal and Ocean Division, 107(1), pp. 1-9.

In this paper 67 inlets were studied along the Atlantic, Pacific and Gulf Coasts of the US. The objective of the research was to develop a quantitative database of stability characteristics for the 67 inlets. The authors relied on aerial photographs to measure their parameters. Four stability indices were defined and measured (minimum inlet width, W and channel length, L. Change in the geographical position and orientation of the inlet channel were defined by two indices. The authors determined that stability of an inlet is, to a large degree, determined by inlet size and use. They examined inlet stability utilizing two different method.

The first was definition of six relative stability parameters which were measured at these inlets. The second method was to express inlet change in terms of absolute parameters that measure change in terms of magnitude (not normalized by inlet size). The relative parameters include three hydraulic parameters (width, length and a product of the first two). The other three parameters are geographical parameters measuring potential movement in the channel, changes in orientation and a product of the first two. Combinations of the six parameters were used to display various stability characteristics. The inlets were classified as stable or unstable based upon a limit selected by the authors. The absolute parameters related inlet width and channel length changes and changes in position and orientation.

The authors conclude that there are a range of inlet instabilities. They found a lack of correlation for inlet response in inlets with regionally homogeneous wave climates which suggests that morphology and hydraulics at specific inlets have a large influence on inlet responses.

Vincent, C.L., Corson, W.D., and Gingrich, K.J., 1991. Stability of Selected United States Tidal Inlets. USACE GITI Report 21. Vicksburg, MS. 167p.

The motivation of this study was continuation of the USACE funded initiative of promoting safe navigation through tidal entrances. Vincent, Corson and Gingrich studied 51 US tidal inlets through a series of historical aerial photographs to examine tidal inlet stability. The paper includes a discussion of previous research on this topic. Vincent, Corson and Gingrich identify four types of inlet instability: geographic, rotational, meandering and channel stretching. They introduce hydraulic parameters (width and length) and positional parameters (migration) related to inlet stability. Stability indices are then derived. The paper discusses stability analysis based on a photographic analysis performed by the authors of the minimum channel width, channel traces and the channels seaward end point. The authors review inlet variability over time to determine the variability of the 51 inlets in the channel width, length, channel position and throat. Relationships among time variant characteristics are added in table form for all combinations of channel width, length, channel position and throat in combinations of time variant properties (random variation, cyclic short period variation, cyclic long period variation and trend variation). Vincent, Corson and Gingrich discuss stability of the 51 inlets examined utilizing relative hydraulic and relative geographic stability parameters. Regional patterns and trends identified through examination of the 51 inlets are described. Appendices include aerial photograph dates, a listing of stability indices (position orientation, width and length) throughout time for the inlets studied, and plots of temporal variations in channel position and orientation, channel width and traces for all inlets studied.

Carr, E.E., and Kraus, N.C., 2001. Morphologic Asymmetries at Entrances to Tidal Inlets. Report Number ERDC/CHL CHETN-IV-33, U.S. Army Engineer Research and Development Center, Vicksburg, MS.

This paper discusses characteristics of selected symmetries in morphological forms at tidal entrances and begins with a listing of potential applications for the research. The sediment bypassing processes and associated morphologic features are identified and discussed. The concept of ebb shoal symmetry/asymmetry is introduced as are the three asymmetry indicators that have been measured at the tidal inlets considered in this study. The asymmetry indicator measurements (WA1, WA2, and L) are utilized to describe the degree of asymmetry in the ebb shoal. WA1 is defined as the distance to the updrift point where the ebb shoal complex attaches to the shoreline. WA2 is defined as the distance where the ebb shoal complex attaches to the shoreline. The variable L is defined as the distance of the offshore extent of the ebb shoal. The measurements of the ebb shoal asymmetry indicators were taken from various aerial photographs and NOS nautical charts. Examples of ebb shoal symmetry and asymmetry from specific inlets are included.

Relationships of the form WA1,WA2=aPb, where P is tidal prism, were developed through linear regression analysis. The data was separated by number of jetties at each inlet to determine the coefficients of each case. The seaward extent of the ebb shoal, L, was similarly related to tidal prism, P.

Finally, temporal changes in the asymmetry indicators are discussed using a case study of St. Augustine Inlet, FL based upon changes from the 1950’s to 1999. A brief discussion on asymmetries of inlet channels is also included.

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