Inlet Geomorph Bibliography-Structural Responses

Tomlinson, R.B. 1991. Processes of Sediment Transport and Ebb Tidal Delta Development at a Jettied Inlet. Proceedings of Coastal Sediments ‘91, pp. 1404-1146.

The paper begins with a short discussion of sediment transport processes due to anthropogenic modifications to inlets. The paper focuses on the development of the ebb tidal delta following the extension of jetties at the Tweed River entrance in northern New South Wales, Australia. A database of coastal processes of this area (Tomlinson and Foster, 1986) formed the basis of this study. The paper provides background information on the study area including history of the structuring of the inlet and river. A model of the ebb delta morphology was developed for the time period beginning in 1873 prior to the 1902 jetty construction and prior to the 1962 extensions.

The impact on the coastal processes and ebb delta development due to the extension of the jetties is discussed. Introduction of the jetties caused the shoal to be established further offshore than previously and with a more symmetrical shape.

The authors were able to determine the temporal delta volume beginning in 1978 from bathymetric surveys. Discussion of the changes in sediment deposition and a prediction of the ultimate size of the ebb delta (using Walton and Adams, 1976) is included. The paper concludes with the evaluation that the delta development transitioned from deposition dominated by tidal flow to a state of dynamic equilibrium between the tidal flow and the wave-induced transport across the delta.

Hansen, M. and Knowles, S., Ebb-Tidal Delta Response to Jetty Construction at Three South Carolina Inlets, Lecture Notes on Coastal and Estuarine Studies, Vol. 29. D.G. Aubrey, L. Weishar (Eds.), Hydrodynamics and Sediment Dynamics of Tidal Inlets, Springer-Verlag, New York, Inc. 1988.

Hansen and Knowles examine three inlets; Charleston Harbor, Murrells Inlet and Little River Inlet in South Carolina. Tidal inlets along South Carolina are considered transitional between wave dominated inlets of the Outer Banks of North Carolina and the tide dominated inlets of southern South Carolina and Georgia (Hubbard, et al., 1977). These South Carolina inlets are within the transitional zone, between wave and tide dominated. These inlets have a semidiurnal tidal range of 1.5 meters, which identifies them as microtidal based on Davies (1964) classification system. All three inlets have rubblemound jetties with parallel ends and weir structures included in their design. The following identifying information was provided about the jetty dimensions.

Name	NE Jetty Extent (m)	SE Jetty Extent (m)	Jetty Tips (m)
Charleston Harbor	4,700	5,800	884
Murrells Inlet	1,053	1,011	198
Little River Inlet	1,001	1,167	305

The paper discusses the way in which construction of the jetties impacted each of the inlets. At Charleston Harbor Entrance the jetties dissected the ebb tidal shoal and diverted the main ebb flow seaward. Geomorphology remained essentially the same as prior to construction. The swash platform migrated seaward. At Murrells Inlet implementation of the jetties created a landward migration of the swash bars. Bar migration and welding of the shoal south of the jetties occurred within 4 years. A small lagoon was formed downdrift of the south jetty and a new ebb delta began forming seaward of the constructed jetties. Less than 5 years of data was available for Little River Inlet but the data indicated swash bar migration with lagoon formation, similar to the changes seen at Murrells Inlet.

The paper indicates that jetty construction at Murrells Inlet and Little River Inlet showed a rapid response, in comparison to Charleston Harbor. The response at the smaller inlets was similar to the response seen in the situation of ebb delta breaching. Confinement of the channel by the jetties created an effect of wave dominance of the ebb deltas in all three cases. Hansen and Knowles identify that at the smaller inlets the channel confinement and shoal migration has, in the time period analyzed, eliminated the typical morphological expressions of ebb deltas.

Pope, J. 1991. Ebb Delta and Shoreline Response to Inlet Stabilization, Examples from the Southeast Atlantic Coast. Proceedings, 1991 Coastal Zone, National Oceanic and Atmospheric Administration, pp. 643-654.

This paper studies four stabilized natural inlets along an ebb-tide dominated barrier island and the coastal and offshore response to jetty construction. Pope reviewed a combination of historic bathymetric change information, shoreline movement data, geomorphic assessments, wave refraction studies and sediment budgets in order to evaluate the impacts of entrance channel jetties on sediment supply, ebb delta modification and inshore erosion rates. The inlets examined are located on beach ridge barrier islands in an area with high tide ranges and low wave energies where, generally, inlets are formed and maintained by tidal currents and not closed by wave-induced longshore sediment transport.

The four inlets examined were: Little River Inlet (NC/SC), Charleston Harbor Entrance (SC), Murrells Inlet (SC), and St. Mary’s Entrance (GA/FL). Murrells Inlet and Little River Inlet have been monitored since construction and have one kilometer long jetties. In comparison the inlets of St. Mary’s and Charleston Harbor are larger with jetties 5 kilometers and 6 kilometers long, respectively. The paper provides details about each inlet and system including histories and details of the studies performed. Based on these observations, Pope developed a conceptual model of inlet evolution in response to stabilization. She concludes that, at these inlets, there is initial thalweg channelization and fillet trapping followed by a fairly rapid collapse of the natural ebb-delta lobe and a steepening of the ebb delta platform. Included in this paper are figures of long term and short term response to jetty construction. It is noted that there appears to be a direct correlation between inlet size and response time of inlet morphology changes.

Galvin, C. 1982. Shoaling with Bypassing for Channels at Tidal Inlets. Proceedings of the Eighteenth Coastal Engineering Conference, ASCE, New York, NY., Vol. II, pp. 1496-1513.

An initial description of sand bypassing, basic tidal inlet function and cross-section is presented. Focus of the paper is on the rate of shoaling and a technique to estimate duration of project depth (tp) (the minimum depth for practical navigation by the design vessel) at the controlling section in the dredged channel. An illustrative graph is presented of the effect of bypassing on channel shoaling for three dredged channels. Bypassing mechanisms are also described. Examples of practical scenarios (bypassing and shoaling) are presented along with a table of duration of project depth. The example for shoaling presents a permanent shallow draft tidal inlet in a relatively sheltered site on a large bay. In this example case, there are desired improvements (dredging) a local company wishes to make and the question is the shipper only wants to dredge once a year, at the end of the monsoon season, how deep must the channel be dredged given the parameters required. In this case, the equation for the duration of project depth (tp) is used to find the solution. A second example of bypassing is presented in the paper utilizing the same information from the shoaling example the question is asked to determine the maximum reduction in bypassing rate due to the trapping of sand in the dredged channel. The maximum trapping rate right after dredging is calculated to find the solution.

Bruun, P., 1995. The Development of Downdrift Erosion. Journal of Coastal Research 11(4), pp. 1242-1257

Bruun addresses the question: How is erosion, due to loss of sand, distributed downdrift as a function of time? He identifies the length of the downdrift shoreline, the cross-sectional retreat of the erosion cut and the rate of expansion of erosion and its distribution downdrift as functions of time. Previous research related to these areas is included in Bruuns discussion. Bruun defines short term and long term erosion effects where the short term effect is a coastal geomorphological feature and the long distance erosion is a materials deficit feature. Bruun presents examples of downdrift shoreline developments at various global locations with a variety of histories and anthropogenic and non-anthropogenic influences these locations are:

• Port Canaveral, FL
• Port St. Lucie, FL
• Lagos Nigeria
• Hirtshals, Denmark
• Indian River, Delaware
• The southwest coast of France
• Nile Delta
• Skasen Denmark
• Rollover Pass, TX
• Cape May Inlet to Cape May Point, NJ
• Sebastian Inlet, FL
• Ft. Pierce Inlet, FL
• South Lake Worth Inlet, FL
• Iioka Port and Beach, Japan
• Oarai Port and Beach, Japan
• Ocean City Inlet, MD
• Charleston Harbor, SC

The short and long term disturbance effects of the erosion is quantified at these inlets and the connection between the short and long term distance development of downdrift erosion is discussed and quantified through example and explanation of models developed by Perlin and Dean (1978). Also discussed is a zero or slowdown area which is an area of near zero erosion which occasionally exists between the areas of short and long distance development.

Inman_Dolan. 1989. The Outer Banks of North Carolina- Budget of Sediment and Inlet Dynamics Along a Migrating Barrier System. Journal of Coastal Research 5(2), pp. 193-237.

Inman and Dolan discuss the inlets along the Outer Banks of North Carolina and include a focus on Oregon Inlet. The paper discusses the coastal processes along the Hatteras littoral cell and the dynamics of Oregon Inlet and the nearshore sedimentary processes of the outer banks including multiple references in their discussion. They also discuss sea level rise and barrier transgression, sediment transport, and seasonal and long term changes of the barrier islands in the study area.

The paper focuses on Oregon inlet, history, inlet dynamics, a discussion of channel cross-sectional area and tidal prism, wind and waves, pathways of sediment transport and sediment volume. Inman and Dolan discuss longshore transport relations and include transport rates along the Hatteras littoral cell in table form. They discuss a sediment budget and its application for the area and develop a continuity model for shoreline change to investigate sediment processes and associated volume fluxes of sand.

Dabees, M.A., and Kraus, N.C., 2008. Cumulative Effects of Channel and Ebb Shoal Dredging on Inlet Evolution in Southwest Florida. In: Proceedings of the 31st International Conference on coastal Engineering, 2008, W.S., 2303-2315.

Dabees and Kraus utilize a case study for Longboat Pass in southwest Florida to examine natural inlet evolution and changes in the inlet and ebb shoal following inlet navigation improvements. This paper provided a detailed history of the inlet and its processes. The authors relied upon regional modeling of previous authors which extend 100 km along shore along the Gulf of Mexico coastline which included 10 inlets connecting the bays to the Gulf. Modeling consisted of regional hydrodynamics, detailed or local-process of waves, flow, and sediment transport, and long-term morphology change. The authors applied the Inlet reservoir Model (IRM), which calculates sediment transport rates and volume change of identified morphologic features and bypassing rates for an inlet, to Longboat Pass.

The IRM assumes that each feature has a maximum (equilibrium) sand-retention capacity that cannot be exceeded. Once the feature has reached its capacity, all additional sediment transport arriving to this feature will bypass to the next feature and so forth until the sediment is bypasses past the inlet. Using the IRM the authors predicted the transport rates of Longboat Pass and calculated ebb shoal volumes and volumes adjacent to the inlet on the upland beaches of Anna Maria Island and Longboat Key. The authors utilized actual measured volume calculations to verify the results. Their intention is to utilize the IRM as an inlet management tool with a general methodology for simulating the evolution of different features and assessing consequences of interruption in sediment transport across inlets.

Stauble, D. K., and Morang, A., 1992. Using Morphology to Determine Net Littoral Drift Directions in Complex Coastal Systems. Coastal Engineering Technical Note, US Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, Vicksburg, MS. 8p.

The authors provide guidance in the use of morphologic indicators to determine the net littoral drift direction along coastal areas. They caution making assumptions based on large regional scale indicators for a number of reasons including that transport may be affected by temporal variations.

They recommend a methodology for determining a net drift direction at a project site that includes:

1. Office examination of data

2. Field visit with aerial over flight

3. Discussions with specialists

4. Review of wave records

5. Collection of supplemental field data.

They discuss longshore drift and provide nine examples of morphologic indicators including diagrams to increase clarity. The nine indicators are:

1. Headland

2. Tidal Inlet or Stream

3. Spit

4. Beach Ridge Headlands

5. Groins

6. Jetties

7. Seawall

8. Shore connected breakwater and

9. Detached breakwater

They also discuss natural and/or man-made influences on drift indicators and provide two case studies (Bethune Beach, FL and East Pass, FL).

Dombrowski, M.R., and Mehta, A.J., 1996. Ebb Tidal Delta Evolution of Coastal Inlets. In: Coastal Engineering, pp. 3270-3283.

Dombrowski and Mehta examined the influence of effects of currents and waves on ebb delta growth rates and developed diagnostic approach. Their initial condition was a new inlet with no delta present. The model calculated combined shear stress (τb) from tidal currents and superimposed waves to evaluate delta accumulation height. The model determined the delta volume when the seafloor reaches an equilibrium elevation due to a balance in shear stresses and the estimate of the time for equilibrium to occur.

When the combined shear stress (τb) is smaller than the critical shear stress (τcr) deposition will occur until the shear stresses are balanced τb=τcr , when equilibrium is reached. Dombrowski and Mehta determined a governing equation for ebb delta height variation with time. With model parameters of ebb delta area (AD), suspended sediment concentration (Cs), sediment grain size (D50), deep water wave height and period (H), friction factors fw (due to waves), and fc (due to current), tidal prism and spring tidal range.

Illustrations of influence of suspended sediment concentrations, sediment grain size diameters and deep water waves on calculated delta growth rate are presented. The authors discuss the time-evolution of sand volumes of five selected Florida east coast deltas (Jupiter Inlet, S. Lake Worth Inlet, Boca Raton Inlet, Bakers Haulover Inlet, and Sebastian Inlet). They utilized the wave energy to tidal energy ratio, α, and plotted the influence of α on delta growth. They found that, as α increases, ebb delta volume has a tendency to decrease and vice versa. Finally, they evaluated delta volume vs. maximum wave height for Sebastian inlet and found that the delta volume is in a quazi-equilibrium condition due to variations in sea conditions and the sink being not available to accumulate more sand.

They found that an increase in the suspended sediment concentration increases the rate of approach to equilibrium, but does not result in a change in the equilibrium volume. On the other hand, a change in sediment size and the deep water wave height affect both the rate of growth and the equilibrium volume. Thus, an increase in the sediment diameter increases the rate of growth due to the dependence of the particle fall velocity on sediment size, and increases the critical shear stress resulting in an increase in the equilibrium volume. An increase in the deep water wave height increases the near-bed orbital velocity at the site of the delta, hence decreases the rate of growth. The equilibrium delta volume likewise decreases.

It was also shown that through application of the model to five Florida inlets, there is a dependence between the ebb delta volume and the wave to tidal energy ratio, α. The growth of the delta is determined by the rate at which the sand, supplied by the littoral system, is deposited by the ebb tidal flow. As wave action increases, thus increasing α value, the delta growth rate decreases as wave and current induced bottom shear stress scours sand deposited on the delta.

Byrnes, M. R. and Li, F., 1998. Regional Analysis of Sediment Transport and Dredged Material Dispersal Patterns, Columbia River Mouth, Washington/Oregon, and Adjacent Shores. Applied Coastal Research and Engineering. Mashpee, MA, pp46.

Byrnes and Li conducted a regional analysis of shoreline and bathymetry change between 1868 and 1994 at the Columbia River entrance to evaluate sediment transport dynamics associated with natural processes and engineering activities. They found that shoreline change data for the periods 1868/74 to 1926 and 1926 to 1950/57 illustrate net shoreline advance throughout the study area. However, significant shoreline retreat zones were found to be present along the northern 5 km of Clatsop Spit (5.6 m/yr) and the northern 17 km of Long Beach Peninsula (3.6 m/yr; 1926 to 1950/57). From 1868/74 to 1950/57, average shoreline change north of the Columbia River entrance was found to be 2.2 m/yr. South of the entrance jetty, and net shoreline advance was documented at 5.5 m/yr.

The authors compiled three bathymetry surfaces in order to quantify geomorphic change. The authors were able to identify four distinct depositional trends for the area.

1) The modern ebb-tidal delta developed as a result of jetty construction

2) The center of deposition for sedimentation on the ebb shoal is to the north of center, and it migrates to the north with time

3) Northward-directed sediment transport from the entrance has resulted in net accretion along the shoreline and on the continental shelf seaward of Long Beach Peninsula; and

4) Erosion south of the south jetty is the result of sediment blocking by the jetty and subsequent transport towards the ebb shoal and onto the continental shelf.

The authors utilized the information they obtained in their study to recommend areas for future sediment deposition.

______________________________________________________________

Back to Inlet Geomorphic Annotated Bibliography