Coastline Retreat Research Articles

Un patrimoine paysager à protéger : les dunes littorales de Merlimont et de Berck (Pas-de-Calais)

The coastal dunes of Merlimont and Berck (Pas-de-Calais, France) : an outstanding landscape to protect. The earliest coastal dunes, between the Canche and Authie estuaries, formed probably at the end of the sedimentary development of the «Plaine maritime picarde», around 2300-2100 BP (Subatlantic), after the last marine invasion which took place 2500-2370 years ago. Briquet's researches on historical development of the Merlimont and Berck coastal dunes are recalled. Since the last World War, the western dune system has changed significantly. The height of the coastal foredune has increased from a few meters to more than 15 m. At the same time, the rate of coastline retreat was 1 m per year at least. Both phenomena are related to the regional marine and aeolian dynamics. The foredune evolution with blowouts, gaps and rear sand-sheets (called «pourrières» in Picardy) implies massive sand supply from the beach. On the contrary, «caoudeyres» (deep blowouts) and parabolic dunes which form at the rear of the foredune by deflation scouring and progressive dune translation develop with a very low rate of beach sand supply.

Definition of erosion and inundation hazard zones in Todos Santos Bay, Baja California, Mexico

A prediction of coastline retreat was made based on relative sea level rise, considering three projected scenarios of 0.5, 1.0 and 1.5 meters, obtaining also the local component of sea level rise for Todos Santos Bay, Baja California. The “Brunn Rule” was applied with certain modifications, to calculate the coastline retreat from 1983 to 2100. Taking into account the sea level rise scenarios and the geomorphologic characteristics of the coast, the erosion and inundation hazard zones were defined, pointing out the recommendations for the development planning of the area.

Seed Production and Germination Response of Four Louisiana Populations of Uniola paniculata (Gramineae)

Sea oats, Uniola paniculata, is a characteristic and often dominant perennial dune grass of the southeastern Atlantic and Gulf coasts of the United States. However, U. paniculata loses its dominance and becomes almost nonexistent along a relatively narrow portion of its range, from west of the Mississippi River delta, Louisiana, through northeastern Texas. In Louisiana, U. paniculata is abundant on the Chandeleur Islands east of the delta, but along the barrier island chain west of the delta only three sizable populations have been identified, all on the Caminada-Moreau coast. We measured seed production and germination response to various moisture and temperature combinations in these populations. Seed production was found to range from one to three orders of magnitude less than what has been reported in areas where U. paniculata is dominant. Rates ranged from 0.091 seeds/spikelet on the Chandeleur Islands to only 0.002 seeds/spikelet on the Caminada-Moreau coast; one population failed to produce any seeds at all. Seed germination in an 18.3–35.0 C alternating thermoperiod was high (65–88%) after exposure of the seeds to a variety of pregermination moisture and temperature conditions. Exposure to 4.4 C during imbibition did not increase percentage germination, but did significantly increase the rate of germination over the pregermination treatments that did not include moisture. The very low seed production rates of these populations could explain the limited distribution of this species along the Louisiana coast, where overwash events are frequent, and rates of coastline retreat often exceed the highest measured rates of vegetative lateral spread.

SEED PRODUCTION AND GERMINATION RESPONSE OF FOUR LOUISIANA POPULATIONS OF UNIOLA PANICULATA (GRAMINEAE)

Sea oats, Uniola paniculata, is a characteristic and often dominant perennial dune grass of the southeastern Atlantic and Gulf coasts of the United States. However, U. paniculata loses its dominance and becomes almost nonexistent along a relatively narrow portion of its range, from west of the Mississippi River delta, Louisiana, through northeastern Texas. In Louisiana, U. paniculata is abundant on the Chandeleur Islands east of the delta, but along the barrier island chain west of the delta only three sizable populations have been identified, all on the Caminada‐Moreau coast. We measured seed production and germination response to various moisture and temperature combinations in these populations. Seed production was found to range from one to three orders of magnitude less than what has been reported in areas where U. paniculata is dominant. Rates ranged from 0.091 seeds/spikelet on the Chandeleur Islands to only 0.002 seeds/spikelet on the Caminada‐Moreau coast; one population failed to produce any seeds at all. Seed germination in an 18.3–35.0 C alternating thermoperiod was high (65–88%) after exposure of the seeds to a variety of pregermination moisture and temperature conditions. Exposure to 4.4 C during imbibition did not increase percentage germination, but did significantly increase the rate of germination over the pregermination treatments that did not include moisture. The very low seed production rates of these populations could explain the limited distribution of this species along the Louisiana coast, where overwash events are frequent, and rates of coastline retreat often exceed the highest measured rates of vegetative lateral spread.

Progradation of the late Quaternary Gediz delta, Turkey

Detailed 3.5-kHz seismic-reflection profiling and coring have shown that the continental shelf break and slope off Izmir Bay, Turkey, are formed by prograding deltaic silty mud sequences. The muds contain shallow brackish-water benthic and cold-water planktonic foraminifera. They were deposited when sea level was about 110 m below its present position, during the last Pleistocene glaciation. Slumping took place on the prodelta slope, leaving rotational slump scars and imbricate slump blocks downslope. Delta-top truncation took place in shallow water by erosive coastline retreat after distributary abandonment. There has been little or no sedimentation since that time: outer Izmir Bay is thus floored by relict sands. Following rapid post-glacial transgression, the Gediz delta was reestablished in Izmir Bay. Archaeological evidence shows it has prograded during the last 3000 yrs. At least six shifts in the position of the Gediz mouth are distinguished during this time, and abandoned delta-top channels can be correlated with submarine delta-lobe sequences.

Holocene Sedimentary Environment of the Atlantic Inner Shelf off Delaware

High-resolution subbottom profiles have been used to identify and map the pre-Holocene erosional surface in Delaware Bay and in the Atlantic Ocean off the Delaware coast. Vibracoring has revealed the nature and age of the various seismic layers. Age identifications based on radiocarbon dating, on oxidation zones, and on lithologic characteristics confirm the partial retention of Holocene coastal environments under the inner shelf. The Holocene transgression across the ancient Rehoboth and Indian River lagoons has involved erosion through the Holocene lagoonal sediments in some areas, leaving pre-Holocene ridges exposed on the inner-shelf sea floor where once there may have been headlands. Where the ancient lagoonal deposits are thickest over depressions in the pre-Holocene surface, Holocene coastal sediments were retained. The presence of marsh peat, dated as ∼7,500 yr B.P., and overlying very fine lagoonal mud proves that lagoonal conditions existed east of Delaware even then. The position of the barrier complex related to these earlier Holocene lagoons is projected on a paleographic reconstruction to be at least 12 km (7 n mi) east of the present coast. This yields a minimum average coastline retreat rate of 1.6 horizontal m per yr. (6 ft per yr). This study of the shallow subsurface geology also revealed that the bottom morphological features of the inner shelf off Delaware are related to dynamic molding of hydraulic bedforms in equilibrium with the present marine environment. Although one ridge form was found to be a subcrop of Pleistocene sand and gravel, most of the ridge and channel topography was found to be formed within the upper Holocene sediments. This is especially true of the shore-face-connected ridges off Rehoboth Bay and Bethany Beach, the inlet-associated shoals near the mouth of Delaware Bay, and the Delaware shelf-valley flood channel.