Barrier island erosion and overwash study -- effect of seawalls. Volume 2

This is the second of a pair of reports documenting the effects of storms on beach systems including the presence of seawalls. With the aim of simulating the effects of overwash on barrier islands with seawalls and characterizing their response, a series of eight experiments was conducted at the Coastal Engineering Laboratory of the University of Florida. The barrier island was simulated by a 400 feet wide horizontal crest and an initially uniform mildly-sloped (1:19) beach. The effects of positioning the seawall at two different locations as well as the effects of various storm surge levels and accompanying overtopping were investigated. Experiments were conducted with both regular and irregular storm waves. With the seawall located at the slope break between the crest and the sloping beach of the barrier island, and the crest of the seawall just submerged in sand, the effects on the sediment transport process were found to be minimal. For the same position of the seawall but with the crest of the seawall raised above the surrounding ground level, overtopping caused washover of sand indicating substantial transport in suspension. Increased levels of overtopping tended to accentuate bed profile changes but supress bar formation (as did irregular waves). Positioning the seawall at the Mean Sea Level shoreline caused significant scour both immediately landward as well as immediately seaward of the seawall. A prominent scour trough developed further seaward. The longshore bar was highly three-dimensional. It appears that seawalls need to be located adequately landward of the shoreline to discharge their function effectively without adverse effect to the beach. In addition, concerns for safety warrant the presence of an adequate buffer-zone between the seawall and the upland property. (61 pp.

Barrier island erosion and overwash study - volume 1

This is the first of a pair of reports documenting the effects of storms on barrier island systems. The present report (Volume 1) investigates storm effects on natural island conditions whereas Volume 2 addresses the effects of seawalls. With the aim of simulating the effects of overwash on barrier islands and characterizing their response, a series of nine experiments was conducted at the Coastal Engineering Laboratory of the University of Florida. The barrier island was simulated by a 400 feet wide (prototype units) horizontal crest and an initially planar (1:19) beach. The effects of various storm surge levels and accompanying overtopping were investigated. Experiments were conducted with both regular and irregular storm waves. Regular waves without overtopping caused the formation of a substantial berm in the swash zone and a prominent longshore bar offshore. Increasing degrees of overtopping resulted in substantial loss of sand from the barrier island system. The longshore bar was considerably more subtle for the highest water level tested (11.5 ft. above mean sea level). Simulation of a storm-surge hydrograph with rising and falling water levels indicated that the presence of the bar tends to occur only during a relatively steady or slowly changing water level. The experiments with irregular waves were conducted with reasonably similar wave heights and carrier periods as those with regular waves. The major difference was in the characteristics of the longshore bar response. In comparison with cases with regular waves, the bar was less distinct without overtopping, subtle with minimal overtopping and absent in cases with substantial overtopping. These experiments seem to indicate that offshore bars are simply break-point bars which require a fairly steady break-point and undertow (return of mass transport) for optimal formation. (Document has 84 pages.

Functional Analysis of ESCRT-Positive Extracellular Vesicles in the Drosophila Wing Imaginal Disc

International audienceA large number of studies have shown that proteins of the Endosomal Sorting Complex Required for Transport (ESCRT) can trigger the biogenesis of different types of Extracellular Vesicles (EV). The functions that these vesicular carriers exert in vivo remain, however, poorly understood. In this chapter, we describe a series of experimental approaches that we established in the Drosophila wing imaginal disc to study the importance of ESCRT-positive EVs for the extracellular transport of signaling molecules, as exemplified by a functional analysis of the mechanism of secretion and propagation of the major developmental morphogen Hedgehog (Hh).Through the combined use of genetic, cell biological, and imaging approaches, we investigate four important aspects of exovesicle biology: (1) The genetic identification of ESCRT proteins that are specifically required for Hh secretion. (2) The imaging of ESCRT and Hh-positive EVs in the lumenal space of both living and fixed wing imaginal discs. (3) The receptor-mediated capture of Hh-containing EVs on the surface of Hh-receiving cells. (4) The effect of manipulations of ESCRT function on the extracellular pool of Hh ligands