Jens Figlus

Wave Overtopping and Overwash of Dunes

Wave-induced overwash of sand dunes may cause rapid profile changes and possible dune destruction, thus increasing the flood risk landward of dunes. Accurate modeling of the wave overwash processes is therefore essential in predicting dune profile evolution during overwash events. However, available field and laboratory data are very limited. We measured dune profile evolution and overwash transport rates for three tests with different initial dune geometries in front of a low-crested vertical wall exposed to the same wave conditions in a wave flume. In all three tests, the transition from minor to major overwash occurred rapidly but the resilience of the dune against destruction depended on its initial geometry. During minor overwash, offshore sediment transport caused most of the dune crest lowering. These tests are used to assess a numerical model for wave overtopping and overwash of a dune. The numerical model is shown to be in agreement with the measurements of the free surface elevations, fluid velocities, and dune profiles. However, beach erosion in front of the exposed wall is underpredicted.

Going with the flow or against the grain? The promise of vegetation for protecting beaches, dunes, and barrier islands from erosion

Coastlines have traditionally been engineered to maintain structural stability and to protect property from storm-related damage, but their ability to endure will be challenged over the next century. The use of vegetation to reduce erosion on ocean-facing mainland and barrier island shorelines – including the sand dunes and beaches on these islands – could be part of a more flexible strategy. Although there is growing enthusiasm for using vegetation for this purpose, empirical data supporting this approach are lacking. Here, we identify the potential roles of vegetation in coastal protection, including the capture of sediment, ecological succession, and the building of islands, dunes, and beaches; the development of wave-resistant soils by increasing effective grain size and sedimentary cohesion; the ability of aboveground architecture to attenuate waves and impede through-flow; the capability of roots to bind sediments subjected to wave action; and the alteration of coastline resiliency by plant structur...

Onshore Migration of Emerged Ridge and Ponded Runnel

AbstractRidge-runnel features can comprise large volumes of sand, and their migration can have a significant influence on the coastal sediment budget and beach recovery after a storm. Numerical modeling of ridge-runnel migration is challenging partly because of the strong interactions between the hydrodynamics and morphology and partly because of limited available field and laboratory measurements. This study investigated the effect of water ponding and runnel drainage on onshore ridge migration in an experiment in a sand flume where detailed free‐surface and velocity measurements were taken in the ponded water zone of the runnel and in the intermittently wet and dry zone on the ridge crest. The test scenario with a drained runnel showed a ridge migration speed five times larger than the scenario in which water and sediment could only exit the runnel as offshore return flow over the ridge. The time-averaged numerical model CSHORE was modified to include the ponded water effect in the sediment transport fo...

Evolution of Gravel Beach Profiles

An experiment was conducted in a wave flume to examine the processes of gravel beach profile evolution under irregular waves. Two erosion tests were performed on a steep slope of 1/2 with two different significant wave heights. An accretion test was conducted on a mild slope of 1/5 until its profile became quasi-equilibrium. Another test was initiated with a gravel bar constructed at the toe of the equilibrium profile. The bar migrated onshore and resulted in the seaward shift of the equilibrium profile. Quasi-equilibrium profiles observed after 18 or 36 bursts of 400-s wave action were similar but affected by the differences in the wave height and initial profile. A numerical model developed for damage progression of stone armor layers is shown to predict the profile changes of the two erosion tests. The bed load formula used in the model is adjusted to better predict the onshore bar migration and the accretional change on the mild slope. More extensive comparisons of the numerical model with data will b...

The Effects of Coastal Dune Volume and Vegetation on Storm-Induced Property Damage: Analysis from Hurricane Ike

ABSTRACT Sigren, J.M.; Figlus, J.; Highfield, W.; Feagin, R.A., and Armitage, A.R., 2018. The effects of coastal dune volume and vegetation on storm-induced property damage: Analysis from Hurricane Ike. In response to numerous recent high-profile cases of tropical storm and hurricane damage to coastal communities, there has been increasing attention on the storm protection services provided by coastal ecosystems. However, substantial knowledge gaps exist regarding the quantitative economic benefits of such services, particularly for coastal vegetated dune ecosystems. A novel geographic information system (GIS)-based technique for delineating, quantifying, and relating coastal dune volume, vegetation area, and geographic and built-environment covariates to sustained property damage was used for the upper Texas coast following Hurricane Ike in 2008. The multivariate regression analysis contained more than 1000 homes spanning both sides of the storms path. Dune volume and vegetation were both significantly related to reduced sustained property damage for the west side of the storm. For this area, model results showed that dune sediment was worth roughly

Estimating tsunami inundation from hurricane storm surge predictions along the U.S. gulf coast

50 per cubic meter and dune vegetation was worth roughly

MAINTENANCE OF BEACH AND DUNE FOR COASTAL FLOODING REDUCTION

140 per square meter. However, because these variables were collinear and modeled separately, these amounts should not be viewed additively. The total property damage offset value of dunes across the study area was estimated to be more than

Numerical study of turbulence and wave damping induced by vegetation canopies

8 million, or approximately

Coastal sand dunes and dune vegetation: Restoration, erosion, and storm protection

8200 per homeowner. Based on the frequency of storms for this area over the last 115 years, coastal vegetated dunes were valued at roughly

Numerical modeling of the morphodynamic response of a low-lying barrier island beach and foredune system inundated during Hurricane Ike using XBeach and CSHORE

86,000 per hectare per year. The results indicate that dunes could play an integral role in coastal hazard mitigation strategies and offer a unique opportunity where bioengineered, green infrastructure can be used as an alternative to hard coastal structures.