Longshore variation in coastal foredune growth on a megatidal beach from UAV measurements

<p>Coastal dunes are both a vital natural coastal defence and a key ecological habitat; therefore, understanding their evolution is important to inform coastal management. Megatidal environments are the world largest tidal ranges and hence provide a unique endmember of the tidal range continuum. A study site at Crymlyn Burrows, Swansea Bay, UK is monitored here; the area was originally of applied interest due to its identification as a key receptor of the Swansea Bay Tidal Lagoon project. The study site comprises of 2km of dune frontage bounded to the west by hard sea defences and to the east by the River Neath estuary. The intertidal is characterized by a shallow slope and crescentic intertidal bars. Mean spring tidal range at the nearby Mumbles tide gauge is 8.46m; mean wave heights at a wave buoy offshore of the site (depth 9m LAT) are 0.66m and storm wave heights exceed 3m; predominant wind direction is in an alongshore – onshore direction.</p><p>A Sensefly Ebee-RTK drone with a Sony RGB camera has been used to map the dune system and the mid to upper intertidal beach on a monthly – bimonthly frequency since October 2018. Initial post-processing was conducted in the Sensefly Emotion3 software; Pix4D was then used to generate a point cloud from the georeferenced images. RTK-GPS surveyed ground control points distributed over the study area were used to improve the accuracy of the solution. Point clouds were cleaned to remove noise using Cloud Compare, an open source point cloud editor, before being interpolated onto a gridded surface. Comparison of the gridded surface against RTK-GPS surveyed points gave a vertical mean absolute error (MAE) of 0.05m over the beach area. Comparison in the dune area is more complex since the raw point cloud includes the vegetation and hence over-estimates height compared to the bare earth. Based on the raw point cloud, MAE over the dune area was 0.22m; however, when vegetation points were removed using artificial neural network based colour discrimination, the MAE was 0.05m.</p><p>Longshore variation in dune evolution is clearly evident. At the eastern and western ends of the dune system, dune progradation can be observed whereas in the central portion the frontal dune is cliffed and the dune foot position is static or eroding landward. Pressure transducers have been deployed in a longshore array at the neap high tide level to assess variation in wave energy reaching the upper intertidal over the study area.</p><p>This presentation will explore whether this variation in behavior is due to longshore variation in wave energy (erosion potential), variation in sediment availability (accretion potential) or the persistence of antecedent morphology.</p>

Verpachting van duingronden op Texel van 1855 tot 1885

Lease of the coastal dunes of the island of Texel from 1855 to 1885 In 1855, the province of North Holland started exploiting the coastal dunes of the island of Texel. The dunes were divided into 19 large plots, each of which was leased for several years. This map from around 1840 served as an official document till 1886 and was regularly updated. It shows the plots and lists of tenants and rents for each lease period. Also interventions such as the construction of ditches and dikes were drawn. The map uniquely shows the Mient (‘commons’), a low and moist dune landscape which was botanically very rich, but which was almost completely drained and forested around 1900. The present dune area of Texel still bears the traces of the lease and the interventions from the 19th century.

Modeling the Evolution of a Freshwater Lens under Highly Dynamic Conditions on a Currently Developing Barrier Island

The drinking water supply on barrier islands largely depends on freshwater lenses, which are also highly relevant for island ecosystems. The freshwater lens presented in this study is currently developing (since the 1970s) below the very young eastern part of the North Sea barrier island Spiekeroog, the so-called “Ostplate.” Due to the absence of coastal protection measures, formation, shape, and extent of the freshwater lens below the Ostplate are unaffected by human activities but exposed to dynamic changes, e.g., geomorphological variations and storm tides. The main aim of this paper was to reconstruct the evolution of the freshwater lens over several decades in order to explain the present-day groundwater salinity distribution. In addition, the study assessed the impact of geomorphological variations and storm tides on the freshwater lens formation. Detailed field observations were combined with a transient 2-D density-dependent modeling approach. Both field observations and simulations show an asymmetric freshwater lens after ~42 years of formation, whereby the horizontal extent is limited by the elevated dune area. The simulations indicate that the young freshwater lens has nearly reached quasi-steady-state conditions mainly due to the continuous mixing with seawater infiltrating during storm tides, which inhibits further growth of the freshwater lens on the narrow island. The findings further show that (i) a neglection of storm tides results in a significant overestimation of the freshwater lens extent, and (ii) the modeled present groundwater salinity distribution and shape of the freshwater lens are predominantly determined by the position and extent of the elevated dune area at the past ~20 years. Hence, annual storm tides have to be directly implemented into numerical models to explain the groundwater salinity distribution and the extent of young freshwater lenses located in highly dynamic tidal environments.

Sand transport characterization on the foredune area of Parangtritis, Indonesia

The aim of the research are to determine the characteristics of sand deflation on Parangtritis foredune area. The development of tourism activity on surrounding area could be has a big impact to the sand transport process. Data required in this research are wind direction and its speed, the sand mass collected from sand sampler, sand grain size, roundness and sphericity, and interview from tourists. Sand that transported by wind collected by sand sampler with dimension of 0.76 cm height and 1 cm width. Sand transport rate or deflation calculated by Bagnold’s formula. The results showed that the deflation process is bigger at daytime observation that at night, it is average 2.42 g.m-1s-1during day and 0.03 g.m-1s-1during night. Each samples location have different deflation characteristics of material that transported. Grain diameters ranging from 0.318 mm to 0.395 mm with dominance texture is medium sand. Sphericity and roundness of sediment material was on a scale of 0.5 and 0.7. This natural process that occurred on the research area didn’t knowing well either by local communities or tourists. Therefore need some proper management for support the continuity of deflation process for supplying material to the main sand dune area of Parangtritis.

MEGA-NOURISHMENTS AND AEOLIAN DEVELOPMENTS: LESSONS LEARNED SIX YEARS INTO THE SANDMOTOR PILOT PROJECT

In 2011 a multifunctional peninsula-shaped nourishment project (the Sandmotor) was implemented on the West coast of the Netherlands. Its objectives included an increase in sediment supply towards the dunes to maintain their function as a flood defense on the longterm as well as the development of (temporary) new dune area for nature and recreational purposes. In this contribution we will present an overview of the observed developments related to aeolian processes at the Sandmotor in the first six years after implementation of the nourishment, as well as discuss the relation of these developments to specific characteristics of the design and management of the Sandmotor.

Nước dưới đất trong cồn cát ven biển phía nam Quảng Bình và định hướng khai thác sử dụng

Groundwater in coastal sand dune area in the south of Quang Binh province and posibility for exploitation

Mô hình thử nghiệm quản lý tầng chứa nước bổ sung tại Bắc Bình, Bình Thuận

The Model for Management of Aquifer Recharge in sand dune area of Bac Binh, Binh Thuan