The development of blowouts in ‘de blink’, a coastal dune area near Noordwijkerhout, The Netherlands

Abstract

Surface changes in six blowouts in the coastal dunes near Noordwijkerhout between 's-Gravenhage and Zandvoort were measured weekly over a period of two years at 80 erosion pin sites. Readings were correlated with wind variables derived from nearby Valkenburg airbase for the same weekly periods. The values of the wind variables is determined by the number of hours that specific average wind speeds and directions were recorded.The first part of this paper deals with the process of wind erosion. Special attention is given to the relationship between surface changes and wind speed, wind direction, season and rain. Surface changes are associated with wind speeds as low as 1.25 m/s, but net lowering, i.e. erosion, is best correlated with wind speeds between 8.75 and 10 m/s. At higher wind speed there is a tendency for the blowouts to be filled in. Winds from an easterly direction generally correlate with accumulation, whereas winds from the west correspond with accumulation at low speeds and with erosion at high speeds. Springtime and autumn are the most important seasons for blowout development. The effect of rain seems to be limited: the correlations are not improved by excluding rainy days, perhaps because wet sand will be dried rapidly by strong winds.In the next part of the paper, the response of blowouts to the erosion process is discussed. Wind erosion is dominant at the windward side because contrarily to what is often assumed the erosivity decreases as soon as the air is loaded with sand. As a result, blowouts grow southwestwards against the prevailing wind. Nevertheless, much sand is also shifted by winds from other directions. The forms of the blowouts determine in their turn the efficacy of the wind. The errosivity of the wind is most pronounced in circular blowouts, it decreases as the blowout grows in length.Finally, a model of blowout development is proposed which is controlled by width, depth and length ratios.

Crinalium epipsammum sp. nov.: a filamentous cyanobacterium with trichomes composed of elliptical cells and containing poly- -(1,4) glucar (cellulose)

“…Crinalium epipsammum was isolated from microbial crusts, collected from so-called 'blow outs' (aeolian erosional depressions) on southexposed slopes of sand dunes (Jungerius et al, 1981) in a coastal dune area on the Dutch North Sea coast, which were especially enriched at the edges and centre with this organism. Crust material was suspended in medium BG-11 and incubated at 20 "C under continuous illumination with a photon flux density (PFD) of 40 pmol m-* s-l. after 5 d the enrichment cultures were plated on BG-11 medium solidified with I % (w/v) agar (Difco Bacto).…”

Airflow and sediment movement within an inland blowout in Hulun Buir sandy grassland, Inner Mongolia, China

“…Spatial differences in sand transport influence the patterns of erosion and deposition within blowouts and play an important role in their morphological development. Sediment transport within blowouts has been measured using erosion pins (Jungerius et al, 1981;Jungerius and Meulen, 1989;Jungerius et al, 1991;Pluis, 1992;Byrne, 1997;Hugenholtz and Wolfe, 2009), sand traps (Gares, 1992;Byrne, 1997) and topographic surveys (Gares and Nordstrom, 1988;Käyhkö, 2007). However, only Smyth et al (2014) have measured sediment transport in relation to near surface wind speed within a coastal trough blowout; they found that where airflow was steadiest, sediment transport rate was greatest.…”

The Netherlands

“…Wind erosion along the Dutch North Sea coast has been studied fairly extensively over the past 20 years, with a view to arriving at sound management practices of the coastal zone (Van Bohemen, 1990). Examples of subjects of study in the coastal zone are the development of blowouts in the coastal dunes (Jungerius et al, 1981;Jungerius and Van der Meulen, 1989; Van den Ancker et al, 1985;Pluis, 1993), the testing of an acoustic sediment sensor (Spaan et al, 1991), the sand budget of the foredunes (Arens, 1994), the aeolian transport of beach nourishment sand (Van der Wal, 1999) and the modelling of air flow and sand transport across transverse dunes . A main issue in coastal management is stabilization versus so-called 'dynamic' or 'integrated' management of the coastal zone, coastal defence and safety being only one of the management aims.…”