Study Area: The Backbarrier Tidal Flats of Spiekeroog

The Wadden Sea of the southern North Sea covers an area of about 9.300 km2 and represents one of the largest intertidal regions on earth (Fig. 3.1.1). Between Den Helder and the Jade Bay (near Wilhelmshaven), the West and East Frisian Wadden Sea forms a classical barrier island chain (Backhaus 1943). The island Spiekeroog is located in the eastern part of this chain. Its backbarrier system, the main research area of ELAWAT, is connected to the North Sea via the Otzumer Balje (Fig. 3.1.2), a tidal inlet which separates Spiekeroog from the neighbouring island Langeoog in the west. Referring to mean tide high water (MThw), the tidal basin of the Otzumer Balje covers an area of about 73.5 km2 (Walther 1972). The basin is bordered by two watersheds: In the west by the Langeooger Plate, in the east by the Hohe Bank. The distance between the island and the mainland averages 6.5 km and the island has a length of approx. 10 km. The intertidal section of the Spiekeroog backbarrier system covers about 80 % of the area and is comparable to that of other East Frisian tidal basins. The North Frisian and the Danish Wadden Sea have about 70 % tidal flats on average, but the Sylt-R0m0-bight comprises only 30 % intertidal areas (Reise & Riethmiiller 1998). With an average tidal range of 2.7 m at the western end of Spiekeroog island and of 2.9 m in the front of the mainland, mesotidal conditions prevail in this backbarrier system (Niemeyer & Kaiser 1994). At standard sea level (NN) the water volume in the catchment area amounts to 0.112 km3. The volume of water that is exchanged during a tidal cycle via the Otzumer Balje is calculated to be 0.292 km3 on average (Chap. 3.3).