A method is presented to calculate indirectly the heat budget of a tidal flat area from downstream observations of temperature and horizontal velocity in a tidal channel. It is only necessary to establish a relationship between the velocity and the volume flux. Then the heat budget of the upstream region is determined by integrating the heat flux over one tide. The proposed method is applied to long-term measurements obtained in 2004 at two sites in a tidal channel in the Hörnum Basin, German Wadden Sea. At the site located farther downstream in the channel, the upstream catchment area is diagnosed to export heat (heat gain in the interior) from March to August, while import is diagnosed for the same period of time at the other upstream site. From September to November the situation is reversed. An analytical estimate suggests that the sign of the budget is controlled by the tidal prism and the length of the dry-falling period of the flats in the respective upstream region. In addition, a simple model is developed which can be used to determine the integral bottom heat flux of the tidal flats.

The KFKI project BELAWATT used a coupled model system for simulating a 2-year timeseries of currents and waves in the Hornum tidal basin (German Bight, North Sea). This article deals with the model results concerning the effects of waves on currents and water levels and the input of wave energy into the coastline. During a storm event (wind 13 m/s from NW) the wavegenerated radiation stress produces an increase of the current velocity of 1 m/s above parts of the tidal ebb delta and it produces a water level increase of more than 20 cm in parts of the tidal basin. The model system also calculates the maximum energy input into the coastline during the storm event „Anatol“ (3./4.12.1999). Only 3 % of the maximum energy input into the west coast of Sylt island reaches the coastline of the tidal basin. A scenario-run for December 1999 with a water level increase of 50 cm and a wind velocity increased by 10 % shows that the input of wave energy into the west coast of Sylt island increases by 30 % compared to present conditions. With regard to the forecasted near-future (WOTH, WEISSE and V. STORCH, 2006) increase of strong storm surges, the scenario results indicate an increased risk of coastal erosion in the surf zone of Sylt island.