AERIAL PHOTOGRAPHIC WATERLINE SURVEY OF AN ESTUARY

Abstract

The project of a "barrage across an estuary in Northern Germany was accompanied by a programme to monitor the hydrologic and morphologic situation. This became necessary in order to avoid dangers resulting from the sensitivity of the shallow wadden area to human interference. Various methods to record the morphology were tested. The aerial photographic waterline survey proved superior as it supplies a complete and economic record and allows accurate analysis of the topography. The principle consists in taking aerial photographs at short time intervals between low water and high water, each photo showing a different waterline. The scale chosen was 1:18000, corresponding to a flight altitude of 2700 metres. Rectification of the distorted photos requires reference markers to be distributed over the survey area which measures about 140 km^. By using simultaneous tide gauge records, contour lines can be constructed from the photographed waterlines. This morphologic record is supplemented by submarine survey of the estuary. It is expected that details of sediment transport and of tidal prism changes may be revealed. Predicted and actual effects of the barrage will be compared, which might lead to a better understanding of such coasts.