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In the mesotidal (tidal range 3.5–4.9 m) Westerschelde estuary (The Netherlands) the intertidal part of a sandbank was the subject of systematic observations of: (1) hydrographic properties, (2) the distribution and response pattern of various types of bedforms, ,and (3) the sedimentary structures produced. Ebb and flood usually differ considerably in strength, giving rise to a clear dominance of one over the other, which may change over the neap-spring tide period. Parallel, long-crested sand-waves and irregular, short-crested dunes have a different response to the neap-spring variation in current velocity. Because one tide (usually the flood in our area) predominated over the other, the internal structure largely consists of unidirectional cross-bedding, separated into a succession of tidal bundles, each formed during one tide. The tidal bundles are arranged in a lateral sequence reflecting neap-spring tide periods and differing in character with location. Within the tidal bundle, reactivation, full vortex and slackening structures reflect acceleration, full stage and deceleration of flow respectively in the dominant tide. The full vortex structures tend to be well developed around spring tide but disappear towards neap tide. The subordinate tide carves ‘pause planes’ which enclose the tidal bundles. These pause planes are either erosional or depositional (mud). [ABSTRACT FROM AUTHOR]

In Dutch sub-tidal waters, mud settling from suspension can produce a layer with a thickness of only some millimetres in one slack-water period. However, consolidated mud layers of 10–25 mm thickness in sub-tidal deposits are often observed. This indicates that mud may be preserved over several slack-water periods. This is only possible if the critical shear velocity (U∗c) for the initiation of sediment movement is not surpassed after slack water. Tube and flume experiments reveal: (1) Thicker mud layers have smaller initial consolidation rates and lower values of U∗c. (2) A higher sand content of the mud always gives a more rapid initial consolidation. The U∗c-values increase to a maximum which is reached at a sand content of 40%. Higher sand contents lead to decreasing values of U∗c. (3) For one particular mud sample the U∗c-values increase linearly with the mud concentration Of the bed material. (4) After three hours of consolidation a mud layer may carry a sharply bounded sand layer 0.5 cm thick. By application of the results of the experiments to natural conditions in tidal water some tentative explanations are possible of the formation of flaser, lenticular and sand-clay alternating bedding. [ABSTRACT FROM AUTHOR]

Land, Sea and Human Effort was the central theme of the 28th IGU Congress in The Hague, The Netherlands. This volume contains the key-note addresses highlighting this central theme. Three major issues regarding low-land coasts came to the fore: land-use, environmental quality and safeguarding of the land. An interesting question is whether the concentration of human activities in large urban nodes will continue, or that such nodes and hierarchies will no longer structure our world, because of the ever-increasing importance of all means of communication and transport, as indicated by Johnston. Functions may disperse to specialised environments. A similar specialisation may be encountered in e.g. the development of tourism in the coastal zone. As Gormsen has elucidated, tourism has over time extended in a sequence of spatial 'peripheries'. Consequently, phases in development may be identified with a growing impact and participation of local tourism interwoven with international growth. The environmental quality of coastal zones is seriously under threat, due to ever-increasing population pressure and human exploitation. The major problems are pollution andthe availability of good quality water. Oudshoorn explored the world's resources of drinking water, indicating the great need for political awareness of this huge problem. Cross-sectoral planning is advocated by Oudshoorn, even if water management often trespasses international boundaries and the harmonisation of the planning strategies is mostly difficult. The environmental quality of the coastal zone is alsoaffected by the exploitation of oil and gas resources. Odell demonstrates that the conditions for this exploitation in the North Sea are unique, especially because of the great impact of an international agreement on offshore exploitation. Planning in sea areas is becoming an issue of increasing importance as it has to cope with the many, often conflicting interests, such as shipping, fishery, mining, waste disp [ABSTRACT FROM AUTHOR]