Beekdallandschappen : een morfologisch onderzoek in de zandgebieden van Nederland

At the beginning of this century the landscape of the Dutch Pleistocene areas had a clear and coherent structure. The stream valleys were an important part of this structure. During this century the old landscape structure has largely disappeared. Topographical maps illustrate these changes and show that the stream valleys can now hardly be recognized as separate parts of the landscape of the Pleistocene areas.

In spite of these changes, stream valleys can be important in helping to solve the spatial problems of the Pleistocene areas because stream valleys are spatial elements on which a sustainable and coherent landscape structure can be based.

In this thesis the changes in the landscape that have taken place and the changes that will take place in the near future will be studied from an landscape architectural point of view. This means that the form of the landscape is the central issue. Form and changes in form or transformations are narrowly related to the underlying processes. This is the basis of the next central research question:

Which transformations took place and will take place in the stream valley landscapes; and is it possible to relate these transformations to the underlying factors and processes?

The absence of a useful instrument to analyze and typify stream valley landscapes leads to the derived research question:

Is it possible to develop an instrument which analyze and typify the form of stream valley landscapes while also taken the underlying factors and processes into consideration?

The first part of this thesis consists of a survey of the genesis and development of the stream valleys. The genesis begins in the Saalian. In this period the major forms of the present landscape of the Pleistocene areas were created. During the Weichselian these major forms were further shaped and achieved there present form. In the Holocene the form of the stream valleys was limited by returning vegetation. In the Pleistocene areas the hydrological system played an important role and can be regarded as the 'circulatory system' of the Pleistocene areas. The stream valleys were and still are the 'veins' of the hydrological system. The lowland stream is the type of stream that is characteristic of the stream valleys. Initially, the stream valleys were distinguished from the surrounding landscape by hydrological circumstances but also by the soil and vegetation.

Natural stream valley landscapes have long disappeared. The eighth century onward stream valley landscapes have been subjected to major changes. In spite of these changes the pattern of the landscape at the beginning of this century still revealed the main outlines of its medieval origins.

As part of this landscape, stream valleys were recognizable by the multitude of hedgerows, tree belts along the stream, meandering streams and there being used as meadows and pastures. In the second part of the nineteenth century developments in agriculture caused drastic changes in the stream valley landscapes. Heath, fens and marshes were reclaimed, streams were regulated and hedgerows and tree belts along the streams were removed. In recent decades re-allocations also caused important changes.

To describe and analyze the transformation process of the stream valley landscapes the landscape morphological model has been developed. This model comprises three morphological layers: terrain forms, networks and verticals. The terrain forms are the underlayer upon which the networks and verticals are draped. Networks are defined as spatial elements without height but with a strong linear character. (i.e. roads, railways and streams). Verticals are defined as spatial elements characterized by height and mass (i.e. trees, woods, houses and dikes).

The landscape morphological model is applied to describe and analyze the stream valley landscapes from two points of view: 'the perspective of space' and 'the perspective of spatial elements'. The analysis demonstrates that stream valleys landscapes can be considered as complex systems of forms and there is a great diversity in the relation between the three morphological layers.

The relation between the three morphological layers and the form of space is the basis for a morphological typology of stream valley landscapes. This typology distinguishes twelve types of stream valleys. With the help of this typology, stream valley landscapes were categorized both for the situation at the beginning of this century and for the present situation. This categorization demonstrates that at the beginning of this century there were clear regional differences in the presence or absence of the types of stream valleys. Moreover there were differences within the system of stream valleys: Some types were only present in the upper reaches of the streams valleys, whereas other types were only present in the downstream reaches of the stream valleys. At the moment, both the regional differences and the differences within the system of stream valleys have largely disappeared.

The typology of the stream valleys makes it possible to visualize this transformation. This means that this typology is also a useful instrument to visualize the spatial problems of the stream valley landscapes.

In order to obtain more insight into the transformation process, several maps of the different stages of the transformation process were made. These maps show that the transformations can be related to different processes. These processes cannot be regarded individually, because some of the processes reinforce each other or follow each other chronologically.

The research project demonstrates how the landscape morphological model can be applied to describe and analyze the form of stream valley landscapes. The use of the landscape morphological model and the derived typology has lead to more insight into the spatial problems of the stream valley landscapes and to more insight into the underlying processes. Because the outlines of the model are general valid, the landscape morphological model is also applicable in other landscapes and on other spatial levels.

The landscape morphological model can also contribute to the design process because the model makes it possible to search for specific relationships between terrain forms, networks and verticals or to search for contrasts between the three morphological layers.

Finally, the landscape morphological model can be useful in analyzing spatial plans systematically.