Landschapsplanning en watersystemen in de zandgebieden van Nederland : naar een watersysteembenadering voor landschapsplanning, toegespitst op de ruimtelijke problematiek van de Nederlandse zandgebieden

Landscape planning and hydrological systems in the pleistocene sandy areas of the NetherlandsThe main theme of this doctoral thesis is the relationship between landscape architecture and hydrology. Knowledge of hydrological processes - with the stress on the resulting spatial and temporal relationships - is applied for purposes of landscape planning. To this, the situation of the landscapes in the Dutch pleistocene sandy areas is central. Prologue (Chapter 1)Water and landscape architectureFrom early days, water has played an important role in the planning and design of our environment. As historic garden and park design shows, traditional landscape architecture focused primarily on the aesthetic and symbolic aspects of water. The current situation in many landscapes nonetheless calls for a broader approach, in which such aesthetic qualities are combined with what might be called the 'ecologicalfunctional' significance of water. The key to this is found in the hydrological processes, together with the spatial and temporal relationships concomitant with them, and in the resulting environmental conditions and spatial landscape patterns. In short, water plays a pivotal role in the determination of landscape. This hydrologically-based approach to landscape planning is also the perspective from which the relationship between landscape architecture and hydrology is examined in this thesis. Pleistocene sandy areas in the Netherlands and the concerns of landscape planningThe 'Dutch sandy areas' are the geographical focus of this thesis. This term is conventionally applied as a collective term that refers to the sand-soil landscapes in the northern, eastern, central and southern Netherlands (fig. 1.2). The rapid and radical changes currently taking place in these landscapes have given rise to a complex range of environmental problems. These are primarily the result of the intensity and dynamics of urban and agricultural land-use, which have subjected other forms of land-use more related to natural, abiotic conditions, to great pressure. From the point of view of landscape planning, the problems faced in the sandy areas can be defined as an inadequate siting of the various land- use types. It is therefore the concern of landscape planners to seek a planning approach that allows for the sustainable development of the relevant land-use and to create a structural framework that makes use of underlying natural patterns. This framework concept is a planning concept by whose means planning in the sandy areas can be addressed.The research questionsWater plays an important role in the problems currently being encountered in the Dutch sandy areas. Normally water systems result in spatial coherence in a landscape. Recent developments however have resulted in a change, or even a loss of hydrological relationships between landscape components. For a possible solution of these problems the following research questions are important:- how does water function in the landscape as a basis for spatial coherence?- how could knowledge of hydrological systems be applied in landscape planningwithin the three principal components of the design and planning process: analysis, synthesis and evaluation?Water in the landscape (Chapter 2)The hydrological cycleThe hydrological cycle is the overall system of relationships resulting from hydrological processes (fig. 2.1). At the earth's surface, these processes lead to characteristic landscape patterns such as the network of surface waters, floodplains and brook valleys as well as vegetation and land-use patterns. The flows of both groundwater and surface water contribute to this system of spatial relationships and landscape patterns.GroundwaterflowsThe flow-concept developed by Toth makes it possible to see the flows of water both at and below the earth's surface as a hierarchically organised set of superimposed groundwater flow-systems of various orders connected to a hierarchy of surface water systems (fig. 2.3). The existence and function of these systems is dependent both on natural factors (e.g., climate, topography and geological structure) and on anthropogenic factors (such as groundwater extraction and water-level regulation). The properties of the groundwater systems depend on the ways in which the factors determining groundwater systems are manifested. A number of quantitative and qualitative properties are important: flow and velocity, form, origins, position relative to other systems, behaviour over time, and the chemical composition of the groundwater. In the Dutch pleistocene sandy areas these factors have given rise to four different types of groundwater systems (fig. 2.4).Surface waterflowsThe flows of surface water create a hierarchical structure of catchments of different orders, defined here as the surface water flow systems. Factors such as discharge, slope, the transport of sediment, river-bed texture, the nature of the banks, and of aquatic and riverbank vegetation determine the properties of these flow-systems, such as their width, depth, maximum depth, flow rate, sinuosity and meander-width. In the Dutch sandy areas, all surface-water flow-systems originate in groundwater. These surface waters are termed lowland streams; their typical characteristics are a relatively low flow-velocity, periods in which water is stagnant or watercourses are dry, and a characteristic sequence of plan forms and crosssections (figs. 2.8 and 2.9).The hydrological landscape structureThe flow processes in groundwater and surface water create relationships in a landscape of varying intensity, nature and direction, both in time and space. Specific patterns develop (figs. 2.13, 2.14 and 2.15) with varying environmental conditions as well as potentials for land-use. in this thesis such an organisation and the resultant relations and patterns are called the hydrological landscape structure. Figure 2.18 shows the implications of the identification of such a structure for landscape planning.Towards a hydrological systems approach tolandscape planning (Chapter 3)A landscape planning process normally comprises three steps: analysis, synthesis and evaluation. In the hydrological systems approach to landscape planning these steps can be elaborated as follows.The analysis phaseThe analysis phase of the hydrological systems approach to landscape planning comprises the following elements:- a description of the hydrological landscape structure of the area in question, involvingthe application of the 'regional hydrological system analysis' method;- an analysis of the ways in which water links various forms of land-use; this is followed by an elaboration of the planning problem involved per case.The regional hydrological system analysis (which has been developed in the Netherlands and advocated by a group from the Vrije Universiteit Amsterdam and in the Netherlands institute for Applied Geoscience (NITG) around Engelen) is a method for classifying hydrological systems by type, scale, interdependence, spatial distribution and behaviour over time. A working method has been described for the performance of this system analysis (fig. 3.4). The outcome of the regional hydrological system analysis is a map of the hydrological landscape structure. The results of hydrological system analyses make it possible for a land-use analysis to be carried out. The proposed land- use analysis comprises the production of a series of overlays in which land-use maps are compared with those of the hydrological landscape structure (fig. 3.5). It can thus be verified whether, and to what extent, water flows create problems between conflicting land-use categories. At the same time, a distinction can be made between problems that arise when one or more of the following changes takes place with regard to a flow: decrease, termination, reversal, increase; or the appearance of, or an 'addition' to a flow (i.e., pollution (fig. 3.6).The synthesis phaseDuring the synthesis phase new options - i.e., plans - are generated which help address the problems defined in the analysis phase. Insights derived from hydrology enable the generation of options that will provide for the elaboration of concrete solutions (fig. 3.7).It is expected that these options will fall into three general categories (fig. 3.8):- land-use redesignation, in which specific areas within the hydrological landscape structure are used to relocate land-use types such that they are no longer or in an optimal way interlinked;- land-use adaptation, in which the nature of land-use is modified to avert negative influences upon other forms of land-use;- the manipulation of the hydrological landscape structure, whereby existing relationships are broken up (so-called isolation) or original relationships are restored.Of the three options redesignation and manipulation fall clearly within the domain of landscape planning. The former concerns the level of strategic planning. Figure 3.9 shows the concrete planning measures this makes available for the location of landuse. Manipulation concerns the level of operational planning. Planning measures at this level are shown in figs 3.10 - 3.12.The evaluation phaseEvaluation in the planning process involves testing the planning proposals that arise from the synthesis phase. it comprises the following steps (fig. 3.13): - interpretation of the planning proposals in hydrological terms; - calculation of their hydrological effects; - assessment of these effects. The final phase makes it possible to indicate whether or not the planning proposals are sufficient. if they are insufficient, or if they are expected to give rise to unacceptable side-effects, earlier phases of the design process are consulted. This iterative procedure is continued until the design objectives have been attained to a satisfactory degree and significant undesirable side-effects are no longer encountered.Pilot studies: applications of the hydrological systems approach within landscape planning (Chapters 4,5 and 6)The hydrological systems approach to landscape planning was developed, refined and tested in a series of pilot studies. Three of these studies, all involving the catchment area of the Regge in the province of Ovedissel (fig. 4.1) are discussed. Each of these three examples stresses a different phase in the hydrological systems approach examined above.An analysis of the Regge catchment (Chapter 4)An analysis is made of the geological origins, historical occupation patterns and hydrological landscape structure of the Regge catchment. With regard to the latter, a distinction is made between groundwater and surface-water flow-systems in both a historical situation (approximately the first half of the 19th century: see figs. 4.14 and 4.24) and a contemporary situation (see figs. 4.26 and 4.27). Comparison of these two situations shows that radical changes have taken place. The most important of these changes are represented in 4.25. A significant proportion of the former exfiltration areas disappeared (4.28).An analysis is then made of the manner in which land-use (nature conservation, water extraction and agriculture) is positioned in the hydrological landscape structure, and of the consequences this has to the land-use forms and to any interrelationships between them. The outcome of this analysis is an elaboration of the problems generally encountered in the Dutch sandy areas. Nature areas represent the most striking problem. The disappearance of wetland areas is particularly evident (4.33). The earlier network of extensive and strongly-interrelated wetland areas has been reduced to a series of small, isolated entities. The relationships with the highly-intensive urban and agricultural areas (cf. fig. 3.35) mean that future prospects for these remaining wetland areas are not rosy. The widespread incidence of urban or agricultural land-use in the infiltration zones of drinking-water pumping stations (fig. 4.34) represents a threat to drinking water quality.Planning at a strategic level (Chapter 5)At a strategic level the design of a landscape framework that would create sustainable preconditions for the development of the most threatened land-use forms was the central aim. it would also enable hydrologically-based planning measures to be used insuch a way that the situation of the framework in the hydrological landscape structure would have the following effects:- it would avert or minimise any negative influences upon the framework via water flows from surrounding areas;- it would create the preconditions for the development and maintenance of the environmental diversity and landscape patterns characteristic of the areas concerned.The plan (see fig. 5.6) was drawn up by means of a step-by-step procedure to which the creation of favourable preconditions for the recovery and regeneration of wetland areas was central. For this, the recovery and sustainable protection of the principal groundwater flow-systems is an essential condition.In the first step of the plan, it was proposed to achieve this condition by including the infiltration and exfiltration zones in the relevant flow-systems in the framework as nature areas (fig. 5.1). Despite the many hazards, the planning assignment described here means that any remaining wetland areas have considerable potential. The most important of these areas and the areas necessary for their protection were all mapped in the second planning phase (fig. 5.4). Finally, in the last step, a number of the patterns characteristic of streams and brook valleys were added to the plan (fig. 5.5).The resulting plan represents a series of interrelated areas that reflect the main abiotic patterns in the Regge catchment (fig. 5.6). By applying the planning measures incorporated in the hydrological systems approach, hydrologically-interlinked areas were included in the network so as to create an entity that could function relatively independently. Figs. 5.6 and 5.7 show that the plan offers potential for the entire range of environmental conditions that were original features of the area. Many ecological gradients may be developed as well.Planning at an operational level (Chapter 6)Planning at an operational level in this thesis comprises the development and evaluation of planning proposals that would combine drinking water production with the regeneration of former wetland areas and the creation of new wetlands. This study resulted in the NADORST pilot plan, in which the study area was a hydrologically contiguous part of the Regge catchment (fig. 6.1). A computer model was used which enabled the simulation of groundwater flows and of the changes occurring within it. Planning followed the hydrological systems approach for landscape planning. it resulted in a working method that comprised one analysis phase and two design phases (fig. 6.2). During analysis, the most important abiotic, biotic and anthropogenic patterns and processes were discussed, with hydrological analysis occupying a key position (figs. 6.6 and 6.7). The first design-phase, which was of a strategic nature, comprised a systematic examination of the development potential within the planning area. To this end, 'planning models' were designed. These involved the redesignation of land-use on the basis of the hydrological landscape structure (fig. 6.8). These models were evaluated (figs. 6.9 - 6. 11) in order to select a strategy for further development. in the second design phase, this strategy was elaborated into a landscape plan, which involved the proposal of planning measures for interventions in the existing hydrological landscape structure. This design involved the introduction of a new drinking-water production site (fig. 6.14), changes to the surface water system (fig. 6.15) and changes in land-use. The hydrological conditions were simulated (figs. 6.16 - 6.18), and it was indicated what the principal implications would be for drinking water production (table 6.2 and fig. 6.19), vegetation (figs. 6.20 and 6.21) and agriculture (6.22). The landscape plan (fig. 6.23) shows a design interpretation of the proposed measures. The pilot study demonstrated that it is Possible to combine drinking water production with the restoration or creation of wetland nature areas.Epilogue (Chapter 7)Research resultsThis thesis addresses the ecological-functional significance of water to landscape planning, and introduces two concepts: the hydrological landscape structure and the hydrological systems approach to landscape planning. The thesis can therefore be regarded as a hydrological interpretation of the 'landscape-ecological' tradition of landscape planning in whose development McHarg has played a leading role. The pilot studies described in the thesis show the feasibility of using hydrological knowledge as a basis for designing landscape plans. The understanding of one of the factors most crucial to the functioning of landscapes can thus be applied during planning. The patterns arising from the hierarchically-ordered hydrological landscape structure provide valuable points of reference for the design of a landscape whose underlying functional structure is clearly expressed. One example of this might be an ecological network that simultaneously contains a wide variety of environmental conditions while being exempted from the deleterious effects of anthropogenic hydrological flows. The combined development of water collection areas and of both dry and wetland nature areas might thus become and important weapon against desication. Wetland areas are of strategic importance in the Dutch sandy areas. It may be argued that the creation of conditions favourable to the development of these areas at the outlets of groundwater flow systems will mean the progressive restoration of ecological qualities to the wider landscape. The search for solutions to problems in the Dutch sandy areas has thus found a logical starting point. Planning activities will be able to focus on what is simultaneously one of the weakest and one of the most important links in the landscape system.