Experiences in the Netherlands about references and assessment

Transcription

1 Experiences in the Netherlands about references and assessment Miel van Oirschot RIZA; Institute for Inland Water Management and Waste Water Treatment. P.O. box AA Lelystad The Netherlands I. Introduction In this contribution You will be informed about the special circumstances in the Netherlands on watermanagement. Attention will be paid on historical facts, on policy on Nature and finally on the assessment of surfacewaters II. Review on the genesis of the Netherlands In figure 1-2 the geographical development and genesis of the Netherlands during the last millenium has been shown. In the ninth century: Two thirds of the Netherlands could be considered as a delta. In the course of time much has changed; in 1990 only the south western part could be considered as a delta. Because of the construction of dikes, the reclamation of land, the drainage of marshes and lakes, damming etc, etc the total surface of natural habitats has decreased enormously. Undisturbed areas have declined from almost 100 % in the ninth century to less as 8% in Especially brackish inter-tidal areas have been lost. Fresh water and brackish water lakes arised from sea, and rivers are caught within a narrow corset of dikes. The next figure focusses on the transformation of the last century. In that century the closing off and reclamation of the Zuyderzee has taken place. The closure dam with large discharge sluices was completed in 1932, creating Lake IJssel. By constructing four polders ha of Lake IJssel were reclaimed, with on the borders various borderlakes. So far the development of Lake IJssel and the border lakes in that area. After also in the South-West of the Netherlands big changements have taken place. The storm surge of february 1953 gave the final impulse to the Delta Project with the aim of damming the estuaries in the South-West to provide protection against storm surges. The Rotterdam Waterway and the Western Scheldt were excluded from it because of their importance as entrances to the ports of Rotterdam and Antwerp. Due to the improvement of the fresh water situation in the south west of the Netherlands, it became possible to assure a larger supply of water to the northern and north western parts of the country in dry periods. Diversion of water from the west to the north has been realized by canalisation of rivers and by building sluices. Figure 3 shows another picture of the Netherlands of this moment: The area, marked in blue will be flooded, when there are no dikes or flood-protection. Watermanagement is an essential part of dutch society; spatial re-arrangements are essential for the country and. The dutch people is proud on it!! (figuur uit: water in the Netherlands: a time for action van september 1989 op pagina 7, figure 1)

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3 Protection against storm surges and salinization in the 20th century before main dam km km 1970 Driel km Saline water Fresh water Weir

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5 III. Dutch Policy on Nature In the Netherlands conservation of nature is a compromis with landuse. The dutch policy on conservation of nature takes full account of these circumstances Dutch policy uses, the idea of Types of Nature -Targets, when conservation of nature comes up for discussion. These Types of Nature-Targets are defined as the desired combination of abiotic and biotic characteristics, on a particular spatial scale. A map of the Netherlands can be composed by these types of Nature-Targets. The desired types (units) of Nature-Targets can be mapped. Three main categories of Nature-Targets and 1 category, so called multifunctional can be distinguished. In this last one the landuse is starting point, but with an optimum potential for nature. Each of the categories of Nature Targets is subdivided in various Types of Nature-Targets. main nature-target types (Dutch policy on nature) 1. nearly natural 2. accompanied - natural 3. half - natural 4. multifunctional types derived from 1, 2 and 3. Figure 4 main nature target types In this system of Nature-Target-types, only the sea and some of the brackish transitional surfacewaters have been classed in the group of nearly natural. The rest of the surfacewaters has been placed in the group of accompanioned natural or in the group of half natural. The tentative definitions of these categories of Nature Targets are:

6 Definitions of Nature-Targets Category 1: nearly natural: undisturbed functioning of processes ( biotic and abiotic) on large scale for the benifit of natural differentiation Category 2: accompanied natural: antropogenic influence on processes only on large scale (biotic and abiotic). These natural processes determine differentiation on a larger scale Category 3: half - natural: promoting development of specific types of nature on smaller scale by means of active (water-) management Almost all Dutch inland surfacewaters belong to category 2 or 3; only the sea and some bigger intertidal waters to category 1 figure 5 (tentative definitions of Nature Tatgets) So, starting from the viewpoint of Dutch policy for nature, it could be stated a bigger part of dutch surface waters would belong to the categories of Heavily Modified or Artificial waterbodies; but it has to be emphasized: it depends on the scale. In any case, many arguments plead for an identification as Heavily Modified, provisionally at least. The objective of the Water Frame Work Directive is: achieving a Good Ecological Status. A riverbasin - approach is required. Concerning transboundary rivers the designation of Waterbodies should be done in any case in consultation with neighbouring countries. The scale to be taken in account could be of importance. On a larger scale you could define reference conditions in general terms. These reference conditions should correspond more or less with those of the category of nature-target types : accomponied natural

7 Reference conditions reference state is the presentday potential state, which harmonise to a state that would establish itself after abandoning all existing uses in and on the water and its floodplains but maintaining the actual main infra structure on behalf of watermanagement figure 6 (reference conditions) IV. Common practices on ecological assessment of surfacewaters in the Netherlands. The administration on watermanagement in the Netherlands has a long tradition; but is is rather complex. In the Netherlands we distinguish the larger surfacewaters, which are administrated by the State and further on the smaller waterbodies, which are administrated by waterboards. Groundwater, for the time being, is administrated by the provinces. Different assessment methods are in use. For the state managed surfacewaters the so called Amoebe method is used (figure 4). In the Amoebe the reference state is based on historical data (for the river Rhine 1930) and is presented by the circle. The indicator species are selected by expert judgement. In the figure, both the target state and the present state (1988) are plotted; No further classification has been done. The objective is to take measures in order to go in the direction of the target state. The Amoebe method considers not only the aquatic organisms but also other species related to surfacewater, such as birds and the mammals. Amoebes have been made for all Dutch surfacewatersystems and subsystems, administrated by the State.

8 River-amoeba Situation 1988 Year of reference (1930) Target situation Floodplain forest Side channels Natural river banks Flooded river foreland Badger Otter Phytoplankton Water gentian Scirpus triqueter Pondweed Meadow clary Inula britannica Corncrake Sand martin Cormorant Tufted duck Night heron Twaite shad Sturgeon Barbel Bream Midge larvae 1 (Microtendipes) Midge larvae 2 (Cripotopus) Caddis larva (Hydropsyche) Palengenia Pea clam

9 A different assessment-method is applied on the smaller surfacewaterbodies, administrated by the waterboards. Different types of inland waterbodies are distinguished: running waters, shallow lakes, canals, ditches and sand/gravel pits. The assessment is based on multivariate pattern analyses on a large database, which covers the whole country. The database contains both biotic and abiotic data and is good enough to determine statistic relationships between abiotic parameters (like streamvelocity, trophic state etc, ) and biota. Yardsticks have been developped ( five classes) for different abiotic factors. (streamvelocity, trophic and saprobic state, substrate, foodstrategy). Indicators are different kinds of species of macro-invertebrates. The figure shows the main factors. The height of each column could be considered as relative weightfactor. The reference state is a hypothetical surfacewater in an undisturbed state. food strategy highest substrate trophic state (idem) (idem) nearly highest saprobic state (idem) assessment smaller waterbodies for dfferent elements of ecological functioning (macroinvertebrates middlemost lowest stream-velocity beneath lowest figure 8 ( Assessment of smaller waterbodies, administrated by waterboards) The next figure shows the results of an assessment for an hypothetical watercourse. The results are presented separately for each element.

10 results of an assessment of a waterbody for the different elements food strategy substrate trophic state highest nearly highest saprobic state middlemost lowest stream-velocity beneath lowest figure 9 ( hypothetical result of an assessment) V. Developments on assessment in the Netherlands. State and Waterboards are cooperating in order to develop a Framework on ecological assessment of Waterbodies. A schematic draft is shown in the next figure. A database will be coupled to this framework of Assessment.

11 Framework for the identification and charakterisation of waterbodies in the Netherlands Ems Rhine Sc figure 10 ( draft of a framwork for identification of waterbodies) The use of this draft will be multifunctional; not only for the Water Frame Work Directive but also for national and regional planning. Not only for water management but also for nature management;