Sub-Project 4

 

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A complex River Basin Model of the Havel

B. Pfützner, BAH Berlin

During dry summers discharge and flow velocity in the Havel river drop considerably, which induces serious reductions in water quality. One way to handle these low flow periods is to compensate the inter-annual discharge fluctuations by storing water in high flow periods (during winter) and providing this surplus during summer. Therefore, additional storage capacities in the river network have to be established or reactivated. Alternatively, the retention of the river basin itself may be increased.

However, such measures also result in

bullet an increased evapotranspiration, due to rising groundwater table depths in wetland areas and an increase of such areas
bullet a reduction in flow dynamics, especially in high flow periods
bullet a reduction of existing benefits for the river net due to floods.

Since the increased evapotranspiration influences the total water balance, only a part of the water stored during winter can be released as additional flow in summer. The reduced flow dynamics impacts lowland (or wetland) biotopes, which in general depend on changing water tables or even on flooding periods. Like long-term low flow periods, missing flooding effects may lead to mud generation in the rivers, to a disturbed nutrient balance and dramatic changes in living conditions of aquatic organisms. This means that a less fluctuating annual discharge also induces negative impacts on the river network and the basin itself.

The aim of the present sub-project is to model the actual hydrological conditions in the Havel river basin, taking into account various boundary conditions. Simulations will be performed for

bullet the reference state in order to delineate the ‘good ecological state’ with respect to discharge dynamics
bullet the actual hydrological state to derive management options
bullet the assessment of the impacts due to various management measures heading for a less fluctuating annual discharge regime.

Based on the precipitation-runoff model established for the Upper Havel in the Elbe-Ecology project and actually improved in the GLOWA-Elbe project, a complex river basin model will be developed for the Havel basin. The inflow from the Spree river including the Berlin portion (which is not part of the study region in the present project) will be transferred from the GLOWA-Elbe project. With this basic Havel model the impacts of a changed landuse (or of a changed climate) on discharge can be described in a highly temporal and spatial manner. The basic model will be extended in order to assess management options in the basin and their influences on discharge in the river system. Model components will be developed to describe

bullet all relevant management options like water withdrawal and transfer, irrigation and drainage as well as the influences of dams, pumps and storages
bullet retention effects in all open water bodies (hydrologic and hydraulic approaches including the detailed studies performed in sub-project 3)
bullet the interaction between ground- and surface water (as a basis to evaluate the effects of an increased water retention on the regional water balance).

A general aspect in developing these components is the use of generally available data. Thus, the quality of these data will determine the quality of the new model components.

To validate the simplified model components, detailed precipitation-runoff models will be developed for two focus regions. Besides the detailed hydraulic studies of sub-project 3, high resolution satellite data will be included on this scale. Since the focus regions are part of the overall Havel model, comparisons of results obtained at two different spatial scales will deliver information on the accuracy of the simpler model approach chosen at the Havel scale.

Basis for the intended studies is the hydrological modelling system ArcEGMO (Pfützner 2002, Becker et al. 2002, www.arcegmo.de), which played a key role already in developing the management plan for the Salza river basin. Post-processing tools integrated in ArcEGMO provide various statistical discharge values according to DVWK-121/1992 for every river section as well as other eco-hydrologic values (see e.g. Richter et al. 2000). These statistical numbers represent the basis to evaluate changes in flow dynamics due to management measures.

Thus, the main results of the sub-project will be the development of a suitable methodology to assess the goals of the European Water Framework Directive, the derivation of the ‘good ecological state’ (considering flow dynamics) and the development of a complex Havel river basin model. By using this model, a considerable contribution to the aspect ‘discharge and discharge dynamics’ is expected in deriving a management plan in one of the largest lowland river basins in Northern Germany. This model will be provided to the water authorities of the Country of Brandenburg, supporting the analysis of different scenarios in the framework of sub-project 8.

Becker, A., Klöcking, B., Lahmer, W. and Pfützner, B. (2002). The Hydrological Modelling System ARC/EGMO. In: Mathematical Models of Large Watershed Hydrology (Eds.: Singh, V.P. and Frevert, D.K.). Water Resources Publications, Littleton/Colorado. 891pp. ISBN 1-887201-34-3, p. 321-384.

Pfützner, B. (2002). ARC/EGMO. In: Barben, M., Hodel, H.-P., Kleeberg, H.-B., Spreafico, M. und Weingartner, R. (Hrsg.). Übersicht über Verfahren zur Abschätzung von Hochwasserabflüssen – Erfahrungen aus den Rheinanliegerstaaten. Bericht Nr. I-19 der Internationalen Kommission für die Hydrologie des Rheingebietes-KHR, p. 151-154. ISBN 90-36954-11-8.

Richter, B.; Baumgartner, J.; Powell, J. (2000). A Method for assessing Hydrologic Alteration within Ecosystems (s. unter www.stream.fs.fed.us)

 

Please respond to W. Lahmer (werner@wernerlahmer.de or webmaster@havelmanagement.net)
02/07/05

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