Entwicklung eines Langfristgewässergütemodells für flache Standgewässer

Water quality models meant to support sustainable water resources management need a long-term, integrative perspective on the river catchment level. Until today, water quality models for lakes and reservoirs have been implemented into catchment scale water quality models only rarely and in strongly reduced form with limited prognostic capabilities. As a particular property of shallow lakes and reservoirs, the vertically well-mixed, entirely productive water column is in permanent contact with the sediment. Thus, the sediment is of immediate importance as a long-term nutrient and pollutant storage, while exchange processes with the water column are closely coupled to hydrodynamics. After comprehensive literature study, the objective of this thesis is the development of a water quality model which specifically addresses characteristic features of shallow lakes and reservoirs with a potential for long-term water quality effects and, at the same time, is designed as a compact, computationally efficient entity appropriate for implementation into a higher-level, catchment scale water quality model. The developed model consists of a module and a module driver. As a result, the model allows for standalone applications, whereas the module is designed for implementation into higher-level catchment scale frameworks. The module is based on the numerical solution of the deterministic 3D transport and reaction equations. Apart from the water column, the active sediment layer is explicitly included into the spatial discretization. A closed formulation of sediment burial is developed based on conservation of sediment volume. Sediment-water exchange consists of both diffusive transport of dissolved substances and particle transport. As a key to computational efficiency, a new approach for the implementation of hydrodynamics is developed, i.e. a reduced scheme of interpolation between the pre-calculated, aggregated results of highly resolved hydrodynamic simulations. This allows for parameterization of net sediment resuspension based on bottom shear stresses. Based on the eutrophication model WASP5 by the U.S. EPA, the focus of implementing additional water quality constituents and processes with a potential for long-term effects is on iron and the interaction of iron and phosphate. For the shallow Spremberg reservoir in the catchment basin of the river Spree, a large amount of data is available that allows to verify and validate the model. First, the results of highly resolved, three-dimensional hydrodynamic simulations are confirmed by comparison to ADCP measurements. Then, further hydrodynamic simulations are performed to establish and test the reduced hydrodynamic data interpolation scheme. As a result of calibration, the water quality model successfully reproduces both the sediment composition and the discharge concentrations over a period of five years. In the case of phosphate, the strong buffering capacity of the sediment caused by the high iron content can be reproduced. The calculation time requirements of the module are on the order of 0,14 seconds per month of simulation time. As a result of idealized long-term simulations over a time period of 50 years it is possible to quantify the eutrophication effects caused by initial changes of external loading with nutrients and iron. Depending on the scenario, the reaction of the water body features a long-term component which prevails over decades and is related to the gradual adaptation of sediment composition. It can only be quantified by means of the chosen combination of model constituents.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2007

Author dc:creator

• Rubbert, Sebastian

Contributors dc:contributor

• Köngeter, Jürgen

• info:eu-repo/classification/ddc/620
• Numerische Strömungssimulation
• ADCP
• Eutrophierung
• Wassergüte
• Mathematisches Modell
• Stehendes Gewässer
• Ingenieurwissenschaften
• Gewässergütemodellierung
• Langfristmodell
• flache Standgewässer
• Strömungsmessung
• water quality modeling
• long-term model
• shallow lakes and reservoirs
• eutrophication
• hydrodynamic simulations

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-123880%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:62305