The core product of MuDak-WRM was to develop models, tools and guidelines to facilitate the management of reservoirs in order to improve or maintain good water quality. We also aimed on the prediction of medium to long-term changes of water quality in reservoirs, based on reduced complexity approaches and integration of globally available data sources, like satellite data. The key aspect was to reduce the complexity of the underlying scientific-mathematical approaches and the data required for the adapted models (LARSIM - water balance model, MoRE - emission model and Delft 3D - water quality model) to enable the application of the models with reasonable effort and in a meaningful way in regions with limited data availability.

The interdisciplinary research group on the German side was a consortium of four research (university) and five industry partners. Each work package was handled by one or two German partners. On the Brazilian side, three research and four industry or public partners were involved in the project, so that the areas of competence were mirrored. German and Brazilian partners were joined to optimally facilitate the exchange of knowledge and the close cooperation on the scientific and practical tasks.

The project team set out to improve the still limited understanding of processes in the catchment and the reservoir, which so far hinder the development simplified approaches. The project hypotheses was that water quality changes of reservoirs react on long-term scales and that reactions of changing conditions (inputs) can be modelled and verified by the interpretation of monitoring data. The MuDak team aimed to deliver advanced results in practical form, which can be used by international reservoir operators and authorities to describe the actual status of one reservoir and to predict the future development of water quality under the consideration of certain management options.

The MuDak project was able to successfully link the erosion and transport processes in the catchment area with the siltation tendencies and water quality changes in the reservoir. For this purpose, satellite data were automatically analyzed and directly used as input parameters for the erosion model. In parallel, a water balance model was implemented that, on the one hand, coped with small input data sets and larger data gaps, and, on the other hand, provided the runoff components needed for the input modeling and hydrodynamic modeling in the reservoir. 

Studies in the reservoir showed that the high nutrient inputs did not directly cause algal blooms. A large part of the introduced phosphorus remains stored in the sediment. Thus, there is currently no threat to water quality in terms of water treatment, but environmental changes can lead to a release of this phosphorus storage. In particular, oxygen deficiency directly related to the number of days the water body is stratified can lead to increased input from the sediment (internal loading). 

Two exemplary measures could be identified to maintain water quality over the long term. First, it was calculated which areas in the watershed would have to be reforested to achieve a significant reduction in sediment and thus nutrient input. Here, as little as 3% of the area would result in a 26% reduction in the annual amount of sediment. Another measure, is the construction of an upstream "pre-dam". This is common in Germany, but very rare in Brazil. This could also lead to a significant reduction of inputs into the main lake.

The project data and in particular the real-time water quality data from the reservoir were linked and made available via a sensor web. It allows not only to view the data, but also to make long￾term comparisons. For this purpose, data management and visualization were developed for various data types, such as raster data or vertical profiles. Thus, the reservoir operator has all information for the assessment of the current situation but also the development immediately available.

Project PIs: A. Lorke (Co-PI)

Key Publications:

• Ishikawa, M., Bleninger, T., & Lorke, A. (2021). Hydrodynamics and mixing mechanisms in a subtropical reservoir. Inland Waters, 11(3), 286-301. https://doi.org/10.1080/20442041.2021.1932391
• Ishikawa, M., Gonzalez, W., Golyjeswski, O., Sales, G., Rigotti, J. A., Bleninger, T., Mannich, M., & Lorke, A. (2022). Effects of dimensionality on the performance of hydrodynamic models for stratified lakes and reservoirs. Geosci. Model Dev., 15(5), 2197-2220. https://doi.org/10.5194/gmd-15-2197-2022
• Ishikawa, M., Gurski, L., Bleninger, T., Rohr, H., Wolf, N., & Lorke, A. (2022). Hydrodynamic Drivers of Nutrient and Phytoplankton Dynamics in a Subtropical Reservoir. Water, 14(10). https://doi.org/10.3390/w14101544
• Ishikawa, M., Haag, I., Krumm, J., Teltscher, K., & Lorke, A. (2021). The effect of stream shading on the inflow characteristics in a downstream reservoir. River Research and Applications, 37(7), 943-954. https://doi.org/10.1002/rra.3821
• Marcon, L., Bleninger, T., Männich, M., Ishikawa, M., Hilgert, S., & Lorke, A. (2024). Exploring the temporal dynamics of methane ebullition in a subtropical freshwater reservoir. Plos One, 19(3), e0298186. https://doi.org/10.1371/journal.pone.0298186 

PhD thesis: Ishikawa, Mayra: Fate of nutrients in a subtropical reservoir according to hydrodynamic processes and its effects on phytoplankton dynamics. University of Koblenz-Landau. 2022: https://kola.opus.hbz-nrw.de/files/2381/2022+Ishikawa.pdf