This study aims at evaluating the geographical influences of rice-based protection dykes on floodwater regimes along the main rivers, namely the Mekong and the Bassac, in the Vietnamese Mekong Delta (VMD). Specifically, numerous low dykes and high dykes have been constructed particularly in the upper delta’s floodplains to protect the double and triple rice cropping against the annual flooding. For the whole deltaic domain, a 1D-quasi-2D hydrodynamic model setup was used to simulate seventy-two (72) scenarios of dyke construction development in the context of low, medium, and high floods that occurred in the VMD to examine the effects of different flood magnitudes on a certain dyke construction area. Based on the model simulation results, we established an evaluation indicator, the so-called Geographical Impact Factor (GIF), to evaluate the impacts of zone-based dyke compartments on the floodwater regimes along the main rivers for different kinds of floods. Our findings revealed different rates of influences on the floodwater levels along the Mekong and Bassac Rivers under different scenarios of zone-based high-dyke developments. GIF is a useful index for scientists and decision-makers in land use planning, especially in rice intensification, in conjunction with flood management for the VMD and for similar deltas worldwide.

Populated karst landscapes can be found all over the world, although their natural boundary conditions mostly lead to distinct challenges regarding a sustainable water supply. Especially in developing and emerging countries, this situation aggravates since appropriate technologies and water management concepts are rarely available. Against this background, the interdisciplinary, German-Indonesian joint project “Integrated Water Resources Management (IWRM) Indonesia”, funded by the German Federal Ministry of Education and Research (BMBF), focused on the development and exemplary implementation of adapted techniques to remedy the partly severe water scarcity in the region Gunung Sewu. This karst area, widely known as “Java’s poorhouse”, is located on the southern coast of Java Island and distinctly suffers from the mentioned constraints. Under the aegis of the Karlsruhe Institute of Technology (KIT), the conceptual and technical achievements of the “IWRM Indonesia” joint research project are characterized by a high potential for multiplication not only for karst areas but also for non-karst regions. One of the project’s major accomplishments is the erection of an innovative hydropower-driven water supply facility located in a karst cave 100 m below ground and continuously supplying tens of thousands of people with fresh water. Referring to the plant’s innovative character and the demanding conditions on-site, the implementation was a highly iterative process leading to today’s autonomous operation by an Indonesian public authority. Based on the experiences gained during design, construction, operation and monitoring phase, this paper introduces an implementation approach for adapted technologies as well as a comprising technical and economical assessment of the plant’s operation.

In the presented work, design conditions for breakwaters were derived from offshore climate reanalysis data (ERA5), which were downscaled to the nearshore by two numerical approaches, i.e., SwanOne and Delft3D, for different average and extreme wave and weather conditions. Model validation was performed using in situ measurements. The advantages and disadvantages of both numerical approaches were investigated. Both models showed sufficient accuracy according to measurements in the field, where SwanOne offers a simple and fast calculation method, while Delft3D provides a more complete representation, not only of waves but also current dynamics. However, it requires a much broader amount of input parameters and more complex boundary conditions. Then, SwanOne was applicable to calculate nearshore wave characteristics based on the input parameters extracted from the statistical analysis of long-term ERA5 data. Based on this process, design wave heights and periods at the nearshore were determined for 10- to 100-year return periods. For breakwater design on the west coast of the Mekong Delta, maximum wave heights in a range of 1.1 m to 1.3 m at a distance of 100 m to 300 m could be determined for a return period of 20 years, corresponding to water depths of 2.33 m and 2.88 m, respectively.