Rationale:

Flooding continues to be the most lethal and one of the most damaging natural hazards worldwide. "The search for solutions needs to draw upon the talents and innovative ideas of scientists, engineers, and societal leaders worldwide to overcome traditional and nationalistic paradigms that have so far been inadequate to meet these challenges. 

Introduction:

In July 2023, eight transdisciplinary US graduate students and several mentor professors participated in a two week field excursion to California, Germany, and the Netherlands. Our advanced studies institute was convened by World Water at UC Davis, in partnership with IHE Delft and supported with funds from the National Science Foundation’s International Research Experiences for Students (IRES) program.  While visiting the Rhine River Basin in Germany and the Netherlands and the Sacramento River Basin in California, we met with flood managers, toured flood management infrastructure, and learned about the people and ecosystems impacted by flooding. Our objective: study transboundary flood risk management paradigms to identify parallels and global lessons for enhancing flood risk mitigation and the protection of vulnerable communities.With a length of 1233 km, the Rhine River starts in the Alps and passes through nine countries before emptying into the North Sea, making it one of the largest and most important rivers in Europe. The Rhine River has a rich history as a vital transportation route and still serves that role today, with a deep dredged channel allowing boats passage. The river is prone to seasonal flooding, which has caused significant damages to infrastructure, property, and human lives, most recently in 2021. Over the years, various flood risk management measures have been implemented along the Rhine to mitigate these risks and safeguard surrounding communities. Flooding along the Rhine has been tackled in a combination of structural and non-structural measures. Structural measures include the construction of dams, levees, and flood control channels, while non-structural measures refer to land use planning, floodplain zoning, and ecosystem-centered methods. Transboundary cooperation and active stakeholder engagement are essential for effective flood management decisions in the shared catchment. 

The Sacramento River is located in northern California in the United States. Compared to the Rhine River, the Sacramento is notably smaller. The Sacramento River serves as a valuable source of agricultural and municipal water. Precipitation in the Sacramento Basin is highly seasonal, primarily falling in the winter months while water demand is highest during the summer growing months. Additionally, the region experiences a boom and bust cycle of water availability, with drought years intermixed with wet years. Therefore, water is stored in many dams and reservoirs within the catchment. Similar to the Rhine, heavy flooding remains a complicated problem that has seen a necessary evolution of management strategies including structural and non-structural measures.

While the Sacramento and Rhine River basins both crucially support human and ecological communities, they vary in scale, hydrologic usage, and flood management approaches. The larger Rhine River basin is home to 54 million people, an order of magnitude greater than the 2.8 million residents in the Sacramento basin. The dominant water use also differs between the two basins, with the Rhine used primarily as a riverine transportation corridor while the Sacramento primarily serves as a source of agricultural and municipal water supply. Consequently, the Rhine River has very few dams so as to remain navigable while the Sacramento River has many dams to store water for downstream use.  For all their differences, both regions are prone to heavy seasonal flood events that have high potential economic effects and loss of life. Comparing the evolution of flood mitigation activities over time across both settings allows us to break down flood management paradigms and better prepare for a changing future. Both catchments exemplify the ongoing challenges and opportunities in managing a vital waterway in a highly populated and dynamic region. By implementing innovative approaches and incorporating lessons learned from past experiences as well as other basins, communities in the Sacramento River Basin can better understand what has worked in the past, and what may work in the future.