Letting the Thur river flow, naturally again
The Thur is Eastern Switzerland’s predominant river, flowing from the limestone Alps into the Rhine river on the border with Germany. The name Thur comes from the Indo-European word dhu, meaning “the hurrying one”. And hurrying it does, sometimes spilling over its own banks and flooding adjacent land. Without any natural or artificial retention areas, the river caused at times great havoc. Today the basin benefits from nature-based solutions to absorb the excess water whilst the river flows, and hurries, the natural way again.
Mario Schirmer is the hydrogeologist in charge of the RECONECT project managing the Thur River Basin. He has worked on the restoration of the Thur river for the past 14 years and is no stranger to the challenges and opportunities of river restoration.
“Extreme events such as flooding will only increase in the coming decades due to climate change. The intensity and duration of these extreme events is worrying and require us to invest much more in mitigation strategies, backed by strong legislation and financial commitments”.
Mario Schirmer, EAWAG hydrogeologist in charge of the Thur River Basin restoration project.
The need for political support and adequate funds towards river restoration is something Switzerland has taken seriously. In the age of climate change and biodiversity loss, the Swiss government realised that it is crucial to protect ecosystem health, preserve water resources and maintain flood protection. In 2011, Switzerland revised a law and made the restoration of riverine ecosystems a legal obligation. It further plans to restore 4000 km of rivers in Switzerland by 2090[1].
Early on the Thur riverine populations relied on levees to protect their land, animals and housing. But the floodings increased and became more severe in intensity. The levees were not enough anymore. In 2008, Mario and his team at the Swiss Federal Institute of Aquatic Science and Technology (Eawag) began a large-scale, multi-disciplinary research project to evaluate river restoration based on natural solutions[2]. They focussed on riverine areas the cantonal authorities had bought back from farmers, allowing the river to spill into the floodplain forests which in turn also benefits groundwater recharge and quality.
Yet the floodplains alone were not sufficient to stem the rising flood levels and water once again encroached surrounding lands. This was seen as a huge setback, both financially, ecologically and scientifically. An additional solution had to be found, in nature. This is where the idea of large boulder rocks came in. Thanks to the national legislation and cantonal funding, a company was contracted to deposit large rocks functioning as flood buffers. It worked! Overtime the river retreated to its old channel and the rocks were absorbed by gravel and sand into the riverbed.
Today the flooding is under control thanks to the river having room to move and (over)flow. The project has become a case study for soil scientists, ecologists and hydrologists working together on monitoring and potentially replicating its success. Yet, as Mario stipulates, it won’t be easy as the project benefitted from strong political support and available funds. This is not the case everywhere.
River restoration projects serve as nature-based solutions because they achieve both environmental objectives (e.g. higher biodiversity) and increased social and economic welfare (e.g. providing recreational opportunities and reducing the risk of flooding). Yet, the costs of restoration are often high[3]. A cost-benefit comparison however showed that the Thur river restoration was economically justified and that the Swiss tax payer is willing to pay substantially more for restoration projects at the local level than is even legally required by the existing national policy on river restoration.
“Involving all stakeholders, from local municipalities to farmers to riverine populations, is key in achieving a successful restoration project, and this from the very beginning of the undertaking”
“At the onset of the project management design a thorough feasibility study needs to be undertaken, and obviously working with the contracting offers that are best, not necessarily cheapest”.
Mario Schirmer, EAWAG hydrogeologist in charge of the Thur River Basin restoration project.
[1] Do the societal benefits of river restoration outweigh their costs? A cost-benefit analysis, Journal of Environmental Management, Volume 232, 2019, https://doi.org/10.1016/j.jenvman.2018.11.098.
[2] https://www.eawag.ch/en/department/wut/projects/record-catchment-2012-2016/.
[3] Bergstrom and Loomis, 2017
