Water retention through restoration of the sponge function of drained soils

Natural Water Retention through restoration of the ‘sponge’ function of currently drained soils in the middle-mountains of the Rhine basin is a locally applied nature-based solution to flood mitigation with potential impacts at basin scale. We argue that the benefits of the proposed solution are not only local, but will also favour end-users further downstream. This solution fits a systems approach and contributes to achieve water, agriculture and nature policy objectives as well as delivering societal benefits such as recreation and carbon capture.
Technology validated in lab.
Basic technological components are integrated to establish that they will work together. This is relatively “low fidelity” compared with the eventual system. Examples include integration of “ad hoc” hardware in the laboratory.
Whereas the terms “technical readiness” and “prototype” allow a fairly clear guideline on how to describe the stage of a technical project, they are less applicable to describe the level op development of a nature-based solution. That being said: we strongly feel our concept is at Technical Readiness Level 4 and perhaps even higher because the following crucial elements to allow a scale-up are available: - several field projects in which the positive effects are demonstrated on a local scale (several Waterboards are implementing the concept on local scale for local aims) - a conceptual framework, GIS research and first hydrological calculations which, at the very least, make it plausible that upscaling of the approach will not only translate into more local effects, but also has a positive impact (on nature, climate resilience, flood control) basin-wide. Being able to better demonstrate the latter is crucial to harness financial, policy and political support on a national or even international level. In fact, our project proposal aims to reach this tipping point: from local application for local purposes to (multiplied) local application for (inter)national purposes.

How does it work?

The most suited location for restoring the natural sponge function is at the foot of slopes in U-shaped valleys. Removing drainpipes and ditches would slow down the runoff response of a much larger area than the space needed for the measure itself. Calculations for local catchments in the Mosel basin (the case study area) shows potential for local peak reductions of 5 – 8 % in the tributaries to the Rhine, and provide partial evidence for the hypothesis that natural retention can result in substantial reduction of flood peaks. Critical to bridging the gap between our innovative approach and the end-users is to provide more clarification regarding the location and scale of implementation as well as the expected effects of the measure.