*Water* **2018**, *10*, 1646

*Water* **2018**, *10*, 1646

In addition to the dredging of existing channels, river widening is increasingly seen as a "nature-based solution". River widening in lower stretches of a river basin decreases peak water levels, as the river is provided with "more room" to discharge its flood waters [86]. In addition, such measures restore both ecological values and biodiversity [87]. A U.K. cost estimate for widening a small rural river system by excavating river floodplains varies between \$4.5 and \$18/m<sup>3</sup> [81], mainly for excavation.

An example of a large-scale river widening program is "Room for the River" in The Netherlands [86]. This program entails 35 projects along the lower branches of the river Rhine, and the main goal is to enhance the maximum discharge capacity from approximately 15,000 to 16,000 m3/s. Each of the individual projects address one or more measures that lower the river bed through excavation, setback of dikes, or widen the (side-) channel (s) (Figure 3). The total investment cost of this project is around \$2.64 billion [82]. Some projects within the program, such as those near the city of Nijmegen, are relatively expensive, as they involve costly engineered protection measures, which were implemented in a densely populated urban environment [82].

**Figure 3.** Measures applied in the "Room for the River" project in The Netherlands [88].
