Assessing Nature-Based and Cassical Engineering Solutions for Flood-Risk Reduction in Urban Streams
Hellenic Open University
Hellenic Centre for Marine Research
Elias Dimitriou   

Hellenic Centre for Marine Research
Data publikacji: 01-02-2020
J. Ecol. Eng. 2020; 21(2):46–56
Urbanization of stream ecosystems with the purpose of managing flash-flood events is considered nowadays responsible for habitat loss and alteration of the natural flow regime with severe implications for the ecosystem functioning. Not surprisingly river scientists have started seeking alternative options inspired from nature for mitigating flood-risk and maintaining the stream at its natural state. With this article we demonstrate the effects of a nature-based solution (NBS) for managing an urban stream based on the use of bioengineering materials (e.g. plants) and the implementation of actions that restore the stream to its natural form (e.g channel widening). We employed the HEC-RAS software to simulate flow and hydraulic components of an approximately 800m long reach of an urban stream under three different scenarios of flood risk management with a design flow set to 400m3/s. The first scenario was based on the current situation of the stream, the second scenario concerned the stream restoration by following nature-based solutions while the third scenario was based on the classical “grey” engineering approach of concrete channelization. In order to develop a detailed 3D model of the studied reach that accurately captured the current geomorphology we used Unmanned Aerial Vehicle (UAV) photogrammetry methods and the software Pix4Dmapper. Our results showed that with concrete channelization the average and maximum flow of the stream increases significantly in relation to the current situation, from 2.48 and 4.88m/s to 9.82 and 11.22 m/s respectively while the average Froude number raises from 0.36 to 1.69 implying super-critical flows. In contrast the NBS scenario retained lower flow velocities and average Froude number similar to those under the current conditions. In addition, a cost estimation analysis for both stream management techniques revealed that the NBS costs much cheaper than the traditional channelization (1,1 mil € vs 5,6 mil €). In conclusion, our findings suggest that future restoration of urban streams should consider nature-based solutions since i) they can be effective with regard to the reduction of flood-risk, ii) are cheaper than traditional “grey” techniques and iii) most importantly maintain the natural state of the ecosystem which improves not only the ecosystem functioning but also the aesthetic value within the urban context.