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Assessing Nature-Based and Classical Engineering Solutions for Flood-Risk Reduction in Urban Streams

Ourloglou Olga, Stefanidis Konstantinos, Dimitriou Elias

Journal of Ecological Engineering

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2020

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Vol. 21, nr 2

46--56

EN

Urbanization of stream ecosystems with the purpose of managing the flash-flood events is nowadays considered responsible for habitat loss and alteration of the natural flow regime with severe implications for the ecosystem functioning. Unsurprisingly, the river scientists have started seeking alternative options inspired from nature for mitigating the flood-risk and maintaining the stream at its natural state. With this article the authors 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 the actions that restore the stream to its natural form (e.g channel widening). The HEC-RAS software was employed to simulate the 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 400 m3/s. The first scenario was based on the current situation of the stream, the second scenario concerned the stream restoration by following the nature-based solutions, while the third scenario was based on the classical “grey” engineering approach of concrete channelization. Unmanned Aerial Vehicle (UAV) photogrammetry methods and the Pix4Dmapper software were used in order to develop a detailed 3D model of the studied reach that accurately captured the current geomorphology. The obtained 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 is much cheaper than the traditional channelization (1.1 mil € vs 5.6 mil €). In conclusion, our findings suggest that the future restoration of urban streams should consider the nature-based solutions since i) they can be effective with regard to the reduction of flood-risk, ii) are cheaper than the traditional “grey” techniques and, most importantly, iii) maintain the natural state of the ecosystem which improves not only the ecosystem functioning but also the aesthetic value within the urban context.

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Ocena warunków hydromorfologicznych cieków miejskich metodą Urban River Survey

Hamerla A M, Trząski L., Łabaj P.

Inżynieria Ekologiczna

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2015

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Nr 41

26--35

PL

W artykule przedyskutowane zostały niektóre aspekty możliwego wykorzystania brytyjskiej metody oceny warunków hydromorfologicznych dla koryt i korytarzy cieków miejskich – Urban River Survey (URS) w warunkach polskich. Aspekty i kryteria URS uwzględniają specyfikę cieku miejskiego, pomijaną w bardziej rozpowszechnionej w Europie metodzie RHS (River Habitat Survey) oraz w przyjętej w Polsce metodzie MHR. Metoda URS może być wykorzystana w klasyfikowaniu cieków wg ich stanu ekologicznego, jak i w budowaniu scenariuszy możliwych działań rewitalizacyjnych. Monitorowanie cieku metodą URS może być ważnym elementem systemu zarządzania lokalną zlewnią miejską.

EN

In the paper some aspects of potential use of the Urban River Survey (URS) method for hydromorphological assessment of urban river channels/corridors in Poland are discussed, includingthe URS aspects and criteria. The URS aspects/criteria take into account the specificity of urban watercourse omitted both in the RHS (River Habitat Survey) which is more prevalent in Europe, and in Polish MHR method. The URS can be used to classify urban watercourses according to their ecological status, as well as in building scenarios of possible reclamation/restoration activities. The watercourse monitoring with the use of URS can be an important element of the local urban catchment management.

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Water quality study of the Condor and Capivara Streams, Porto Alegre Municipal District, RS, Brazil, using epilithic diatom biocenoses as bioindicators

Lobo E.A., Callegaro V. L. M., Wetzel C.E., Hermany G., Bes D.

Oceanological and Hydrobiological Studies

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2004

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Vol. 33, No. 2

77--93

EN

The aim of this work was to evaluate the water quality of two urban streams, Condor and Capivara, in the Municipal District of Porto Alegre, RS, Brazil, by measuring physical, chemical and biological variables. Between May 1999 and August 2000, six field trips were taken to sample five sites distributed along the streams. Multivariate canonical correspondence analysis (CCA) was applied for the complete evaluation of physical, chemical and biological data. It was confirmed that phosphate had the largest impact on ordination and exhibited an evident eutrophication gradient. Mayamaea atomus, Amphora montana, Sellaphora pupula and Cyclotella meneghiniana were extremely abundant under such conditions.