Effectiveness of Nature-Based Solutions in Mitigating Flood Hazard in a Mediterranean Peri-Urban Catchment

Carla S.Ferreira,Georgia Destouni,Zahra Kalantari,Milica Kasanin-Grubin,António J.D Ferreira,Sandra Mourato

doi:10.3390/w12102893

Abstract

Urbanization alters natural hydrological processes and enhances runoff, which affects flood hazard. Interest in nature-based solutions (NBS) for sustainable mitigation and adaptation to urban floods is growing, but the magnitudes of NBS effects are still poorly investigated. This study explores the potential of NBS for flood hazard mitigation in a small peri-urban catchment in central Portugal, prone to flash floods driven by urbanization and short but intense rainfall events typical of the Mediterranean region. Flood extent and flood depth are assessed by manually coupling the hydrologic HEC-HMS and hydraulic HEC-RAS models. The coupled model was run for single rainfall events with recurrence periods of 10–, 20–, 50–, and 100–years, considering four simulation scenarios: current conditions (without NBS), and with an upslope NBS, a downslope NBS, and a combination of both. The model-simulation approach provides good estimates of flood magnitude (NSE = 0.91, RMSE = 0.08, MAE = 0.07, R2 = 0.93), and shows that diverting streamflow into abandoned fields has positive impacts in mitigating downslope flood hazard. The implementation of an upslope NBS can decrease the water depth at the catchment outlet by 0.02 m, whereas a downslope NBS can reduce it from 0.10 m to 0.23 m for increasing return periods. Combined upslope and downslope NBS have a marginal additional impact in reducing water depth, ranging from 0.11 m to 0.24 m for 10– and 100–year floods. Decreases in water depth provided by NBS are useful in flood mitigation and adaptation within the peri-urban catchment. A network of NBS, rather than small isolated strategies, needs to be created for efficient flood-risk management at a larger scale.

Highlights

The growing global population is increasingly living in cities and this trend is expected to continue, with projections indicating that more than 60% of people globally will be living in urban areas byWater 2020, 12, 2893; doi:10.3390/w12102893 www.mdpi.com/journal/water2030 [1]
For the Drable sub-catchment (Figure 1), the goodness-of-fit is highly acceptable according to all four evaluation criteria (NSE = 0.75, root mean square error (RMSE) = 0.07, mean absolute error (MAE) = 0.05, R2 = 0.77; Table 2), but the predictive performance of the model is only acceptable according to RMSE (0.01–0.10) and MAE (0.00–0.06)
This paper investigates the flood hazard in Ribeira dos Covões peri-urban catchment, where floods driven by intensive rainfall events have been recorded and enhanced by urbanization

Summary

Introduction

The growing global population is increasingly living in cities and this trend is expected to continue, with projections indicating that more than 60% of people globally will be living in urban areas byWater 2020, 12, 2893; doi:10.3390/w12102893 www.mdpi.com/journal/water2030 [1]. Urban floods affect a large number of people worldwide, causing human fatalities and significant damages [6]. The magnitude of the hydrological changes is affected by several biophysical parameters, such as soil type, topography, the percentage of sealing and the spatial heterogeneity of the urban features [11,12]. These parameters influence the heterogeneity of rainfall-runoff dynamics and the connectivity of water fluxes within catchments [11]. Intensive rainfalls lead to high and quick runoff generation, and comprise a major cause of urban floods, together with failure of storm drainage systems [13]

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