Author(s): Patricio Bohorquez; Francisco Jose Perez-Latorre; Raquel Jimenez-Melero; Gema Parra-Anguita

Linked Author(s): patricio bohorquez

Keywords: Guadalquivir basin; Distributed hydrological modelling; IBERPLUS; Saint-Venant; Nature-based solution

Abstract: In this work, we quantify the hydrological effects of implementing natural measures for flood management and prevention of soil losses in a steep-slope Mediterranean catchment subject to climate change. The development of extreme hourly rainfall events in the last decade has led to unprecedented runoff depth and streamflow that can only be attenuated with a valid land management policy at the catchment scale and channel and floodplain restoration at specific sites. We seek to find optimal measures that minimise the interventions. Among others, we consider temporary wetland, barriers in gully or torrent, fascine, irrigation pond, pools and reconstruction of part of the existing artificial channel by green engineering methods. We present numerical results for rainfall-runoff processes and river flows using the distributed hydrological-hydraulic model Iber+ (https://www.iberaula.es/), both in the present and intervened scenarios. We use a sub-metric grid size to represent the geometry of the nature-based measures in the digital elevation model accurately. The implementation of different soil conditions caused by various agricultural practices in soil management is accounted for by increasing hydraulic resistance. The numerical simulations rely on the two-dimensional Saint-Venant equations, which were solved in a graphics processing unit (GPU) to deal with the massive computational mesh. High-resolution numerical simulations show the benefits of the selected nature-based solutions for olive orchards, which can be straightforwardly applied in other Mediterranean catchments. In the current climate change scenario, overland flows have increased flow depth and velocity because of soil water repellence, magnifying the impacts of the higher precipitation intensity. The simulation reproduces the water flow along the open channel that should protect the urban area from flooding. However, the increase in discharge led to erosion and overtopping channel failure. The severe damages in the hydraulic infrastructure are explained in terms of the flow depth and velocity magnitude. The numerical simulation also captures the urban flood across the streets, as observed in reality. In the modelled scenario with nature-based solutions, the hydrograph shows the expected delay of concentration-time and attenuation of the peak water discharge. Modifying the existing channel near urban areas and restoring the natural river course are required. Temporary wetlands ahead of artificial ponds serve as sediment traps, increasing water quality and availability for irrigation purposes in the semi-arid basin under study. Another advantage is that naturalised ponds can act as reservoirs of biodiversity, ecological corridors and carbon sinks. Overall, the suggested interventions contribute to interrupting surface flows of water and sediment, increasing soil infiltration, storing water and slowing water by raising resistance to its flow. This work was supported by “Programa Operativo FEDER 2014-2020” and by “Conserjería de Economía y Conocimiento de la Junta de Andalucía”.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221053

Year: 2022