Author(s): S. Paola Bianucci; Ismael Ait-Chaib; Belen Quinteiro Seoane; Laura Fernandez Nunez; Juan Ignacio Nino; Alvaro Sordo-Ward; Jose Manuel Perez Quintanilla

Linked Author(s): Álvaro Sordo-Ward, José Manuel Pérez Quintanilla

Keywords: River flood management; Controlled flooding areas; Urban floodplains

Abstract: Frequently, urban development causes a more accused anthropic pressure over the riverbanks and the associated river flooding areas. Consolidated urban areas hinders the implementation of direct structural measures such as widening the cross section of the watercourse due to, mainly, their socio-economic impact. To overcome this problem, soft structural measures may be considered. Among these types of measures, the implementation of areas that favor controlled flooding may be efficient. Additionally, these areas can be converted into public parks and green spaces. Storage areas have been used to attenuate urban floods associated to storm events (considering the concept of sustainable urban drainage, SuDS). In this study, we present a case study in which the storage area was used for flood river management. Water Authority in Galicia is applying a novel approach to flood risk management by developing detailed plans for particularly complex floodplains. Great effort is being made to involve Public Administrations at different levels and public participation. In this context, the Flood River Management Specific Plan for the potential significant flood risk area of Lagares River (Vigo, Spain) was carried out. Implementation of controlled flooding areas was one of the measures analyzed. The controlled flooding zone projected consists in a storage area equipped with a lateral weir which regulates the entry and retention of water. A drainage system permits the return of the flow from the reservoir to the river channel. The storage area has an extension of 7.3 ha. To ensure the retention and attenuation of river flood hydrograph, interconnected ponds are design in the inner zone of the storage area generating a circuit that enlarges the travel time of the wave. We modelled the Lagares River (Vigo, Spain), for the current situation and implementing the controlled flood area, using HECRAS (1D). For design purpose, we considered two hydrographs with return periods of 10 (T10) and 100 (T100) years respectively. We obtained a peak flow reduction of 15.7% (T10) and 14.1% (T100). Finally, we ran a Cost (C) – Benefit (B) analysis to assess the efficiency of the proposed solution. We assumed a period of analysis equal to 50 years. For this period, we obtained a very high B/C relationship due to a reduction in damage cost of 26.8 M€. Consequently, storage areas may be socially accepted and environmentally sound providing an efficient solutions to mitigate flood river risk in urban floodplains.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022538

Year: 2022