Evaluación del peligro de las aguas de avenida en cruces de puentes sobre ramblas: el caso de estudio de la costa murciana (SE de España)

Abstract

Bridges are usually built when traffic or the importance of the road network justifies the cost. Most road bridges are permanent structures and are vulnerable to extreme hydrologic events. Streams, particularly in semiarid regions, can significantly overflow their banks and may change course, defying the bridge’s ability to perform its intended function. This article proposes a way of assessing flood hazards at bridge crossings over ephemeral streams. Two hazard indices associated with floodwaters at bridge crossings have been tested for ephemeral channels on the South-East coast of Spain: a Flood Hazard Index for bridge crossings (FHIBC), and a Geomorphological Hazard Index (GHIBC). FHIBC is based on the exposure and effectiveness of drainage works for dealing with floods of different return period. The second index, GHIBC, integrates parameters related to hydraulic resistance and potential bed erosion in large floods. Variables such as granular bed susceptibility to incision, critical velocity and transitory scouring have previously been estimated based on field data. The results show that FHIBC is an appropriate index for obtaining an overall evaluation of the flood hazard at this crossing type, while GHIBC provides useful information on the main hydromorphological factors which endanger the stability of the bridges over ephemeral streams. The joint implementation of both indices may also be an efficient tool for identifying high-risk crossings and improving the planning of future infrastructures over channels in the study area.