Post-Evaluation of Flood Hazards Induced by Former Artificial Interventions along a Coastal Mediterranean Settlement

Abstract

Inappropriate artificial activities can escalate the frequency, the intensity, and the magnitude of floods and aggravate their aftermath. Additionally, urban sprawl is responsible for increasing the manifestation of flood events in coastal areas. In this study, the effects of diachronically formulated artificial stream-channel modifications and registered urban expansion on flood hazards were quantified. Initially, land-use changes were monitored over time and a detailed field topographic survey was performed. The peak discharge for a 50-year return period storm event was found to be equal to 42.3 m3/s, as computed by the rational method. A steady flow analysis with a mixed flow regime was then performed so as to compute the water velocity and surface runoff elevation at 49 discrete cross sections for the years of 1945, 1981, and 2009, whereas the inundation extent was found equal to 12,208, 10,519, and 9,530 m2 for the same years by implementing another model. Although the water level and inundation extent were respectively reduced by 5.5 and 9.2% in 2009 compared with that in 1981, more houses had been constructed on the riverbed, and thus the flood hazard was greater in 2009 than in 1981. Despite the fact that the flood area was larger by 16.1% in 1945 compared with 1981, the flood hazards were diminished in 1945 because the households were settled more than 78 m away from the stream centerline. Thus, in 1945, the stream would have successfully sustained flood events even with a 50-year recurrence period.