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Floods affect road infrastructure physically and operationally, increase road user costs and road agencies cost, and eventually isolate communities. The research of the effect of floods on vehicular circulation is mainly focused on the stability of vehicles. There are few studies related to the regime of still water in the trafficability. In still water, the speed flow is low and does not compromise the vehicle stability. In this case, the vehicle’s wading height becomes relevant. This article proposes a procedure to estimate the traffic interruption probability caused by floods in roads, considering the still water regime. The procedure uses the first-order reliability method to estimate traffic interruption probabilities, based on the difference between the probability density functions (PDF) of still water depth (or waterlogging depth) and vehicle wading height. A specific procedure to estimate the PDF of wading height based in the geometric characteristics of light and heavy vehicles was developed. The PDF for water depth was estimated using water level profile simulation software. The procedure was applied in the south of Chile. The PDF of wading height was obtained from a record of 166,155 vehicles tagged in open road tolls. The PDF of waterlogging depth was obtained from discharge records of 10 fluviometric stations. 42 probability curves were obtained for six vehicle classes and return periods between 4 and 500 years. The still water depth obtained for traffic interruption probability of 1,0 varied between 70 and 90 cm for light vehicles and between 110 and 150 cm for heavy vehicles.

Since 2010, a large area of Chile is in a period of severe drought, with impacts on the population and the water resource systems. Therefore, it is necessary to carry out research on drought behavior in Chile, its prediction and monitoring, should be addressed to find suitable measures to reduce its effects. A simple calculation model is presented for the SPI, PPN, DEC and EDI indexes. Based on the hypothesis that these indexes are an indicator of the drought condition in the central-southern area of Chile; the proposed model takes as the only input variable the cumulative number of raining days. The most efficient index for the model is identified, the study is regionalized and temporal and spatial analysis of the model is carried out. A modified index of drought is obtained, based on a simple rainfall day counter. The model represents an efficient method to show a drought event.

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