Some hydrologic effects of urbanization in Catalan rivers

Studies of the yearly discharge of rivers draining the Catalan Coast, before and after an increase in urbanization within their watersheds, show marked changes in total runoff, peak discharges and lag times between rainfall and runoff. The cumulative curve of annual precipitation shows a steady increase over the years, thus indicating no change in rainfall during the study period. By contrast the cumulative curve of annual runoff shows one or two breaks, corresponding to an increase in runoff during the end of the fifties and the end of the sixties. These periods correspond to pulses of industrial and urban development of the area. The degree of urbanization in 1980-1981 for various basins shows and increase that ranges between two to five times that of 1951-1955. Floods are a common feature in recent years in urban areas, specially in the coastal ramblas, and can be related both to an increase in peak discharges and a shortening of the lag time in the draining of rainfall. These increase in water flow is bound to cause channel changes associated with erosion and sedimentation.