Effect of Peri‐urban Development and Lithology on Streamflow in a Mediterranean Catchment

Predicting the impact of urbanization on the hydrology of peri-urban catchments remains a challenge. Using data from nine streamflow gauges installed in a small Portuguese catchment, this study investigates the streamflow responses over a three-year period. The catchment comprises unique nested sub-catchments, characterized by (1) varying proportions of non-urban land-use (17-97%) and impermeable surfaces (6-36%), distances between the urban areas and the stream network, and storm drainage systems (piped vs dispersed); and overlying distinct lithologies consisting of sandstone and limestone. The results show that in the peri-urban catchment (39% urban and 22% impervious surfaces), most water infiltrated and annual storm runoff varied between 9-13% of rainfall. In urban sub-catchments (≈50% urban), 29% of rainfall became storm runoff on sandstone and 17% on limestone. In sub-catchments with more than 80% forest, storm runoff coefficients were averaged 6% independent of the lithology. Sub-catchments with storm runoff drainage systems and downslope urban areas had shorter response times (<20 min) than dispersed urban sub-catchments, in which part of the runoff infiltrated, and the response time was up to 1h. Baseflow contributed between 25-33% upstream and 37-38% downstream of the sandstone total runoff, but was less than 5% in limestone areas independent of location. Hydrological impacts of urbanization may be minimized in planning through disconnecting the urban areas from the stream network thereby enabling runoff from impervious areas to infiltrate into the soil in downstream forest patches before reaching the stream.