Parameters influencing run-off on vegetated urban soils: A case study in Marseilles, France

In urban areas, episodes of extreme precipitation may generate run-off floods, but urban soils are seldom considered in spatial planning documents. Our aim was to assess the infiltration of vegetated urban soils and to identify the soil parameters affecting infiltration in order to explore the potential of these soils for run-off mitigation under a Mediterranean climate with extreme precipitation episodes. We compared vegetated soils in the urban zone of the Marseilles' 16th district (France) either lying on former clay quarries or file factories (T) or not (NT) and with different land-uses. We used a simplified method to measure field saturated hydraulic conductivity (K-fs), measured penetration resistance in the first 0.15 m (Q(d)) and analysed physico-chemical properties in the first horizon. Levels of run-off production were estimated according to Kfs and an adaptation of USDA Hydrologic Soil Groups. All soils were Technosols or Anthrosols regardless of their prior history. We found that land-use history influenced K-fs, with T soils and soils with current vegetated land-use younger than 13 years having lower K-fs than NT soils and soils with land-use older than 13 years. Soil organic matter content influenced K-fs positively when soils were young, while vegetation cover and penetration resistance (most of the soils had Q(d) > 2 MPa) had not a clear effect on K-fs. Overall, combining K-fs and soil depth, 14.3% of the T soils and 84.6% of the NT soils had low levels of run-off production. It is therefore recommended that 1) Technosols or Anthrosols should be characterised for their unique physico-chemical and physical properties but also for their land-use history, and 2) the infiltration of these soils should be considered in spatial planning documents.