title: Effects of biofilm on river-bed scour.
abstract: Biofilm acts stabilising river-bed sediments, interfering with particle entrainment and, consequently, preventing bed disturbance. In this paper we present the results of a series of experiments carried out in indoor channels, aimed to understand biofilm alteration of bed material motion and topographic changes in stream channels. We analysed the erosion patterns and bedload rates in non-cohesive sediments in channels colonised by biofilms and compared them to biofilm-free others. All the channels had the same conditions of light irradiance, temperature, slope, and particle size (sand). Discharge and water surface slope were modified to create a range of hydraulic conditions, with pairs of colonised and non-colonised channels subjected to the same flows. We observed that biofilm slightly modified bed roughness and flow hydraulics, but that highly influenced bed disturbance. Biofilm caused bed scour to occur in patches unevenly distributed along the channel length, as a result of localised weaknesses of the biofilm. Once biofilm was ripped up it was transported in chunks, and sand grains were observed attached to these chunks. In non-colonised sediments the erosion was more homogeneous and the formation and movement of bedforms were observed. On average, bedload rates were 5 times lower when biofilm was present. Overall, the protective effect of the biofilm prevented generalised erosion of the channel and delayed the entrainment and transport of sand grains. Results emphasised the important role of biofilm in the incipient motion of bed-material in stream channels; this role may affect the magnitude and frequency of subsequent river bed processes, notably the onset of bedload and associated channel morpho-dynamics.
authors: Catalan Institute for Water Research (ICRA), Science and Technology Park of the University of Girona, H2O Building - C/Emili Grahit, 101, 17003 Girona, Catalonia, Spain; Fluvial Dynamics Research Group -RIUS, University of Lleida, Av. Alcalde Rovira Roure, 191, 25198 Lleida, Catalonia, Spain. Electronic address: gpique@icra.cat.
authors: Gemma
authors: G
authors: Piqué
authors: Fluvial Dynamics Research Group -RIUS, University of Lleida, Av. Alcalde Rovira Roure, 191, 25198 Lleida, Catalonia, Spain; Forest Sciences Centre of Catalonia, Ctra Sant Llorenç de Morunys, Km. 2, 25280 Solsona, Catalonia, Spain. Electronic address: dvericat@macs.udl.cat.
authors: Damià
authors: D
authors: Vericat
authors: Catalan Institute for Water Research (ICRA), Science and Technology Park of the University of Girona, H2O Building - C/Emili Grahit, 101, 17003 Girona, Catalonia, Spain; GRECO, Institute of Aquatic Ecology, University of Girona, Campus de Montilivi, 17003 Girona, Catalonia, Spain. Electronic address: sergi.sabater@udg.edu.
authors: Sergi
authors: S
authors: Sabater
authors: Catalan Institute for Water Research (ICRA), Science and Technology Park of the University of Girona, H2O Building - C/Emili Grahit, 101, 17003 Girona, Catalonia, Spain; Fluvial Dynamics Research Group -RIUS, University of Lleida, Av. Alcalde Rovira Roure, 191, 25198 Lleida, Catalonia, Spain. Electronic address: rbatalla@macs.udl.cat.
authors: Ramon J
authors: RJ
authors: Batalla
mesh_terms: D018441:Biofilms; D019015:Geologic Sediments / Q000032:analysis*; D057446:Hydrodynamics; D045483:Rivers; D013030:Spain
keywords: Bed roughness; Bedload; Biofilm; Erosion patterns; Indoor channels; Sand