The Arc River (French Alps) undergoes consistent suspended sediment transport, therefore hydroelectric facilities are affected by high rates of sedimentation. To clarify suspended sediment transport in this river a tracing experiment has been set in March 2013. Flow discharge was near the minimum instream flow. A known volume of fluorescent tracer (RhodamineWater Tracer) was injected (Dirac- type pulse) in the river and monitored over 7km downstream using immerged field fluorometers located in 5 measurement sites. On every site, measurements show a clear pattern of tracer transport which shape evolves from upstream to downstream sites, showing the advection-dispersion process. Additional monitoring of the flow (with water level and surface radar velocity measurements) was done during the tracer experiment. Additionally, a 1D advection-dispersion and hydrodynamic numerical model (MASCARET COURLIS, part of TELEMAC MASCARET SYSTEM) was compared with in-situ measurements. Constant dispersion coefficients are tried out as well as different formulae depending on hydraulic parameters. The numerical model well reproduces the data. However, approximation due to the one dimensional approach limited the whole comparison with field data. Using, the measurements on both sides of the river bed, a discussion of the mixing dynamic is proposed.