The monitoring of the suspended sediment concentration (SSC) in rivers is essential for the management and control of the quality of waterways. Moreover, the knowledge about the SS sources is important to establish a good support framework to measure and model the solid flux. The study was performed on the Moulinet and the Oir streams watershed, in Basse- Normandie region. The watershed area is 4,53 km2 and 87 km2 respectively. In these catchments, agriculture is moderately intensive, with mostly dairy farming. The main objectives are: 1) to measure and describe the temporal dynamics of the SSC, and 2) to relate these dynamics with the SS origins, the climatic determinants and the stream's order. In the Moulinet stream, sediments deposited in the bed are good classified with a grain median between 0,6 and 10 mm depending on location. The shield's critical parameter, τ*cr, is 0,052. With this critical parameter sediment with a median diameter of 8 mm will be resuspended for a discharge greater than 75 l/s. The laboratory experimentation showed that turbidity varies linearly with the SSC for a given particle size. The turbidity increases more quickly with the concentration since the particles are fines. The ratio Turbidity/SSC is referred to "specific turbidity", which essentially depends on the particle size and is higher when particles are fines. The specific turbidity varies linearly with the inverse of the mean particle diameter. The specific turbidity of a mixture is the sum of the specific turbidity associated with each size fraction, weighted by their proportion in the mixture. The specific turbidity is comparable or slightly higher in the field and laboratory. Suspended sediment sources in the Moulinet were identified and quantified by different approaches: examine the relationship SSC-discharge, statistical analysis and modeling. The supply of sediment to stream comes from: 1) areas near the stream and the stream's bank erosion. This stock is easily mobilized in late summer, resuspended in the autumn and is less important in the winter; 2) watershed erosion. This source causes the very high of solid flux during certain months of October and May could be due to hydrological favorable condition to erosion, or related to timing of land use and agricultural practices in the watershed, either extreme climatic condition. The hydrological response of the two basins seems generally the same type, despite the size of the watershed and the order of the stream increase. However, in the flood scale, to priori similar rainfall, the Moulinet watershed is more active than the Oir, with a response time shorter to rain. The specific annual solid flux calculated on the Moulinet is higher than on the Oir. In these two streams there is a large dispersion of the relationship between solid flux, Qs , and the daily average water discharge, Q. The relationship is not represented by the only power law Qs = aQb.
