Geomatic simulation of soil erosion and sediment transport in small watersheds

Soil erosion at various places of a watershed often comes with an excessive quantity of suspended sediments in the rivers. The indirect evaluation of erosion by the measurement of the suspended sediments transported at the wa ter shed outlet makes it possible to have a good idea of the environmental impact of agricultural activities. It turns out, however, that it is essent ial, from the point of view of the water quality management, to be able to evaluate soil erosion and suspended sediment transport in order to identify problematic zones on watershed. This estimate implies the handling of a co nsiderable sum of information to describe the watershed environment and the use of complex mathematical models to simulate the hydrological and sedime ntological processes concerned. The recourse to the data processing models of soil erosion and geographical information systems (GIS) is then essentia l. This article presents the development and the application of a geomatic approach of simulation, which implies the joint use of the hydrological mod el CEQUEAU, the erosion model MODEROSS and the geographical information sys tem IDRISI. More precisely this article presents how the software package C EQEROSS was used to predict the hydrosedimentologic behaviour of a small ag ricultural watershed of Quebec (Canada). The total suspended sedimentary lo ads simulated at the outlet of the Lennoxville watershed reached 27.5 tons and 54.1 tons for the periods 1991-92 and 1992-93, respectively. These valu es are similar to the total sedimentary loads of 30.3 tons and 51.3 tons ob served during these corresponding periods. The obtained results show that t he episodical nature of the suspended sediment transport at the Lennoxville watershed oulet was well reproduced by CEQEROSS. The geomatic approach sug gested is sufficiently user-friendly and reliable to be registered inside a n agroenvironmental management tool.