Use of geomatics technologies to evaluate the areal distribution of the soil erodibility factor K in the Chaudiere River watershed.

The integrated modelling system GIBSI simulates soil erosion using the Univ ersal Soil Loss Equation (USLE). The USLE requires the evaluation of the so il erodibility K factor for the studied watershed. This estimate can be dif ficult because it depends on information from soil maps. The use of geomati cs technologies appears to be a good way to manage the physico-chemical cha racteristics of soils and their aerial distribution in the watershed. A met hod for the spatial aggregation of the physico-chemical soil parameters obt ained from published soil surveys was developed and used to calculate, at t he soil polygone level, the K factor for the Chaudiere River watershed (Que bec, Canada). The calculated values of K, for all the surveyed soil polygon es, varied between 0.0043 and 0.0582 t h ha MJ(-1) ha(-1) mm(-1), averaging 0.0236 t h ha MJ(-1) ha(-1) mm(-1) for the watershed. The raster mapping o f these values showed spatial discontinuities at the limits of adjacent soi l counties. Some of these discontinuities were due to the nature and distri bution of soil landscapes on watershed and to the evolution of soil survey techniques between 1957 and 1996.