Sediment source and discharge variability in a small subarctic nival catchment

Discharge, water routing and suspended sediment transport were monitored in a small subarctic nival catchment in North-West Finnish Lapland for two successive snowmelt seasons (1983 and 1984). The study region is in a seasonal ground frost environment with flow in the smaller rivers occurring for approximately 6 months of the year. Collection of short interval, long duration data series of discharge, electrical conductivity, suspended sediment and air temperature at two sites, and regular spatial sampling of suspended sediment and electrical conductivity throughout the river catchment provide an understanding of both the hydrology and sediment supply characteristics. Regression, autocorrelation and cross correlation statistical techniques are employed to aid interpretation of the data series, in terms of catchment processes. Emphasis is placed on the dynamic snowmelt season, when approximately 65% of annual discharge and 95% of the annual suspended sediment load are recorded. Suspended sediment concentrations show a very complex relationship with discharge, with suspended sediment concentrations lagging behind discharge for between 2 and 42 hours during the spring seasons. Explanation of the observed pattern is sought from studies of sediment sources, both within the river channel and on the catchment slopes, and the relationship with the seasonally frozen ground. The routing of snowmelt waters as overland or subsurface flow is largely determined by ground frost conditions. Ground frost measurements, the interpretation of the change in electrical conductivity values through time, and the use of a simple mixing model, allow the transient hydrological development of the river catchment to be traced as the thaw seasons progresses. The hydrological and sediment supply characteristics of the climatically transitional subarctic study area are compared to those of the more climatically extreme arctic permafrost environment and to those of the less climatically extreme cool temperate seasonal frost environment. (D71907/87)