Internal seiche pumping between sill-separated basins

Abstract

Abstract Despite their close proximity and similar dimensions (∼ 200m deep × 10km long × 2km wide) the two eastern basins of Lake Lucerne, Gersauersee and Urnersee, exhibit considerable differences in their internal behaviour, particularly during late winter and spring. The two lakes are separated by a small intermediate basin (∼ 120m deep × 4km long × 1km wide) with sills of approximately 90m depth at each end. We report results of a field program conducted over the period February—May, 1988, when observations were obtained from weekly CTD transects and from three thermistor string/current meter moorings deployed for two months, one near each sill and the third at the southern end of Urnersee near Fluelen. During the observation period the stratification, relative surface to bottom density difference, Δρ/ρ, was 12 × 10−6 in Gersauersee and 4 × 10−6 in Urnersee. Following wind events a large amplitude internal seiche in Gersauersee (vertical excursions of ∼50m and period ∼60 hours) effectively pumpe...