Geometric Modeling: Determining the Largest Lake

During a middle school task, students compare the sizes of Lake Tahoe and Flathead Lake.

Surface seiches in Flathead Lake

Standing surface waves or seiches are inherent hydrodynamic features of enclosed water bodies. Their two-dimensional structure is important for estimating flood risk, coastal erosion, and bottom sediment transport, and for understanding shoreline habitats and lake ecology in general. In this work, we present analysis of two-dimensional seiche characteristics in Flathead Lake, Montana, USA, a large intermountain lake known to have high seiche amplitudes. To examine spatial characteristics of different seiche modes, we used the original procedure of determining the seiche frequencies from the primitive equation model output with subsequent derivation of the spatial seiche structure at fixed frequencies akin to the tidal harmonic analysis. The proposed procedure revealed specific seiche oscillation features in Flathead Lake, including maximum surface level amplitudes of the first fundamental mode in straights around the largest island; several higher modes appearing locally in the vicinity of the river inflow; the "Helmholtz" open harbor mode, with the period approximately twice that of the longest seiche mode, generated by a large shallow bay connected to the main lake basin; and several rotating seiche modes potentially affecting the lake-wide circulation. We discuss lake management problems related to the spatial seiche distribution, such as shoreline erosion, floods, and transport of sediments and invasive species in Flathead Lake.

Surface seiches in Flathead Lake

Standing surface waves or seiches are inherent hydrodynamic features of enclosed water bodies. Their two-dimensional structure is important for estimating flood risk, coastal erosion and bottom sediment transport and for understanding shoreline habitats and lake ecology in general. In this work, we present analysis of two-dimensional seiche characteristics in Flathead Lake, Montana, USA, a large intermountain lake known to have high seiche amplitudes. To examine spatial characteristics of different seiche modes we used the original procedure of determining the seiche frequencies from the primitive equation model output with subsequent derivation of the spatial seiche structure at fixed frequencies akin the tidal harmonic analysis. The proposed procedure revealed specific seiche oscillation features in Flathead Lake including maximum surface level amplitudes of the first fundamental mode in straights around the largest island; several higher modes appearing locally in the vicinity of the river inflow; the "Helmholtz" open harbor mode, with the period approximately twice that of the longest seiche mode, generated by a large shallow bay connected to the main lake basin; and several rotating seiche modes potentially affecting the lake-wide circulation. We discuss the lake management problems related to of the spatial seiche distribution, such as shoreline erosion, floods and transport of sediments and invasive species in Flathead Lake.

Introduced lake trout exhibit life history and morphological divergence with depth

We found that an introduced population of lake trout (Salvelinus namaycush) in Flathead Lake, Montana, USA, exhibited divergent life history, diet, and morphology after the invasion of Mysis diluviana. A correspondence between stable isotopes (δ13C and δ15N) in lake trout muscle and their prey suggests that individual lake trout exhibited depth preferences. Lake trout 451–600 mm total length showed morphological distinctness between shallow (0–25 m) and deep (60–100 m) collections wherein the latter had deeper bodies and larger eyes. Furthermore, these deep lake trout fed more heavily on Mysis, grew slower, and matured at a smaller size. Lack of genetic divergence between depth groups and the rapid divergence of life histories after Mysis invasion suggest a strong role for environment in producing the observed ecotypic variation. Our research supports resource partitioning by depth and diet as a drivers of phenotypic diversity in lake trout, providing insights into the origins of morphotypes and guidance for conservation of native populations.