Dissertation
Lacustrine boundary mixing and lateral transport driven by internal waves
Washington State University
Doctor of Philosophy (PhD), Washington State University
01/2022
DOI:
https://doi.org/10.7273/000004372
Handle:
https://hdl.handle.net/2376/124823
Abstract
This dissertation describes mixing and transport in a small lake, with an emphasis on processes influenced by basin-scale internal waves (i.e., internal seiches). Seiche-induced variations in turbulence, bottom mixed layer entrainment, and offshore advection from the sloping bottom boundary layer (BBL) were evaluated with measurements from the metalimnion, using pulse-coherent acoustic Doppler current profilers and thermistor strings. Over an initial 74-day deployment, estimates of turbulent dissipation, and two different models of mixing efficiency, suggest that >80% of near-bed turbulent buoyancy flux occurred during the downslope flow phase of the internal seiche (seiche period 10–24 hours). During downslope flow, thin bottom mixed layers formed and slowly thickened over hours. Mixed-layer thickening was consistent with a newly developed model, in which the effect of strain-induced periodic stratification (SIPS) on entrainment is proportional to the ratio between layer thickness and a modified Monin-Obukhov length that quantifies a SIPS-induced buoyancy flux. Transitions to the upslope flow phase of the internal seiche were marked by arrivals of sharp, non-breaking (nearly horizontal) cold fronts, which displaced the mixed layers that had formed during the previous downslope phase, lifting them from the bed. The detached mixed layers then flowed offshore above fronts. A second deployment partially resolved the extent of the resulting jet-like intrusions as they transported water offshore from the BBL, along the thermocline, and revealed seiche-coherent vertical propagation from the bed to the base of the surface mixed layer. When averaged over multiple seiche cycles, the separated jets were responsible for a substantial mean lateral flux (1.9 m3s-1, comparable to river discharge into the lake) into the interior at thermocline depths. Mean lateral flux estimates from both ends of the lake suggest flushing times of 2–3 days in the thermocline and overlying surface layer. This work is described by three separate manuscripts herein.
Metrics
Details
- Title
- Lacustrine boundary mixing and lateral transport driven by internal waves
- Creators
- Jeffrey R Nielson
- Contributors
- Stephen M Henderson (Advisor)John A Harrison (Committee Member)Kevan B Moffett (Committee Member)Danielle J Wain (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Environment, School of the (CAHNRS)
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 118
- Identifiers
- OCLC#: 1365390707; 99900883134601842
- Language
- English
- Resource Type
- Dissertation