Date of Award

Fall 12-16-2022

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Department

Civil Engineering

Advisor

Kimberly Huguenard

Second Committee Member

Lauren Ross

Third Committee Member

Kelly Cole

Abstract

Tidal rivers are landward portions of estuarine systems constituting the union between coastal, tidally controlled settings and rivers, where fluvial processes dominate. In these reaches, river discharge (mean flow) and tides are the two most important mechanisms in controlling geophysical flows. The processes governing water levels and current amplitudes in tidal rivers are highly nonlinear and modulated by external forcings- thus requiring sophisticated techniques for accurate prediction and forecasting. Physical oceanographers and estuarine physicists tend to limit their study area to the maximum extent of the horizontal tide (salinity intrusion), not the most landward point influenced by tidal water levels. This is in part because landward reaches are complicated by freshwater tributary inputs, tidal reflection, abrupt hydrographic changes, and backwater dynamics. Understanding river-tide interaction in tidal rivers is important for geomorphology as this synergism impacts salinity intrusion, sediment transport, pollutant fate, channel bifurcation, and deltaic deposition. This thesis aims to satisfy two objectives: (1) to characterize the Penobscot River Estuarine (PRE) system and present field measurements collected in the tidal river section near the extent of salinity intrusion; and (2) to demonstrate the mechanism creating unexpected overtide patterns near the flood limit. To accomplish these objectives, long-term water levels, meteorological, and river discharge datasets are used in conjunction with measurements collected during a field campaign conducted on September 21st, 2021. The results of this research effort reveal the modulations of the D2 tidal species with respect to mean flow and the emergence of hydrographic tidal reflection as a mechanism for the generation of D6. The discussion presents a theory explaining momentum transfer to the D6 band under high mean flow conditions, where contributions from quadratic friction are known to decrease. This has implications in sediment transport, backwater dynamics, and longitudinal shifts of river-tide dynamics.

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