Electronic Theses and Dissertations

Date

2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Civil Engineering

Committee Chair

Claudio I Meier

Committee Member

Farhad Jazaei

Committee Member

Roger Meier

Committee Member

Daniel Larsen

Abstract

The movement of river water into subsurface, near-streambed sediments and its return to the main channel after relatively short travel pathways is known as Hyporheic Exchange Flow (HEF). Hyporheic exchange brings both solutes and particles into high specific surface area environments, where they suffer biogeochemical transformations which impact a streams water quality and ecology. These processes, which are the basis for the self-purification capacity of river systems, depend on the quantity and travel time of flow within the sediments. Most previous research has focused on the net, larger-scale exchange processes between stream water and sediments, but not on the flow within the sediment itself. This work aims to depict travel times of HEF in sediments at high spatial and temporal resolutions, combining realistic physical models and high-resolution measurements of hyporheic flow. We performed a series of laboratory experiments to depict actual HEF travel times, using heat and solute tracers in a one-dimensional, forced convective column, for three different porous materials. Innovative, inexpensive sensors were designed and fabricated to measure electrical conductivity, obtaining solute breakthrough curves (BTCs) in real-time, at high temporal and spatial resolution, using a conservative solute tracer. Thermal BTCs were obtained from using a heat tracer in the same experiments and conditions, using temperature loggers. Solute and thermal BTCs were consistent and highly repeatable under the same conditions. Travel times were estimated from both solute and thermal BTCs based on the average lag times between successive BTCs. Estimated travel times varied by material type with results showing that travel times using heat tracers were lower than those using solute tracers. One-dimensional heat and solute transport equations were modeled numerically using the finite differences technique. Collected BTCs were used to calibrate the model and estimate material properties (i.e., porosity and thermal dispersivity) and effective velocity. The applicability of using heat and solute tracers was also tested and compared in a three-dimensional configuration to mimic flow conditions in river bar sediments. This research enriches the knowledge of HEF travel time estimation and will have impact on its applications.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to ProQuest

Notes

Open Access

Download

Share

COinS