Year of Award

2020

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Geosciences

Other Degree Name/Area of Focus

Water-Energy-Food Nexus

Department or School/College

Geosciences

Committee Chair

Dr. Andrew C. Wilcox

Commitee Members

Dr. Marco Maneta, Dr. Douglas Brinkerhoff

Keywords

Fluvial Geomorphology, Magdalena River, WEF NEXUS, Hydropower, 10Be Cosmogenic Nuclides, Remote Sensing

Publisher

University of Montana

Subject Categories

Data Science | Earth Sciences | Geomorphology | Hydrology | Sustainability

Abstract

The Magdalena River Basin of Colombia has a globally relevant sediment flux, however, studies of the sediment regime in the basin are limited in scope. This knowledge gap limits application of understanding of sediment dynamics to hydropower decision making. To close this gap, we implemented a sediment budget framework to quantify the impacts of hydropower development in a 118,000 km2 portion of the Magdalena River basin. We informed this framework with analysis of background erosion rates derived from 10Be cosmogenic nuclides and modern sediment fluxes derived from monitoring and optical remote sensing. We standardized these data to spatially averaged denudation rates and found that background denudation rates range from 331 to 740 t km-2yr-1 with a mean of 571 ± 101 on tributaries and 358 ± 45 on the mainstem. Meanwhile, modern denudation rates range from 206 to 3415 t km-2yr-1 with a mean of 852 ± 804 on tributaries and 405 ± 206 on the mainstem. Averaged across sites, denudation rates were higher in tributary watersheds than on the mainstem Magdalena, and modern denudation rates were higher than background denudation rates, but these differences were not statistically significant. Modern sediment fluxes on the mainstem Magdalena increase moving downstream; however, at a site to reach scale, background denudation rates were higher than modern values. Over the past three decades, mainstem sediment fluxes have decreased despite the potential inputs from the 1985 Nevado del Ruiz eruption. To link our understanding of sediment dynamics to evaluation of dam impacts, we tested two end-member hydropower development scenarios with equivalent generating capacity and found that development on the mainstem would trap more sediment than on tributaries. Equivalent tributary development scenarios would require 2-9 dams with varied impacts on the downstream sediment balance. The data and framework that we present provide valuable information about sediment dynamics that can be used to inform hydropower decision making in Colombia and a pathway for decision making when long-term field-based monitoring data of sediment fluxes are not available.

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© Copyright 2020 Luke H. Fisher