Modeling stream evolution and its consequences for watershed scale pollutant loading
Date
2018
Authors
Lammers, Roderick W., author
Bledsoe, Brian P., advisor
Arabi, Mazdak, committee member
Nelson, Peter, committee member
Rathburn, Sara, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Throughout the world, streams are degraded due to impaired water quality and erosion and sedimentation caused by hydrologic and sediment imbalances. These two issues are linked. Channel erosion not only damages stream habitat but can be a significant source of fine sediment and nutrient pollution in watersheds. Phosphorus in particular is common in streambanks and when these soils are mobilized – for example during amplified high flows in urban streams – they can contribute to eutrophication of downstream water bodies. Understanding these dynamics is important for reversing these impairments and sustainably managing our water resources. In this dissertation, I provide a new tool to quantify the magnitude of channel erosion as a pollutant source. First, I put this issue in context by reviewing recent literature on stream restoration and its ability to either reduce nutrient loading or enhance natural nutrient removal processes. Results suggest that stream restoration can help reduce nutrient pollution, but quantifying these benefits remains challenging. Despite the rapid growth of the stream restoration industry, there is still insufficient monitoring and assessment of project success. Perhaps this is due to a lack of standardized tools and methodologies. The remainder of this dissertation attempts to fill part of this gap --- providing a new tool to predict watershed sediment and phosphorus loading from channel erosion. I develop a new model to simulate stream channel evolution at the watershed scale. This model is built around specific stream power, a variable that is straightforward to calculate using easily quantified parameters: discharge, slope, and width. I first develop new sediment transport equations based on specific stream power. These are used by the model to simulate channel bed aggradation and degradation. I link these processes with a simplified version of a bank erosion model to account for lateral channel adjustment. Model simulations match physical understanding of channel evolution in response to disturbance as well as field datasets of rivers adjusting to both human and natural perturbations. Importantly, the model is structured to quantify uncertainty in model projections. This is essential for understanding both model limitations and more generally for simulating complex systems in a stochastic world. Finally, I apply this new model to estimate sediment and phosphorus loading from bank erosion in two watersheds: Big Dry Creek, Colorado and Lick Creek, North Carolina. Despite their many differences and their unique simulated responses to disturbance, results for both watersheds suggest that channel erosion may be responsible for nearly all of the suspended sediment pollution, but very little of the phosphorus. This new model has a number of applications in both the scientific and management communities --- exploring river behavior in more detail while also answering relevant management questions as we try to more effectively steward our water resources.
Description
Zip file contains datasets for chapters 2, 3, and 5, and a readme document.
Rights Access
Subject
model
river erosion
channel evolution
sediment
phosphorus