The Water Resources Graduate Program awards both Masters and PhDs. Degrees in the areas of Water Resources Engineering, Water Resources Science, and Water Resources Policy and Management are available. The theses and dissertations produced by students since the program’s inception in 2003 are available here. http://hdl.handle.net/1957/12251 2013-06-19T16:06:19Z 2013-06-19T16:06:19Z Stewart, Ryan D. http://hdl.handle.net/1957/39447 2013-06-17T21:10:40Z 2013-06-05T00:00:00Z

Characterization of hydrologic parameters and processes in shrink-swell clay soils Stewart, Ryan D. Vertisols and other vertic-intergrade soils are found all over the globe, including many agricultural and urban areas. These soils are characterized by their cyclical shrinking and swelling behaviors, where bulk density and porosity distribution both vary as functions of time and/or soil moisture. In turn, alterations in physical soil parameters become manifest as crack networks, which open during the shrinkage phase and re-seal as the soil swells. As a consequence, when present these soils can significantly impact agriculture and infrastructure, and can act as a dominant control on the local hydrology. Therefore, understanding how water moves through and interacts with these soils is of utmost importance to ensure their proper utilization and management. This study had three objectives: 1) to identify the role of initial soil moisture on infiltration in a rigid (non-swelling) soil; 2) to quantify variation in the soil's hydraulic properties, using single-ring infiltration measurements taken in a vertic soil over a 1.5 year period; and 3) to build on these concepts to examine data from a set of instrumented field plots in a vertic soil located in the Secano Interior region of Chile. Significant findings of the study include 1) the development of a new formulation to describe a soil's wetting front potential (a measure of capillary pull) in terms of initial degree of saturation; 2) the creation of a simple correction to approximate the decrease of wetting front potential in wetter soils, thereby improving the accuracy of the traditional Green and Ampt sorptivity model in such conditions; 3) an equation to accurately estimate hydraulic parameters from short-duration infiltration tests, when steady-state conditions have not been realized; 4) a new theoretical model to estimate crack porosity as a function of soil moisture, which was developed based on the soil shrinkage curve; and 5) modification of the traditional two-term Philip infiltration model for use in vertic soils. The field study also showed that crack networks cause highly complex and non-linear wetting of the soil profile, with water simultaneously infiltrating from the soil surface and from the soil-crack interfaces; that cracks can seal at the surface while remaining open and hydraulically active below the surface, which indicates that surface-based monitoring alone may not be sufficient to predict water movement and soil response in vertic soils; and that the transition between infiltration and runoff may be strongly correlated with the cumulative amount of net precipitation that had reached the soil surface, so that cumulative amount of precipitation has the potential to be a simple yet accurate metric to predict runoff in vertic soils. These findings offer improved understanding of soil-water interactions in vertic soils, and reveal that very simple concepts underlie seemingly complex systems. As a result, the concepts and formulations developed in this study should allow for straightforward integration into other studies and models. Graduation date: 2013

2013-06-05T00:00:00Z González Pinzón, Ricardo A. http://hdl.handle.net/1957/39354 2013-06-12T20:34:44Z 2013-05-31T00:00:00Z

Integrating solute transport, metabolism and processing in stream ecosystems González Pinzón, Ricardo A. After three decades of active research coupling hydrology and stream ecology, the connection among solute transport, metabolism and processing is still unresolved. These knowledge gaps obscure the functioning of stream ecosystems and how those ecosystems interact with other landscape processes. We must resolve these challenges to wisely manage water resources, because there is a need to understand controls on stream ecosystems at local, regional and continental scales, and because we need to predict in-stream biogeochemical processes in environments and conditions that do not have supporting data. More robust methods are required to deconvolve signal imprints of solute transport, metabolism and processing, thus allowing the development and implementation of improved decision-making approaches for stream management. Recognizing that uncertainty and equifinality are ubiquitous issues in hydrologic problems, this dissertation focuses on the development of parsimonious methods to couple solute transport, metabolism and processing in stream ecosystems. These methods consist of scaling and predicting relationships for solute transport, efficient modeling frameworks to estimate processing rates in streams, and the use of the smart tracer resazurin to estimate stream metabolism at different spatial scales. This dissertation is the result of lab and field experiments, meta-analyses, and mathematical, statistical and computational modeling. The most significant contributions of this dissertation to the hydrological and biogeosciences are: (1) there are scaling relationships in stream solute transport. We found that the coefficient of skewness (CSK) of conservative tracer breakthrough curves is statistically constant over time and this result can be used to predict solute transport. (2) The CSK of all commonly used solute transport models decreases over time. This shows that current theory is inconsistent with experimental data and suggests that a revised theory of solute transport is needed. (3) Simple algebraic relationships can be used to estimate processing rates in streams. This eliminates the need to calibrate highly uncertain (and intermediate) parameters. (4) Under some common stream transport conditions dispersion does not play an important role in the estimation of processing rates and, therefore, can be neglected. Under such conditions, no computer modeling is needed to estimate processing rates. (5) Even if the reactions of target and proxy tracers happen in exactly the same locations at rates that are linearly proportional, the exact relationship between the two volume-averaged rates can be nonlinear and a function of transport conditions. However, the uncertainty in the estimation of the target processing rate is linearly proportional to the proxy-tracer processing rate. (6) The transformation of resazurin is nearly perfectly, positively correlated with aerobic microbial respiration. Therefore, resazurin can be used as a surrogate to measure respiration in situ and in vivo at different spatial scales (this is an extension of (5)). (7) Community respiration rates in streams may not need to be "corrected" for temperature between daytime and nighttime, because even when photosynthetically active radiation and stream water temperature are different, respiration rates might not be different across nighttime and daytime conditions. Graduation date: 2013; Access restricted to the OSU Community at author's request from June 12, 2013 - June 12, 2014

2013-05-31T00:00:00Z Kalyan, Imtiaz-Ali M. http://hdl.handle.net/1957/39182 2013-06-11T18:41:29Z 2013-05-21T00:00:00Z

Identifying "at-risk" regions of snow accumulation within California's Sierra Nevada Mountains, and assessing implications on reservoir operations Kalyan, Imtiaz-Ali M. California's water resources vary throughout the state owing to the regions varying topography, diverse climate, and the distribution of precipitation. Most of the state's precipitation falls over the northern coastal range and the western slopes of the Sierra Nevada Mountains. Winter snowpack that accumulates within these mountain basins serves as an efficient means of natural water storage. Moreover, the state's two massive water conveyance systems, the State Water Project (SWP) and the Central Valley Project (CVP), are integrally dependent upon winter snowpack accumulation, and subsequent spring snowmelt runoff. The SWP and CVP's extensive network of reservoirs, pipes, and aqueducts are engineered to collect and transport water from the snowcapped Sierra Nevada Mountains where it is plentiful, to farmland and urban communities where it is scarce but in greatest demand. However, increased warming within these mountain basins is causing a declined winter snowpack, altering the fraction of precipitation occurring as snow, and changing the timing of snowmelt derived streamflow. The loss of this immense amount of naturally occurring stored water, and its earlier arrival at the downstream reservoirs, has profound implications on the state's existing water management infrastructure. This work attempts to address these water management challenges that lie in the foreseeable future. Using a binary based deterministic approach, and a climatologically record of temperature and precipitation, "at-risk" snow dominated regions were identified throughout the Feather River Basin, and nested basins of the San Joaquin Watershed. These "at-risk" regions represent locations that would be the first to transition from a snow dominated, to a rain dominated precipitation regime under projected future warming scenarios. Future warming projections ranging from 1°C to 4°C were analyzed relative to the 1971-2000 base period. Results show that if warming trends considered by the IPCC 2007 report to be highly likely continue, nearly all snow dominated regions existing between 1500 and 2100 m in the San Joaquin Watershed would become rainfall dominated. Within the Feather River Basin, in the Sacramento Watershed, implications are even more alarming. A 3°C warming in February would result in approximately 87% of the regions previously snow covered area (SCA) becoming rainfall dominated; only 12% of the basin would remain snow covered. The decline of winter snowpack within all six study basins is closely correlated with elevation and average winter temperatures. Lower elevation, snow dominated regions near the rain to snow transition zone are highly sensitive to warmer temperatures relative to higher elevation, colder snow dominated regions. Furthermore, warming during high precipitation months, from December to February, would yield the largest reductions in loss of Snow Water Equivalent (or SWE). The loss of this immense amount of naturally occurring stored water, and its earlier arrival at the downstream reservoirs poses challenges and opportunities for California's water managers. For reservoir managers, adapting to a rapidly changing climate would require updating rigid flood control rule curves that were established based on hydrological trends during the first half of the twentieth century. Developing greater flexibility into flood-control rule curves could allow reservoir managers to store more water in the winter, thereby mitigating the consequences of snow loss from natural stored water sources. Faced with an expanding population and increased strains on water resources availability, sustaining future water demands hinges on developing adaptive water management strategies. By understanding basin and, at a finer scale, elevation specific vulnerability to snow loss due to warming, water managers can begin to guide effectual adaptation strategies. Graduation date: 2013

2013-05-21T00:00:00Z Danner, Allison G. http://hdl.handle.net/1957/38119 2013-04-11T17:53:29Z 2013-03-21T00:00:00Z

Will we need to change the rules : assessing the implications of climate change for dam operations in Oregon's McKenzie River Basin Danner, Allison G. Dams and reservoirs are important components of water resource management systems, but their operational sensitivity to streamflow variability may make them vulnerable to climate change. Climate change is likely to affect the magnitude and timing of streamflow, motivating the assessment of potential impacts on dams and reservoirs. Here I examine a case study of Cougar Dam, a multipurpose dam in Oregon, USA, to assess potential impacts of future climate change on operational performance. In the first portion of this study, I examine the historical operation of Cougar Dam, to understand (1), whether operational objectives have been achievable in the past despite operational variability, and (2) how climatic variation is expressed in operational trajectories. By analyzing historical streamflow and operations data using a set of metrics, I characterize variability in past operations and how that variability relates to streamflow. I also employ a reservoir model to distinguish operational differences due to streamflow variability from variability due to other factors that affect operations. I find that operational objectives have been achievable, despite variability in operations and departures from the ideal operational trajectory. Throughout the historical period, flood control operations have almost always kept reservoir outflows below the desired maximum outflow. Although filling occurs 9 days late on average, the reservoir has filled in all but 6 out of 37 years. Although drawdown occurs 47 days early on average, early drawdown does not generally impact recreation and allows minimum outflows to be met every day during all but the driest year. I also find that total seasonal inflow is correlated with measures of operational performance, and that other factors besides climate play an important role in determining operational trajectories. I conclude that operations of Cougar Reservoir are vulnerable to climate change, but that operational flexibility may mitigate some of the potential impacts. In the second portion of this study I assume that current operating rules will be kept in place and I aim to understand what types of operational impacts may be expected, when they may be expected to occur, and whether the operational impacts may necessitate changing operational rules. I employ both a traditional climate impacts assessment approach to assess changes over time as well as a scenario-neutral approach to generalize relationships between streamflow and operations of Cougar Dam. I find that projected increases in winter streamflow could result in up to twice the number of downstream high flows than in the past and that projected decreases in summer streamflow could result in earlier reservoir drawdown by up to 20 days on average. Additionally, filling of the reservoir may occur up to 16% more often or 11% less often than in the past, depending on spring flow magnitude and timing. I also find that there are strong general relationships between total inflow volume and flood control performance, and that there are total inflow thresholds for whether or not the reservoir will fill or will be full enough for recreation in late summer. I conclude that future modification of operating policies may be warranted, but that there will likely be tradeoffs between operating objectives in the future even if operating rules are modified. Graduation date: 2013

2013-03-21T00:00:00Z