Water scarcity and reservoir reliability in basins affected by climate and land use change : impacts of hydrogeology, sensitivities, and uncertainties in the Santiam River Basin, Oregon

by M. Cristina Mateus

Institution: Oregon State University
Department: Water Resources Engineering
Degree: PhD
Year: 2015
Keywords: Climate Change; Water-supply  – Oregon  – Santiam River Watershed
Record ID: 2058178
Full text PDF: http://hdl.handle.net/1957/55048


Multipurpose management of hydrosystems face a number of uncertainties related to hydrologic variability and nonstationarity. Anticipated air temperature increases in the Pacific Northwest region are projected to alter the timing and quantity of streamflow associated with precipitation shifting from snow to rain, including shorter winter runoff periods, earlier spring runoff, and longer and drier summers. Changes in land use, such as urbanization, can reduce infiltration and groundwater recharge, thus lowering base-flow levels. Furthermore, these future changes in water supply are likely to vary across catchments with sensitivity to climate and land use changes. In this dissertation, I investigate hydrosystem sensitivities to climate and land use change considering modeling uncertainty across two different hydrologic settings in the Santiam River Basin in Oregon (Chapter 2), the reliability of reservoirs to accommodate these changes given current operating procedures (Chapter 3), and the performance of alternative reservoir operations scenarios in mitigating projected future hydrologic changes (Chapter 4). This research is based on modeled future streamflows forced by temperature and precipitation projections from eight global climate models and two greenhouse gas emissions scenarios. To represent the uncertainty associated with future streamflow, I apply global climate model projections to a groundwater-surface water model (GSFLOW), coupled with a formal Bayesian uncertainty analysis. The land use changes were simulated in GSFLOW by adjusting model parameters based on the proportion of change in land use area within hydrologic response units. I apply streamflow projections as inputs to a reservoir operation model (HEC-ResSim) to analyze reservoir system reliability under future climate. I then use historical records to identify what outcomes are unacceptable to stakeholders, a condition labeled as vulnerable, and establish thresholds of reservoir reliability. I then use projections of future hydrology to identify the likelihood of the system being pushed to that vulnerable state under current and alternate reservoir operations. Modeling and analysis is conducted in the North and South Santiam River basin, Oregon. The North Santiam sub-basin is sourced by the High Cascades, with high elevations but low in relief, deep groundwater and spring-dominated drainage system that sustain base flow during the dry summer months. In contrast, the South Santiam sub-basin is entirely sourced by the Western Cascades geology, with steep drainage network and relatively impermeable rock that generates rapid runoff responses, high peak flows, high flow variability and little groundwater storage. In the context of water scarcity, Chapter 2 presents an analysis of the influence of climate and land use change on the future availability of water resources across sub-basins with different hydrogeological and land use characteristics. In this analysis, I investigate how sub-basin characteristics, including elevation, intensity of…