Date of Award

January 2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geological Engineering

First Advisor

Taufique H. Mahmood

Abstract

The recent changes in hydroclimatic conditions in the Northern Great Plains (NGP) have led to an increase in precipitation and wetland connectivity over the last few decades. The most recent wet period started at 2005 after the last NGP drought (1999-2004). The current wetting is expected to continue and could potentially last into 2038 and beyond. The increases in precipitation during the recent wet period yield an integrated response resulting in hydrologic changes in the NGP. However, the underlying mechanism of the hydrologic changes caused by recent wetting is poorly understood requiring a physically-based modeling framework in order to decipher them. This study utilized a field-tested and physically-based cold region hydrologic model (CRHM) to investigate the impacts of elevated precipitation on recent hydrologic changes by examining the intermediate processes during the 2004-17 period. CRHM is designed for cold regions and has modules to simulate processes, such as blowing snow transport, sublimation, interception, frozen soil infiltration, snowmelt, and subsequent streamflow generation. The modeling of the current study focuses on a tributary basin of the Devils Lake Basin (DLB) known as the Mauvais Coulee Basin (MCB). Since there were very few snow observations in the MCB, a detailed snow survey was conducted at distributed locations estimating snow depth, density, and snow water equivalent (SWE) using a prairie snow tube four times during winter of 2016-17. The MCB model was evaluated against distributed snow observations and streamflow measured at the basin outlet (USGS) for the year 2016-17. Overall, the simulated snow water equivalents (SWEs) at distributed locations and streamflow are in good agreement with observations. The simulated SWE maps exhibit large spatiotemporal

variation during the winter of 2016-17 due to spatial variability in precipitation, snow redistribution from stubble fields to wooded areas, and snow accumulations in small depressions across the sub-basins. The main source of snow appears to be the hills and ridges of the eastern and western edges of the basin, while the main sink is the large flat central valleys. Snowmelt was the primary contributor to annual streamflow with a varying contribution from rain-on-snow (ROS). Detailed diagnosis of simulations identified two phases (pre- and post-2011) exhibiting different cold region hydrologic responses. During the pre-2011 period, the MCB system was dominated by both streamflow and evapotranspiration (ET) while there was extreme ET dominance with very minor influence from streamflow in the post-2011 period. This switch was caused primarily by climatic conditions involving spring/summer rainfall and daytime overcast conditions. Both snowmelt and ROS contributed to annual streamflow in the pre-2011 period while only snowmelt was the prime contributor in the post-2011 period except in 2013. Frozen soil and basal ice conditions during the spring period played a significant role for generating streamflow within the pre-, during, and post-2011 period.

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