Date of Award

January 2023

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Taufique H. Mahmood

Abstract

The Northern Great Plains (NGP), which can be broadly defined as the portion of the Great Plains north of Nebraska, undergoes decadal-scale climatic change in the form of drought and deluge cycles. These are broad, long-term cycles, that are not always well-defined, as has been the case recently. Since 2012, there have been one or two dry years followed by one or two wet years. Conversely, before 2012, there was a well-defined wet period between 2005-2011, preceded by a well-defined dry period from 1999-2004. Understanding drought-deluge cycles is critical to predicting aquifer recharge and groundwater retention, which directly affects how much groundwater is available for use. In the NGP, and especially in North Dakota, the majority of aquifer recharge is a result of snowmelt infiltrating through soil. Because snowmelt is integral to aquifer recharge, snow water equivalent (SWE) is an important factor in the hydrology of the region. The Cold Region Hydrologic Model (CRHM) was used to observe the effects of climate change in the period 1997-2023 to calibrate the model and use those observations to output a prediction of SWE and recharge for three focus years of the winters of 2020-2021, 2021-2022 and 2022-2023 in the watershed of the Oakes Aquifer, which occupies an expanse of flat land which quickly gains elevation in the far eastern portion of the watershed. Ten sampling sites situated on the ground surface atop the aquifer were used to obtain observed SWE and snow depth data. SWE was determined by taking field snow samples at all 10 sites on February 8, at 5 of the sites on March 28 and at 8 of the sites on April 12 during early 2023 and comparing these field measurements with CRHM’s predicted SWE values. The field measurements and model predictions were compared. The same process was used for determining the accuracy of the CRHM model’s predicted snow depth. Aquifer recharge was calculated by subtracting the modeled values of hydrological processes resulting in surface and ground water loss to the region (evapotranspiration, runoff, outgoing drift, ground and canopy sublimation) from the modeled values of hydrological input (incoming drift, precipitation). Rainfall and snowfall data were retrieved from North Dakota Agricultural Weather Network (NDAWN) stations in Oakes, ND as well as National Weather Service (NWS) and National Oceanic and Atmospheric Administration (NOAA) stations in Lisbon, ND., Redeposition of snow by wind controls several millimeters of snow distribution, as snow is redeposited on the eastern slopes and several of the eastern areas consistently show the highest SWE for the water year. Snow also accumulates in depressions, although these depressions are rarely more than a couple of feet deep. The study established a connection between wet or dry precipitation regimes and their effects on snow hydrological processes, with the following findings: of the three winters considered, 2020-2021 was found to be the driest and 2021-2022 was found to be the wettest based on rainfall and snowfall data. The CRHM produced recharge results consistent with these findings; most of the area would have experienced drawdown in 2020-2021, most of the area would have experienced recharge in 2021-2022, and moderate recharge would have occurred in 2022-2023. In 2020-2021, runoff was negligible and nearly all precipitation was evapotranspirated. Conversely, in 2021-2022, there was plentiful runoff and precipitation greatly exceeded evapotranspiration (ET)

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