Award Date

5-1-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering and Construction

First Committee Member

Moses Karakouzian

Second Committee Member

Sajjad Ahmad

Third Committee Member

Donald Hayes

Fourth Committee Member

Douglas Rigby

Fifth Committee Member

Vernon Hodge

Number of Pages

175

Abstract

A water balance model is employed at Lake Mead to monitor and verify changing hydrology that affects total volume at the reservoir. Bank storage, which is defined as the volume of water captured in permeable lithologic layers subject to changes induced by contact and proximity to an open waterbody, is one component that is updated regularly and is based upon data and methods that were developed in the 1960’s from observations made within the first 30 years of the reservoir's maturation. Since this period, the reservoir has undergone further development and a current understanding of additional hydrologic affects to bank storage remain unknown. This study has updated hydrologic data from 1964 to 2018 expanding the current water-balance method and discrepancies are noted. Percent change in calculated bank-storage decline from the early 1960’s until the early 2000’s, with values that transition from positive percent of total-change to negative in the late 1960’s, suggesting other influences on the system are taking place. Previous studies note the affects from the groundwater system may contribute to this potential error yet remain unexplored.

A MODFLOW two-dimensional numerical model is constructed around Boulder Basin to simulate the movement of groundwater and bank storage as affected by change in Reservoir volume. Simulations of water flow through the near-shore aquifer around Boulder Basin suggest that in the first year, the regional-scale groundwater aquifer system interacts with bank storage in unconsolidated sediments and basin-fill deposits during periods of increasing Reservoir volume. Areas of high porosity are quickly saturated and the exchange between the groundwater system and bank storage occurs. Simulated periods of draining at the Reservoir show water that is pulled from unconsolidated sediments, basin-fill deposits, and consolidated and fractured volcanic and carbonate rocks. A system dynamics model is constructed to simulate the water-balance method and is calibrated with available hydrologic data from 1964 to 2018. A statistical comparison of model data and water-balance calculations is done to show potential error and observations. Using a two-dimensional numerical simulation coupled with an analytical solution, this study provides evidence for a strong groundwater influence on the bank-storage component within the Reservoir. Furthermore, potential error associated with data frequency and computation is noted. Given the complications listed in this study, a basic analytical summation of hydrologic properties in a water-balance equation may be insufficient to fully realize a comprehensive total value of bank storage around the Lake Mead reservoir.

This study investigates whether previous methods used to define bank storage are adequate considering the updated knowledge of the natural systems affecting the Reservoir. Results show that a percentage derived from a water-balance equation is insufficient to understand the complexity of the near-shore surface water and groundwater interactions. Included in this analysis is an effort to examine how updated measurements change the Reservoir storage. This study has reduced the 6.5% of total change in Reservoir volume down to 0.54%. This simplification of total bank-storage exchange required a broader evaluation of the region surrounding the Reservoir. This study decreases the previous bank-storage results and increases the value of the connection between the groundwater system and the Reservoir. Finally, results from previous methods are compared to values using the more robust system of analysis outlined in this study. While bank storage quantities are reduced, a broader analysis of the region surrounding the Reservoir should be completed to narrow and refine current calculated values. Data collection using current hydrologic engineering techniques should be employed to address this data gap. This data collection is needed to achieve a more precise value, and a combination of numerical simulations, and higher resolution data collection, incorporated into an analytical model, may be needed to realize this goal.

Keywords

Bank storage; Groundwater; Lake

Disciplines

Civil Engineering | Hydraulic Engineering | Hydrology

File Format

pdf

File Size

30.6 MB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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