High groundwater in irrigated regions: model development for assessing causes, identifying solutions, and exploring system dynamics
Date
2021
Authors
Deng, Chenda, author
Bailey, Ryan T., advisor
Grigg, Neil, committee member
Niemann, Jeffrey, committee member
Paustian, Keith, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Waterlogging occurs in irrigated areas around the world due to over-irrigation and lack of adequate natural or artificial drainage. This phenomenon can lead to adverse social, physical, economic, and environmental issues, such as: damage to crops and overall land productivity; soil salinization; and damage to homes and building foundations. Solutions to waterlogging include implementation of high-efficient irrigation practices, installation of artificial drainage systems, and increased groundwater pumping to lower the water table. However, in regions governed by strict water law, wherein groundwater pumping is constrained by impact on nearby surface water bodies, these practices can be challenging to implement. In addition, current engineering and modeling approaches used to quantify soil-groundwater and groundwater-surface water interactions are crude, perhaps leading to erroneous results. An accurate representation of groundwater state variables, groundwater sources and sinks, and plant-soil-water interaction is needed at the regional scale to assist with groundwater management issues. This dissertation enhances understanding of major hydrological processes and trade-offs in waterlogged agricultural areas, through the use of numerical modeling strategies. This is accomplished by developing numerical modeling tools to: (1) analyze and quantify the cause of high groundwater levels in highly managed, irrigated stream-aquifer systems; (2) assess the impact of artificial recharge ponds on groundwater levels, groundwater-surface water interactions, and stream depletions in irrigated stream-aquifer systems; (3) and gain a better understanding of plant-soil-water dynamics in irrigated areas with high water tables. These objectives use a combination of agroecosystem (DayCent) and groundwater flow (MODFLOW) models, sensitivity analysis, and management scenario analysis. Each of these sub-objectives is applied to the Gilcrest/LaSalle agricultural region within the South Platte River Basin in northeast Colorado, a region subject to high groundwater levels and associated waterlogging and infrastructure damage in the last 7 years. This region is also subject to strict water law, which constrains groundwater pumping due to the effect on the water rights of the nearby South Platte River. Results indicate that recharge from surface water irrigation, canal seepage, and groundwater pumping have the strongest influence on water table elevation, whereas precipitation recharge and recharge from groundwater irrigation have small influences from 1950 to 2012. Mitigation strategy implementation scenarios show that limiting canal seepage and transitioning > 50% of cultivated fields from surface water irrigation to groundwater irrigation can decrease the water table elevation by 1.5 m to 3 m over a 5-year period. Decreasing seepage from recharge ponds has a similar effect, decreasing water table elevation in local areas by up to 2.3 m. However, these decreases in water table elevation, while solving the problem of high groundwater levels for residential areas and cultivated fields, results in a decrease in groundwater discharge to the South Platte River. As the intent of the recharge ponds is to increase groundwater discharge and thereby offset stream depletions caused by groundwater pumping, mitigating high water table issues in the region can be achieved only by (1) modifying fluxes of sources and sinks of groundwater besides recharge pond seepage, or (2) modifying or relaxing the adjudication of water law, which dictates the need for offsetting pumping-induced stream depletion, in this region. The modeling tools developed in this dissertation, specifically the loose and tight coupling between DayCent and MODFLOW, can be used in the study region to quantify pumping-induced stream depletion, recharge pond induced stream accretion, and the interplay between them in space and time. In addition, these models can be used in other irrigated stream-aquifer systems to assess baseline conditions and explore possible effects of water management strategies.