Predicting groundwater effects due to changing land practices in the intermountain west

Graduation Date

2013

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Environmental Systems: Environmental Resource Engineering, 2013

Committee Chair Name

Brad A. Finney

Committee Chair Affiliation

Cal Poly Humboldt Faculty or Staff

Keywords

Surface water/groundwater interactions, Irrigation conveyance, Changing land use, Henry’s Fork Watershed, ModelMuse, Groundwater flow model, Modflow, Humboldt State University -- Theses -- Environmental Resources Engineering

Abstract

Changes in land use practices have coincided with declines in ground-water levels in irrigated areas throughout the United States, particularly in the West. Rural watersheds throughout theWest are experiencing replacement of irrigated agricultural land with nonurban and resort development, increasing water demand and altering irrigation practices. Changes in irrigation practices alters the hydrologic regime of the area, disrupting surfaceground water interactions. Such changes are occurring in the Henry's Fork watershed in southeastern Idaho. In this watershed, surface water is the dominant source of irrigation water and modern day ground-water declines have resulted from complex combinations of decreased recharge incidental to irrigation conveyance and application, increased use of ground water for irrigation and domestic use, and the aforementioned conversion of land from irrigated agriculture to exurban and suburban uses. In order to investigate the effects of land use changes on the local water budget a tool was developed in the form of a MODFLOW2005 groundwater flow model. The model was calibrated to groundwater levels in USGS observation wells and the overall water balance within the model domain for the water years 1980-2008. Three scenarios were investigated with the calibrated model: • Lining canals of North Fremont County in the Henry's Fork Watershed • Removing all overapplication seepage from the fields in the model domain • Lining all of the canals and removing all overapplication seepage in the model domain Across all scenarios, a reduction in the amount of groundwater recharge in the form of conveyance or application seepage resulted in an alteration to the local hydrologic regime. Local groundwater levels lowered; as much as 5.8 feet on average in the third scenario. The lowering of local groundwater levels altered the amount of groundwater inflow to river reaches, causing reaches that were previously gaining in the summer to switch to losing. In the case of two reaches within the model domain, this amounted to an average annual reduction of 66,000 ac-ft. The change in hydrologic regime can impact both irrigators and aquatic wildlife in the area. Regardless of the impacts, these changes lead to an increased amount of water leaving the watershed in the form of surface water and a decreased amount recharging the local groundwater system.

https://scholarworks.calstate.edu/concern/theses/2b88qf51g

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