Investigating the impact of irrigation practices on hydrologic fluxes in a highly managed river basin

Authors: ALMAHAWIS, MOHAMMED - Colorado State University; BAILEY, RYAN - Colorado State University; ABBAS, SALAM - Colorado State University; Arnold, Jeffrey; White, Michael

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2024
Publication Date: 8/1/2024
Citation: Almahawis, M.K., Bailey, R.T., Abbas, S.A., Arnold, J.G., White, M.J. 2024. Investigating the impact of irrigation practices on hydrologic fluxes in a highly managed river basin. Agricultural Water Management. 301. https://doi.org/10.1016/j.agwat.2024.108954.
DOI: https://doi.org/10.1016/j.agwat.2024.108954

Interpretive Summary: Irrigation practices significantly affect water resources, by predicting these impacts we can better manager these resources. In this study, the SWAT+ model integrated with a groundwater module to examine how different irrigation methods impact water availability and hydrologic processes in the Cache la Poudre River Basin in Colorado. SWAT+ was used to simulate scenarios such as using groundwater for irrigation, switching from flood to sprinkler systems, and sealing irrigation canals. The study finds that these practices impact groundwater levels and streamflow. This research aids in making informed decisions about water management in agriculture, promoting sustainable and efficient water use amidst growing concerns about water scarcity and environmental protection.

Technical Abstract: Irrigation practices and sources can have significant impacts on water resources and the hydrologic fluxes that control these resources. To better manage water resources and future water supply, the influence of irrigation practices and management on these hydrologic fluxes should be quantified in time and space at varying scales, under potential irrigation management practices. To fulfill this objective, we apply a surface-subsurface modeling approach to simulate watershed-scale hydrologic processes in the Cache la Poudre River Basin, Colorado, USA (4,824 km2), in which both surface water irrigation and groundwater irrigation are prevalent. The model chosen for this study is the watershed model SWAT+, using the spatially distributed, physically based groundwater module gwflow, in which unconfined groundwater storage, flows, and interaction with land surface features are simulated using a collection of grid cells that represent control volumes of the aquifer. Major groundwater inflows and outflows include pumping, recharge, groundwater-channel exchange, groundwater-lake exchange, and tile drainage outflow. To investigate the impact of irrigation practices, detailed surface and groundwater irrigation routines and canal-aquifer interactions were added to the SWAT+ source code, requiring information of irrigation sources and irrigation canal locations throughout the river basin. Model calibration and testing was performed using monthly stream discharge and groundwater head. The calibrated model is used to quantify the impact of surface water and groundwater irrigation scenarios on water availability and hydrologic fluxes within the river basin. A total of 22 scenarios were conducted and grouped into five main groups: irrigation source, irrigation amount, irrigation type, canal bed thickness, and partial or full sealing of earthen irrigation canals. Using groundwater as the only irrigation source decreases groundwater discharge to streams (by 14%) due to lowering groundwater levels; converting flood irrigation to sprinkler irrigation throughout the basin decreases surface runoff by 22%; and sealing earthen canals leads to a lowering of groundwater levels, which decreases groundwater discharge to streams by 9%, leading to an overall decrease in streamflow in the Cache la Poudre River and changes to temporal patterns in streamflow. Overall, irrigation amount and type and canal sealing have a small impact on total groundwater storage, compared to changes in the percent of fields irrigated by groundwater pumping. Results are helpful for informed decision-making in agriculture water management and can lead to sustainable, efficient, and equitable use of water resources, helping to address the challenges posed by water scarcity and environmental conservation.