Abstract
Water management strategies need to balance water security and food production, particularly in semi-arid regions wherein irrigation is required to supplement rainfall. Irrigated stream–aquifer systems present a unique challenge in this effort, due to complex groundwater–surface water interactions and the high level of human intervention in managing irrigation practices. This paper has two objectives: first, to detail a method for constructing and applying a coupled SWAT-MODFLOW to irrigated stream–aquifer systems; and second, to use the model to quantify the effects of decreasing irrigation on hydrological responses and crop yield. The method is applied to a 734 km2 study region in the Lower Arkansas River Valley, an alluvial valley in Colorado, USA, which has been intensively irrigated for over 100 years and is threatened by shallow water tables. Therefore, a reduction in applied irrigation amounts has the double benefit of conserving water and decreasing waterlogging, given that crop yield can be maintained for food production. The results indicate that an approximate 10% decrease in total applied irrigation water results in decreases of 6% in surface runoff, 8% in evapotranspiration, and 4% in recharge water. It also results in an increase of 4% in groundwater return flow to the Arkansas River, and an actual increase in groundwater levels due to the decrease in groundwater pumping, pointing to the need for targeted irrigation reduction strategies to decrease waterlogging occurrence. The irrigation reduction yields an average 9% decrease in corn and alfalfa yield. This modeling approach is in general transferable to other similar irrigated river valleys.
Highlights
The increasing scarcity of water is an immediate threat to the sustainable development of areas around the world
To explore the impacts of reducing irrigation water on streamflow, groundwater levels, groundwater ET rate, and crop yield, the water stress threshold is set to 0.5 to decrease the surface water irrigation, and the groundwater pumping rates are decreased in the MODFLOW WELL to decrease groundwater irrigation
The model provides a detailed description of surface and groundwater flow processes, thereby enabling a detailed description of watershed processes such as surface runoff, ET, infiltration, soil lateral flow, recharge, groundwater ET, three-dimensional groundwater flow in a heterogeneous aquifer system with sources and sinks, spatio-temporal groundwater and surface water interactions, and streamflow
Summary
The increasing scarcity of water is an immediate threat to the sustainable development of areas around the world. This study showed that changing the traditional irrigation system to a pressurized irrigation system can lead to basin level water conservation and increase crop production They did not capture the individual hydrological responses, especially the interactions of groundwater and surface water [36]. The objective of this study is twofold: first, to detail a method for constructing and applying a coupled SWAT-MODFLOW (modular three-dimensional finite-difference groundwater model MODFLOW) to irrigated stream–aquifer systems; and second, to use the model to quantify the effects of decreasing irrigation on hydrologic responses and food production (i.e., crop yield).
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