Using an ETWatch (RS)-UZF-MODFLOW Coupled Model to Optimize Joint Use of Transferred Water and Local Water Sources in a Saline Water Area of the North China Plain

Abstract

In the saline water area of our research, deep groundwater was over-pumped for agricultural irrigation which resulted in a decline of the deep groundwater level and an increase in the shallow groundwater table. Soil salination was also aggravated due to the strong evapotranspiration (ET) in the shallow groundwater areas, where ET removes water vapor from the unsaturated zone (ETu), and the groundwater (ETg). Joint utilities of multiple water sources of transferred water and local shallow and deep groundwater are essential for reasonable management of irrigation water. However, it is still difficult to distinguish ETu and ETg in coupled management of unsaturated zone and groundwater, which account for the water balance in utilities of multiple water sources in a regional scale. In this paper, we used an RS-based ETWatch model as a source of evapotranspiration data coupled with UZF-MODFLOW, an integrated hydrological model of the unsaturated–saturated zone, to estimate the ETg and ETu on a regional scale. It was shown that the coupled model (ETWatch-UZF-MODFLOW) avoids the influence of ETu on the groundwater balance calculation and improves the accuracy of the groundwater model. The model was used in the simulation and prediction of groundwater level. The eastern North China Plain (NCP) was selected as the study area where shallow groundwater was saline water and deep groundwater cone existed. We compared four different scenarios of irrigation methods, including current irrigation scenario, use of saline water, limited deep groundwater pumping, use of multiple water sources of transferred water and local groundwater. Results indicate that the total ETg for the four scenarios in the study area from 2013 to 2030 is 119 × 108 m3, 81.9 × 108 m3, 85.0 × 108 m3, and 92.3 × 108 m3, respectively, and the proportion of ETg to total ET was 6.85%, 4.79%, 4.97%, 5.37%. However, in regions where the groundwater depth is less than 3 m, ETg accounts for 12% of the total ET, indicating that groundwater was one of the main sources of evapotranspiration in shallow groundwater depth area.

Quantifying the impact of lagged hydrological responses on the effectiveness of groundwater conservation

“…The model simulates flow through variably saturated porous media using the unsaturated zone flow (UZF) package, which uses a kinematic-wave approximation to solve the 1-D Richard's equation (Niswonger et al, 2006;Smith, 1983;Smith & Hebbert, 1983). While numerous models can simulate variably saturated flow, the UZF package for MODFLOW has several advantages for our purposes, including documented use in thick vadose zones (Hunt et al, 2008;Nazarieh et al, 2018), computational efficiency (Kennedy et al, 2016;Niswonger & Prudic, 2009), and widespread use (Bailey et al, 2013;Hou et al, 2020;Morway et al, 2013).…”

Quantifying the Impact of Lagged Hydrological Responses on the Effectiveness of Groundwater Conservation

“…The model simulated flow through variably saturated porous media using the unsaturated zone flow (UZF) package, which uses a kinematic‐wave approximation to solve the 1‐D Richard's equation (Niswonger et al., 2006; Smith, 1983; Smith & Hebbert, 1983). While numerous models can simulate variably saturated flow, the UZF package for MODFLOW has several advantages for our purposes, including documented applications in thick vadose zones (Hunt et al., 2008; Nazarieh et al., 2018), computational efficiency (Kennedy et al., 2016; Niswonger & Prudic, 2009), and widespread use (Bailey et al., 2013; Hou et al., 2020; Morway et al., 2013). Since the top of our model domain represents the bottom of the root zone, we provided UZF with annual values of deep percolation from a linear model fit between simulated deep percolation from a calibrated crop model for the SD‐6 area with and without conservation (Deines et al., 2021), and the sum of annual precipitation and applied irrigation depth following Scanlon et al.…”

“…The model simulated flow through variably saturated porous media using the unsaturated zone flow (UZF) package, which uses a kinematic-wave approximation to solve the 1-D Richard's equation (Niswonger et al, 2006;Smith, 1983;Smith & Hebbert, 1983). While numerous models can simulate variably saturated flow, the UZF package for MODFLOW has several advantages for our purposes, including documented applications in thick vadose zones (Hunt et al, 2008;Nazarieh et al, 2018), computational efficiency (Kennedy et al, 2016;Niswonger & Prudic, 2009), and widespread use (Bailey et al, 2013;Hou et al, 2020;Morway et al, 2013).…”