| 02 Dec 2025
Quantification of Delayed Recharge by Soil Surface and Riverbed Infiltration in a Deep Groundwater Depression Zone in the North China Plain
Abstract. Agriculture on the North China Plain (NCP), home to over 300 million people, heavily relies on groundwater extraction to feed its irrigation systems. This has created a large groundwater depression zone up to 80 m deep, severely limiting sustainable groundwater extraction and crop-production. Effective recharge is essential to restore this depleted zone and secure future sustainability. Few studies, however, have quantified recharge delays and efficiencies in deep vadose zones with complex lithology. Here we simulated infiltration times and percolation velocities in the Ningbailong groundwater depression zone, a typical overexploited site in the NCP using HYDRUS-1D with measured borehole lithology and hydro-meteorological data. Two infiltration modes were considered: precipitation-fed and riverbed infiltration. Spatial distributions of infiltration times and percolation velocities were obtained, and recharge efficiencies were compared between these two infiltrations. Results showed that times for precipitation-fed recharge averaged 446 days and varied with lithology and thickness, from 10 days in western Taihang foothills (dominated by coarse sands) to 1,395 days in central/eastern plains (finer clays and loams). Riverbed recharge was markedly faster, averaging 91 days, indicating higher efficiency than precipitation under equivalent lithological conditions. Regression equations were derived to predict percolation velocities from vadose zone thickness and soil particle fractions. These findings elucidate how vadose zone thickness and lithology amplify recharge lags and control recharge efficiency. They also highlight the potential for managed aquifer recharge strategies, such as constructing infiltration basins for flood capture, offering strategies to reduce groundwater over-exploitation in similar depression zones.
Competing interests: The authors have the following competing interests: Yonggen Zhang is a member of the editorial board of Hydrology and Earth System Sciences. The authors declare that they have no other competing interests.
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The paper addresses an important and very topical problem: delayed recharge in deep vadose zones within a major groundwater depression cone in the North China Plain, comparing precipitation-fed vs riverbed recharge using HYDRUS-1D plus borehole lithology. The regional perspective and explicit focus on lag times and percolation velocities are valuable and fit well within hydrology / groundwater journals. I recommend it for publication after considering below comments:
Abstract
The phrase “two infiltration modes were considered: precipitation-fed and riverbed infiltration” could be tightened to “precipitation-fed soil infiltration and riverbed infiltration”.
When mentioning the regression equations, briefly state the key predictors (vadose zone thickness and particle fractions) to give the reader more context.
Introduction
Some paragraphs are quite long and dense (e.g., lines 41–64, 85–110). Consider splitting into shorter paragraphs to improve readability.
When you review past work (HYDRUS applications, global lag studies), explicitly state the remaining gap you are addressing (combined effect of deep vadose zones, complex lithology, and comparison of two recharge sources under identical profiles). You do this, but it could be more sharply framed at the end of the Introduction.
Study area
It might be helpful to explicitly mention average annual precipitation and reference ET, if available, to characterize the climate quantitatively.
The description of boundaries (Taihang Mountains, Shijiazhuang, Hengshui) is good, but consider adding one sentence stating dominant land use (e.g., double cropping, wheat–maize rotation) to connect with the root uptake assumptions.
Data section (Table 1)
“Depth (cm)” is given for boreholes, but values like 8,080 cm (= 80.8 m) etc. Make clear that these are vadose zone thicknesses down to shallow groundwater table or borehole depth; the phrase “Depth (cm)” is ambiguous.
You might add a column indicating vadose zone thickness vs. total borehole depth if they differ.