A first investigation of hydrogeology and hydrogeophysics of the Maqu catchment in the Yellow River source region

Abstract

Abstract. The Tibetan Plateau is the source of most of Asia's major rivers and has been called the Asian Water Tower. Detailed knowledge of its hydrogeology is paramount to enable the understanding of groundwater dynamics, which plays a vital role in headwater areas like the Tibetan Plateau. Nevertheless, due to its remoteness and the harsh environment, there is a lack of field survey data to investigate its hydrogeology. In this study, borehole core lithology analysis, soil thickness measurement, an altitude survey, hydrogeological surveys, and hydrogeophysical surveys (e.g. magnetic resonance sounding – MRS, electrical resistivity tomography – ERT, and transient electromagnetic – TEM) were conducted in the Maqu catchment within the Yellow River source region (YRSR). The hydrogeological surveys reveal that groundwater flows from the west to the east, recharging the Yellow River. The hydraulic conductivity ranges from 0.2 to 12.4 m d−1. The MRS sounding results, i.e. water content and hydraulic conductivity, confirmed the presence of an unconfined aquifer in the flat eastern area. Based on TEM results, the depth of the Yellow River deposits was derived at several places in the flat eastern area, ranging from 50 to 208 m. The soil thickness measurements were done in the western mountainous area of the catchment, where hydrogeophysical and hydrogeological surveys were difficult to be carried out. The results indicate that most soil thicknesses, except on the valley floor, are within 1.2 m in the western mountainous area of the catchment, and the soil thickness decreases as the slope increases. These survey data and results can contribute to integrated hydrological modelling and water cycle analysis to improve a full-picture understanding of the water cycle at the Maqu catchment in the YRSR. The raw dataset is freely available at https://doi.org/10.17026/dans-z6t-zpn7 (Li et al., 2020a), and the dataset containing the processed ERT, MRS, and TEM data is also available at the National Tibetan Plateau Data Center with the link https://doi.org/10.11888/Hydro.tpdc.271221 (Li et al., 2020b).

A dataset of 10-year regional-scale soil moisture and soil temperature measurements at multiple depths on the Tibetan Plateau

“…The amplitudes of SM ups variations generally decrease with increasing soil depth, with larger variations noted for soil layers above 20 cm and smallest one at the deepest depth of 80 cm. The soil layers below 20 cm are drier than the upper layers in the warm season, whereas the soil at depth of 80 cm is wetter than 40 cm, which might be attributed to absence of evapotranspiration and existence of shallow groundwater (Li et al, 2021). The time series of the ST ups at different depths also show similar seasonality, with peak values in summer and the lowest values in winter, which is in agreement with the seasonal T a dynamics.…”

STEMMUS-MODFLOW v1.0.0: Integrated Understanding of Soil Water and Groundwater Flow Processes: Case Study of the Maqu Catchment, north-eastern Tibetan Plateau

“…Ground surface elevation decreases from 4017 m to 3367 m from the northwest to east. Field campaigns were conducted 230 over Maqu in 2017 and 2018, including lithology survey, water table levels, slug test, magnetic resonance sounding (MRS) and time-lapse electrical resistivity tomography (ERT) measurements (Li et al, 2021). It provides us with detailed hydro-geophysical information of the study area.…”

“…Soil texture is finer at topsoil layers (sandy loam) and coarse at deep soil layers (sand with gravel). The western mountains are feldspathic quartzose sandstone and sandy slate with soil covered at the top (Li et al, 2021). The western boundary, i.e., 240 mountain divide, is the well-defined hydrogeological borders, to which no-flow boundary was applied.…”