Spatial variability and associated factors of riverbed infiltration in two intermittent rivers in arid northwestern China

Study region The Heihe and Xitugou Rivers, two intermittent rivers in arid northwestern China. Study focus In the Heihe and Xitugou Rivers, we integrated shallow soil measurements, tension infiltrometer tests, and depth-resolved ground penetrating radar (GPR) attributes to compare the spatial patterns of saturated hydraulic conductivity (Ks), quantify the response of unsaturated hydraulic conductivity (Ku) to decreasing suction, and identify shallow and subsurface features associated with Ks. New hydrological insights for the region Ks ranged from 0.72 to 2.31 cm·min −1 in Heihe and from 0.73 to 1.14 cm·min −1 in Xitugou. Spatial variability was greater in Heihe, whereas Xitugou consistently had higher channel-centre than bank values. For each 1 cm WC increase in tension head toward 0 cm WC, Ku increased by 21.7% (95% CI, 9.0–35.9%) in Heihe and 21.2% (95% CI, 13.5–29.4%) in Xitugou. Structural differences were concentrated in shallow sediments. In Heihe, Ks was positively associated with the log-transformed particle-size ratio ln(P2/P3). Higher Ks also corresponded to lower log-envelope values at 5.5 and 7.5 m and more homogeneous GPR textures at 6–9 m. In Xitugou, no individual shallow-soil variable showed a stable association with Ks, whereas higher Ks corresponded to lower profile-mean relative energy across 1–9 m. Overall, Ks variability reflected river-specific combinations of shallow-soil conditions and subsurface GPR features.