Journal of Hydrologic Engineering

The permeability coefficient of unsaturated soil and the soil–water characteristic curve (SWCC) plays a significant role in the theory of unsaturated soil mechanics. The pressure plate can quickly obtain the SWCC. Still, the unsaturated permeability coefficient often needs more expensive test equipment or more complex methods to be measured separately, which is time-consuming, laborious, and costly. In this paper, the pressure plate, a standard instrument for measuring the SWCC, is used as the primary measuring device. By using different ceramic plates with various air intake values and changing the sample size, the drainage equilibrium time under each level of matric suction is controlled by the permeability characteristics of the sample. Meanwhile, the reading device of the pressure plate meter is improved. Finally, a new method for synchronous measurement of unsaturated soil permeability coefficient and SWCC based on the axial translation technique is put forward. Taking Hunan clay as the research object, the SWCC and unsaturated permeability coefficient of clay samples with three dry densities were measured. The measured SWCC data points were fitted and analyzed by Fredlund and Xing’s (F-X) model and Van Genuchten’s (VG) model. The Childs and Collis-George’s (CCG) model and Tao Gaoliang and Kong Lingwei’s (TK) model predicted the unsaturated permeability coefficient, and the anticipated results were compared with those obtained by the new method. The results show that the new approach can simultaneously measure the SWCC and unsaturated permeability coefficient of Hunan clay. In the range of matric suction ($<200\mathrm{kPa}$) studied in this paper, the larger the dry density of samples, the smaller the change range of water content with matric suction. Under the same matric suction, the greater the dry density of the soil, the longer the drainage equilibrium time, and the smaller the unsaturated permeability coefficient. The F-X and VG models have a good fitting effect on the measured data for SWCC. The predicted value of the TK model is close to the measured result of the new method, and the predicted error of the CCG model is large.

Permeable pavements equipped with an underdrain are one of the most widely used and efficient types of green infrastructure. They can greatly reduce, delay, and retain surface runoff, given their high surface infiltration rate and storage volume; however, their performance in shallow groundwater environments is poorly understood. Based on the monitoring data of three underdrained permeable pavements in Hong Kong collected from April to November 2017, this study demonstrates and quantifies the impact of shallow groundwater on the hydrologic performance of permeable pavements. All of the permeable pavements achieved 70%–100% and 90%–100% in peak and volume reductions of surface runoff, respectively, for 90% of the rainfall events, even after 1 year of service without maintenance. However, 4,000–10,000 mm of extraneous water—equivalent to three to six times the rainfall depth during the monitoring period—entered the reservoirs of two pavements and was discharged through their underdrains. The drawdown times of these two pavements, both of which were equipped with underdrains, were $>24$ and $>72\mathrm{h}$ for 35% and 20% of the rainfall events, respectively. Underdrains did not reduce drawdown times; instead, they discharged the extraneous water from the subsurface into the sewer system. These findings demonstrate the deficiency of underdrains and the need for careful underdrain design for permeable pavements in shallow groundwater environments. In areas of shallow groundwater, detailed site investigations are recommended. Underdrains, when needed, should be elevated and installed with flow restrictors to restrict their maximum outflow and to strike a balance between drawdown time and underdrain outflow volume. The technical design of the underdrain is demonstrated to be a key factor for green infrastructure in shallow groundwater environments; it should be more highlighted and detailed in the design guidance of green infrastructure.

Spatial variability of rainfall–runoff and rainstorm–flood relationships are very important to water planning and utilization. Taking the mountainous area of Daqing River basin as the studied area, this paper reveals the variability point and inconsistency characteristics of rainfall–runoff and rainstorm–flood and presents a new approach using a copula function and geostatistical method to show spatial variability of rainfall–runoff and rainstorm–flood with the proposed virtual runoff and virtual flood. The results demonstrate that rainfall–runoff and rainstorm–flood relationships exist during great changes before and after variation point. Especially after the variation point, rainfall–runoff and rainstorm–flood relationships show more inconsistency with moderate and strong spatial variability, which are mostly in the northern area of the basin. Meanwhile, spatial variability in the rainfall–runoff relationship is similar to that in the rainstorm–flood relationship.

Changes in surface-soil hydrodynamic properties associated with torrential natural rainstorms are largely unknown. This investigation aimed at verifying if the surface hydrodynamic properties of a sandy-loam soil varied due to the heavy rainfall event (130 mm in nearly three hours) that occurred in the summer of 2020 at Palermo (Italy) and also to establish if soil recovery processes occurred soon after the event. The soil of an orchard was sampled immediately before the rainstorm and a few days and 1.5 months later. The rainstorm determined a moderate decrease (by 1.8 times) of the saturated soil hydraulic conductivity, $K_s$, and an increase of its relative variability. In the subsequent weeks, the lowest $K_s$ values detected soon after rainfall tended to disappear but the soil remained moderately less conductive (by 1.4 times) than before rainfall. Wetting and subsequent drying did not influence the means of macroscopic capillary length, ${\lambda }_c$, characteristic microscopic pore radius, ${\lambda }_m$, and depth of the wetting front, $d_{wf}$, but reduced relative variability of these parameters. Therefore, this investigation confirmed that $K_s$ is a sentinel soil property. It also suggested that a torrential rainstorm can have no more than a moderate impact on the surface-soil hydrodynamic properties. Additional investigations are necessary to (1) verify if the canopy should have a key role on the stability of the soil properties in meteorologically critical conditions; (2) determine if a link between natural and soil-perturbing artificial events can be established to investigate the short-term dynamics of the surface soil properties more easily; and (3) test the hypothesis that the greater the disturbance the faster the onset of reorganization processes.