Hydraulic properties of the porous‐fiber module and its effects on infiltration and runoff

Abstract

The porous-fiber module (PFM) composed of modified hydrophilic rock wool is an advanced product used for rainfall regulation. However, the hydraulic properties of the PFM and the effects of PFM embedding on key water cycle processes are unclear. In this study, to determine the water absorption and desorption properties of the PFM, a wetting front experiment was conducted in a soil box, comprehensively considering several factors, including two densities of PFM, three PFM cube side lengths, and three initial soil water contents. Furthermore, simulated rainfall experiments were conducted with three types of rainfall intensities to quantify the impacts of PFM embedding with two different patterns on soil infiltration and runoff. The results show that the maximum water absorption volume of each PFM was >93%, with that of the PFM with high density 1.75% higher than that of the low-density PFM.For a fully saturated PFM in soil, the horizontal and vertical wetting front advance rates gradually decreased and exhibited a power function relationship with time. The results of the simulated rainfall experiments indicate that a PFM cube embedded in the soil increased the infiltration rate in the later period of rainfall events, while a PFM slice separating the upper and lower soil layers showed an opposite trend. Both PFM embedding patterns effectively increased the average cumulative infiltration of the soil by 0.5-4.5% compared with that of the control groups. Moreover, they delayed the runoff time by 5-35 min and reduced the volume of the surface runoff by 5-100% under various rainfall intensities. INTRODUCTIONSoil regulates water cycle processes (Dobriyal et al., 2012;Wang et al., 2006); this function is affected by its physical Abbreviations: AIR, average infiltration rates; PFM, porous-fiber module; PFM HD , high-density porous-fiber module; PFM LD , low-density porous-fiber module; PFM LD -H, low-density porous-fiber module horizontal fiber; PFM LD -V, low-density porous-fiber module vertical fiber; PFM-IN, porous-fiber module cube embedded in the soil; PFM-SE, porous-fiber module slice separating the upper and lower soil layers; R H , horizontal wetting radius; R V , vertical wetting radius

Experiment Study of Porous Fiber Material on Infiltration and Runoff of Winter Wheat Farmland in Huaibei Plain, China

“…In the early stage of a rainfall event, the PFM water content was often lower than the soil water content in the same depth, which would make soil water suction in the PFM groups higher than the control groups during rain. PFM would actively absorb the free water when the soil pore saturated during the long-duration rain because the difference in potential energy, and the water absorption capacity of hydrophilic rock wool increases with the irrigation time increase, so it can enhance the effect on the infiltration process in a long duration rainfall (Lv et al, 2021). Subsequently, the infiltration rate would reach a stable value faster, which is the reason why the RE values of the control group are higher than the PFM groups.…”

“…Subsequently, surface soil water content would reach the threshold required for runoff faster, and the wetting front moved further down, finally, the surface runoff was accelerated to be formed (Song and Wang, 2019;Zhang J. L. et al, 2019;Rascon-Ramos et al, 2021), but it might be inappropriate in shortduration rain (Choi and Shin, 2019). PFM would actively absorb the free water to alleviate the flood disaster risk in long-duration rainfall after the soil water is closed to saturation, or the soil suction is less than 75 cm (Lv et al, 2021), so it has the different varied trend after the rainfall ended for 1 h under the 100 mm/h and 50 mm/h rainfall intensity. Therefore, the applicability of PFM embedding is better under continuous or long-duration rainfall (Figure 8).…”

“…After the rainfall ended, soil water infiltrated, evaporated, or absorbed by the roots and gradually decreased to the unsaturated. At that time, the soil suction was much higher than PFM, which made PFM continuously release water to alleviate soil water deficit (Gu et al, 2020;Lv et al, 2021).…”

“…After the rainfall experiments, the water rapidly exchanged between the PFM and the surrounding soil on a large scale because of the various potential energy (Lv et al, 2021). The surface soil water decreased quickly, but the deep soil changed slowly.…”

“…Because rock wool could regulate the proportion of water, nutrient, and gas in the plant roots' environment, it has been widely used in soilless culture (Savvas and Gruda, 2018). At the same time, the field observation experiments conducted at the woodland and farmland, which confirmed PFM had significant effects on regulating soil water distribution and increasing infiltration (Gu et al, 2020;Lv et al, 2020;Gu et al, 2021;Lv et al, 2021). The above study preliminarily proved that PFM could improve the soil water-holding capacity and had good application in preventing drought and floods disasters (De-Ville et al, 2017).…”