Relations among Sap Flow, Soil Moisture, Weather, and Soybean Plant Parameters in High Water Demand and Final Growth Stages

The dynamics of sap flow in relation to plant morphology and weather conditions during reproductive growth of soybean (Glycine max. L. Merr.) influence decisions pertaining to efficient irrigation management and other inputs for high yields. Field studies began in 2017 at Marianna, Arkansas to measure moisture dynamics of soybeans during seed fill (R5 to R7) using heat balance stem flow gauges. Sap flow was highly correlated to solar radiation with maximum rates observed during beginning seed fill (R5). A solar radiation efficiency (SRE) value, calculated as hourly sap flow rate per Watt-hour of solar radiation (g/Wh2), is proposed. The SRE relates to crop water demand and hydraulic resistance of the soil-root-stem-leaf-pod-seed pathway. SRE values ranged from 0 - 1.2 g/Wh2. Soil moisture, growth stage, time of day, and weather conditions influenced the SRE, with higher values observed in the morning, late afternoon, and during R5 growth. Peak sap flows of 39 g/h at R5, 25 g/h at R6, and 3 g/h at R7 occurred. The ratio of measured sap flow to estimated crop evapotranspiration was 0.9 to 1.3 during R5 to R6.9 (maximum dry matter), but dropped to 0.2 at R7. Further research is needed to better understand late season reproductive moisture dynamics in soybeans.

Rill flow velocity affected by the subsurface water flow depth of purple soil in Southwest China

Subsurface water flow above the weakly permeable soil layer commonly occurs on purple soil slopes.However,it remains difficult to quantify the effect of subsurface water flow on the surface flow velocity.Laboratory experiments were performed to measure the rill flow velocity on purple soil slopes containing a subsurface water flow layer with the electrolyte tracer method considering 3 subsurface water flow depths(SWFDs:5,10,and 15 cm),3 flow rates(FRs:2,4,and 8 L min^(-1)),and 4 slope gradients(SGs:5°,10°,15°,and 20°).As a result,the pulse boundary model fit the electrolyte transport processes very well under the different SWFDs.The measured rill flow velocities were 0.202 to 0.610 m s^(-1) under the various SWFDs.Stepwise regression results indicated a positive dependence of the flow velocity on the FR and SG but a negative dependence on the SWFD.The SWFD had notable effects on the rill flow velocity.Decreasing the SWFD from 15 to 5 cm increased the flow velocity.Moreover,the flow velocities under the 10-and 15-cm SWFDs were 89%and 86%,respectively,of that under the 5-cm SWFD.The flow velocity under the 5-,10-and 15-cm SWFDs was decreased to 89%,80%,and 77%,respectively,of that on saturated soil slopes.The results will enhance the understanding of rill flow hydrological processes under SWFD impact.

An Efficient Multiple-Dimensional Finite Element Solution for Water Flow in Variably Saturated Soils

Multiple-dimensional water flow in variably saturated soils plays an important role in ecological systems such as irrigation and water uptake by plant roots; its quantitative description is usually based on the Richards＇ equation. Because of the nonlinearity of the Richards＇ equation and the complexity of natural soils, most practical simulations rely on numerical solutions with the nonlinearity solved by iterations. The commonly used iterations for solving the nonlinearity are Picard and Newton methods with the former converging at first-order rate and the later at second-order rate. A recent theoretical analysis by the authors, however, revealed that for solving the diffusive flow, the classical Picard method is actually a chord-Newton method, converging at a rate faster than first order; its linear convergence rate is due to the treatment of the gravity term. To improve computational efficiency, a similar chord-Newton method as for solving the diffusive term was proposed to solve the gravity term. Testing examples for one-dimensional flow showed significant improvement. The core of this method is to produce a diagonally dominant matrix in the linear system so as to improve the iteration-toiteration stability and hence the convergence. In this paper, we develop a similar method for multiple-dimensional flow and compare its performance with the classical Picard and Newton methods for water flow in soils characterised by a wide range of van Genuchten parameters.

Critical effects on the photosynthetic efficiency and stem sap flow of poplar in the Yellow River Delta in response to soil water

To explore the critical relationships of photosynthetic efficiency and stem sap flow to soil moisture,two-year-old poplar saplings were selected and a packaged stem sap flow gauge,based on the stem-heat balance method,and a CIRAS-2 portable photosynthesis system were used.The results show that photosynthetic rates(P_(n)),transpiration rates(T_(r)),instantaneous water use efficiency(WUE)and the stem sap flow increased initially and then decreased with decreasing soil water,but their critical values were different.The turning point of relative soil water content(W_(r))from stomatal limitation to nonstomatal limitation of P_(n)was 42%,and the water compensation point of P_(n)was 13%.Water saturation points of P_(n)and T_(r)were 64%and 56%,respectively,and the WUE was 71%.With increasing soil water,the apparent quantum yield(AQY),light saturation point(LSP)and maximum net photosynthetic rate(P_(n)max)increased first and then decreased,while the light compensation point(LCP)decreased first and then increased.When W_(r)was 64%,LCP reached a lower value of 30.7µmol m^(-2)s^(-1),and AQY a higher value of 0.044,indicating that poplar had a strong ability to utilize weak light.When W_(r)was 74%,LSP reached its highest point at 1138.3µmol·m^(-2)s^(-1),indicating that poplar had the widest light ecological amplitude and the highest light utilization efficiency.Stem sap flow and daily sap flow reached the highest value(1679.7 g d^(-1))at W_(r)values of 56%and 64%,respectively,and then declined with increasing or decreasing W_(r),indicating that soil moisture significantly affected the transpiration water-consumption of poplar.Soil water was divided into six threshold grades by critical values to maintain photosynthetic efficiency at different levels,and a W_(r)of 64-71%was classified to be at the level of high productivity and high efficiency.In this range,poplar had high photosynthetic capacity and efficient physiological characteristics for water consumption.The saplings had characteristics of water tolerance and were not drought resistant.Full attention should be given to the soil water environment in the Yellow River Delta when planting Populus.

Flow-slide characteristics and failure mechanism of shallow landslides in granite residual soil under heavy rainfall

Affected by typhoons over years, Fujian Province in Southeast China has developed a large number of shallow landslides, causing a long-term concern for the local government. The study on shallow landslide is not only helpful to the local government in disaster prevention, but also the theoretical basis of regional early warning technology. To determine the whole-process characteristics and failure mechanisms of flow-slide failure of granite residual soil slopes, we conducted a detailed hazard investigation in Minqing County, Fujian Province, which was impacted by Typhoon Lupit-induced heavy rainfall in August 2021. Based on the investigation and preliminary analysis results, we conducted indoor artificial rainfall physical model tests and obtained the whole-process characteristics of flow-slide failure of granite residual soil landslides. Under the action of heavy rainfall, a granite residual soil slope experiences initial deformation at the slope toe and exhibits development characteristics of continuous traction deformation toward the middle and upper parts of the slope. The critical volumetric water content during slope failure is approximately 53%. Granite residual soil is in a state of high volumetric water content under heavy rainfall conditions, and the shear strength decreases, resulting in a decrease in stability and finally failure occurrence. The new free face generated after failure constitutes an adverse condition for continued traction deformation and failure. As the soil permeability(cm/h) is less than the rainfall intensity(mm/h), and it is difficult for rainwater to continuously infiltrate in short-term rainfall, the influence depth of heavy rainfall is limited. The load of loose deposits at the slope foot also limits the development of deep deformation and failure. With the continuous effect of heavy rainfall, the surface runoff increases gradually, and the influence mode changes from instability failure caused by rainfall infiltration to erosion and scouring of surface runoff on slope surface. Transportation of loose materials by surface runoff is an important reason for prominent siltation in disaster-prone areas.

Soil and water loss in the Lancang River-Mekong River watershed (in Yunnan section, China) and its control measures

According to a lot of hydrological and environmental monitoring data, the condition of soil and water loss in the Lancang River Mekong River watershed (in Yunnan section, China) is described. The occurrence and development of soil and water loss is analyzed. The conclusion is that: (1) generally, the situation of soil and water loss in the Lancang River Mekong River watershed (in Yunnan section, China) is light, however, soil and water loss in some regions is serious, especially in the middle reach area of the river; (2) soil and water loss in the Lancang River Mekong River (in Yunnan section, China) watershed presents developing tendency and it is mainly caused by human beings. In accordance with these results, the control measures for soil and water loss are discussed.

Integrating water use systems and soil and water conservation measures into a hydrological model of an Iranian Wadi system

Water resources are precious in arid and semi-arid areas such as the Wadis of Iran. To sustainably manage these limited water resources, the residents of the Iranian Wadis have been traditionally using several water use systems(WUSs) which affect natural hydrological processes. In this study, WUSs and soil and water conservation measures(SWCMs) were integrated in a hydrological model of the Halilrood Basin in Iran. The Soil and Water Assessment Tool(SWAT) model was used to simulate the hydrological processes between 1993 and 2009 at daily time scale. To assess the importance of WUSs and SWCMs, we compared a model setup without WUSs and SWCMs(Default model) with a model setup with WUSs and SWCMs(WUS-SWCM model). When compared to the observed daily stream flow, the number of acceptable calibration runs as defined by the performance thresholds(Nash-Sutcliffe efficiency(NSE)≥0.68, –25%≤percent bias(PBIAS)≤25% and ratio of standard deviation(RSR)≤0.56) is 177 for the Default model and 1945 for the WUS-SWCM model. Also, the average Kling–Gupta efficiency(KGE) of acceptable calibration runs for the WUS-SWCM model is higher in both calibration and validation periods. When WUSs and SWCMs are implemented, surface runoff(between 30% and 99%) and water yield(between 0 and 18%) decreased in all sub-basins. Moreover, SWCMs lead to a higher contribution of groundwater flow to the channel and compensate for the extracted water by WUSs from the shallow aquifer. In summary, implementing WUSs and SWCMs in the SWAT model enhances model plausibility significantly.

Effect of clay content to the strength of gravel soil in the source region of debris flow

The production of runoff in the source area of a debris flow is the consequence of a reduction in soil strength. Gravel soil is widely distributed in the source region, and the influence of its clay content on soil strength is one of the important questions regarding the formation mechanism of debris flows. In this paper, the clay content in gravel soil is divided into groups of low clay content(1%, 2, 5%), moderate clay content(3.75%, 5.00%, 6.25%, 7.5%) and high clay content(10.0%, 12.5%, 15%). Tests of the unconsolidated undrained shear strength and consolidated drained shear strength were performed. The unconsolidated undrained shearing(UU) experiment simulates the rapid shear failure of loose gravel soil under the conditions of brief heavy rainfall. The consolidated drained shearing(CD) experiment simulates creep failure of consolidated sediment during extended rainfall. The pore water pressure first increased and then decreased as the clay content increased, and the increase in pore pressure was relatively high in the gravel soil sample when the clay content is in the range of 3.25-7.50%, and stress in the gravel soil is relatively low for a moderate clay content. Gravelly soils with a moderate clay content are moreprone to debris-flow initiation. This paper presents a mathematical formula for the maximum shear stress and clay content of gravel soil under two conditions. The key processes whereby the soil fails and triggers a debris flow—volume contraction of soil, expansion of clay soil, and rise of pore pressure―cause reductions in the soil friction force and enhancement of the water content in the clay particles, and subsurface erosion of soil reduces the soil viscosity, which eventually reduces the soil strength so that the soil loses its stability, liquefies and generates a debris flow.

Changes of water chemistry from rainfall to stream flow in Obagbile Catchment, Southwest Nigeria

Water chemistry changes when it flows through different pathways.This study aims to characterize the differences of water(including rainwater,overland flow,soil water,groundwater,and stream water)chemistry of five kinds of water in Obagbile Catchment in Southwest Nigeria,determine the changes in water chemistry that occur as the water moves from one pathway to another,and identify the factors responsible for the water chemistry changes.To do these,we collected 50 water samples from 10 heavy storms that received equal to or more than 10 mm of rain within an hour to test the changes of water chemical properties across various pathways in this study.The results show that overland flow had the highest p H and electrical conductivity(EC)and rainwater had the lowest values of the two parameters.Ca^(2+),Mg^(2+),Cl^(ˉ),and HCOO^(ˉ) were found to have their highest concentrations in stream water;meanwhile,NO_(3)^(–),NH_(4)^(+),and SO_(4)^(2–) were found to have almost the same low concentrations in all the water samples.K+was only dominant in stream water;while dissolved organic carbon(DOC)was lowest in rainwater,same in overland flow,soil water,and groundwater samples,and highest in stream flow.Principal component analysis(PCA)showed that for all the water samples from different pathways,two factors mainly accounted for the total variances.The two factors were related to the crustal and anthropogenic sources in rainwater,suggesting that the high loadings of major cations(e.g.,Ca^(2+) and Mg^(2+)) in rainwater samples are soil-derived.The PCA for the overland flow and soil water showed strong correlations among pH,EC,and the concentrations of Na^(+),Mg^(2+),HCOO^(-),and CH_(3)COO^(-),while the high loadings of all the parameters and the strong correlations among each other were evident in the stream water.In conclusion,the chemical constituents found in water are also the components of pathways through which the water flows.The major factors responsible for the change in the chemical properties of water in Obagbile Catchment are weathering and anthropogenic activities.

Soil surface roughness change and its effect on runoff and erosion on the Loess Plateau of China

As an important parameter in the soil erosion model, soil surface roughness（SSR） is used to quantitatively describe the micro-relief on agricultural land. SSR has been extensively studied both experimentally and theoretically; however, no studies have focused on understanding SSR on the Loess Plateau of China. This study investigated changes in SSR for three different tillage practices on the Loess Plateau of China and the effects of SSR on runoff and erosion yield during simulated rainfall. The tillage practices used were zero tillage（ZT）, shallow hoeing（SH） and contour ploughing（CP）. Two rainfall intensities were applied, and three stages of water erosion processes（splash erosion（I）, sheet erosion（II） and rill erosion（III）） were analyzed for each rainfall intensity. The chain method was used to measure changes in SSR both initially and after each stage of rainfall. A splash board was used to measure the splash erosion at stage I. Runoff and sediment data were collected continuously at 2-min intervals during rainfall erosion stages II and III. We found that SSR of the tilled surfaces ranged from 1.0% to 21.9% under the three tillage practices, and the order of the initial SSR for the three treatments was ZT〈SH〈CP. For the ZT treatment, SSR increased slightly from stage I to III, whereas for the SH and CP treatments, SSR decreased by 44.5% and 61.5% after the three water erosion stages, respectively, and the greatest reduction in SSR occurred in stage I. Regression analysis showed that the changes in SSR with increasing cumulative rainfall could be described by a power function（R2〉0.49） for the ZT, SH and CP treatments. The runoff initiation time was longer in the SH and CP treatments than in the ZT treatment. There were no significant differences in the total runoff yields among the ZT, SH and CP treatments. Sediment loss was significantly smaller（P〈0.05） in the SH and CP treatments than in the ZT treatment.

Severe drought strongly reduces water use and its recovery ability of mature Mongolian Scots pine(Pinus sylvestris var. mongolica Litv.) in a semi-arid sandy environment of northern China

Trees growing in a semi-arid sandy environment are often exposed to drought conditions due to seasonal variations in precipitation, low soil water retention and deep groundwater level.However, adaptability and plasticity of individuals to the changing drought conditions greatly vary among tree species.In this study, we estimated water use(Ts) of Mongolian Scots pine(MSP;Pinus sylvestris var.mongolica Litv.) based on sap flux density measurements over four successive years(2013–2016) that exhibited significant fluctuations in precipitation in a semi-arid sandy environment of northern China.The results showed that fluctuations in daily Ts synchronously varied with dry-wet cycles of soil moisture over the study period.The daily ratio of water use to reference evapotranspiration(Ts/ET0) on sunny days in each year showed a negative linear relationship with the severity of drought in the upper soil layer(0–1 m;P<0.01).The decrease in Ts induced by erratic drought during the growing season recovered due to precipitation.However, this recovery ability failed under prolonged and severe droughts.The Ts/ET0 ratio significantly declined with the progressive reduction in the groundwater level(gw) over the study period(P<0.01).We concluded that the upper soil layer contributed the most to the Ts of MSP during the growing season.The severity and duration of droughts in this layer greatly reduced Ts.Nevertheless, gw determined whether the Ts could completely recover after the alleviation of long-term soil drought.These results provide practical information for optimizing MSP management to stop ongoing degradation in the semi-arid sandy environments.

Water hammer prediction and control:the Green's function method

By Green＇s function method we show that the water hammer （WH） can be analytically predicted for both laminar and turbulent flows （for the latter, with an eddy vis- cosity depending solely on the space coordinates）, and thus its hazardous effect can be rationally controlled and mini- mized. To this end, we generalize a laminar water hammer equation of Wang et al. （J. Hydrodynamics, B2, 51, 1995） to include arbitrary initial condition and variable viscosity, and obtain its solution by Green＇s function method. The pre- dicted characteristic WH behaviors by the solutions are in excellent agreement with both direct numerical simulation of the original governing equations and, by adjusting the eddy viscosity coefficient, experimentally measured turbulent flow data. Optimal WH control principle is thereby constructed and demonstrated.

Soil Moisture Response to Rainfall in Forestland and Vegetable Plot in Taihu Lake Basin,China

Soil moisture and its spatial pattern are important for understanding various hydrological,pedological,ecological and agricultural processes.In this study,data of rainfall and soil moisture contents at different depths(10 cm,20 cm,40 cm and 60 cm) in forestland and vegetable plot in the Taihu Lake Basin,China were monitored and analyzed for characteristics of soil moisture variation and its response to several typical rainfall events.The following results were observed.First,great temporal variation of soil moisture was observed in the surface layer than in deeper layer in vegetable plot.In contrast,in forestland,soil moisture had similar variation pattern at different depths.Second,initial soil moisture was an important factor influencing the vertical movement of soil water during rainfall events.In vegetable plot,simultaneous response of soil moisture to rainfall was observed at 10-and 20-cm depths due to fast infiltration when initial soil was relatively dry.However,traditional downward response order occurred when initial soil was relatively wet.Third,critical soil horizon interface was an active zone of soil water accumulation and lateral movement.A less permeable W-B soil horizon interface(40-cm depth) in vegetable plot can create perched water table above it and elevate the soil water content at the corresponding depth.Fourth,the land cover was an effective control factor of soil moisture during small and moderate rainfall events.In the forestland,moderate and small rainfall events had tiny influences on soil moisture due to canopy and surface O horizon interception.Fifth,preferential flow and lateral subsurface interflow were important paths of soil water movement.During large and long duration rainfall events,lateral subsurface flow and preferential flow through surface crack or soil pipe occurred,which recharged the deep soil.However,in more concentrated large storm,surface crack or soil pipe connected by soil macropores was the main contributor to the occurrence of preferential flow.Findings of this study provide a theoretical foundation for sustainable water and fertilizer management and land use planning in the Taihu Lake Basin.

Distribution Regularity of Debris Flow and Its Hazard in Upper Reaches of Yangtze River and Other Rivers of Southwestern China

In the upper reaches of Yangtze River and other rivers of southwestern China, the debris flows develop and lead to most serious disasters because of the various landforms, complex geological structures and abundant rainfall. The distribution of debris flows has regularity in the regions with different landform, geological structure, and precipitation. The regularities of distribution of debris flows are as following： （1） distributed in transition belts of different morphologic regions; （2） distributed in the area with strong stream trenching; （3） distributed along fracture zones and seismic belts： （4） distributed in the area with abundant precipitation; （5） distribution of debris flow is azonal. The activity of abundant debris flows not only brings harm to Towns, Villages and Farmlands, Main Lines of Communication, Water-Power Engineering, Stream Channels etc., but also induces strong water and soil loss. According to the present status of debris flow prevention, the problems in disasters mitigation and soil conservancy are found out, and the key works are brought up for the future disasters prevention and soil conservancy.

Sap flow rates of Minquartia guianensis in central Amazonia during the prolonged dry season of 2015–2016

Minquartia guianensis Aubl.is a slow-growing species with several uses.In the juvenile state,it is well-adapted to low light conditions of the forest understory.However,it is still unknown how climate variability affects transpiration of this species,particularly under drought stress.In this study,we aimed to assess the effect of climatic variability on sap flow rates(SFR).SFR and radial growth were measured in six trees(14-50 cm diameter)in 2015 and 2016.Climate(precipitation,irradiance,relative humidity and temperature)and soil water content(SWC)data were also collected.SFR tended to increase in the dry season,with a negative relationship between SFR and SWC and precipitation(p<0.001),while there was a positive association between radial growth and monthly precipitation(p=0.004).Irradiance and temperature were the environmental factors more closely correlated with SFR during daytime(p<0.001),whereas relative humidity and vapor pressure deficit were the most important factors at night(p<0.001).Although negative SFR were sometimes recorded at night,the mean nocturnal sap flow was positive and across trees the nighttime sap flow accounted for 12.5%of the total daily sap flow.Increased transpiration during the dry season suggests that the root system of Minquartia was able to extract water from deep soil layers.These results widen our understanding of the ecophysiology of Amazonian trees under drought and provide further insight into the potential effect of the forecasted decline in precipitation in the Amazon region.

Stem sap flow of Haloxylon ammodendron at different ages and its response to physical factors in the Minqin oasis-desert transition zone, China

Haloxylon ammodendron, with its tolerance of drought, high temperature, and salt alkali conditions, is one of the main sand-fixing plant species in the oasis-desert transition zone in China. This study used the TDP30(where TDP is the thermal dissipation probe) to measure hourly and daily variations in the stem sap flow velocity of H. ammodendron at three age-classes(10, 15, and 20 years old,which were denoted as H10, H15, and H20, respectively) in the Minqin oasis-desert transition zone,China, from May through October 2020. By simultaneously monitoring temperature, relative humidity,photosynthetically active radiation, wind speed, net radiation, rainfall, and soil moisture in this region, we comprehensively investigated the stem sap flow velocity of different-aged H. ammodendron plants(H10,H15, and H20) and revealed its response to physical factors. The results showed that, on sunny days, the hourly variation curves of the stem sap flow velocity of H. ammodendron plants at the three age-classes were mainly unimodal. In addition, the stem sap flow velocity of H. ammodendron plants decreased significantly from September to October, which also delayed its peak time of hourly variation. On rainy days, the stem sap flow velocity of H. ammodendron plants was multimodal and significantly lower than that on sunny days.Average daily water consumption of H. ammodendron plants at H10, H15, and H20 was 1.98, 2.82, and 1.91kg/d, respectively. Temperature was the key factor affecting the stem sap flow velocity of H. ammodendron at all age-classes. Net radiation was the critical factor influencing the stem sap flow velocity of H.ammodendron at H10 and H15;however, for that at H20, it was vapor pressure deficit. The stem sap flow velocity of H. ammodendron was highly significantly correlated with soil moisture at the soil depths of 50and 100 cm, and the correlation was strengthened with increasing stand age. Altogether, our results revealed the dynamic changes of the stem sap flow velocity in different-aged H. ammodendron forest stands and its response mechanism to local physical factors, which provided a theoretical basis for the construction of new protective forests as well as the restoration and protection of existing ones in this region and other similar arid regions in the world.

Evaluation of the WEPP Model in a Belgian Agricultural Watershed

The physically based WEPP （Water Erosion Prediction Project） model was implemented in a small agricultural watershed located in central Belgium, called Ganspoel. The watershed, mainly agricultural and resulting in a smooth topography, covers about 115 ha in a landscape typical of large parts of central Europe. Seventeen runoff, peak flow and sediment yield events, collected during a 2-year monitoring period, were simulated by the model. Even though the runoff volume predictions were well correlated to the corresponding observations, WEPP prediction capability was generally unsatisfactory also when different set-up methods of the soil effective hydraulic conductivity were used. The poor performance achieved for runoff volume and peak flow simulations affected sediment yield predictions. The differences between observed and simulated values for runoff, peak flow and sediment yield events may depend on： i） the great number of small runoff and sediment yield events within the available database with which is associated large natural variation and which in many cases are not well reproduced by WEPP; ii） the lack of model calibration processes; iii） the scarceness of information about some important soil physical and hydrological parameters; iv） the land use heterogeneity and crop schedule complexity of the Ganspoel watershed.

Stable isotopes applied as water tracers for infiltration experiment

The δD and δ18O vertical profiles of soil water were measured prior to and after a rainfall event.Mechanisms of soil water movement were deciphered by comparing the soil water isotope profiles with the isotopic composition of precipitation.The results show that evaporation at the upper depth led to enrichment of the heavy isotopes.Compared to the loess profile,the shallow soil water of sand profile is relatively enriched in D and 18O due to macro-pore and low water-holding capacity.The precipitation is infiltrated into soil in piston mode,accompanied with significant mixing of older soil water.The preferential fluid flow in loess was observed at depths of 0-20 cm,caused by cracks in the depths.The hydrogen and oxygen isotopic compositions in outflow are close to the precipitation,which shows a mixing of the precipitation and old soil water,and indicates that the isotopic composition of outflow water is mainly controlled by that of the precipitation.The δD and δ18O in outflow decreased with time until stable δ values of outflow are close to those of the precipitation.

Centrifuge model tests of the formation mechanism of coarse sand debris flow

Using the self-developed visualization test apparatus, centrifuge model tests at 20 g were carried out to research the macro and microscopic formation mechanism of coarse sand debris flows. The formation mode and soil-water interaction mechanism of the debris flows were analyzed from both macroscopic and microscopic points of view respectively using high digital imaging equipment and micro-structure analysis software Geodip. The test results indicate that the forming process of debris flow mainly consists of three stages, namely the infiltration and softening stage, the overall slide stage, and debris flow stage. The essence of simulated coarse sand slope forming debris flow is that local fluidization cause slope to wholly slide. The movement of small particles forms a transient stagnant layer with increasing saturation, causing soil shear strength lost and local fluidization. When the driving force of the saturated soil exceeds the resisting force, debris flow happens on the coarse sand slope immediately.

排渗失效下尾矿库溃坝三维模型试验研究

针对尾矿库渗透破坏模式,为克服二维试验槽边壁效应对模型渗流走向及溃决位置的影响,本文以某尾矿库为原型,基于自主设计的三维尾矿库溃坝模型试验平台,进行了排渗设施失效诱发的尾矿库溃坝模型试验研究,揭示了该尾矿库的溃决模式及溃决机理。结果表明:(1)排渗失效导致的溃坝呈现局部流土破坏-坝体累计变形-深层滑动面发展贯通-整体突发失稳的渐进伴突发型溃决演化模式;(2)坝体孔隙水压力骤变是坝体发生滑动破坏的关键响应指标,预示着坝体将在短时间内由滑动体前后缘局部散浸软化、流土、塌陷转变为大范围溃决,可作为坝体溃决事故的前兆信息;(3)排渗失效导致的尾矿库溃坝过程具有渐进性和突发性的特点,发生散浸与流土破坏的过程时间较长,发生深层滑动和溃决的时间短暂,该特征可为尾矿库渗透破坏隐患治理及坝体溃决应急响应提供参考。研究结果对尾矿库溃坝的灾害预防具有重要的现实意义。