Impact of the Rainfall Intensity and Seepage on Slope Stability in Loess Plateau

In recent years,with the increase of traffic construction in mountainous areas in China,road slope traffic accidents have become more and more common.In addition,natural disasters such as landslides,collapses and subgrade settlements caused by rainfall,driving load,seasonal variation and groundwater distribution are frequent.In particular,rainfall is one of the most common factors leading to slope instability(landslide).Therefore,this paper proposes the seep module based on the application software Geo-studio,and analyzes the slope soil parameters and slope stability under five types of rainfall conditions:light rain(10 mm/d),moderate rain(25 mm/d),heavy rain(50 mm/d),rainstorm(100 mm/d),and torrential rain(250 mm/d).The critical safety factor under rainfall intensity is fitted with nonlinear curve by sine function.The results show that the fitting curve of rainfall intensity and safety factor on the upper slope is excellent.The residual points are evenly distributed in the belt area of±0.1,and the data basically conform to the nonlinear sine model,indicating that the curve plays an essential role in slope health diagnosis.

Impacts of Rainfall Intensity on Soil Solute Loss in a Small Basin

[Objective] The study aimed to analyze the impacts of rainfall intensity on soil solute loss. [ Method] Hydrus-1D model was used to sim- ulate surface runoff process and soil solute loss process under different rainfall intensities in Meilin basin, Yixing City, and its reliability was verified. Afterwards, the model was used to simulate the movement of total nitrogen （TN） in the soil under various rainfall intensities. [Result] Hydrus-1D model had a good effect in the simulation of soil moisture and TN content in surface soil. During the rainfall, TN loss from surface soil （0 -20 cm） accounted for above 95% of total loss from the whole soil （0 -100 cm）. In addition, TN loss increased with the enhancement of rainfall intensities. However, TN loss tended to be stable when rainfall intensity exceeded 0.030 0 cm/min. [Conclusion] The research could provide theoretical refer- ences for the control of agricultural nonpoint source pollution in future.

Evaluation of rainfall threshold models for debris flow initiation in the Jiangjia Gully,Yunnan Province,China

Systematically determining the discriminatory power of various rainfall properties and their combinations in identifying debris flow occurrence is crucial for early warning systems.In this study,we evaluated the discriminatory power of different univariate and multivariate rainfall threshold models in identifying triggering conditions of debris flow in the Jiangjia Gully,Yunnan Province,China.The univariate models used single rainfall properties as indicators,including total rainfall(R_(tot)),rainfall duration(D),mean intensity(I_(mean)),absolute energy(Eabs),storm kinetic energy(E_(s)),antecedent rainfall(R_(a)),and maximum rainfall intensity over various durations(I_(max_dur)).The evaluation reveals that the I_(max_dur)and Eabs models have the best performance,followed by the E_(s),R_(tot),and I_(mean)models,while the D and R_(a)models have poor performances.Specifically,the I_(max_dur)model has the highest performance metrics at a 40-min duration.We used logistic regression to combine at least two rainfall properties to establish multivariate threshold models.The results show that adding D or R_(a)to the models dominated by Eabs,E_(s),R_(tot),or I_(mean)generally improve their performances,specifically when D is combined with I_(mean)or when R_(a)is combined with Eabs or E_(s).Including R_(a)in the I_(max_dur)model,it performs better than the univariate I_(max_dur)model.A power-law relationship between I_(max_dur)and R_(a)or between Eabs and R_(a)has better performance than the traditional I_(mean)–D model,while the performance of the E_(s)–R_(a)model is moderate.Our evaluation reemphasizes the important role of the maximum intensity over short durations in debris flow occurrence.It also highlights the importance of systematically investigating the role of R_(a)in establishing rainfall thresholds for triggering debris flow.Given the regional variations in rainfall patterns worldwide,it is necessary to evaluate the findings of this study across diverse watersheds.

Incorporating a rainfall intensity modification factorγinto the I a-S Relationship in the NRCS-CN method

The Natural Resources Conservation Service runoff curve number(NRCS-CN)method is widely used to simulate direct runoff,but the impact of rainfall intensity has not been considered.In this study,a rainfall intensity modification factor(γ)was incorporated into the Ia-S relationship of the NRCS-CN method,and the modified method(NRCS-CN-γ)was compared with the NRCS-CN method withλ=0.2 andλ=0.05 in three watersheds of the Walnut Gulch Experimental Watershed(WGEW).The results showed that for 2016-2018 period,the simulation performance of the NRCS-CN-γmethod was close to the NRCS-CN(λ=0.05)method and better than the NRCS-CN(λ=0.2)method.When the new data(2009 data with high variance)was added,the significant improvement was observed by NRCS-CN-γmethod with all the evaluation parameters being the best in the three watersheds,indicating a more adapted capa-bility of the modified method with highly uneven rainfall intensities.The covariance between rainfall intensity and the simulated runoff were 19.01,15.14,and 16.35 for the three methods,respectively.When the optimal CN changed,the relative errors representing CN sensitivity were 6.25,6.49 and 17.39 for the methods,respectively.It is suggested that the NRCS-CN-γmethod outperformed the other two methods and could contribute to a more accurate estimation of direct runoff where rainfall intensity greatly varied,especially in monsoon region or under the context of climate change.

Relationships between Rainy Days,Mean Daily Intensity and Seasonal Rainfall in Normal,Flood and Drought Years over India

here are limitations in using the seasonal rainfall total in studies of Monsoon rainfall climatology. A correlation analysis of the individual station seasonal rainfall with all India seasonal mean rainfall has been made. After taking the significance test (strictly up to 5% level) the stations which are significantly correlated have been considered in this study in normal, flood and drought years respectively. Analysis of seasonal rainfall data of 50 stations spread over a period of 41 years suggests that a linear relationship fits better than the logarithmic relationship when seasonal rainfall versus number of rainy days is studied. The linear relationship is also found to be better in the case of seasonal rainfall versus mean daily intensity.

Effects of rainfall intensity on the sediment concentration in the Loess Plateau,China

To study the effects of changes in the rainfall intensity on sediment concentrations in the Loess Plateau,the observed rainfall intensities and sediment concentrations from three typical small watersheds were used to analyze the relationship between these parameters.The results showed that the sediment concentration generally increased with the increasing rainfall intensity on slope scale.However,at watershed scale,a significant threshold phenomenon was observed for the effects of the rainfall intensity on the sediment concentration.When the rainfall intensity exceeds the threshold,the flood sediment concentration will no longer increase with the increase in the rainfall intensity.The rainfall intensity threshold increased with increasing vegetation coverage.The rainfall intensity threshold was 10–15 mm/h during 1956–1969,reached 20 mm/h from 1990 to 1997 and is approximately 40 mm/h at present.Due to a rainfall intensity of 10–15 mm/h almost happened every year,the vegetation did not change much from the 1950s to 1980s.Sediment yield mainly depends on soil erosion caused by surface flow,but the surface flow speed does not increase indefinitely with the increase in the flow discharge.Thus,the annual maximum sediment concentration of the tributaries in the loess area has been basically stable before the 1990s.

Critical rainfall intensity for safe evacuation from underground spaces with flood prevention measures

Underground space in urban areas has been expanding rapidly during recent decades, and so has the incidence of fatal accidents and extensive damage to facilities resulting from underground flooding. To evaluate the safe evacuation potential of individual underground spaces in flood-prone urban areas, the hydraulic effects of flood prevention measures, e.g., stacked flashboards or sandbags and elevated steps, were incorporated in a proposed formula for estimating the depth of inundation of an underground floor. A mathematical expression of the critical rainfall intensity for safe evacuation from underground space was established and then evaluated for two types of underground spaces, an underground shopping mall and a building basement. The results show that the critical rainfall intensity for any individual underground space can be determined easily using the proposed analytical or graphical solution. However, traditional underground flood prevention measures cannot improve safety if people refuse to evacuate immediately once water intrudes into the underground space.

Determination of a Mathematical Model of Erosion Taking into Account the Intensity of Rainfall and Soil Slopes from the Global MNT Model

Our study is being carried out in the Wouri Estuary more precisely in the Nylon area, Douala. This area is influenced by abundant rainfall which promotes the phenomenon of rain erosion. This erosion contributes to the degradation of structures and soils. To better understand and predict this phenomenon of rainfall erosion, we set out to establish a mathematical model that takes into account precipitation and topography. To this end, the data collected in the field and in the laboratory made it possible. First, we graphically modeled the variation of the potential as a function of the intensity of rainfall and the slope of the ground. Next, we identified a mathematical model from cubic spline surface interpolation. Finally, we obtained the mathematical model which makes it possible to evaluate and predict the erosion potential. The results obtained allowed to have an erosion potential of 153.67 t/ha/year with field data and 153.94 t/ha/year with laboratory data. We compared the results obtained with those existing in the literature on the same study site. This comparison made it possible to validate the established mathematical model. This mathematical model is a decision support tool and can predict problems related to water, erosion and the environment.

Inter-comparison of Raingauges on Rainfall Amount and Intensity Measurements in a Tropical Environment

The HKO （Hong Kong Observatory） has been carrying out an inter-comparison of automatic raingauges since 2011 for identifying raingauges that can meet the ~ 5% accuracy requirement of the WMO （World Meteorological Organization） in measuring rainfall amount. The inter-comparison was conducted at HKO＇s meteorological stations at King＇s Park and Hong Kong International Airport in Hong Kong. Two 0.1-mm resolution Pluvio-OTT weighing gauges were introduced in 2013. This type of raingauges has outperformed others in the WMO＇s field inter-comparison held between October 2007 and April 2009. The performances of 14 raingauges, comprising five different measurement methods, viz. drop-counting, weighing, tipping bucket with software correction, tipping bucket with extra pulse correction and tipping bucket without correction, were evaluated. The focus was to study their performances in rainfall intensity measurement, especially during heavy rain situations. Different high rainfall intensity episodes were selected for analysis. Among these episodes, the maximum 1-minute rainfall intensity as high as around 130 mm/hr was recorded by the Pluvio-OTT raingauges. This paper serves to conclude the 3-year （2011-2013） inter-comparison exercise for rainfall amount measurements and to provide preliminary 1-year （2013） comparison results on rainfall intensity measurements.

Infiltration regulation and stability analysis of soil slope under sustained and small intensity rainfall

Rainfall infiltration depth and mode can severely influence slope stability.With the sustained rainfall,the influenced region of slope gradually expands.By using the Green-Ampt model to the soil slope,infiltration regulation was discussed under sustained and small intensity rainfall.And the infiltration rate of unsaturated soil was proposed according to the saturated infiltration theory.Because of the changing of initial moisture content in depth of slope,the saturated or unsaturated infiltration rate and depth could also be changeable with the sustained rainfall infiltration.Based on the principle of strength reduction,the calculation model of slope safety factor was established under different initial moisture contents and infiltration modes.Then,the slope stability was quantitatively analyzed through software FLAC3D.The calculation results of soil slope engineering show that there is a shorter period for slope stability under different initial moisture contents and unsaturated infiltration ways at the slope wetting front.The stability period of slope is 33.3%according to different initial moisture contents of wetting front less than that of the same initial moisture content of wetting front.And the slope is easier to fail under the unsaturated infiltration.The results agree well with the actual situation under sustained and small intensity rainfall.

Rainfall Factors in the Prediction of Rainfall-induced Debris Flow

Various rainfall factors,which affect the activities of rainfall-induced debris flow,are discussed in this paper.The factors include antecedent precipitation,current precipitation,rainfall duration,intensity,peak,and rainfall pattern.Rainfall-induced debris flow is trigged by the co-action of current rainfall and antecedent rainfall.The advanced system of precipitation monitoring and forecasting in the rainfall-induced debris flow forecast system is established,which consists of four methods-numerical weather prediction,stationary meteorological satellite,weather radar echo and automatic weather station.Since the forecast of rainfall-induced debris flow is based on the prediction of precipitation,the prediction models objectively require more detailed and precise prediction products,which put forward a new research subject for meteorologists.

Rainfall and Tillage Impacts on Soil Erosion of Sloping Cropland with Subtropical Monsoon Climate- A Case Study in Hilly Purple Soil area, China

Under global warming, storm events tend to intensify, particularly in monsoon-affected regions. As an important agricultural area in China, the purple soil region in the Sichuan Basin, where it has a prevailing monsoon climate, is threatened by serious soil erosion. Tillage operations alter runoff and soil erosion processes on croplands by changing the physical properties of the soil surface. To clarify the relationship between tillage and soil erosion in the purple soil region, three different tillage practices in this region were investigated at the plot scale over 4 years： bare land with minimum tillage （BL）, conventional tillage （CT） and seasonal no-tillage ridges （SNTR） which was initially designed to prevent soil erosion by contoured ridges and no-tillage techniques. The results showed that although there were no significant differences in the surface runoff and soil erosion among the three oractices, BL caused relatively high surface runoff and soil erosion, followed by CT and SNTR. Classification and comparison of the rainfall events based on cluster analysis （CA） verified that the surface runoff was not significantly different between most intensive event and long intensive events but was significantly different between most intensive and short and medium-duration events. Only the rainfall events with the highest rainfall intensity could trigger serious soil erosion, up to 1000 kg ha^-1 in the region. Further detailed investigations on the effects of tillage operations on the soil erosion in a subtropical region with a monsoon climate are needed to provide a basis for modeling catchments and designing better management practices.

Influence of rainfall on skid resistance performance and driving safety conditions of asphalt pavements

To study the influence of rainfall on pavement skid-resistance performance and driving safety,the water film thickness(WFT)concept considering the longitudinal and transverse slopes of the pavement was utilized based on the total discharge formulation and turbulence theory of slope flow.Using experimental data measured using the British pendulum test under varying WFT levels,a model for calculating the skid resistance,namely the British pendulum number(BPN),was formulated and used to quantitatively evaluate the effects of rainfall intensity,transverse,and longitudinal slopes on the computed BPN.The study results reveal that skid resistance is linearly proportional to the pavement transverse slope and inversely proportional to the rainfall intensity and the pavement longitudinal slope.In particular,rainfall intensity,along with pavement texture depth,exhibited a significant impact on the tire-pavement friction and skid-resistance performance.The results further indicate that driving safety under wet weather is predominantly governed by skid resistance and visibility.The BPN and sideway force coefficient(SFC60)values for new asphalt pavements under different rainfall intensities are provided along with some modification to the stopping sight distance(SSD)criteria.Safe driving speed limits are also determined using a safe-driving model to develop the appropriate speed limit strategies.The overall study results provide some insights,methodology approach,and reference data for the evaluation of pavement skid-resistance performance and driving safety conditions under different pavement slopes and rainfall intensities.

Influences of sand cover on erosion processes of loess slopes based on rainfall simulation experiments

Aeolian-fluvial interplay erosion regions are subject to intense soil erosion and are of particular concern in loess areas of northwestern China. Understanding the composition, distribution, and transport processes of eroded sediments in these regions is of considerable scientific significance for controlling soil erosion. In this study, based on laboratory rainfall simulation experiments, we analyzed rainfall-induced erosion processes on sand-covered loess slopes （SS） with different sand cover patterns （including length and thickness） and uncovered loess slopes （LS） to investigate the influences of sand cover on erosion processes of loess slopes in case regions of aeolian-fluvial erosion. The grain-size curves of eroded sediments were fitted using the Weibull function. Compositions of eroded sediments under different sand cover patterns and rainfall intensities were analyzed to explore sediment transport modes of SS. The influences of sand cover amount and pattern on erosion processes of loess slopes were also discussed. The results show that sand cover on loess slopes influences the proportion of loess erosion and that the compositions of eroded sediments vary between SS and LS. Sand cover on loess slopes transforms silt erosion into sand erosion by reducing splash erosion and changing the rainfall-induced erosion processes. The percentage of eroded sand from SS in the early stage of runoff and sediment generation is always higher than that in the late stage. Sand cover on loess slopes aggravates loess erosion, not only by adding sand as additional eroded sediments but also by increasing the amount of eroded loess, compared with the loess slopes without sand cover. The influence of sand cover pattern on runoff yield and the amount of eroded sediments is larger than that of sand cover amount. Furthermore, given the same sand cover pattern, a thicker sand cover could increase sand erosion while a thinner sand cover could aggravate loess erosion. This difference explains the existence of intense erosion on slopes that are thinly covered with sand in regions where aeolian erosion and fluvial erosion interact.

Characteristics of run off and sediment generation of forest vegetationon a hill slope by use of artificial rainfall apparatus

We studied the impact of forest vegetation on soil erosion, surface runoff, and sediment generation by using field simulated rainfall apparatus. We measured runoff and sediment generation of five 4.5 × 2.1 m runoff plots （a bare soil as a control; two Pinus tabulaeformis forest plots and two Platycladus orientalis forest with row spacing of 1 m × 1 m and 1.5 m× 1.5 m, respectively） in Beijing Jiu Feng National Forest Park under three rainfall intensities （0.42, 0.83, 1.26 mm per minute）. Forest vegetation significantly reduced soil erosion and sediment yield. Mean total runoff volume in the four tree stand plots was 93% of that in the control plot, demonstrating the limited effectiveness of forest vegeta- tion in runoff control. With increasing rainfall intensity, runoff reduction in forest plots declined from 28.32% to 2.1%. Similar trends in runoff coefficient and the relationship between runoffvolume and rainfall duration was observed. Mean total sediment yield and mean sediment yield reduction rate under different treatments was 55.05% and 43.17% of those in the bare soil control plot, respectively. Rainfall intensity played an important role in runoff and sediment generation processes, and had a greater impact on runoff than on soil erosion and sediment generation. When considering several factors in runoff and sediment transport processes, the P. tabulaeform plot with row spacing at 1 × 1 m had a greater effect on soil and water conservation than did other forested plots.

Effects of Shrub on Runoff and Soil Loss at Loess Slopes Under Simulated Rainfall

Improved understanding of the effect of shrub cover on soil erosion process will provide valuable information for soil and water conservation programs.Laboratory rainfall simulations were conducted to determine the effects of shrubs on runoff and soil erosion and to ascertain the relationship between the rate of soil loss and the runoff hydrodynamic characteristics.In these simulations a 20° slope was subjected to rainfall intensities of 45,87,and 127 mm/h.The average runoff rates ranged from 0.51 to 1.26 mm/min for bare soil plots and 0.15 to 0.96 mm/min for shrub plots.Average soil loss rates varied from 44.19 to 114.61 g/(min·m^2) for bare soil plots and from 5.61 to 84.58 g/(min·m^2) for shrub plots.There was a positive correlation between runoff and soil loss for the bare soil plots,and soil loss increased with increased runoff for shrub plots only when rainfall intensity is 127 mm/h.Runoff and soil erosion processes were strongly influenced by soil surface conditions because of the formation of erosion pits and rills.The unit stream power was the optimal hydrodynamic parameter to characterize the soil erosion mechanisms.The soil loss rate increased linearly with the unit stream power on both shrub and bare soil plots.Critical unit stream power values were 0.004 m/s for bare soil plots and 0.017 m/s for shrub plots.

Numerical Simulations of Intense Meiyu Rainfall in 1991 over the Changjiang and Huaihe River Valleys by a Regional Climate Model with p-σ Incorporated Coordinate System

Based on the primitive equation model with p- σ incorporated coordinate system originally developed by Qian et al., a one-way nested fine mesh limited area model is developed. This model is nested with ECMWF T42 data to simulate the extra-intensive rainfall event occurring in the Changjiang and Huaihe River valleys in summer of 1991. The results show that the model has certain capacity to fairly reproduce the regional distribution and the movement of the main rainfall belts. Therefore it can be used as a regional climate model to simulate and predict the short-range regional climate changes.

The Extraordinary Rainfall over the Eastern Periphery of the Tibetan Plateau in August 2020

A large amount of accumulated precipitation was recorded over the Eastern Periphery of the Tibetan Plateau(EPTP)in August 2020.Using hourly rain gauge records and the ERA5 reanalysis dataset,we analyzed the unique characteristics of rainfall in August and the accompanying circulation conditions and conducted a comparison with previous data.This record-breaking amount of accumulated rainfall was centered on the northern slope of the EPTP.This location was in contrast with the historical records of the concentration of rainfall over the middle and southern slopes.The hourly rainfall in August 2020 was both more frequent and more intense than the climatological mean rainfall.An amplification effect of the topography was observed,with the precipitation over the EPTP showing a more significant change with terrain height in August 2020.A circulation analysis showed that cold(warm)anomalies existed over the north(south)of approximately 35°N compared with those in the years when the southern EPTP received more rain.The western Pacific subtropical high was more intense and extended to the west,and the low-level cold air from the north was more active.The enhanced low-level southerly winds on the periphery of the subtropical high injected warm,moist air further north than the climatological mean.These winds became easterly near the northern EPTP and were forced to ascend by the steep terrain.

Effects of intense rainfall on stability of infinite terraced slope

For fully understanding the hydrological dynamics of an infinite terraced slope, the infiltration process was studied by employing the Green and Ampt infiltration model. The limit equilibrium method and the Mohr-Coulomb failure criterion were adopted to derive a stability model for the infinite terraced slope subjected to an intense rainfall. Numerical simulation was performed for verifying its applicability. The results of numerical simulation indicate that a set of stepped wetting fronts are found during infiltration, and the infiltration of terraced slope covered by coarse-textured soils can be approximated as one-dimensional infiltration. The potential sliding surfaces from the numerical method are all parallel to the slope line, and the proposed model and framework can provide an approximate method of estimating how the infiltration affects the stability of an infinite terraced slope.

Slope Debris Flows in the Wenchuan Earthquake Area

Avalanches and landslides,induced by the Wenchuan Earthquake on May 12,2008,resulted in a lot of disaggregated,solid material on slopes that could be readily mobilized as source material for debris flows.Rainstorms triggered numerous slope debris flows with great damage to highways and rivers over the subsequent two years.Slope debris flows(as opposed to channelized debris flows) are defined as phenomena in which high-concentration mixtures of debris and water flow down slopes for short distances to highways and river banks.Based on field investigations and measurements of 19 slope debris flows,their main characteristics and potential mitigation strategies were studied.High rainfall intensity is the main triggering factor.Critical rainfall intensities for simultaneous occurrence of single,several and numerous slope debris flow events were 20 mm/day,30mm/day,and 90 mm/day,respectively.Field investigations also revealed that slope debris flows consist of high concentrations of cobbles,boulders and gravel.They are two-phase debris flows.The liquid phase plays the role of lubrication instead of transporting medium.Solid particles collide with each other and consume a lot of energy.The velocities of slope debris flows are very low,and their transport distances are only several tens of meters.Slope debris flows may be controlled by construction of drainage systems and by reforestation.