Bailong River Research Articles

Identifying the spatial drivers of net primary productivity: A case study in the Bailong River Basin, China

Net primary productivity (NPP) is an important indicator of regional vegetation growth status and ecosystem health. In the ecologically fragile Bailong River Basin (BRB) of China, particularly in its arid valley (AV) region, vegetation is extremely sensitive to anthropogenic interferences and natural influences. Therefore, there is an urgent need to identify NPP drivers in this region. Human activities shape the landscape and affect NPP dynamics. In addition, other factors including climate, soil, and topography play pivotal roles in NPP dynamics. Hence, identifying the interactions among these variables is essential for environmental management. Here, we aimed to identify the key drivers of spatial variation in NPP and evaluate the associations among these variables. We calculated the NPP based on moderate resolution imaging spectrometer data from 2018. Redundancy analysis and variation partitioning were used to identify the key drivers and to determine the unique, shared, and total explanatory variables of these sets of variables in the BRB and AV. The spatial heterogeneity of vegetation NPP was evident, and NPP in the north was lower than that in the south. Moreover, the natural and social factors of various townships in the two regions synergistically controlled vegetation growth. In the BRB, the first four axes explained 83.4% of the total variation in NPP across all townships. Meanwhile, in the AV, the first four axes explained only 80.06% of the total variation in NPP. Mean annual temperature, solar radiation, elevation, and slope were identified as the key drivers of NPP. Variation partitioning revealed complex inter-relationships among all sets of variables, with most explanatory variables being unique or shared; as such, climate factors was important explanatory variables of NPP in the BRB. In the AV, NPP was the most affected by topographic factors. Our results may aid the policymakers and planners in implementing sustainable vegetation restoration and conservation programs.

The unusual recent streamflow declines in the Bailong River, north-central China, from a multi-century perspective

The streamflow of the Bailong River, which is a secondary tributary of the Yangtze River located on the eastern Tibetan Plateau, has declined in recent decades. Although instrumental records for the Bailong River are short, historical streamflow reconstructions enable us to evaluate the recent streamflow reductions from a multi-century perspective. Here, we present the first water-year streamflow reconstruction for the Bailong River using six tree-ring chronologies covering the period 1681–2017 CE. The reconstruction shows that the recent declines in streamflow are unprecedented over the past 337 years, with the most prolonged and severe low flows occurring in the 1990s and 2000s. Together, higher temperatures and declining precipitation have resulted in a decrease in the streamflow of the Bailong River. The mean contribution of temperature to streamflow departures is about −10.5%, while the mean contribution of precipitation to streamflow departures is about −4% for the period 1995–2011 CE. We find that temperature has a stronger influence on streamflow than precipitation, and that the influence of temperature on streamflow has increased since 1995. At the same time, the runoff efficiency has decreased dramatically. With regard to large-scale climatic forcing, ENSO and NAO exert a significant influence on the regional moisture and streamflow variations by regulating the water vapor flux and the Asian Monsoon. Extreme high-streamflow events correspond with the negative ENSO mode and the positive NAO phase. Continued warming will likely cause a continued decline in the streamflow of the Bailong River, with repercussions on the local water supply, societal well-being, and economic development.

Distribution and characteristics of large landslides in a fault zone: A case study of the NE Qinghai-Tibet Plateau

The NW-SE-striking fault zone in the Bailong River Basin in the northeastern margin of the Qinghai-Tibet Plateau have the most densely distributed, large complex landslides in China. However, the failure of large complex landslides along the fault zone and the causes of their complex geomorphic characteristics are unclear. The purpose of this study was to explore the relationship between the fault zone and the spatial distribution, direction of movement, and geomorphic characteristics of large landslides. We inventoried 29 large landslides in the middle reaches of the Bailong River and described their characteristics. Statistical analysis revealed differences in the spatial relationship between the faults and landslides of different scales. Almost all of the landslide bodies with an area > 1 km2 are distributed on the faults; in addition, the strike of the faults was found to constrain the direction of movement of the landslides to the WNW-ESE direction. Statistical results show that the cross sections of landslides in the study area are asymmetric arc, corresponding to which there are significant differences in the geomorphological characteristics of the north and south sides of landslides. The geometric characteristics, physical properties (i.e., material weakness) of the fault zone and rapid uplift of the hanging wall were responsible for the asymmetric shape of landslide cross sections and the geomorphic difference. We present a conceptual model based on the relationship between the fault zone and landslides, which facilitates an improved understanding of the relationship between the fault zone and landslide evolution.

Early identification and characteristics of potential landslides in the Bailong River Basin using InSAR technique

The Bailong River Basin is located in the southeast of Gansu Province and situated at the intersection of the Qinghai-Tibet Plateau, the Loess Plateau, and the Sichuan Basin. Geohazards, such as landslides and debris flows, have high frequency and wide distribution due to the impact of rainfall, tectonic activity, and earthquakes. These phenomena pose a serious threat to the safety of life and property of the local people. Investigating a new method to detect potential landslide and study its characteristics is important to provide key supports for local disaster prevention and mitigation.In this study, an InSAR technique called Small Baseline Subset was selected to process 60 Sentinel-1A SAR images acquired from March 2018 to March 2019. Moreover, the study area was clipped into 8 blocks to improve the efficiency of data processing and minimize the errors caused by the complex terrain of the region.On the basis of the abovementioned method, the mean surface displacement rates ranging from -158 and 100 mm/year along the line-of-sight direction were detected during March 2018 and March 2019. A total of 114 potential landslides were investigated and identified in the Bailong River Basin based on optical image interpretation and field survey. Statistical analysis of their basic information shows that most of the potential landslides tend to develop in the S, SSW, and SSE-faced slope with a gradient of 20°-40°. The elevation difference of potential landslides is less than 150 m. The slope material is mostly composed of slope deposits and heavy weathered rocks, such as phyllite. The majority of potential landslides have an area less than 5×104 m2.Yahuokou landslide, which was investigated as a potential landslide with displacement rates > 38 mm/year, broke and ran into Min River from 19 July 2019. On the basis of the analysis of landslide pre-cursory deformation and geomorphology, the landslide was divided into three sections: source, propagation, and accumulation areas. The successful identification of potential landslide demonstrates the applicability and efficiency of InSAR technique in landslide investigation and identification. This research provides foundation and scientific support for landslide mapping and disaster prevention in Bailong River Basin. © 2021, Science Press. All right reserved.

Distinct periods of fan aggradation and incision for tributary valleys of different sizes along the Bailong River, eastern margin of the Tibetan Plateau

Understanding the mechanisms of fan incision/aggradation provides key insights into the dynamics of fan evolution and hazardous fan-forming processes. This paper focuses on the discrepancy in fan evolution for two nearby valleys of different catchment areas along the Bailong River. Specifically, we study fan evolution in the small-sized CJB valley (watershed area being 1.1 km2) using sedimentary analyses and 14C dating. Sedimentary logging of seven exposed profiles indicates that mudflows and debris flows are the primary fan-forming processes. Seven samples were taken from paleosols developed in mudflow sediments, and the humin fraction was extracted for 14C dating. These ages constrain the fan aggradation period to between 10 and 4.9 cal kyr BP, and then the incision period occurred after 4.9 cal kyr BP. As the mudflow sediments may contain organic matter from hillslope legacies, the fan aggradation period may be later than the 14C ages defined in this study. In any case, the time of fan incision/aggradation in CJB is younger than that of the GLP valley (watershed area being 20 km2) where fan aggradation occurred in 21.7–7 ka and incision occurred afterward. The fan aggradation period defined by the 14C ages in CJB is consistent with an alluvial fan of similar thickness in the southeastern Tibetan Plateau and two other fans along the Bailong River. This consistency may suggest a plausible climatic control on fan evolution for small-sized tributary valleys, while the inconsistency with the larger GLP valley may suggest different climate-response regimes for tributary valleys of different sizes. More research on similar types of alluvial fans and cross-validation of different dating methods is needed.

GIS-based Analysis of Distribution and Development Characteristics of Landslide Hazards in the Bailong River Basin

The Bailong River Basin is one of the most landslide prone areas in China. Based on landslide interpretations from field investigations and high-precision remote sensing images, the influencing factors, distribution rules, and development characteristics of landslides in this region are examined using the powerful spatial analysis capability of the ArcGIS platform. This study identifies the following major influencing factors and provides corresponding conclusions. (1) Fault and tectonic activities: landslides in the study area are distributed mainly in the vicinity of the large and secondary fault zones (< 10 km) and in areas with high peak acceleration and seismic intensity (with a peak motion acceleration of 0.3 g and seismic intensity of a VIII-degree area). (2) Hydrological conditions: the closer to the river (an area of < 200 m), the higher the likelihood of a landslide to occur. Landslide density is highest in areas with substantial short-term rainfall (maximum rainfall amount within 30 min shows the highest correlation with landslides). (3) Topographic parameters of slopes: landslides are distributed mostly on sunny slopes (facing south, southwest, and southeast), gentle slopes (with an incline of approximately 15°–30°), and high mountain areas (with an elevation of approximately 1000–2000 m). (4) Vegetation: areas with low FC coverage (approximately 10%–45%) are prone to landslides, which are distributed mainly in grasslands and cultivated lands. (5) Human engineering activities: densely populated areas (urban areas) and both sides of roads (approximately 0–200 m from a road) are prone to landslides. Overall, landslides are sudden, periodic, synchronous, and occur in groups. The research results have certain reference value for hazard prevention and mitigation in the Bailong River Basin area.

Quartz OSL chronology of the loess deposits in the Western Qinling Mountains, China, and their palaeoenvironmental implications since the Last Glacial period

Extensive loess deposits exist in the Western Qinling Mountains (WQM), which constitute the transition zone between the Tibetan Plateau and the Chinese Loess Plateau (CLP). These deposits are one of the most important terrestrial archives regarding past dust activity and environmental changes in East Asia; however, they remain insufficiently known and poorly understood. Herein, we conducted detailed quartz optically stimulated luminescence dating and multi‐proxy analysis on the Zhouqu loess sequence. Our results show that the loess on the high terrace of the Bailong River started to accumulate by at least ~60 ka. The mass accumulation rate (MAR) in Zhouqu significantly varied during the Last Glacial period. The Marine Isotope Stage (MIS) 3 MARs were relatively high and stable. The highest MAR occurred in MIS 2, with peak MARs during 25–19 ka, and it decreased with rapid changes during the Holocene. The discrepancy in the MARs of the WQM loess since the Last Glacial period compared with the rates in the CLP may imply different dust deposition processes in the WQM. The reconstructed palaeoenvironmental records indicate climate changes with warm‐moist climate patterns and low dust flux in interglacial periods and cold‐dry conditions with high dust flux in glacial periods, consistent with those on the CLP. The results contribute to better understanding of the linkages between dust accumulation and climate change in the WQM area.

Characteristics and geomorphology change detection analysis of the Jiangdingya landslide on July 12, 2018, China

The reactivation of landslides has always been a prominent problem that has endangered town construction and people’s safety worldwide. At about 8 a.m. on July 12, 2018, on a mountain near the Bailong River in Nanyu Township, Zhouqu County, Gansu Province, China, a landslide collapse event occurred. About 10,000 m3 of sloped material slid into the Bailong River, with the largest stone reaching 3 m3. As a result, a large number of houses were flooded. Highways and bridges were destroyed. Using field investigations, unmanned aerial vehicle (UAV) photography, InSAR traces, historical records, and multiple remote sensing images, we extracted the landslide’s geometry and geomorphic parameters to quantify the characteristics of the Jiangdingya landslide. Based on high-resolution topographic data collected before and after the landslide, the change in the geomorphological factors, geomorphologic stability, and detection of the precursory motion before the landslide failure were analyzed to fully investigate the temporal geomorphological changes. Synthesizing the above research, we discuss the causes of landslide reactivation. The Jiangdingya landslide is a typical ancient landslide formed by the coupling of internal and external dynamics. Rainfall, seismic fault zone activity, human activities, and river erosion were the main causes of this reactivation event.

Evaluation of the Effects of Forest on Slope Stability and Its Implications for Forest Management: A Case Study of Bailong River Basin, China

Previous studies have shown that the mechanical effects of vegetation roots on slope stability can be classified as additional cohesion effects and anchorage effects. The present study investigated the combined mechanical effects (additional cohesion effects and anchorage effects) of vegetation on a slope with coarse-grained soil in the mountainous region (significantly prone to slope failure) of Gansu Province, China. A detailed survey of tree density, root system morphology and slope profiles was conducted, and we also assessed the soil cohesion provided by the root systems of monospecific stands of Robinia pseudoacacia growing in different locations on the slope. The measured data were incorporated into a numerical slope model to calculate the stability of the slope under the influence of trees. The results indicated that it was necessary to consider the anchoring effect of coarse roots when estimating the mechanical effects of trees on slope stability. In particular, the FoS (factor of safety) of the slope was increased by the presence of trees. The results also demonstrated that vegetation increased slope stability. The reinforcing effects were most significant when the trees were planted along the entire slope. Although the reinforcing effects contributed by trees were limited (only 4–11%), they were essential for making optimal use of vegetation for enhancing slope stability. Overall, vegetation development can make a major contribution to ecosystem restoration in the study region.

An Improved Two-Step Multitemporal SAR Interferometry Method for Precursory Slope Deformation Detection Over Nanyu Landslide

A major landslide in Nanyu township, Zhouqu county, Western China, occurred on July 12, 2018, causing widespread damage and blocking the Bailong river. As a widely used surface deformation measurement technique, persistent scatterer interferometry (PSI) method fails in the precursory slope deformation detection over Nanyu landslide for two reasons: the high rate slope deformation of the landslide body before the occurrence of the disaster and the low density of measurement points in the widespread nonurban regions over hillside area. To solve these problems, a two-step multitemporal interferometric synthetic aperture radar (MTInSAR) method is proposed in this letter. In the proposed method, first, a carefully designed small baseline subsets (SBASs) method is applied to extract the linear high rate deformation component, which is then subtracted from the wrapping interferogram to reduce the likelihood of signal aliasing. In the second step, a two-tier network-based MTInSAR method by exploiting both persistent scatterers (PSs) and distributed scatterers (DSs) is employed to retrieve the residual deformation. The proposed method is applied to 47 Sentinel-1 images acquired between December 2016 and July 2018 and successfully detects the precursory deformation over Nanyu landslide for the first time. Experiment results illustrate the advantage of the proposed method for measuring high rate deformation compared with the traditional PSI. By using the proposed algorithm, the deformation rate map shows a clear landslide boundary and precursors of the rapid slope movements with a maximum displacement rate of 483 mm/year along the line of sight of the satellite.

AI-based identification of low-frequency debris flow catchments in the Bailong River basin, China

Debris flow is a major geohazard in mountainous regions and poses a significant threat to life and property. The damage caused by debris flows have increased with the expansion of human settlements and activity into the mountainous regions of China. In regards to risks from debris flows, previously unrecognized low-frequency debris flow catchments constitute an especially significant threat. According to our investigation, only about 500 catchments have debris flow records in >2000 catchments of Bailong River basin. The main purpose of this paper is to introduce a new methodology using Artificial Intelligence (AI) that can simultaneously input parameters related to geomorphological conditions and material conditions to better distinguish low-frequency debris flow catchments (LFDs) from medium-high frequency debris flow catchments (MHFDs). A total of 449 prototypical debris flow catchments, 15 parameters, and 9 commonly used learning machines were used to build identification models. Debris flow catchments are divided into 4 cases (LO1-LO4) based on different sample ratios of LFDs and MHFDs, which are input into each classifier one by one. Based on model evaluation, the CHAID model in the case LO2 performs best, which only uses five parameters (formation lithology index, land use index, vegetation coverage index, drainage density and landslide density index) to predict LFDs. The results indicate that LFDs are mainly distributed in areas with less landslide distribution and better vegetation coverage compared with MHFDs. However, the distribution of LFDs is concentrated on FLI (formation lithology index) =4, which is the weak lithology area. The tree classifier seems to be better at classifying fluvial processes. The model developed in this paper can help us quickly find LFDs in similar areas, and help to assess the risk of debris flows.

Geohazards mitigation strategies simulation and evaluation based on surface runoff depth: A case study in Bailong River basin

Geohazards often cause a lot of damage to human life and property. Among the geohazard mitigation measures, ecological restoration engineering is an ecomonic and widely-used one, but the effectiveness varies with the alternatives' settings and the local stand conditions, and there is a lack of effective means to assess it. The objective of this paper is to evaluate the effectiveness of vegetation restoration alternatives on mitigating geohazards in Bailong River Basin (BRB), where the soil erosion and debris flow are very severe. Given the significance of surface hydrological process in the formation of geohazards, the surface runoff depth (SRD) simulated by the Soil and Water Assessment Tool (SWAT) was chosen to evaluate the effectiveness of the mitigation alternatives. We designed four groups of ecological restoration scenarios, among which the first three groups returned the cropland with slope above 0, 15 and 25°, respectively, to one type of vegetation from evergreen forest, deciduous forest, mingled forest, shrub and grassland. The fourth group returned two slope levels of cropland to combination of two from the above five vegetation types. At the basin level, it was shown that all the alternatives could reduce the SRD. The evergreen forest alternative performs better than other vegetation types, and converting cropland above 15° is more efficient than converting cropland above 0 and 25°. The combination of evergreen and shrub in group 4 reduces SRD the most. At the subbasin level, the spatial heterogeneity of restoration alternatives effectiveness was shown. The reduction rate of SRD at the subbasin level reveals that the restoration measures would perform well in the northeastern basin and the eastern area of midstream. The reduction of SRD per unit returned cropland area reveals that the efficiency of reducing more SRD with less returned cropland is higher in the northeastern basin. Further, a map of most efficient group 4 scenarios at the subbasin level is obtained. Our work is expected to provide information regarding the establishment or improvement of ecological restoration policy in mitigating geohazards.

The distribution of formation lithology and its control on geological disasters in the Bailong River basin of southern Gansu Province, China

Formation Lithology is one of the key parameters that determine sediment yield, and geology structure, thus its importance has grown in studying the magnitude and frequency of debris flows and landslide disaster. In this paper, we analyze the distribution of Formation Lithology and its relationship with the geology disaster in the Bailong River Basin in China’s Gansu Province. The soft rock strata exposed in Bailong River Basin, like limestone, phyllite, slate, shale and Quaternary loess, are more susceptible to geological effects, because they are weak and broken, and with poor erosion resistance. Landslides and collapses are easily formed under the endogenetic and exogenic forces to the mountain, which provide abundant material conditions for the development of debris flow. It indicates that the long-timely exposed strata distributes more wildly in this area, which, with large rate of weathering and poor erosion resistance, is easily influenced by external conditions and sudden factors, thus providing favorable conditions for the occurrence of debris flow. Therefore, it is also a high risk area for debris flow.

The siltation of debris flow behind check dam in the midstream of Bailong River

Siltation gradient and siltation length are important parameters for designing gravity check dams for debris flows, which directly affect the accuracy of estimates of interception capacity. At present, siltation gradient calculations are based primarily on empirical values, and range from 0.4 to 0.95 times the channel slope coefficient. The middle reaches of the Bailong River are one of the four areas in China that are most severely affected by debris flow hazards. Gravity dams are widely employed in this mountainous area. However, field studies of their capacity are lacking. In this paper, the operations of check dams were investigated. Based on field investigation results and theoretical analysis, calculations for siltation gradient, siltation length, and dam storage capacity are established. The impact of debris flow density, channel slope, and particle size weight percentages are discussed. The calculations show that the theoretical values for siltation gradient are consistent with measured values with 83.6% accuracy; and theoretical values of siltation length are consistent with measured values with 91.6% accuracy. The results of this research are an important reference for optimal height and spacing of dams, estimation of dam storage capacity, and disaster prevention.

Response of a loess landslide to rainfall: observations from a field artificial rainfall experiment in Bailong River Basin, China

Rainfall-induced landslides are a significant hazard in many areas of loess-covered terrain in Northwest China. To investigate the response of a loess landslide to rainfall, a series of artificial rainfall experiments were conducted on a natural loess slope, located in the Bailong River Basin, in southern Gansu Province. The slope was instrumented to measure surface runoff, pore water pressure, soil water content, earth pressure, displacement, and rainfall. The hydrological response was also characterized by time-lapse electrical resistivity tomography. The results show that most of the rainfall infiltrated into the loess landslide, and that the pore water pressure and water content responded rapidly to simulated rainfall events. This indicates that rainfall infiltration on the loess landslide was significantly affected by preferential flow through fissures and macropores. Different patterns of pore water pressure and water content variations were determined by the antecedent soil moisture conditions, and by the balance between water recharge and drainage in the corresponding sections. We observed three stages of changing pore water pressure and displacement within the loess landslide during the artificial rainfall events: Increases in pore water pressure initiated movement on the slope, acceleration in movement resulting in a rapid decrease in pore water pressure, and attainment of a steady state. We infer that a negative pore water pressure feedback process may have occurred in response to shear-induced dilation of material as the slope movement accelerated. The process of shear dilatant strengthening may explain the phenomenon of semi-continuous movement of the loess landslide. Shear dilatant strengthening, caused by intermittent or continuous rainfall over long periods, can occur without triggering rapid slope failure.

Effect of rainfall on a colluvial landslide in a debris flow valley

A colluvial landslide in a debris flow valley is a typical phenomena and is easily influenced by rainfall. The direct destructiveness of this kind of landslide is small, however, if failure occurs the resulting blocking of the channel may lead to a series of magnified secondary hazards. For this reason it is important to investigate the potential response of this type of landslide to rainfall. In the present paper, the Goulingping landslide, one of the colluvial landslides in the Goulingping valley in the middle of the Bailong River catchment in Gansu Province, China, was chosen for the study. Electrical Resistivity Tomography (ERT), Terrestrial Laser Scanning (TLS), together with traditional monitoring methods, were used to monitor changes in water content and the deformation of the landslide caused by rainfall. ERT was used to detect changes in soil water content induced by rainfall. The most significant findings were as follows:(1) the water content in the centralupper part (0~41 m) of the landslide was greater than in the central-front part (41~84 m) and (2) there was a relatively high resistivity zone at depth within the sliding zone. The deformation characteristics at the surface of the landslide were monitored by TLS and the results revealed that rainstorms caused three types of deformation and failure: (1) gully erosion at the slope surface; (2) shallow sliding failure; (3) and slope foot erosion. Subsequent monitoring of continuous changes in pore-water pressure, soil pressure and displacement (using traditional methods) indicated that long duration light rainfall (average 2.22 mm/d) caused the entire landslide to enter a state of creeping deformation at the beginning of the rainy season. Shear-induced dilation occurred for the fast sliding (30.09 mm/d) during the critical failure sub-phase (EF). Pore-water pressure in the sliding zone was affected by rainfall. In addition, the sliding L1 parts of the landslide exerted a discontinuous pressure on the L2 part. Through the monitoring and analysis, we conclude that this kind of landslide may have large deformation at the beginning and the late of the rainy season.

A comparative study of landslide susceptibility mapping using weight of evidence, logistic regression and support vector machine and evaluated by SBAS-InSAR monitoring: Zhouqu to Wudu segment in Bailong River Basin, China

The determining of landslide-prone areas in mountainous terrain is essential for land planning and hazard mitigation. In this paper, a comparative study using three statistical models including weight of evidence model (WoE), logistic regression model (LR) and support vector machine method (SVM) was undertaken in the Zhouqu to Wudu segment in the Bailong River Basin, Southern Gansu, China. Six conditionally independent environmental factors, elevation, slope, aspect, distance from fault, lithology and settlement density, were selected as the explanatory variables that may contribute to landslide occurrence based on principal component analysis (PCA) and Chi-square test. The relation between landslide distributions and these variables was analyzed using the three models and the results then used to calculate the landslide susceptibility (LS). The performance of the models was then evaluated using both the highly accurate deformation signals produced by using the Small Baseline Subset Interferometric Synthetic Aperture Radar technique and Receiver Operating Characteristic (ROC) curve. Results show more deformation points in areas with high and very high LS levels, and also more stable points in areas with low and very low LS levels for the SVM model. In addition, the SVM has larger area under the ROC curve. It indicates that the SVM has better prediction accuracy and classified ability. For the interpretability, the WoE derives the class of factors that most contributed to landsliding in the study area, and the LR reveals that factors including elevation, settlement density and distance from fault played major roles in landslide occurrence and distribution, whereas the SVM cannot provide relative weights for the variables. The outperformed SVM could be employed to determine potential landslide zones in the study area. Outcome of this research would provide preliminary basis for general land planning such as choosing new urban areas and infrastructure construction in the future, as well as for landslide hazard mitigation in Bailong River Basin.

基于综合指数法的白龙江流域生物多样性空间分异特征研究

基于综合指数法的白龙江流域生物多样性空间分异特征研究

甘肃白龙江流域生态系统粮食生产服务价值时空分异

甘肃白龙江流域生态系统粮食生产服务价值时空分异

Effectiveness of debris flow mitigation strategies in mountainous regions

Debris flows represent major hazards in most mountainous regions of the world where they repeatedly result in disasters. In order to protect people and infrastructure against future debris flows, many debris flow catchments have been artificially intervened by employing various mitigation measures, including civil engineering works. However, the commonly adapted engineering measures, such as check dams, are not effective for every debris flow catchment, and the failure of such measures even causes more damage, e.g. the Sanyanyu debris flow catchment in Zhouqu, China, killed 1756 people. In order to research the effectiveness of engineering strategies and explore much more effective mitigation works for debris flows in the mountainous regions, we took the Bailong River catchment of Southern Gansu of China as study area, with special emphasis on Sanyanyu debris flow catchment (with civil engineering works) and Goulinping debris flow catchment (without civil engineering works), and comparatively analysed the two catchments. The comparative results show that both catchments have similar material source, geomorphological/environmental and climatic conditions, however, vegetation cover and rock hardness are poorer in Goulinping than in Sanyanyu, the catchment that underwent larger-scale debris flows, suggesting that the mitigation measures had been applied in Sanyanyu catchment were inappropriate. Subsequently, we simulated the effectiveness of controlling debris flow peak discharge with check dams at the lower part of Sanyanyu and Goulinping catchment using the Kanako simulator, and summarised argument based on the hypothesis and facts from positive and negative aspects. We draw the conclusion that it is not reasonable to build check dams in the two catchments and instead, drainage channels should be primarily considered for reducing debris flow hazards in such densely populated areas. Finally, we undertook detailed field investigations and experiments on the native plants in the region, and found that the ecological mitigation measure with planting Robinia Pseudoacacia on the debris flow deposits is an effective method to alleviate debris flow hazards. It is concluded that channel works combined with ecological measures are the preferable approaches to minimize the debris flow damage in debris flow catchments characterised with high mountains, concentrated rainfalls and active neotectonic movement.