Daduhe River Research Articles

Evaluating Coseismic Landslide Susceptibility Following the 2022 Luding Earthquake: A Comparative Analysis of Six Displacement Regression Models Integrating Epicentral and Seismogenic Fault Distances within the Permanent-Displacement Framework

Coseismic landslides have the potential to cause catastrophic disasters. Thus, it is of crucial importance to conduct a comprehensive regional assessment of susceptibility to coseismic landslides. This study rigorously interprets 13,759 coseismic landslides triggered by the 2022 Luding earthquake within the seismic zone. Employing the Newmark method, we systematically assess the susceptibility to coseismic landslides through the application of six distinct displacement regression models. The efficacy of these models is validated against the actual landslide inventory using the area under the receiver operating characteristic (ROC) curve. A hazard map of coseismic landslides is generated based on the displacement regression model with the highest degree of fit. The results show that Moxi Town, Detuo Town, the flanks of the Daduhe River, Wandonghe River, Hailuogou River, and Yanzigou River are high-susceptibility areas for coseismic landslides. This study explores factors influencing model fit, revealing that the inclusion of the epicentral distance and the distance to the seismogenic fault in displacement prediction enhances model performance. Nevertheless, in close proximity to fault zones, the distance to the seismogenic fault exerts a more significant influence on the spatial distribution density of coseismic landslides compared to the epicentral distance. Conversely, in regions situated further from fault zones, the epicentral distance has a greater impact on the spatial distribution density of coseismic landslides compared to the distance to the seismogenic fault. These findings contribute to a nuanced understanding of coseismic landslide susceptibility and offer valuable insights for future Newmark method-based coseismic landslide displacement calculations.

Survey on performance of vertical slot and nature-like fishways at Angu hydropower station, Southwest China

To restore dam-blocked natural fish migratory passages, a growing number of artificial fishways have been built in water conservancy and hydropower projects in China. The Angu hydropower station involved diverse important fish habitats in the lower reaches of the Daduhe River in Southwest China. Therefore, a vertical slot fishway (VSF) and a nature-like fishway (NLF) were built near the backwater area of the reservoir to connect the upstream and downstream habitats. Hydrodynamic and aquatic ecological surveys were conducted after the completion of the project to estimate the fish passing effect of the two fishways. The results indicated that both fishways were in effective operation and could maintain the desired hydrodynamic conditions and be used by several local fish species. During the survey, 149 fish from 15 species and 111 fish from 17 species were captured by the traps in the VSF and NLF, respectively, while 1 263 fish from 27 species were found in the downstream area. Some species captured in the VSF were not found in the NLF, and vice versa, which implied the different preferences of fish. Meanwhile, 3 789 signals including 2 099 upward ones and 1 690 downward ones were monitored with an ultrasonic fish detector at the inlet of the VSF. These findings revealed the characteristics of fish species observed in and near the fishways and provided valuable insights into the different fish passing capabilities of VSF and NLF.

3D physics-based ground motion simulation and topography effects of the 05 September 2022 MW6.6 Luding earthquake, China

On September 5, 2022, a MW6.6 earthquake occurred in Luding, Sichuan Province, which caused a large number of casualties and serious damage to infrastructures. To represent the strong ground motion of the destructive shock, the SPECFEM 3D code is adopted to model the wave propagation and a hybrid kinematic source to model the fault rupture. As for the hybrid fault source, spatial heterogeneities aimed to simulate the high-frequency radiation are added to a prescribed asperity model used to generate the low-frequency part. With a conforming mesh of the established 100 km × 100 km × 60 km numerical model and the developed hybrid fault source, the maximum resolved frequency of the simulation is 5 Hz. First, the numerical model is validated by comparing the simulated results with the six recorded waveforms as well as the corresponding Spectral acceleration and Fourier amplitude spectra. Then, the wave fields and Synthetic seismograms are presented to investigate the velocity pulse-like ground motion in the near-fault region. Finally, the topographic effect on the ground motions is identified by comparing the results from the numerical model with (Topo) and without topography (Flat). It is demonstrated that the simulated ground motion well reproduces the near-fault fling-step effect and the wave scattering effect caused by the surface topography. The hill-canyon topography significantly amplifies the surface motion, with the amplification factors (Topo/Flat) of PGV at the peak of Gonggashan mountain and at the bottom of Daduhe river reach 1.9 and 1.4, respectively. Moreover, the PGV amplification factor is in good correlation with the topography's elevation, indicating that the topographic amplification can be predicted by establishing the relationship between amplification factor and elevation.

Available acid consumption capacity of sediments in six water bodies in the Yangtze River Basin in China

Acid-base reactivity is a fundamental property of sediments and is responsible for sediments’ multiple roles in aquatic ecosystems. However, little information currently exists about the composition, magnitude, and change of the available acid consumption capacity (AACC) of sediments. To optimize reaction conditions, we developed operational procedures to determine AACC using base titration to recover surplus acid in suspensions. We characterized the sediment AACC of Dianchi Lake (DL), Daduhe River (DR), Tuojiang River (TR), Honghu Lake (HL), Wuhan Donghu Lake (DhL), and Taihu Lake (TL) in the Yangtze River Basin, China. The procedure demonstrated that reacting 40 mL 0.1 M HCl with fresh sediments equivalent to 1.0 g dry weight for 4 h and recovering surplus acid in the suspension by NaOH titration to an endpoint pH of 3.0 could determine sediment AACC. Sediment AACC in the Yangtze River Basin had high regional variability. The mean magnitude of AACC among sites was ranked DL > DR > DhL > TR > HL > TL, which is extremely similar to their geographical location from the upper to lower reaches of the Yangtze River Basin. Qualitative results from acid titration curves showed that more components contributed to AACC in DL, DR, TR, and DhL sediments than to those in HL and TL sediments. The correlation between AACC and the total amount of multivalent cations released indicated that AACC depended significantly on labile acid-soluble minerals that contain multivalent cations (Fe3+, Fe2+, Ca2+, Al3+, Mg2+, and Mn2+) (p < 0.01). Based on the contribution percentages of multivalent cations to AACC, sediment AACC of six water bodies were divided into two types: Ca-Mg dominated (DL, DR, and TR) and Fe-Al dominated (HL, DhL, and TL). We suggest that sediment AACC complexing with pH can contribute to a better description of the acid-base characteristics of sediments.

Allopatric divergence and hybridization within Cupressus chengiana (Cupressaceae), a threatened conifer in the northern Hengduan Mountains of western China.

Having a comprehensive understanding of population structure, genetic differentiation and demographic history is important for the conservation and management of threatened species. High-throughput sequencing (HTS) provides exciting opportunities to address a wide range of factors for conservation genetics. Here, we generated HTS data and identified 266,884 high-quality single nucleotide polymorphisms from 82 individuals of Cupressus chengiana, to assess population genomics across the species' full range, comprising the Daduhe River (DDH), Minjiang River (MJR) and Bailongjiang River (BLJ) catchments in western China. admixture, principal components analysis and phylogenetic analyses indicated that each region contains a distinct lineage, with high levels of differentiation between them (DDH, MJR and BLJ lineages). MJR was newly distinguished compared to previous surveys, and evidence including coalescent simulations supported a hybrid origin of MJR during the Quaternary. Each of these three lineages should be recognized as an evolutionarily significant unit (ESU), due to isolation, differing genetic adaptations and different demographic history. Currently, each ESU faces distinct threats, and will require different conservation strategies. Our work shows that population genomic approaches using HTS can reconstruct the complex evolutionary history of threatened species in mountainous regions, and hence inform conservation efforts, and contribute to the understanding of high biodiversity in mountains.

In Situ Creep Model Testing for the Tunnel Anchor Foundation of Xingkang Suspension Bridge in Luding of China

Due to the limitations of geography and geology, cast concrete tunnel anchors were used to provide counterforces for Xingkang Suspension Bridge foundation at the left bank of Daduhe River. In this study, the in situ creep tests were conducted on two model tunnel anchors at a scale of 1:10 near the real working anchor site. Thus, the long‐term deformation of the real working tunnel anchors installed at the bridge foundation could be determined from the creep test of model tunnel anchors. The creep tests were conducted under three different loads and lasted for 102.2 h, 167.5 h, and 189.4 h, respectively. The model anchor, the surrounding rock, and their interface were all monitored and measured during the creep testing. In addition, the numerical calculation, in which the Burger creep constitution was used for describing the surrounding rock and the Mohr–Coulomb criterion for describing the concrete anchor, was performed to further evaluate the long‐term stability of the real working tunnel anchors. The numerical calculations are in good agreement with the laboratory testing results, and the creep deformations of the anchor and the surrounding rock have the same order of magnitude. The results show that the tunnel anchor and surrounding rock of Xingkang Bridge are in a stable creep state under the three different loads.

Quantitative assessment of fish passage efficiency at a vertical-slot fishway on the Daduhe River in Southwest China

Fish passage facilities are constructed to enable fish to pass anthropogenic barriers such as dams though their efficiency varies across species and location. There are a number of studies that assess the efficiency of fish passage facilities, yet rarely have such assessments been conducted in Asia. We conducted one of the first quantitative assessments of the efficiency of a vertical-slot fishway in Asia on the Daduhe River in Southwest China. Quantitative assessment of fish passage efficiency was conducted using a combination of methods, including fish sampling, video recordings and a Passive Integrated Transponder (PIT) system for tracking individually-tagged fish (N = 69 of 6 species). Fish sampling revealed 40 species assembled downstream of the dam. Fish captured closer to the fishway tended to be larger than fish caught more distant from the fishway. Half of the fish species observed downstream of the fishway were also observed at the entrance to the fishway (i.e. 153 individuals across 20 species). Video records revealed that overall passage rates were 71.2% based on the number of fish observed at the exit of the viewing chamber relative to that observed passing the entrance viewing chamber. Most fish passed the fishway at night with peak passage occurring in June. PIT technology results revealed that passage efficiency among the six tagged species ranged from 0% to 60% (four species successfully ascended the fishway). Transit time from the fishway entrance to exit was variable both among and within species that successfully ascended the fishway (i.e. 17.9–20.3 h for Schizothorax davidi, 6.4–88.8 h for Schizothorax preuanti, 46.4 h for Silurus meridionalis, 22.1–53.9 h Semilabeo prochilus). Fishway performance varied by species such that there is evidence that the fishway may be useful for maintaining river connectivity for some species. However, passage was often restricted during periods when there was sufficient flow in the fishway. Additional research is needed to put these findings in an ecological context given the overall low number of fish that passed the dam.

Evaluation and uncertainty attribution of the simulated streamflow from NoahMP-RAPID over a high-altitude mountainous basin

Accurate hydrological simulations in high-altitude mountainous basins are important for optimizing reservoir operations in hydropower production and flood control. However, the simulations experience substantial uncertainties from the sparse precipitation measurements over complex mountainous topography and the imperfect hydrological process representations over the heterogeneous surface. At the Daduhe river basin, which is a high-altitude mountainous river basin located in the eastern slope of the Tibetan Plateau, daily streamflow over the 2-year period of 2014 and 2015 is simulated using the Noah land surface model with multi-parameterizations (NoahMP) and Routing Application for Parallel computation of Discharge (RAPID) coupled model driven by the Chinese Meteorological Forcing Dataset (CMFD). Two different runoff parameterization schemes of NoahMP are used for the simulations: SIMGM, which is derived from TOPMODEL and parameterizes surface runoff using water table depth, and NOAH, in which surface runoff is parameterized using soil moisture content based on the Philip infiltration model. The simulated streamflow is evaluated at two mainstream gauges on the Daduhe river, Tongjiezi and Longtoushi, in terms of Nash-Sutcliffe Efficiency (NSE), correlation coefficient, bias, and standard deviation. The uncertainty of the simulated streamflow is attributed to different runoff parameterization in NoahMP, the flow wave celerity parameter of RAPID, and the forcing CMFD precipitation data. Results show that the NOAH runoff parameterization scheme outperforms the SIMGM scheme. NOAH satisfactorily reproduced the observed streamflow anomaly and flood timing at the two mainstream gauges, and the correlation coefficients between the simulated and observed streamflow are above 0.85. The NSE for NOAH is approximately 0.3. The mathematical decomposition of NSE reveals that the relatively low NSE value is mainly attributed to the significant streamflow bias. Without the bias, NSE can be improved to approximately 0.7. The bias shows little dependency on the flow wave celerity parameter of RAPID and the runoff parameterization of NoahMP, whereas it closely corresponds to the forcing CMFD precipitation data bias. Comparing the estimated precipitation from Budykos curve and the observed streamflow, CMFD significantly underestimates the basin-averaged precipitation, which leads to the significant streamflow underestimation in the hydrological simulations. CMFD does not correctly represent the orographic effects on precipitation in the Daduhe river basin. Comparing the rain gauge measurements located in low-altitude river valleys, the CMFD precipitation is significant underestimated, suggesting a significantly underestimation in high-altitude precipitation. This study shows that streamflow bias can be reduced by densifying rain gauges at high altitudes. Despite the bias, the NoahMP RAPID coupled model can satisfactorily reproduce streamflow anomalies and flood timing in mountainous basins. As a dam model is already included, the coupled model can be further used to optimize reservoir operations for hydropower production and flood control.

Risk Analysis for Reservoir Real-Time Optimal Operation Using the Scenario Tree-Based Stochastic Optimization Method

The inherent uncertainty of inflow forecasts hinders the reservoir real-time optimal operation. This paper proposes a risk analysis model for reservoir real-time optimal operation using the scenario tree-based stochastic optimization method. We quantify the probability distribution of inflow forecast uncertainty by developing the relationship between two forecast accuracy metrics and the standard deviation of relative forecast error. An inflow scenario tree is generated via Monte Carlo simulation to represent the uncertain inflow forecasts. We establish a scenario tree-based stochastic optimization model to explicitly incorporate inflow forecast uncertainty into the stochastic optimization process. We develop a risk analysis model based on the principle of maximum entropy (POME) to evaluate the uncertainty propagation process from flood forecasts to optimal operation. We apply the proposed methodology to a flood control system in the Daduhe River Basin, China. In addition, numerical experiments are carried out to investigate the effect of two different forecast accuracy metrics and different forecast accuracy levels on reservoir optimal flood control operation as well as risk analysis. The results indicate that the proposed methods can provide decision-makers with valuable risk information for guiding reservoir real-time optimal operation and enable risk-informed decisions to be made with higher reliabilities.

A Risk-Based Model for Real-Time Flood Control Operation of a Cascade Reservoir System under Emergency Conditions

Real-time flood control operations of a cascade reservoir system under emergency conditions can reduce the social and economic loss caused by natural disasters. This paper proposes a risk-based model for real-time flood control operation of reservoirs under emergency conditions and uncertainties. The proposed model consists of three modules: emergency scenarios establishing, Monte Carlo simulations, and risk analysis. The emergency scenarios considered are earthquakes, extreme floods and failure of the spillways of a reservoir. The uncertainty factor considered is the forecast error of reservoir inflows, arising from model structural uncertainty and parameter estimating. The Monte Carlo simulations conduct the real-time flood control operation of reservoirs considering the proposed emergency events and uncertainties. The module of risk analysis performs the assessment of the operation schedules and calculates the risk of dam overtopping, based on the results from Monte Carlo simulations. The proposed model is applied to a cascade reservoir system in the upper reaches of Daduhe river basin in China. The results show that the maximum initial water level of the Shuangjiangkou reservoir is 2447 m a.s.l. (meters above sea level) using the release capacity model and is 2444.5 m a.s.l. using the command model under the scenario of upstream dam break. The integrated risk of the reservoir increases with the initial water level and the uncertainty degree of the reservoir inflows. The decision-makers can choose the operation models according to the actual initial water level of the reservoir under different emergency scenarios.

Real‐Time Optimal Flood Control Decision Making and Risk Propagation Under Multiple Uncertainties

AbstractMultiple uncertainties exist in the optimal flood control decision‐making process, presenting risks involving flood control decisions. This paper defines the main steps in optimal flood control decision making that constitute the Forecast‐Optimization‐Decision Making (FODM) chain. We propose a framework for supporting optimal flood control decision making under multiple uncertainties and evaluate risk propagation along the FODM chain from a holistic perspective. To deal with uncertainties, we employ stochastic models at each link of the FODM chain. We generate synthetic ensemble flood forecasts via the martingale model of forecast evolution. We then establish a multiobjective stochastic programming with recourse model for optimal flood control operation. The Pareto front under uncertainty is derived via the constraint method coupled with a two‐step process. We propose a novel SMAA‐TOPSIS model for stochastic multicriteria decision making. Then we propose the risk assessment model, the risk of decision‐making errors and rank uncertainty degree to quantify the risk propagation process along the FODM chain. We conduct numerical experiments to investigate the effects of flood forecast uncertainty on optimal flood control decision making and risk propagation. We apply the proposed methodology to a flood control system in the Daduhe River basin in China. The results indicate that the proposed method can provide valuable risk information in each link of the FODM chain and enable risk‐informed decisions with higher reliability.

Phenotypic variations in cones and seeds of natural Cupressus chengiana populations in China

A total of 13 phenotypic traits from 11 natural populations of Cupressus chengiana were investigated by using nested analysis, variation coefficient, phenotypic traits differentiation coefficient, and un-weighted pair-group method by arithmetic averages (UPGMA) cluster analysis. Phenotypic variations among and within populations of C. chengiana were discussed, the relationship among phenotypic traits and that between phenotypic traits and environmental factors were analyzed, and the 11 populations were divided. The results showed that there was significant difference in phenotypic variation both between and within populations. Variation within populations (49.7%) was greater than that between populations (28.6%). The mean coefficient of phenotypic differentiation between populations was 43.4% suggesting the differentiation between populations was relatively larger. The average variation coefficient of cone mass was the highest (37.2%), followed by seed mass in single cone, and that of cone length was the smallest (8.0%) indicating the cone length was the most stable phenotypic trait. The phenotypic diversity was greatest in Kangding County and smallest in Wudu County. The mean annual temperature of the hottest month and mean annual precipitation of growing season were the main environmental factors on phenotypic diversity in cones and seeds of C. chengiana in the study region. According to the 13 phenotypic traits, the 11 populations could be divided into two groups and three subgroups, which showed how C. chengiana distributed in three watersheds. Phenotypic traits in cones and seeds of C. chengiana populations were the best in Daduhe River watershed, and those were the worst in Minjiang River watershed.

A multi-criteria decision-making model dealing with correlation among criteria for reservoir flood control operation

Flood control operation in a multi-reservoir system is a multi-criteria decision-making (MCDM) problem, in which the considered criteria are often correlated with each other. In this paper, we propose an MCDM model for reservoir flood control operation to deal with correlation among criteria. Considering the flood control safety of reservoirs and downstream protected regions, we establish the hierarchical structure of the criterion system. We use the principal component analysis method to eliminate the correlation, and transform the original criterion system into an independent comprehensive criterion system. The comprehensive decision matrix coupled with the weight vector obtained by the improved entropy weight method serves as the input to TOPSIS method, fuzzy optimum method, and fuzzy matter-element method, by which we determine the ranking order of the alternatives. We apply the proposed model to a cascade system of reservoirs at the Daduhe River basin in China. The results show that the dimensionality of the criterion system is reduced and the correlation among criteria is eliminated simultaneously, and the ranking order of the alternatives is reasonable. The proposed model provides an effective way to deal with correlation among criteria, and can be extended to wider applications in many other MCDM problems.

Magnetostratigraphy of a Loess‐Paleosol Sequence from Higher Terrace of the Daduhe River in the Eastern Margin of the Tibetan Plateau and Its Geological Significance

Magnetostratigraphy of a Loess‐Paleosol Sequence from Higher Terrace of the Daduhe River in the Eastern Margin of the Tibetan Plateau and Its Geological Significance

Seismic Landslides and the Environmental Impact in the Middle Reach of Daduhe River

There are 15 large-scaled rock landslides in the middle reach of Daduhe River in the western Sichuan. As they even dammed the Daduhe River for a long time, the dammed accumulation are well widely developed, relatively wide bottom valley have been formed in the reach. Now, there are about 80000 people lived in the valley of the reach, as the region is in high intensity (VIII-IX), the latest large earthquake (magnitude is 7.7)happened in 1876 and dammed the River, causing over ten thousand people die in the huge flood after the dam broke. As the construction velocity is faster than before, the hydropower station, highway, new village construction are put on the schedule, but people seem forgetting the historical earthquakes and seismic landside’s impact, hidden dangers may come at any time. The present paper tries to introduce the characteristics of the landslides and its environment impacts such as deep overburden, soft soil, sand liquefaction and landslide reactive. So as to call peoples’ attention for the environment during they are engaged in the large scale construction. Based on the RS interpretation and field comprehensive investigations, 15 large scaled rock landslides have been found in the reach, the volume of each is over 1000,000m3, although the remains are stable on the whole, the front part is potential unstable, if they are active triggered by the future earthquake or storm, they can dam the Daduhe River again and cause huge geo-hazards. Several ideas can be concluded as follows：(1)The reach is composed of Proterozoic acid intrusive rock and underwent several large tectonic movements, the rock mass is cut by structural planes formed in the different tectonic epoch; (2) The middle reach of Daduhe River is one part of SN strike tectonic belt in China, the main advantageous structural planes is SN strike, which is parallel to the flow direction of Daduhe River; (3) The reach is within a high intensity region with over VIII degrees, seismic landslides are well developed and they are easily reactive in the future, people confront with the deep overburden, soft soil, sand liquefaction; (4) the villages and town is generally located on the second Terrace and easily influenced by the seismic large slides, their vulnerability is high; (5) engineering measurements are necessary to protect the town villages and it is urgent to built disaster warning system.

The Characteristics and Mechanism of Large Scale Landslides between Huangjinping and Detuo in Daduhe River

Daduhe River is in western Sichuan Basin which is across the Songpan-Ganzi geosynclinal fold system and the Yangtze para-platform. There are some complex geological backgrounds in this region, such as active new tectonic movements, frequent earthquakes and high seismic intensity. Remote sensing interpretation shows that there are lots of large-scale landslides existing between Huangjinping and Detuo in the upper reaches of Daduhe River. It has been shown by the research that the reason why large-scale landslides happened frequently in this region has a close relationship with its special fault structure, landform and strata distribution. Landslides always develop along the concave bank, free face of mountain or the thin mountain ridge and they all have close connection with fault in different degrees. Although the lithology of this section is constituted by ancient Kangding complex, yet the adverse rock mass discontinuity and free face combination lay a foundation for slope’s deformation and progressive failure. The earthquake force, however, is the key factor triggering landslides.

Episodes of Cenozoic Gold Mineralization on the Eastern Margin of the Qinghai-Tibet Plateau: 40Ar/39Ar Dating and Implication for Geodynamic Events

Abstract A lot of new gold deposits have been found on the eastern margin of the Qinghai-Tibet Plateau during the past two decades. Among them, three main types of gold deposits have been recognized, including quartz-vein-type, shearzone-type and porphyry-type. The former two types of gold deposits are mainly hosted within metamorphic rocks, while the latter is related to Cenozoic magmatism. Although all of these gold deposits are believed to have been formed during the uplift process of the Qinghai-Tibet Plateau in the Cenozoic era (Wang et al., 2002b), precise isotopic age constraints have still been lacking until quite recently. This paper presents new 40Ar/39Ar data of some gold deposits on the eastern margin of the Qinghai-Tibet Plateau, which indicate that gold mineralization in the region occurred in response to the episodic stages of the orogenies. Recently obtained 40Ar/39Ar data on quartz and feldspars from several gold deposits, such as the Sandiao deposit, the Baijintaizi deposit, the Pusagang deposits, provide new constraints on gold mineralization on the eastern margin of the Qinghai-Tibet Plateau. Geochronological studies of gold deposits along the Daduhe River indicate that there are three stages of gold mineralization. The early two stages occurred as early as 65.1 Ma in the Shuibaiyang deposit and 58.95 Ma in the Ruoji deposit, while the latter stage occurred as late as 25.35 Ma in Baijintaizi and 24.70 Ma in Sandiao. Isotopic dating of three plagioclases from the Beiya deposit, Zhifanggou deposit and Luobodi deposit and a K-feldspar from the Jinchangqing deposit in Yunnan Province indicates that these deposits were formed at two stages. The Zhifanggou and Jinchangqing deposits have early stage records as old as 58.82 Ma in Zhifanggou and 55.49 Ma in Jinchangqing, but all of the above four deposits in Yunnan have late stage records of 23.18 Ma in Jinchangqing, 24.54 Ma in Zhifanggou, 24.60 Ma in Luobodi and 24.56 Ma in Hongnitang. The above results suggest that the gold deposits on the eastern margin of the Qinghai-Tibet Plateau were formed concentratedly at two main episodes, i.e. the end of the Paleocene (about 58 Ma) and the boundary between the Paleogene and the Neogene (about 25 Ma). The later episode appears to be looks like more important and was coupled with the Sichuan movement, which was extensively activated at that period. The beginning of the Cenozoic Era (about 65 Ma) might be another episode of gold mineralization, but only one deposit (Shuibaiyang) in this study has been proved to have been be formed at this stage and might be earlier than the initial collision between the Indian Plate and the Eurasia Plate. In view of geology, the above three episodes of gold mineralization are associated with three events of tectonic-magmatism and/or fluid events. Even though the gold deposits (for example, the Shuibaiyang deposit, Ruoji deposit and Pusagang deposit) were formed at different episodes, all of them are genetically related to tectonic movements in large-scale shear zones. It looks like theat tectonic events (including large-scale strike-slip) between Paleogene and Neogene had a wide influence upon gold mineralization, with new deposits formed and old deposits enriched or superimposed to be a higher grade by new stage of mineralization. The above data suggest that gold deposits were not only concentrated in some areas, but also formed mainly at different boundaries of geological times, indicating that there existed some peak stages of gold mineralization (metallogenic episodes), and that the gold deposits were formed mainly by episodic mineralization.

Characteristics and sediment deposition in Gongzhui Reservoir of the Dadu River

龚咀水库库容3.1×10⁸m³,是大渡河上最大的水库,从1971年蓄水以来的15年间,淤积量达2.2096×10⁸m³,占库容的71.3%。淤积可分蓄水初期,三角洲发展和淤积接近平衡三个时期,其淤积率分别为83.5%,53%和2.9%。淤积物的平均粒径从1.82mm增加为3.38mm。卵砾推移质移动至坝前。淤积量变化过程即为输沙能力调整恢复过程。;The total storage capacity of Gongzhui Reservior, the largest one in the Daduhe River, was 3.1×10⁸m³.The average annual runoff of the Daduhe River is 4.74×10¹⁰m³/a, while the amount of sediments is 3.249×10⁷t/a.of which pebble bed load is 9.24×10⁵t/a.making up 2.85% of the total.At Gongzhui Reservior there is about 88% of pebble and gravel bed load with hardness being more than 6 (measured by Mo-hardness metre).Gongzhui Reservior began to impound water in October 1971.During fifteen years of oparation, up to the end of 1986, the total sediments reached to an amount of 2.2096 ×10⁸m³, making up about 71.3% of storage capacity.About 2.14 ×10⁸m³ of sediments depositing in the dead capacity were silted up.Meanwhile the loss of effective capacity was l.2%.According to the deposition processes, the depositional development in Gongzhui Reservoir can be considered as three stages, namely, reservior imounding water in initial stage, delta development, and equilibrium transport and deposition.Fig.2 shows the change of the accmulated deposits with time.It can be seen that in this figure the cumulative deposition increased rapidly in the first stage and the depositional rate reached up to 83.5%.In the second stage, the reservior delta devolops rapidly, moving toward the dam while the deposition amount reduced gradually with the deposition rate 53%.After sedimentation, the sediments became much coarser with an average grain size (d_cp) increasing from 1.82mm to 3.38mm.However, in the third staget the depositional rate was only 2.9%, approaching to equilibrium.At the same time gravel and pebble bed loads moved toward the dam and then settled down to it.In conclusion.deposition process can be regarded as sediment transportation process.