鄂西长江三峡库区产流降雨特征的研究

鄂西山地连绵起伏，在暴雨作用下。坡面花岗岩风化层流失的大量粗沙在河流沟谷网中堆积起来，随时间推移逐步进入长江。根据坡面径流小区资料，在一次产流降雨中，降雨量（Ｈ），最大１０分钟（ｉ＿（１０））、３０分钟（ｉ＿（３０））和６０分钟（ｉ＿（６０））雨强对产流的作用都比较显著，它们的极值分布可用于估计不同频率Ｈ、ｉ＿（１０）、ｉ＿（３０）和ｉ＿（６０）设计值。对于林地、荒坡地和梯田，降雨侵蚀力指标以组合结构Ｅｉ＿（１０）。较适宜，而坡耕地则以组合结构Ｈｉ＿（１０）较好。根据天然降雨观测资料分析，鄂西地区的降雨类型基本上可分为均匀型、递降型、突发型和峰值型四种雨型，洪水过程和降雨过程相对应，实验流域的输沙量随Ｅｉ＿（１０）增大而增大。但对长历时降雨来说，在以蓄满产流为主的花岗岩风化土体上，Ｅｉ＿（１０）组合结构还是掩盖了降雨过程中一部分非侵蚀降雨的累积效应。

长江三峡工程库首区滑坡与线性构造的关系

三峡工程库首区分布着许多大型滑坡 ,在空间上具有丛集性规律。为探明滑坡空间上丛集性与线性构造关系 ,并查明线性构造的发育特征 ,采用了SPOT卫星像片线性构造解译及线性构造密度统计和失真指数分析方法。结果显示 。

三峡库区顺层基岩岸坡稳定性影响因素与破坏机制分析

随着三峡库区移民迁建工程实施,三峡一带的地质构造逐步受到关注。尤其是长江三峡库首区广泛分布的具有变倾角结构的顺层岸坡,常常是引发大中型岩质滑坡的罪魁祸首。一般情况下,它们状态比较稳定,然而一旦遭到破坏时,其后果不堪设想。长江三峡库首区是库区地质环境最为复杂特殊、受水库蓄水影响最大的地段之一,同时这些变倾角顺层岸坡处也是人类活动最为频繁地带,分布着大量的人口和工程建设设施。因此,对长江三峡库首区变倾角顺层岸坡的稳定性影响因素和破坏机制分析,具有相当重大的理论价值和社会意义。着重从内在因素的影响、外在动力的诱发以及顺层岸坡的破坏机制三大块着手分析。

Filling of the Three Gorges Reservoir to the 135-m Level: Instant Effects on the Yangtze Discharge and Suspended Sediment Concentration Entering the Estuary

Via the valuable opportunity of the Three Gorges Reservoir (TGR) 135-m filling in June 2003, the Yangtze discharge and suspended sediment concentration (SSC) entering the estuary during the period from 15 May to 15 July 2003 were analyzed to examine the instant effects of the filling on them. The Yangtze discharge and SSC entering the estuary in the periods before, during and after the filling clearly indicated three phases: 1) the pre-storage phase characterized by natural conditions, in which the SSC increased with increasing water discharge; 2) the storage phase, during which the SSC decreased dramatically with decreasing water discharge; and 3) the post-storage phase, during which both the SSC and water discharge remained at relatively low levels first until the end of June, then the SSC increased gradually with increasing water discharge. It seems that the times for the instant effects of the decreasing discharge downstream from the upper Yangtze on the Yangtze discharge and SSC entering the estuary due to the TGR 135-m filling to take place were about 5 d and 1 d respectively, while both were about 18 d for those of the increasing discharge. This probably reflects the buffering and resultantly hysteresis of the 1800-km stretch from the upper Yangtze to the estuary. The results are helpful for scientific and hydrological investigation of the Yangtze mainstream downstream from the TGR Dam and of the estuarine and adjacent coastal waters.

Impact of soil texture and sweetpotato cropping system on soil erosion and nutrient loss in the Three Gorges Reservoir Area of the Changjiang River

This study investigated the impact of soil texture and sweetpotato cropping system on soil erosion and nutrient loss in the drought infield of the Three Gorges Reservoir Area of Changjiang River under field conditions. A factorial experiment was conducted in the study using five soil textures and two cropping systems. The lost soil during the crop season was recovered by a soil-blocking device and the dry weights for the total lost soil and its nutrient components, such as ammonium nitrogen, effective phosphorus, K^＋ and organic matter were analyzed. We found that soil texture significantly affected the dry weights of the total lost soil, effective phosphorus, K^＋, and organic matter, while sweetpotato cropping systems and interaction between soil texture and sweetpotato cropping system affected the dry weights of the total lost soil, the effective phosphorus and organic matter. Among the five soil textures tested, Da and Huang caused significantly less soil erosion and nutrient loss compared with the other three soil textures; intercropping sweetpotato with corn significantly reduced soil erosion and nutrient loss.

Change in Sediment Load of the Yangtze River after Wenchuan Earthquake

On May 12, 2008, an earthquake of 8.0 magnitude on the Richter scale and its numerous aftershocks devastatingly hit Wenchuan County and its nearby region along the Longman Mountains in Sichuan Province, China. The heavy ruined area was up to 30,000km2 and 13% of its land surface was denuded by the extremely terrible quakes. The mountain collapses, landslides and debris flows induced by the earthquake not only scared the landscape at the immense scale, but also poured L66-billion-m3 sediment combined with offscourings and rubble into the Yangtze River and its breaches. This amount of sediments is 3 times more than the normal amount discharged into the Yangtze River, and will significantly increase sediment transportation of rivers and decrease storage capacities of reservoirs downstream. The dramatic increase in sediment load will imperil the engineering safety and impact the operation of the giant Three-Gorge Hydro-power Station if no proper prevention measures are taken.

The M_S 4.1 Reservoir-induced Hujiaping Earthquake in the Yangtze Three Gorges Reservoir Region

In this paper,based on the collected data and earthquake field investigation,characteristics of the MS4.1 Hujiaping earthquake of November 22,2008 at Guizhou town in Zigui county,Hubei Province and the geological and hydrogeological conditions and seismicity background of the area are analyzed,and the earthquake disaster is presented. Some scientific issues relating to earthquake precursors and the cause of the earthquake is discussed. The authors consider that the earthquake is a tectonic type reservoir-induced earthquake,occurring along the Xiannvshan fault under the joint action of reservoir water loading and water infiltration,and that there were certain suspected anomalies appearing in the gravity field before the earthquake. The cause of the earthquake may also be related to the effect of the Wenchuan earthquake on the local stress field.

The flood control and regulation of Three Gorges Project

The important role of Three Gorges Project (TGP) in the flood management of the Yangtze River Basin is summarized.The Optimal Regulation Schemes of the Three Gorge Reservoir is briefly described.The flood regulation effect of TGP is analyzed.Typical issues related to reservoir operation for flood regulation are discussed and suggestions are put forward for the future work.

Intensive Observation of Reservoirinduced Seismicity and Preliminary Analysis on the Causes of Earthquakes in the Three Gorges Reservoir Area,Yangtze River

In accordance with the requirements of the National Key Technology R＆D Program of the 11th ＂Five-year Plan＂, a densified seismic network consisting of 26 seismic stations was established at the Three Gorges Reservoir area in the section of Hubei Province in March 2009 （21 short-period seismographs, 5 broadband digital seismographs）. From March to December, 2009, a total of 2,995 ML -0. 8 - 2. 9 earthquakes were detected during the trial impounding of the Three Gorges Reservoir （ water level rose from 145 m to 172.8m）. Using the double difference earthquake location algorithm, 2,837 earthquakes were precisely re-located. The results show that the pattern of small local earthquake swarms in the Three Gorges Reservoir area took on a linear distribution or mass-like cluster distribution, the mass-like clusters of events were generally within a distance of 5 km from waterfront, and the linear distribution of the earthquakes could be extended to a distance of 16 km away from the waterfront. In the Hubei section of the Three Gorges Reservoir, earthquakes were mainly concentrated in the northern end of the Xiannvshan and Jiuwanxi faults near the Xiangxihe River, and along the banks of the Yangtze River at the west of Xietan township and the Shenlongxi area on the northern bank in the Badong region, with focal depths less than 10km, and 4km in average. Earthquake frequency in the reservoir region had a positive correlation with reservoir water level fluctuations, indicating that the seismicity belongs to reservoir induced earthquakes. Along the Shenlong River in the reservoir area, earthquakes showed three linear distributions in the northern Badong county, and distributed according to Karst distribution. There are underground rivers in the carbonate strata. When the reservoir was impounded, water permeated into the underground rivers, thus inducing earthquakes. Earthquakes in the areas on the crossriver segment of Xiannvshan fault, the Jiuwanxi fault and at the areas west of Xietan, Shazhen and Xizhen, may be related to the softening of discontinuities, such as the Nukou fault, the Xiannvshan fault, or the bedding joints, which would lead to failure of rock masses, thus, inducing earthquakes. However, convincing conclusions about the triggering mechanism still need further study. Additionally, near the areas south of Wenhua and Yanglin of Zigui county and at Rangkou town east of Badong county, mininginduced earthquakes occurred at the mines nearby, and on the shores of the reservoir are some collapse earthquakes.