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131.
淤积泥砂对水平地运动作用时刚性坝面动压力的影响 总被引:1,自引:0,他引:1
文章基于固体介质,流体介质,液固两相饱和介质的时域显示有限元波动分析方法,研究了可压缩库水条件下淤积泥砂对水平地运动作用时刚性坝面上动压力的影响,研究中分析了作为两相介质处理的淤积泥砂的饱和度、厚度、渗透系数和孔隙率对坝面动压力的影响,还比较了作为流程两相介质,单相固体介质、单相重流体介质处理的不同淤积泥砂层模型间的计算结果差异。 相似文献
132.
Jean‐Jacques Macaire Saïda Bellemlih Christian Di‐Giovanni Patrick De Luca Lionel Visset Jacques Bernard 《地球表面变化过程与地形》2002,27(9):991-1009
In the Négron River catchment area (162 km2), surface‐sediment stores are composed of periglacial calcareous ‘grèze’ (5 × 106 t) and loess (21 × 106 t), and Holocene alluvium (12·6 × 106 t), peat (0·6 × 106 t) and colluvium (18·5 × 106 t). Seventy‐five per cent of the Holocene sediments is stored along the thalwegs. Present net sediment yield, calculated from solid discharge at the Négron outlet, is low (0·6 t km?2 a?1) due to the dominance of carbonate rocks in the catchment. Mean sediment yield during the Holocene period is 7·0 t km?2 a?1 from alluvium stores and 7·6 t km?2 a?1 from colluvium stores. Thus, the gross sediment yield during the Holocene period is about 18·7 t km?2 a?1 and the sediment delivery ratio 3 per cent. The yield considerably varies from one sub‐basin to another (3·9 to 24·5 t km?2 a?1) according to lithology: about 25 per cent and 50 per cent of initial stores of periglacial grèze and loess respectively were reworked during the Holocene period. Sediment yield has increased by a factor of 6 in the last 1000 years, due to the development of agriculture. The very high rate of sediment storage on the slope during that period (88 per cent of the yield) can be accounted for by the formation of cultivation steps (‘rideaux’). It is predicted that the current destruction of these steps will result in a sediment wave reaching the valley floors in the coming decades. Subboreal and Subatlantic sediments and pollen assemblages in the Taligny marsh, where one‐third of the alluvium is stored, show the predominant influence of human activity during these periods in the Négron catchment. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
133.
134.
黄河中游降雨特性对泥沙粒径的影响 总被引:6,自引:3,他引:6
以黄河中游36个有泥沙粒径资料的水文测站流域为样本,在不同自然地理类型流域划分的基础上,建立了流域泥沙粒径特片与降雨特性的关系。结果表明,在不同类型流域,流域泥沙的粗细与降雨季节性变率和年际变率之间存在着相当好的线性正相关关系;而与年降雨量和降雨不均匀系数之间呈明显的非线性关系。流域地面物质、植被和地貌发育程序等下垫面环境因素对泥沙粒径特性与降雨特性之间关系起着十分重要的控制作用。不同类型流域曲线的斜率各不相同,在图中所处的位置也不相同。 相似文献
135.
该文依据美国陆地卫星 (Landsat)接收的MSS、TM资料 ,得到廉州湾海区表层悬沙分布的解译图 ,分析廉州湾及湾外海区水流流场特征、悬沙的分布及输移扩散特征 ,并就潮流、径流等水动力对湾内悬沙运动、滩槽冲淤的作用和影响进行了讨论 相似文献
136.
山东月湖的沉积物分布特征及搬运趋势 总被引:12,自引:0,他引:12
1998年 11~ 12月和 1999年 8~ 9月各一个月对月湖进行的野外工作 ,共取得表层沉积物样品 131个 ,应用激光粒度仪并结合传统的筛分法对这些样品进行粒度分析 ,进行矩法计算获得粒度参数。采用Gao命名方法 ,将沉积物划分出 5种主要类型。利用Gao -Collins粒径趋势分析模型 ,计算该区沉积物粒径趋势所显示的沉积物净搬运方向 ,结果表明 ,沉积物从四周向湖中心搬运 ,同时显示湾顶的西部和北部、涨潮三角洲以及湖心等地貌单元是沉积的优势区域。 相似文献
137.
Combining ordination techniques and geostatistics to determine the patterns of diatom distributions at Lake Lama, Central Siberia 总被引:4,自引:0,他引:4
The patterns of spatial variation of diatom assemblages from surface sediments in Lake Lama were quantified using a combined approach of ordination and geostatistics. The aims were (i) to estimate the amount of variation between diatom assemblages within the lake, (ii) to model the spatial variability of the diatom assemblages and their diversity, and (iii) to map the diatom distributions in the lake. A correspondence analysis (CA) separated the diatom assemblages into a planktonic and a periphytic group. Rheophilic taxa were found within the periphytic group. Variogram analysis showed that only the sample scores of the first CA axis and the Shannon diversity index were spatially structured. The range of spatial correlation was estimated to be 55 km for both variables. The diversity and, to a lesser extent, the sample scores had considerable small-scale variability of about 20 and 3%, respectively. Estimates of the first component of the CA and the Shannon index were derived using block-kriging. The maps of the estimates provided a basis for partitioning Lake Lama according to the spatial structures into an eastern and a western basin, a north–south connection between the basins, and a north–south directed tip at the far eastern end. It was shown that variation in diatom assemblages is mainly spatially structured at the catchment scale and that there is a considerable amount of variation at smaller scales. According to the modeled spatial distribution, the assemblages are most likely affected by the lake size, morphology, and the water and nutrient input introduced by rivers. This has to be taken into account when paleolimnological interpretations are drawn from records of complex lake systems like Lake Lama. 相似文献
138.
Robert Gilbert 《Journal of Paleolimnology》2003,29(2):209-220
A sub-bottom acoustic survey of Devil Lake on the Canadian Shield in southern Ontario reveals three acoustic facies: (I) a moderately acoustically transparent, laminated sequence interpreted as a glacilacustrine deposit in glacial Lake Iroquois or a subsequent phase in water depths up to 200 m greater than at present, (II) a transitional more transparent, less layered facies interpreted as being deposited in a more distal glacial lake from erosion of sediment in the watershed exposed by the failure of the ice dam and lowering of the glacial lake before stabilization by the development of forests, and (III) an acoustically transparent facies with similar transmissivity to the water column, interpreted as Holocene gyttja. Each is spatially variable in extent and thickness in response to those processes. There is only a very weak relation between sediment thickness and the water depth in which it was deposited. Wave processes prevent deposition in water depths less than about 6 m and evidence of erosion to the greatest depths of the lake (>40 m) is pervasive. The data demonstrate the value of acoustic survey in assessing lacustrine processes and the history of lakes, and the significance of such documentation in planning a coring program and in interpreting the results. 相似文献
139.
Simon J. van Donk Xuewen Huang Edward L. Skidmore Alan B. Anderson Dick L. Gebhart Valerie E. Prehoda Elizabeth M. Kellogg 《Journal of Arid Environments》2003,54(4):687-703
Military training activities reduce vegetation cover, disturb crusts, and degrade soil aggregates, making the land more vulnerable to wind erosion. The objective of this study was to quantify wind erosion rates for typical conditions at the Marine Corps Air Ground Combat Center, Twentynine Palms, CA, U.S.A. Five Big Spring Number Eight (BSNE) sampler stations were installed at each of five sites. Each BSNE station consisted of five BSNE samplers with the lowest sampler at 0·05 m and the highest sampler at 1·0 m above the soil surface. Once a month, sediment was collected from the samplers for analysis. Occurrence of saltating soil aggregates was recorded every hour using Sensits, one at each site. The site with the most erosion had a sediment discharge of 311 kg m−1 over a period of 17 months. Other sites eroded much less because of significant rock cover or the presence of a crust. Hourly sediment discharge was estimated combining hourly Sensit count and monthly sediment discharge measured using BSNE samplers. More simultaneously measured data are needed to better characterize the relationship between these two and reconstruct a detailed time-series of wind erosion. This measured time-series can then be used for comparison with simulation results from process-based wind erosion models such as the Wind Erosion Prediction System (WEPS), once it has been adapted to the unique aspects of military lands. 相似文献
140.
Exploring some relationships between biological soil crusts, soil aggregation and wind erosion 总被引:5,自引:0,他引:5
A portable wind tunnel was used to test the contribution of biological and physical elements to overall soil aggregation on a soil dominated by biological soil crusts in south-eastern Australia. After moderate disturbance and simulated wind erosion, 90% of surface aggregates on the loamy soil and 76% on the sandy soil were dominated by biological elements (cryptogams). Lower levels of biological bonding were observed on the severely disturbed treatment. Linear regression indicated a significant positive relationship (r2=0·72) between biological soil crust cover and dry aggregation levels greater than 0·85mm. To maintain sediment transport below an erosion control target of 5gm−1s−1 for a 65kmh−1 wind at 10m height, a crust cover of approximately 20% is required. When a multiple regression model which sequentially fitted biological crust cover and dry aggregation greater than 0·85mm was applied to the data, dry aggregation accounted for more of the variation in sediment transport rate than biological crust cover. These data were used to develop a conceptual model which integrates crust cover and dry aggregation, and provides a useful framework within which to predict the likely impacts of changes in soil crust cover and aggregation. 相似文献