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排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
Jan Nyssen Wim Clymans Katrien Descheemaeker Jean Poesen Ine Vandecasteele Matthias Vanmaercke Amanuel Zenebe Marc Van Camp Mitiku Haile Nigussie Haregeweyn Jan Moeyersons Kristine Martens Tesfamichael Gebreyohannes Jozef Deckers Kristine Walraevens 《水文研究》2010,24(13):1880-1895
Impact studies of catchment management in the developing world rarely include detailed hydrological components. Here, changes in the hydrological response of a 200‐ha catchment in north Ethiopia are investigated. The management included various soil and water conservation measures such as the construction of dry masonry stone bunds and check dams, the abandonment of post‐harvest grazing, and the establishment of woody vegetation. Measurements at the catchment outlet indicated a runoff depth of 5 mm or a runoff coefficient (RC) of 1·6% in the rainy season of 2006. Combined with runoff measurements at plot scale, this allowed calculating the runoff curve number (CN) for various land uses and land management techniques. The pre‐implementation runoff depth was then predicted using the CN values and a ponding adjustment factor, representing the abstraction of runoff induced by the 242 check dams in gullies. Using the 2006 rainfall depths, the runoff depth for the 2000 land management situation was predicted to be 26·5 mm (RC = 8%), in line with current RCs of nearby catchments. Monitoring of the ground water level indicated a rise after catchment management. The yearly rise in water table after the onset of the rains (ΔT) relative to the water surplus (WS) over the same period increased between 2002–2003 (ΔT/WS = 3·4) and 2006 (ΔT/WS >11·1). Emerging wells and irrigation are other indicators for improved water supply in the managed catchment. Cropped fields in the gullies indicate that farmers are less frightened for the destructive effects of flash floods. Due to increased soil water content, the crop growing period is prolonged. It can be concluded that this catchment management has resulted in a higher infiltration rate and a reduction of direct runoff volume by 81% which has had a positive influence on the catchment water balance. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
983.
Hendrik Rujner Günther Leonhardt Jiri Marsalek Anna‐Maria Perttu Maria Viklander 《水文研究》2018,32(5):644-654
The effects of soil water content (SWC) on the formation of run‐off in grass swales draining into a storm sewer system were studied in two 30‐m test swales with trapezoidal cross sections. Swale 1 was built in a loamy fine‐sand soil, on a slope of 1.5%, and Swale 2 was built in a sandy loam soil, on a slope of 0.7%. In experimental runs, the swales were irrigated with 2 flow rates reproducing run‐off from block rainfalls with intensities approximately corresponding to 2‐month and 3‐year events. Run‐off experiments were conducted for initial SWC (SWCini) ranging from 0.18 to 0.43 m3/m3. For low SWCini, the run‐off volume was greatly reduced by up to 82%, but at high SWCini, the volume reduction was as low as 15%. The relative swale flow volume reductions decreased with increasing SWCini and, for the conditions studied, indicated a transition of the dominating swale functions from run‐off dissipation to conveyance. Run‐off flow peaks were reduced proportionally to the flow volume reductions, in the range from 4% to 55%. The swale outflow hydrograph lag times varied from 5 to 15 min, with the high values corresponding to low SWCini. Analysis of swale inflow/outflow hydrographs for high SWCini allowed estimations of the saturated hydraulic conductivities as 3.27 and 4.84 cm/hr in Swales 1 and 2, respectively. Such estimates differed from averages (N = 9) of double‐ring infiltrometer measurements (9.41 and 1.78 cm/hr). Irregularities in swale bottom slopes created bottom surface depression storage of 0.35 and 0.61 m3 for Swales 1 and 2, respectively, and functioned similarly as check berms contributing to run‐off attenuation. The experimental findings offer implications for drainage swale planning and design: (a) SWCini strongly affect swale functioning in run‐off dissipation and conveyance during the early phase of run‐off, which is particularly important for design storms and their antecedent moisture conditions, and (b) concerning the longevity of swale operation, Swale 1 remains fully functional even after almost 60 years of operation, as judged from its attractive appearance, good infiltration rates (3.27 cm/hr), and high flow capacity. 相似文献
984.
985.
Cyanuric acid is a suspected gastrointestinal or liver toxicant in humans. Therefore, determination of trace cyanuric acid is very important, in this work a novel, sensitive, and reliable method was developed using differential pulse polarography. Optimum conditions for analytical determination were found to be at a pH of 9.5, Britton–Robinson at a reduction potential of ?105 mV. Experimental results indicate an excellent linear correlation between the peak current and the concentration in the range of cyanuric acid from 0.5 to 27.0 µM (0.06–3.5 µg mL?1) with a correlation coefficient of 0.997. The limit of detection and limit of quantification were obtained as 0.15 and 0.5 µM (0.02–0.06 µg mL?1), respectively. The proposed method was successfully applied to the determination of cyanuric acid in pool water and in spiked milk. Cyanuric acid level in swimming pool water was found as 2.54 ± 0.47 µg mL?1 (19.7 ± 2.29 µM) in swimming pool water for N = 4 and 95% confidence interval. The recoveries were found to be sufficient. Also, the standard deviation of the data was low which shows high accuracy and precision of proposed differential pulse polarographic method. The influences of some other commonly found inorganic salts on the determination of cyanuric acid were also examined. Some interfering species were eliminated using complexing agents, e.g., EDTA. 相似文献
986.
淮安市典型土动力特性的试验研究 总被引:3,自引:2,他引:3
通过对淮安市典型的全新世沉积粉土和粘性土进行室内自振柱试验及粉土的动三轴液化试验,把粉土和粘性土的自振柱试验结果与Seed和Idriss建议的砂土及饱和粘土的剪切模量比G/Gmax-γ曲线和阻尼比λ-γ曲线的变化范围进行对比,结果表明:粉土的剪模量比要比饱和粘土的大,而比砂土的剪模量比要小,其阻尼比接近于砂土的阻尼比;粘性土的剪模量比要比一般饱和粘土的大,而与砂土的剪模量比相近,其阻尼比要比砂土的略低;粉土的抗液化强度与液化振次之间的关系可以用指数函数来表示,其振动孔隙水压力的发展规律可以用反正弦三角函数拟合;粘粒含量是影响淮安市全新世沉积粉土抗液化强度的主要影响因素。 相似文献
987.
A series of stress relaxation experiments have been carried out on faulted and intact Tennessee sandstone to explore the influence of pore water on strength at different strain rates. Temperatures employed were 20, 300 and 400°C, effective confining pressure was 1.5 kb and strain rates as low as 10–10 sec–1 were achieved. Most samples were prefaulted at 2.5 kb confining pressure and room temperature. This is thought to have secured a reproducible initial microstructure.The strength of the dry rock was almost totally insensitive to strain rate in the range 10–4 to 10–10 sec–1. In contrast, the strength of the wet rock decreased rapidly with strain rate at rates less than 10–6 sec–1. Brittle fracture of the quartz grains which constitute this rock is the most characteristic mode of failure under the test conditions used.The experimental data are discussed in terms of the possible deformation rate controlling processes, and it is suggested that in the wet experiments at intermediate to high strain rates (10–7 to 10–4 sec–1) the observed deformation rate is controlled by the kinetics of water assisted stress corrosion, whilst deformation at low strain rates (ca. 10–9 sec–1) is controlled by a pressure solution process.The results have implications for the rheology of fault rocks at depths of perhaps 10 to 15 km in sialic crust. 相似文献
988.
长江三角洲水环境水资源研究 总被引:7,自引:0,他引:7
长江三角洲包括三角洲平原及周边丘陵山地,天然的水环境良好,多年平均当地水资源量为537.79×108m3,长江干流多年平均过境水量9730×108m3,水资源丰富。目前,长江总体水质尚好,主泓水质多为Ⅱ类,沿岸部分具有Ⅲ类水。太湖是上海、苏州、无锡的主要饮用水源,但水质一直在下降,总体为Ⅲ类水(占70%),Ⅱ类水仅占15%,其他河道、小湖泊均为Ⅳ类和Ⅴ类水。钱塘江水系以Ⅱ类、Ⅲ类水为主。京杭运河为Ⅴ类、劣Ⅴ类水。随着人口增加、城镇扩展和乡镇企业快速发展,水环境污染日趋严重,清洁淡水水源日益缩减。长江三角洲平原地区出现水质性缺水,浙东宁波舟山主要是缺乏工程调剂用水。文章建议:1)应用GIS技术,作流域性水环境水资源模型,以解决平原水网区水质、水量的调控、决策和管理;2)浙东缺水区需从全省范围规划建设大区域水利工程,解决供水,避免各县市单独、分散局部规划建设;3)三角洲的洪涝灾害主要是不合理开发引起的。建议按水系自然规律整治河道,去除障碍,减少淤积,降低水位,让洪水流量有畅通去路,同时配合非工程防洪措施以综合防治洪水灾害。长江三角洲由于水环境污染造成的水质性缺水提供了人们研究人和自然环境和谐地相关发展的一个最好例证。 相似文献
989.
燕山板内造山带中段近东西向中生代右行走滑构造系统 总被引:20,自引:0,他引:20
阐述了分布燕山板内造山带中段的近东西向中生代右行走滑构造系统的几何学与运动学特征,指出该右行走滑断裂系统由古北口-平泉断裂和密云-喜峰口-锦西断裂两条主干断裂,以及夹于其间的北西向张性断层和张裂脉,北东向压性断层和褶皱等共同组成,近东西向主干断裂具有右行右列“P破裂”结构形式,北西向的张性断层和张裂脉则具有“T破裂”性质,主干断裂与北东向压性断裂和褶皱构成了一幅右行走滑双重构造(strike-slip duplexs)格局,而不是不同期次变形的产物。该走滑断裂系统形成于侏罗纪末一早白垩世初(147-132Ma),由于它恰好构成了位于辽西的走向北东,向南东逆冲的逆冲推覆构造系统与冀北,冀西北地区北东走向,上盘向北西逆冲的推覆构造的转换和调节部位,所以本文提出了一个右行走滑构造系统的统一构造模式,在该模式中,辽西和冀北,冀西北同时代而运动方向相反的逆冲构造系统分别构成了近东西向右行走滑系统的断盘前缘挤压逆冲构造区,认为惦记山板内造山带总体构造格局的区域构造作用方式是:在总体北西一南东向挤压的一级构造应力场作用下,造山带北部的块体相对于中生代华北地台为主体的块体做向东的右景下,燕山板内造山带可能构成了亚洲东部另一个重要的“挤出构造带”或“逃逸构造域”,这种推测需要得到北部东西向断裂系具有同期左行走滑运动的支持。 相似文献
990.
煤矿突水溃砂灾害的发生与煤层上履含水层性质、岩性特征及破坏程度等诸多因素有关。通过研究己15煤层顶板基岩与第四系底部的含、隔水性能及顶板覆岩岩性组合特征,计算出一次全部开采3.6m煤层时,其导水裂缝带最小发育高度为38.46m,最大为47.95m,确定了采煤活动导致的上覆顶板含水层发生水力联系的范围,认为己15—13030工作面煤层开采时发生顶板突水的可能性不大;计算一次全部开采3.6m煤层时,防砂安全垂高最大为23.5m.防塌安全煤岩柱最大垂高为12.5m,结合煤层顶板基岩及第四系底部岩层的水文地质特征,认为工作面回采时顶板溃砂的可能性也不大。强调在生产过程中,要加强顶板涌水的观测,同时增加现有排水系统的排水能力,从而为工作面安全回采提供支持。 相似文献