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961.
Distributed discharge and sediment concentration predictions in the sub‐humid Ethiopian highlands: the Debre Mawi watershed
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Seifu A. Tilahun Christian D. Guzman Assefa D. Zegeye Dessalegn C. Dagnew Amy S. Collick Birru Yitaferu Tammo S. Steenhuis 《水文研究》2015,29(7):1817-1828
Experimental research in the Ethiopian highlands found that saturation excess induced runoff and erosion are common in the sub‐humid conditions. Because most erosion simulation models applied in the highlands are based on infiltration excess, we, as an alternative, developed the Parameter Efficient Distributed (PED) model, which can simulate water and sediment fluxes in landscapes with saturation excess runoff. The PED model has previously only been tested at the outlet of a watershed and not for distributed runoff and sediment concentration within the watershed. In this study, we compare the distributed storm runoff and sediment concentration of the PED model against collected data in the 95‐ha Debre Mawi watershed and three of its nested sub‐watersheds for the 2010 and 2011 rainy seasons. In the PED model framework, the hydrology of the watershed is divided between infiltrating and runoff zones, with erosion only taking place from two surface runoff zones. Daily storm runoff and sediment concentration values, ranging from 0.5 to over 30 mm and from 0.1 to 35 g l?1, respectively, were well simulated. The Nash Sutcliffe efficiency values for the daily storm runoff for outlet and sub‐watersheds ranged from 0.66 to 0.82, and the Nash–Sutcliffe efficiency for daily sediment concentrations were greater than 0.78. Furthermore, the model uses realistic fractional areas for surface and subsurface flow contributions, for example between saturated areas (15%), degraded areas (30%) and permeable areas (55%) at the main outlet, while close similarity was found for the remaining hydrology and erosion parameter values. One exception occurred for the distinctly greater transport limited parameter at the actively gullying lower part of the watershed. The results suggest that the model based on saturation excess provides a good representation of the observed spatially distributed runoff and sediment concentrations within a watershed by modelling the bottom lands (as opposed to the uplands) as the dominant contributor of the runoff and sediment load. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
962.
A. Zuber S. Witczak K. Raski I.
liwka M. Opoka P. Mochalski T. Kuc J. Karlikowska J. Kania M. Jackowicz‐Korczyski M. Duliski 《水文研究》2005,19(11):2247-2275
A comprehensive study of a sandy aquifer of deltaic origin in southern Poland included water chemistry, isotopes, dissolved trace gases and transport modelling. Tritium, sulphur hexafluoride (SF6) and freons (F‐11, F‐12 and F‐113) showed the presence of modern waters in the recharge areas and shallow confined parts of the aquifer. The presence of older Holocene waters farther from the recharge areas was indicated by lack of 3H, SF6 contents ≤0·02 fmol l−1 and relatively low 14C values. The discharge from the system is by upward seepage in the valley of a major river. Pre‐Holocene waters of a cooler climate, identified on the basis of δ18O, δ2H, 14C, Ne and Ar data, were found in some distant wells. Concentrations of N2, Ne and Ar determined by gas chromatography were used for calculating the noble gas temperatures, air excess needed for correction of SF6, and nitrogen content released by denitrification process. The time series of 3H content available for some wells supplied quantitative information on age distributions and the total mean ages of flow through the unsaturated and saturated zones. The derived 3H age distributions turned out to be very wide, with mean values in the range of about 30 to 160 years. For each well with determined 3H age, the SF6 data showed either a lower age range or the possibility of a lower age as expected due to shorter travel times of SF6 through the unsaturated zone, which most probably also resulted in different types of age distributions of these tracers. Freons appeared to be of little use for individual age determinations. A quantitative estimation of two‐component mixing from SF6 3H relations is not possible unless the travel time of 3H through the unsaturated zone is comparable to that of SF6. The ratio of integrals of the response function over the age range with tracer and the whole response function yields the ratio of water with tracer to total flow of water. That ratio is a tracer‐dependent function of time. Transport modelling of SF6 tracer done with MT3D code yielded initially large discrepancies between calculated and measured tracer concentrations. Some discrepancies remained even after calibration of the transport model with SF6. Simulation of tritium contents with a calibrated transport model yielded reasonable agreement with measured contents in some wells and indicated a need for further investigations, particularly in the eastern part of the aquifer. The existence of distinct hydrochemical zones is consistent with the tracer data; young waters with measurable 3H and SF6 contents are aerobic and of HCO3 Ca or HCO3 SO4 Ca types. Slightly elevated Na and Cl contents, as well as the highest concentrations of SO4 and NO3 within this zone are due to anthropogenic influences. Anaerobic conditions prevail in the far field, under the confining cover, where pre‐bomb era Holocene waters dominate. In that zone, dissolved oxygen, NO3 and U contents are reduced, and Fe, Mn and NH4 contents increase. In the third zone, early Holocene and glacial waters occur. They are of HCO3 Ca Na or HCO3 Na types, with TDS values higher than 1 g l−1 and Na content higher than 200 mg l−1, due to either small admixtures of ascending or diffusing older water or freshening of marine sediments, a process that is probably occurring till the present time. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
963.
A. P. J. De Roo 《水文研究》1991,5(2):215-227
The 137Cs radioactivity of soils was used as a tracer of soil erosion in a catchment in the Netherlands: 143 samples were analysed to map the 137Cs redistribution using geostatistical interpolation methods. Caesium-137 activities on grassland are significantly higher than on arable land. Also, 137Cs activities on waning slopes are higher and activities on steep slopes are lower. The soil erosion estimates, derived from the 137Cs data, are used to validate the USLE erosion model. The recent Chernobyl nuclear accident also contributed to the 137Cs activity. However, the Chernobyl input of 137Cs, with a constant ratio of 1.765:1 to 134Cs, cannot be used as a tracer of soil erosion. Because of the rapid decay of 134Cs, we will not be possible to separate the sources of 137Cs in the near future in areas significantly influenced by Chernobyl fallout and in these areas 137Cs can no longer be used as a soil erosion tracer. 相似文献
964.
范秋林 《大地测量与地球动力学》1994,(1)
由于地震构造的许多重要信息在卫片上显示往往比较隐晦,必须对其进行增强处理,以取得最佳的解译效果。本文以历史上曾发生过八级地震的华县地震构造带为例,讨论辐射增强、多波段频谱变换、空间变换假彩色增强、分类等计算机图象处理方法的若干功能,以及这些功能在不同背景条件下的处理效果,为分析该地区活动断裂、地质构造等提供了有意义的信息,也为这种处理手段在地震构造信息分析等方面的推广应用提供参考。 相似文献
965.
We propose suitable modifications in the concept of Roche equipotentials to account for the effect of mass distribution inside
a star. The Kippenhahn and Thomas (1970) approach is used to incorporate the effects of rotational and tidal forces in the
equations of stellar structure. The proposed method is applied to compute structures of certain rotationally and tidally distorted
polytropic models. 相似文献
966.
有许多原则严格限制西方报章记者的表达自由。这些原则禁止记者在报道新闻时加上自己的评论、判断、解释或推论,以确保新闻的客观性、可靠性的公正性。客观的新闻工作者懂得新闻的概念,遵循严格的中立原则,避免经济、宗教、政治或民族偏见。尽管如此,报章的编辑、经营者和老板却能左右新闻。他们可以决定是否发表,发表多少以及在哪儿发表某条新闻,这一情形及其他因素对新闻的客观性构成威胁。 相似文献
967.
知识经济时代文献信息资源是知识创新的源泉,信息服务业成为知识经济的先导产业。以高校高科技产业为例,说明了高校图书馆要立足于知识经济社会,只有拓宽文献信息服务的内容,同时为教学、科研服务,发展高科技产业。并对知识经济时代的高校图书馆文献信息服务提出了一些建议。 相似文献
968.
利用国际联测和综合处理 ,得到昆明GPS站地壳形变速率每年以( -4 .3± 0 .5)mm下沉趋势 ,水平分别以 3 7.5mm ,方位 1 47°± 1 .°5运动。利用最新国际地球自转服务 (IERS)发布的国际地球参考架ITRF2 0 0 0速度场 ,建立最新反映全球板块模型 ,基于最新的ITRF2 0 0 0地球参考架和欧亚板块的欧拉矢量 ,估计得到昆明站的地壳垂直形变速率为每年 -0 .0 1mm呈下降趋势 ,水平形变速率为每年 ( 8.1± 0 .2 0 )mm ,方位 1 3 7°± 1 .°5;并进一步分别基于几百万年地质地磁模型NNR -NUVEL1A和ITRF96、ITRF97模型的欧亚板块的欧拉矢量 ,得到较一致的结果 ,说明全球板块运动稳定性与模型的可靠性。本文基于不同板块模型分析了昆明GPS站相对于欧亚板块运动 相似文献
969.
970.
刘军 《成都信息工程学院学报》2004,19(1):40-43
根据用户的访问记录,以及每次检索输入的关键词、用户的动作来动态更新用户的兴趣点.提出了一个能较好吻合这一思想的数据挖掘模型,以用户的停留时间、访问频率和用户输入的检索关键词为数据对象,进行用户兴趣分析,动态跟踪用户需求意向,简化检索过程,提高WEB资源的使用效率. 相似文献