Coarse woody debris and channel morphology interactions for undisturbed streams in southeast Alaska,U.S.A.     

E. George Robison  Robert L. Beschta 《地球表面变化过程与地形》1990,15(2):149-156

Coarse woody debris and channel morphology were evaluated for five low-gradient streams that ranged from first to fourth order (0.7 to 55 km² watershed area). Debris volumes were directly related to variations in bankfull width. Woody debris was associated with 65 to 75 per cent of all pools and the relative proportion of types of pools (i.e. plunge, lateral scour, etc.) varied with stream size. High variability in channel depths and widths was common. The results provide benchmark values of woody debris loadings and channel morphology for undisturbed coastal Alaskan stream systems.  相似文献   

延安市冬季边界层风、温场特征分布     

李丁华  吴敬之 《高原气象》1988,(3)

本文利用1985年12月25日—1986年1月9日的实测资料,分析了延安市冬季边界层风、温场特征。结果表明:延安市冬季低层逆温持续时间长、强度大,逆温持续期近地面几十米表现为混合层结构。边界层风场十分复杂,时空变化大,地面常为小风状态,风向、风速沿垂直方向有明显切变,低层流场有显著渠道效应,山谷风明显。  相似文献   

Channel change,fluvial geomorphology and river engineering: The case of the Afon Trannon,Mid-Wales     

G. J. Leeks  J. Lewin  M. D. Newson 《地球表面变化过程与地形》1988,13(3):207-223

The Afon Trannon, a gravel-bed river in mid-Wales with a catchment area of 72 km², has recently been the subject of an engineering flood protection scheme. Following the enlargement and grading of the channel, lateral instability has produced considerable problems of maintenance. Geomorphological investigations are described which attempt to pinpoint the lessons of the scheme. Historical studies of floodplain sediments and channel change indicate firstly, an initially rather stable channel, but secondly a considerable, early history of channelization which may still have repercussions for system stability. This early channelization has now been modified in the recent scheme. Contemporary field study by survey and sediment tracing using the magnetic technique indicates the present instability of the sediments in a meandering channel given a trapezoidal cross-section and varied banks. Low-flow adjustments are as important as flood adjustments in the lower, straightened reach. Lessons for engineering schemes include the desirability of assessing erosion risk by rapid, cheap field techniques and historical investigations, and the consideration of more ecologically acceptable channel designs.  相似文献   

The ostracod fauna of an intertidal Sabellaria reef at blue anchor, somerset, England     

David J. Horne 《Estuarine, Coastal and Shelf Science》1982,15(6)

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大洋性次-中层混合水团隶属函数的拟合及南海水团分析   总被引：3，自引：2，他引：3  

李凤岐  谢骏  俎婷婷 《中国海洋大学学报(自然科学版)》2004,34(5):861-866

讨论了铅直向叠置 3层水团 ,即次表层水团、次 中层混合水团和中层水团的分布与水团特征。改进了大洋性次表层水团和中层水团隶属函数的拟合方法 ,并进一步提出包络曲线法用以拟合次 中层混合水团的隶属函数 ,使铅直向叠置 3层水团隶属函数的拟合方法得以配套。应用新方法计算了 3层水团在南海全海域的分布 ,从整体上把握了次表层高盐水团、次 中层混合水团和中层低盐水团在南海中的分布及变化情况 ,讨论了它们的特征、差异和形成原因。  相似文献   

A preliminary study of the influence of a coastal frontal structure on ichthyoplankton assemblages in the English Channel   总被引：3，自引：2，他引：3  

Grioche  A.; Koubbi  P. 《ICES Journal of Marine Science》1997,54(1):93-104

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朝鲜海峡气候特征     

李培  唐晓卫  佀长刚  俞慕耕 《海洋预报》2007,24(1):45-50

本文收集了1960～1990年间的水文气象资料进行累年统计,并参考有关航海资料和海洋图集,详细地对朝鲜海峡进行了分析研究,阐明了该海峡气候及水文特征的变化规律。  相似文献   

Holocene beaver damming, fluvial geomorphology, and climate in Yellowstone National Park, Wyoming     

Lyman Persico  Grant Meyer   《Quaternary Research》2009,71(3):340-353

We use beaver-pond deposits and geomorphic characteristics of small streams to assess long-term effects of beavers and climate change on Holocene fluvial activity in northern Yellowstone National Park. Although beaver damming has been considered a viable mechanism for major aggradation of mountain stream valleys, this has not been previously tested with stratigraphic and geochronologic data. Thirty-nine radiocarbon ages on beaver-pond deposits fall primarily within the last 4000 yr, but gaps in dated beaver occupation from ~ 2200–1800 and 950–750 cal yr BP correspond with severe droughts that likely caused low to ephemeral discharges in smaller streams, as in modern severe drought. Maximum channel gradient for reaches with Holocene beaver-pond deposits decreases with increasing basin area, implying that stream power limits beaver damming and pond sediment preservation. In northern Yellowstone, the patchy distribution and cumulative thickness of mostly < 2 m of beaver-pond deposits indicate that net aggradation forced by beaver damming is small, but beaver-enhanced aggradation in some glacial scour depressions is greater. Although 20th-century beaver loss and dam abandonment caused significant local channel incision, most downcutting along alluvial reaches of the study streams is unrelated to beaver dam abandonment or predates historic beaver extirpation.  相似文献   

基于沉积模式的地震多属性量化沉积微相解释方法——以松辽盆地北部高台子地区泉头组三-四段为例   总被引：2，自引：0，他引：2       下载免费PDF全文

陈树民  沈加刚  宋永忠  张尔华  乔彦国  于兴河  关晓巍 《地质科学》2009,44(2):740-758

本文针对松辽盆地北部扶杨油层赋存的泉头组三.四段河道砂体地震识别问题开展了地震地质综合研究.以高分辨率层序地层学原理和沉积岩石学理论为指导,识别了沉积微相和河道砂体沉积特征,用钻井和地震联合分层对比的方法建立层序地层格架和区域沉积微相展布模式,确定了地震剖面上具有可对比追踪性的四级层序界面.通过地震多属性多元回归与聚类分析拟合含砂率,在沉积模式的指导下对含砂率平面图进行沉积微相解释,确定河道砂体的宅间展布和有利区,经钻探验证说明取得了较好的预测效果.  相似文献   

Impact of vertical structure on water mass circulation in a tropical lagoon (Ebrié, Ivory Coast)     

Isabelle Brenon  Olivier Audouin  Nicolas Pouvreau  Jean-Christophe Maurin 《Journal of African Earth Sciences》2009,55(1-2):47

A one-dimensional vertical model has been developed to simulate the water mass circulation along the vertical structure in all deep coastal areas. The model has hydrodynamic and transport components solved using finite difference scheme. The one-dimensional vertical model results are coupled to the vertically averaged two-dimensional model results at each point of a horizontal grid. A theoretical salinity profile is introduced for each vertically integrated value obtained from the 2DH model results. A viscosity profile, simulating a viscosity value close to zero at the surface and with large viscosity gradients, is applied along the water column. The model is applied to the Vridi channel, connecting the Ebrié lagoon to the sea (Ivory Coast).The response of the Ebrié lagoon is studied in terms of inflow and outflow of water in the system through the Vridi channel. Due to the abrupt variation of the surface slope, vertical velocities along the water column show an anticlockwise spiral from bottom to surface during a tidal cycle. Due to the bottom friction and to the vertical viscosity profile, velocities decrease from surface to bottom. However, the freshwater inflow slows down the tidal propagation during the flood and causes the surface velocity to be smaller than the bottom velocity at mid-tide. Close to the bottom, velocities follow an anticlockwise movement due to the tidal propagation. At the water surface, velocities follow only an alternative movement of either ebb or flood, along the channel direction. No cross shore velocities can develop at the surface in the channel.  相似文献