Architecture,formation and implication of active structure-controlled intraslope channel system southeast offshore Sendai,Tohoku, Japan

Located off the Pacific coast of central Tohoku (NE Japan), the Ishinomaki slope channel (ISC) provides an excellent opportunity to study a structure-controlled intraslope channel and downslope sedimentation along the active margin. The seismic reflection data across ISC show an extensive basal surface and overlying channel complexes between the basement structures of the Abukuma ridge to the south and Kitakami massif to the north, indicating that the formation of the intraslope basin, channelization of ISC and sedimentation of the downstream channel-lobe transition zone (CLTZ) are very likely to be structure-controlled. The oblique channel stacking pattern, faulting of the seafloor and subsurface Abukuma ridge in the upper and lower domains of ISC, collectively suggest that ISC has migrated northward and is currently under the influence of active compression. Differences in styles of accommodation space between the upper and lower domains of ISC suggest that differential subsidence occurred along the strike-slip tectonic line. Based on the regional strike-slip tectonic line, we propose that a Kitakami-Abukuma ridge existed before the formation of ISC. The strike-slip faulting divided the Kitakami-Abukuma ridge into the Kitakami massif to the north and the Abukuma ridge to the south, and an intervening fault trough as the precursor of the intraslope basin and ISC. As the subduction of the Pacific Plate and associated compressional events continued, the Abukuma ridge was reactivated to narrow the intraslope basin into a confined channel. Located near the epicentre of the devastating 2011 Tohoku earthquake event, the ISC, downstream CLTZ and underlying intraslope basin provide information on active basement structure and the evolving sediment routing system on the tectonically active margin.     

Instream flow requirements for sediment transport in the lower Weihe River

Estimation of instream flow requirements for sediment transport (IFRST) in the downstream Weihe River is important for the maintenance of a healthy ecosystem of the river. In this study, the IFRST for the lower Weihe River is estimated on the basis of the observed hydrological data during the period 1960–2001. The results showed that the mean annual IFRSTs for the reach between Lintong and Huaxian and the reach below Huaxian were 6·85 and 7·62 billion m³/year, respectively, and the standard errors were 0·50 and 0·76 billion m³/year, respectively. The results also showed that the Sanmenxia Reservoir is an important driver for the changes in channel morphology and hydraulics, as well as the IFRST. Furthermore, according to the hydrological frequency (p value) estimated from annual instream flow data during the period 1960–2001, four typical years (p = 25%, 50%, 75% and 90%) for the two reaches of the Weihe River were determined. The analysis showed that the IFRST has a negative power functional relationship with the sediment concentration. On the basis of the efficiency coefficients (R²) during three sub‐periods 1960–1973, 1974–1990 and 1991–2001, the annual IFRSTs in the above two reaches for the four typical years were estimated under different deposition and erosion–deposition conditions. The results provide useful references for restoration and water resource management of the Weihe River. Copyright © 2010 John Wiley & Sons, Ltd.     

Quaternary features beneath Lake Simcoe,Ontario, Canada: drumlins,tunnel channels,and records of proglacial to postglacial closed and overflowing lakes

Lake Simcoe is a large lake 45 km across and in places over 30 m deep, located between Lake Huron and Lake Ontario, in the glaciated terrain of southern Ontario, Canada. Seismostratigraphic analysis of high-resolution seismic reflection profiles, together with lakebed sediment sampling and pollen study, revealed distinctive sequences in the sediments beneath Lake Simcoe, Ontario. A surface unit (Blue Sequence) of soft Holocene mud (low-amplitude surface reflection, discontinuous parallel internal reflections) lies in the deeper basins of the lake. The underlying unit (Green Sequence) is characterized by high-amplitude parallel internal reflections; basal sediments of this sequence consist of clay rhythmites with dropstones. The Green Sequence was deposited by lacustrine sedimentation in proglacial Lake Algonquin; sedimentation persisted until the basin was isolated from other glacial lakes at about 10 ¹⁴C ka at the Penetang post-Algonquin phase. Subsequent erosion of the uppermost portion of the Green Sequence is attributed to wave action in a low-level early Holocene lake, possibly closed hydrologically and coeval with closed lowstands in the Huron and Georgian Bay basins. Two sequences with high-amplitude surface reflections and chaotic internal reflections (Purple and Red Sequences) lie below the Green Sequence. Northeast-southwest trending ridges, tens of metres in height, on the Red Sequence (the lowermost of these two units) are interpreted to be drumlins. An erosion surface descends into narrow valleys 50–80 m deep beneath the lake in bays to the west and south of the main lake basin. These depressions are interpreted as subglacial tunnel channels cut by rapid flows of meltwater. The sediments of Purple Sequence are interpreted as channel-fill sediments rapidly deposited during waning stages of the meltwater drainage. The Red Sequence is correlated with the Newmarket Till of the last glacial maximum identified beneath the Oak Ridges Moraine to the south.     

调水调沙以来黄河尾闾河道冲淤演变及其影响因素

2002年开始的黄河调水调沙改变了进入黄河口的水沙条件,必然引起尾闾河道地貌的显著调整.根据黄河尾闾河道利津以下的断面实测高程数据,建立基于正交曲线网格的河道DEM,结合河床形态与水沙条件变化,综合研究黄河尾闾河道冲淤的时空演变及其影响因素.结果表明,调水调沙以来尾闾河道冲刷明显,2002-2017年累计冲刷6240万...     

Temporal evolution of scour at bridge abutments in compound channels

Bridge abutment-induced sediment scour in compound river channels is time-sensitive during floods, and, thus, estimating the scour rate has significance in design. In the current study, large-scale laboratory experiments were done to examine the influence of multiple factors on scour evolution, including channel geometry, bed mobility (clear-water or live-bed), and lateral (embankment intrusion) and vertical (deck submergence) flow contractions. A new method is applied for scour measurement and determination of characteristic scour trends. Results show that the non-dimensional time scale is related to flow intensity and may peak before reaching the clear-water scour threshold; the corresponding equations also are derived. It is found that the use of scour countermeasures has a significant impact on the scour rate, and the existing equations for unprotected abutments have limitations. Under clear-water conditions, the scour rate is closely related to the overall flow contraction, which can be better reflected by the ratio of the approaching unit discharge to that at the bridge section. Specifically, the effect of vertical flow contraction on scour rate is more dominant than other factors. Two scour rate curves are derived to suit different structural and flow contraction types for clear-water scour. In contrast, the live-bed scour rate data are generally consistent and fall in a narrow band, showing less dependence on other factors. Finally, a new design approach is established to estimate the time scale and scour rate using the new equations proposed in this paper.     

基于RS和GIS的城市化进程中河道时空演变分析——以深圳市布吉河为例

为研究城市化对城市河道的影响,论文选择处于粤港澳大湾区的典型高度城市化流域布吉河流域为研究区,基于1988-2015年10期Landsat系列遥感影像、2003-2017年9期Google Earth高分辨率遥感影像、2019年深圳市水系图以及1980年以来的河道整治相关文献,应用RS和GIS技术,构建城市河道演变特征...     

隔河岩遥测地震台网无线信道计算及测试

隔河岩遥测地震台网是由７个遥测地震台、２个中继站和１个接收记录中心组成的地方性遥测台网，其目的是监测隔河岩水库诱发地震活动。台网的合理布局保证了在台网检测范围内地震定位的精度优于Ⅰ类，重要地段的地震监测能力为ＭＬ≥０．５级。台网采用了２２３ＭＨｚ频段的无线传输地震遥测设备。测试结果表明，无线信道功率裕量均在３０ｄＢ以上，信道可靠性优于９９．９９％，各道信号实际连续率在９９．６７％以上，超过规范规定的要求。自１９９３年运行以来，获得了高质量的产出。     

德州市深层地下水水质演化研究

德州市属于典型的黄河下游冲积平原孔隙水水文地质区,这一地区地下淡水的天然水环境条件非常敏感和脆弱。由于持续开采地下水,使该区域地下水的水动力场和水化学场发生了较大变化。根据德州市地下水水质监测数据,本文论述了深层地下水的水质特征,分析研究了深层地下水的水质演化。结果表明:在开采条件和自然条件的共同作用下,HCO3-和Na+浓度呈现出持续升高趋势,矿化度、总硬度及其它主要水质指标的浓度变化较小。深层地下水水质演化的特点表现为水化学动态并不随季节变化,而是在开采条件下,随着深层地下水系统压力、氧化?还原环境条件的改变有所变化。地下水水质指标浓度的历年变化主要受到水文地球化学环境的影响。针对研究区地下水水质的演化趋势,提出了应进行深层地下水人工回灌和降氟改水的水质改善措施。     

Limited Downstream Response of Stream Channel Size to Urbanization in a Humid Tropical Basin*

Stream channel changes are often assumed to propagate downstream of the disturbed or urbanized reach, especially where the main controlling variables of discharge and sediment load vary regularly in the downstream direction. A survey of bankfull cross-sectional sizes at 10 stations along a tropical stream shows that downstream propagation of the disturbance may not always occur. Serial regression analysis suggests that a reduction in channel size induced by urbanization did not extend beyond the urbanized reach. Furthermore, local channel change did not alter the downstream log linear trend between channel size and basin area. Apparently, the storage of floodwaters and sediments on floodplains reduced the downstream effects of urbanization.