乌兰布和沙漠腹地古湖存在的沙嘴证据及环境意义

通过大范围的系统野外考察发现,在乌兰布和沙漠腹地存在众多干盐湖,其周围存在不同高度的湖岸堤.其中,贺日木西尼沙嘴最为典型.该沙嘴呈NW-SE走向,海拔高度从1052 m下降至1035 m,长达11 km.是古湖泊发育和存在的重要证据和标志.通过对湖滨沉积物的OSL年代测定,该沙嘴形成于全新世的8.6-7 ka BP阶段,与中国西部许多沙漠出现的相对湿润环境状况相一致.其主要由强劲的风力作用和吉兰泰古湖沿岸流以及丰富的松散物质传输堆积而成.依据该沙嘴的海拔高程和形成年代来推测,在乌兰布和沙漠腹地曾经发育面积巨大的古湖,其范围西到吉兰泰盆地,东延河套盆地西部,形成早全新世的吉兰泰古湖.之后,受区域构造运动和干旱气候的影响,古湖水位下降,水域面积缩小,古大湖解体,导致该沙漠腹地的古湖部分水体逐渐向西退缩,形成了吉兰泰盐湖.在古湖退缩过程中,乌兰布和沙漠腹地残留众多湖泊,随着气候干旱化和蒸发作用的加剧,这些湖泊逐渐演变成盐湖.在强劲的风力驱动下,古湖周围的松散物质被侵蚀、搬运、扩散、堆积成现在的乌兰布和沙漠.     

小浪底工程修建对黄河河口淤积影响

本文在整理、分析黄河小浪底工程建成后 ,坝下游来水来沙条件变化的基础上 ,利用若干经验关系式 ,就小浪底工程修建后对黄河河口区清水沟流路的淤积特征和变化趋势进行了研究 ,得到了 :在小浪底水库初期蓄水拦沙运用阶段 ,淤积减少、河口砂嘴发展速度变缓 ;在后期正常调水调沙运用阶段 ,淤积又有所恢复 ,河口砂嘴发展加快的认识。     

Sand spit dynamics in a large tidal-range environment: Insight from multiple LiDAR,UAV and hydrodynamic measurements on multiple spit hook development,breaching, reconstruction,and shoreline changes

Sand spits with distal hooks have been well documented from coasts with low to moderate tidal ranges, unlike high tidal-range environments. Datasets from 15 LiDAR and 3 UAV surveys between 2009 and 2019 on the Agon spit in Normandy (France), a setting with one of the largest tidal ranges in the world (mean spring tidal range: 11 m), combined with in-situ hydrodynamic records between 2013 and 2017, highlight a three-stage pattern of spit hook evolution. Stage 1 (2009–2013) commenced with the onshore migration and attachment of a swash bar, followed by persistent spit accretion updrift of the bar and erosion downdrift because of the slow speed of bar migration in this large tidal-range environment. In stage 2 (2013–2016), three overwash events and a 220 m-wide breach culminating in the total destruction of the spit during winter 2015–2016 involved the landward mobilization of thousands of cubic metres of sand. These events occurred during short durations (a few hours) when spring high tides coincided with relatively energetic waves, underscoring the importance of storms in rapid spit morphological change. Strong spring tidal currents maintained the breach. Stage 3 (2016–2019) has involved new hook construction through welding of a swash bar and spit longshore extension, highlighting the resilience of the spit over the 10-year period, and involving a positive sediment balance of 244 000 m³. The three stages bring out, by virtue of the temporal density of LiDAR and UAV data used, a high detail of spit evolution relative to earlier studies in this macrotidal setting. The large tidal range strongly modulates the role of waves and wave-generated longshore currents, the main process drivers of spit evolution, by favouring long periods of inertia in the course of the spring–neap tidal cycle, but also brief episodes of significant morphological change when storm waves coincide with spring high tides. © 2020 John Wiley & Sons, Ltd.     

Spit and Inlet Morphodynamics of a Tropical Coastal Lagoon

The morphological changes of spits and inlets of the Chilika lagoon, the largest brackish water tropical coastal lagoon in Asia, are investigated using real-time kinematic GPS observation and numerical models during 2009–2013. The seasonal/interannual variations of the spit and inlet cross-sectional areas with varying widths and depths are recorded in association with different physical processes. The results show significant changes in spit morphology: particularly, the south spit accreted continuously, while the middle and north spits eroded. The cross-sectional depth of inlets becomes narrower and deeper during summer and winter seasons, while they are wider and shallower during the monsoon. The model results show that sediment transport rate is larger during monsoon and summer, while it is relatively less during the winter. Alongshore, sediment transport is predominantly northward throughout the study period. The result shows that gain/loss of the spits and closure/opening of inlets are significantly controlled by the high wave power, longshore drifts, and river discharge. The study demonstrates that the combined use of observational and numerical models is very effective to understand the changes of spit and inlet morphology and their impact on ecological conditions of the lagoon environment.     

Sand spit rhythmic development: A potential record of wave climate variations? Arçay Spit, western coast of France

This study aims at showing the sedimentary and geomorphological records of wave climate variations by spits. The studied spit (Arçay Spit) is located on the French Atlantic coast and has displayed a rapid elongation since the beginning of the 19th century that potentially represents a two century-long wave climate record. Wave climate and spit growth relationships are studied from two complementary methods: (1) numerical modelling of wave and longshore transport temporal and spatial variabilities, and (2) morphological monitoring based on the analysis of 4 historical maps (1811–1945), 8 aerial photographs (1945–2000) and 17 satellite SPOT images (1987–2005).Results at seasonal to interannual time-scales show that the sand spit area gain variations are the result of variations in longshore transport, themselves modulated mainly by wave height. Moreover, energetic swells seem to cause massive sand accumulation and spit elongation, whereas less energetic swells appear to be responsible for small sand accumulation and spit curvature. At longer time scale (decades to centuries), increasing spit growth phases are also synchronised with periods of energetic swells or high storm surge frequency. These results suggest that wave climate variations are the main factor controlling spit morphological evolutions.     

Spit-platform temperate carbonates: the origin of landward-downlapping beds along a basin margin (Lower Pliocene, Carboneras Basin, SE Spain)

ABSTRACT Lower Pliocene temperate carbonates exhibit landward‐downlapping beds at the southern margin of the Carboneras Basin in south‐eastern Spain. This rarely documented stratal geometry resulted from the accumulation of bedded bioclastic carbonate sand and gravel by longshore currents along a spit platform located a few hundred metres from the palaeoshoreline. The top of the spit platform was covered by shoals that extended over a gently dipping ramp inclined to the north. On the landward slope of the spit, sediments washed over from the shoal area were deposited in parallel‐laminated beds with a southward dip of 8–11°. These beds aggraded and retrograded after an increase in accommodation space, probably related to an Early Pliocene eustatic sea‐level rise. As a result, the beds downlap onto the underlying unconformity surface in a shoreward direction. Eventually, the depression between the shoreline and the spit platform was filled, and a gentle ramp became established. These Pliocene exposures in the Carboneras Basin and a similar Upper Miocene example in southern Spain suggest that landward‐downlapping stratal geometries can be expected in nearshore temperate carbonates along basin margins, and demonstrate a similarity in sedimentary dynamics to siliciclastic sands and gravels.     

The Spey Bay geomorphological study

The Spey Bay coastline and the estuary of the River Spey exhibit a rapidly evolving planform. They provide an opportunity to study geomorphological changes in a coupled coastal/estuarine system which can be measured over hours and days rather than the years and decades associated with more slowly evolving landscape features. Attempting to understand coastal and estuarine geomorphology provides engineers and earth scientists with an exciting intellectual challenge. This is not, however, simply an academic challenge because the successful management of coastal and estuarine environments depends on improving this understanding. The impetus behind our work in this area is the protection of land-use interests. It is in this context that Babtie Dobbie Limited have been employed in studying the River Spey since 1962. This paper is based on a practical case study performed for coastal and river engineering purposes between 1990 and 1992. The case study was formulated using the results and conclusions of earlier geomorphological studies of the area undertaken over the past 32 years. Knowledge gained from previous studies was crucial in designing the detailed methods and techniques employed in the 1990–1992 geomorphological study. Methods used included historical analyses, photogrammetry, numerical modelling, geographic information systems (GIS) and interpretation of the complex processes which drive landform changes in the estuary and along the adjacent shoreline. The improved understanding of geomorphological processes that has been achieved has enabled engineers to formulate a new management strategy. Central to this strategy are engineering solutions to river and coastal stability and flooding problems which are in sympathy with the environment and which take maximum advantage of our understanding of geomorphological processes.     

近期黄河口沙嘴演变遥感信息的拓扑模型研究

利用卫星遥感信息,阐述了近期黄河口沙嘴演变中的时空属性和时间维的概念化系统,以此进行相关参数的量化和沙嘴空间结构的拓扑分析,并建立符合表达黄河口沙嘴延伸和发育的模型。就此指出沙嘴发育指数趋近于0时,其已发育至晚期的后阶段,加之科氏力和海洋动力的增强,依据平行四边形法则,现行流路上的河口沙嘴进入深水区再难以向海延伸,从而促使黄河入海流路“人工改汊”的综合治理。