长江上游年产泥沙5.12×105t，经宜昌输入中游，长江中游干流及各支流年产沙约0.80×108t, 这两部分中约1.24×108t沉积于中游河湖中，4.68×108t经大通输入下游，沉淤于河道及长江三角洲或入海。长江中游的泥沙，总体是淤大于冲，但是冲淤的地理分布、时间段分布和河床断面分布不均衡。长江干流的宜昌-城陵矶段、九江-大通段冲大于淤或冲淤平衡，淤积主要发生在长江干流以武汉为中心的螺山-武汉-黄石段以及洞庭湖区和鄱阳湖区。即使在主要淤积江段，也有局部时段和江段以冲刷为主。主泓所在河槽以冲刷为主，而河道两侧或河道之间的洲滩，则以淤为主，形成高而平的漫滩，往往被人为改造成圩垸。荆江以北的江汉平原因有大堤从长江隔开，只有汉水少量泥沙供应，冲淤量很小，再加上构造沉降的累计效应，其地面高程绝大部分低于干流洲滩数米，螺山-武汉-黄石段的淤积导致该段及以上江段洪水位抬高。 干流断面冲槽淤滩使长江中游河道的典型形态呈深河谷、高漫滩，靠干堤保护堤内平原。这种断面在洪水时成为在同等水量下，水位不断抬高的原因。高水位要高堤来防堵，这就增加了堤防压力、水头压力，容易导致管涌、渗漏等险情。堤外滩及洪水位与构造沉降的堤内平原间的高差不断增大，三峡工程建成后，水库拦沙及中游河道冲深，可使同流量下水位大幅度降低，但城陵矶-武汉段冲刷量很小，不能解决该段及以下江段的泥沙淤积问题，因此江汉平原因相对于洪水位地势过低而造成的洪涝灾害及相关环境问题，仍将是中游长远的重大隐患。

The base of bed 27c in the Meishan section Changxing County, Zhejiang Province, China, is recommended as GSSP for the basal boundary of the Triassic System. The Meishan section is easily accessible, well exposed, and records continuous marine sedimentation from the Changxingian(latest Permian) into the Early Triassic. The global boundary stratotype point is placed at the first occurrence of the conodont species Hindeodus parvus in the evolutionary lineage latidentatus-parvus-turgida-isarcica, which is transitional between Hindeodus and Isarcicella. Integrated stratigraphic study of the Meishan section includes radiometric dating, and chemo, sequence, eco, and event-stratigraphy. The latter involves the records of possible impact events as well as volcanic, anoxic, and transgressive events. The latter three studies have identified events the appear to be recorded on a pan-Tethyan or even a global scale.