The Xingu River is an important tributary of the Amazon River, contributing 5% of its total water discharge. Nevertheless, it does not contribute substantially to the sediment load. The lower reach of the Xingu River forms a ria, a result of the Holocene sea-level rise. The Xingu is also classified as a tidal river, with tides >1 m at its confluence with the Amazon River. This study evaluated the morphology and sedimentology of the area, correlating both with hydrodynamics to understand the infilling process of the Xingu ria. The study area encompasses a stretch of ~160 km, between the Xingu–Amazon confluence and the narrowing of the fluvial channel. During the season of maximum sediment-discharge of the Amazon River (i.e., Feb 2016), 109 bottom sediment samples were collected. Eleven of the sampling sites were re-sampled during the minimum water-discharge period of both rivers (i.e., Nov 2016). During the maximum water-discharge period of the Amazon River (i.e., Jun 2018), additional water-level measurements were undertaken simultaneously at several locations along the Xingu River. The ria morphology was evaluated on the basis of the bathymetric surveys of the Brazilian Navy (DHN). The results show that the infilling process of the ria has taken place from both the upstream and downstream directions. From upstream, the Xingu River is forming a prominent bayhead delta. From the Xingu-Amazon River confluence, tides have transported Amazon River sediments into the Xingu Ria. There is a central portion of the ria lake with a large cross-sectional area, where relatively small amounts of muddy sediments are accumulating in a quiescent environment. Sands prevail along the lateral margins, where wave action causes bluff erosion and limits fine-sediment deposition. Sands are also common in the bayhead delta and the confluence areas. Results suggest that the sediment input from the Amazon River into the Xingu ria has been reduced over time, likely as result of a reduction in tidally driven flux from the Amazon River into the Xingu River, which has occurred with a gradual increase in the constriction of the confluence as Amazon floodplains prograde.

新谷河是亚马孙河的重要支流，贡献了其总排水量的5％。然而，它基本上不会增加​​沉积物负荷。全新谷海平面上升的结果是，新姑河下游形成一个河口。新谷也被归类为潮汐河，与亚马逊河汇合处潮汐> 1 m。这项研究评估了该地区的形态和沉积学，并与流体动力学相关联，以了解新谷地区的填充过程。研究区在新谷—亚马逊河合流与河流通道变窄之间，延伸约160公里。在亚马孙河最大的泥沙排放季节（即2016年2月），收集了109个底部泥沙样品。在两条河流的最小排水期间（即2016年11月），对其中的11个采样点进行了重新采样。在亚马孙河的最大排水期间（即2018年6月），在新姑河沿岸的多个地点同时进行了额外的水位测量。根据巴西海军（DHN）的水深测量评估ria形态。结果表明，ria的填充过程是从上游和下游两个方向进行的。从上游开始，新谷河正在形成一个突出的湾头三角洲。潮汐从新谷-亚马逊河汇流处将亚马逊河沉积物运至新谷河谷。里亚湖的中央部分有很大的横截面积，在静止的环境中聚集相对少量的泥状沉积物。砂子沿侧缘盛行，波浪作用引起钝化侵蚀并限制了细沉积物的沉积。在贝德河三角洲和汇合区域，沙子也很常见。结果表明，随着时间的流逝，从亚马逊河流入新谷河的泥沙输入量已减少，这可能是由于从亚马逊河流入新谷河的潮汐驱动通量减少所致，而随着河道收缩率的逐渐增加，这种情况发生了。随着亚马逊洪泛区的发展，汇合处。