Downstream changes in channel morphology and its flow were investigated over a monsoon dominated Dwarkeswar river from the western part of West Bengal. The basin has developed over the Proterozoic Granite Gneiss Complex to recent Holocene alluvium, forming three distinctive geomorphological regions of the basin e.g., dissected plateau, plate-fringe and alluvial plain area. Sixty cross-sections along the entire main stream were surveyed and bankfull channel parameters were measured. Sediment samples from each location were collected and Manning’s roughness (n) value for respective reaches were estimated and flow velocity, discharge, stream power and shear stress were calculated. The result has shown that channel width and channel capacity in the dissected plateau are increasing downstream, in the plateau-fringe area the trends are relatively constant. But in alluvial plain, width (87.3%), flow area (81.3%), discharge (84.1%), W/D ratio (91.3%) decreases downstream. Downstream decreasing channel width and channel capacity are strongly related to elevation, slope, HSI, TSI and SSI. Extremely low slope, channel switching, cohesive bank materials and vast flood plain width facilitates the river flow to spill over from the channel and spread to the surrounding area resulting diminishing discharge and thereby the channel morphology in downstream. Frequency of flow crossing bankfull limit has increased downstream resulting frequent flood diminishing channel morphology with distance down the valley.

中文翻译：

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西孟加拉邦季风主导的 Dwarkeswar 河下游河道形态特征

在来自西孟加拉邦西部的季风主导的 Dwarkeswar 河上调查了河道形态及其流动的下游变化。盆地在元古界花岗岩片麻岩杂岩上发育至最近的全新世冲积层，形成了盆地解剖高原、板块边缘和冲积平原区三个独特的地貌区域。对沿整个干流的 60 个横截面进行了调查，并测量了满岸通道参数。收集来自每个位置的沉积物样品，估计各个河段的曼宁粗糙度 (n) 值，并计算流速、流量、流功率和剪切应力。结果表明，解剖高原的通道宽度和通道容量在下游增加，在高原边缘地区，趋势相对稳定。但在冲积平原，下游宽度（87.3%）、流域（81.3%）、流量（84.1%）、水深比（91.3%）减小。下行通道宽度和通道容量递减与海拔、坡度、HSI、TSI 和 SSI 密切相关。极低的坡度、河道转换、粘性的堤岸材料和广阔的洪泛平原宽度有利于河流从河道溢出并扩散到周围地区，导致流量减少，从而导致下游河道形态。越过岸边限制的水流频率在下游增加，导致随着河谷下游距离的增加，洪水减少的渠道形态频繁。下行通道宽度和通道容量递减与海拔、坡度、HSI、TSI 和 SSI 密切相关。极低的坡度、河道转换、粘性的堤岸材料和广阔的洪泛平原宽度有利于河流从河道溢出并扩散到周围地区，导致流量减少，从而导致下游河道形态。越过岸边限制的水流频率在下游增加，导致随着河谷下游距离的增加，洪水减少的渠道形态频繁。下行通道宽度和通道容量递减与海拔、坡度、HSI、TSI 和 SSI 密切相关。极低的坡度、河道转换、粘性的堤岸材料和广阔的洪泛平原宽度有利于河流从河道溢出并扩散到周围地区，导致流量减少，从而导致下游河道形态。越过岸边限制的水流频率在下游增加，导致随着河谷下游距离的增加，洪水减少的渠道形态频繁。粘性的堤岸材料和广阔的洪泛平原宽度有利于河流从河道溢出并扩散到周围地区，导致流量减少，从而导致下游河道形态。越过岸边限制的水流频率在下游增加，导致随着河谷下游距离的增加，洪水减少的渠道形态频繁。粘性的堤岸材料和广阔的洪泛平原宽度有利于河流从河道溢出并扩散到周围地区，导致流量减少，从而导致下游河道形态。越过岸边限制的水流频率在下游增加，导致随着河谷下游距离的增加，洪水减少的渠道形态频繁。