为明确淮河中游典型分汊河道水沙特性变化及分水分沙规律,采用累积距平、M-K分析法、R/S分析法和Morlet小波分析法等方法,研究了分汊河道濛洼段1985—2020年来水来沙特性,探讨了水沙条件突变及变化趋势的驱动因素,基于水沙关系曲线分析了水沙协同关系与输沙能力的变化,定量给出了濛洼段各汊分流比和含沙量比。结果表明:王家坝站(总)年径流量总体未呈明显增减趋势,含沙量则表现出明显的减小趋势,未来一段时间继续呈减小趋势,在1995年左右发生突变,水库拦沙、农业种植改变下垫面及水土保持措施是含沙量减小的主要驱动因素;来沙系数呈减少趋势,外界影响系数a值逐渐减少,输沙特性拟合系数b值逐渐增大;濛河分流比与本段总来流基本呈正相关,随着流量增加,濛河分流的权重也逐渐升高,6 000 m³/s流量级以下分流能力略有萎缩,6 000 m³/s流量级可以与淮河干流平分上游来流,各汊点河道的含沙量比值近似等于各河道的水流挟沙力比值。以上结果为淮河中游水沙数值模拟中分汊河道含沙量计算模式提供理论支撑,为淮河中游河道整治采用长距离疏浚方案提供科学依据。

[Objective] Current research on water-sediment characteristics of the Huaihe River mainstream mainly focuses on single channels, while studies on water-sediment characteristics, relationships, and diversion patterns in its bifurcated channels are limited. This study selects the typical bifurcated section from Wangjiaba to Nanzhaoji (hereinafter referred to as “Mengwa section”) in the middle reaches of the Huaihe River, aiming to clarify the variations in water-sediment characteristics and diversion patterns of typical bifurcated channels. [Methods] A combination of cumulative anomaly analysis, Mann-Kendall (M-K) trend test, R/S analysis, and Morlet wavelet analysis was used to study the water-sediment inflow characteristics of the bifurcated channels in the Mengwa section from 1985 to 2020. The driving factors of abrupt changes and variation trends in water and sediment conditions were explored. The water-sediment coordination relationships and sediment transport capacity variations were evaluated using water-sediment relationship curves, and quantitative ratios of flow and sediment diversion across bifurcated channels of the Mengwa section were provided. [Results] The annual runoff at Wangjiaba station (total) showed no significant increasing or decreasing trend, while the sediment concentration displayed a pronounced decreasing trend, stabilizing below 0.15 kg/m³ after 2010 and continuing to decrease in the future. An abrupt change occurred around 1995. Sediment retention by reservoirs, agricultural land use changes altering underlying surfaces, and soil and water conservation measures were the primary driving factors of sediment concentration reduction. The sediment coefficient showed a decreasing trend, with external influence coefficient “a” gradually decreasing and sediment transport fitting coefficient “b” gradually increasing. This indicated a continuous reduction in sediment inflow intensity and an enhancement of the channel’s sediment transport capacity, promoting channel scouring. Meanwhile, the main channel cross-section exhibited sustained expansion, indicating an ongoing erosional state in this river section. The flow diversion ratio of the Menghe River was generally positively correlated with total flow in this section. At 2 000 m³/s (low-to-medium flow level), the main channel on the Huaihe River’s southern branch served as the primary flow passage. As the flow increased, the weight diverted through the Meng River progressively rose. Below the flow level of 6 000m³/s, its diversion capacity slightly declined, while at 6 000m³/s, the flow achieved equitable flow diversion with the mainstream of the Huaihe River. The sediment concentration ratios of each bifurcated channel were approximately equal to the ratios of their respective flow sediment transport capacity. [Conclusion] These findings provide theoretical support for sediment concentration calculation models in bifurcated channels during numerical simulations of water and sediment dynamics in the middle reaches of the Huaihe River, while offering a scientific basis for adopting long-distance dredging schemes in the river’s channel regulation strategies.