Over the last several decades,various sediment transport capacity formulations have been used by geomorphologists and engineers to calculate fluvial morphological changes.However,it remains poorly understood if the ad...Over the last several decades,various sediment transport capacity formulations have been used by geomorphologists and engineers to calculate fluvial morphological changes.However,it remains poorly understood if the adaptation to capacity could be fulfilled instantly in response to differing inflow discharges and sediment supplies,and thus if the calculation of morphological changes in rivers based on the assumed capacity status is fully justified.Here we present a numerical investigation on this issue.The distance required for sediment transport to adapt to capacity(i.e.,adaptation-to-capacity length) of both bed load and suspended sediment transport is computationally studied using a coupled shallow water hydrodynamic model,in line with varied inlet sediment concentrations.It is found that the adaptation-to-capacity length generally decreases as the Rouse number increases,irrespective of whether the inlet sediment concentration increases or reduces.For cases with vanishing inlet sediment concentration a unified relationship is found between the adaptation-to-capacity length and the Rouse number.Quantitatively,the adaptation-to-capacity length of bed load sediment is limited to tens of times of the flow depth,whilst that of suspended sediment increases substantially with decreasing Rouse number and can be up to hundreds of times of the flow depth.The present finding concurs that bed load sediment transport can adapt to capacity much more rapidly than suspended sediment transport,and it facilitates a quantitative criterion on which the applicability of bed load or suspended sediment transport capacity for natural rivers can be readily assessed.展开更多
Mosul dam is the biggest hydraulic structure in Iraq located on the River Tigris 60 km northwest of Mosul city. Its storage capacity is 11. 11 × 109 m3 and it had been in operation since 1986. A physical distorte...Mosul dam is the biggest hydraulic structure in Iraq located on the River Tigris 60 km northwest of Mosul city. Its storage capacity is 11. 11 × 109 m3 and it had been in operation since 1986. A physical distorted model with movable bed having a vertical scale 1： 100 and a horizontal scale 1：1000 was used to conduct the experiments relating the water level at the reservoir and water discharge upstream the reservoir with the bed load transport rate. The model represents the first 15 km of most northern part of Mosul dam reservoir. The construction of the model was based on bathymetric survey conducted in 2009. Twenty-four experiments were executed using four different discharges （0.5, 1.0, 1.5, and 2.0 L/s） which represent the average discharges in the flood period of River Tigris. At each individual discharge six operations were assumed where the reservoir＇s water level was 305, 307, 309, 310, 312, 315 meters above sea level respectively. In all the experiments conducted, bedload transport was measured in the physical model at section representing the River Tigris 1 km upstream the reservoir. The results showed that the bedload rate was decreasing when the water level within the reservoir was increasing. It was also evident that bedload transport rate dramatically decreased at level 310 meters above sea level onward. This is due to the fact that at this level represent the effect of backwater which was noticeable on the river cross section展开更多
基金funded by Natural Science Foundation of China (Grants Nos. 11172217, 10932012 and 10972164)
文摘Over the last several decades,various sediment transport capacity formulations have been used by geomorphologists and engineers to calculate fluvial morphological changes.However,it remains poorly understood if the adaptation to capacity could be fulfilled instantly in response to differing inflow discharges and sediment supplies,and thus if the calculation of morphological changes in rivers based on the assumed capacity status is fully justified.Here we present a numerical investigation on this issue.The distance required for sediment transport to adapt to capacity(i.e.,adaptation-to-capacity length) of both bed load and suspended sediment transport is computationally studied using a coupled shallow water hydrodynamic model,in line with varied inlet sediment concentrations.It is found that the adaptation-to-capacity length generally decreases as the Rouse number increases,irrespective of whether the inlet sediment concentration increases or reduces.For cases with vanishing inlet sediment concentration a unified relationship is found between the adaptation-to-capacity length and the Rouse number.Quantitatively,the adaptation-to-capacity length of bed load sediment is limited to tens of times of the flow depth,whilst that of suspended sediment increases substantially with decreasing Rouse number and can be up to hundreds of times of the flow depth.The present finding concurs that bed load sediment transport can adapt to capacity much more rapidly than suspended sediment transport,and it facilitates a quantitative criterion on which the applicability of bed load or suspended sediment transport capacity for natural rivers can be readily assessed.
文摘Mosul dam is the biggest hydraulic structure in Iraq located on the River Tigris 60 km northwest of Mosul city. Its storage capacity is 11. 11 × 109 m3 and it had been in operation since 1986. A physical distorted model with movable bed having a vertical scale 1： 100 and a horizontal scale 1：1000 was used to conduct the experiments relating the water level at the reservoir and water discharge upstream the reservoir with the bed load transport rate. The model represents the first 15 km of most northern part of Mosul dam reservoir. The construction of the model was based on bathymetric survey conducted in 2009. Twenty-four experiments were executed using four different discharges （0.5, 1.0, 1.5, and 2.0 L/s） which represent the average discharges in the flood period of River Tigris. At each individual discharge six operations were assumed where the reservoir＇s water level was 305, 307, 309, 310, 312, 315 meters above sea level respectively. In all the experiments conducted, bedload transport was measured in the physical model at section representing the River Tigris 1 km upstream the reservoir. The results showed that the bedload rate was decreasing when the water level within the reservoir was increasing. It was also evident that bedload transport rate dramatically decreased at level 310 meters above sea level onward. This is due to the fact that at this level represent the effect of backwater which was noticeable on the river cross section
