Grain Size Characteristics of Flood Sediment from the "11·03" Jinsha River Baige Barrier Lake Outburst
[Objective]To study particle size characteristics of the burst flood sediment in barrier.[Methods]Com-position of flood sediment particle samples from the "11·03" Baige dammed lake outburst flood on the Jinsha River were analyzed,and size parameters of sediment were calculated. Changes in sediment characteristics from upstream to downstream and its causes were analyzed. Then,the granularity characteristics of this flood sediment were com-pared with those of other primary river basins in China,while sand particle size characteristics of ancient flood sedi-ment were discussed.[Results and Discussions]The sediment types of the Baige barrier lake outburst flood were silt,sandy silt,and silty sand,with 23.65％,64.19％ and 12.16％,respectively. All particle sizes of sediment in barrier lake were less than 2.0 mm. The proportion of silt was 55.18％,sand of 32.86％,and clay of 11.97％. The silt content gradually increased,while the sand content gradually decreased from the upstream Maoding village to the downstream Shigu town. Moreover,the clay content always fluctuated around 12％. As the flow rate of the flood was reduced gradually,the ability of hydrodynamic to carry particulate matter was weakened by degrees. The clay was less affected by the hydrodynamic conditions as a result of the small particles and the electric charge,that's why the clay had a relatively stable proportion during the flood peak process. The median particle size was 41.34 μm,and the average particle size was 31.73 μm. Both of the value decreased gradually in pace with the increasing distance from the White River barrier lake. The skewness value was 0.27,which is a positive deviation. The peak value was 0.94 and was moderately sharp. The sorting coefficient was 0.57,indicating good sorting performance. Bimodal distribution accounted for 52％ of the grain size distribution curve of sediment. The main peak was high and narrow,located at 100 μm. And the secondary peak is low and wide,the peak value located at 10 μm. The single peak accounted for 48％,with a narrow peak at 50 μm. All sediment sizes in the profile were less than 2.0 mm. There were very small differences in composition. The predominant component was the sand. The silty content was slightly less than the fine sand,and the proportion of clay content was approximately 11.0％. The median value of particle size was larger than the average,both have a tendency to increase from the surface layer to the bottom. The sorting coefficient was less than 0.6,with the extremely positive deviation and the moderate peak state. Compared with other floods,the "11·03" outburst flood had a finer sediment particle size of mainly silt,followed by a smaller median and average value of par-ticle size,with wider peak state and positive skewness,indicating better sorting performance by this flood.[Conclu-sions]The research results have important reference value for understanding the sediment characteristics in barrier lake outburst floods,burst flood hydrodynamic transport process and mechanism in the future. It will promote the de-velopment of water conservancy and hydropower projects and ecological civilization construction in river basins.
outburst floodsediment grain sizeBaige barrier lake
万方数据
