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PDF(4198 KB)
PDF(4198 KB)
陆水水库建库近60年泥沙淤积、库区演变及影响
Sedimentation and Evolution of Lushui Reservoir and Their Impacts over the Past 60 Years since Construction
研究库区泥沙淤积情况对于水库的运行和管理十分重要,结合陆水水库建库前及近期库区地形,复核了陆水水库建库前库容曲线,采用断面法和栅格地形法分析了陆水水库库区的淤积时空分布特征,开展了淤积重点区域的河道演变分析,并从多个方面综合分析了库区淤积的影响。总体而言,陆水水库泥沙淤积总量不大,但局部库段淤积比较突出,对防洪、航运、灌溉、发电等功能发挥带来了不利影响,建议采取机械清淤、加强汛期排沙调度等措施,控制库区泥沙淤积,保持水库有效库容。研究成果可为水库相关管理工作提供参考。
[Objective] This study systematically examines the characteristics of sediment deposition and river evolution in Lushui Reservoir over 60 years since its construction and evaluates their comprehensive impacts. [Methods] Based on pre-construction (1959) 1∶10 000 topographic maps and recent (2018) 1∶5 000 maps, sediment volumes and stage-capacity curves were calculated using the cross-section method and 10 m × 10 m grid-based method (combined with Simpson’s 3/8 rule). [Results] The total deposition was 32.397 million m3, accounting for only 4.6% of the total storage below the design flood level, indicating overall light siltation. However, the spatial distribution was highly uneven—74% of the deposition was concentrated below the flood-limit water level, with the Hongshang-Shikeng downstream 11km reach becoming the core deposition zone, accounting for 51% of the total (local maximum deposition thickness up to 11.79 m), while the Hongshang-Langkou reach was likely in a scouring state due to unregulated sand mining and reduced sediment inflow. For channel evolution, the thalweg in the Hongshang-Shikeng reach rose on average 6.27 m, and the shoreline at the 45 m dead water level elevation shrank markedly; maximum thalweg migration reached 660 m (at the Lashupu widening), and the depositional pattern tended toward a deltaic form—with the Hongshang-Shikeng reach dominated by main-channel deposition, and sections above Hongshang mainly showing floodplain deposition. Deposition significantly impaired reservoir functions: (1) For flood control, 6.856 million m3 of flood-control capacity was lost (4.2% loss rate), and the cross-section area in the Hongshang-Shikeng reach was reduced by 26% on average (up to 54%), markedly lowering discharge capacity and raising the regulated flood levels under design floods. (2) For beneficial use, 17.193 million m3 of active storage lost (equal to an annual power loss of 842 000 kW·h), and 12.29 million m3 between the dead water level and flood-limit level was lost (8.1% of mean annual irrigation withdrawal). (3) For navigation, thalweg elevations were generally at or above the 45 m dead water level elevation, severely restricting navigation during low-flow periods. [Conclusion] Although the overall sedimentation rate of Lushui Reservoir is low, local deposition poses a significant threat to flood-control and navigation functions. Mechanical dredging in the key reach (Hongshang-Shikeng) and optimization of sediment-flushing schedules during the flood season are urgently needed to control sediment and maintain effective storage capacity. These findings provide a scientific basis for sediment management in long-operating reservoirs and for the development of “modern reservoir operation and management matrix” proposed by the Ministry of Water Resources.
陆水水库 / 泥沙淤积 / 地形法 / 河道演变 / 淤积影响
Lushui Reservoir / sedimentation / topographic method / river channel evolution / sedimentation impacts
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以长江中游荆江新厂至监利河段实测水沙与河道地形资料为基础，采用输沙量法与地形法，分别估算了1987年6月至1991年5月该河段的河道冲淤量，并初步对比分析了2种方法的差异、适用性与关键影响参系数。计算分析表明：①采用输沙量法，假设床沙质冲泻质分界粒径为0.062 5 mm，1987年6月1日至1991年5月31日新厂至监利河段河道淤积量为0.431 4亿t；采用地形法，假设平滩水位为34.0 m，1987年5-6月至1991年5月该河段的河道淤积量为0.4383亿t。2个估算结果非常接近。②影响输沙量法的关键参系数为床沙质冲泻质分界粒径与悬沙级配；影响地形法的关键参系数为平滩水位与泥沙干密度。③在河道冲淤基本平衡和造床条件下，合理确定床沙质冲泻质分界粒径（输沙量法）和平滩水位（地形法），输沙量法与地形法估算的河道冲淤量可以一致或接近；偏离冲淤平衡与造床条件越远，2种方法的估算结果差异越大。
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Regarding Xinchang-Jianli reach of the Middle Changjiang Jingjiang River as an example, on the basis of field data of runoffs, sediment loads and morphologies of river channels, deposition-erosion amounts of Xinchang-Jianli reach from Jun.1987 to May 1991 are estimated by sediment budget method and morphological change method. Difference, suitability and key influential parameters or coefficients of these two methods are preliminarily contrasted and analyzed. Main conclusions are as follow: (1) By means of sediment budget method and under separated sand size 0.0625mm of wash load and bed material load, the deposition amount of XinChang-JianLi reach from 1st Jun. 1987 to 31st May 1991 is estimated at 0.4314×10 8 t, while by means of morphological change method and under bankfull stage of 34.0 m, the deposition amount of XinChang-JianLi reach from May-Jun.1987 to May 1991 is estimated at 0.438 3×10 8 t., and two estimates are very close. (2) The key parameters or coefficients influencing sediment budget method are the separated sand size of wash load and bed material load and the suspended sediment grading curves, while those affecting morphological change method are the bankfull stage and the sediment dry density. (3) Under quasi-equilibrium of deposition-erosion and conditions of channel-forming, once the separated sand size of wash load and bed material load (for sediment budget method) and the bankfull stage (for morphological change method) are properly selected, deposition-erosion amounts estimated by both Methods can be obtained identical or very close, the more deviation from deposition-erosion equilibrium and channel-forming condition, the more different of results of these two methods.
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在生产实践中,采用不同计算方法得出的冲淤量结果往往差别很大,部分河段、部分时段甚至存在冲淤性质相反情况。采用大量的实测水沙、地形资料,运用断面地形法、网格地形法和输沙量平衡法3种方法计算了三峡水库蓄水后三峡坝下游宜昌至监利河段的实测河床冲淤量,对不同计算方法的计算结果和影响计算精度的因素进行了分析,运用非线性分形理论对河床起伏程度与断面代表性关系进行了研究。研究结果表明输沙量平衡法需对悬沙测验成果进行改正,并考虑泥沙测验定线误差、水量不平衡、河道采砂和分流洪道冲淤;断面地形法需在弯道、汊道、河道急剧放宽和束窄的局部河段布置相对较密的断面;网格地形法需选择适宜的插值方法,且网格尺寸不宜大于施测断面点间距。
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<p>In practice, the amount of riverbed erosion and deposition in the same reach or in the same period calculated by different methods differs significantly from each other. At present, the calculation methods by using cross-section morphological variation, DEM grid morphological variation, and sediment balance are widely used. The amount of riverbed erosion and deposition in the reach from Yichang to Jianli of Yangtze River downstream of Three Gorges Project after impoundment was calculated using the above mentioned three methods based on topographic map, cutting cross-section on topographic map and sediment data of hydrologic stations. Furthermore, the calculation results and the factors affecting the calculation accuracy were analyzed, and the nonlinear fractal theory wasused to study the relation between riverbed fluctuation degree and section’s representativeness. Research results suggest that to improve the sediment balance method, suspended load near riverbed needs to be modified, and the alignment error of sediment measurement, water imbalance, sand mining and sediment diversion should be taken into consideration; as for the method of cross-section’s morphological variation, relatively close sections must be laid in river bends, bifurcated reaches or contractive and expansive reaches; while appropriate interpolation method must be employed for the method of grid morphological variation, and the grid space should be no larger than the distance between measuring points.</p>
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