三峡水库变动回水区急弯分汊河段鱼类生境营造

    Fish habitat creation in meandering braided reaches of Three Gorges fluctuating backwater area

    • 摘要: 三峡水库变动回水区朝天门至涪陵河段处于长江上游四大家鱼国家级种质资源保护区。该河段在三峡水库蓄水期具有水深大、流速小的特点,适合四大家鱼生存; 而在消落期、汛期,河道恢复天然河流特性,水深减小、流速增大,导致四大家鱼适宜生境区范围减小。变动回水区急弯分汊河段具有特殊地貌特征:急弯后河道多呈放宽、分汊形态,近岸间隔分布大量石梁,为营造连续浅埂-深潭生境提供了天然的地形基底。在河段清礁弃渣作业中,弃渣被置于近岸深潭区,对四大家鱼栖息地造成一定影响。为此,依托三峡水库变动回水区朝天门—涪陵4.5 m水深航道工程,以大箭滩急弯分汊河段为典型代表,提出利用航道整治工程清礁弃渣营造四大家鱼栖息地方案。采用MIKE 21建立工程河段平面二维水动力数学模型并进行了验证,计算了不同水文组合下河段的水动力分布; 基于栖息地适宜度指数(HSI)模型,选择水深、流速作为关键影响因子,分析了急弯分汊河段浅埂-深潭生境营造方案对四大家鱼生境水动力条件的改善效果。结果表明:在三峡水库变动回水区急弯分汊河段利用浅埂进行生境营造,相较于方案实施前,栖息地适宜度指数最大可增加0.4,显著改善了消落期、汛期四大家鱼栖息地生境质量。

       

      Abstract: The Chaotianmen to Fuling reach in the fluctuating backwater area of the Three Gorges Reservoir is located within the National Germplasm Resource Protection Area for the four major Chinese carps in the upper Yangtze River. During the impoundment period of the Three Gorges Reservoir, the water depth is large and the flow velocity is low, which is suitable for the survival of the four major Chinese carps. During the drawdown and flood seasons of the Three Gorges Reservoir, the river channel restores its natural fluvial characteristics, characterized by reduced water depth and increased flow velocity, thereby narrowing the scope of suitable habitats for the four major Chinese carps. The meandering braided reaches in the fluctuating backwater area of the Three Gorges Reservoir feature distinctive geomorphic characteristics: after sharp bends, the river channel often widens and branches, with numerous stone ridges distributed at intervals along the nearshore area. This provides a natural topographic foundation for the creation of continuous shallow-bar and deep-pool habitats. During reef-clearing and spoil disposal operations in this river section, the waste spoil is often placed in nearshore deep-pool areas, which has a certain impact on the habitats of the four major Chinese carps. To address this issue, relying on the 4.5 m-depth waterway project from Chaotianmen to Fuling in the fluctuating backwater area of the Three Gorges Reservoir, and taking the Dajiantan meandering braided reach as a typical case, a scheme was proposed to create habitats for the four major Chinese carps using the reef-clearing spoil from the waterway regulation project. A 2D hydrodynamic model of the project reach was established and validated using MIKE21, and the hydrodynamic distributions under different hydrological conditions were calculated. Based on the Habitat Suitability Index (HSI) model, water depth and flow velocity were selected as key influencing factors to analyze the improvement effect of the shallow-bar and deep-pool habitat creation scheme in the meandering braided reach on the hydrodynamic conditions for the four major Chinese carps. The results show that in the meandering braided reaches of the fluctuating backwater area of the Three Gorges Reservoir, habitat creation using shallow bars can increase the HSI by up to 0.4 compared with the pre-project condition. This significantly improves the habitat quality for the four major Chinese carps during the drawdown and flood seasons and can provide a reference for habitat restoration in similar river reaches.

       

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