THE INFLUENCE OF WETLAND VEGETATION ON TIDAL STREAM CHANNEL MIGRATION AND MORPHOLOGY
THE INFLUENCE OF WETLAND VEGETATION ON TIDAL STREAM CHANNEL MIGRATION AND MORPHOLOGY
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DOI：
10.2307/1352081
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发表时间：
1980-01-01
期刊：
影响因子：
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通讯作者：
GAROFALO, D
中科院分区：
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作者：
GAROFALO, D
利用摄影测量技术计算了32年（1940-1972年）的平均相对河道迁移率为0.21米/年的盐水潮汐湿地河道，和0.32米/年的淡水潮汐湿地渠道。含盐湿地河道的平均弯曲指数较高，即，总河道长度与下游直线距离之比（1.95），与淡水潮汐河道的弯曲度（1.46）相比。这种差异是由于盐碱和淡水潮汐湿地环境中植被类型和土壤持水能力的差异。由于河岸有密集的根系支撑，盐水水道变得根深蒂固，而淡水潮汐水道流经更均匀的基底，其行为很像穿过潮间区泥滩的水道。较高的平均曲流振幅（1/2的峰谷距离的一个给定的曲流波）为盐水通道（171米）与较低的振幅为淡水通道（114米）表明，曲流回路的盐水通道主要是由河岸的侵蚀特性和其他当地因素，而不是由水动力因素，如流速或流量。曲流迁移功能不会发生在同质土壤材料的倾向，形成这些功能的盐通道是由于差异侵蚀引起的根系密度的变化。淡水潮汐通道的形态受到包括流量在内的水动力因素的影响，这是由于存在更均匀的物质，即，没有广泛根系的泥泞土壤。利用现有的潮流速度和高地流量记录，对每个潮汐通道的落潮和洪水流量数据进行分析，支持这样一个事实，即盐沼的侵蚀力比新鲜的潮沼地区要大。河道迁移率和水力水流数据（如流速和流量）之间的统计相关性较差，由于采用了近似潮汐流量值的方法，因此必须谨慎接受。在正常的潮汐条件下，盐水和淡水潮汐通道迁移很少，如果有的话，代表一个明显平衡的相对低能量系统。在咸水和淡水湿地中，大多数河道迁移都是由于风暴造成的力量增加而发生的。
Average relative stream channel migration rates of 0.21 m/yr for saline tidal wetland stream channels, and 0.32 m/yr for freshwater tidal wetland channels were calculated for a 32 yr period (1940-1972) using photogrammetric techniques. Saline wetland stream channels averaged higher indices of sinuosity, i.e., the ratio of total channel length to linear downstream distance (1.95), when compared with sinuosities of freshwater tidal channels (1.46). The difference is due to differences in vegetation types and consequent soil holding capacity between saline and freshwater tidal wetland environments. Saline channels become entrenched because the banks are supported by dense root systems, while freshwater tidal channels flow through a more homogeneous substrate and behave much like channels which cross mud-flats in the intertidal zone. Higher average meander amplitudes (1/2 the peak to trough distance of a given meander wave) for saline channels (171 m) vs. lower amplitudes for freshwater channels (114 m) suggest that meander loops for saline channels are determined primarily by the erosional characteristics of stream banks and by other local factors rather than by hydrodynamic factors such as flow velocity or discharge. Meander migration features do not occur in homogenous soil materials; the tendency of saline channels to form these features is attributed to differential erosion caused by variations in root system density. The morphology of freshwater tidal channels is influenced by hydrodynamic factors including discharge, and is due to the existence of more homogenous materials, i.e., muddy soils devoid of extensive root systems. An analysis of ebb and flood discharge data arrived at for each tidal channel using existing tidal current velocity and upland discharge records supports the fact that relatively greater erosive forces occur in salt marsh than in fresh tidal marsh areas. A poor statistical correlation between rates of stream channel migration and hydraulic stream flow data such as velocity and discharge must be accepted with caution due to the method of approximating tidal discharge values. Under normal tidal conditions both saline and freshwater tidal channels migrate little, if any, and represent an apparently balanced relatively low energy system. Most stream channel migration in both saline and freshwater wetlands occurs as a result of increased forces due to storms.