Dykstra Steven L, Dzwonkowski Brian, Torres Raymond
School of Earth, Ocean, and Environment University of South Carolina Columbia SC USA.
Department of Marine Sciences University of South Alabama Dauphin Island Sea Lab Dauphin Island AL USA.
J Geophys Res Oceans. 2022 Mar;127(3):e2021JC018007. doi: 10.1029/2021JC018007. Epub 2022 Mar 28.
As tides propagate inland, they become distorted by channel geometry and river discharge. Tidal dynamics in fluvial-marine transitions are commonly observed in high-energy tidal environments with relatively steady river conditions, leaving the effects of variable river discharge on tides and longitudinal changes poorly understood. To study the effects of variable river discharge on tide-river interactions, we studied a low-energy tidal environment where river discharge ranges several orders of magnitude, the diurnal microtidal Tombigbee River-Mobile Bay fluvial-marine transition, using water level and velocity observations from 21 stations. Results showed that diurnal tidal attenuation was reduced by the width convergence in seaward reaches and height convergence of the landward backwater reaches, with the channel convergence change location ∼40-50 km inland of the bayhead and seaward of the largest bifurcation. River events amplified tides in seaward regions and attenuated tides in landward regions. This created a region of river-induced peak amplitude seaward of the flood limit (i.e., bidirectional-unidirectional current transition), allowing more tidal energy to propagate inland. Tidal currents were attenuated and delayed more by river discharge than water levels, making the phase lag dynamic. The river impacts on the tides were delineated longitudinally and shifted seaward as river discharge increased, ranging up to ∼180 km. Results indicated the longitudinal shifts of river impacts on tides in alluvial systems can be estimated analytically using the ratio of river discharge to tidal discharge and the geometric convergence of the system. Our simple analytical theory provides a pathway for understanding the tide-river-geomorphic equilibrium along increasingly dynamic coasts.
随着潮汐向内陆传播，它们会因河道几何形状和河流流量而发生变形。在河流条件相对稳定的高能潮汐环境中，通常可以观察到河海过渡区的潮汐动力学，而河流流量变化对潮汐和纵向变化的影响却知之甚少。为了研究河流流量变化对潮汐与河流相互作用的影响，我们研究了一个低能潮汐环境，即日潮微小潮的汤比格比河 - 莫比尔湾河海过渡区，该区域河流流量变化范围达几个数量级，我们利用21个站点的水位和流速观测数据进行研究。结果表明，向海河段的宽度收敛和内陆回水段的高度收敛降低了日潮衰减，河道收敛变化位置在湾头内陆约40 - 50公里处且在最大分流点向海一侧。河流事件增强了向海区域的潮汐并减弱了内陆区域的潮汐。这在涨潮极限向海一侧（即双向 - 单向水流过渡区）形成了一个河流诱发的峰值振幅区域，使得更多的潮汐能量能够向内陆传播。与水位相比，河流流量对潮流的衰减和延迟作用更大，使得相位滞后具有动态性。河流对潮汐的影响在纵向上得以界定，并且随着河流流量增加而向海移动，移动范围可达约180公里。结果表明，冲积系统中河流对潮汐影响的纵向移动可以通过河流流量与潮汐流量的比值以及系统的几何收敛性进行分析估算。我们简单的分析理论为理解沿日益动态化海岸的潮汐 - 河流 - 地貌平衡提供了一条途径。
