Tidal and subtidal current velocity structure and forcing mechanisms are important to forecasting estuary conditions linked to water quality problems in coastal areas. This study combined current velocity, salinity, temperature, and water level data with analytical and numerical models to understand dynamics in a small estuary in Downeast Maine, USA. Both the tidal and subtidal flow, as well as the drivers of the subtidal flow, were found to have substantial spatial variation along the estuary. An analysis of the along-channel momentum balance indicates that advection and friction alternate in balancing Stokes drift and the barotropic pressure gradient along the estuary, switching at locations of estuary width constriction or expansion. These dynamics influenced along-channel subtidal flows producing highest velocity at the shoals and lowest velocity in the channel in the mid-reaches of the estuary when advection was more influential than friction. This pattern reversed when friction dominated over advection, producing the highest velocity in the center of the channel, which is corroborated by field measurements. The idealized model produced a spatial structure of along-channel residual flows that do not align with field measurements and numerical simulation results due to the simplicity of the estuary geometry used in the model. The outcome of the analyses suggests that slight variations in along-channel geometry and bathymetry can alter tidal and subtidal flows and transport, even in small (<10 km in length) tidally dominated estuaries with relatively little spatial variation in hydrodynamic conditions within a tidal cycle.

潮汐和潮下流速度结构和强迫机制对于预测与沿海地区水质问题相关的河口条件很重要。这项研究将流速、盐度、温度和水位数据与分析和数值模型相结合，以了解美国缅因州东南部一个小河口的动态。潮汐和潮下流以及潮下流的驱动因素都被发现沿河口具有显着的空间变化。对沿河道动量平衡的分析表明，在平衡斯托克斯漂移和沿河口的正压压力梯度时，平流和摩擦交替，在河口宽度收缩或扩张的位置切换。当平流比摩擦力的影响更大时，这些动力学影响了沿河道的潮下流，在浅滩产生最高速度，在河口中游河道产生最低速度。当摩擦力超过平流时，这种模式会发生逆转，在通道中心产生最高速度，现场测量证实了这一点。由于模型中使用的河口几何结构的简单性，理想化模型产生了与现场测量和数值模拟结果不一致的沿河道剩余流的空间结构。分析结果表明，沿河道几何形状和水深测量的轻微变化可以改变潮汐和潮下流和运输，即使是在小（<