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首页> 外文期刊>Estuarine Coastal and Shelf Science >The salt wedge position in a bar-blocked estuary subject to pulsed inflows
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The salt wedge position in a bar-blocked estuary subject to pulsed inflows

机译：条形阻塞河口中的盐楔位置受脉冲流入的影响

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A series of laboratory experiments were carried out to investigate the response of a bar-blocked, saltwedge estuary to the imposition of both steady freshwater inflows and transient inflows that simulate storm events in the catchment area or the regular water releases from upstream reservoirs. The trapped salt water forms a wedge within the estuary, which migrates downstream under the influence of the freshwater inflow. The experiments show that the wedge migration occurs in two stages, namely (ⅰ) an initial phase characterized by intense shear-induced mixing at the nose of the wedge, followed by (ⅱ) a relatively quiescent phase with significantly reduced mixing in which the wedge migrates more slowly downstream. Provided that the transition time t_T between these two regimes satisfies t_T > g′h~4L/q~3α, as was the case for all our experiments and is likely to be the case for most estuaries, then the transition occurs at time t_T = 1.2(gα~3L~6/g′~3q~2)~(1/6), where g′= gΔρ/ρ_0 is the reduced gravity, g the acceleration due to gravity, Δρ the density excess of the saline water over the density ρ_0 of the freshwater, q the river inflow rate per unit width, and L and α are the length and bottom slope of the estuary, respectively. A simple model, based on conversion of the kinetic energy of the freshwater inflow into potential energy to mix the salt layer, was developed to predict the displacement x_w over time t of the saltwedge nose from its initial position. For continuous inflows subject to t< t_T, the model predicts the saltwedge displacement as x_w/h = 1.1(t/τ)~(1/3), where the normalizing length and time scales are h = (q~2/g)~(1/3) and τ = g′α~2h~4L/q~3, respectively. For continuous inflows subject to t > t_T, the model predicts the displacement as x_w/h = 0.45N~(1/6)(t/τ)~(1/6)/α, where N = q~2/g′h~2L is a non-dimensional number for the problem. This model shows very good agreement with the experiments. For repeated, pulsed discharges subject to t < t_T, the saltwedge displacement is given by (x_w/h)~3 - (x_0/h)(x_w/h)~2 = 1.3t/τ, where x_0 is the initial displacement following one discharge event but prior to the next event. For pulsed discharges subject to t > t_T, the displacement is given by (x_w/h)~6 ― (x_0/h)(x_w/h)~5 = 0.008 N(t/τ)/α~6. This model shows very good agreement with the experiments for the initial discharge event but does systematically underestimate the wedge position for the subsequent pulses. However, the positional error is less than 15%.
机译：进行了一系列实验室实验，以研究条形阻塞的盐楔河口对稳定的淡水流入和瞬时流入的施加的响应，这些流入模仿了集水区的暴雨事件或上游水库的定期放水。捕获的盐水在河口内形成楔形，在淡水流入的影响下向下游迁移。实验表明，楔形运动发生在两个阶段，即（ⅰ）初始阶段的特征是在楔形尖端出现强烈的剪切诱导的混合，然后是（a）相对静止的阶段，混合明显减少，其中楔形向下游迁移的速度较慢。假设这两个区域之间的过渡时间t_T满足t_T> g'h〜4L / q〜3α，就像我们所有实验的情况一样，并且对于大多数河口来说可能都是这样，那么过渡发生在时间t_T = 1.2（gα〜3L〜6 / g'〜3q〜2）〜（1/6），其中g'=gΔρ/ρ_0是减小的重力，g是由于重力引起的加速度，Δρ是整个盐水的密度过剩淡水的密度ρ_0，单位宽度的河流入流量q，L和α分别是河口的长​​度和底坡。建立了一个简单的模型，该模型基于将淡水流入的动能转换为势能以混合盐层的功能，以预测盐楔鼻梁从其初始位置开始随时间t的位移x_w。对于t t_T的连续流入，模型预测位移为x_w / h = 0.45N〜（1/6）（t /τ）〜（1/6）/α，其中N = q〜2 / g' h〜2L是该问题的无量纲数。该模型与实验结果非常吻合。对于t t_T的脉冲放电，位移由（x_w / h）〜6 ―（x_0 / h）（x_w / h）〜5 = 0.008 N（t /τ）/α〜6给出。该模型显示出与初始放电事件的实验非常吻合，但系统地低估了后续脉冲的楔形位置。但是，位置误差小于15％。

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