The ability of the NewWave focused wave group (the scaled auto-correlation function) to represent the average shape in time of large waves in a random sea state makes it a useful tool for the design of offshore structures. However, the profile has only been validated against field data for waves on deep and intermediate water depths. A similar validation is advisable when applying NewWave to shallow water problems,where waves are less dispersive and more nonlinear. For this purpose, data recorded by two Channel Coastal Observatory (CCO) wave buoys during two large storms in January 2014 are analysed to assess the ability of NewWave to replicate the average shape of large waves in shallow water. A linear NewWave profile is shown to successfully capture the average shape of the largest waves from the Perranporth and Porthleven wave buoys during these large storm events. The differences between the measurements obtained by a surface-following buoy and a fixed sensor become important when considering the ability of a second-order corrected NewWave profile to capture weakly nonlinear features of the measured data. A general expression for this effect is presented for weakly nonlinear waves on intermediate water depths, leading to Lagrangian second-order sum corrections to the linear NewWave profile. A second-order corrected NewWave profile performs reasonably well in capturing the average features of large waves recorded during the January storms. These findings demonstrate that the NewWave profile is valid in relatively shallow water (kpD values less than 0.5), and so may have potential for use as a design wave in coastal engineering applications

Mixing processes downstream of river confluences impacts the ecology and the related environmental management of river networks. A clear understanding of such processes is challenging, especially for confluences having width‐to‐depth ratios larger than 100, due to the limited available field data. In this study, four field surveys based on hydro‐acoustic and conductivity measurements were conducted near the confluence between the Yangtze River and the Poyang Lake, which are the largest river and freshwater lake in China, respectively. It was found that mixing dynamics at the confluence were controlled by a complex interaction among the momentum flux ratio, secondary flow and the lock‐exchange flow associated to the density contrast between the two tributaries. Slow mixing was observed during high‐flow conditions that generated dual counter‐rotating secondary cells, with the downwelling flow acting as a barrier in the post‐confluence channel. In contrast, more rapid mixing was observed during low‐flow conditions when only a single channel‐scale secondary flow was identified. The mixing processes were also affected by the lock‐exchange flow associated to the density difference between the two confluent flows. Such lock‐exchange enhanced mixing when the Yangtze River waters had higher temperature, that is, lower density than that of the Poyang Lake. In low flow condition, the penetration of the much larger momentum flux of Yangtze River created a “two‐layers” structure with the contribution of the density difference, which further enhanced the curvature‐induced helicity. The findings from the present study improve our current understanding of mixing dynamics in large river confluences.

This paper presents an experimental study of local scour at submerged weirs with different downstream slopes. Thirty-three tests of coarse sand ($d_{50}=0.85\mathrm{mm}$ ) and 24 tests of fine sand ($d_{50}=0.26\mathrm{mm}$ ) were carried out in a sand-recirculating flume. The tests for each sand type used four weirs with different downstream weir slopes ($\pi /6$ , $\pi /4$ , $\pi /3$ , and $\pi /2$ to horizontal for the fine sand; $\pi /12$ , $\pi /6$ , $\pi /4$ , and $\pi /2$ to horizontal for the coarse sand). The results show that the upstream scour depth is independent of the downstream weir slope $\beta$ . For both sand types, the downstream weir slope has no effect on the downstream scour depth when it is greater than the upstream slope of the downstream scour hole $\theta$ . For $\beta <\theta$ , the downstream weir surface is partly exposed to flow, resulting in a downstream scour depth at the weir surface $d_w$ , which can be increased by the increase in either downstream scour depth or $\theta$ . In this situation, the upstream water level rises because of the reduced flow cross-section area, and the overflow jet is deflected to be approximately aligned with the downstream weir surface. For the coarse sand tests, when $\beta =\pi /6$ , the effect of the rising upstream water level is predominant because $\beta$ is close to ${\theta }_a$ (time-averaged value of $\theta$ ). This results in larger downstream scour depths. When $\beta$ is considerably smaller than ${\theta }_a$ , the effect of jet deflection starts to be predominant in the coarse sand tests, generating lower downstream scour depths when $U_0/U_c<2.6$ . Those two effects balance each other when $2.6<U_0/U_c<3.1$ for $\beta =\pi /12$ , resulting in the same downstream scour depths as those for a rectangular weir. For the fine sand tests, the jet deflection effect is predominant because the downstream weir slope has limited effect on the upstream water level. A conservative design method accounting for both effects is proposed for the local scour at downstream sloped submerged weirs.