Under stable sea level conditions, estuaries tend to accumulate sediment resulting in changes that can be conceptualised as a progression from a juvenile system to maturity. Sea level rise results in an increase in accommodation space within the estuary that can effectively reverse the progression towards maturity. This effect was investigated for Tairua Estuary, New Zealand, using a set of MIKE 21 HD (hydrodynamic) and MIKE 21 ST (sediment transport) numerical models forced by tides, wind and fluvial discharges. A range of scenarios of sea level rise and changing fluvial inputs were simulated. The simulation results predicted a general trend of increasing tidal range with sea level rise, which was partially offset by higher fluvial discharges within high fluvial input scenarios. Under present conditions, the estuary is ebb-dominated with predominantly fluvial inputs, but with increasing sea level, the estuary becomes increasingly flood-dominant and the transition from fluvial to marine sediments within the estuary progressively moves landward. If the sediment supply increases in tandem with the accommodation space, the result would be no significant change to the estuary’s hydrodynamics and sediment transport patterns. Under present conditions, observations and modelling indicate that sediment is exported by ebb-dominant conditions, suggesting a capacity to compensate for increasing accommodation space. However, modelling indicates a sediment deficit at higher projected sea levels, resulting in sediment being scavenged from the seaward margin of the sandy barrier spit enclosing the estuary. Scavenging would increase the coastal erosion hazard for the residents of the barrier spit. This situation does not arise if the rate of increase in accommodation space remains below the annual fluvial sediment supply. Ultimately, our results show the importance of considering catchment-derived sediment supply and morphological complexity, when predicting how the changing hydrodynamics modulate the interplay between sediment stored within the estuary and the open coast, and determining the fate of the coast during sea level rise.

中文翻译：

---

应对海平面上升的河口复兴：以新西兰泰鲁阿河口为例

在稳定的海平面条件下，河口往往会积累沉积物，从而导致可以将其概念化为从幼年系统到成熟系统的变化。海平面上升导致河口内的住宿空间增加，可以有效地逆转向成熟的进程。使用一组 MIKE 21 HD（流体动力学）和 MIKE 21 ST（沉积物输送）数值模型，研究了新西兰泰鲁阿河口的这种效应，这些模型受潮汐、风和河流排放的影响。模拟了海平面上升和不断变化的河流输入的一系列情景。模拟结果预测了潮差随着海平面上升而增加的总体趋势，这部分被高河流输入情景中更高的河流排放所抵消。在目前条件下，河口以河流输入为主，以河流输入为主，但随着海平面的升高，河口变得越来越以洪水为主，河口内从河流沉积物到海洋沉积物的过渡逐渐向陆地移动。如果沉积物供应与容纳空间同步增加，结果不会显着改变河口的水动力和沉积物输送模式。在目前的条件下，观测和建模表明沉积物在落潮优势条件下输出，表明有能力补偿增加的容纳空间。然而，建模表明在较高的预测海平面上存在沉积物不足，导致沉积物从包围河口的沙质屏障的向海边缘被清除。清除会增加屏障吐痰居民的海岸侵蚀危险。如果容纳空间的增长速度低于年度河流沉积物供应量，则不会出现这种情况。最终，我们的结果表明，在预测不断变化的流体动力学如何调节河口和开阔海岸内储存的沉积物之间的相互作用以及确定海平面上升期间海岸的命运时，考虑集水区沉积物供应和形态复杂性的重要性。