A method for using shoreline morphology to predict suspended sediment concentration in tidal creeks Geomorphology

Improving mechanistic prediction of shoreline response to sea level rise is currently limited by 1) morphologic complexity of tidal creek shorelines that confounds application of mechanistic models, and 2) availability of suspended sediment measurements to parameterize mechanistic models. To address these challenges we developed a metric to distinguish two morphodynamic classes of tidal creek and tested whether this metric could be used to predict suspended sediment concentration. We studied three small tidal creeks in North Carolina, U.S.A. We collected suspended sediment at one non-tidal and two tidal sites in each creek and measured the wetland and channel width using a geographic information system. In each creek, tidal harmonics were measured for one year, sediment accretion on the salt marsh was measured for three years, and shoreline erosion was measured from aerial photographs spanning 50 years. Additional total suspended solids measurements from seven creeks reported in a national database supplemented our analysis. Among the three intensively studied creeks, shoreline erosion was highest in the most embayed creek (having a wider channel than the width of adjoining wetlands) and lowest in the wetland-dominated creek (having a channel narrower than the width of adjoining wetlands). Wetland sediment accretion rate in the wetland-dominated creek was four times higher than the accretion in the embayed creek. The wetland-dominated tidal creek had over twice the suspended sediment as the most embayed creek. Based on these results, we conclude that our metric of embayed and contrasting wetland-dominated creek morphology provides a guide for choosing between two types of morphodynamic models that are widely used to predict wetland shoreline change. This metric also allowed us to parse the 10 tidal creeks studied into two groups with different suspended sediment concentrations. This relationship between suspended sediment concentration and creek morphology provides a method to estimate sediment concentration for individual tidal creek shorelines from spatial data alone, enabling more accurate parameterization of shoreline change models.

当前，提升海平面上升对岸线响应的机制预测能力仍受两大瓶颈制约：一是潮沟岸线的地貌复杂性会干扰机制模型（Mechanistic Model）的应用；二是缺乏可用于参数化机制模型的悬浮泥沙实测数据。为应对上述挑战，本研究构建了一项用于区分两类潮沟动力地貌类型的指标，并验证了该指标能否用于预测悬浮泥沙浓度（Suspended Sediment Concentration）。本研究以美国北卡罗来纳州的3条小型潮沟为研究对象：在每条潮沟的1个非潮汐站点与2个潮汐站点采集悬浮泥沙样本，并借助地理信息系统（Geographic Information System，GIS）测量湿地与沟道宽度；针对每条潮沟，开展了为期1年的潮汐谐波观测、为期3年的盐沼泥沙沉积速率监测，并通过跨度达50年的航空影像解译岸线侵蚀状况。本研究还补充采用了某国家数据库中公开的7条潮沟的总悬浮颗粒物（Total Suspended Solids，TSS）实测数据，以辅助分析。在这3条重点研究的潮沟中，岸线侵蚀速率最高的为湾道型潮沟（其沟道宽度大于毗邻湿地的宽度），最低的则为湿地主导型潮沟（其沟道宽度小于毗邻湿地的宽度）；湿地主导型潮沟内的湿地泥沙沉积速率是湾道型潮沟的4倍，其悬浮泥沙浓度更是达到湾道型潮沟的2倍以上。基于上述结果，本研究得出结论：本研究提出的湾道型与湿地主导型潮沟地貌分类指标，可为两类广泛用于预测湿地岸线变化的动力地貌模型的选型提供参考依据。该指标还可将本研究涉及的10条潮沟划分为悬浮泥沙浓度存在显著差异的两个组别。悬浮泥沙浓度与潮沟地貌间的上述关联，提供了一种仅通过空间数据即可估算单条潮沟岸线泥沙浓度的方法，从而可实现岸线变化模型的更精准参数化。