Collaborative Research: Oligohaline dispersion: transport processes at the estuary-tidal river transition

控制河口盐度分布的输运过程随着河流流量、潮汐和气象事件的变化而动态变化。我们对输运过程的理解大多是基于对河口中央河段的研究。上游位于盐侵向陆边界附近，具有明显的物理特征，使得盐侵运移过程不同于中游。该项目将结合联合收割机现场和船上观测、染料释放研究和现实的高分辨率建模来量化特拉华州河口上游的潮汐扩散。通过直接比较，观测和建模的分析将紧密联系在一起，它们将一起用于量化分散率并确定机制。水深特征，如渠道收缩和弯曲，以及人为的修改，如码头和疏浚渠道，预计将是特别重要的创造盐度和速度异常，导致净向陆运输。特拉华州是世界上许多河口的代表，在这些河口中，随着海平面上升、降水量变化和疏浚，寡盐河段向陆地转移，来自潮汐河流的供水日益受到威胁。具体而言，费城水区（PWD）的饮用水取水口位于研究区域的上游，特拉华州河流流域委员会（DRBC）控制河流流量条件，调节盐入侵，保护数百万人的供水。该项目将建立在PWD和DRBC的PI和同事之间的既定关系的基础上，以确定知识差距，并将研究结果与管理决策联系起来。PI还将为一系列研讨会做出贡献，这些研讨会将科学家和水资源管理人员聚集在一起，评估全球盐入侵对供水的威胁。该项目将支持罗格斯大学的一名研究生，他将参与研究的各个方面，包括观测、建模和推广。寡盐河段（0. 5 -5 psu）是许多生态和生物地球化学过程的重要过渡区，但很少有研究探讨了运输的物理机制。几个关键特征将寡盐区与中央河口区区分开来。在淡水渐近线，沿河口盐度梯度减小，河口交换流减弱。分层也减少，减少了稳定的盐通量和增加混合，这减少了振荡剪切分散。河道变窄影响横向交换和捕获，特别是在城市化河口与海岸线修改。该项目使用多种互补方法来量化该区域的运输过程。在低河流流量的观测将捕捉空间和时间的演变与潮汐和气象强迫的盐度，染料释放将直接量化分散在地形特征的规模。建模将使用嵌套网格方法来表示驱动扩散的测深特征，沿着Dronkers和货车de Kreeke（1986年）提出的一种新的分析方法来隔离非本地盐通量的来源。对寡盐河段运输过程的理解对于了解那里的条件如何随着气候变化和持续发展而演变至关重要。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

Transport processes controlling the salinity distribution in an estuary vary dynamically with the river discharge, tides, and meteorological events. Most of our understanding of the transport processes is based on studies of the central reach of estuaries. The upper reach near the landward limit of the salt intrusion, has distinct physical characteristics that make transport processes different from the central reach. This project will combine in-situ and shipboard observations, dye release studies, and realistic high-resolution modeling to quantify tidal dispersion in the upper reach of the Delaware River estuary. Analysis of the observations and modeling will be closely linked through direct comparisons, and together they will be used to quantify dispersion rates and identify the mechanisms. Bathymetric features like channel constrictions and bends as well as anthropogenic modifications like piers and dredged channels are expected to be particularly important to creating salinity and velocity anomalies that lead to net landward transport. The Delaware is representative of many estuaries around the world where water supplies drawn from tidal rivers are increasingly threatened by landward shifts in the oligohaline reach with sea level rise, changing precipitation, and dredging. Specifically, drinking water intakes for the Philadelphia Water District (PWD) are located just upstream of the study region, and the Delaware River Basin Commission (DRBC) controls river flow conditions regulate the salt intrusion and protect the water supply for millions. This project will build on established relationships between the PIs and colleagues at both PWD and DRBC to identify knowledge gaps and link study findings to management decisions. The PIs will also contribute to a series of workshops bringing together scientists and water resources managers to assess threats to water supplies by salt intrusion globally. The project will support a graduate student at Rutgers who will be involved in all aspects of the study, including observations, modeling, and outreach.The oligohaline reach (0.5-5 psu) is an important transition zone for many ecological and biogeochemical processes, and yet few studies have examined the physical mechanisms of transport. Several key characteristics distinguish the oligohaline from the central estuary. In the asymptote to freshwater, the along-estuary salinity gradient decreases and estuarine exchange flow weakens. Stratification also decreases, reducing the steady salt flux and increasing mixing, which reduces oscillatory shear dispersion. Channel narrowing affects lateral exchange and trapping, particularly in urbanized estuaries with shoreline modification. This project uses multiple, complementary approaches to quantify transport processes in this region. Observations during low river discharge will capture the spatial and temporal evolution of salinity with tidal and meteorological forcing, and dye releases will directly quantify dispersion at the scale of topographic features. Modeling will use a nested-grid approach to represent the bathymetric features driving dispersion, along with a novel analysis approach to isolate sources of non-local salt flux, as put forth by Dronkers and van de Kreeke (1986). A process-based understanding of transport in the oligohaline reach is critical to understanding how conditions there will evolve with climate change and continued development.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.