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。我们对输运过程的大部分理解都是基于对河口中央河段的研究。上游靠近盐入侵的陆地边界，具有明显的物理特征，使运输过程不同于中央河段。该项目将结合现场和船上观测、染料释放研究和现实的高分辨率建模来量化特拉华河河口上游的潮汐扩散。对观测数据的分析和建模将通过直接比较紧密联系在一起，它们将一起用于量化分散率和确定机制。航道收缩和弯曲等水深测量特征以及码头和疏浚航道等人为修改对于造成盐度和流速异常从而导致净向陆地输送特别重要。特拉华州是世界上许多河口的代表，在这些河口，由于海平面上升、降水变化和疏浚，低盐度河段的陆上变化日益威胁着潮汐河流的供水。具体地说，费城水区(PWD)的饮用水取水口就位于研究区域的上游，特拉华河流域委员会(DRBC)控制河流流动状况，调节盐分入侵，保护数百万人的供水。这一项目将建立在项目主管与预科和DRBC同事之间已建立的关系基础上，以确定知识差距，并将研究结果与管理决策联系起来。PIS还将协助举办一系列讲习班，让科学家和水资源管理人员齐聚一堂，评估全球食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，他将参与研究的方方面面，包括观察、建模和外展。低盐度河段(0.5-5 PSU)是许多生态和生物地球化学过程的重要过渡地带，但很少有研究检验运输的物理机制。有几个关键特征将寡盐与中央河口区分开来。在淡水渐近线上，河口沿岸盐度梯度减小，河口交换流减弱。层结也减少了，减少了稳定的盐通量，增加了混合，从而减少了振荡切变弥散。河道变窄影响侧向交换和圈闭，特别是在岸线改变的城市化河口。该项目使用多种相辅相成的方法来量化该区域的运输过程。低流量时的观测将捕捉到潮汐和气象强迫作用下盐度的时空演变，染料释放将直接在地形特征尺度上量化扩散。建模将使用嵌套网格方法来表示驱动扩散的水深特征，以及Dronkers和van de Kreeke(1986)提出的分离非局部盐通量来源的新分析方法。以过程为基础的对低盐度河段运输的了解，对于了解那里的条件将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，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.