Innovating Stormwater Retention Pond Design

城市地区的雨水径流对河流有重大影响。一个问题是下游洪水的增加;城市流域更不受影响，这加快了径流向河流的传输。这些径流也对河流水质产生负面影响。在它携带的许多污染物中，沉积物是一个重要的问题，因为它对鱼类和其他水生生物有影响。城市径流中的细沉积物是有毒的，携带重金属，以及影响湖泊富营养化的营养物质。许多城市使用雨水蓄水池试图缓解这些洪水和水质问题，作为美学特征，在一些城市，用于娱乐。然而，目前的设计程序已经产生了许多池塘，不能提供可靠的沉积物和其他污染物的保留。池塘中的水流经常短路，这减少了处理和沉积物沉淀的时间。这项研究计划的长期目标是发展基本的理解和一套工具，以允许设计提供可靠的水质改善的蓄水池。当前的重点是确保池塘去除沉积物。第一个短期目标是评估是否可以使用反向旋转的涡流来消除池塘中的短路，并提供符合标准的沉积物截留水平。第二个目标是更好地了解池塘底质可蚀性。将进行计算流体动力学和物理建模，以评估具有反向旋转涡流的池塘的行为。首先，使用单涡流，一个理科硕士学生将测试消除二次流的方法，二次流使靠近床的流动部分比期望的更快地移动到池塘出口。然后是博士学位一名暑期班学生将协助一名学生，研究两个平行设置的涡流池中的水流动力学，并评估停留时间和沉积物滞留量。这项工作将在不同的池塘直径与深度比和一系列潜在的流动条件下进行。为了评估池塘沉积物的可蚀性，一位博士。学生，由四个本科暑期学生的支持下，将样本床材料从池塘下不同的水化学，风，和时间从雨事件。可蚀性随样品深度的变化将在实验室测试中沿着样品成分、岩土性质和结构一起确定。 了解侵蚀性是必要的，以提高计算模型的能力，沉积物再悬浮在池塘，这是必要的，如果池塘的性能在沉积物保留，以满足标准一致。 反向旋转涡流池为池塘设计者提供了一种创新的方法，以最大限度地减少短路，同时提供可靠的沉积物保留。它还为加拿大社区提供了一种廉价改造其运行不良的池塘的方法。

Stormwater runoff from urban areas has a significant impact on rivers. One issue is an increase in downstream flooding; urban watersheds are more impervious, which speeds transmission of runoff to a river. This runoff also negatively impacts river water quality. Of the many pollutants it carries, sediment is a significant concern because of its impacts on fish and other aquatic life. Fine sediments in urban runoff are toxic and carry heavy metals, as well as nutrients that impact eutrophication of lakes. Many cities use stormwater retention ponds to attempt to mitigate these flooding and water quality issues, as aesthetic features, and, in some cities, for recreation. However, current design procedures have produced many ponds that do not provide reliable retention of sediment and other pollutants. The flow in ponds often short-circuits, and this lessens the time for treatment and sediment settling. The long-term objectives of this research program are to develop the fundamental understanding and a set of tools to allow for the design of retention ponds that provide reliable improvements in water quality. The current focus is to ensure sediment removal by ponds. The first short-term objective is to evaluate whether counter-rotating vortices can be used to eliminate short-circuiting in ponds and provide levels of sediment retention that meet standards. The second objective is to understand pond bed sediment erodibility better. Computational fluid dynamics and physical modelling will be conducted to assess the behavior of a pond with counter-rotating vortices. First, using a single-vortex, an M.Sc. student will test means to eliminate the secondary flow that moves the portion of the flow near the bed to the pond outlet more quickly than desired. Then, a Ph.D. student, supported by one summer student, will study the flow dynamics in a pond with two vortices set in parallel and evaluate the residence times and sediment retentions. This work will be done for various pond diameter to depth ratios and under a range of potential flow conditions. For the assessment of the pond sediment erodibility, a Ph.D. student, supported by four undergraduate summer students, will sample bed material from ponds under different water chemistries, wind, and times from rain events. The variation of erodibility with depth into the sample will be determined in laboratory testing along with the sample composition, geotechnical properties, and structure. The understanding of erodibility is needed to improve computational modelling capabilities for sediment resuspension in ponds, which are necessary if pond performance at sediment retention is to be enhanced to meet standards consistently.  The counter-rotating vortex pond offers an innovative approach for pond designers to minimize short-circuiting while providing reliable sediment retention. It also offers Canadian communities a way to retrofit their poorly operating ponds inexpensively.