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；城市流域更不透水，这加快了径流向河流的传输。这些径流也对河流水质产生了负面影响。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的影响。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来缓解这些洪水和水质问题，作为审美特征，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。池塘里的水流经常短路，这减少了处理和沉淀的时间。这项研究计划的长期目标是发展基本的认识和一套工具，以便设计能够可靠地改善水质的保留池。目前的重点是确保池塘清除沉积物。第一个短期目标是评估反向旋转漩涡是否可以用来消除池塘中的短路，并提供符合标准的沉积物保留水平。第二个目标是更好地了解塘底沉积物的可蚀性。计算流体动力学和物理模型将进行评估一个池塘的行为与反向旋转的漩涡。首先，使用单涡，一个硕士学生将测试消除二次流的方法，二次流使靠近床的部分流比预期更快地移动到池塘出口。然后，一名博士生将在一名暑期学生的支持下，研究两个漩涡平行设置的池塘中的流动动力学，并评估停留时间和沉积物保留。这项工作将在不同的池塘直径与深度比下进行，并在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，一名博士生将在四名本科生的支持下，在不同的水化学、风和降雨事件时间下对池塘的床层材料进行取样。可蚀性随进入样品深度的变化将在实验室测试中与样品组成、土工性质和结构一起确定。为了提高池塘泥沙再悬浮的计算模拟能力，需要了解可蚀性，如果要提高池塘泥沙保持性能以始终达到标准，这是必要的。反向旋转漩涡池为池塘设计师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运营不善的池塘的方法。

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.