United States Department of Transportation
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Alternative Title:Technical report 14-17 : outlet diffusers to increase culvert capacity.
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Abstract:Aging infrastructure and changing weather patterns present the need to increase the capacity of existing highway culverts. This research approaches this challenge through the use of diffuser outlet systems to increase pipe capacity and reduce outlet losses. A summary of relevant literature, Computational Fluid Dynamics (CFD) modelling studies, and test results of scale model diffusers provide the background information necessary to understand the design requirements of diffusers and how they function. Properly designed inlets, diffuser outlets, and outlet weirs are all important components of an effective diffuser system. Incorporating these requirements, a prototype diffuser was designed, installed and tested on an existing undersized pipe in Thorndike, Maine. The diffuser was monitored through the fall, winter and spring of 2015-2016. A method for calculating flows was developed using a drawdown technique involving the ponding and releasing of water through the diffuser system. This data was used to quantify the performance of the diffuser, and to compare it to traditional straight pipes as well as diffuser systems discussed in the literature. The Thorndike field study demonstrated that a diffuser system could be inexpensively fabricated, easily installed, and successfully used to consistently increase pipe capacity. To the best of our knowledge, this is the first successful field test of a diffuser in a highway application.
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