Lady Bird Lake / East 4th Street Drainage Improvements Study and Design, City of Austin, Texas

This project included the evaluation of secondary street flooding conditions within an older area of East Austin. The existing storm drain system was modeled using StormCad, and it was determined that the storm drains did not have the capacity to pass the 10-year storm. An initial feasibility study of this area identified over $15 million in storm drain improvements, ranging in size from a 24-inch line to a 10-foot-by-6-foot box culvert. During the preliminary engineering phase of the project, Plummer was able to reduce the size of the improvements to a 9-foot-by-6-foot box culvert, reducing the cost to $12 million. This cost savings was produced through refined modeling techniques and the development of a flow-split concept to better utilize the capacity of the existing system. The design of the first phase of these improvements included 2,600 lf of 9-foot-by-6-foot box, 6,500 lf of 66- and 72-inch storm drains, and associated junction boxes, manholes, and inlets. During the initial design phase of these improvements, Plummer refined the design of proposed additions to the Pedernales storm drain system in order to substantially alleviate flooding in the residential neighborhoods in the vicinity of the project. The results of HEC-RAS and additional StormCAD modeling efforts were used to modify the design as needed to accommodate a new street reconstruction and wastewater pipeline project in the area. This project was under construction at a bid of $5.5 million.