As a part of an ongoing effort to replace aging and inadequate storm drainage systems, the City of Pharr and the Texas General Land Office needed to upgrade a smaller, reinforced concrete pipe (RCP) drainage system that included a main trunk line of large box culverts which intercepted approximately 320 acres of surface runoff in densely populated residential and commercial areas. Not only would the needed concrete boxes be difficult to install in such tight site constraints, the manufacturing costs and logistics required were expensive and exceeded project budget. The City decided to pursue alternative solutions, and after careful deliberation selected Contech Engineered Solutions’ polymeric ULTRA FLO® - a corrugated metal pipe (CMP) solution that is one of the most hydraulically efficient storm sewer systems available due to its smooth interior surface, longer length, fewer joints and prefabricated junctions that include elbows, manholes and catch basins.
There was also a 36” pipe specified to go through a 48” casing pipe that was bored under the highway. Because ULTRA FLO uses a thinner wall, Contech was able to size up to 42” and increase flow capacity. As the City had never used a CMP system before, Contech modeled the system internally to ensure hydraulic equivalency of 78” round pipe to 8’x4’ and 7’x5’ boxes while the 12 gage polymer coating provided added durability and the required service life.
The contractor on-site, Saenz Utility, knew CMP would be much easier to install than reinforced concrete boxes in city streets. Due to the nature of the high-density, mixed-use site constraints, a crane would have been required to install the boxes. All told, there was also a total of $90,000 savings given back to the city. The installation took approximately three months - well under the original time frame estimated.
“With the tight constraints of the project in a residential area the alternative solution of using ULTRA FLO - CMP was the answer” stated City Engineer for the City of Pharr, William Ueckert, Jr., P.E.