21st Street Storm Sewer System Improvements – System 007

CobbFendley worked with the City of Harlingen under their drainage on-call contract to provide engineering plans for drainage and roadway improvements along 21st Street from Theresa Street to East Van Buren Avenue. CobbFendley was contracted in the Fall of 2022 to prepare the complete design, including drainage calculations and recommendations, on an expedited four-month design schedule to meet the requirements of the FEMA grant.

Drainage and Roadway Services: The project included producing plans, specifications and construction estimate (PS&E) to replace existing drainage inlets, manholes, and storm  sewer lateral pipes from the inlets to the trunk line. The project utilized the model done for the scope area in August 2008 for the City of Harlingen’s Drainage Master Plan as the basis for the design phase. The project replaced 6,174 linear feet of reinforced concrete pipe and included minor utility adjustments along with pavement restoration. Two existing  parallel storm sewer trunk lines running along both sides of 21st street were discovered and analyzed as to what would be the most cost-effective approach to address them. One trunk line was left in place and the other one was replaced and upgraded to accommodate the storm water runoff coming to the roadway. The twin trunk lines were treated as a system and lateral pipes connected them.

Rail Services: The existing 48-inch diameter storm sewer trunk line crosses a UP Railroad line. The proposed storm sewer trunk line will be upsized to a 5’x5 Reinforced Concrete Box. CobbFendley has prepared the permit application and plans for this crossing. The project is currently awaiting funding for construction. As Railroad permits have a 6-month expiration date, CobbFendley is holding on submitting the final application until construction funding is secured.

Surveying Services: Surveying the existing storm sewer system was critical to analyze if any portion of the system could be re-used to reduce construction costs. Upon receiving the surveying information, CobbFendley analyzed various options and determined it was best and most cost-effective to keep the existing storm sewer trunk line in place and add an additional trunk line on the other side of the roadway.
H&H Engineering: An H&H study was done and used to size the new trunk line and storm sewer laterals. The H&H study was also used to determine proposed inlet spacing and inlet extensions. Surveying was also critical to determine the locations of existing underground utilities to avoid them as much as possible. The plans were completed by the deadline, to the satisfaction of the City of Harlingen.