City awards contract for Purgatory Creek Improvements project's next phase

The City of San Marcos’ Purgatory Creek Channel Improvements project moves forward with the city awarding a contract to civil engineer firm Lockwood, Andrews & Newnam, Inc. to begin work on its next phase. 

The city hired LAN in April 2018 to develop a preliminary design to mitigate flooding conditions on Purgatory Creek from Wonder World Drive to its confluence with the San Marcos River, which is approximately 2 miles. Alongside flood mitigation, the city saw a chance to enhance the quality of water entering the river and establish sustainable, multi-use trails for public use through this project. 

“The City of San Marcos has had a history of major flooding events including within the Purgatory Creek watershed,” said John Espinoza, City of San Marcos project manager. “With the support of city council and its citizens, we are taking a holistic approach to address flood mitigation and to improve water quality and public space/connectivity. The Purgatory Creek project is one of the many important projects the city is currently conducting and gives us a great opportunity to partner with our stakeholders including local foundations and civic groups.”

Purgatory Creek carries flow from the entire Purgatory watershed through the city, reaching the San Marcos River through Children’s Park at Bicentennial Park. Flood prone areas exist adjacent to the creek, which causes street crossing to be over-topped during storms, causing traffic disruptions.

Additional firms have been selected as subconsultants to join LAN’s project team, including Hicks & Company for permitting, Asakura Robinson for landscape architecture and Lady Bird Johnson Wildflower Center for ecosystem restoration.

The project exists in two phases — Phase 1 begins upstream from Johnson Avenue and ends at the confluence of the San Marcos River. Phase 2 extends from Johnson Avenue upstream to Wonder World Drive. LAN completed preliminary design on Phase 1 in March 2019. The next phase of design on Phase 1 is currently underway and is expected to be completed in December 2020.

“The improvements will incorporate design features to establish a stable, natural channel that will support a sustainable ecosystem and reduce maintenance requirements,” LAN stated in a press release. “These include a meandering earthen pilot channel with riffle pool complexes at strategic locations to provide for aquatic habitats, invasive species management, tree protection, and selective native plantings. Near the San Marcos River, high flows will be diverted through a new diversion channel/spillway providing a park amenity for river access.  The project will include the establishment of ‘riparian’ and/or “grow zones” to provide the transition of flows between the overbank and channel areas.”

The Purgatory Creek improvements will include bridge/culvert modifications or replacements at the creek’s crossings at  South Mitchell Street, Jackman Street, Guadalupe Street, South LBJ Drive and South CM Allen Parkway. To improve creek connectivity, a low-water crossing modification will be made at the Comal Street crossing. 

Trail, sidewalk and pedestrian improvements are also featured with the project. 

“The path will be pedestrian and bike-friendly with access for maintenance vehicles along the trail,” LAN stated. “Trail design will include way-finding and illumination and consider ADA-compliant guidelines. Trail connectivity along the San Marcos River will be maintained with the installation of the spillway at the Children’s Park and connect to trails at the Purgatory Creek Natural Area located west of Wonder World Drive.”

Approximately 4,000 linear feet of sidewalk will be added with the project. 

The project will include extensive environmental investigations, permitting and approval from several state and federal agencies in coordination and approval from the Texas Department of Transportation and Union Pacific Railroad. 

The project will require acquisition of right-of way and easements.