Walter P Moore is providing engineering services for a Low Impact Development Pilot Project for the City of Houston’s Almeda Road Reconstruction Project from MacGregor to Old Spanish Trail.
Overview
Located in southeast Houston, Texas, Almeda Road is a prime artery providing access to the Texas Medical Center (TMC) and Hermann Park. The TMC is the world’s largest medical complex, serving approximately 160,000 people daily and 7.2 million annually (which is more than the population of Los Angeles, San Francisco, and Houston combined). Hermann Park is a 445-acre public park that hosts approximately 6 million visitors annually. The Almeda project is federally funded with matching funds from the City.
Almeda Road was originally designed to be a major highway corridor with a 160-ft wide right-of-way utilizing a wide median typical of a rural highway section and wide shoulders for drainage and future expansion. Due to its proximity with Brays Bayou, about one-third of the project limits are within the 100-year floodplain. The road is an important part of the area traffic management providing a link from south of the city limits to downtown and the section that is part of this project is an important access to the Texas Medical Center during major tropical storm events.
Walter P Moore suggested a low-impact design (LID) solution for the Almeda corridor to improve traffic flow, pedestrian accessibility, and encourage more bicycle travel in addition to the improved drainage and water quality benefits inherent in LID projects. The project involves converting the existing 4-lane roadway to 6 lanes and narrows the 60-ft median to the City’s standard 16-ft width to improve intersection capacity. A 10-ft wide multi-use trail will connect to the existing trail system at Hermann Park and continuous sidewalks will line the opposite side of the improved roadway for improved pedestrian connectivity. Continuous, tree-lined green zones on either side of Almeda will separate traffic from the multi-use trails and sidewalks and provide the LID features. The project will add approximately 200 new trees while saving many of the existing trees.
Key features of the LID solution designed for Almeda Road are the roadside grass swales that intercept and treat initial flush runoff using rapid-flow-rate filters by means of the FocalPoint System. The filter media consist of layers of mulch, high filtration media, and bridging stone. The filtered runoff is then collected and routed to the existing storm sewer network. The filtration bed is landscaped for both aesthetics and for water treatment. Typical maintenance of the system include mowing of the swale, annual replacement of the mulch layer, and plant maintenance.
Filtration of storm water utilizes physical, chemical and biological mechanisms of a soil, plant and microbe complex to remove pollutants typically found in urban storm water runoff. The swales also provide storm water attenuation to mitigate the increased runoff from the added lanes and compensating storage for floodplain storage impacted by the new roadway. In an event in excess of the capacity of the filter system, the excess runoff overflows to a raised grate set above the filter which carries the runoff to the existing storm sewers without ponding in the travel lanes.
The LID approach was new for both the City of Houston and for the Texas Department of Transportation (TxDOT). Walter P Moore worked with the agencies to address the questions on maintenance costs, providing proper training on the maintenance of LID features and drainage impact while following the City of Houston Infrastructure Design Manual guidelines.
A portion of the project is in the floodplain and therefore the displaced floodplain storage had to be mitigated. The mitigation was achieved by lowering the roadway profile and the design of the roadside swales. The profile adjustments had to be carefully adjusted as the Hermann Park side nor the opposite side right-of-way could accommodate large grade changes due to driveways, fences, and other existing features.
Walter P Moore was able to save approximately $1 million with the use of LID concepts over traditional design by reducing the amount of storm sewer and providing effective onsite mitigation. As a pilot project, the City of Houston Project Manager, Michelle Randon, P.E. and the Assistant Director, John Kuo, P.E., worked closely with Walter P Moore to ensure that the city’s needs were met and that the LID designed elements would not place an unsustainable maintenance burden on the city.
According to Ms. Randon, “We, the City of Houston, prefer to use context-sensitive designs, as we are charged with looking at the bigger picture when installing or improving infrastructure while taking into consideration the needs of the community, various uses of the infrastructure, location, cost-efficient maintenance, and a limited impact to affected citizens, especially given the location of this project being a primary means of travel for the medical center.
We had a unique opportunity that offered the elevation and space needed for a Low Impact Design project, or LID project, providing the ability to improve drainage and infrastructure while minimally impacting the flow of traffic and providing features that add to the aesthetics of the community. As a pilot project, we are implementing training that will use this and other projects as tools to prepare contractors and COH employees to design, bid, build, and maintain any future LID projects.
We are also including the public in this education and training process, providing citizens and business owners along Almeda Road the opportunity to assume some maintenance of the LID features through the adoption process and even the ability to replace the vegetation within the required parameters should they wish to coordinate with their landscaping.
The City is confident that the Almeda Road LID pilot project should prove to be a great success and pave the way for future LID projects when applicable.
The project was bid in mid-June 2015 and is expected to be complete in early 2017.
