The Cottage Grove Low Impact Development project, for the City of Houston (COH), has set the standard for urban redevelopment and the viability of incorporating Low Impact Development (LID) practices into future city projects. Jones|Carter (JC) evaluated various LID features related to roadway design in the redevelopment of Houston’s Cottage Grove subdivision as necessitated by polluted waters. We investigated solutions for utility conflict resolution, hydraulic evaluation of the drainage system to meet COH standards, evaluation of variances between LID and COH standards, and long and short term operation and maintenance of the proposed features. As a result of this work, JC helped COH complete its first LID roadway project constructed completely in the right-of-way.
Original or Innovative Application of New/Existing Techniques
As part of the COH’s CIP, and with grant assistance from the Texas Commission on Environmental Quality (TCEQ),
a two-block area of Cottage Grove in Houston, Texas was designated for this pilot project to utilize LID features in a
residential street reconstruction project. LID features are new to the Houston area, particularly in regard to roadway
redevelopment, and this project was the COH’s first LID project located chiefly in a right of way. Cottage Grove is an urban area transitioning from small, single-family residences into dense townhome development, increasing the impervious surface area from
50% to 90%, and overall density from six dwellings per acre to 26. COH selected JC for our innovative approach to address the polluted waters while creating minimal impact to this dense, urban environment. We utilized our knowledge of roadway design, research we gathered from LID competition, LID solutions already in place throughout the US, and our development of LID criteria for Harris County to devise the right solution for our own city’s needs.
The project includes a monitoring component with sampling devices installed at strategic locations to test water quality and gather water quantity measurements. In addition to Jones|Carter, the project team included COH, Whatearth, and Rice University. Rice University continues to collect samples for testing to monitor benefits of the incorporated LID features as part of the project objective.
Current engineering thinking and the process by which redevelopment is approached in Houston’s inner urban core will be impacted by the strategic use of tree boxes, rain gardens, and the sampling features. Each of these LID-focused design elements are part of an overall drainage system being implemented for the first time fully in the city’s right-of-way. Employment of these innovative LID
features will assist in determining if they improve water quality in the bayou while still maintaining basic city, street, and drainage criteria.
Future Value to the Engineering Profession
The project demonstrates that sustainable LID features can be integrated effectively in a dense redevelopment area with limited right-of-way width. Cottage Grove is an urban area experiencing redevelopment which is markedly increasing density in the area and taxing limited resources. In order to address potential flooding issues due to rapid redevelopment, the LID elements highlight a highly
successful application of sustainable techniques. Not only can sustainable/LID components be an integral part of the www.jonescarter.com design intent, weaving together a thoughtful and creative engineering solution, they can also set the future standards by which communities are redeveloped to mitigate the potential for flooding and water pollution at the outset.
Social, Economic, and Sustainable Design Considerations
The primary objective of this project was to show that sustainable LID features can effectively be installed in lieu of traditional design methods. Specifically, this project focused on designing and constructing LID features in an urban roadway to provide water quality benefits and address stormwater concerns without compromising services. The project benefits overall public health through cleaner
stormwater runoff. Additionally, roadway improvements converting the existing roadside ditch system into a more standard, safer roadway section has increased safety and welfare, while augmenting homeowner’s property values. As an added benefit, the project serves to beautify the community, providing aesthetics and standards that a savvy public now demands.
The project included the complexities of incorporating LID features into the limited rights-of-way along with other utilities such as gas, electric, water, and sanitary sewer. The project faced unique challenges related to on going townhome development along the roadway and the resulting coordination to maintain residents’ access, parking issues, conflicts with townhome contractors, and maintaining project site access during construction. Narrowing the pavement width at the Darling/Detering intersection provided the opportunity for additional water quality features. This ingenious solution served a dual purpose as a stormwater collection/water quality feature while providing a “calming” traffic effect, increasing public safety. While these innovations were used in a city that has
had minimal experience with them, it provided a unique opportunity to begin a dialogue with City staff on how to handle maintenance of LID features for this project as well as future projects
Exceeding Client/Owner Needs
This unique project did not fit within the current COH design standards. As a result, the Jones|Carter team, along with the COH staff, developed and defined standards for LID-type projects within the City (that will be maintained by the City). We provided a demonstration project with LID features for evaluation and measurement of water quality benefits to substantiate that LID features can effectively be incorporated into an urban roadway redevelopment project. The project resoundingly met that goal with the COH, the TCEQ, and local residents.
The final cost of the project was higher than a traditional street reconstruction project, but on Darling Street we installed Low Impact Development features that mitigated the increased runoff from the street ultimately improving stormwater quality. For a traditional street reconstruction project, detention and stormwater quality would have to be addressed off-site, or with increased pipe sizes for detention and an underground storm water quality feature. With these factors taken into account, the cost to reconstruct Darling Street with LID features compares favorably to a traditional street reconstruction project. In light of this, the final budget excluded the original estimate for traditional detention and mitigation costs, which would have added significant cost to the bottom line.
The construction schedule was impacted by site conditions and the unique nature of the project. On-going townhome development caused relocation of several features, a redesign of the pavement and tree boxes, and coordination with existing utility companies took more time than anticipated due to the narrow right-of-way. Tree removal and backyard drain pipes also impacted the schedule. The uniqueness of the project caused some delays, however the construction schedule was accomplished in accordance with orginial timeframe.