By Mike McGough, P.E., NCSPA and Ed Reichert, P.E., CONTECH
Underground detention system provides safer, more cost-effective method to manage stormwater for high school.
New Braunfels Canyon High School Expands
The Comal Independent School District needed to make several major renovations and additions to the existing New Braunfels Canyon High School campus due to the population growth in the New Braunfels area. The existing campus sits along the IH-35 northbound frontage road, where the value of the land surrounding the campus continues to increase, even in a depressed economy.
One of the main challenges that the design engineer, Gil Civil Engineering, had to consider was the best utilization of this land, while providing the necessary parking required for the campus and surrounding sports facilities.
Limited Land Tests Stormwater Management
Most commonly, design engineers utilize large detention ponds located somewhere on the campus in which the stormwater runoff can be stored and then discharged at the predevelopment rates. This solution can be cost effective when the value of the land is low and the design engineer has a large site to work with. However, this was not the case with the N.B. Canyon High School site. With the increasing value of the land along the IH-35 NB frontage road, Gil Civil Engineering turned to CONTECH Construction Products Inc. to offer the most feasible solution to address the stormwater detention requirements.
In addition to the high cost of the surrounding land, the project posed a number of other challenges:
- The site was extremely flat without much fall for a conventional storm drain system to discharge the stormwater into the Texas Department of Transportation’s existing box culverts.
- A standard detention pond would have needed to be rather large, running along the length of the school building, and would have significantly limited access to the building.
- A detention pond close to the school would have posed a potential safety hazard to the students, as well as a health hazard as a potential breeding ground for mosquitoes.
- A detention pond close to the school would have been very unsightly.
Designers Look Underground for Solution
Gil Civil Engineering worked with CONTECH’s stormwater specialists to provide an underground detention system (UGDS) design, consisting of roughly 9,000 LF of 42″ diameter Aluminized Type 2 corrugated steel pipe (CSP). Not only did the detention system meet all of the site challenges, it also provided the following benefits:
- Created additional “usable space” by designing a parking lot on top of the UGDS.
- Eliminated the safety and health hazard of a detention pond so close to the school.
- Improved campus beautification with the elimination of the detention pond.
- Provided long-term cost benefits by eliminating the need for ongoing maintenance of mowing, re-grading and possibly the removal of the silt and sand material that a detention pond would have required.
An underground detention system proved to be the most cost-effective and beneficial system for New Braunfels Canyon High School, and the school can expect an estimated 75-year service life with the Aluminized Type 2 CSP product chosen for the UGDS.
While UGDS systems typically cost more to install than traditional detention ponds, the long-term cost benefits make them a great alternative. By allowing designers to build more usable/leasable space on the site using underground storage, the initial investment quickly pays for itself.