Let’s talk about stormwater management. Planning for stormwater during development in Houston has always been important, but recent storms have shone a spotlight on the issue, calling for increased attention and imperative to plan for high waters. As Civil Engineers, this has become a central consideration in almost all of our projects.
One of our stormwater experts at ALJ Lindsey answers a few questions about what is happening in the industry post-Harvey, including emerging trends in stormwater management and what we should expect to see in the future.
Houston Sees Stricter Detention Regulations
In the wake of several large, consecutive 500-year storms, local Houston regulators have been rewriting and restructuring their design manuals, enforcing higher detention criteria for new developments and redevelopments across the Houston area. Many jurisdictions are becoming stricter on their detention regulations. From a developer’s standpoint, new regulations are adding an increased investment on top of already ever-increasing construction costs.
The Limitations of Traditional Detention Solutions
Traditionally, the cheapest option for controlling run-off water has been to dig an earthen detention pond on-site. Unfortunately, as Houston and surrounding areas become increasingly developed, the cost of land is soaring. To add to that, detention volume requirements per site are increasing. These factors are forcing developers to create underground detention solutions in order to maximize their developments. Currently, the industry standard cost of traditional underground detention varies anywhere from $10-$15/cf depending on detention volume and project size. This can end up being a very costly item in a developer’s proforma.
Tremendous Benefits to Underground Detention Reduction
A combination of factors has historically made stormwater planning challenging for Houston, these include, clay soils, which allow for little infiltration, Gulf Coast storms that often bring intense and extended rains, high annual average rainfall, and an overall flat terrain. However, consistency and frequency of flooding in the past few years has brought this issue to the forefront and initiated rapidly evolving stormwater regulations.
In turn, stormwater management experts have been encouraged to think outside the box and create innovative ways to combat detention issues and maximize storage across the entire development. One solution ALJ Lindsey is increasingly utilizing is Low Impact Development (LID). LID uses practices such as: bioretention, bioswales, vegetated structural roadway shoulders, permeable pavers and rainwater harvesting and reuse. The goal of LID is to reduce the impact of development and promote the natural movement of water within an ecosystem. By mimicking predevelopment flow and slowing down developed sites’ run-off rates, LID practices generally lead to decreased detention requirements (sometimes upward of 40%). Additionally, LID is often multifunctional, as it not only decreases detention requirements–reducing infrastructure costs, it also works to reduce flood risk and improve stormwater quality. Moreover, it treats double the standard treatment volume of traditional stormwater quality devices! Using Low Impact Development techniques provide tremendous benefits to developers and (ecological preservation) alike.
What does LID look like? A Recent Example.
The Problem: ALJ Lindsey was recently challenged with a complicated stormwater management project. The developer wanted to construct a Member’s Choice Credit Union on a small site which required the inclusion of a significant amount of parking places. Additionally, the location had shallow outfall, so there was limited depth for water storage volumes and the developer didn’t want to add the additional cost of pumping the system.
The Solution: This project, permitted by Harris County, allowed a reduced detention rate of 0.35 acre-feet per acre when using Low Impact Development features vs. the traditional rate of 0.65 acre-feet per acre. Taking advantage of this reduced detention rate, ALJ Lindsey incorporated a combination of LID and traditional practices of stormwater management to create a superior solution to a complex problem. The initial LID approach for this project was to implement a unique biofilter feature for a stormwater quality, concrete permeable pavers and swales. An underground detention system was then created to capture the remaining detention volume required for this site.
By using the permeable pavers, ALJ Lindsey was able to eliminate 90% of the storm sewer pipes and inlets since the pavers would act as a storm sewer. Furthermore, by using Low Impact Development ALJ Lindsey received a reduction in detention volume by 30%, which in this scenario, equated to approximately 7,000cf of detention. At a current average price of $10-$15/cf for underground detention, LID practices saved the client $70,000 just on detention. Through the use of LID, ALJ Lindsey was able to save the client on both detention, storm sewer prices, and prevented loss of land to a detention pond.
See more pictures of the Member’s Choice Credit Union here.
Are LID Practices Easy to Implement?
Low Impact Development is relatively easy to implement in jurisdictions that allow it. Harris County, for example, actively encourages developers to implement LID practices and have created separate review processes for LID sites that allow for a more streamline submittal process.
While Civil Engineering firms don’t necessarily need specialized programs or teams to implement LID techniques, the engineer must be comfortable with hydraulic calculations, and of course being familiar with stormwater management is certainly helpful.
Will LID Always Save The Developer Money?
Cost reduction from LID practices typically depends on the site and jurisdiction. For example, currently, the City of Houston doesn’t offer many incentives to encourage LID. In cases where there are limited LID incentives, it makes more sense to do underground detention or a traditional detention pond.
While LID and detention ponds can often compete on price, they are both consistently cheaper than underground detention. In Harris County, the amount of land a developer will agree to forgo in lieu of the necessary detention pond is a considerable factor in the stormwater planning process. While Low Impact Development may not always save money compared to detention ponds (though often does), LID will significantly lower developer land footprint and can increase revenue through building or parking additions, ultimately providing a superior solution.
LID Will Become Increasingly Important.
Houston is the fourth largest city in the U.S., growing by almost 11% between 2010-2019. Furthermore, Houston is expected to see another population surge of about 1.2 million between 2020 and 2029! With Houston’s population and economy booming, development and the price of land will continue to soar. Detention ponds may become less feasible, and the increased price of real estate will put more burden on developers, forcing them to become more creative with their land and finances. These factors, in combination with increasingly stringent detention regulations and criteria for new developments, will continue to push stormwater planning to innovate, moving from traditional to more inventive solution-based approaches to stormwater management.