Upgrades to homeowner association ponds help withstand flooding & erosion
The ponds and lakes around the greater Houston, Texas, area add a beautiful dimension to the communities and to the city as a whole. While these community lakes are aesthetically pleasing, their purpose is to capture the storm water runoff during rain events in order to mitigate flooding and improve water quality downstream. These storm water basins are an important part of the flood control system, as evidenced in the extensive flooding in many Houston-area neighborhoods in recent storms and Hurricane Harvey.
Storm Water Ponds
Because cities and neighborhoods have so many impervious spaces, such as roads, rooves, driveways and sidewalks, rain events cause runoff to move at an increased rate, and large storm events increase the volume and velocity of this runoff, which contributes to flooding and erosion downstream. The design of the storm water pond is to capture this water and release it slowly over an extended time to decrease flooding. It also allows sediment and contaminants that were picked up along the way to settle before the water is released downstream.
In addition to flooding, this increased water volume and velocity during rain events causes erosion around the shoreline of many storm water ponds. The result of this erosion is not only large amounts of sediment deposited downstream, but also decreased water holding capacity of these ponds. This means the pond will hold less water during and after rain events, which further increases the risks of flooding.
A critical component of keeping any storm water system effective and working properly is to maintain it properly. Understanding this, some communities just south of Houston have taken a proactive approach to maintaining their storm water ponds and recently completed projects to remedy their erosion issues.
Storm Water Solutions, based in Houston, is a professional engineering firm that specializes in preparing and managing storm water prevention plans for municipal utility districts (MUD). The firm helps ensure that developers and MUDs are in compliance at all times with regulatory agencies.
After the devastating effects of Hurricane Harvey, many MUDs and communities in the greater Houston metropolitan area began to take a closer look at their storm water systems to see how they could be more effective in moving water away from homes and roadways. Taking a proactive approach, Brazoria County MUD No. 28 enlisted the help of Storm Water Solutions to do bathymetric profiles and sediment surveys of their existing waterways.
Brazoria County MUD No. 28 oversees the waterways of the two homeowner association (HOA) communities in these studies. Both HOA communities are located in Pearland, Texas. With recent flooding in the area, the HOAs experienced the same ill effects of embankment erosion. The engaged studies help to determine how much accumulated sediment from erosion and upland runoff has been deposited in their ponds, lakes and channels. Not only was accumulated sediment reducing the water holding capacity of these features, but continuing and progressive erosion also was occurring around the shorelines of the storm water ponds.
“There were visual signs of the havoc reaped by fluctuating water levels and velocity of incoming water during rain events,” said Kaz Jones, professional engineer for Storm Water Solutions. “The erosion along the embankments had caused undercutting along the shoreline, clumps of grass and dirt were falling into the water, and gullies were beginning to form in some places. At one of the ponds, the embankment around their cypress trees had eroded over time and exposed the roots, so they were at risk of losing their trees. Of course, all of this material from the erosion ends up in the pond. You don’t see it, but it’s there, and it takes up the space we need to hold water.”
To rehabilitate the shorelines of these storm water basins and to prevent future erosion, a bioengineered polyethylene fabric was used to create a living shoreline. The fabric is anchored below the surface to firm ground above the embankment, then backfilled with locally sourced materials, such as sand and mulch.
“I take pride in installing a product that looks like mother nature put it there and knowing that it is safe for the environment and for the homeowners who enjoy this pond,” said Steve Perry, project manager for Envirodredge. “Because the system is anchored below the surface, there are no trip hazards, no cement blocks to shift under foot or fall on, and nothing to run over with a lawn mower. It’s just plush grass all the way to the water.”
The fabric also can be vegetated with native plants other than grass, and because the material is knitted, it will not unravel if it accidentally is punctured or cut by animals or machinery. The installation was completed April 23. According to Perry, the installation withstood 4 ft of water after heavy rain.
The purpose of storm water ponds is not only to detain water during storm events, but also to prevent pollutants from carrying downstream and ending up in lakes and rivers.
“Being able to immediately revegetate the embankments means we have an immediate buffer zone that filters the runoff of fertilizers and other contaminants that enter our waterways," Jones said. "It’s a win-win for every community.”