City Repairing Storm Sewer Outfalls

One of the most often overlooked points of failure in drainage systems is the lowly storm sewer outfall. When rain flows into the storm sewer on your street, it travels through pipes underground until it reaches the “outfall” at a stream or drainage ditch. If the outfall becomes blocked or damaged, it can back water up and contribute to street flooding.

Often, the damage to the outfall is so remote and difficult to find, that unless someone makes it his or her specific mission, it can go undetected.

Chris Bloch Takes on the Mission

Luckily for Kingwood residents, retired engineer Chris Bloch has made it his mission to identify damaged outfalls and bring them to the attention of the City of Houston. In his quest to help the Kingwood community, Bloch has trudged through mud, muck, brambles and underbrush for years. But his persistence has finally started paying dividends.

Recently the City repaired four outfalls that empty into Bens Branch. The repairs coincided with Harris County Flood Control District’s project to restore conveyance of the channel between Rocky Woods and Kingwood Drive. The result: reduced flood risk to surrounding neighborhoods.

Locations of four outfalls recently repaired by City of Houston in conjunction with HCFCD restoration of Bens Branch

Below: pictures before and after the repairs.

Outfall #1: Cedar Knolls At Woods Estates

Outfall #1 before repairs. Severe erosion exposed then partially severed pipe. The erosion resulted from churning water behind a logjam in the natural section of Bens Branch.
The logjam that created the erosion has since been removed by HCFCD.
Outfall #1 drained approximately 10.7 acres.
The outfall repaired by the City was upstream of HCFCD’s Ben’s Branch restoration project. Of the two other outfalls in this photo, HCFCD repaired the one in the foreground and the City repaired the one in the middle. See Outfall #4 for more info on that one.

Outfall #2: Laurel Garden and Bens Branch

At point #2, drain pipe had cracked and was pushed upward, causing water to back up.
How the same outfall looks today.

A sinkhole also developed along this line. That usually results from part of the pipe collapsing in on itself. Dirt above the hole then erodes into the pipe. The City plans to address the sinkhole now that Flood Control has finished its work.

Outfall #3: Wildwood Ridge Near Deerbrook

According to Bloch, this area originally had 22 feet of corrugated metal pipe and another 50 feet of concrete pipe sections that failed. Erosion undercut the pipe and washed it away.

Outfall #3 before repairs.
Outfall #3 before repairs.

As erosion widened and deepened the area around the destroyed pipe and a manhole, trees fell into the widening “ditch.” The blockages caused the water to churn, creating even more erosion.

Below is the “after” shot. Instead of replacing all the pipe, the City created a wider ditch that will greatly improve street drainage in this watershed.

The area eroded by the damage to outfall #3 has been replaced by a side ditch. It will provide more than enough conveyance to handle water exiting the 36″ pipe.

In the picture above, the rocks surrounding the outfall are called riprap. Riprap is a permanent layer of large, angular stone, cobbles, or boulders typically. Riprap armors, stabilizes, and protects the soil surface against erosion and scour in areas of concentrated flow, such as at outfalls.

The storm sewer outfall #3 services a drainage area of 28.6 acres.

Outfall #4: East Side of Bens Branch at Rocky Woods and Wildwood Ridge

During a storm, the cover on this manhole blew off. Later, young people threw wood into the open manhole and started fires while they drank beer.

Before repairs. The manhole acted as a chimney that made it easy to have a roaring fire.
People also threw beer cans and other debris into the manhole.

Eventually the sewer line became completely blocked according to the City. As a result, storm water backed further up the line. Increased pressure lifted covers off of all upstream manholes. In addition, the pressure forced storm water out between the concrete pipe joints and created a number of sinkholes.

Due to all of this damage approximately 580 feet of 24-inch sewer line and three manholes had to be replaced by the City. This is probably one of the most expensive cases of vandalism Kingwood has experienced.

Chris Bloch

With the line completely blocked, it was of no use and storm water runoff from this area would flow further down Wildwood Ridge where several homes suffered flood damage.

The old outfall.
Outfall #4 after repairs. Note also replacement of the manhole. Not shown: the 580 feet of other repairs including more manholes.
The drainage area serviced by this sewer is only 5.6 acres, the 24-inch line was more than adequate for this acreage.

Kudos to the City and Bloch

These are just four of several repairs underway. More news to follow.

Thanks to the City of Houston, Mayor Pro Tem and District E Council Member Dave Martin, and his staff for coordinating these repairs with the Public Works Department. Residents will sleep much better in the next big storm.

Thanks also to Chris Bloch for his tireless efforts in reporting these issues. If you find similar problems near your home or business, please report them through the contact page on this web site. I’ll make sure they get to Chris who will make sure they get to the people who can help.

Posted by Bob Rehak on 4/18/2021 based on information and photos collected by Chris Bloch

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