outfalls Archives - Reduce Flooding

Concerns Over Proposed Cypress Creek Flood Tunnel Outfall Location

The Kings Forest Community Association (KFCA) board has expressed concerns about the outfall location for the proposed Cypress Creek flood tunnel. Phase 2 of the tunnel study showed two potential outfalls in the Humble/Kingwood Area: one immediately upstream from the I-69 bridge, the other farther downstream near River Grove Park.

KFCA does not oppose the tunnel. But it does want assurances from the Harris County Flood Control District (HCFCD) that it will have NO adverse impact on:

The community’s flood risk
Potential damage to homes and businesses
Oilfield infrastructure
Water quality in Lake Houston
Bridges

Further, KFCA requested that “no adverse impact” be demonstrated with the latest flood data compiled after Harvey and that the data be based on mitigation improvements already in place, not planned efforts that could fall through for funding or political reasons.

KFCA concerns have to do with flood peaks shifted by both a tunnel and upstream development that could cause altered peaks to coincide and heighten flooding even more.

Feet Above Flood Stage Highest at US59 And West Fork

HCFCD has a long-standing policy of not supporting flood-mitigation projects for one area that would make flooding worse in another. But the KFCA board fears that the location of the outfall could make flooding worse in the Humble/Kingwood Area.

Said the board, “The tunnel would add stormwater to Lake Houston at a location that experienced the highest flooding in northern Harris County and had some of the heaviest damage as a result.”

worst first — *Chart showing feet above flood stage at 33 gages for misc. locations in Harris County during Harvey.*

Potential Damage to Homes/Businesses

The heat map below shows cumulative flood damage since 1978. The Humble, Kingwood, Huffman area appears to have sustained even more damaged than Cypress Creek to the west.

*Historical flood loss map of Harris County since 1978. Source: MAAPnext.*

Proximity to Humble Salt Dome/Oilfield Infrastructure

Additionally, the outfall location(s) contain hundreds of active and abandoned oil-and-gas wells around and over the Humble salt dome. The map below, from the Railroad Commission of Texas, shows their locations and density. The proposed Cypress Creek Tunnel would have to snake its way through these if it goes beyond US59.

*Active (green) and abandoned (white) wells over and around the Humble Salt Dome. Source: Railroad Commission of Texas.*

The 240,000 Cubic Feet Per Second shooting through this area during Harvey destroyed wells, tanks and pipes, exposing the public to pollution. The photos below illustrate damage to the Noxxe lease in Forest Cove near the West Fork.

Water Quality

The photo below shows pollution in Lake Houston from flood-damaged oil field assets.

*Oil on water by abandoned Noxxe lease in Forest Cove*

It took the Railroad Commission 4.5 years to clean up this mess after the operator declared bankruptcy. Yet the proposed Cypress Creek tunnel would outfall into the headwaters of Lake Houston, the source of drinking water for two million people.

Bridges

The Union Pacific Railroad Bridge had to be replaced after Harvey, affecting rail traffic for years. Reconstruction took until April 2020.

The I-69 Southbound Bridge was out of commission for 11 months due to scouring of the bridge supports. This caused detours and massive delays for tens of thousands. Repairs cost TxDoT $20 million.

I-69 repairs — *TxDoT repairs to the I-69 bridge cost $20 million.*

The West Lake Houston Parkway bridge also required extensive repairs after Harvey.

The Request: Demonstrate No Adverse Impact Using Latest Data Before Proceeding

The Kings Forest letter said, “While we are sensitive to the flooding issues along Cypress Creek, we believe that letting a Cypress Creek flood tunnel outfall at this location is not wise. It could lead to further damage and potential environmental/health dangers.”

The letter ended with a plea for HCFCD to demonstrate “no adverse impact” before proceeding with Phase 3 of the tunnel study and again at some future point if the Phase 3 study recommends construction of the flood tunnel.

“We also request that your “no adverse impact” evaluation reflect actual, current conditions,” said the directors. “Please DON’T base the evaluation on planned mitigation measures, which might not happen for political reasons.”

“Also, please DON’T base the evaluation on outdated conveyance data for the San Jacinto West Fork,” they continued. “Montgomery County is the second-fastest growing county in the region. It allows new subdivisions to use hydrologic timing surveys to avoid building floodwater detention basins. In 2019, Harris County Engineering and Flood Control proposed eliminating that practice, but MoCo Commissioners voted no. As a result, the Humble/Kingwood area faces constantly increasing flood risk from thousands of upstream acres being developed without sufficient mitigation.”

Those new developments shift flood peaks in a way that could potentially coincide with an altered peak from Cypress Creek.

See the full letter here.

To review HCFCD’s flood tunnel studies and leave a public comment, click here.

Posted by Bob Rehak on 9/23/22

1851 Days since Hurricane Harvey

In the interest of transparency, I should disclose that I am a member of the KFCA board.

Sinkholes Often Sign of Damaged Storm Drains

Most of us have seen sinkholes. And most of us have probably given little thought to what causes them.

Retired engineer Chris Bloch, a local flood fighter, measured a 13-foot deep sinkhole near Taylor Gulley earlier this year that had become overgrown with vegetation. Working with the City of Houston and a local homeowner who first reported the problem, they found the sinkhole related to a nearby storm drain.

*Bloch lowered this length of PVC pipe into the Taylor Gully sinkhole to measure the depth.* *Note how the hole had become overgrown with vegetation.*

Other things can cause sinkholes, but in this area and in this part of the world, “storm drain gone bad” ranks high on the list of things to investigate.

Corrugated Pipe Commonly Used At Outfalls When Kingwood Built

According to Bloch, when Friendswood built Kingwood, they commonly used corrugated metal pipe (CMP) at storm sewer outfalls. CMP has an expected service life of approximately 35 years, says Bloch. And corrosion commonly causes failure at older outfalls constructed with such pipe.

For example, see the section of pipe below. This photo was taken on Ben’s Branch, not Taylor Gully, but it shows how the pipe rusted, bent, and crimped. Also look just to the right of the wooden posts, and you can even see a large hole in the pipe. It even tilts upward before it reaches the creek.

Corrugated metal pipe replaced earlier this year as part of a project to restore the conveyance of Bens Branch between Rocky Woods and Kingwood Drive. This area also developed a sinkhole near the manhole.

Taylor Gully Sinkhole One of Many In Area

Bloch frequently walks ditches looking for sinkholes to report to the City. He says he’s aware of at least five right now.

The 72-inch outfall to Taylor Gully serviced drainage area G03408-00-OUT which encompasses all of Greenriver Valley Drive and Mountain Bluff Lane as well as portions of Appalachian Trail, Natural Bridge and Echo Falls Drives. That area comprises 33.4 acres. See below.

*Service area for damaged outfall encompasses 33.4 acres where several homes flooded.*

The transition from a 72-inch concrete storm sewer to the 72-inch CMP outfall is at a manhole on the edge of the Taylor Gully right of way. See below.

Over the years, the CMP at the connection to the manhole failed. The earth above the failed pipe washed into the outfall and then downstream where it helped reduce the conveyance of Taylor Gully.

Repairs Started But Not Complete

The City of Houston has already repaired several storm sewers with failed corrugated metal outfalls. At least five additional storm sewer outfalls with sinkholes have been identified that have not yet been repaired.

Vegetation frequently hides the presence of these sinkholes. In addition to posing a danger to citizens walking along the banks of the drainage channels, the soil that falls into the sewer can be held up by the corrugations of the metal pipe reducing the flow capacity of the sewer, says Bloch.

Even without obstruction from soil falling into a sewer outfall, the rough surface of the corrugated metal pipe generates greater friction than smooth concrete. The friction slows the flow of storm water and reduces flow capacity which becomes critical during high intensity rains that cause street flooding.

Bloch somehow convinced the City of Houston Public Works Department to replace the damaged CMP at Taylor Gully with concrete pipe. See below.

“This upgrade in the outfall piping will significantly improve the flow capacity of the storm sewer system,” says Bloch.

*Concrete pipe replaced CMP at the location of the 13-foot sinkhole on Taylor Gully. Installed by City of Houston Public Works Department* *after HCFCD repaired Gully.*

Concrete Better for New Atlas-14 Rainfall Intensities

When Friendswood Development installed stormwater sewers in Kingwood, they met standards which applied at that time. With new Atlas-14 rainfall projections, we now understand that we should expect more rainfall. Several homes along Appalachian Trial suffered flood damage during Tropical Storm Imelda.

How to Report Sinkholes When You Find Them

As they say, it takes a village to reduce flooding. Now that you know the story behind sinkholes…

If you jog or walk along drainage ditches, exercise caution. Look out for developing sinkholes. And report them to 3-1-1 when you find them. They can pose dangers to children and even grown adults. To put that in perspective, Bloch (shown in the first photo) is more than 6 feet tall, but the sinkhole dwarfs him.

For More Information about Sinkholes

I highly recommend:

The US Geological Survey has an in-depth discussion of different types of sinkholes in different parts of the country and how each forms. This is geared toward students in science classes.

This NBC News story on YouTube has some spectacular examples of sinkholes in Florida along with easy to understand animations that show how they form.

Another 7 minute YouTube video from a series called Practical Engineering focuses on how sinkholes form. It contains both real world examples and table-top experiments that bring the processes to life.

Posted by Bob Rehak based on information and photos provided by Chris Bloch

1492 Days since Hurricane Harvey

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.*

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.

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.

*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

1328 Days since Hurricane Harvey

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