Tag Archive for: Woodridge Forest

HCFCD Recommends Expanding Diversion Ditch as First Priority in Kingwood

At the Harris County Flood Control District’s (HCFCD) Kingwood Area Drainage Analysis meeting tonight, HCFCD recommended that expansion of the Kingwood Diversion Ditch should be the community’s highest priority.

The Diversion Ditch project would help address several potential problems. Expanding it would remove 62 structures from inundation areas and another 586 structures would benefit from improved local drainage. In addition, the project:

  • Can divert floodwater from Ben’s Branch, which will be a much more complicated project, taking more time.
  • Has a 300-foot right-of-way, of which only half is being used
  • Has bridges that already span the entire 300 feet.
  • Will help carry floodwaters from rapidly growing south Montgomery County.

History of Diversion Ditch

In the early days of Kingwood, Friendswood Development Company built the Diversion Ditch to reduce water flowing into Ben’s Branch. But since then, upstream development and larger rains have stressed the capacity of both Ben’s Branch AND the Diversion Ditch. Engineers estimate that peak flows have doubled since 1985.

Most of Ben’s Branch is Natural Channel

Ben’s Branch cuts diagonally through the heart of Kingwood. See red lines below. More than half its length – between Woodland Hills and Rocky Woods Drive is natural channel. Widening it will be complicated and take much time.

Red Line indicates approximate path of Ben’s Branch through Kingwood.

Ben’s Branch Now at 2-Year Level of Service

However, areas on both sides of Ben’s Branch are threatened by flooding as you can see in the image below from FEMA’s Flood Hazard Viewer.

Ben’s Branch once had a 100-year level of service, meaning it had enough carrying capacity to prevent homes from flooding in everything but a 100-year rain. Models based on new Atlas-14 rainfall probability frequencies indicate that the channel’s capacity is now down to a 2-year level of service. That means it will flood in minor rains, exactly as St. Martha School did last year.

Worse yet, Ben’s Branch has decreased to a 2-year level of service throughout its length.

HCFCD Kingwood Area Drainage Analysis
Source: Fema’s Flood Hazard Layer Viewer. Cross-hatched equals floodway, aqua = 100 year floodplain, brown = 500-year floodplain. Floodplains shown above are based on pre-Atlas-14 rainfall probability statistics. An Atlas-14 hundred-year rain is about 30-40% higher than the old hundred-year rain.

When flood maps are updated based on Atlas-14 statistics, those floodplains will likely expand…unless we do something to handle more floodwater before then.

However, Ben’s Branch will not move to preliminary engineering right away.

How to Protect Against Bigger Rains and More Upstream Development

The Kingwood Area Drainage Analysis sought to understand what we need to do to restore a 100-year level of service to all ditches and streams based on Atlas 14. Of the 19 ditches and streams studied, nine need improvement. The level of service for some, including Ben’s Branch, has been reduced to 2 years.

Expanding the Diversion Ditch is the fastest way to take pressure off of Ben’s Branch.

The Diversion Ditch intersects Ben’s Branch at the new St. Martha Church. It then flows south to Deer Ridge Park and then winds through River Grove Park. See the white line below.

Kingwood Diversion ditch (white line) intersects Ben’s Branch near the new St. Martha Church.

Expansion Capacity Already Built into Diversion Ditch

Engineers foresaw the day when Kingwood would need more drainage capacity due to upstream development in Montgomery County. They built the Kingwood Diversion Ditch to handle the extra stormwater. They also made the bridges over the diversion ditch wider than they needed at the time. Finally, they dedicated a flood easement on both sides of the ditch that was wider than they needed, so they could expand the ditch later without encroaching on neighboring properties. Here’s how it looks from the air.

Looking north across Northpark Drive toward Bens Branch, which cuts diagonally from left to right through the middle of the frame. Note the ample clearance under the bridge and the wide shoulders of the ditch. St. Martha Church is in the upper left.
Looking south toward Kingwood Drive at the Diversion Ditch. King’s Mill is on right in foreground.

Both Kings Mill and Kings Manor now drain into the Diversion Ditch. But they came long AFTER Diversion Ditch construction. Other new upstream developments that drain into the Diversion Ditch and Ben’s Branch include Brooklyn Trails and Woodridge Forest, both in Montgomery County.

As a result, the Diversion Ditch itself has decreased to a 2- to a 25-year level of service in places. However, it still offers a 100-year level of service in others.

Looking NE toward Deer Ridge Park from over Hamblen Road. A corner of Deer Ridge Estates is on the left. The diversion ditch cuts in front of the park (upper left to lower right) and goes into an area largely undeveloped on its way to the river (out of frame to the right).

Impact on River Grove Park

Once the Diversion Ditch passes through the area shown in the photo above, it enters wetlands and winds through River Grove Park. Two questions arise. How do we protect, from additional flow:

  • The park?
  • People downstream on the West Fork?

The first question is simple: split the flow in two. Take part through the undeveloped area west of the park. See the green below.

Green Line represents one possible route for diversion of the diversion ditch.

The second question is more complicated. We need a retention basin to hold the extra stormwater until the peak of any flood passes on the West Fork. But where? The closer you get to the river, the lower the elevation. Because of that, the basin could fill with floodwater from the river before it fills with floodwater from upstream. Fortunately, some large tracts of land exist on higher ground that could be purchased. HCFCD estimates the need at 1248 acre-feet. Preliminary engineering should start soon to address these issues.

Upstream Development Not Addressed by Analysis

Unfortunately the Kingwood Area Drainage Analysis did not address upstream development issues in Montgomery County. That was beyond the scope of work. Regardless, such issues must be addressed somehow, someday soon. Otherwise, even the improvements we invest in today could soon be overwhelmed by additional floodwaters.

In that sense, these channel improvements represent a stopgap measure. The real solution lies in making everyone in the region realize that we are all in this together.

Additional Resources

If you missed the presentation, you can view it on YouTube.

Here is a PDF that contains the District’s summary of the Kingwood Study. It includes a spreadsheet comparing the improvements plus data sheets on the nine recommended projects.

The ten remaining channels/streams already offer a 100-year level of service. Therefore, no improvements are needed. HCFCD felt Taylor Gully should be the next priority after the Diversion Ditch. But the possible purchase of Woodridge Village may require re-thinking project requirements. Specifically, if Woodridge turns into a giant detention basin, the channel may not need as much deepening or widening.

Posted by Bob Rehak on 10/20/2020

1148 Days since Hurricane Harvey

Part II: When Is A Detention Pond Not A Detention Pond?

Q: When is a detention pond not a detention pond?
A: When it’s just a wide spot on a stream.

The defining characteristic of a detention pond is an “outfall” smaller than the inlet. The pond holds back rain in a storm and releases it later at an acceptable rate. This reduces downstream flooding.

From the Montgomery County Drainage Criterial Manual

That’s the theory, at least. In practice, sometimes things don’t always work out that way. It often depends on maintenance.

Unrestricted Outfalls

On 2/13/2020, I reported on one Woodridge Forest detention pond on Ben’s Branch that had an outfall LARGER than its inlet. Harvey and Imelda blew out the pond’s outfall.

This week, I discovered that a second pond immediately upstream also apparently has an unrestricted outfall.

Two tributaries of Ben’s Branch come together in the foreground pond. The pond also collects runoff from surrounding commercial and residential areas. Photo taken 2/13/2020.
Water flows toward exit in upper right. Photo taken 2/13/2020.
Note height and width of exit. Photo taken 2/13/2020.

The low area in the picture above measures more than 200 feet wide in Google Earth. That’s far wider than the combined inlets. Net: this pond provides little if any detention capability.


Same Problem with Second Pond

Neither does pond beyond it that I highlighted last week provide much detention capacity.

Note how Ben’s Branch flows both through and around the next pond. Direction of flow is from bottom to top of frame. Photo taken 2/13/2020.
Reverse angle looking NW. Direction of flow is now toward camera. Note how the outfall (foreground) is larger than the inlet. Also note how runoff from residential streets (upper right) is channeled outside the pond. Photo taken 2/13/2020.

Both Ponds Provide Little Detention Benefit, If Any

Both of these ponds provide little detention benefit, if any.

Neither pond has a maintenance road around it, even though Section 7.2.8 of the Montgomery County Drainage Criteria Manual specifies that “A 30-foot wide access and maintenance easement shall be provided around the entire detention pond.”

Sometimes, what looks like a detention pond is really just a pond. Or a wide spot in a stream.

Recent Surge in Downstream Flooding

During the May 7th and Imelda floods in 2019, water flowing through these ponds then flowed over Northpark Drive and flooded homes in North Woodland Hills. It also flooded numerous homes and businesses downstream on Ben’s Branch between Woodland Hills Drive and the San Jacinto River West Fork.

One wonders whether those damages could have been averted if the ponds had detained water.

As Harris County Flood Control conducts the Kingwood Area Drainage Study, engineers must consider the possibility that this area may be dumping more water downstream than planned.

The Woodridge Municipal Utility District apparently is responsible for these ponds.

Posted by Bob Rehak on 2/16/2020

901 Days after Hurricane Harvey and 150 after Imelda

The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.

Imelda Floods Ben’s Branch Schools, Homes at Three Choke Points

Disclaimer: I spent the better part of a day driving down every street that borders Ben’s Branch. I saw damage clustered in three areas. It’s possible other areas were affected but the City had removed trash before I got there.

At least two schools, 7 homes, and one business flooded along Ben’s Branch in Kingwood during Imelda. All were located near choke points along the creek. And massive recent upstream development likely played a role in each case. That new development also played a role in eroding the margin of safety between floodwaters and foundations all along the creek – even for homes and businesses that did not flood. Total damages will likely exceed $3 million along Ben’s Branch in Kingwood.

Three circles represent choke points where virtually all structural flooding happened on Ben’s Branch during Imelda. See discussion below.

Ben’s Branch Now and 10 Years Ago: Influence of Upstream Development

Area in white box is roughly 800 acres. Three quarters of it was not developed ten years ago (see below). Red line marks the course of Ben’s Branch through a series of retention ponds and new ditches that now contribute more water faster during heavy rains.
Same area in 2009, only ten years ago.. Neither Woodridge Forest, Woodridge Village, nor the Kroger Center at 59 had started development yet, though some areas had been cleared.

Imelda Tested Design Limits of Drainage Systems

Most drainage systems are designed to protect homes and businesses from a hundred-year flood. Imelda was a hundred year flood. The storm tested the design limits of flood infrastructure everywhere along Ben’s Branch in Kingwood.

Based on its peak intensity of 4.56 inches in one hour (as measured at the US59/West Fork gage), Imelda qualified as a 100-year storm. Streets, storm drains and ditches are designed to handle that much as an upper limit. And for the most part they did. Especially because builders usually elevate most structures at least two feet above the hundred-year flood plain.

Those extra two feet act as a margin of safety and as a hedge against future upstream development.

Limits Exceeded in Several Places During Imelda

In each case where homes, businesses or schools flooded along Ben’s Branch, unique circumstances eliminated that margin of error and resulted in flooded structures.

With the exception of one low-lying home I found in Hunter’s Ridge very close to the creek, all of the structural damage took place at three choke points along the creek.

Choke Point #1: Northpark and Ben’s Branch

Where Ben’s Branch crosses under Northpark Drive, two things happen. A ditch from the new Woodridge Forest subdivision joins it. And then all that water is forced into a culvert that crosses under Northpark Drive.

These two culverts constrained water flowing under Northpark Drive and backed it up past Hidden Pines at the stoplight in the background. When water started flowing over the road for approximately two blocks, this part of Kingwood was cut off.

To my knowledge, no one has ever upgraded that culvert despite significant upstream development. It backs water up for several blocks during heavy rains and forces water OVER Northpark Drive. This caused at least six homes near Aspen Glade west of Hidden Pines to flood.

When water backed up and flowed over Northpark, it cut off both inbound and outbound traffic. It also broke through the fences of homes that back up to Northpark.

East-West fences were pushed in from the north by water overflowing across Northpark Drive. This location is a block west of the culverts.
Looking north toward Northpark Drive at Hidden Pines. North-South Fences were pushed out to the East by water trying to return to Ben’s Branch across Hidden Pines to the right. Note the new fence. It had just been replaced after the May 7th flood.
The scene on Aspen Glade Drive in North Woodland Hills. These homes are west of Hidden Pines and back up to Northpark Drive.
A resident of Aspen Glade shows how high the water got in front of his house during Imelda.
A worried Lela Yorba wonders how her family will ever recover from the second flood in four months, and whether she should even try. Despite living on Aspen Glade for decades, her home had never flooded before May of this year.
The interior of Yorba’s flooded home during Imelda. Image courtesy of Lela Yorba.
Yorba’s garage during the peak of Imelda. Image courtesy of Lela Yorba.
Floodwaters crept up to the foundations on the far side of the street but did not enter homes according to Yorba. Image courtesy of Lela Yorba.
One week after Imelda, Yorba tries to turn wet walls back into dry walls.

Impact of New Development

Net: the flooding of homes on Aspen Glade was likely caused by an undersized culvert at North Park that could not convey all the water coming from hundreds of acres of new development. When the water backed up, it rushed over North Park for approximately two blocks. Eyewitness reports and FaceBook videos peg the height at a foot above the roadway.

In the last 10 years, more than 600 acres have been developed north of North Park between 59 and Woodland Hills. More new homes are being built every day.

Much of the drainage from the new development joined Ben’s Branch just before it reached the culverts.

This drainage ditch from many of those new homes in Woodridge Forest joins Ben’s Branch east of Hidden Pines in the background where multiple homes flooded. This is additional drainage coming into the creek at a point where part of it can not be siphoned off into the diversion ditch that runs down the west side of the villages of North and South Woodland Hills.

Choke Point #2: Woodland Hills Drive and Ben’s Branch

About two or three blocks east of the culverts under Northpark, between St. Martha Catholic School and Kids in Action, Ben’s Branch narrows down again. It quickly funnels from a wide, excavated ditch to a narrow stream cutting through dense forest. See photo below.

Hovering over Woodland Hills Drive in a helicopter looking east. Ben’s Branch narrows between Kids in Action on the left and St. Martha’s school (out of frame on the right). Both flooded. Note how the fence was pushed in by the force of the water.

At this choke point, both the school and Kids in Action, flooded. Repairing the school after the May flood cost St. Martha $900,000. Repairing Kids in Action cost $500,000. This time it will cost each even more.

Behind St. Martha’s, Ben’s Branch becomes a narrow creek filled with trees. This further slows water down and backs it up. It remains like this most of the way to Kingwood Drive. Image courtesy of Father TJ Dolce.
The natural creek also makes many tight turns. Here, it makes a 150 degree turn followed by a 90 degree turn. Image courtesy of Father TJ Dolce.

The results were costly. St. Martha’s lost two classroom buildings plus its playground.

One of the two St. Martha School buildings flooded by Imelda.
Flooded corridor.
Flooded classroom.

Until the school buildings can be dried, disinfected and rebuilt, classes are being held on upper floors and in other parish buildings. No children were ever endangered by the flood. Parish personnel started evacuations to higher buildings as soon was water started coming into the parking lot, the lowest point on the campus.

Across the creek, Kids in Action, one of Kingwood’s most popular day care and after school facilities, had its own problems.

A distraught Diane Havens, owner of Kids in Action, tries to keep a brave face after she loses the use of her beautiful facilities for the second time in four months.
Hand sanitizer is the second thing you see in the reception area now.
Havens is bringing in four of these mobile units to hold classes until the first floor of Kids in Action can be restored again.

Haven’s spent $500,000 repairing her facilities after the May 7th flood. That’s a lot for a small business. She’s determined to weather this storm, too. But she worries that some of her clients may grow impatient in the inconvenience during repairs.

Choke Point #3: Kingwood Drive and Ben’s Branch

As Ben’s Branch approaches Kingwood Drive from the northwest, it spreads out into a 100+ acre forested area that includes the Creekwood Nature Center. But just before it crosses under Kingwood Drive, Ben’s Branch’s flood plain funnels down between Kingwood High School and the old H-E-B shopping center. At that point, a second branch of the stream joins it from the north. After crossing under Kingwood Drive, it is further constricted on the east side by commercial development. This represents another choke point.

The Kingwood High School Gym and Natatorium (bottom left) took on floodwater during Imelda.

The Kingwood High School gym and natatorium took on several inches of water during Imelda when drains and/or Ben’s Branch backed up. Merchants in the old H-E-B shopping center also report being stranded in their stores for two hours at the peak of Imelda as water from Ben’s Branch raced through the parking lot. Merchants said the water was inches from coming in their stores.

While many of the businesses south of Kingwood Drive in Town Center and Kings Harbor reported having water lapping at their foundations, I found none that reported flood damage.

No Simple Fix

I can’t think of a simple fix to all of three of these problems. Fixing one could compound the others. For instance, it would be simple to replace the culverts under Northpark with a bridge when the street is widened. However, that would just increase the volume of water backing up where the creek narrows between St. Martha’s School and Kids in Action. That would likely flood them even worse.

Channelizing the creek all the way to Kingwood Drive would likely be unpalatable from a political point of view. Four reasons: Few people in that area were affected. They all love their greenbelts. And the costs would be high. That would make the Benefit/Cost ratio of the project a non-starter.

One Possible Solution

One possible solution: convert the unused land around St. Martha’s new church north of Northpark Drive to additional detention. That’s valuable land and detention is expensive, but it may be a better alternative than losing the school which was just expanded in 2008. Father TJ Dolce is pitching that idea and hopes the Archdiocese would approve the use of their vacant land for detention. The big question: Would it be enough to make a difference.

Drainage Study Already Under Way

Thankfully, Harris County Flood Control is conducting a Kingwood-wide drainage study right now. They are studying Ben’s Branch. Hopefully, their talented engineers will be able to find the optimum solution that protects everyone. I sure hope they find it soon because these people are every bit as desperate as the people who flooded twice in Elm Grove and North Kingwood Forest.

Ben’s Branch may affect fewer structures. But it probably affects more people when you add up enrolled students and their families.

Posted by Bob Rehak on 10/1/2019 with help from Father TJ Dolce, Diane Havens, Lela Yorba, Daryl Palmer and National Helicopter Service.

763 Days since Hurricane Harvey and 12 since Imelda