Last week, while driving through Forest Cove, I noticed construction activity and Harris County Flood Control District signs at the Kingwood Diversion Ditch near Walnut Lane. The area downstream from the bridge has some of the worst erosion of any ditch in Kingwood.
Area Now Under Repair As It Looked in 2009
Kingwood Diversion Ditch in 2009. Looking south from Walnut Lane. Forest Cove on right.
Erosion was bad for years and only got worse during major storms in 2015, 2016, and 2017. Massive slabs of the banks broke off in chunks, threatening trails and adjacent homes.
Since the picture above in 2009, the ditch has eroded both down and outward to increase its conveyance as new subdivisions upstream scabbed off of Kingwood’s infrastructure.
Pictures of Work in Progress Today
Oh, what a difference a decade makes! Note the exposed storm drains in the pictures below that you cannot see in the picture above.
Looking south from Walnut Lane Bridge.Exposed, elevated and crushed storm drains due to erosion.
The erosion left storm drains elevated and exposed to the ravages of floodwaters. Some were crushed, causing water to back up into streets and drainage ditches during heavy rains.
The area that collapsed circa 2009 above is the same area shown under construction today.
The velocity of water through this ditch during floods has earned it the nickname “Kingwood Rapids” from white-water enthusiasts.
Storm drains left exposed and elevated as the ditch widened and deepened itself to accommodate upstream development such as Woodridge Forest.HCFCD works to restore and stabilize banks, and repair damaged storm drains.Crumpled drains being removed by excavator.
How the Diversion Ditch Got Its Name
The Kingwood Diversion Ditch got its name when Friendswood realized that Ben’s Branch could not hold all the water being brought to it by adjacent subdivisions.
So Friendswood literally built a ditch that diverts a portion of the water coming down Ben’s Branch from Montgomery County just above Northpark Drive.
The point of diversion. Believe it or not, that’s Ben’s Branch flowing from bottom to top. As Ben’s Branch squeezes down, it forces water into the diversion ditch, which splits off to the right, just south of the new St. Martha’s Catholic Church.From there, the ditch goes under Northpark Drive, past Woodland Hills, and south to the river.
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.
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.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/02/20200213-RJR_8533.jpg?fit=1200%2C800&ssl=18001200adminadmin2020-02-16 05:49:322020-02-16 10:57:58Part II: When Is A Detention Pond Not A Detention Pond?
Great news! Tuesday, Harris County Commissioners Court approved a $700,000 contract with Neel-Schaffer, Inc. for a Kingwood Area drainage study. The engineering firm will identify flooding sources in the Kingwood area and develop potential solutions.
Data shows that portions of Kingwood have potential for significant offsite flows from Montgomery County as well as ponding locations due to inadequate overland flow conveyance. Said another way, new upstream development is taxing Kingwood’s drainage infrastructure. This project will help ensure that a 100-year flood plain remains a 100-year flood plain, and doesn’t turn into a 10-, 20- or 50-year flood plain.
Area of investigation outlined in red.
Drainage Study Details Outlined in Contract
The contract for the work indicates its scope and details. Discussion of those begins in Appendix A on page 14. The goal of the study is to identify mitigation strategies that will return 12.4 miles of existing drainage ditches and streams within Kingwood to their originally designed 100-year service levels.
Harris County Flood Control District (HCFCD) entered into an interlocal agreement with TIRZ 10 (Kingwood) to perform a drainage study of five main Kingwood streams to their confluence with the West and East Forks of the San Jacinto River. The five include:
G103-33-00 Bens Branch – From Rocky Woods Drive to WFSR (Length= 3.1 miles)
G103-33-01 – From North park Drive to the confluence with Bens Branch (Length= 1.3 miles)
G103-38-00 (Kingwood Diversion Ditch)- From Harris County Boundary to WFSR (Length = 4.0 miles)
G103-80-01 (Green Tree Ditch) – From Woodland View Dr to the EFSR (Length= 1.5 miles)
G103-80-03.1B (Taylor Gully)- From Harris County Boundary to Whiteoak Creek (Length= 2.5 miles)
Flood Control Will Fund Remainder of Streams/Ditches
In addition to the interlocal agreement, Harris County Flood Control District will also study all remaining streams and ditches within the Kingwood Area. Those include another 19.9 miles:
G103-33-00 Bens Branch – From Harris County Boundary to Rocky Woods Drive (Length = 2.2 miles)
G103-33-02 – From North park Drive to the confluence with Bens Branch (Length= 0.2 miles)
G103-33-03 – From Hidden Pines Dr. to the confluence with Bens Branch (Length= 0.1 miles)
G103-33-04 – From W Lake Houston Pkway to the confluence with Bens Branch (Length= 1.2 miles)
G103-36-00 (Bear Branch)- From Woodland Hills Dr. to WFSR (Length= 2.7 miles)
G103-36-01 – From Woods Estates Dr. to the confluence with Bear Branch (Length= 0.8 miles)
G103-36-02 – From Woodland Hills Dr. to the confluence with Bear Branch (Length = 0.9 miles)
G103-36-02.1- From Kingwood Dr. to the confluence with Bear Branch (Length= 0.4 miles)\
G103-36-03- From Royal Circle Dr. to the confluence with Bear Branch (Length= 0.4 miles)
G103-38-01- From Laurel Springs Ln. to the confluence with Kingwood Diversion Ditch (Length= 1.3 miles)
G103-38-01.1- From Red Oak Terrace Ct. to the confluence with Kingwood Diversion Ditch (Length = 0.4 miles)
G103-38-02- From Harris County Line to the confluence with Kingwood Diversion Ditch (Length= 0.7 miles)
G103-39-00- From Palmetto Ln. to the WFSR (Length= 1.3 miles)
G103-41-00 (Sand Branch) – From Sycamore Creek Dr. to the WFSR (Length= 2.0 miles)
G103-41-01- From Elk Creek Dr. to the confluence with Sand Branch (Length= 0.8 miles)
G103-45-00- From Trail Tree Ln. to the WFSR (Length= 0.4 miles)
G103-46-00- From Forest Cove Dr. to the WFSR (Length = 1.0 miles)
G103-46-01- From Sweet Gum Ln. to the confluence with G103-46-00 (Length= 0.7 miles)
G103-80-01.1- From Autumn Sage Ln. to the confluence with Green Tree Ditch (Length= 0.3 miles)
G103-80-03.1A (Mills Branch) – From Same Way to Whiteoak Creek (Length = 1.5 miles)
G103-80-04 (Blackland Gully) – From Maple Knob Ct. to the EFSR (Length = 0.6 miles)
The scope of work includes several stakeholder meetings with TIRZ 10, homeowner associations, and the community at large. Their purpose: to increase public awareness and understanding of the magnitude of the watershed problems, their complexities and the cost of solutions.
Drainage Study Data Acquisition Phase
The contractor will start by collecting all available information and data including:
Construction plans
Previous drainage studies
HCFCD historical flooding data
High Water Marks
Watershed Masterplan data
FEMA Repetitive Loss properties
Flooding reports
LiDAR DEM data
Aerial maps
HCFCD watershed maps
Hydrologic and hydraulic models
City of Houston GIMS data
Any other pertinent technical data in the development of this scope of services.
Field Reconnaissance Phase
Neel-Schaffer engineers will then conduct field reconnaissance of the existing drainage systems, outfalls, and drainage patterns within the project area. That will include field measurements of 27 bridge crossings, 32 culvert crossings, 16 pedestrian bridge crossings and 6 drop structures to be incorporated in the development of hydraulic models.
During this stage, Neel-Schaffer will also measure high water marks; update floodplains; and analyze stream performance and capacity to illustrate flooding issues to the County, TIRZ and community.
Identification of Structural and Non-Structural Mitigation Alternatives
The Engineer will determine structural and non-structural improvement alternatives to bring all streams back up to the 100-year level-of-service.
Neel-Schaffer will perform this analysis using full conveyance at peak flows. Engineers will identify the major constraints that affect the available solutions for each stream.
They will then consider both structural and non-structural alternatives for mitigation.
Structural Alternatives
Structural alternatives include:
Improved drainage channels including widening, deepening, and/or lining for increased conveyance capacity.
Watershed diversions using enclosed conduits (following existing roadway alignments or other public ROW).
New regional or sub-regional detention basins and modification of existing detention basins including inlet and/or outlet structures.
Enhanced conveyance using selectective clearing and re-shaping of natural channels.
Enhanced flood storage in natural and park areas using small-scale berms and grading.
Non-Structural Alternatives
Non-Structural Alternatives include:
Property buy-outs.
Coordinated ROW dedications for future improved channels and regional detention basins.
Regional detention fees for new development.
Drainage Study Will Consider Detention Ponds
This contract includes identifying detention needs, identifying potential locations, and developing schematic layouts of the detention ponds. It also includes:
Proposed Right of Way acquisition
Preliminary Cost Estimates
A project priority and implementation plan
It is not clear at this point how long this project will take.
This post is dedicated to Barbara Hillburn, the president of the Kingwood Lakes HOA, who fought long and hard to get a project like this started. Thank you, Barbara!
Posted by Bob Rehak on 8/14/2019 with thanks to Barbara Hillburnand Precinct 4 Commissioner Jack Cagle
715 Days since Hurricane Harvey
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