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.