Perry Detention Ponds Pass First Modest Test, But Eroded Badly

The official rain gage at West Lake Houston Parkway and the West Fork San Jacinto recorded 2.32 inches of rain between 7 and 9 a.m. this morning. That was officially a 1-year rain. (See Atlas-14 chart below.) As rains go, it was not a severe test; it was more like a pop quiz.

After the rain subsided, Taylor Gully in Elm Grove was less than half full.

The good news: Taylor Gully was well within its banks and no one in Elm Grove or North Kingwood Forest flooded. The bad news: Perry’s detention ponds experienced severe erosion, enough to warrant repairs and perhaps delay the schedule.

The even worse news: Harris County’s meteorologist, Jeff Lindner predicts another one to two inches of rain tonight with isolated totals of three to four.

West Lake Houston Pkwy. Gage Showed 2.32 Inches In 2 Hours

24 hour rain totals for WLHP gage showed bulk fell in 2 hours.

2.32 inches in two hours qualifies as a one-year rain according to the new Atlas-14 rainfall precipitation frequency estimates. Even if you considered the entire 3.12 inches in 24 hours, it would still only be a one year rain.

Atlas 14 Precipitation Frequency Table for the Kingwood Area.

Aerial Images Show How Perry Detention Ponds Performed

These aerial images taken shortly after noon today when the rain stopped show that:

  • The detention ponds are starting to do their work and hold back water.
  • That kept the level in Taylor Gully manageable
  • The overflow spillway between S2 and the concrete-lined channel was apparently not needed.

However, the images also show that:

  • Portions of the detention pond walls severely eroded and appear to have collapsed in places.
  • The water in the N1 pond overcame temporary dirt barricades sending water and silt down to N2.
  • The newly excavated N2 was entirely covered with water for the first time. It also received a significant amount of erosion.
  • N3 merges with Taylor Gully to form one large detention pond that holds water all the way from the northern end of the pond to the county line.
  • Rain has halted construction for the last two days and could delay it into next week.
Expanded, giant N2 detention pond was covered entirely with water for first time. Looking West toward western border of Woodridge Village.
However, erosion re-deposited large amounts of soil within the pond. Looking North along Western Border of Woodridge Village.
Rainwater entering the site from Joseph street in Porter (center left) shows by comparison how much silt the Perry water held. Looking north along western border of Woodridge Village.
Still looking north, but farther up western border, you can see silt slumping into ditch.
Looking SE toward Elm Grove and North Kingwood Forest from the NW corner of site. Water coming in N1 pond from left exited right, down the western border. Water washed out a temporary dirt barrier that appeared designed to hold water in the pond.
Looking east. Note erosion from former utility corridor on left that has turned into a new drainage ditch along northern edge of property.
Looking at western wall of N3 which runs along eastern border of Woodridge Village.
Another portion of the western wall of N3 shows severe erosion.
Standing water from rest of property is slowly making its way into detention ponds.
Looking South along eastern border toward Taylor Gully. At present, N3 (bottom left) simply merges with the concrete channel by S2 (top right). It appears to have nothing to control the outflow.
Looking north along eastern border. Silt fences prove inadequate at stopping erosion. In fact, most of site has no silt fences.

More Rain Likely Tonight

Jeff Lindner, Harris County meteorologist, says that today’s wet pattern should remain in place through the weekend, contrary to earlier predictions that saw rain chances ending by Friday.

Storms currently in the Gulf near Corpus Christi are tracking toward Houston late tonight and Friday morning. They will probably not be as severe as this morning’s storms. With that said…the air mass remains tropical over the region and excessive rainfall rates of 2-3 inches per hour will be possible, warns Lindner.

As of 6 p.m. Thursday, the National Weather Service decided NOT to issue another flash flood watch for tonight, but stay alert to see if a more significant threat may develop.

Expect rainfall amounts of generally 1-2 inches tonight with isolated totals of 3-4 inches.

To Get Up-to-the-Minute Forecasts and Stream Alerts

You can always find up to the minute weather forecasts at this National Weather Service page.

To check on rising rivers and major streams, visit the Harris County Flood Warning System, and click on channels and channel status simultaneously. To see further upstream, click on All Gages. That will show you the status of gages operated by the SJRA in Montgomery County.

Posted by Bob Rehak on 6/25/2020

1031 Days since Hurricane Harvey and 280 since 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.