New Perry Detention Ponds Held Surprising Amount of Rain Last Weekend

The northern section of Perry Homes’ Woodridge Village now has three detention ponds in various stages of completion. As of a week ago, on May 11, 2020, all three were capable of holding water and did during last weekend’s rains. That meant much rainfall that previously might have overwhelmed the two southern detention ponds had places to hold up instead of overflowing into Elm Grove and flooding residents.

No Record Rainfall, But No Flooding Either

Harris County’s Flood Warning System shows that the area received about two and a half inches of rain last weekend. A 2.5 inch rain is far from a record. But forecasters predicted much more. And some areas to the south and east of Lake Houston got more than 10 inches! So Elm Grove residents lucked out, but they were rightly worried.

In the end, whether it was the additional detention capacity or the lighter rain, no one flooded. And that’s what counts.

*The Harris County Flood Warning System shows that the nearest official rain gage to Elm Grove is at West Lake Houston Parkway. It registered 2.52 inches of rain in 3 DAYS.*

*2.52 inches would have to fall in 3 HOURS to even make this chart, and then it would be something we could expect every year.* *Source: NOAA*

Status of Detention Pond Construction

So what is the current status of construction? As of last Monday, the two ponds on the southern section (S1 and S2) were complete.

Of the three ponds on the northern section:

N1 was partially excavated, with most of the capacity in the “tail” leading south toward N2.
N2 was about 80% excavated. Workers were expanding the new section and deepening the old section, developed by Montgomery County many years ago.
N3 was approximately half complete.

*Part of N1 Excavation as of May 11, 2020*

*Massive N2 pond in southwest corner of northern section. Grassy portion was previously excavated by MoCo, but contractors are deepening it. Photo taken May 11, 2020.*

*Looking south at Woodridge Village N3 detention pond photo from week ago, May 11, 2020.* *Elm Grove is out of sight beyond top of frame.*

As last week wore on, each pond expanded compared to the three images you see above. Jeff Miller, an Elm Grove resident who lives near Woodridge Village, estimates that all three detention ponds on the northern section were about 80% excavated by the end of last week. However, he also noted that much work remains in terms of sloping the sides, stabilizing soil, building pilot channels and connecting ponds.

Barring further major rains and at the current rate, Miller estimates contractors could finish all three ponds in June.

How They Performed Last Weekend

N1

The first shot below shows the tail of N1. It was not yet connected to N2 so water could not drain out of it.

*Photo of N1, looking north, by Jeff Miller on Saturday after rains stopped.*

N2

I have no pictures showing how well N2 did at holding back rain, but neither Taylor Gully nor the southern detention ponds overflowed.

N3

*Prior to the rain, this portion of N3 was deep enough to conceal all but the top of a large dump truck.* *N3 might have held approximately 5 feet of water according to Miller.*

Additional Culverts for Connecting N1 and N3

Jeff Miller also photographed these 4×4 box culverts stacked up north of N3.

*Note the concrete box culverts stacked up north of N3. Plans call for connecting N1 and N2 with such culverts.* *Also notice how land has been sloped from left to right to flow into N3.* *See water draining into N3 from a temporary ditch that cuts through the bottom of the image.*

Layout and Capacity of All Ditches

*Layout of detention ponds on Perry Homes’ Woodridge Village.*

This pie chart shows the relative capacity of Woodridge Village detention ponds. In the May flood last year, only the blue pond was complete. By the September flood, Perry had also completed the green pond. The three northern detention ponds hold 77% of planned storage capacity. None of those had even started.

Conclusion

Last week’s rains were a small test. But results showed the work already done has added to to detention capacity.

Miller says that water from the northern section did not appear to spill over into S2. His pictures also showed that S2 was only half full.

That meant the entire rain, with the help of new detention ponds, was able to drain out through a 3 foot corrugated pipe that connects Taylor Gully on either side of the county line, just like it used to.

This is welcome news for flood-weary Elm Grove and North Kingwood Forest residents who feared the worst.

No Progress to Report on the Political or Purchase Fronts

Even though the deadline for a Harris County purchase of Woodridge Village from Perry has passed, and even though Commissioners are not supposed to discuss the buyout in tomorrow’s Commissioner’s Court meeting, Precinct 4 Commissioner Jack Cagle says negotiations are ongoing.

The County made an offer to buy the land in order to build a regional flood detention facility. But the offer was contingent on the City of Houston donating $7 million worth of other property to the Flood Control District to help offset costs. The City also had to adopt County drainage criteria. It reportedly is more conservative than current City standards.

Posted by Bob Rehak on 5/18/2020 with photos and reporting from Jeff Miller

993 days since Hurricane Harvey and 242 since Imelda

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