How Woodridge Village Neighbors Fared in Last Large Rain and Why

Rains this week were neither as fast, nor as heavy as the May rains that caused extensive flooding on all four sides of Woodridge Village in May. Also, since the May rains, the developer had excavated much more of a crucial detention pond near the areas hardest hit by the May floods. As a result, I heard of no reported flooding in Elm Grove, North Kingwood Forest or Porter this week.

How Much Rain We Got

The screen capture below from the Harris County Flood Warning System shows the total rainfall for Lake Houston Area gages on June 5th and 6th. They range from about 1.5″ to 4″, with the higher totals on the southern side of the area. About 90% of these totals fell on Wednesday, June 5, during the morning hours.

Rainfall totals June 5-6 associated with first tropical disturbance of season. The rain fell on dry ground. No flooding was reported in the Lake Houston area, though Fort Bend and coastal counties received up to 14″. Source
During the 7 hours from 5 a.m. to noon, we received about 3.5 inches of rain at the nearest official gage. Source

Residents Anxious About a Repeat of May 7 Flood

Woodridge Village is the 268-acre clearcut area currently under development between Kingwood and Porter along the Harris/Montgomery County line. Two hundred homes in Kingwood and dozens in Porter that border the new subdivision flooded during more intense rains on May 7th.

So when the first tropical depression of the year approached earlier this week and merged with a second low coming out of the west, residents were on edge. Especially when the National Weather Service announced a flash flood watch that spread over two days.

However, repeat flooding was avoided. That was because of a combination of factors. Compared to May 7, we had lower rainfall totals, lower rainfall intensity, and most of Woodridge detention pond S2 (the second southern pond) had been excavated.

How Woodridge Village Handled the Rain This Week and Why

This sequence of pictures shows what the part of Woodridge immediately near Elm Grove and North Kingwood Forest looked like after the May 7 storm up through the peak of last Wednesday’s storm (6/5/19).

Engineers planned a huge detention pond for the entire southeast section of Woodridge. It should hold approximately 50 acre-feet of stormwater.

Approved plans for S2 Detention Pond (the second pond in the southern section).
Approximate S2 outline superimposed over keyframe from drone footage taken on May 9, 2019, two days after the May flood. This shows percentage of S2 actually excavated at time of flood: very little. Note also, the absence of silt fences. Virtually the entire 268 acres drains toward the culvert in the lower right. Drone footage courtesy of Jim Zura, Zura Productions. Zura is an FAA-licensed drone pilot.
By May 30, much more of S2 had been excavated. Outline of pond was becoming visible. Photo Courtesy of Jeff Miller. In the background, notice the black silt fence has finally been installed. It should have been installed before they started clearing land.

On the evening of June 4, Jeff Miller took the shot below from on top of the concrete box culvert where all of Woodridge Village drains into Taylor Gully.

Notice the depth of excavation in the deepest part. It had not rained for three weeks and the water was missing on May 30. Note also, the rocks in wire cages designed to hold back silt in a flood. The height of the bikes gives you a feeling for how tall the rocks are. Photo courtesy of Jeff Miller on 6/4/2019.

The next day, on 6/5/2019, we got the bulk of the rain from the storm. Jeff Miller went out again in the afternoon and took this shot showing how full the pond was.

6/5/2019 photo of S2 by Jeff Miller showing the amount of rainwater detained from the day’s storms. The low area in the center of the image leading to the pond is an overflow channel for the ditch behind the camera position that narrows down into a three-foot pipe.

Just after the rain stopped on the 6/5/19, Nancy Vera took this shot, near the peak of the flow.

At the peak of the flow, water covered the circled rocks (see swimming shot) now lining the channel to prevent silt moving downstream. Photo courtesy of Nancy Vera.
It appears that a 4″ rain spread out over a day – when the ground was not saturated – did not tax the capacity of the culvert either. This should be some comfort to residents. Image courtesy of Nancy Vera.
Even the 3′ culvert that runs along the western edge of North Kingwood Forest had room to spare. Photo courtesy of Nancy Vera.
Even Taylor Gully had plenty of room to spare. Photo courtesy of Nancy Vera.

Sleep a Little Easier

So what can we deduce from all of these observations.

  • The expansion of the S2 detention pond since the May 7th flood has created a greater margin of safety.
  • Elm Grove and North Kingwood Forest residents should sleep a little better knowing that they are protected from storms as large as we got on Wednesday, June 5.
  • Based on the latest NOAA Atlas 14 figures (see below), it looks like Wednesday’s rain ranked as a 1- to 2-year event.
  • It appears that there may be even more capacity to absorb even bigger rains.
  • However, with all ponds not yet complete, it’s unclear whether these ponds could handle a storm like we had on May 7th or a major hurricane.
NOAA Atlas-14 Rainfall Frequency Chart. Find the line that represents how much rain fell during a given period of time. Then look up to the top of that column to find the average recurrence interval (ARI). 3.5 inches of rain in a 7-hour period would be a rain we could expect every year or two.

Posted by Bob Rehak on June 8, 2019 with help from Nancy Vera, Jim Zura and Jeff Miller.

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