Woodridge Village Pre-Cristobal Detention Pond Update

Perry Home’s new contractors have excavated the vast majority of virtually all three detention ponds on the north section of Woodridge Village. That means they have almost completed 77% of the detention pond capacity for the whole site in two months. The previous contractors completed only 23% in approximately twenty months.

That represents approximately a 30x increase in productivity.

Overview of Woodridge Village Detention Pond Capacity

The pie chart below shows how that capacity breaks down. And the map shows where it is.

*Percentage of detention pond capacity in acre feet for each of the five Woodridge Village ponds.* *Source: LJA Drainage Addendum.*

*General layout of detention ponds on Perry Homes’ property.*

Contractors Scurry as Cristobal Churns in Gulf

Tropical Storm Cristobal could be a game changer next week if it hits Houston. It’s track is far from certain at this point, but the National Hurricane Center still puts Houston within the cone of uncertainty.

Cristobal has the potential to create massive erosion and set the work schedule back. The aerial photos below taken on 6/2/2020 show the current “pre-storm” status of construction for the three northern detention ponds. The two southern detention ponds were completed earlier this year.

N1 Nearing Completion of Excavation

N1 Starts at the northern boundary of the site and runs halfway down the western edge to Mace Street.

*Looking north at N1 from Mace Street in Porter to the northern boundary.*

*The area between the culverts will eventually become an extension of Mace Street (top of photo) which will traverse the entire subdivision to Ford Road on the eastern side.*

*While some contractors continue excavating, others work on installing concrete pilot channels. Shown here, the pilot channel near Ivy Ridge in Porter.*

*The northern part of N1 is not yet complete. Contractors still use the Webb Street entrance (upper left as their main access point to the site.* *Note how height of road dwarfs excavator in pit.*

Still Widening and Deepening N2 Pond

The area left of the diagonal road is the expansion of N2. The area near the diagonal embankment is deep enough to conceal trucks and excavators. However, the grassy triangle in the middle left was a previous detention pond constructed my Montgomery County in the early 2000s.

*Contractors are deepening the MoCo pond a small amount to create additional storage capacity.* *The dirt is being used to build up other portions of the site.*

Looking north along the western boundary from the southern part of the grassy triangle. Much work remains to extend the N1 channel south to N2. Jeff Miller reported today that contractors started working on this *this morning.*

*On 6.3.20, contractors were removing dirt from the northward extention of N2 with three dump trucks running in a relay fashion. Photo courtesy of Jeff Miller.*

*Twin culverts installed in Taylor Gully will control outflow rates from N1 and N2*.

N3 All Excavated

N3 cuts down the eastern side of Woodridge Village and joins Taylor Gully right above S2.

*Looking north. Excavation of N3 appears complete although few of the finishing touches have yet been installed.*

*N3 widens out about halfway down the eastern border.*

Then it narrows down again *to help control outflow speed* *as it approaches the junction with Taylor Gully.*

Water from the entire site converges here. Erosion patterns, fence damage and grass matting show this is where the overflow started that contributed to the flooding of Elm Grove (right) and North Kingwood Forest (left) twice last year.

The pile of dirt in the picture above could be shoved into the connecting channel in the event that Cristobal should strike Houston. That would then help retain water in N3 until after the storm.

All the runoff from the approximately 200-acre northern portion of the site converges here and tries to make its way through a 3-foot culvert at the end of the concrete channel.

Uncertain Still Surrounds Corner of Chaos

Some Elm Grove and North Kingwood Forest residents have called the complex flow patterns in the photo above “The Corner of Chaos.”

Overflow from the concrete lined channel is supposed to go into the kite-shaped S2 pond, and then through the twin culverts into Taylor Gully. However, a hydrology consultant for the plaintiffs in flooding lawsuits contends that floodwaters went the other way. They escaped out of the inflow channel, he says. He further claims that LJA Engineering failed to model the performance of that connecting channel.

If the design of the flow at this “Corner of Chaos” is flawed, there’s little contractors can do to fix that at this point without some major re-engineering.

In that regard, we should also remember that LJA designed these ponds before Atlas 14, so they will only hold approximately 60% of a 100-year rainfall as defined by Atlas 14 standards adopted in Harris County.

How Contractors are Temporarily Funneling Water into Ponds

Because storm drains are not yet installed, contractors are relying on temporary channels to intercept runoff and direct it to detention ponds.

*Small ditches like one on right catch runoff and direct it to ponds for the time being.*

Next Steps in Completing Detention Ponds

A modest amount of excavation remains to complete the full detention pond capacity.

But the capacity already in place should reduce flood risk compared to last year by more than 3X for storms equivalent to May 7 and September 19, 2019.

As some crews focus on completing excavation, others are putting the finishing touches on ponds. Those include concrete pilot channels, backslope interceptor swales, drain pipes, and culverts to control the rate of outflow.

Racing Against Hurricane Season

At this point, contractors are racing against time and the hurricane season. Cristobal underscores the risk of having waited for months to begin the three northern detention ponds in April. Had they begun them immediately after J. Carey Gray’s letter to Mayor Turn in October, they could easily have finished by now.

Posted by Bob Rehak on 6/4/2020 with thanks to Jeff Miller

1010 Days after Hurricane Harvey and 258 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.