News - Reduce Flooding

Flood Regs: What County Wants City to Do as Part of Woodridge Village Purchase Deal

Through a Freedom of Information Act (FOIA) request, ReduceFlooding.com has obtained details of Harris County’s request to the City of Houston to revise its flood regs. Complying with the request is one of two conditions the City must meet before the County will purchase Perry Homes’ Woodridge Village.

Background

Woodridge Village twice contributed to flooding in Elm Grove and North Kingwood Forest last year. Ever since, flood-weary residents have pled with Harris County and City of Houston officials to buy the property and build regional floodwater-detention facilities there that would protect them. The City initially declined. The County agreed, but with two conditions.

First, the County wanted the cash-poor City to pay for half the purchase through the donation of land that the County could then use to help offset costs for other HCFCD projects.
Second, the County wanted the City update to its stormwater and floodplain ordinances to make them consistent with the County’s.

Harmonizing the regulations would provide consistency between the three largest governmental agencies tasked with drainage projects in the our area: Harris County Engineering Department, Harris County Flood Control, and the City of Houston.

This is the first step in getting all municipalities and County governments that drain to Harris County to adopt similar standards to help reduce flooding risks and protect the billions of dollars of drainage infrastructure investments currently being made in the area.

A Houston Chronicle article (that didn’t even mention Elm Grove) said, that in the future, the county would not share flood bond money with any of 34 different municipalities within its jurisdiction that have not updated and harmonized their regulations with Harris County’s.

So what were the requested changes?

Below are revisions needed for the City of Houston to comply with Harris County Infrastructure Regulations (2019 version) and the HCFCD Policy, Criteria and Procedures Manual.

In all cases cited below, Harris County flood regulations exceed the City of Houston’s. The County does not ask the City to relax any guidelines.

Houston Chapter 9 (Stormwater Design Requirements – July 2019)

General Note – The City updated this Chapter in late 2019 to add Atlas 14 rainfall information for use in storm sewer design. The County also added Atlas 14 to its regulations.

However, the County requests that the City make additional changes as follows:

Section 9.2 Design Requirements:

9.2.01(B)(3)(a)(1) Table of Rational Method Runoff Coefficients – Must be updated for lots greater than ¼ acre to be consistent with Harris County requirements.
9.2.01(C)(7)(d) Table 9-2 – Revise inlet capacities for Type A, D, D-1, C-2, C-2A, D, D-1, and E inlets to be consistent with Harris County requirements.
9.2.01(D)(3)(c) Relationship of Structures to Street – Revise finished slab elevation criteria to be consistent with Harris County requirements of 18” above the 100-year floodplain, one foot above the maximum ponding depth within a 10’ radius of the structure or at or above the 500-year floodplain, whichever is higher.
9.2.01(H)(2)(d) Waiver of Detention Requirements – Remove this section; it would allow developments to be constructed without detention.
9.2.01(H)(3)(a-e) Calculation of Detention Volume – Revise to remove detention rates based on tract size, revise detention rates to be consistent with Harris County requirements of 0.75 acre-feet/acre for storm sewer outfalls and 1.0 acre-feet/acre for roadside ditch outfalls, or HCFCD requirements if outfalling to HCFCD facility.
9.2.01(H)(3)(a-e) Tracts >50 acres – Refer to HCFCD requirements if outfalling to HCFCD facility, otherwise refer to Harris County requirements if outfalling to storm sewer or roadside ditch.
9.2.01(H)(4) Calculation of Outlet Size – Revise to be consistent with Harris County requirements, remove minimum restrictor size, remove allowable discharge rates of 0.5 cfs and 2.0 cfs per acre and include calculated allowable rates.
9.2.01(H)(5)(a) Private Facilities – Include Harris County pumped detention information including detention rate, allowable drain times, and percentage that must be drained by gravity. Add minimum bottom slopes and pilot channel slopes from Harris County requirements.

Houston Code of Ordinances, Chapter 19 Floodplain (September 2018)

Under Article III: Standards for Flood Hazard Reduction:

19-33(a) Base Flood Elevation Requirements – Must also include a provision that no fill will be allowed to elevate structures proposed for the 100-year floodplain. These structures must be on open foundations designed by a structural engineer.
19-33(c) AO Zones – Revise to require finish floor elevation of three feet above the depth number noted in the specific zone, or 6 feet if no depth number is specified.
19-34(a)(4) – Remove this item that allows fill to be placed in the 0.2% floodplain without mitigating excavation.
19-34(d) Critical Facilities – Add requirement for these facilities to have the lowest floor elevated 24” above the crown of the adjacent street if that is higher than 3’ above the 0.2% elevation.
19-43 (c)&(d) Floodways – Require an engineering report for the foundation in addition to the “no-rise” analysis and mitigation requirements. Add Harris County requirements for foundation design.
19-43(e) Bridges – Add requirement that all bridge construction that modifies the base flood elevation or that modifies the geometry of the bridge or channel must submit a CLOMR and LOMR.
19-75 Manufactured home placement in a floodway or coastal high hazard area – Remove this section that allows for manufactured homes to be placed in these areas.

The County also recommends that the Harris County Floodplain Administrator should review Chapter 19 for additional changes to ensure consistency with Harris County floodplain regulations.

Negotiations Still Reportedly Ongoing

City of Houston did not discuss conditions of the Perry purchase in last week’s City Council session. Neither are County Commissioners scheduled to discuss them this week. However, negotiations with Perry are reportedly continuing despite the passage of Perry’s extended deadline.

Meanwhile, with hurricane season less than two weeks away, Perry Homes’ new contractors continue to put the full-court press on construction of detention ponds. They have made more progress in two months than the previous contractors did in two years.

Posted by Bob Rehak on 5/19/2020 with keyframe from Jim Zura, Zura Productions

994 Days after Hurricane Harvey and 243 after Imelda

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

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.

Erosion: Sometimes Sudden

Erosion can sometimes be sudden. It’s not always a slow process of water grinding away at dirt and dissolving it, or wearing down rocks. This post will examine several examples around us and look at their implications. I intend it as a continuation of yesterday’s post about ditch maintenance.

*The Northpark Woods development (right) on the West Fork San Jacinto River (background)*

There are four main types of erosion.

Hydraulic action – When rapidly moving water churns against river banks and scours or undermines them.
Abrasion – Caused by small pebbles moving along a river bank or bed and knocking other particles loose. Think of sandpaper.
Attrition – When rocks carried by the river knock against each other. They break apart to become smaller and more rounded. This is how boulders turn into gravel.
Solution – When water dissolves certain types of rocks, for example limestone. We often see this in Florida, where sinkholes frequently develop.

Most of these processes happen slowly. But the first can be sudden. One storm. One flood. And boom. That river bank where you used to sit and quietly contemplate nature is gone.

Now You See It; Now You Don’t

Sometimes large slabs of a river bank or ditch suddenly slump into a river, almost like mini landslides. One flood expert commented on the picture above; he said “The owners of those new homes may suddenly find the ditch in their backyards.”

At other times, the size of a flood forces a river to widen. We saw this during Harvey and Imelda. The relentless pounding of flood waters carries away everything in their path. Cutbanks (the outside of a river bend) are especially vulnerable. Water slams directly into them like a firehose and washes them away. This action actually changes the course of a river over time.

Most of the time, it happens so slowly, we barely notice it. But during large floods, it’s sometimes sudden, large, and devastating to homeowners or businesses near rivers.

Three More Examples of Hydraulic Action

Example A: East End Park

*East End Park in Kingwood. In 2019, the San Jacinto East Fork removed approximately 50-100 feet of river bank during Imelda,* *including this part of the Overlook Trail.*

Example B: Balcom House and River Migration

*Note a long peninsula south of the Balcom House on the San Jacinto West Fork before Hurricane Harvey.*

*After one monster storm, the peninsula was gone. The Balcoms lost 175 feet of riverfront property.*

Example C: River Aggregate Mine on West Fork in Porter

The third example comes from the abandoned River Aggregates sand mine beyond the new development in the first picture above. It’s a spectacular example of river migration.

In this case, the San Jacinto West Fork migrated 258 feet toward the mine’s dike in 23 years. When I first photographed the dike after Harvey, the river had eaten away an average of 12.4 feet per year. At the time, the dike was only 38 feet wide, and I predicted it could soon fail. It did. Within approximately a year.

*Image taken on 9/14/2017, shortly after Hurricane Harvey. At the time, only 38 feet stood between the abandoned mine in the background that the San Jacinto west fork in the foreground.*

*Note how the pond in the foreground disappeared when the river took the last 38 feet of river bank.*

Wait a minute, you say! What happened to the pond. After the river bank collapsed, the pond drained, exposing sediment already within it. And the action of draining concentrated more sediment in it, like all the remnants of food trapped in your sink drain after you’re done washing dishes.

History of Pond

The missing, shallow pond in the foreground above used to be the settling pond for River Aggregates.

*This satellite image from 2004 shows that* *River Aggregates used the missing pond as a settling pond.*

*This is how the mine looked in 2017 after River Aggregates abandoned it.* *Note river bank is still intact.*

*This is how the abandoned mine looked in January of 2019. The river bank was gone. The pond had drained. And a steady stream of silty water from other ponds leaked into the West Fork.*

Here’s how it looks today from a helicopter.

*River Aggregates mine now leaks a steady stream of silty water into the West Fork San Jacinto.* *This is the same area as above, but from the reverse angle.*

Lessons of Life Near a River

Most people never live long enough to see massive changes such as these in rivers. In most places, river change happens on a geologic time scale. But along the Gulf Coast, hurricanes can create floods that make rivers change on a human time scale, as these examples have shown.

What can we deduce from this?

Around here, we need to give rivers room to roam. Parks, green spaces, and golf courses, often represent the highest and best use of land near a river, bayou or ditch.
Building too close to rivers, bayous and drainage ditches can be costly. Disturbing wetlands and topsoil accelerates erosion. That, in turn, can threaten everything in its path. Be prepared to maintain anything you build near a watercourse, including the watercourse itself. And be prepared to fight what ultimately becomes a losing battle.
We need greater separation between mines and the San Jacinto river. Keep mines out of the meander belt. They worsen downstream sedimentation. And as we have seen, that can contribute to sediment build ups that require public money to remove. The alternative, leaving them in place, contributes to flooding.

Here’s a current list of ditch maintenance projects in the Kingwood area.

Posted by Bob Rehak on 5/18/2020

993 Days since Hurricane Harvey