What Went Wrong, Part IV: Perry Homes Develops Flood Plain That Wasn't

Chapter 9 of the Montgomery County Drainage Criteria Manual discusses development in flood plains. Perry Homes and LJA Engineering somehow “overlooked” many of the points in this chapter. A flood plain ran through the property, but FEMA had not yet mapped it. LJA used that as an excuse to claim none existed.

*Notice how flood plain mapping stops at county line. Perry Homes has the undeveloped property along and above the county line.* *Color code: Cross-hatched = floodway; aqua = hundred year flood plain; brown = 500-year flood plain.* Source: MoCo Maps

Unfortunately, physical boundaries of flood plains do not observe political boundaries. Taylor Gully bisects this property, if you look at the flood maps, it magically defies flooding on the MoCo side of the county line.

Montgomery County Regulations Affecting Flood Plains

Below are guidelines from the Montgomery County Drainage Criteria Manual that Perry Homes would have had to follow had the property been mapped.

From Section 9.1.1 Floodplain Regulations:

“No fill or encroachment is permitted within the 100-year floodway which will impair its ability to discharge the 100-year peak flow rate except where the effect on flood heights has been fully offset by stream improvements.” [Emphasis added.]

“Placement of fill material within the floodplain requires a permit from the County Drainage Administrator. Appropriate fill compaction data and hydrologic and hydraulic data are required before a permit will be issued.”

From Section 9.1.2 Floodplain Development Guidelines and Procedures

“Construction within the floodway is limited to structures which will not obstruct the 100-year flood flow unless fully offsetting conveyance capacity is provided.”

“The existing designated 100-year floodplain and floodway should be plotted on a map of the proposed development.”
“The effect of the proposed development and the encroachment into the flood plain area should be incorporated into the hydraulic model and the resulting flood plain determined.”
“Careful consideration should be given to providing an accurate modeling of effective flow areas taking into account the expansion and contraction of the flow.”
“Once it has been determined that the proposed improvements adequately offset the encroachment, a revised floodway for the stream must be computed and delineated.”

From Section 9.2 Downstream Impact Analysis

“Pursuant to the official policy for Montgomery County, development will not be allowed in a manner which will increase the frequency or severity of flooding in areas that are currently subject to flooding or which will cause areas to flood which were not previously subject to flooding.”

What LJA Said About Perry Homes’ Project

On Page 1-2 of its Drainage Analysis, LJA Engineering explicitly states, “As shown on Exhibit 3, the proposed development is outside the 100-year floodplain.”
Phyllis Mbewe, P.e., CFM, LJA Project Manager – Hydrology and Hydraulics

LJA Exhibit 3 shows the floodplain stopping at the county line. LJA also did its best to make the .2 percent risk area blend into the area of minimal flood risk. This visually minimizes the amount of floodplain bordering MoCo, *so the abrupt stoppage at the county line becomes less visible.* *Source: LJA.*

Ms. Mbewe then states in her conclusion, “Based on these findings, the proposed development of the 268-acre tract creates no adverse drainage impacts for events up to and including the 100-year event.” [Emphasis added.]

What Does “No Adverse Impact” Really Mean?

People often twist the definition of terms you think are self evident. Especially in legal, technical, and political contexts.

To me, “No Adverse Impact” should mean, “Downstream people who didn’t flood before won’t flood after development.” That’s what section 9.2 states explicitly.

But when I talked to a flood professional, I got a different answer. To that person, “no adverse impact” meant, “the amount of water flowing across the property did not increase after development.” Much narrower! And seemingly contradictory to the spirit of 9.2.

“Floodplain” Definition Shocked Me

But that person’s definition of floodplain really shocked me. To me, floodplain means “the area adjacent to a stream that fills with floodwater after a very heavy rain.” But the professional told me I was WRONG. To the professional, a floodplain was “an area on a map that FEMA designated a floodplain for insurance purposes.”

In that person’s mind, because FEMA had never mapped the area in question, a floodplain did NOT EXIST. Whether or not the area flooded!

To me, that’s like saying an apple is something you see in a Kroger’s flyer, not something you eat. We’re talking about the difference between a symbol of something and the reality of it.

This discussion proved once again that words and phrases have different meanings that depend on the social context of usage.

In the minimum compliance environment of Montgomery County, LJA and Perry Homes argued that there was no floodplain. They found someone in the county engineer’s office who agreed with them…or was told to agree with them.

FYI, the official FEMA definition says, “Any land area susceptible to being inundated by floodwaters from any source.”

Consequences of Overly Narrow Definition

So did Elm Grove flood because Perry Homes, LJA and Montgomery County did not enforce the floodplain regs in section 9.2 of the Drainage Criteria Manual?

They certainly did not offset peak flows with stream improvements.
They did not plot the REAL-WORLD floodway and floodplain on a map of the proposed development (see above).
LJA did not incorporate encroachment into the floodplain in its hydraulic modeling, because they denied a floodplain existed.
Neither did LJA provide “an accurate modeling of effective flow areas taking into account the expansion and contraction of the flow.”
Finally, LJA did not compute, revise and delineate the floodway for the stream.

Had they done all these things, perhaps people would have seen that downstream homes that had never flooded were now subject to greater flood risk. But that’s really something for the jury to decide. And it would require FEMA to model the floodplain after the fact.

But like the narrow definition of floodplain, this whole discussion symbolizes a bigger problem.

How Do You Fix a Permissive, Minimum-Compliance Environment?

LJA had an obligation to its client and a higher one to the public that it ignored in my opinion.

Perry Homes could have demanded honest answers from its engineers, not the ones they wanted to hear.

FEMA could label areas like Woodridge Village “UNMAPPED”. This would send a signal to potential home buyers if sellers tell them they’re NOT in a floodplain. That might make developers think twice.

Home buyers need to demand integrity in this process. They need to ask better questions. They need to learn more about flooding.

But at the end of the day, Montgomery County Commissioners must define the kind of future they want. Do they want constant flooding? Or not. Because right now, they’re competing with other areas for new development on the basis of willful blindness and self-serving definitions.

Thirty years down the road, when it’s too late to fix the infrastructure problems they ignore today, MOCO residents will be paying the price. Some, who have flooded repeatedly, might argue they already are.

Posted by Bob Rehak on 8/26/2019 with help from Jeff Miller

820 Days after Harvey and 69 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.