San Jacinto River Master Drainage Plan Draft Provides First Look at Final Report Due Out in August

On 7/23/2020, consultants for the San Jacinto River Basin Master Drainage Plan gave the SJRA Board and the public a first look at a draft of the plan. The final report is due out at the end of August. The draft shows the broad outline of the team’s efforts.

Draft Shows Broad Outline of Recommendations

It shows the types of recommendations they will make. However, this draft does not yet include specific recommendations as to prioritization of projects. Those will change before the final report. For instance, much of the draft focuses on upstream detention. But specific detention site recommendations have not yet been finalized.

Funding and Partners

Below are the key slides and a brief explanation of the main point behind each. This drainage study is 75% funded by a FEMA Hazard Mitigation Grant and 25% by four local partners: the SJRA, City of Houston, Harris County Flood Control, and Montgomery County.

Scope of Study

The study area covers almost 3,000 square miles and the tributaries listed on the left.
The SJRA primarily has responsibility for the portion of the watershed in Montgomery County. However, the scope of the drainage study extends to other counties including Waller, Grimes, Walker, Liberty, and San Jacinto.

Heat Map Shows Where Most Damage Occurs

The team started by looking at where flooding has occurred historically. The tan areas above show where the most damage has occurred.

Goals and Methodology

The partners started by looking at vulnerabilities and identifying mitigation possibilities. Their main goals are in red. The final report will make specific recommendations for detention, buy-outs and improving conveyance. Recommendations will also improve flood warning and communication.
The team started by integrating and updating all existing hydraulic and hydrologic models in the watershed as reflected on the latest 2018 lidar terrain data. They now take into account new construction, growth, additions to impervious cover, and Atlas-14 rainfall probabilities (which vary by sub-watershed within the larger watershed).
To calibrate and verify its H&H models, the drainage study team examined four historical storms that, together, impacted the entire study area. They then adjusted the models using radar rainfall data, and USGS high water marks and peak flow data. The objective: to make the models reflect “ground truth.”
The team is also looking at strategies to reduce sedimentation. However, this is not a major focus of this study. Their purpose is not to evaluate the relationship between sediment and flooding. Other studies will do that.

Three Main Areas of Focus

This slide shows the three major thrusts of drainage study effort over the last 1.5 years. The primary focus has been on: a) identifying the best locations for upstream detention that can reduce the volume of water coming downstream to populated areas during floods, b) where to install additional gages to improve flood predictions and warning times, and c) improving communication during emergencies.
This shows the steps the drainage team went through to evaluate and rank-order potential sites for detention.

Areas of Highest Potential for Mitigation

Here’s where they found the highest and lowest potential for mitigation. The box explains the watersheds that see the most effective solutions within the SJMDP study area, as explained in the list to the left of the slide.
Some drainage projects recommended in previous plans are no longer possible today because of upstream development. However, areas that once held potential for a single large project still hold potential for several smaller projects that add up to significant flood reduction.

Mitigation Project Funding

The cost all the drainage projects identified adds up to about $3 billion. They only reduce flooding of structures worth about $756 million dollars. Because costs exceed benefits, FEMA will not likely fund all of these.
However, many of the projects are in areas with low to moderate income (brown and tan areas). See the large concentration in the eastern watershed. That opens up other sources of funding, such as the Department of Housing and Urban Development where the benefit/cost ratio may not be as important.

Harmonizing Regulations Throughout Region

The team will also make recommendations to harmonize floodplain development regs throughout the region. Continuing to allow unmitigated upstream development in floodplains could destroy any new investment made to protect highly populated downstream areas.

Some Problems May Only Be Solved Through Buyouts

Buyouts usually have a high benefit-to-cost ratio relative to construction projects such as detention ponds. Buyout strategies can target the most vulnerable properties, such as those in the 2- and 5-year floodplains. None of the detention projects recommended by the team will likely remove those from danger.

Steps Still Not Completed

The team has finished the steps in red. They in the process of prioritizing projects and developing a phasing plan. The last bullet point is not part of this study.

More Upstream Gages Needed to Eliminate Blind Spots

The team has also identified locations for additional upstream gages and local partners who can help maintain those gages. Think of these like a “distant early warning” system. They give river forecasters visibility into “blind spots.” Forecasters will be able to add up the rainfall on various tributaries and predict the impact and timing of flooding downstream. That could give people more time to evacuate.

Ways to Improve Communication

The team is also looking at ways to communicate better during flood emergencies. They are looking at inundation mapping, evacuation routes, and improved communication protocols.

Timetable for Remainder of Project

This chart outlines the project workflow. It shows completed steps in red, and incomplete steps in yellow.
The final report with specific recommendations should be released at the end of August or in early September.

Every Little Bit Helps

I can’t wait to see this report in its final form. During the presentation, the presenter talked about reducing flooding downstream at the West Fork and I-45 by up to six feet if all upstream projects are implemented.

One thing to keep in mind: there is no single silver bullet that can solve the regions flood problems. All of these steps are additive. In my personal opinion, a foot here and a foot there can help offset future releases from Lake Conroe. People in the Lake Houston Area benefit from any and all upstream improvements.

Posted by Bob Rehak with thanks to SJRA and HCFCD

1064 Days since Hurricane Harvey and 313 since Imelda

SJRA Report on Spring Lowering of Lake Conroe

After three months of histrionic, apocalyptic debate about SJRA’s policy of seasonally lowering Lake Conroe, the lowering turned out to be neither the end of the world, nor the salvation of the Lake Houston Area. Simply put, no megastorms tested the policy. So there was no proof that it succeeded or failed.

Instead, regular smaller rains kept the lake close to its monthly averages. Neither drought nor excessive heat caused lake levels, property values, business or tax revenues to plummet. Everything functioned much as it normally has since Lake Conroe was built in 1973.

Lake Stayed Near Monthly Averages

In the two months between April 1 and May 31, the lake only dropped below 200 feet by an inch or two for three or four days and then promptly refilled. In fact, at the end of May, 2.5 inches of rain caused the lake to rise above its seasonal norm, prompting a second release.

Two releases and smaller, spread-out rains kept the Lake Houston Area safe and Lake Conroe close to its monthly averages (200.32 for April and 200.44 for May; see below). Source: SJRA Board Presentation 7/23/20.
Lake Conroe seasonal levels by month for 46 years. In April and May, Lake Conroe averages 200.32 and 200.44 respectively. Source SJRA Board Presentation.

During that time, the Lake Houston Area never flooded. Yet Lake Conroe was above its monthly average for the first three weeks of April. And it was only down about three inches for about three weeks in May.

The assertion that Lake Conroe is “normally” at 201 is a myth. That is the level at which the SJRA normally starts releases. Due to evaporation, which can take an inch a day, the lake is almost always well below that. A more accurate term for 201 would be “full pool.”

River Levels Up Slightly, but No Flooding

West Fork river levels rarely rose more than 2 or 3 feet even when rainfall was added to the release rate from Lake Conroe.

Release rates averaged about 600 cubic feet per second (cfs) and rarely exceeded 1000 cfs.

If the exercise proved anything, it was that releasing at those rates didn’t flood anyone.

River levels vs. rainfall for the last two weeks of the spring lowering. Source: SJRA Board Presentation 7/23/20.

Fall Lowering Starts This Saturday

The Houston Area lucked out with Hanna. Had the storm veered towards us, we would have received the torrential rains that swamped the Valley.

This fall, the lowering will be split into two phases: to 200 feet in August and 199.5 in September. The City of Houston has the right to call for an additional half foot in the event of a named storm.

Restatement of SJRA lake lowering policy for this year. Source: SJRA Board Presentation 7/23/20.

Even though Hanna missed us and Gonzalo fizzled, the next storm may not.

Near-Term Tropical Outlook

The NHC gives this disturbance an 80% chance of formation in the next five days. It’s moving west northwest at 15 to 20 mph and should impact the leeward islands late Wednesday.

The fact that Lake Conroe rebounded so quickly will likely calm debate in the future.

The Lake Conroe level at this instant stands at 200.22 feet. That’s less than half an inch below the July average for the last 46 years. Note that that’s also 3.5 inches above the August average.

Finally, note that the target level for August (200 feet) is about an inch ABOVE the normal monthly average. So if evaporation does its job, the SJRA will not have to lower the lake.

Posted by Bob Rehak on 7/27/2020

1063 Days after Hurricane Harvey

west fork flood during Harvey

NY Times Covers Harris County Flood-Bond Spending, but Omits Spending Data

The New York Times ran a story on flood-bond spending, but forgot to look at where the budget to date has gone.

The story by Christopher Flavelle was titled, “A Climate Plan in Texas Focuses on Minorities. Not Everyone Likes It.” It outlined arguments on each side of the equity debate in flood-bond spending. From a balance point of view, it did a great job. However, it came up short in two areas.

Problems with Article

First, the headline misleads. This isn’t about climate. The story is about how to distribute flood-bond dollars equitably.

Second, it makes no mention of where flood-bond dollars to date have actually gone. Nor does it mention historical spending except in a generalized way. It implies poor people got none; rich people got it all. By avoiding research into actual current and historical spending, it perpetuated myths that do little to protect people from flooding.

Had the author checked, he would have found that those “underfunded,” disadvantaged neighborhoods have actually received 79% of the flood-bond projects to date.

Had he bothered to check historical or federal spending, he might have found an even more exaggerated pattern.

Trap Laid by Ellis

Mr. Clavelle fell into the trap that Commissioner Ellis laid. In effect, the argument goes like this. “Because homes in poor neighborhoods cost less than those in rich neighborhoods, it brings down the benefit/cost ratio for poor neighborhoods. FEMA considers that ratio in grant requests. That disadvantages grants for poor neighborhoods and perpetuates a downward cycle.”

That’s literally true – if you look only at FEMA grants. But it’s the exact opposite for HUD grants which heavily favor disadvantaged neighborhoods. Mr. Clavelle fails to mention that. As do Mr. Ellis and his surrogates whenever they talk on this subject.

Approximately 70% of those HUD grants MUST go to disadvantaged neighborhoods. The actual percentage varies by storm and type of grant. After Harvey, Harris County received a billion dollars. And the City of Houston received $1.1 billion. Together, that’s almost as much money as in the $2.5-billion flood bond. And there are still billions of additional dollars available from HUD through the General Land Office.

Preserve Your Community

If more of this money continues to go south, the Lake Houston Area is sunk in the next big storm.

But the County is considering a Community Resilience Task Force that would institutionalize this spending bias for the next 30 years.

The County Judge’s office is inviting the public to share their thoughts and ideas on the proposed draft bylaws of the Community Resilience Task Force. You can register your opinion from now until July 30th, 2020, via one of the following methods:

  • Email CRTF@cjo.hctx.net and submit comments digitally, beginning July 21
  • Join a virtual focus group via Zoom. After registering, participants will receive a confirmation email containing information about joining the meeting.
  • Offer input during the July 28th Commissioner’s Court

Please express your opinions to the county judge. Nothing is more important to the future of the Lake Houston Area than achieving more balance in flood-bond spending.

Some Key Facts to Consider

Some key points I intend to make:

  • 79% of flood bond projects to date have gone to neighborhoods that rate high on the social vulnerability index leaving only 21% to everyone else. We need to tweak the formula to achieve greater balance.
  • The argument that FEMA’s emphasis on Benefit/Cost Ratios disadvantages minority neighborhoods ignores the fact that billions of dollars in HUD grants advantage minority neighborhoods. Focusing only on one without acknowledging the other is intellectually dishonest.
  • HCFCD and USACE have historically underfunded flood mitigation projects in the Lake Houston Area. In the history of HCFCD, the District has not developed ONE USACE-funded project in this area.

For More Information

For more information on the “equity bias,” see this series on “Where Flood Mitigation Dollars Have Really Gone.” It was developed a year ago so the focus is on historical spending.

Or this series on “Equity”:

Posted by Bob Rehak on 7/25/2020

1061 Days after Hurricane Harvey