Tag Archive for: SJRA

What Happened Downstream During Harvey as Lake Conroe Released 79,000 CFS

Last night, I posted some statistics about Lake Conroe levels after the SJRA started the release during Hurricane Harvey. Tim Garfield and R.D. Kissling, two top geologists, now retired from one of the world’s largest oil companies, have looked at the release from a downstream perspective. Last year, they put everything they learned into this 69-page presentation delivered to the University of Houston Honors Program.

From “A Brief History of Lake Houston and the Hurricane Harvey Flood,” by Tim Garfield and RD Kissling with help from Bob Rehak, 2019.

Recap of Key Points About Lake Conroe Release

To recap several key points:

  • The SJRA never did let Lake Conroe rise to its allowable flowage easement. The water level in Lake Conroe peaked at 7 a.m., August 28, 2017, at 206.23 feet. The SJRA’s flowage easement is 207 feet.
  • Outflow exceeded inflow by 8:30 a.m. on the 28th and stayed that way for the duration of the storm. As the lake level declined, the lake had up to 3 available feet of storage capacity.
  • Yet the SJRA kept releasing, on average, 2X – 10X more water than it was taking in. At one point, the ratio exceeded 100:1.

Tracking the Release Down West Fork

Garfield notes that the discharge ramp up that began the evening of the 27th reached a peak discharge rate of more than 79,000 cubic feet per second (cfs) just before noon on the 28th. The discharge rate didn’t dip below 70,000 cfs until 4 a.m. on the 29th – more than 16 hours later.

Following in lockstep with the Conroe release, flow rates at downstream gauges ramped up, in lockstep. By lining up the peaks of gages downriver, you can literally see the water surging down the West Fork all the way to Lake Houston. (See left side of image above.)

Significantly, Garfield says, these gauges all showed flattening flow-rate curves before the release ramp up. Those curves then turned and steepened upward as the Conroe release pulse arrived at those gauges.


Timing and Impact of Release in Lake Houston Area

Peak flow at the Humble gauge was reached shortly after noon on the 29th, roughly 24 hours after peak discharge was reached at the dam and roughly 30 hours after the high-rate release ramp up began.

Water started creeping under the doors of Kingwood Village Estates, a senior living center in Kingwood Town Center about 1.4 miles from the West Fork, at 3 a.m., on August 29th, 2017. It kept rising all morning and finally stopped another mile further inland. Water entered the last (highest) house to flood in Kings Point (the Kingwood subdivision closest to the main body of Lake Houston) at 2 p.m. that same day, according to Elise Whitney Bishop.

Residents trying to escape as Harvey's floodwaters rose
Kingwood Village Estates residents trying to escape as Harvey’s floodwaters rose. Twelve later died.

The level of upper Lake Houston, as measured at US59, rose an additional 7 feet during this period.

Significant additional flooding of Kingwood homes can be tied to this same period of increased discharge.

Flow rates measured at the Grand Parkway gauge and calculated at the Humble gage indicate a flow rate increase in this period of between 70,000 to 80,000 cfs, corresponding closely to the 79,000+ peak flow rate added by the Conroe dam discharge.

“The data from the affidavits further supports several key conclusions from the Harvey Flood Fundamentals section of our University of Houston talk,” said Garfield. Those include:

  • The large sustained release from Lake Conroe made West Fork flooding worse. The extra 80,000 cfs increased the West Fork flow 50%.
  • The release occurred as the storm was abating. It significantly increased flood damage in the Lake Houston area.
More than 4,400 structures flooded in Humble and Kingwood along the West Fork. Source: HCFCD.

The list of damages ran well over a billion dollars.

The SJRA Argument

The SJRA maintains to this day that Lake Conroe is a water-supply reservoir, not a flood-control reservoir. See the affidavits of Hector Olmos and Chuck Gilman. Olmos is a consultant who helped design the operations manual for the gates at Lake Conroe. Gilman is the SJRA’s Director of Flood Management, hired the year after Harvey.

They are basically claiming, “We don’t have the right tool to prevent downstream flooding.”

Editorial Opinion

Editorial opinion: That excuse has always sounded hollow to me. It attempts to curtail discussion of whether the SJRA waited too long to start releasing water, released too much at the peak, and then kept on releasing too much for days.

That discussion is a matter of public concern that could save lives and property in the future. We need to have it.

Sadly, it will take the courts to figure this out. In the meantime, the SJRA has hired some of the highest priced lawyers in the country and now appears to be angling for legislative immunity by hinting at higher water prices “statewide” if liability can’t be controlled.

It all smacks of similar arguments in other industries. If you’ve lived long enough, you’ve heard them all before, such as car companies that would be driven out of business if forced to install seat belts and other safety features. Well, that prediction didn’t quite work out! Luckily, for General Motors, the addition of safety features helped fuel its resurgence.

Posted by Bob Rehak on 6/12/2020 with thanks to Tim Garfield and RD Kissling

1018 Days after Hurricane Harvey

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.


Region H Water Plan May Ask Legislature To Clarify Potential Flood Liability of Dam Operators

The current draft of the Region H Statewide Water Plan contains a recommendation that many of those who flooded during Harvey may take issue with.

On page 18 of the executive summary, there’s an overview of the recommendation. It requests that “… the State consider legislation clarifying the liability exposure of reservoir operators for passing storm flows through water supply reservoirs.”

Sounds innocent enough. However, the explanation for the recommendation on page 1,411 of the appendices is a little more ominous. I reprinted it verbatim below, but italicized some phrases for the discussion that follows.

Explanation for Recommendation

The explanation says, “Flood control reservoirs are generally drawn down at the beginning of the annual wet season so that when large rain events occur, the runoff may be captured and later released more slowly into the receiving stream. These reservoirs therefore reduce downstream flood levels and prevent inundation in low areas. In contrast, water supply reservoirs are operated to capture and retain as much stream flow as allowable under their permits in order to have supply available during periods of high demand.”

“This practice results in less available storage volume to capture runoff during major storms. When a major storm event occurs upstream or above a water supply reservoir, the reservoir operator must sometimes release flood flows during and after the event to prevent flooding upstream of the reservoir or to prevent damage to the dam and other facilities associated with the reservoir.

“Although this flood flow can contribute to downstream flooding, most reservoirs actually reduce the amount of flooding which could have occurred had the reservoir not been constructed.

“In recent years, plaintiffs with property in the downstream floodplains have brought multiple lawsuits against major water supply reservoir operators. Some recent court decisions have held the operators liable for damages to the downstream properties.

“If this trend is allowed to continue, it will increase insurance rates for these entities and will force operational changes to occur that may result in less available water supply for periods of need. The net effect to water users will be an increase in the cost of surface water throughout the state.”

During Harvey, the SJRA released more than 79,000 cubic feet per second from Lake Conroe.

Sounds Like SJRA

The SJRA has hammered these themes since Harvey.

The text of the explanation sounds as though it is paving the way for a declaration of legislative immunity for Water Authority actions during floods.

Concerns About Recommendation and Explanation

On the surface and in the abstract, the individual claims in the explanation sound reasonable. However, on deeper inspection, they contain logical fallacies, generalizations, false choices, contradictions and questionable assumptions.

  1. The explanation draws a distinction between flood control and water supply reservoirs – as if we have a choice. This area is too flat to allow the construction of classical flood-control reservoirs, such as those described in the text. So our reservoirs must do double duty.
  2. Their rationale only allows the possibility of releasing water during and after the event. It makes no mention of before.
  3. “…most reservoirs actually reduce the amount of flooding…” Hmmm. Is this admitting that they do have a dual purpose? Flood prevention was one of the objectives in the SJRA’s enabling legislation.
  4. “Some recent court decisions have held the operators liable for damages to the downstream properties.” Aren’t courts the proper venues for such decisions? How can the legislature possibly foresee the actions of every operator in response to every storm?
  5. “If this trend continues…” What trend? Aren’t we talking about one event? Sounds like a plea for “legislative immunity” even if the recommendation itself doesn’t use those words.
  6. “…force operational changes to occur that may result in less available water supply for periods of need.” True, but with proper controls in place, might they not also strike a balance between water supply and flood reduction?
  7. “…increase the cost of surface water throughout the state.” If a court finds the actions of one operator deficient, how does that affect the insurance of every other operator in the state?

Real Question

No doubt, low lying properties were doomed to flooding during Harvey by the nature of the storm itself.

But did the SJRA have to open Lake Conroe’s gates when they did, as wide as they did, for as long as they did? Could an earlier, smaller, shorter release have avoided some of the flood damage?

I, for one, would feel much more comfortable having a judge answer questions like that after the fact rather than the having the legislature limit liability beforehand in a blanket fashion. Limiting liability also limits accountability.

Such recommendations buried in a statewide water plan on page 1,411 of an appendix show why the public REALLY DOES need to review this plan and give input.

Once approved in October, all recommendations will carry the weight of a state agency. The legislature rarely acts against such recommendations, especially when heavily lobbied behind the scenes. If you have the same concerns I do, the time to speak up is now.

How to Register Concerns about Water Plan

Here’s how to make your voice heard on this or any other issue in the Water Plan. You need to go through the SJRA.

The Region H Water Planning Group (RHWPG) will accept written comments until 5:00 p.m. June 28, 2020. Written comments should be provided to: Hon. Mark Evans, Chair, RHWPG c/o San Jacinto River Authority P.O. Box 329, Conroe, Texas 77305-0329

Written comments about the water plan without attachments also may be emailed to info@regionhwater.org. Comments will be documented in the summary of public comments in the 2021 Region H Water Plan.

Questions or requests for additional information may be submitted to: Jace Houston, General Manager, San Jacinto River Authority, P.O. Box 329, Conroe, TX 77305-0329, telephone 936-588-3111. The San Jacinto River Authority is the Administrator for the RHWPG.

Posted by Bob Rehak on 6/10/2020

1016 Days after Hurricane Harvey

NHC Gives 40-50% Chance of Tropical Cyclone Formation In Gulf This Week

NHC Special Tropical Weather Outlook NWS National Hurricane Center Miami FL 805 AM EDT Sun May 31 2020 For North Atlantic, Caribbean Sea and Gulf of Mexico:

Source: National Hurricane Center 5 Day Tropical Outlook for Atlantic as of 7:05AM CDT on 5/31/2020

The National Hurricane Center (NHC) forecasts the Eastern Pacific Tropical Storm Amanda, now centered inland over southeastern Guatemala, to weaken into a remnant low or dissipate over Guatemala or southeastern Mexico by tonight.

However, the NHC also predicts that the remnants of Amanda will move northwestward within a broader area of disturbed weather, possibly emerging over the southeastern Bay of Campeche on Monday.

If the remnants move back over water, environmental conditions appear conducive to support some redevelopment of the system while it moves little through the middle of this week.

Regardless of redevelopment, heavy rainfall is likely to continue over portions of southern Mexico during the next few days. For additional information on the rainfall threat, see products from your national meteorological service.

The next Special Tropical Weather Outlook will be by 3 PM EDT today, or earlier if necessary.

  • Formation chance through 48 hours…medium…40 percent.
  • Formation chance through 5 days…medium…50 percent.

 If it does become a named storm, it would be Cristobal.

Tropical Storm Amanda will likely cross into the Gulf of Mexico on Monday. (Source: NOAA via Space City Weather).

Too Early to Predict Direction of Storm

Jeff Lindner, Harris County Flood Control District meteorologist, says, “Where exactly any center forms will determine what sort of longer term track would be possible … across the Gulf of Mexico.”

“Regardless of development,” he continues, “a large plume of tropical moisture will be moving into the SW and eventually the western Gulf of Mexico this week. Some of this moisture will likely get directed toward the Texas coast by late week and next weekend.”

“As with any tropical system in this stage of potential development, there is lots of uncertainty.”

“The best course of action is to monitor weather forecasts daily and National Hurricane Center outlooks for any changes.”

Jeff Lindner, Harris County Flood Control meteorologist

Preparedness

Hurricane season starts tomorrow. The NHC predicts above-average activity this hurricane season.

Source: National Hurricane Center prediction on 5/21/2020.

Now would be a good time to prepare. The major risks in the Lake Houston area include river and street flooding (as we saw with Harvey, Allison and Imelda) and wind damage (as we saw with Ike). Ike led to prolonged power outages due to trees falling against power lines.

Make sure you have fresh batteries and a backup supply, as well as a weather radio.

Also make sure you have a way to charge your cell phone (vehicle or power block). And make sure you learn how to use the Harris County Flood Warning System to increase your situational awareness.

Familiarize yourself with the LINKS page of this website. It contains links to many useful sites specializing in preparedness and weather.

Remember: the COVID crisis presents an extra layer of complication this year.

Lake Level Report

As of this morning, the level of Lake Conroe was 200.23 feet and the SJRA continues releasing 1581 cubic feet per second. Their goal: to bring the lake down to 200 feet by tomorrow.

Also as of this morning, the Coastal Water Authority indicates that the level of Lake Houston is down approximately one foot.

Lake Level41.46 ft.
Normal Pool42.4 ft.
Source: Coastal Water Authority readings as of 7:30am 5/31/2020.

Posted by Bob Rehak on 5/31/2020

1006 Days after Hurricane Harvey

SJRA Resumes Seasonal Release 3 Days Before Scheduled End

For the record, this morning, the SJRA resumed lowering Lake Conroe just three days before the scheduled end of its Spring seasonal release. As of 1PM, the SJRA is releasing 1581 cubic feet per second. Recent rains raised the lake level more than a half foot from the target of 200 feet to 200.53 feet.

Source SJRA.net as of approximately 11 a.m. on May 29, 2020.

SJRA Coordinated with CoH

The lake had risen to approximately 200.4 feet for the last two weeks of May. And, when heavy rains entered the forecast, readers began to ask whether SJRA would lower it to 200 again. However, SJRA did not resume lowering at that time.

Reportedly, the City of Houston was worried about overloading Lake Houston at a time when:

  • Dam repairs were in progress
  • Heavy rainfall was in the forecast

So the SJRA held water back.

What 500 CFS looks like. Photographed 7/31/2018, during a tour of the Lake Conroe Dam. The current release is three times this rate.

According to sources, the Coastal Water Authority has opened its gates on Lake Houston and is coordinating release rates with the SJRA so as not to flood downstream residents.

Exact Text of Spring Lake Lowering Policy

For the record, here is the official SJRA lake lowering policy renewed with some modifications after months of divisive debate. Lake Houston residents wanted the extra buffer against flooding. Lake Conroe residents claimed there was no proof it worked. They also claimed that it was lowering their property values and destroying their tax base.

In the Spring, the policy calls for:

“Beginning April 1, release only an amount of water from Lake Conroe to create a one foot capacity to catch rainfall and storm runoff (from 201’ mean sea level to 200’ msl). Recapture of lake level beginning June 1.”

Average Lake Level By Month for 46 Years

Also note that the lake level rarely reaches 201. The average varies each month depending on rainfall and evaporation. So when Lake Conroe reached 200.53, it exceeded the norm.

Lake Conroe seasonal levels by month. Source: SJRA

We need to watch this closely. In 2.5 days, this release should stop until the SJRA resumes seasonal releases on August 1. Please report any flooding through the contact page on this web site.

Text of Fall Policy

The fall seasonal lowering coincides with the peak of hurricane season. The SJRA Fall seasonal lowering policy states:

Beginning August 1, release only an amount of water from Lake Conroe to create a one foot capacity to catch rainfall and storm runoff (from 201’ msl to 200’ msl). After September 1, increase capacity an additional six inches (from 200’ msl to 199.5’ msl). If a named storm is predicted to impact our region, the COH may initiate an additional release of six inches (to 199’ msl) by notifying SJRA in writing of their call for release. Recapture beginning October 1.

Posted by Bob Rehak on 5/29/2020

1004 Days after Hurricane Harvey

Video From Boat of 7.5-Acre Area in San Jacinto West Fork Mined for Sand

Yesterday, I posted pictures taken from a helicopter of a 7.5-acre sand bar in the San Jacinto West Fork that had been mined without a permit. Then last night, Josh Alberson sent me some video from a boat of the same area. Gabe Gosney, a passenger in Alberson’s jet boat, shot the video on GoPro and wants to share it with the community.

Giant Sand Bar Now Looks Like Example of Pit Capture

The area in question lies on the west side of the river, just south of SH99. When Alberson first saw it, he excitedly texted me, saying he found an example of “pit capture” on the West Fork. The only problem: there was no pit to capture. And no recent flood.

As Alberson sped down the West Fork, he spotted the area and slowed. Gosney shot hand held from the boat. Here’s what the carnage looked like from the river.

3 minute 15 second video by Gabe Gosney of 7.5 acre area in San Jacinto West Fork being mined for sand.

Changes to Riverine Environment

Several things become apparent immediately upon viewing the video.

  • Humans caused extensive damage to the river ecosystem (property of the state).
  • What looked like the edge of a sand bar from 300 feet up in a helicopter is actually small piles of sand left by the miners.
  • River current now flows through the mined area, but at a slower rate than the river itself.
  • Trees that used to form a small part of the edge of the bar in one area have toppled.
The sand bar outlined above in this Google Earth satellite image from 12/1/2019 no longer exists.
It has been mined out of existence.

Alberson says the river was up about a foot to a foot and a half compared to normal because of the SJRA’s seasonal release of 529 cubic feet per second from Lake Conroe. He said the current was quite fast – difficult to stand in. He did not get out of the boat to see how deep the water was in the mined area, but his impression was that it was shallow.

Mining Not Permitted According to Authorities

The TCEQ regulates mining in the floodplain. Texas Parks and Wildlife Division regulates mining in the river. And the SJRA has commissioned a study on the possibility of building “sand traps” in the river.

All three groups say they have no record of issuing any permits for river mining in the San Jacinto.

Potential Dangers

During floods, the dying trees you see in the video will dislodge and float downstream where they will cause property damage or get lodged in bridge supports, form dams, and cause flooding.

When floodwaters spread out in this area, they will slow and deposit their sediment load. However, where the river channel becomes narrower downstream, the river will speed up again and likely accelerate erosion of river banks and other people’s property.

Texas Parks and Wildlife is investigating. More news to follow.

Posted by Bob Rehak on 4/24/2020 with thanks to Josh Alberson and Gabe Gosney

969 Days since Hurricane Harvey

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.

TPWD Investigates River Mining Without Permit on San Jacinto West Fork

A 7.5-acre point bar outside a San Jacinto West Fork sand mine has disappeared, the apparent victim of river mining. River mining is prohibited in many countries because of its dangers. Texas does not prohibit it, but taxes it at a higher rate than floodplain mining to discourage the practice. The dangers include:

  • Upstream and downstream erosion
  • Destruction of riverbanks and river properties
  • Undermining infrastructure (such as bridges and pipelines)
  • Increases in turbidity
  • Lowering of the water table
  • Loss of riparian vegetation.
Location of River Mining on West Fork Just South of Highway 99

No Permits on File With Key Regulatory Bodies

A check with the San Jacinto River Authority (SJRA), Texas Commission on Environmental Quality (TCEQ), and Texas Parks and Wildlife Division (TPWD) showed the following:

A TCEQ investigator has spoken to the Texas Parks & Wildlife Department (TPWD) Wetlands Conservation Program. “If the facility is digging in or very near the water’s edge,” said the TCEQ’s Jonathan Walling, “the facility would most likely need a permit from TPWD.”

Tom Heger of TPWD said Montgomery County Parks & Wildlife officials are investigating.

Compare the satellite image above to the shots below. Google Earth measurements show the sand bar that no longer exists was bigger than most of the pits in the mine itself.

Looking downriver, you can still see outlines of point bar and marks from excavator.
Close up of marks left by teeth of excavator.
Looking toward West Fork where point bar used be. Vehicle tracks lead back to mine behind camera position.
Pits created in the river.
Relationship of river mining to flood plain mine in background.
Well-used road between excavation and mine.
The disappearance of sand is not because of the seasonal release of water from Lake Conroe. Hundreds of bars both up and downstream appeared normal.
Google Earth shows the river to be approximately 350 feet wide at this point.

Texas Rules on River Mining

The State of Texas governs the taking of sand from rivers. See the regulations and laws on this FAQ page at: https://tpwd.texas.gov/faq/landwater/sand_gravel/. Key points include:

  •  If the stream is perennial (flows most of the time), or is more than 30 feet wide between the banks (even if it is dry most of the time), the State claims the bed and the sand and gravel in it as State-owned. 
  • A permit from the Texas Parks and Wildlife Department is required to “disturb or take” streambed materials from a streambed claimed by the State.

According to TPWD, the operator did not have a permit. In fact, no one on the entire San Jacinto river has a permit, according to TPWD.

How River Mining Degrades River Beds/Channels: Academic Insights

San Diego State University summarizes some of the issues associated with river mining. The paragraph below, taken from their excellent website, explains why most governments discourage river mining.

…bed degradation occurs when mineral extraction increases the flow capacity of the channel. A pit excavation locally increases flow depth and a barskimming operation increases flow width. Both conditions produce slower streamflow velocities and lower flow energies, causing sediments arriving from upstream to deposit at the mining site. As streamflow moves beyond the site and flow energies increase in response to the “normal” channel form downstream, the amount of transported sediment leaving the site is now less than the sediment carrying capacity of the flow. This sediment-deficient flow or “hungry” water picks up more sediment from the stream reach below the mining site, furthering the bed degradation process.

G. Mathias Kondolf of the University of California/Berkeley published this illustrated paper on the hungry water effect.

Professor Kondolf also published “Geomorphic and environmental effects of instream gravel
mining.” It contains an excellent, well documented discussion of the impacts of river mining.

SEDIMENT MINING IN ALLUVIAL CHANNELS: PHYSICAL EFFECTS AND MANAGEMENT PERSPECTIVES by M. RINALDI, B. WYZGA and N. SURIAN contains an thorough discussion of the dangers of river mining and public policy. (Warning: Copyrighted paper; costs $49.)

Mine Ownership

According to the TCEQ, the sand mine in the photos is called the Spring Wet Sand and Gravel Plant. Their registration database shows Multisource Sand And Gravel Co., Ltd. owns and operates it, under APO registration number AP0002459. Multisource Sand and Gravel Co. Ltd. is based in San Antonio at 126 East Turbo Drive. It is a subsidiary of Sage LLC. Lee C. McCarty and Benjamin Davis manage it from the Turbo Drive offices.  Daniel E. McCarty and Lee C. McCarty manage Sage.

The mine owners could not be reached for comment. Their phones went unanswered, perhaps because of the COVID crisis.

Posted by Bob Rehak on 4/23/2020

968 Days since Hurricane Harvey

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.

SJRA Starts Seasonal Release to Lower Lake Conroe

After the Easter weekend, the San Jacinto River Authority (SJRA) started its seasonal-release plan. The river authority is currently releasing at a rate of 529 cubic feet per second (CFS) from Lake Conroe. At that rate, the lake should reach its target level of 200 feet above sea level by the end of April, according to Jace Houston, general manager of the SJRA.

Seasonal Release from Lake Conroe, 529 cfs from one tainter gate open six inches.
SJRA Seasonal Release on 4/15/2020. One tainter gate open six inches releases a slow, steady stream of 529 cfs. Image courtesy of SJRA.

The slow rate of release avoids flooding downstream property and the lower lake level provides additional capacity in the lake. That additional capacity provides a buffer against flooding for downstream residents.

About Seasonal Lake Lowering Policy

Houston said the River Authority will hold the lake at 200 feet through the end of May, then allow it to reach its normal level for most of the summer.

Lake Conroe actually reached 200.75 feet before SJRA began its seasonal lowering this week. A reduction of .14 feet equates to about one and two-thirds inches of lowering so far.

At 200.75 feet, Lake Conroe was actually above its highest average monthly level for the year, which is 200.44 feet in May. The normal level for April is 200.32 feet.

Lake Conroe seasonal levels by month. From SJRA board presentation by Chuck Gilman in January.

Earlier this year, a bitter fight broke out between upstream and downstream property owners over the seasonal lake lowering policy. The SJRA board decided to extend the lake lowering plan, but modify it. In the fall, they will let the City of Houston, which owns two-thirds of the water in the lake, decide whether to take the lake down below 199.5 feet.

The extra lowering in the fall helps protect against hurricanes and tropical storms, such as Harvey and Imelda. The SJRA begins slowly lowering the lake in August for the peak of hurricane season in September and then letting it resume its normal level again in October. For the exact details of the policy adopted by the board in its February meeting, click here.

Lake Houston Level Declining

Despite the start of the seasonal release and last week’s rains, the level of Lake Houston has declined this week. And rivers are far from flooding.

Normal level for Lake Houston is 42.5 feet, but City is still lowering lake for spillway maintenance.

Uncertain Weather for This Weekend

Jeff Lindner, Harris County meteorologist, predicts that storms this weekend could bring several inches of rain. “With the Gulf of Mexico water temperatures running several degrees above average for this time of year, winds blowing off the Gulf will need little time to supply a rich moisture-laden air mass.” 

The NWS predicts a 30-40% chance of showers and thunderstorms for this weekend as a front passes. However, Lindner notes, models diverge widely in their predictions. The Global Forecast System (GFS model) predicts that most rain will happen over the Gulf with little impact to land.

However, the European Medium Range Forecast Model (ECMWF) predicts a very wet weekend with several rounds of storms and several inches of rainfall for much of southeast Texas.

Which Model is Better?

ECMWF is considered one of the premiere global forecasting models for the mid-latitudes. Statistically, it has been more accurate than the GFS model.

NOAA has tripled spending on supercomputing capacity to make GFS the best model in the world again.

Posted by Bob Rehak on 4/15/2020

960 Days after Hurricane Harvey

HCFCD Partners with SJRA on Sediment Trap Project

The SJRA announced earlier this week that the Harris County Flood Control District will partner with the River Authority on a “sediment trap” pilot study for the East and West Forks of the San Jacinto. The two have hired engineering firm Freese & Nichols to conceptually design the traps and identify the optimal locations for them.

Finding the Right Combination of Factors

Most sediment traps are big holes dug in a river or channel though some are off to the side. As water passes them, velocity decreases. Suspended sediment and sand being pushed along the river bed fall into them.

Source: EPA. The hole reduces water speed which accelerates deposition in a fixed location that’s easy to clean out.

Sediment traps vary by depth, width, length, shape (wide, long, triangular, etc.), and placement relative to the channel. And as this Army Corps study shows, modifying any one of those factors can greatly affect their efficiency. The challenge: to find the optimal shape, size and location.

The optimal length, for instance, depends on the speed of floodwaters and the settling rate of sediment particles. The trap needs to be long enough to give suspended sand time to fall out of suspension. Otherwise, sand just passes over the trap and continues downriver.

The hope: that the right type of traps placed in the right locations could help reduce flooding by reducing the amount of sediment migrating downriver and then blocking the mouths of each river branch.

Coming Out of HB1824 and River Basin Study

House Bill 1824, passed just last year, helps make sediment traps financially feasible. It allows the partners to remove material from the San Jacinto River and its tributaries to restore, maintain, or expand storm flow capacity without the need for state permitting or a royalty payment to the state.

Also note that the project will use data developed for the San Jacinto River Basin Master Drainage Study. It started in April of 2019 and is now about two-thirds complete.

Scope of Work Outlined

The scope of work outlined for Freese & Nichols includes, but is not limited to:

  • Reviewing and comparing: current and historical LiDAR surveys and aerial photos to gauge sediment erosion, deposition and location
  • Evaluating digital elevation maps to identify constrictions
  • Identifying the ten areas with the largest volumes of sediment deposition, including the two largest at a sand mine.
  • Reviewing FEMA floodplain, National Wetland Inventory, Texas Historical Commission and Texas Parks and Wildlife information for any problems related to each potential site.
  • Core sampling of sand bars to determine silt content
  • Ranking preliminary locations using the following: sediment deposition volume, potential sediment storage volume, proximity to existing roads, proximity to existing APO facilities.
  • Selecting the four locations with the highest potential based on drainage area, sediment load, geology, road access, etc.
  • Narrowing that to three locations in conjunction with SJRA and HCFCD
  • Developing sediment trap conceptual solutions specific to each of the final three selected sites
  • Estimating rate of sediment accumulation and clean-out intervals
  • Estimating reduction of sediment accumulation due to trapping
  • Submitting a final report.

The project does NOT extend into Lake Houston. Freese & Nichols will examine both the East and West Forks plus three miles upstream from the East and West Forks along certain tributaries. Tributaries would include, for instance, Lake Creek and Caney Creek. The idea is to intercept sediment before it can make its way into the lake.

Project Timing

The project timetable indicates completion in early fall of 2020, about the same time as the entire San Jacinto River Basin Study. Thus, any recommendations coming out of this project would not be constructed for this hurricane season. SJRA currently hopes to have the trap(s) installed by the end of 2022.

Pros and Cons of Sediment Traps

Proponents say sediment traps can reduce expensive dredging, restore fish habitat, reduce flood risk and more. However…

The scientific literature on sediment traps reveals mixed reviews. Many efforts fail, primarily because of lack of maintenance budgets and regular clean-outs. The SJRA and HCFCD plan to address that issue upfront by involving the sand mining industry. Notice that of the four location-ranking criteria bolded above, three favor proximity to sand mines:

  • Sand mines have pits to store sediment.
  • They have roads that lead to the river that can carry heavy equipment.
  • Mines have cleaning, sorting and transportation facilities onsite to reduce transportation costs, and thus make material more attractive for resale.

Compensation for Sand Miners

A compensation agreement for sand miners who remove sediment from traps has not yet been worked out. However, Matt Barrett, SJRA’s project engineer, says, “The intended benefit to the APOs of participating in the public-private partnership would be that they could utilize or sell the material they remove from the trap(s). ” 

Concerns of Environmental Groups

One of the concerns environmental groups have had about HB1824 (which began life as SB2126) is that it could potentially open the door to river mining and all of its risks.

River mining is outlawed in Europe, many other first-world nations, and even in some third world countries.

It tends to alter the gradient of rivers; cause upstream and downstream erosion; destroy private property along river banks; and undermine infrastructure such as bridges and pipelines.

Thus, the sediment traps raise a question of potential liability. If a pipeline or bridge is undermined or if property is eroded by the traps, who is responsible?

“Stability of the river is key to the long term safety and well-being of our community. We know that our public agencies have an important task. Before spending additional taxpayer dollars, don’t we want to make sure that projects won’t make problems worse AND won’t raise taxpayer costs?” said Jill Boullion, Executive Director of the Bayou Land Conservancy.

SJRA Response to Concerns

The SJRA has consistently denied that it would permit wholesale river mining. Most recently, Matt Barrett, the River Authority’s engineer for the sediment trap project said, “SJRA has no intention of engaging in or facilitating river mining in the San Jacinto River or any of its tributaries. The legislative language in HB1824 allows for the removal of material for the purpose of restoring, maintaining, or expanding the capacity to convey storm flows. Any projects undertaken by SJRA to remove or facilitate the removal of material from the San Jacinto River or its tributaries would be for this purpose.”

“River mining is not part of what we are doing. Only sediment in the trap will be removed,” he said.

Barrett is aware of potential hazards. “SJRA and its consultant are aware of the potential negative impacts that can be caused by trapping and removing sediment from a river or stream – changing the sediment balance – and prior to constructing any sediment trap or implementing removal of any material will perform analysis to ensure that any potential negative effects do not offset the positive.”

He sees the current design project as part of a pilot study that can scale up later. “One of the goals of this relatively small scale project is to serve as a “pilot” that gives us data on the real-world effectiveness of sand traps.  If data indicates this is a viable flood risk mitigation solution, then additional funding and partnerships could be sought to expand the concept.  We are excited to start this project and seek solutions to reduce flood risk.

For More Information

For more on how on sediment traps work, see this presentation found on the EPA site about a project in Michigan. It’s not directly analogous to south Texas because rainfall rates, soil types and gradients differ. But helps explain the theory of traps.

Click here to see Freese & Nichols’ full scope of work on the sediment trap project on the San Jacinto.

Posted by Bob Rehak on 4/3/2020

948 Days after Hurricane Harvey and 197 since Imelda

Lake Conroe Level Now Exceeds Average for April a Week Early

The rain earlier this week continues to filter into Lake
Conroe and raise the lake level. As of today at 3 p.m. today, the level reached 200.35 msl (mean feet above sea level).

Lake Conroe level as of 3pm on 3/24/2020

That means the lake level now exceeds the average for April – and there’s still a week left in March. With additional rain or inflow, the lake could soon reach its highest point in an average year.

Monthly variation in average levels of Lake Conroe dating back to 1973 when the dam was built.

The highest monthly average happens in May when the lake reaches 200.44 feet. That means the lake is now 0.09 feet (1.08 inches) from its average annual peak in May.

That also means that the SJRA will begin releasing water on April 1 as part of its seasonal lowering plan to reduce flood risk to downstream communities.

Posted by Bob Rehak on 3/24/2020

938 Days since Hurricane Harvey

Additional Rain Puts Lake Conroe Within 1 inch of April Average

Yesterday, I posted about rains that quickly brought Lake Conroe back up to its average for March. Additional rain last night and today brought the lake up another 3.24 inches to 200.23 as of 9pm on 3/22/2020. That means the lake is now within about 1 inch of its average level for April.

Source SJRA.net. Readings as of 9pm on Sunday, March 22, 2020.
46-year average levels for Lake Conroe. Variation due to rainfall, evaporation and releases. Source: SJRA.net. Chuck Gilman presentation and January 2020 board meeting.

This now means that SJRA would release enough water starting April 1 to reduce the level of the lake to 200 feet above sea level. If the lake remains at this level, that would mean lowering it about 3.24 inches starting April 1.

The purpose of the SJRA’s temporary seasonal lake lowering program: to provide a margin of safety against flooding until downstream mitigation measures can be put in place. Those include West Fork mouth bar dredging and additional floodgates on Lake Houston to lower the level of the lake faster during a flood.

Renewal of the policy was the subject of a bitter fight between Lake Conroe and Lake Houston between December 2019 and February 2020. It culminated in a board meeting attended by approximately 1500 residents from both communities.

Posted by Bob Rehak on 3/22/2020

936 Days since Hurricane Harvey