Tag Archive for: sedimentation

Have You Given Feedback Yet to TWDB on State Flood Assessment?

Last weekend, I posted about a statewide flood assessment by the Texas Water Development Board (TWDB) that will help shape public policy toward flooding. After reading the report, I became concerned by the lack of a serious discussion about the role of sedimentation in flooding. So I urged readers to send feedback before Wednesday at 5pm – the close of public comment.

If you haven’t had time to read the report yet…

Consider sending an adaptation of the email below.

Address email to: 

PUBLIC-COMMENT@twdb.texas.gov

In subject line put:  

Public Comment on State Flood Assessment

First, thank you for an excellent report. I support all of your findings, but am concerned about one critical omission: sedimentation.

I live n the Humble/Kingwood/Lake Houston area. Sedimentation was and still is a major contributing factor to flooding here. The Army Corps of Engineers agrees. As a result, as taxpayers, we’re about to spend hundreds of millions of dollars on dredging. It could take a year or more to unclog our river and drainage ditches.

Here’s an example of a sand bar that largely formed during Harvey, blocks the San Jacinto West Fork where it meets Lake Houston. This giant bar elevated flood levels throughout the highly populated Humble/Kingwood corridor where more than 3300 businesses and 16,000 homes were damaged or destroyed.

Sadly, a large part of the sediment we received during Harvey was preventable. It came from sand mines upstream from us on both the East and West Forks of the San Jacinto. While this sand didn’t cause the flood, it exacerbated the flood.

Moving sand mines out of the floodway would be a simple way to reduce sedimentation and flood risk. Many states have minimum setback requirements in their permitting procedures and best practice guides. Texas has no such requirement. Neither does Texas require sand mines to:

  • Reclaim land when a mine is played out.
  • Slope banks to reduce erosion and strengthen dikes.
  • Avoid clearing land until it is ready to mine.
  • Post performance bonds to cover the cost of damage they cause.

Simply observing common-sense best management practices used in other states and countries could radically reduce the sediment escaping from sand mines during floods.

Additionally, I would point out that some counties (like Montgomery) may unwittingly encourage sand mining by giving miners timber exemptions on their real estate tax that they don’t qualify for.

For instance, one Montgomery County mine on the East Fork pays $288 a year in tax on 218 acres! All because of a timber exemption that hasn’t been valid for more than a decade!

It’s a pattern. In 53 out of 53 Montgomery County sand mine properties the ReduceFlooding.com examined, not one was appraised as a sand mine! More than 90% were appraised as vacant land or ag/timber even though they were not vacant and they had no trees. So, my suggestions are to:
  • Recognize the contribution of sedimentation to flooding
  • Document sources of sedimentation
  • Encourage legislation that reduces sedimentation from the sources we can control.

Thanks.

Sincerely,

(Your Name and contact info)
Posted by Bob Rehak on 10/2/2018
399 Days since Hurricane Harvey

Sand Mining Best Management Practices: Vegetation

Sand mining best practices throughout the country and the world urge operators to leave vegetation in place until they are ready to mine an area. The reason: to reduce erosion. However, approximately 60 acres of the sand mine below on the East Fork of the San Jacinto where it meets Caney Creek and White Oak Creek was cleared but not mined – just in time for two 500-year floods.

Approximately 65 acres of this mine were cleared before two five-hundred year floods, contributing to downstream sedimentation in the East Fork, even though only about three acres of the area was mined.

Removing Vegetation Risks Sedimentation Downstream

The cleared area lies totally in the 100-year flood plain and was inundated. Satellite images of the area downstream from the cleared land show a sudden buildup of sand. While the sand did not all come from the cleared area, one wonders how much sedimentation could have been prevented by following best practices.

The following sequence of images shows the rapid removal of vegetation.

The white outlined area will be totally cleared before Harvey. On April 8, 2014, it was all dense forest. 

By March 3, 2016, most of the area was cleared.

By January 23, 2017, just before Harvey, the area was entirely cleared.

Risk from Flooding

This FEMA flood hazard map shows that the entire area lies within with 100-year flood plain (aqua) and adjacent to the floodway (cross-hatched area).

Before and After: Results

This image from 2014 shows the area in question when it was still forested. Note how little sand is in the river downstream from the mine.

Here’s the same view after vegetationwas cleared and the area was inundated by Harvey in 2017. Note all the sediment in the river downstream.

Much of the sand and sediment washed downstream is invisible to satellite photos because it’s under dense forest canopy. This area (downstream the sand mine being discussed) was once wetlands. A boardwalk through those wetlands had to be excavated from several feet of sand after Harvey.

Here’s what part of the same trail looked like before it was excavated. Approximately 30 acres of the park were blanketed with dunes up to 10 feet tall after Harvey. Every trail in the park required repairs. Total cost: approximately $200,000 to Kingwood residents.

A bird’s nest that was ten feet up in a tree is now knee high. Many of the trees along the Eagle Point trail in East End Park are buried under so much sand that they are dying. 

An Ounce of Prevention

It’s impossible to tell how much of the sand above resulted from the removal of vegetation?  Previous posts showed how the mines stockpile also eroded. The river itself contributed sediment. However, if the mine were not in the flood plain and if the miners had not removed so much vegetation so far in advance of mining, we wouldn’t be having this discussion.

So why do miners favor the floodplains and floodways? Why to they remove vegetation years before it will be mined? Is it all about the relentless pursuit of efficiency at the expense of safety?

Tomorrow, we will look at economics, taxation and how some well-intentioned laws passed in the late seventies to protect family farms helped fuel a boom in sand mining.

Posted September 24, 2018

391 Days since Hurricane Harvey

TCEQ Approves SJRA and City Plan to Temporarily Lower Lake Conroe

This morning, I received a press release announcing that the Texas Commission on Environmental Quality (TCEQ) had approved the joint decision by the City of Houston and the San Jacinto River Authority to temporarily lower the level of Lake Conroe during the peak of hurricane season. The lake will be lowered by two feet from 201 mean feet about sea level (msl) to 199 msl between mid-August and the end of September. This will provide buffer against flooding while the Army Corps of Engineers removes excess sediment from the West Fork deposited by Hurricane Harvey that is exacerbating flooding. Because this has legal implications and the Lake Conroe Association fought the lowering, I’m reprinting the entire text of the press release below…with special thanks to Houston City Council Member Dave Martin, Mayor Sylvester Turner,  and SJRA Board Members Kaaren Cambio and Mark Micheletti who lobbied long and hard for this. Also to all the Lake Houston and Lake Conroe residents who made the trek to testify about this issue to the SJRA board.

Text of Press Release

CITY AND SJRA RECEIVE APPROVAL TO MOVE FORWARD WITH TEMPORARY FLOOD MITIGATION PROPOSAL FOR LAKE HOUSTON AND LAKE CONROE

Texas Commission on Environmental Quality will use “enforcement discretion” if flood mitigation releases for Lake Houston and Lake Conroe exceed annual water rights

HOUSTON, TEXAS – Hurricane Harvey deposited tremendous amounts of silt in the West Fork of the San Jacinto River. The silt physically changed the river’s ability to safely pass flows during storms and created the need for a significant dredging project to restore the river’s capacity. As a temporary flood mitigation solution, the City of Houston and the San Jacinto River Authority (SJRA) proposed a temporary, joint reservoir operations strategy for Lake Houston and Lake Conroe. The temporary flood mitigation would be in place for up to two years or until the dredging project is completed.

The proposed strategy involves the pre-release of water from Lake Houston immediately prior to certain storms and the seasonal lowering of Lake Conroe’s water level during the Spring and Fall.  

A significant hurdle to final consideration of the proposed temporary strategy was a decision by the Texas Commission on Environmental Quality (TCEQ) on how releases of water from the two reservoirs would be “accounted for” by the state. TCEQ issues permits that limit how much water can be diverted each year from water supply reservoirs like Lake Houston and Lake Conroe.

The proposal from Houston and SJRA highlights the difficulty of balancing the state’s long-term need for reliable water supplies with the short-term goal of protecting public health and safety while emergency measures are implemented to reduce flood risks.

In a letter to the City of Houston and SJRA on Friday, June 15, 2018, the TCEQ expressed its intent to use enforcement discretion to allow the two agencies to move forward with finalizing their temporary flood mitigation strategy.

The letter states that “if flood mitigation releases . . . result in an exceedance of the annual permitted amounts for diversion or release by SJRA of the City of Houston, the TCEQ Executive Director will exercise enforcement discretion with respect to such exceedance.” The TCEQ’s decision acknowledges the importance of accounting for all diversions from the state’s water supply reservoirs, but it also recognizes the emergency nature of the flood mitigation work being conducted in the San Jacinto River.

The City of Houston and SJRA express their sincere appreciation to the leadership and staff at the TCEQ for their thoughtful consideration of the unique flood challenges that our region is facing. We look forward to finalizing the details of our proposed joint reservoir operations strategy. Additional details on the project including a timeline will be provided as they become available.

ABOUT HOUSTON PUBLIC WORKS

Houston Public Works (www.HoustonPublicWorks.org) is responsible for streets and drainage, production and distribution of water, collection and treatment of wastewater, and permitting and regulation of public and private construction covering a 627-square mile service area. Houston Public Works is accredited by the American Public Works Association. Facebook & Twitter:@HoustonPWE

ABOUT SAN JACINTO RIVER AUTHORITY

Created by the Texas Legislature in 1937, the San Jacinto River Authority is a government agency whose mission is to develop, conserve, and protect the water resources of the San Jacinto River basin.  Covering all or part of seven counties, the organization’s jurisdiction includes the entire San Jacinto River watershed, excluding Harris County.  SJRA is one of two dozen river authorities in Texas, and like other river authorities, its primary purpose is to implement long-term, regional projects related to water management and development. For more information, visit www.sjra.net.