Is River Restoration Possible on the San Jacinto?

River restoration may never be completely possible in an urban environment between two major dams. Especially with 20 square miles of sand mines immediately upstream. However, as we seek to reduce sedimentation via various strategies, it’s useful to have a high-level goal in mind, so we can evaluate the usefulness of those strategies in getting us closer to the ideal.

Sand mine dikes along the San Jacinto restrict the floodway and often blow out during floods. During Harvey, 131,000 cubic feet per second swept through approximately 20 square miles of sand mines on the West Fork. Floodwaters also eroded banks up and down the river, resulting in excess sedimentation.

Will SB 2126 Help Restore the River?

SB 2126 is a senate bill designed to reduce sedimentation by removing it from the river in unspecified ways, no permits necessary. I fear that the vagueness in the language could open the door to river mining on the San Jacinto. It passed the Senate yesterday 21-10 without any amendments to clarify the language.

Although proponents talk about restrictions on the practice, the language of the bill contains none.

A Leading Expert in River Restoration

After reading SB 2126, a reader recommended consulting Dave Rosgen, PhD, a Professional Hydrologist and Geomorphologist, to see what he would recommend. His field experience in river work spans 49 years. Twenty of those were with the U.S. Forest Service. He developed:

  • A stream classification system
  • The BANCS streambank erosion model
  • The FLOWSED/POWERSED sediment transport models
  • The WARSSS methodology for cumulative watershed assessment
  • A geomorphologic approach to Natural Channel Design restoration. 

Rosgen has authored Applied River Morphology, Watershed Assessment of River Stability and Sediment Supply (WARSSS), and more than 70 reports and articles in research journals, symposia, and federal agency manuals. Time, Science, 5280, National Geographic, The Denver Post, and The New York Times have all featured his projects.

Rosgen also conducts short courses in watershed management, river morphology, restoration, and wildland hydrology for federal, state, and local watershed managers.

His company, Wildland Hydrology, has implemented more than 70 large-scale river restoration projects in North America, Africa, Central America, and South America.

Rosgen’s Take on River Mining Vs. Other Alternatives

I asked Rosgen, “What’s the best way to reduce unnaturally large rates of sedimentation?”

He started out by describing what NOT to do: “Letting people dredge the San Jacinto River without specific criteria for width/depth ratio and multi-stage channel shape will ensure that sediment deposits return. There are several complex issues in post-flood restoration.”

  1. “A very large portion of sediment supply during high flows is from streambank erosion. If this supply is not reduced, a future repeat is guaranteed along with land loss and increased flood risk. We use toe wood and woody riparian on a bankfull bench against steep high eroding banks to reduce erosion rate and sediment supply in anticipation of future high flows.
  2. “You must shape a channel with a low flow (inner berm) channel, a bankfull channel (normal high flow), and a floodplain surface to efficiently transport sediment. Just dredging and over-widening a channel will result in rapid sediment deposition during normal flows as well as floods.
  3. “The backwater created by the lake will always induce sediment deposition. That’s why you need to reduce the sediment source or supply.
  4. “Shaping a multi-stage channel helps distribute sediment following a lowered lake stage level.  
  5. “Lake levels should be lowered in advance of anticipated runoff events (or during hurricane seasons) to provide more detention storage and reduce the elevation of upstream backwater.

Giving carte blanche for uncontrolled dredging is a license for continued failure without regard to the basic fundamentals. – Dave Rosgen, PhD

Success in Houston Area

“Where toe wood has been placed  with good restoration design in the Houston area, it held up well to Harvey.  We have implemented these recommendations successfully in your area,”  says Rosgen.

“I am about a year away from publishing a book on river restoration. It will describe  design details. Uncontrolled dredging is a short-term solution to a very big problem. That problem can be solved, but not without expense and good designs.”  

In conclusion, Rosgen said, “Uncontrolled river mining will make things worse due to channel adjustment, including increased bank erosion. That’s because a lowered stream bed increases bank height. That will cause new bars to develop rapidly. Hope this helps alert you to problems you will face.”

Giving Nature a Chance to Heal Itself

We are 30 days away from the end of this legislative session. SB 2126 may or may not have enough backers to put it on the governor’s desk. If it gets there, I hope the legislature spells out restrictions. The way it’s worded right now could open the door to wholesale river mining.

On the other hand, we are about 18 months away from the completion of the San Jacinto River Basin Study. Hopefully, we can use that time to inform the community about river restoration strategies and options. When complete, the study may illuminate the way forward.

Efforts as large as this won’t happen overnight. It may take decades and legislation requiring greater sand-mine setbacks. We need to give nature a chance to heal itself.

Posted by Bob Rehak on 5/1/19

610 Days since Hurricane Harvey