San Jacinto Master Drainage Plan Uses Gage UPSTREAM from Sand Mines to Estimate West Fork Sedimentation
Appendix F of the San Jacinto River Basin Master Drainage Plan discusses the sediment contribution to Lake Houston of various tributaries. It asserts that Cypress Creek, Spring Creek, and West Fork sub-watersheds are the highest contributors of suspended sediment to Lake Houston, contributing an estimated 38.7 percent, 26.8 percent, and 13.0 percent of the total sediment load, respectively.
However, to measure sediment on the West Fork, the study team used a gage at I-45 – UPSTREAM from virtually all West Fork sand mines. This explains a huge disparity between measured data and visual observations. But the report never even acknowledges the visual observations.
I have previously posted about the 3600-page master plan. In many respects, it is a masterpiece that contains good and valuable information that will help mitigate flooding throughout the watershed. The comments in this post relate ONLY to Appendix F on sedimentation, which in my opinion contains a serious flaw.
Misleading Impressions
The problem with using the gage at I-45: it rules out certain contributions to sedimentation that the report barely acknowledges.
Cypress Creek and Spring Creek combine before merging with the West Fork. Thus, you would expect five times more sediment coming from Spring and Cypress Creeks than the West Fork, based on their findings. Yet almost every time I photograph the confluence of the West Fork and Spring Creek, I see more sediment coming from the West Fork, despite the fact that Lake Conroe blocks sediment coming from the upper part of the watershed. See below.
Location of West Fork Gage Never Fully Specified in Report
The West Fork gage number is listed on page 114 of Appendix F. But the description says only, “W Fk San Jacinto Rv nr Conroe Tx, Gage #08068000.” At another point (page 115), it lists the gage near Lake Conroe. To find the exact location of the gage, one must go outside the report to a USGS site. Then to see where the gage sits relative to West Fork sand mines, one must back up to page 61 of Appendix F. Most readers will just assume, given the scientific nature of the report, that the authors used a gage at a representative location, not one that ruled out sediment from sand mines.
Even a careful reader of the report could conclude that the contribution of sand mines to sedimentation is minor in the grand scheme of things. TACA would welcome such a conclusion.
The report ignored thousands of photos posted on ReduceFlooding.com as well as TCEQ reports citing sand mines for non-compliance.
The implications of measuring sediment upstream from sand mines, overlooking visual evidence, and ignoring official reports calls into question some of the report’s recommendations. For instance, #2 suggests using “existing [emphasis added] stream gage data” … to “inform where higher suspended sediment is originating within each sub-watershed.”
Sorry, you can’t get there from I-45. And if sand mines are an issue, neither can you get there from LIDAR surveys taken every several years, which the report also recommends. Sand mine discharges happen frequently and sporadically, often under the cover of darkness.
Sand Mining Not Seriously Considered as Possible Source of Sedimentation
The report, for the most part, blames sedimentation on new development and stream bank erosion. It does not consider:
Sedimentation Report Needs More Gages
You can’t document the volume of such breaches and illegal pumping from a helicopter. However, you can’t overlook such practices either.
What we really need is a sediment gage downstream from the sand mines just before the West Fork joins Spring Creek. A gage at that location would go a long way toward calculating the volume of sediment escaping from sand mines.
Report Also Needs Revision Before Legislative Committees Meet on Sand Mining
The authors also need to amend this report quickly. The amendments should highlight the location of the West Fork gage, the implications of that, and limitations on the use of the data – especially by the legislature.
My biggest fear is that sand miners will attempt to use this report to defeat reasonable legislative reforms of the industry. They have used similar reports in the past to do exactly that. I have personally testified in four House and Senate committee hearings about sand mines only to have TACA trot out figures from the 2000 Brown and Root Study. B&R drew similar conclusions because it used the same West Fork gage at I-45.
To protect the scientific integrity of its report and the validity of its recommendations, the authors need to act quickly. The legislature is considering new sand mining regulations at this instant. Such regulations could protect downstream residents from excess man-made sedimentation, huge dredging costs and potential flooding.
The Master Drainage Plan, including Appendix F on sedimentation, is intended to guide flood mitigation efforts for the next 50 years and help inform the expenditure of potentially billions of dollars during that time. The larger report has many good points. But Appendix F is seriously flawed. I hope the partners – City of Houston, SJRA, Montgomery County, HCFCD and their consultants – fix it before lasting damage is done.
Posted by Bob Rehak on 1/28/2021
1248 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.
