Now is the Time to Start Thinking about Maintenance Dredging

As we prepare to dredge portions of the West Fork of the San Jacinto River for the first time, it’s also time to start planning and budgeting a regular maintenance dredging program. Let’s make sure that’s included in the August 25th $2.5 billion flood bond referendum.

Back in 2000:

Before the exponential growth of sand mining along the West Fork
Before four 500-year storms
Before flood plain maps were redrawn
Before Conroe became America’s fastest growing city

…Brown & Root conducted a Regional Flood Protection Study for the Lake Houston Watershed Flood Program. At that time, Brown & Root recommended dredging as the best option to deal with sediment in the river that had accumulated from major floods in 1994 and 1998. They also recommended regular maintenance dredging every five to 10 years.

Engineers concluded (on Page E-5), that, “…channel enlargement, primarily through sediment removal, was considered one of the more practical alternatives for achieving flood-level reduction” in this area.

Importance of Maintenance Dredging

On page 47 of its report, Brown & Root also states, “Based on the estimated sediment rate, it is expected that regular maintenance dredging at five to ten-year intervals may be necessary in maintaining the current channel conditions.”

But no dredging ever took place, even though (in conclusion on page 70) Brown & Root said, “…sedimentation may progressively aggravate future flooding as depositional areas develop in the area downstream of the Lake Houston Parkway bridge toward Lake Houston. Sediment control along the West Fork channel can be an effective means to minimizing these continued sedimentation problems.”

Ignoring Recommendations Proved Costly

Today, that report sounds prophetic. Sedimentation is exactly what happened where Brown & Root said it would happen. Here’s how the West Fork looks today where it joins Lake Houston.

During the three 500-year floods in the last three years, this West Fork sand bar at the head of Lake Houston grew exponentially. Engineers say that sediment is not being carried out into Lake Houston (background) as expected.

Major Changes Since 2000 that Have Exacerbated Flooding

Since the Brown & Root report, several major things have changed that make dredging, as well as maintenance dredging, even more important:

We’ve been hit by four “500-year storms” (2001, 2015, 2016, 2017). They left massive amounts of sediment in the river that have blocked drainage ditches and backed up the river itself.
Development has boomed between here and Lake Conroe. Upstream development brings more water to the river faster, exacerbating downstream flooding.
According to the Houston Chronicle, the National Oceanic and Atmospheric Administration is redefining a 100-year flood for Harris County. Instead of basing it on 12 to 14 inches of rain in a day, the new standard will be 15 to 18 inches. Said another way, many homes that weren’t in the 100-year flood plain soon will be. That’s because a 100-year flood will be based on a greater volume of rain.
Sand mining on the West Fork has radically increased. The orange outlines on the first map below show the locations of sand mines between Lake Houston and Conroe today. Note also the one East Fork mine.

Orange outlines show sand mines currently upstream from Lake Houston area. FM1960 Bridge over Lake Houston is in bottom right of image. Courtesy of Google Earth.

This next image from 1999 shows how many fewer sand mines existed then and how many fewer acres they occupied. Note the changes within the outlines.

At the time of the Brown & Root survey, upstream sand mines occupied approximately one fourth the acreage that they do today.

Maintenance Dredging Could be Included in New Flood Bond

The proposed Harris County flood bond initiative currently includes language that would permit dredging of the West Fork and drainage ditches.

It is important to remember when considering this bond proposal that the US Army Corps of Engineers is only returning the river to pre-Harvey levels. That’s because they’re working with FEMA money which can only be used on Harvey-related damage.

The Harris County bond proposal, in its current, not-yet-final form states that bond funds may be used for…

…FINANCING FLOOD CONTROL PROJECTS FOR THE DISTRICT, INCLUDING … CONSTRUCTION OF IMPROVEMENTS, INCLUDING DETENTION BASINS, CHANNEL MODIFICATIONS AND OTHER WORKS SUITABLE FOR USE IN CONNECTION WITH FLOOD DAMAGE REDUCTION, AND FOR THE MAINTENANCE AND OPERATION OF SUCH IMPROVEMENTS…

Upcoming Meetings: Bond Meeting Postponed

The Harris County Flood Control District originally scheduled for 6pm on June 14th at the Kingwood Community Center has been postponed due to a conflict with Ed Emmett’s schedule. Stay tuned for updates on the new meeting date. Your attendance is important. Let’s clarify the County’s position on additional dredging and whether they support it. The language above seems sufficient to permit it, but we should clarify that.

And please also attend the meeting on June 11th, starting at 6:30pm, also at the Kingwood Community Center. It will feature the dredging project manager from the US Army Corps of Engineers.

When Dredging Will Help the Most

Dredging alone will not save many people from another storm as intense as Harvey. However, preliminary modeling suggests it could be valuable in preventing flooding from smaller and more frequent events, such as 25-, 50- and 100-year storms. Dredging and maintenance dredging are important parts of a more comprehensive solution to flooding in this area.

Posted on June 4, 2018 by Bob Rehak

279 Days since Hurricane Harvey