Dredge Finally Reaches Mouth Bar
The Army Corps of Engineers announced last week that it had received a mission assignment from FEMA to dredge 500,000 cubic yards in the area of the mouth bar of the San Jacinto West Fork. This week, the dredge operated by Great Lakes was sighted within 200 yards of the bar. (See videos below.)
Dredging Could Start Next Week
Officials close to the project say actual dredging could start as early as next week. Dredgers only need more 24″ pipe to pump the sediment 10 miles back upstream to placement area #2, an old sand pit near Kingwood College. However, the City and Corps are still debating the volume deposited by Harvey. The Corps has not yet divulged where it plans to start dredging, what its objectives are for this phase of the project, or what the contributions of other partners will be.
More Meetings Needed to Finalize Volume
All parties will meet in the coming days to finalize the volume and a plan. The City of Houston and Army Corps are still 900,000 cubic yards apart in their estimates of the amount of sediment deposited by Harvey. The City hopes to get the Corps to increase its estimate of 500,000 cubic yards. However, that hasn’t happened so far. Meanwhile everyone wants to reduce flood risk by removing as much sediment as possible before the peak of hurricane season.
New Drone Video of Mouth Bar by Jim Zura of Zura Productions
New drone footage of the West Fork mouth bar shows just how much the mouth bar has grown since Harvey. I took the still shot immediately below from a helicopter two weeks after Harvey. To see what it looks like today, scroll down. Kingwood-based Jim Zura of Zura Productions shot two new drone videos this morning. They show what the mouth bar looks like 22 months later. As you watch the videos shot from different elevations, consider the immensity of the bar compared to the dredge at the tail end of each video.
How Far Would 500,000 Cubic Yards Get Us?
Five hundred thousand cubic yards will not come close to restoring the full conveyance of the West Fork. How does 500,000 cubic yards compare with what NEEDS to be dredged?
Let’s start by looking at the channel that the Corps is dredging upriver and assume that they will extend that between the mouth bar and Atascocita Point. That strategy follows the relict channel. The relict channel is also the path with the least sediment at the moment. So that would make the most efficient use of funds.
Let’s also assume that the channel needs to be dredged an average of five yards (15 feet) deeper than its current depth along that path in order to match the profile below.
A “budget” of 500,000 cubic yards would allow you to dredge a channel 133 yards (400 feet) wide 5 yards deeper and 752 yards long. That equals 500,080 cubic yards. But 752 linear yards is only about one-fourth of the 3,000+ yards to the FM1960 bridge. And we haven’t even touched the mouth bar!
Extending the channel through the bridge is important because of the sediment built up behind it.
Clearly, dredging the rest of the way to the bridge will require more money from the State, County and/or City. Thankfully for the Lake Houston Area, all of those entities have already allocated funds.
Details Yet to Work Out
However, the City, Harris County, and State of Texas have even more hurdles to clear beyond the volume debate.
They must find a suitable storage site that can accommodate all the sediment they hope to dredge. The storage site represents the biggest obstacle at the moment and a limiting factor.
The Corps would prefer a below ground site, i.e., an abandoned sand pit. That would reduce the risk of future floods carrying sediment back into the river. Also, it would NOT encroach on the flood plain.
Finally, the closer the site is to the dredging, the faster and cheaper the project. Long pipelines lead to more breakdowns. And each additional booster pump uses 1000 gallons of diesel per day.
Latest on Madden Property
The largest property evaluated so far is a 4000-acre site owned by Berry Madden of Humble. Madden’s property is close – half the distance of the sand mine on Sorters Road. It is also large enough to accommodate all the sediment people want to remove – including sediment from maintenance dredging down the road. Permitting one property instead of several would save lots of time (perhaps years).
But storage on Madden’s property would be above ground. Until someone builds on it, that introduces an element of risk that below-ground storage does not have. Madden has conducted an environmental survey of his property and is now conducting an archeological survey required for a storage permit. The Corps has not yet approved his property.
A source close to negotiations says the Corps is considering approving half of the Madden site for now while it performs additional evaluations of the rest of the site. That might be enough to accommodate immediate needs, reduce the cost of pumping sediment ten miles upstream, and provide storage room for future maintenance dredging.
80,000 CY More Sediment Deposited Since Last Survey
Meanwhile, time and sediment march on. Sources say the Corps recently found another 80,000 cubic yards of sediment deposited in the mouth bar area since the last survey after Harvey.
This supports the theory of two top local geologists, RD Kissling and Tim Garfield, who predicted that the mouth bar would form a dam that accelerated sedimentation. That theory also explains why the mouth bar must be removed, or at least why we must dredge a channel around it ASAP.
Posted by Bob Rehak on 6/18/2019 with drone footage courtesy of Jim Zura, Zura Productions
658 Days since Hurricane Harvey