Aerial photos of the West Fork Mouth Bar show that the above-water portion on this once-massive sand bar is now down to the width of one excavator for most of its length. A mouth bar is a sand bar where the mouth of a river or stream meets a standing body of water, such as Lake Houston. As water slows when it reaches the standing water, sediment carried downstream drops out of suspension.
The Before Shot
The first photo below shows the West Fork Mouth Bar immediately after Harvey and before any remediation work took place.
At that point in time, the mouth bar extended five feet above water in places. It was 3/4 of a mile wide and a half mile from the northernmost part to the small island in the channel south of the bar. But the part you can’t see, below water, is even bigger.
This massive blockage backed water up throughout the Humble/Kingwood/Atascocita area, and contributed to the flooding of thousands of homes and businesses.
I took the shot below on Sunday night, 10/4/2020. While the camera position and lens perspective are slightly different, they are close enough to show the progress made in removing the blockage, or at least the portion above water.
Close comparison of these two photos shows several smaller islands beyond the mouth bar that the Army Corps removed a year ago. At the completion of the Emergency West Fork Dredging Program (2018/19), FEMA agreed to dredge 500,000 cubic yards (CY) of sediment in a 600-acre area between the mouth bar and Atascocita Point in the upper right of the photos. After dredging the 500,000 CY, the Corps increased the average depth of that area to 5.5 feet. However, within weeks, Imelda filled much of that back in.
This year, the City of Houston started excavating the above-water portion of the mouth bar. The bar is now down to width of the excavators used for mechanical dredging. To fund this effort, the City used money left over from Hurricane Harvey cleanup.
Biggest Part Remains Below Water
But like icebergs, most of the sediment in sand bars lies below the surface. So even when there’s nothing left for me to photograph from the air, most of the blockage will remain. Two local geologists recently measured several cross sections of the river. The river’s profile looks like this.
River depth upstream near Kings Harbor and downstream near the 1960 Bridge is more than 22 feet. Between those two points (which lie about three miles apart), the deepest part of the channel is only about 6-7 feet. Not far from the main channel, however, the river gets much shallower. It’s one to three feet in most places.
The continued presence of this plateau will slow water down and trap more sediment, undermining the effectiveness of earlier efforts.
More Dredging Slated
Restoring the conveyance of the river after decades of deferred maintenance will require much more dredging after the above-water mouth bar is gone.
Luckily, FEMA has agreed to dredge another million cubic yards, according to Houston Mayor Pro Tem Dave Martin. State Representative Dan Huberty also secured an additional $30 million in funding in the last legislature to continue the effort.
Stephen Costello, the City’s Flood Czar, is currently working on developing a next-phase plan, but has not yet announced it.
Posted by Bob Rehak on 10/5/2020
1133 Days since Hurricane Harvey