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San Jacinto West Fork Before-After Photos Show Dramatic Conveyance Improvements from Dredging

After a year of dredging, the Army Corps and its contractors are gone. Even though they didn’t get all of the West Fork Mouth Bar, they made dramatic conveyance improvements on the West Fork as these before/after photos show.

Sand Island Before Dredging

The first was a blockage that dredging contractors nicknamed “Sand Island.” It sat in the middle of the river just downstream from River Grove Park in Kingwood. According to the Corps, it blocked 90% of the river.

Sand Island formed during Hurricane Harvey. Boats that drew 18 inches of water could not navigate upstream past this giant sandbar. Photo taken 9/14/2019.

Sand Island After Dredging

Sand Island is now Gone Island. Photo taken 12/3/2019.

The Corps removed approximately 15 feet of sand over a 15 acre area that was 566.7 feet wide at its widest point. An acre is about the size of a football field. So this would be like stacking sand on a football field 225 feet high (15×15)! And that doesn’t even include the sand they removed from the channels on either side of the island in the background.

Sand Island Dredging Profile.

Diversion Ditch Bar Before Dredging

A second huge sand bar deposited by Harvey blocked the Kingwood Diversion Ditch, also at River Grove Park. The Diversion Ditch empties the western third of Kingwood. Approximately 600 homes flooded above this one blockage. They were in Barrington, Kingwood Cove, Trailwood, Kingwood Lakes and Kings Forest.

Diversion Ditch (center left) was virtually closed off by a new sandbar deposited by Harvey. Photo taken 9/14/2017.

Army Corps measurements show that at its highest point this bar measured 10 feet about the water surface. It forced water coming out of the ditch to make a 90 degree left turn where it then hit another downstream blockage.

Diversion Ditch Bar After Dredging

Photo taken 10/2/2019 after dredging opened up the channel and reduced the downstream bar.
Photo of same area taken on 11/4/2019, but looking upstream.

The Corps dredged a channel 150 feet wide through this bar to a depth of 35 feet above sea level. That’s about 7.5 feet below the normal water surface elevation of the Lake. The channel narrowed to 50 feet wide where it meets the mouth of the ditch.

From the highest point on the bar to the target depth, the Corps removed 17.5 vertical feet of sand. From the mouth of the channel to the outer edge of the bar measured 750 feet.

Comparison in Satellite Images from Google Earth

Here’s how this section of the river looked from a satellite BEFORE dredging. The numbers refer to the discussions above.

Here’s how it looked AFTER. (Note this image was taken on 2/23/19 and the dredge was still removing sand island.

Altogether, the Corps removed approximately 2.3 million cubic yards of sediment. Even if the Corps didn’t finish the mouth bar, that’s a lot to be grateful for. Thank you, FEMA, Army Corps, Great Lakes Dredge and Dock and Callan Marine.

Have a merry Christmas!

Posted by Bob Rehak on 12/24/2019

847 Days after Hurricane Harvey

Before and After Harvey Images Show Impact of Sediment on West Fork Flooding

Below are two videos taken by Jim Zura of Zura Productions before and after Harvey. Together with other still images, flooding statistics and the Army Corps’ Value Engineering report, they demonstrate how radically Harvey transformed the West Fork. As you review these, keep in mind that the proposed new high-rise development in this area based its engineering on pre-Harvey assumptions.

Zura, a videographer and local drone pilot, shot this first video in 2016. River Grove Park looked pristine. Beyond it, a massive clear cut area surrounds an idyllic little lake. This is where a developer plans to build a high-rise resort around a marina. The drone then rotates to reveal a river without blockages downstream, or in front of the boat docks. In just 18 months, everything would radically change.

River Grove Before Harvey and the Sand

Hurricane Harvey brought with it massive rainfalls that washed sediment downstream, clogging the West Fork. Onshore, they reached up to five feet and stretched 450 feet inland.

Still frame from Jim’s video compared to a shot I took from a helicopter two weeks after Harvey. The angles are slightly different but they show the same location.

Result: a park that normally floods once every over year flooded six times in one year – three times in the last month alone – 12X greater than normal.

The Reason for Increased Flooding Frequency

It’s called reduced conveyance of the river. The Army Corps documented this in its Value Engineering Study. Here are some shots I took after Harvey from a helicopter. Consider them within the context of the videos above and below. You will understand why River Grove has been near-continuously inundated for a month. I wonder how the owners of luxury high-rise condos would feel about not being able to access their property for that long.

To get a feeling for how much sand was left in the river by Harvey, see how much lined both shores of the West Fork.
Sand on both side of the river stretched 450 inland after Harvey. Nearest the river, it reached 5 feet in height through this reach of the West Fork.
A giant sand bar 12 feet high and 1500 feet long was deposited in one event: Harvey. It blocked the drainage ditch that empties the western third of Kingwood. The proposed new high-rise development would also depend on this ditch.

I fail to see how the high-rise developer filling in hundreds of additional acres of floodplain with 12-feet of fill could have zero net impact. If every engineering survey ever submitted for a flood plain development were correct, the world would have no flooding problems.

River Grove after the Christmas flood. Water went down briefly then came back up during the next flood in early January. As of today, the soccer fields were still flooded. See the area that compares to the first video at the end of this one.

Posted by Bob Rehak on 1/8/2018

497 Days after Hurricane Harvey

Houston Advanced Research Center Pre-/Post Harvey Mapping Tool

A novel GIS mapping tool developed by the Houston Advanced Research Center (HARC) now makes it easy to see how Hurricane Harvey changed the San Jacinto River.

This novel, 4-pane mapping tool allows users to view pre- and post- Hurricane Harvey images in natural and infrared colors.

The four panels make it very helpful when looking at how river and stream channels changed before and after the storm. Zooming and scrolling in the upper-left pane automatically zooms and scrolls the other panes to match, so all four images remain in perfect register.

Hurricane Harvey brought more than 50 inches of rain in a single week to a region that normally receives 45 inches of rainfall in a year. This amount of rainfall in such a short period of time brought widespread flooding and destruction of property throughout the Houston-Galveston region. This mapping tool lets you easily see it.

The natural color images make it easy to see changes in the river. The infrared images make it easy to see changes in vegetation. This link provides an overview of how to interpret the colors in infrared images.

Seven Areas of Interest

Here are several striking images that jumped out at me as I scrolled around the Humble/Kingwood Area.

Note how the channel under the US59 Bridge seems to have shifted north.

Note the massive sand deposition along the banks of the river between 59 and Forest Cove.

Note the huge extension of the sand bar that blocked the drainage ditch coming out of River Grove Park.

Note the massive enlargement of the mouth bar between Kings Point and Atascocita Point.

Note the enlargement of the sand bars blocking the East Fork at East End Park.

Note the destruction in Forest Cove along Marina Drive.

Note the blockage in the river south of Kingwood County Club that altered the entire channel.

Explore for Yourself

Explore other areas, perhaps closer to your home, by visiting this link: Effects of Hurricane Harvey: Pre & Post Regional Aerial Imagery.

The before imagery has resolution down to one meter. The after imagery has resolution down to one foot.  What does that mean? If you left a shoe in your driveway when the plane was flying over, you could see it in the image.

My only wish is that the site had a ruler tool for measuring distance. But overall, this is an outstanding and valuable tool.

HARC is a research hub providing independent analysis on energy, air, and water issues to people seeking scientific answers. They are focused on “building a sustainable future that helps people thrive and nature flourish.”

Posted on November 10, 2018

438 Days after Hurricane Harvey