Tag Archive for: diffuser pipe

What 470 Cubic Yards of Muck Per Hour Looks Like at 1/8000th of a Second

I visited Placement Area 1 this morning . Muck was shooting out of the “diffuser pipe” at 470 cubic yards per hour. That’s enough to fill up 47 dump trucks every hour! A truly impressive sight. So I grabbed my Nikon D5 and started clicking. Only after downloading the images did I realize that I had the shutter set to 1/8000th of a second.

Liquid Looks Like Glass at 1/8000th

Normally, when shooting flowing water, you want to use shutter speeds in the range of 1/8th to 1/60th of a second. Slower speeds blur the liquid and create a sense of motion. The faster speed, however, froze the motion and made the liquid look like glass.

In photography, sometimes mistakes make the shot. This may have been one of those times. As I stared at the effluent, I became transfixed by the thousands of bursting bubbles within it. You can also see how the further the “spray” gets from the pipe, the bursting bubbles begin to reform into smaller droplets.

Effect of Diffusion Pipe

Dredgers call this a diffusion pipe because of those rings on the end of it. They allow the dredger to control the spread of the effluent. By adjusting the spread, they can make it shoot out far like a fire hose or spread out wide.

In this case, they had it set to “wide” so that it would be more controllable.

Diffuser pipe at Placement Area #1 shooting out effluent at 470 cubic yards per minute. Shot with a Nikon D5 at 1/8000th of a second.
A slightly wider shot shows sand piling up. All the water in the effluent finds its way back into the river after sediment drops out of suspension and it is filtered by gravity.
This shot shows three separate activities: a) the pit being filled, b) an excavator moving sand out of the flow, and c) loading a sand truck which will haul it away.

Now Selling Sand from Placement Area #1

A worker told me that early last week, the pit owner started selling sand from the site to an asphalt company. At the present rate, they are hauling it away about half as fast as the pit is being filled. This will help create extra storage area in the pit should the US Army Corps of Engineers choose to use it for the next phase of dredging – the mouth bar.

Max Flow Rates

As impressive as this flow is, I’m told it can go even higher – up to about 1,000 cubic yards per hour. The rate depends on factors such as the density and hardness of the spoils, as well as the distance they are pumped.

Details Still Being Worked Out on Mouth Bar

Still no official word yet on details of Phase 2 – the mouth bar project. The Corps is still evaluating placement areas. It could be that they need to permit more than one to contain the entire mouth bar. However, they also need to move quickly to make sure the dredgers don’t move on to another job.

Because of the lengthy amount of time permitting a placement area can take, the Corps may try to buy time by directing spoils to one or both of the current placement areas which are already permitted.

The more sand that pit owners can sell, the more capacity they will have, and the faster phase two of West Fork dredging can start.

FEMA will not pay to remove the entire mouth bar. FEMA has been working with the Corps and the City of Houston to determine how much of the mouth bar was due to Harvey. By statute, that’s all FEMA can pay to remove.

Variables Complicate Decisions

The City, State and Harris County will have to pay to remove the rest. That’s part of the contingency planning at this point. No details have yet been released about how all the pieces of this jigsaw puzzle will fit together.

Planners are now trying to optimize for at least ten variables that I have heard discussed.

  • Volume due to Harvey
  • Time required to dredge it
  • Available storage in existing placement areas
  • Additional cost to move it to those placement areas (pipe, booster pumps, fuel, etc.)
  • Productivity loss due to additional distance from mouth bar
  • Cost versus amount funded by FEMA
  • Placement areas and cost for any volume FEMA does not fund
  • Time required to permit new placement area(s)
  • Where money will come from to cover what FEMA does not cover
  • When additional funds will be available

Not simple! We can only wish that they could make the decision in 1/8000th of a second.

Posted by Bob Rehak on 5/2/2019

611 Days since Hurricane Harvey