Dredge Report, August 12, 2011

Friday, August 12

By 7:15 am we were on the dredge preparing for the day. Moving around on the dredge is a careful dance among a tangle of hoses and gear, and we are always looking for ways to make things more organized, comfortable and safe. After moving the water pump yesterday, Timmy decided we could use less hose curled on the deck, so he shortened the water pump intake hose and cut our wash-water hose in half, enlarging our ohso- limited free deck space.
Around 8 am we started pumping and one trip across the canal and back took 2 hours. We are reaching the limit of the discharge hose at our current configuration and will have to move the dredge to a new part of the canal next week. We shut down early because of impending storms.
With thunder growling in the distance, we made a quick visit to the test site. With low water, the fill was again exposed, and there was green growth everywhere! Spikerush (Eleocharis sp.) is spreading rapidly to cover the mud surface, and the Bacopa that we tossed in over the last few weeks is spreading to make nice clumps. Three-square (Scirpus olneyi) is sending runners along the perimeter in several areas. The Spartina alterniflora planted along the inside of the containment has become quite lush.

The test site fill was exposed and being covered by spikerush and Bacopa.

Photo showing vegetative growth of Bacopa and S. alterniflora at the containment adjacent to the test site walkway: left- June 2, 2011; right – August 12, 2011.

Bacopa and spikerush around former outfall(left). Scirpus moving into adjacent spikerush covered mud(right).

The mud has settled into a thick, cohesive, stabile substrate, and by the walkway it is roughly 6-8 inches deep. The reed containment is full of mud and water, and is starting to decompose inplace as expected. With the vegetation growing along and in it, it should remain a barrier for mud retention for a while longer yet.The threatening weather was still bypassing the work area, so we had time to visit the experimental site. The low water conditions and the fluid mud in Cell 4 kept us from getting very close to the discharge by canoe, but we were able to check out the extent and direction of the finer particle plume.

View to the east, showing the eastern shore of Cell 4 and the newest delta. Red arrow marks location of the outfall that formed C4-d1, and green arrow marks the outfall for C4-d2. Fluid mud extends almost to the bottom of the photo where the ripples start. Containment 5d is to the right of this photo, and is shown below.

The above photo is to the left; this shows containment 5b and further extent of fluid mud.Containment 4c. View to the west from Cell 4.

The mud plume was throughout Cell 4 and extended into all other cells. The main plume from the current outfall was directed toward the south shore of Cell 4, and it was obvious that there was fine grain sediment escaping through the reed containment 4c  and 4d since the water in the greater pond on this side of SAVs was almost the same color as that of Cell 4. However, we were unable to locate a large enough break in the larger  containment 4c to account for that much of a plume.

To the left of 4c is the smaller containment 4d, which also appeared to be intact and performing well to block the flow. However, to the left of the containment, we could see that there was water flow into Cell 4, diluting the muddy water.

We pushed our way into the embayment to find a well established water exchange through the marsh to east of containment 4d. Apparently, the tide was coming in without the discharge running, and will let it out when tide and flow allows. We could not find a channel to block, and decided to leave it for the moment, since it seems most of the escaped fill stays near the area. We will inspect this further by airboat or by LSU’s remote aerial planes.
This is further evidence that we won’t be able to completely contain dredge discharge within a marsh shoreline. We know this is not the only exchange through the marsh perimeter because of the flow pattern evidenced by the plume. The water has to come in and out somewhere until we get the material stacked above tidal action.
A map of the current estimated conditions is on the following page.

This figure shows the estimated status of the experimental cells as of August 12, 2011 and 55.5 hours of pumping. Legend: estimated extent of fluid mud or fill (bright pink), plume (purple), outfall locations and above marsh level deltas (yellow crescents), location of hose (blue), completed containment (green), planned containment (orange), outflow channel (dark red).

Karen A Westphal, National Audubon Society Louisiana Coastal Initiative
6160 Perkins Road, Suite 215, Baton Rouge, LA 70808
225-768-0921 office, kwestphal@audubon.org
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