Gravel Bar Removal Summary and Update

15 May 2011 by admin, Comments Off on Gravel Bar Removal Summary and Update

Storm debris removal started late in January.  The company in charge of the project built a crane pad on the south hill using a chain link fence as the base layer and about a two foot layer of rock above that.  There was a one week delay after Barton Springs had closed awaiting the first of two cranes to arrive.

The first crane  (20 ton capacity) arrived and proceeded to build the coffer dam.  Building the dam they would take three inner tubes and float pieces (braces) of the frame to a small, one-man barge.  Once they got them out there a diver would attach the braces at the bottom.  Also, they were limited to a 10 foot high coffer dam.  The expectation was a 12 foot high dam.  Sand bags were used in the deeper areas to raise the base and set the dams on top of, to increase the height.  The building of the dam took approximately two weeks.

The water level inside the dam was lowered over approximately two days.  Throughout the project there was unexpected leaking of water into the dammed area.  The water had to be removed into and filtered through bladders for the sediment to be separated. The water was pumped uphill to the bladders in the south side of the park which took a lot of energy. There was a lot of care taken with what they did with the water and debris to protect the surrounding ecosystems.  There was an environmentalist on site throughout the project.

Two bobcats on tracks were lowered into the pool inside the drained coffer dam area where they removed debris and river rock for three-four days.  The bobcats would create a pile of rock and the clamshell crane, the second and bigger (80 ton capacity) of the two cranes, would lift the rock into an awaiting dump truck.

The dump truck would drive onto a scale in the staging area in the south parking lot because the contractors were paid based on the weight removed.  After the 1,000 tons of debris were removed, the dammed area was refilled with water and the dam was removed.  The water bladders were disassembled and the rocks on the crane pad were removed as well.  Grass was replanted where the crane pad was.  Once the sediment settled, the area inside the pool looked quite barren.  Following this project was the one week spring clean when the lifeguards started working on removing the sediment.

Since then, plants have been planted inside the pool in that area and the grass on the hill is growing back well.  The water clarity is markedly better and the pool looks cleaner than it has in years.  All in all, a good balance has been returned to the pool as far as plants and water clarity.

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