The Alpharetta City Council has approved up to $100,000 in emergency repairs to the Big Creek Greenway where a sinkhole opened up.
The sinkhole and eroded area, about 50 feet long and 3 to 4 feet deep and extending roughly three to four feet under the trail, developed just south of Preston Ridge Road. Alpharetta retained Pond & Co., engineering consultants, to investigate and come up with a repair plan, staff said in a report to the council.
Pond believes elevated creek water levels and flow likely caused erosion, while a large, decomposing tree trunk next to the trail could have contributed to the sinkhole, as could have runoff from an apartment complex upstream, staff said.
The consultant recommended removing the stump and other debris; filling the empty space with flowable fill; placing a gabion wall to help stabilize the slope; adding backfill behind the gabion wall and surge stone and/or rip rap below it to the creek bank; and looking into minor grading upstream to help guide runoff to existing culverts.
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