The Rosendale floodwall is declared stabilized by DEC. This picture was taken in February. (Photo by Lauren Thomas)
After six months of work by project engineers J. H. Maloy, Inc. of Albany and geotechnical consultants Hayward Baker, the New York State Department of Environmental Conservation (DEC) has determined that the first phase of the Rosendale Floodwall project has been completed and that the wall is now “stabilized.” Additional work remains to be done to reestablish proper drainage behind the wall and to remove the structures created to accomplish the work, including the riprap access road built through the Rondout Creek from Snyder Road to the point just downstream from the Keator Avenue bridge where the wall was threatening to give way.
The floodwall is part of the superstructure erected by the US Army Corps of Engineers in the 1970s to control periodic flooding of downtown Rosendale. In December 2018, DEC divers began investigating the extent of the erosion problem that was causing a section of the wall to separate from the northern embankment and lean in toward the riverbed. “The panels have shifted out, and there’s nothing holding them up,” highway superintendent Bob Gallagher reported to the Rosendale Town Board in February. “The water comes underneath the apron into the creekbed, and excavates up to seven feet deep underneath.” Gallagher surmised that the source of the water flow was from the mines and caves in Joppenbergh Mountain, which were filling up with rain and snowmelt from an unusually wet winter.
According to the DEC, the “scour hole” that had developed underneath the concrete apron of the wall has been stabilized by the insertion of grout bags and injection of tremie grout. Riprap laid down in front of the footings will remain in place to prevent future scouring while the rest of the temporary road is removed over the months to come. Hayward Baker brought in an enormous drill to extract cores for testing and make channels for soil anchors through the bulging wall, three to each of four concrete panels. Square boxes can now be seen at each point where the tieback rods were inserted. While the wall panels still lean out, the anchors are expected to prevent further movement.
Weep holes in the wall were also cleaned out as part of the project, and jet filters will be installed to keep them clear. Unspecified additional improvements reestablishing drainage behind the wall of runoff from Joppenbergh remain to be done, according to a DEC spokesperson. The fence and temporary wooden stairs that provided access to the construction zone behind the Roos Arts and Canal Press buildings, as well as a wooden work platform, have already been removed. The biggest mess still to be amended is the temporary coffer dam and the access road, which is nearly half a mile in length and required the delivery of more than 20,000 tons of rock. DEC promises that the contour of the creekbed will be restored to its “original design elevation” by the placing of armor stone.
The remediation work is expected to be completed in 2019, and DEC will continue to monitor the status of the retaining wall and its enhanced drainage system in the future. ++
