GEOLOGICAL CONSIDERATIONS FOR CONSTRUCTING A RAFTING AND KAYAKING COURSE ON THE CHATTAHOOCHEE RIVER, COLUMBUS, GEORGIA

A 2.5 mile long raft and kayak course, designed by McLaughlin Whitewater Design Group of Denver, CO, is being constructed in the Chattahoochee River where it passes through the downtowns of Columbus, Georgia and Phenix City, Alabama. Two historic dams, the Eagle and Phenix dam and the City Mills dam, will be removed restore the river to near original free flowing conditions and allow the whitewater course construction. To facilitate construction of the whitewater features, river flows are being diverted around the construction site at the Eagle Phenix dam and cofferdams are then being used locally at individual structures. The existing channel bottoms are first being cleaned and shaped. Then whitewater structures of grouted boulders or grout bags are being constructed. Several potential concerns were identified early in the planning: permeability of bedrock to seepage flow; availability of large slabs of rock for shaping the channels; and the effect of blasting on existing structures. Early field work on the west side of the river by Schamel and others identified these exposures as Phenix City gneiss and provided a basis for understanding the large exposures below and on the east side of the Eagle and Phenix dam. Large scale air photos of the Eagle and Phenix and the City Mills sites were extremely useful for remotely mapping linear features and for mapping joints and other structures on the ground. Observations of joint distribution, distribution of other planar structures, the way the planar structures control breakage of the rock, erodibility of joints, and presence of potholes help understand these issues. A weathered pegmatite dike emplaced in a fracture zone was encountered during the modification of the central channel. Though not discovered during earlier mapping, the study provided a context for understanding it. Goal for completion of the course is late 2013.