Figure 2-1: Plan View of Installation of the Rip Rap along Gabion Mattress. Approximately 9,300 square feet of existing substrate will be removed, replaced with rip rap tied to downstream roughened channel at a 10:1 slope, and re-covered and choked with the removed existing substrate. Figure 2-2: Cross Section of the Spillway Toe Showing Proposed Location of Rip Rap Installation.