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1.7 Proiect Authoritv: The proposed action is authorized by Section 14 of the Federal Flood Control Act of 1946 (Public Law 79-526), as amended. This Act authorizes Federal expenditures to prevent flood or erosion damages to endangered roads and highways, highway bridge approaches, public works, and non-profit public facilities, by the construction or repair of emergency riverbank and bank protection works. 2.0 PROPOSED AND ALTERNATIVE ACTIONS 2.1 The proposed action is to protect all three sites with riprap stone. At Leeper Island Park approximately 250 feet of failed wall sections within the protection reach would be reconstructed to maintain the aesthetic continuity of the site. The riprap would be placed against the wall to an elevation of approximately 668, to prevent undermining and rotation of the wall and would extend down the bank into the river. The level of flood protection at Leeper Island Park coincides with the top of the wall (approximately 671 feet), which is about one foot lower than the two-year flood occurrence elevation (approximately 672 feet). _ 2.2 Protection for the North Shore Drive and CSO sites would be provided to the 50 -year recurrence flood elevation (approximately 675 feet). Upper riverbank trees at the -North Shore Drive site would be preserved by using a bio -engineered erosion control turf mat instead of riprap above the two-year flood occurrence elevation (approximately 670 feet). Over time, aesthetics and wildlife habitat will improve within the turf mat area by natural establishment of native shrubs and other vegetation. This soft -engineered bank protection has a lower cost than riprap, but is not as durable and therefore cannot be used on the lower riverbank. 2.3 Riprap was selected because of its lower overall cost compared to other bank protection methods, such as articulated (interlocking) concrete blocks, gabions (stone -filled wire cages), and mechanically stabilized embankment walls (such as decorative landscape blocks mechanically anchored into the bank). Another alternative, considered for North Shore Drive, was a sheet pile wall at the toe of the riprap slope to reduce excavation and backfill quantities, but this alternative would have been more costly, would be less aesthetically appealing than . riprap, and :would not provide aquatic habitat. The alternative of No Federal Action also was considered, but was not selected because the erosion ultimately would destroy several . stormwater outfalls and.utility lines, would undermine North Shore Drive, and eventually cause disruption and damage to the municipal water intakes on Leeper Park Island. 2.4 The bank protection was designed with a steep slope (but not to exceed the existing slope) to minimize riprap surface area, cut and fill volumes, and encroachment into the river channel. At Leeper Park the riprap would be finished to a 1 vertical to 3 horizontal slope (about 18.5") with a geo-textile filter under the riprap (Figures 4 and 5, Attachment A, Pages A-4 and A-5). At the North Shore and CSO sites the riprap would be finished to a 1 vertical on 2 horizontal slope (about G") W lil a 11.5 )40Ut tii:ri riprap layer over a g sued gravel r,. cr (Figures 6 through 8, Attachment A, Pages A-6 through A-8). The gravel filter layer is required for steeper slopes, whereas geo-textile filter is suitable for the gentler slope at the Leeper Park. -3-