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d C) e These dirt roads will be used primarily for access to the mitigation site and will not be used for landfill �- hauling operations. Similar to the existing channel, the proposed channel will have creek crossings linking the landfill borrow area with the landfill site. The three crossings proposed in the mitigation plan will replace three existing crossings of Littlejohns Creek (Figure 3-2). Maintaining Flood-Control Function l- The realigned channel will emulate the existing stream channel, having a similar channel length, channel slope, and average meander-belt width. By connecting to the existing creek at the City's east and west property lines, the slope of the relocated channel.will change only minimally, the creek distance will increase by approximately 200 linear feet, and the meander-belt width will equal that of the existing creek (Figure 3-1). In addition, the proposed channel will include a gently Fmeandering low-flow channel across the width of the proposed floodplain. The floodplain capacity must be constructed to accommodate 100-year floodflows, as required Fby SJCFCD. Unlike the existing channel, which is cleared of vegetation, the realigned channel is designed with a broader floodplain to accommodate floodflows while maintaining the riparian vegetation. Additional floodplain capacity would be provided in the 11.0-acre area west of Austin Road that would be subject to shallow flooding with an average depth of 1 foot. The project engineer will design the flood channel using an appropriate Mannings "N" coefficient that will allow for dense , riparian vegetation with no or limited maintenance. The City will perform a HEC 11 analysis to demonstrate that the new channel meets the 100-year floodflow standard. If it does not meet the expected standard, the conceptual channel design will be modified prior to the final design. Special Requirements The proposed mitigation concept also accommodates the goals of governing agencies for this project. Three bridge crossings over the relocated creek are proposed by the City for access to the landfill from Austin Road and for access between the landfill and the proposed borrow site. The SJCFCD requires the following to be included in the creek realignment program (Callahan Pers. comm.): 1) that these bridge crossings have 3 feet of freeboard during a 100-year-flood event and conform to San Joaquin County design codes, 2) that a sedimentation collection point be created upstream (just west of the existing wetland site),and 3)that erosion-control methods (including using j riprap materials) be incorporated at sharp bends in the realigned channel. Revegetatiort Planting , After completing-the floodplain and chann&l-grading operations and installing the irrigation system and cover-crop seeding, revegetation operations should take place the following fall. Planting will be divided into three distinct ecological planting habitats (Figures 3-2 and 3-3): Chapter 3. Wetland Mitigation and Monizorin Wetland Mitigation and Monitoring Plan for the Chap g g Plan Austin,Road landfill Expansion, U.S.ArrnY Corps of Engineers File 199400974 r.1. Cin•of Srockron 3-3 April 5. 1996