ARCHIVED REPORTS_MAY & JULY 2014-TPR

Home Browse Search

1-5 1.7.3 Floodplain The Forward Landfill is located between the North Fork and the South Fork of the South Littlejohn's Creek; the RRF is south of the South Fork of the South Littlejohn's Creek (see Figure 5). Based on the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps (FIRMs) for the San Joaquin Valley, Forward Landfill is located within four FIRM Panels: 0490F; 0495F; 0630F; and, 0635F. From the FIRM Legend, the majority of the landfill (including the RRF and Composting Facility) is located within "Zone X", which are areas determined to be outside the 0.2 percent annual chance of being in a floodplain. The area east of Austin Road at the North Fork of South littlejohn'S Creek is labeled as "Zone AO, (Depth 1)", which are areas with flood depths of one to three feet. This information was factored into the North Fork realignment of the South Littlejohn's Creek relocation design. For additional information regarding the floodplain, refer to the 2014 RCSI (SWT). The North Fork of South Littlejohn's Creek was relocated to allow continued development of the Forward Landfill. The 7,600-foot reach of the creek relocation was designed to channel the 100-year flood-flow of 1,025 cubic feet/second (cfs) within its banks with an additional one foot of freeboard. In the event that a 500-year flood occurs (1,100 cfs, according to FEMA Flood Flows), the excess flow will spillover the northern bank and into the adjacent farm land, rather than affecting Forward Landfill. Based on the realignment of the North Fork of South Littlejohn's Creek, the landfill property is not located within the predicted elevation of the 500-year flood zone. Therefore, the existing realignment does not require an assessment for potential erosion or saturation of the landfill. The South Fork of South Littlejohn's Creek runs south of and adjacent to the southern perimeter of the refuse footprint of the landfill. From the FIRM map (Map No. 06077C Panels 0635F and 0630F), the existing South Fork of South Littlejohn's Creek is labeled as "Zone AO, (Depth 1)", indicating depths of one foot, and Zone AE, indicating base flood elevations within the creek. These current flows are very slow and non-erosive and as a result, will not inundate or potentially erode the adjacent creek or inundate the landfill. The predicted elevations from the 500-year flood event range from 40.5 feet on the southwest edge to 43 feet on the east edge of the landfill along Austin Road and this level is only one to two feet higher than the toe of existing landfill slopes. The existing South Fork of South Littlejohn's Creek was designed to channel the 100-year flood flow of 1,550 cfs within its banks and an additional one foot of freeboard. In the event that a 500-year flood occurs (1,700 cfs, according to FEMA Flood Flows), the excess flow will spill over the southerly bank and into the adjacent area, rather than impact the Forward Landfill. The South Fork of South Littlejohn's Creek alignment is also a very flat gradient, 0.0006 feet per foot; therefore, erosion is not a significant concern. Forward Resource Recovery Facility SWT Engineering Transfer/Processing Report -MayJ..uJy 2014 z:\projects\ailied waste\forward\resource recovery facility\5 yr permit rvw 2013-14\tpr 2014\text\secl.doc