Apple Creek Channel Relocation and Floodplain Lowering

The City of Appleton, Wisconsin has designed the relocation of a portion of Apple Creek North, located in the northern portion of the City. In conjunction with this design project, the floodplain in the Apple Creek Subwatershed is being remodeled to account for upstream storage and development changes that have occurred within the subwatershed. In 1999 a Floodplain analysis was performed to determine the extent of the Floodplain of the Apple Creek corridor. This floodplain was approved by WDNR, but was never formally approved by FEMA. In 2007 ACEOM conducted the Apple Creek Subwatershed Leverage Floodplain Mapping Study. Since the 1999 floodplain analysis was completed, the Subwatershed has experienced rapid development, and therefore, changes in stormwater discharges have occurred. Urbanized areas prior to 2004 have no detention unless they are tributary to Holland Pond (a regional on-line stormwater detention pond). Development within the City that has occurred since 2004 was required to follow the City Stormwater Ordinance and meet a requirement to reduce peak flow to presettlement conditions. A hydrologic model was created to determine the peak flow changes due to the changes in land use, detention facilities, and flow routing. A hydraulic model was created initially using the data from the 1999 hydraulic model, and then updated using additional field survey information that was gathered in areas where changes have occurred. Once all of the information was gathered and internally quality checked, a floodplain and floodway was created and submitted to WDNR. The WDNR approved the floodplain and used the elevations for the remapping of the Apple Creek Subwatershed as part of the statewide Digital Flood Insurance Rate Map (DFIRM) update process. The City of Appleton has prepared a CLOMR for the Apple Creek Subwatershed. The CLOMR includes the Apple Creek North relocation project, and additional upstream detention that was constructed since the 2007 floodplain analysis was completed. The Apple Creek North relocation project consists of channel naturalization and floodplain lowering project for a portion of Apple Creek North. The design included naturalizing approximately 4500 feet of channel and relocating the channel to the north. Design constraints involved the future development of adjacent lands, future widening of County Highway to south, expansion of existing waterway crossings, constructability of access to site, and earth work balancing. The goals of the project included the relocating the channel to allow for roadway expansion and to change the floodplain limits (through reduction of the floodplain elevation) to allow the adjacent lands to be removed from the floodplain (once a LOMR was issued). The flow splits were analyzed along Apple Creek North to determine floodplain effects of routing additional flow south towards the main branch of Apple Creek. Four waterway crossings are being designed to convey the 100-year flood flows. The channel naturalization and waterway crossing improvements reduced floodplain elevations from one to two feet within the project corridor and have water surface elevation reductions further downstream.