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HomeMy WebLinkAbout6A Prior Lake Floodplain Update Report Phone 952.447.9800 / Fax 952.447.4245 / www.cityofpriorlake.com 4646 Dakota Street SE Prior Lake, MN 55372 CITY COUNCIL AGENDA REPORT MEETING DATE: MAY 7, 2018 AGENDA #: 6A PREPARED BY: PETE YOUNG, WATER RESOURCES ENGINEER PRESENTED BY: PETE YOUNG AGENDA ITEM: PRIOR LAKE FLOODPLAIN ELEVATION UPDATE PRESENTATION DISCUSSION: Introduction The purpose of this agenda item is to update the City Council on a process that has resulted in an update to the floodplain elevations for Prior Lake. The Federal Emergency Management Agency (FEMA) issued a letter on February 20, 2018 (Attachment 1) outlining their decision to revise the floodplain based primarily on data provided in the 2016 Prior Lake Stormwater Management and Flood Mitigation Study (Flood Study). This study was completed jointly by the Prior Lake- Spring Lake Watershed District (PLSLWD) and the City of Prior Lake. FEMA’s decision affects all residents and businesses with property adjacent to Prior Lake. The 100-year flood elevation for the lake is often the basis for decisions on flood insurance and building elevations or locations. A 100-year floodplain is an area that has a 1% chance of being inundated by a flood event in any given year. The 100-year flood elevation for Prior Lake was set at 909.0 feet above mean sea level in 1978. FEMA revised the elevation to 908.9 in 1997. Neither of those efforts considered the effects of the Prior Lake Outlet Structure (PLOS) and Prior Lake Outlet Channel (PLOC) which has been in place since 1983. After considering more recent information, FEMA has informed us that the updated 100-year flood elevation for Prior Lake will be lowered to 906.9 feet, effective July 9, 2018. History FEMA is a federal government agency that coordinates the federal government's role in preparing for, preventing, mitigating the effects of, responding to, and recovering from all domestic disasters, whether natural or man-made. FEMA uses the following acronyms frequently: • FIS: Flood Insurance Study – A compilation and presentation of flood risk data for specific flood hazard areas within a community. When a flood study is completed, the information and maps are assembled into an FIS. The FIS report contains detailed flood elevation data in flood profiles and data tables. • FIRM: Flood Insurance Rate Map – The official map of a community on which FEMA has delineated both the special hazard areas and the risk premium zones applicable to the community. • LOMR: Letter of Map Revision – FEMA’s modification to an effective FIRM. • LOMA: An official amendment for an individual property that establishes a property’s location in relation to the floodplain. LOMAs are usually issued because a property has been inadvertently mapped in a floodplain, or as an update after a home has been raised out of the floodplain. The legislature of the State of Minnesota has, in Minnesota Statutes Chapter 103F and 462 (Zoning Enabling Statute) delegated the responsibility to local government units to adopt regulations designed to minimize flood losses. The City of Prior Lake therefore adopted City Code Section 1105, Flood Plain Regulations. This section of the City Code officially adopts the FIS and FIRM, sets the Regulatory Flood Protection Elevation, and regulates uses within floodplain areas. The first FIS for Prior Lake went into effect in 1978 and set the 100-year flood elevation at 909.0 feet. The 1997 FIS update set this elevation at 908.9 feet. Even though the PLOS and the PLOC existed by 1997, FEMA did not consider them in the FIS at the time because of the way the PLOS was configured and operated – FEMA could not be assured that it would function under all conditions. The PLSLWD, Cities of Prior Lake and Shakopee, and the Shakopee Mdewakanton Sioux Community (SMSC) updated a partnership agreement to maintain and operate the PLOC in 2006. This agreement was an important factor in FEMA considering the PLOS/PLOC system to be a true outlet for Prior Lake. In the spring of 2014, the Prior Lake area experienced record amounts of precipitation which led to a historic flooding event. This event triggered many questions and highlighted the need to develop watershed modeling and evaluate flood mitigation strategies for future events. Prior Lake reached an elevation of 906.17 feet on June 30, 2014. This is the highest elevation recorded by the Minnesota Department of Natural Resources (DNR) since records were kept starting in 1906. The Flood Study indicates that the 100-year flood elevation for Prior Lake should be 906.9 instead of 908.9. The updated elevation includes consideration of the PLOS/PLOC, updated precipitation depths and frequencies, and more accurate topographical data. Because the Flood Study indicates that the 100-year flood elevation for Prior Lake was set at a higher elevation than it should be, the City of Prior Lake, in its role as state-delegated floodplain regulator, initiated a process to update this elevation through a LOMR and contracted with Barr Engineering, the firm that completed the Flood Study, to assist with the LOMR process. Before FEMA could accept the LOMR request, the Minnesota Interagency Hydrology Review Committee (IAHRC) was required to review the Flood Study data to determine if the request to change the flood elevation was valid. The IAHRC determined that the modeling methodology and results met their requirements (Attachment 2). The LOMR request to FEMA was made in June 2017 and their review process was completed in February 2018. FEMA agreed with the IAHRC determination and approved the new, lower 100-year floodplain elevation of 906.9 feet for Prior Lake, with an effective date of July 9, 2018. FEMA published a notice in the Federal Register and in the Prior Lake American on March 3, 2018 and March 10, 2018. FEMA-required notices were sent to a few property owners where the floodplain increased in elevation; the new FIRMs (Attachment 3) indicate that none of the notified homes will be brought into a mapped 100-year floodplain and some may have been taken out of mapped 100-year floodplain. Current Circumstances FEMA does not require any further notification before the LOMR becomes effective on July 9, 2018. However, FEMA encourages the City to disseminate the information in the LOMR to the community so that interested persons, such as property owners, insurance agents, and mortgage lenders can benefit from the information. Some residents may wish to complete a LOMA for their property. City staff is available to help with questions about LOMAs. City staff, along with representatives from PLSLWD and Barr Engineering, will host a community meeting on May 17, 2018 at 6:00 PM. Staff will present information about the floodplain elevation update and its implications. The goal of the meeting will be to give residents and business owners the information and tools they will need to make decisions about flood insurance and construction projects that must follow the City’s floodplain ordinance and state building code. Additional information will be posted on the City’s website. ISSUES: Residents with federally-backed mortgages who are currently required to pay for flood insurance based on the current 100-year floodplain elevation may no longer be required to do so. The City will provide information to residents that they can use when deciding if they will pursue a change to their flood insurance policies. While residents may still wish to carry flood insurance, it may no longer be required in some instances. Anyone can buy flood insurance and rates are significantly reduced for areas outside the floodplain. Residents constructing or reconstructing homes around Prior Lake may have a lower regulatory minimum elevation requirement, meaning that they may not need to add as much fill near the lake to construct a home above the floodplain to meet City requirements. The City requires homes to have a lowest floor elevation of at least one foot above the 100-year floodplain elevation. It is always an option to voluntarily build a home higher out of the floodplain than the minimum requirement. City staff has reviewed existing City ordinances and determined that no updates are required as a result of the LOMR; there are references to the 100-year floodplain elevation, but no specific elevations are listed. City staff will update any handouts or information on our website that refers to the existing 100-year floodplain elevation for Prior Lake in advance of the LOMR effective date. FINANCIAL IMPACT: There will be no financial impact on the City as a result of this LOMR. ALTERNATIVES: 1. Motion and second to accept this report acknowledging the new100 year flood plain elevation of 906.9. 2. Take no action recognizing that the new elevation will take effect regardless on July 9, 2018. RECOMMENDED MOTION: Alternative 1. Minnesota Department of Natural Resources • Division of Ecological and Water Resources 500 Lafayette Rd, Box 25, St. Paul, MN 55155-4025 April 25, 2017 Mrs. Karen Chandler Barr Engineering Company 4300 MarketPointe Drive Suite 200 Minneapolis, MN 55435 Dear Mrs. Chandler, The Interagency Hydrology Review Committee (IAHRC) has reviewed the hydrology analysis and results for the Prior Lake Spring Lake Watershed in Scott County, Minnesota. Our review was based on your letter dated February 24, 2017, supporting documentation (SWMM model, technical memorandum, and topographic workmap) and the responses to our review comments (uploaded April 12, 2017). The modeling methodology and results meet the requirements of the IAHRC. As required for modifications to hydrology in Minnesota, this letter should be included as part of the Letter of Map Revision (LOMR) submittal to FEMA. While the IAHRC does appreciate the responses to our March 30, 2017 comments, please note that we still suggest that the watershed district consider zero evaporation during the 30-day rainfall period. This results in a more conservative estimate of the lake elevation. If you have questions regarding this letter please contact me at 651-259-5802 (rita.weaver@state.mn.us) or Suzanne Jiwani at 651-259-5681 (suzanni.jiwani@state.mn.us). Sincerely, Rita Weaver, P.E., CFM Floodplain Action Hydrologist CC: Suzanne Jiwani, MnDNR Terry Zien, USACE James Fallon, USGS Amanda Deans, USDA