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Attachment A Memorandum Date: May 4, 2025 To: Honorable Mayor and City Councilmembers Jessica Jagoe, Interim City Administrator From: The Karth Lake Improvement District Board, in coordination with the Rice Creek Watershed District Subject: Karth Lake Level Modeling Project as Pertains to the 2026 PMP Street and Utility Improvement Project The Project: Over the past three years, the KLID board has led an effort to model Karth Lake's water level and pumping practices as it relates to flood resiliency, erosion and water quality. Contributors to that effort have been the City of Arden Hills, Department of Natural Resources, Rice Creek Watershed District and, through RCWD funding, a hydrology consulting firm, Houston Engineering.' The project's findings are startling: • Without pumping, Karth Lake would periodically overflow onto Amble Drive, flooding at least half of the houses on the Lakeshore and spreading to off -lake houses in the watershed. This finding is supported by the fact that the City of Arden Hills has pumped a total of 36 feet from the lake level since 1984. • This means that Karth Lake pumping is an essential component of the City's surface water management responsibilities within the entire watershed. It is not merely a means to protect the lowest -lying properties or to enhance the aesthetics of Lakeshore properties. Accordingly, the cost of improvements to the pumping infrastructure is more appropriately borne by owners of all properties within the watershed, not merely owners of Lakeshore property. • The upcoming City's 2026 PMP Street and Utility Improvements project (2026 PMP) design should incorporate equipment to automate the current labor-intensive pumping and monitoring process to better control lake level fluctuations.2 • A cinder block pump house could serve as the retaining wall replacement planned within the 2026 PMP and may have a similar cost to a landscape block type of retaining wall. This would provide a vandal resistant enclosure for anew fixed pump and ' Contributors to the Project include the Karth Lake Improvement District Board (KLIDB), City of Arden Hills (City), Minnesota Department of Natural Resources (DNR), Rice Creek Watershed District (RCWD) and Houstin Engineering (HE). HE is a hydrology consulting firm retained by RCWD to assist with the Project under a Minnesota Pollution Control Agency (MPCA) Stormwater, Wastewater, and Community Resiliency grant. 2 Methods for automated lake level measurement are relatively inexpensive. The DNR has extensive experience with this and is ready to be a resource for the City's planners. Further, equipment to remotely monitor and control the existing and potential new pump is available. Page 1 of 4