WORKSHOP ITEM - Robert Therres, Public Services Manager/Assistant City Manager
Title
LADDIE LAKE STUDY UPDATE
Background
The City entered into an agreement with Coon Creek Watershed District (CCWD) to model the Laddie Lake drainage area to determine if there were specific areas where flooding would be of concern and what the possible solutions would be to address the flooding. Areas of concern focused on excessive street flooding or flooding of homes. The agreement also requested that CCWD address the outlet structure at Laddie Lake.
CCWD has completed the Laddie Lake Drainage Study, which is included with this item. The study shows that the existing trunk storm sewer line, which runs under 87th Avenue from Hastings Street to Laddie Lake, is at or slightly below capacity for the 10-year storm event (10% chance that a storm will be equaled or exceeded in any one year) using the current standards for precipitation and rainfall type. The model indicates there will be temporary localized flooding at some of the intersections along 87th Avenue during the 10-year event with durations ranging from two to one hundred minutes during the storm. Under typical rainfall amounts, there will be minimal to no flooding according to the study.
At this time, the CCWD suggestions regular inspections and maintenance of the storm sewer system to remove obstructions and keep the catch basin inlets free and clear of debris to maximize the capability of the system.
CCWD is still working on a design for the outlet structure at Laddie Lake and staff will provide an update when a design is proposed.
Recommendation
Continue regular inspections and maintenance of the storm sewer system.