City Council Meeting Date: February 14, 2017
To: Mayor and City Council
City Administrator
From: David E. Bennett, Public Works Director/City Engineer
Title
Review of Spring Creek Flood Mitigation.
Body
Action Requested:
The Northfield City Council discusses Spring Creek Watershed Study and additional information received.
Summary Report:
At the November 24, 2015 City Council work session, staff, along with a consultant, shared findings of the Spring Creek Watershed Study (Attachment 1). A comprehensive model of the watershed was created and the model was updated to reflect the most current statistical rainfall data for the 1% chance in the year or what is typically referred to as the 100-year storm.
The previous typical standard that was used is called TP-40 and had a 1% chance storm rainfall amount of 6 inches in 24-hours, the new data called Atlas 14 increases that chance to 7.3 inches in 24 hours. With the updated model, impacts to properties were reviewed along with consideration for some mitigation items. There are 6 properties that appear to be more prone to a risk of flooding. In 2016 the City surveyed the low openings on these properties and found that only one property, 1300 Parmeadow Drive, does not have any separation from the 1% chance storm or what is typically referred to as Freeboard.
Address
Low Opening Elevation
Atlas 14 - 1% Chance Elevation
Freeboard (Ft)
1300 Parmeadow Dr
937.4
937.4|10 10|1304 Parmeadow Dr
938.3
937.4
0.9'
1103 Fairhaven Ct
941.4
939.8
1.6'
1105 Fairhaven Ct
941.4
939.8
1.6
1400 Woodley St
946.6
944.3
2.3'
905 Superior Dr
963.5
961.7
1.8'
In the study, potential benefits from various improvement were quantified, they include:
1. Bridgewater Township Flood Hazard Mitigation Projects, these indicate a benefit of reducing the flood profile elevation on average 0.3 feet.
2. Future development of the undeveloped urban expansion area. Increase the storm water management requirement from the 100-year 1% runof...
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