TO: Mayor and Members of City Council
THRU: Adam Lindsay, Assistant City Manager
FROM: Sheila Thomas-Ambat, Public Services Director
DATE: August 5, 2024
RE:
Title
Arran Lake West Dam Overtopping Protection
end
COUNCIL DISTRICT(S):
Council District(s)
6
b
Relationship To Strategic Plan:
High Quality Built Environment
Executive Summary:
Staff seeks concurrence from City Council to move forward with project development and design of the Arran Lakes West Dam (ALWD) Overtopping Protection Project.
Background:
In December 2021, Council directed staff to begin design of two projects identified in the Beaver Creek 3 Watershed Study. The two projects were the Rhemish Drive Drainage Improvements and the Rockford Drive Drainage Improvement.
Both of these projects are currently under design. As part of the design process, staff use hydraulic models to predict the rise of stormwater elevations down gradient of the project site caused by the new infrastructure, under various storm conditions. Staff evaluates the downstream impacts as far downstream as the models show any significant increase in water surface elevations resulting from the proposed infrastructure.
There are several things from this analysis that may trigger a modification to the design of the proposed project infrastructure (possibly to include acquisition or condemnation). One is if the models show the "level of service" downstream would be reduced, meaning the increased volume or velocity of water projected downstream reduces the efficiency of downstream, existing stormwater infrastructure.
Both the Rockford Drive and Rhemish Drive projects discharge into Beaver Creek Tributary B (BCTB). Downstream of BCTB is Arran Lakes West Dam (CUMBE-067), a private "high" hazard dam with a City maintained roadway overtop of the dam.
Downstream impacts from the proposed improvements do not lower the existing level of service of the dam, however the depth and frequency of overtopping ...
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