HomeMy WebLinkAbout2023 06 12 Art Gallo input GATE OPERATION PROTOCOL FOR GEE CREEK WEIR AT LAURA STREET
LAST UPDATED:JULY 9, 2019
CITY OF CASSELBERRY
Overview:The Gee Creek weir at Laura Street controls flow from Lake Kathryn and other upstream lakes
prior to discharge into Gee Creek. Most of this weir is at a fixed control elevation, but a small operable
gate allows for some control of discharge.The purpose of this document is to establish a Gate Operation
Protocol to define when this gate should be opened and closed. The intent of such operation is to help
reduce potential flood risk (especially within Summerloch Green, which is particularly vulnerable) while
avoiding negative environmental impacts to the upstream lake systems.Considerations for both upstream
and downstream vulnerabilities have been factored into this Gate Operation Protocol.
Elevation Reference: Elevations/stages stated in this document refer to stage elevations measured on the
Seminole County staff gauge located just upstream of the Gee Creek weir at Laura Street unless otherwise
noted. All elevations are in feet NAVD 1988. (The City of Casselberry has also installed telemetry at the
weir, and the telemetry stage data are considered equivalent to this same Seminole County staff gauge.)
Statement on Effectiveness & Emergency Protocols: It should be noted that the overall effectiveness of
gate operation to mitigate flood risk is limited. Many lakefront and creek-front properties are vulnerable,
and, at best,operation of the gate may only make a difference in peak flood stages by a few inches or less
and only at certain locations. Notification protocols for flood risk should not be altered because of gate
operation. Specifically, it is advised that at a minimum residents of Summerloch Green be provided early
warning of potential flooding under the following conditions:
1) If the gauge elevation is at 50.0 ft or higher and a storm capable of producing 6 inches or more is
expected in the next 72 hours.
2) If the gauge elevation is at 51.0 ft or higher and a storm capable of producing 5.5 inches or more
is expected in the next 72 hours.
The above conditions are expected to likely at least result in nuisance flooding (e.g., certain roads and/or
yards) in Summerloch Green, even if the gate is opened in advance of these events. For reference, road
flooding begins in this development when the gauge is at about 51.2 ft;yard flooding begins at about 51.6
ft; and the lowest finished floor in Summerloch Green is at 53.44 ft.
Noticing Requirement: Prior to opening the gate,the City of Casselberry shall notify the City of Winter
Springs City Engineer in writing via email. Casselberry shall also provide subsequent confirmation notices
to Winter Springs of the time that the gate is opened and when it is subsequently closed. Internally, the
Casselberry City Engineer (or his/her designee) shall notify the Casselberry Public Works Director and
Casselberry City Manager prior to opening the gate.
Role Assignments: The City of Casselberry City Engineer (or, in his absence, his/her designee) shall
determine when the gate should be operated (based on this Operation Protocol document). Casselberry
Stormwater Division staff will be responsible for physically opening and closing the gate at the direction
of the Casselberry City Engineer(or designee).
Operation Scenarios: Generally the gate should only be opened when the initial stage (prior to opening)
is at 50.0 ft or higher. In most cases, the gate should not remain open once the stage is down to 49.65 ft
or less (49.65 ft is the elevation of the main weir crest). The following "if/then" scenarios should be used
in determining when to open and close the gate:
1) If the stage is at 50.0 ft or higher and a storm capable of producing 4.4 inches or more is expected
in the Casselberry area with reasonably high confidence within the next 72 hours, then the gate
should be fully opened. The gate should be fully closed once the storm has passed and the stage
is down to 49.65 ft.
2) If the stage is at 50.0 ft or higher and a tropical storm or hurricane capable of producing 6 inches
or more per 24 hours is expected in Seminole County with reasonably high confidence within the
next 120 hours, then the gate should be fully opened. The gate should be fully closed once the
storm has passed and the stage is down to 49.65 ft.
3) In absence of any impending storm meeting the above conditions, if the stage is at 51.0 ft or
higher, then the gate should be fully opened. The gate should be fully closed once the stage is
down to 50.0 ft.
It is understood that other factors may need to be considered by the Casselberry City Engineer(or his/her
designee) in determining when the gate should be operated, including, but not limited to, time of
year/seasonal variations,expected storm outlook, projected cumulative impacts from daily storm activity
plus anticipated major storms, certainty of storm outlook, downstream construction work, upstream or
downstream blockages, upstream or downstream damage/condition, etc. In light of this, while this
Operation Protocol is meant to be the primary guide for gate operation, it is not intended to define every
real-world scenario, and so some professional judgment from the City Engineer will be needed.
Storm Severity Reference Information: For reference purposes, the following are key storm intensities
and return frequencies (i.e., probabilities) considered in establishing this Operation Protocol:
Return Period Duration Rainfall Depths(in.)
Mean Annual 24-hour 4.4
10-year 24-hour 6.8
25-year 24-hour 8.5
100-year 24-hour 11.5
Revisions to Operation Protocol: It is anticipated revisions to this document will be needed from time to
time as more information and experience is gathered, including model updates, telemetry calibration,
various data from large storm events,etc. No revisions to this protocol are to be made without the express
permission of the Casselberry City Engineer(or his/her designee). All revisions to this Operation Protocol
are to be shared with the Casselberry City Manager,Casselberry Public Works Director,and Winter Springs
City Engineer.
Key Technical Reference: Gee Creek Basin Drainage Model Update prepared for City of Casselberry,
Singhofen & Associates, Inc., March 2018 — available upon request by contacting the City Engineer at
kbrock@casselberry.org
Network location of the latest version of this Operation Protocol: O:\PUBWRKS\Stormwater\Weir
Protocol