Henderson, R. and Beamer, E., 2014. Fisher Slough Floodgate Report for Water Year 2013. Skagit River System Cooperative, La Conner, WA. pp. 47.

This report describes floodgate monitoring efforts for the Fisher Slough floodgate, located in the South Fork Skagit River tidal delta. Monitoring results relate to measurements of floodgate door openness, water depth, water velocity, water surface elevation, and floodgate operation for Water Year (WY) 2013, the period of October 1, 2012 through September 30, 2013. The floodgate was originally installed to provide flood protection from Skagit River floods to the Fisher Slough basin. In 2009, old barn-style doors were replaced with a self-regulating floodgate designed to improve fish passage and tidal exchange through the gates while still maintaining flood protection.
We compare monitoring results to floodgate operational criteria that were established based on fish passage and flood protection needs. We also discuss monitoring results and criteria in order to provide information useful to adaptively manage the Fisher Slough floodgate, if necessary, to achieve and balance its multiple objectives of fish passage, flood protection, drainage, and irrigation.
Monitoring instruments used to collect water surface elevation and floodgate door openness data were shown to collect results accurately with one exception. Instrumentation on the south floodgate door did not measure door openness accurately and should be replaced or repaired.
Fisher Slough floodgate operation met the Hydraulic Project Approval (HPA) criteria established for two of the three operational periods of WY 2013. The criterion for the Fall/Winter Flood Control Period was met (minimum closure setting of 7.5 ft NAVD88). During the Spring Juvenile Chinook Migration Period all four criteria (gates open for 90% of the time, minimum closure setting of 9.5 ft NAVD88, minimum water depth of 0.5 feet over the sill, and maximum water velocity not to exceed 8 feet per second) were met.
During the Summer Irrigation Period the criterion that the floodgate doors shall be open was not met. There were a total of 61 closures (when the doors went from open to closed) during the entire operational management time period. Fifty-nine of the closures were during the time when the floodgate doors were operated as normal; all closures occurred when WSE was greater than 9.0 ft NAVD88. A predicted high water event on September 28, 2013 prompted Dike District 3 to change the floodgate settings from that of Summer Irrigation Period to Fall/Winter Flood Control Period on September 28, three days earlier than normal. The floodgate doors closed twice on September 28 and then were closed for the remainder of the Summer Irrigation Period. The floodgate doors were open 91.38% and 91.27% of the time during the entire operational management time period, and were open 93.17% and 93.22% of the time when the floodgate was operated as normal (north and middle door, respectively).