Henderson, R. and Beamer, E., 2016. Fisher Slough Floodgate Report for Water Year 2015. Skagit River System Cooperative, La Conner, WA. pp. 38.

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 surface elevation, and floodgate operation for Water Year 2015 (WY2015), the period of October 1, 2014 through September 30, 2015. 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. For the vast majority of WY2015 the management criteria for floodgate operation were met. Overall, only two instances of criteria not being met were recorded with monitoring data. However, data logger malfunctions resulted in a loss of usable data for 41% of the Fall/Winter Flood Control Period.
During the Fall/Winter Flood Control Period the criterion that the floodgate doors be set to close at a minimum elevation of 7.5 ft NAVD88 was met. The floodgates were set to close at 9.5 ft NAVD88, 2 feet higher than the minimum. During the time when the loggers were operating correctly the criterion of doors being open at least once per day to allow adult spawner (i.e. salmon heading upstream to spawn) passage was met with one exception: on November 27, 2014, during flood conditions on the Skagit River, all three doors remained closed. However, meeting floodgate door opening criterion during flood conditions on the Skagit River is not required under special provision of the 2012 Fisher Slough Floodgate Operations and Maintenance Plan.
During the Spring Juvenile Chinook Migration Period, the criteria are that 1) the gates be set to close at 9.5 ft NAVD88, 2) the gates be open at least 90% of the time, and 3) the water shall not be less than 0.5 ft (0.15 meters) over the top of the sill more than 10% of the time. The floodgates were cabled open for the entire Spring Juvenile Chinook Migration Period. The doors did close one time on March 1 in the early morning before adjustments were made to cable the doors open. Otherwise the floodgate doors remained open and were open for over 99% of the time during the Spring Migration Period. The criterion that water depth be at least 0.5 feet (0.15 meters) deep for more than 90% of the time across the floodgate sill was met in WY2015; water depth was greater than 0.5 feet over the sill 100% of the period. A water velocity criterion was not evaluated this year.
During the Summer Irrigation Period the floodgates were cabled open 100% of the time and the submerged flapgate was open June 15 through the end of the operation period, 15 days less than required.