Replace and Extend Stormwater Outfall IJKL, Crissy Field
As part of the Doyle Drive Presidio Parkway Project, the Presidio Trust and the California Department of Transportation (Caltrans) are proposing to replace the IJKL stormwater drain and outfall (IJKL) located on Crissy Field, an area under the jurisdiction of the National Park Service (NPS). NPS, as the landowner, is considering whether to authorize Caltrans to conduct the work on NPS land. The proposed construction window for this project is between May 16 and October 31, 2015.
Purpose and Need: The purpose of the project is to increase discharge capacity of IJKL, reduce flooding onto Mason Street, and extend the stormdrain and outfall to just beyond the 50-year sand accretion point. The shoreline at Crissy Beach has accreted, and is anticipated to continue accreting over the next decades. To ensure long-term function of the stormdrain, the outlet is being located beyond the anticipated accretion point. Increasing the capacity of IJKL is needed to accommodate additional stormwater runoff from Park Presidio (Doyle Drive).
The existing IJKL Outfall is a 42 inch diameter storm drain pipe located on the western part of Crissy Beach, in Area A of the Presidio. It drains parts of Mason Street and areas of the Presidio. The storm runoff from the new Presidio Parkway (Doyle Drive) will soon be directed to this drain as well. Currently, the existing outfall, located on Crissy Beach, is frequently clogged during high tides from littoral sand movement, causing water to back up in the pipe and eventually flooding Mason Street. To minimize flooding, frequent maintenance is necessary to open the clogged outfall. This is done by driving a backhoe on to the beach several times a day to excavate and unclog the outfall. These actions are labor intensive and disruptive to wildlife and visitors. The pipe outfall is located in the Crissy Field Wildlife Protection Area (WPA) that is protected habitat for the Snowy Plover, an endangered bird that may occur there between July and early May each year.
Proposed Action: To address the deficiency of the existing pipeline, Caltrans, the Federal Highway Administration (FHWA), and the Presidio Trust propose to replace approximately 170 ft of the existing stormdrain with a larger diameter pipe buried under the beach, and extend the larger diameter pipe on pilings approximately 300 ft. into the bay. With the extension of the pipe the stormwater outfall will discharge under water in the bay, just beyond the expected 50 year beach accretion point. This will improve long-term function of the pipe, and reduce the need for use of heavy equipment for maintenance on the beach, with the resulting disturbance to wildlife and visitors. Most of the pipe will not be visible. The last set of pilings, approximately 300 feet into the bay, will be above the mean higher high water (MHHW) and delineated with signage as a safety measure.
To minimize impacts to natural resources, minimal vegetation disturbance will occur and the disturbed area will be revegetated. Construction on the beach inside the WPA could occur between from April 16 through June 2015, when snowy plover are typically not present. Biological surveys will be completed prior to the start of work. During the months of July through October, construction will occur in the nearshore environmental and out into the bay. Monitoring for aquatic species will occur during this period.
During the project, visitor access will be limited through the site for public safety. The beach through the WPA will be closed during beach construction, with reduced access during the in-water construction. Caltrans has proposed to erect a fenced staging and storage area on the Crissy Airfield adjacent to the construction area.
Photo Credit: "San Francisco, California" by Paxson Woelber