Sheldrake River Tunnel, Mamaroneck, New York. Hydraulic Model Investigation.
ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS HYDRAULICS LAB
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It is proposed to permanently divert the Sheldrake River, in southeast New York, from upstream of the confluence with the Mamroneck River through a concrete-lined tunnel into the West Basin of the Mamroneck Harbor. Included in the proposed plan are improvement of the existing channel, construction of an uncontrolled ogee drop structure and converging approach to at tunnel inlet portal, construction of 3,550 ft of concrete-lined tunnel, including a 16.25-ft-square section and a 17.5-ft horseshoe section with an intermediate transition, and construction of a standard stilling basin energy dissipator at the juncture with the West Basin. A 125-scale model was used to determine the flow conditions in the proposed project for Mannings n values of 0.013 and 0.010 up to the Standard Project Flood SPF, which peaked at 4,039 cfs. Tide effects were investigated for tides of -2.7 ft, 6.7 ft, 10.0 ft, and 16.8 ft, National Geodetic Vertical Datum. Flow conditions were improved in the model by modifying the tunnel alignment, the shape of the tunnel, and transitions near the middle of the tunnel. The stilling basin was modified to improve flow conditions for the varying tide effects. Riprap protection downstream of the stilling basin was verified as being adequate for the SPF. Stage-discharge relations were determined as were flow velocities and water-surface profiles in the tunnel approach. Hydraulic grade lines were determined for the tunnel for several flows. Flow velocities at the stilling basin end sill are presented as are velocities in the West Basin of the Mamaroneck Harbor.
- Civil Engineering