The once concealed and heavily polluted Saw Mill River now runs free as an environmental restoration site. In an effort to mitigate frequent flooding and create space for construction and development the City of Yonkers, NY concealed a portion of the Saw Mill River with a concrete flume in the early 20th century.
In the early 21st century, the city decided to daylight a portion of the hidden river and turn it into open space. For this major redevelopment project, McLaren Engineering Group inspected and studied improvements to provide public access to the river, daylighting and re-alignment. The area is now dubbed as a stunning example of environmental and urban design melded together and has earned Yonkers Urban Wildlife Refuge Partnership city status by the U.S. Fish and Wildlife Service’s National Wildlife Refuge System.
For this $48 million environmental restoration project, McLaren provided marine and civil engineering on the flume that channeled and concealed the Saw Mill River underground for decades.
McLaren’s Engineer divers inspected the entire culvert/flume structure, roughly three-quarters of a mile, beginning at the Hudson River and continuing upstream to the spillway located near Waring Row. The inspection included a one hundred percent visual inspection of the culvert/flume structures, including abutments and the retaining wall undermining. Structural assessments and details on the cause of structural deficiencies and deteriorated elements were presented in the condition survey report.
In order to figure out the measures needed to unearth the Saw Mill River, hydraulic and hydrologic analyses were performed. This included the study of peak flows and preliminary HEC-RAS/Backwater. The design analysis help guide solutions for a healthier river: steps were added to create a waterfall and prevent rising saltwater tides from reaching the Saw Mill’s freshwater pool, the city’s sewage drain was separated from a stormwater drain to improve water quality, and rocks were placed alongside the river to create turbulence and increase the stream’s velocity.
The parking lot within Larkin Plaza had to be displaced for daylighting construction. McLaren prepared alternate parking layouts with the landscape architect for construction of the replacement parking as a deck within the I – Park lot north of Wells Avenue and also within the area south of Nepperhan Street. McLaren conducted an analysis of alternate alignments within the strict project requirements and developed schematic cost estimates and utility relocations.
For the Super Block bounded by Nepperhan Avenue, New Main Street, Palisade Avenue, and Elm Street, McLaren prepared site plans for the Preliminary Site Plan Approval. Improvements included the pedestrian walkways, retaining walls, terraces, small pedestrian bridges and riverside landscaping and stabilization to enhance the appearance and public access. Design services included coordination of the layout of all of the site components with the Architect, Landscape Architect and Structural Engineer. McLaren provided the design of all storm, sanitary, and storm drain connections from the buildings and plaza area and coordinated the locations of the gas and electrical connections with the MEP consultant.
The Saw Mill River is one of the only ones in the northeast that has been daylighted, perhaps paving the way for more environmental restoration projects in New York City in the coming years.