Design Modifications and Rehabilitation of an Existing Levee Protecting a Waste Water Treatment Plant

CDM Smith was retained by the Narragansett Bay Commission (NBC) to perform a geotechnical evaluation to rehabilitate the flood protection levee at the Bucklin Point Wastewater Treatment Facility (BPWWTF) located in East Providence, Rhode Island. The facility was constructed in 1952 on a low-lying peninsula on the east bank of the Seekonk River. In 1973, tidal flats in the Seekonk River were filled to expand the site, and the flood protection levee was built around the perimeter of the expanded peninsula to protect the facility from a 100-year storm event. The levee consists of an approximately 3,000-foot-long, U-shaped, earthen fill, levee with exposed heights ranging between about 8 and 19 feet. Two stormwater drainage basins are located at the landside toe of the levee. At each stormwater drainage basin, an 18-inch-diameter pipeline passes under the levee through a sluice gate chamber to an outfall at the riverside toe.
The NBC had included an evaluation of the Bucklin Point levee system and facility system upgrades in a design contract with CDM Smith in order to continue to protect the BPWWTF from significant storm events. After a major storm event caused serious damage to another Rhode Island wastewater treatment plant that was protected by a levee, the NBC’s position was further reinforced. CDM Smith performed the evaluation in two phases. Phase one included a field inspection to document deficiencies and areas of concern along the existing levee. CDM Smith also performed a topographic survey of the levee to evaluate the level of protection based on the Federal Emergency Management Agency 2009 flood insurance rate map for the Seekonk River. Phase two of the evaluation included a subsurface investigation to evaluate slope stability, seepage, and settlement along the levee. CDM Smith prepared design contract documents for the rehabilitation of the levee. Improvements included raising the crest of the levee by approximately 3 feet, restoring and fortifying riverside slopes with riprap, and building out the landside slope. Improvements also included gabion walls to support the built-out landside slope to maintain the storage volume of two adjacent stormwater drainage basins. The construction for the rehabilitation of the levee lasted about nine months from February to October 2012.