On Saturday evening, August 27, 2011 through Sunday morning August 28, 2011, Hurricane/Tropical Storm Irene impacted New Jersey with high rainfalls, damaging winds, and widespread flooding throughout the state, causing record flows and water levels in many waterways.
In Boonton Township, Morris County, the rising waters of the Rockaway River caused severe erosion of the embankment supporting northbound I-287, a major, six-lane arterial highway. Damage to the embankment at milepoint 44.7 was approximately 600 feet (183 meters) downstream of the I-287 bridge over the Rockaway River.
Approximately 8.5 inches (21 cm) of rain fell on the already saturated Rockaway River watershed. Based on NJDEP and USGS methodologies, flow rates for the Rockaway River had a return period of somewhere between 200 and 500 years. At its peak, the flow exceeded 9,000 cubic feet (255 cubic meters) per second. Prior to the event, the flow was less than 300 cubic feet (8.5 cubic meters) per second.
As a result of this extreme event, the right asphalt shoulder of northbound I-287 washed away and the right travel lane was severely undermined. The need to protect the remaining embankment of northbound I-287 was paramount to prevent a progressive collapse of the remaining embankment and roadway. The original pavement construction consisted of a concrete slab, which ultimately “cantilevered” over the void created by the floodwaters.
Mott MacDonald teamed with IEW Construction to complete emergency reconstruction of I-287 following Hurricane/Tropical Storm Irene, which severely eroded the embankment supporting the northbound lanes near the Rockaway River.
Field personnel placed large stone fill in the area under the most direct attack from the floodwaters. Once this area was stabilized and the erosive forces redirected toward the south, the fill operations were moved to protect the remaining south embankment, and subsequently to fill the remaining “gap” for the embankment.
Mott MacDonald and IEW Construction worked closely with NJDOT to complete this critical reconstruction to reopen the northbound interstate I-287 roadway to traffic. Round the clock operations started Monday morning August 29, 2011 and the entire roadway was open for the morning rush hour on September 1.
The emergency repairs stabilized the embankment for northbound I-287 and facilitated the reconstruction of the roadway and the reopening of all travel lanes. Mott MacDonald completed hydraulics studies to quantify the storm event and make recommendations for permanent repairs.