Work began Monday in waters off Waikiki Beach on a project to dredge 20,000 cubic yards of sand from a channel 2,000 feet offshore and pump it onto the beach, the state Department of Natural Resources said.

The $4 million project is a collaboration between the DLNR Office of Conservation and Coastal Lands and the Waikiki Beach Special Improvement District Association, which will contribute $1 million.

The current project is a follow-up to the 2012 Waikiki Beach Nourishment Project, which took 24,000 cubic yards of sand from outside the Canoes surf break and added it to the beach stretching between the Kuhio and Royal Hawaiian groins, Sam Lemmo, OCCL administrator, said in a phone interview.

“We were allowed to do a second round of sand nourishment,” Lemmo said, noting that the nourishment was needed to bolster the shrinking sands of Waikiki due to erosion caused by waves and seawalls, and sea level rise due to global warming.

But Keone Downing, a member of the local environmental group Save Our Surf, argued adding 20,000 cubic yards of sand should have been included in the current environmental impact statement preparation notice for a proposed Waikiki Beach Improvement and Maintenance Program, for which DLNR filed a public notice Dec. 16 and the public comment period ended Friday.

“(DLNR is) circumventing the process by calling it maintenance,” he said. “Seems like they’re adding more sand than they had in 2012. Are they telling us that 20,000 cubic yards has left the beach and there’s only 4,000 now?”

“The reason it’s 20,000 and not 24,000 cubic yards is we were limited (as) to how much,” Lemmo said. “The 20,000 cubic yards is more than enough to bring (the beach) back to what it was” after the 2012 replenishment.

The scope of a second, maintenance sand deposit as foreseen in the 2010 final environmental assessment for the 2012 project was considerably less than 20,000 cubic yards. After an “initial nourishment” of up to 24,000 cubic yards of sand was projected to restore the beach to approximately its 1985 size, “a second nourishment of up to 12,000 cubic yards would be accomplished after 7-10 years to further maintain the beach,” the assessment stated.

Downing added he was unconvinced that “in eight years all that sand went back to those same spots where they dredged it.”

Lemmo said he was confident it had. “The evidence points to the sand moving strongly from east to west, and when it hits the Royal Hawaiian groin area, (the current) kicks it offshore, where it works its way out to the channel between Queens (surf break) and Canoes (surf break),” he said. “We dredged it before. It seems to fill in pretty quickly.”

Downing additionally worried about damage to the reef from sand silting and questioned the accuracy of the dredging, noting that in 2012 it brought up coral rock as well as sand, “and people stepped on it and complained for months.”

Lemmo agreed that was a mistake and would be corrected. “Sometimes you get dead coral rubble washed into and buried in these sand fields, so when we dredged it got in the mix, but this time around we’re going to screen the sand before we place it.”

He said silting would not be a problem, and added he foresaw no injury to the surf shaped by the reef. “The inner reef does sometimes have a veneer of sand, but once you go off into deeper water, sand accumulates in the channels, not the reef tops.”

Lemmo said he was confident in the accuracy of the dredging, for which “everything’s GPS’d and preordained from surveys, identifying where the reef is.”

During the three- to four-month project, the Kuihio Beach/Diamond Head swim basin will be partially closed for receiving and dewatering pumped sand, and the Kuhio Beach/Ewa swim basins and Royal Hawaiian beach will have daily intermittent, partial closures between 8 a.m. and 5 p.m. to allow heavy-equipment movement.

The proposed Waikiki Beach Improvement and Maintenance Program foresees adding more sand to Waikiki Beach and constructing three T-head groins from the Halekulani hotel to the L-shaped Royal Hawaiian groin, which was rebuilt in August and would effectively be converted to a fourth T-head groin under the plan. For more information, visit wbsida.org/waikiki-­beach-maintenance.