Destroyed dams, flooded homes and collapsed roadways were among the worst damage after a storm dumped an unexpected 6 to more than 9 inches of rain in parts of northern Suffolk County on Sunday night into Monday.

Local, state and federal officials toured the most heavily impacted locations Tuesday and Wednesday as cost estimates began to emerge and rebuilding plans began to materialize. Some of the most devastated areas, like the dam under Stony Brook’s Harbor Road, could take years and cost tens of millions to restore. Local officials are hoping to make a case to the federal government to make Federal Emergency Management Agency funds available to help recover from the damage.

On Wednesday, county officials dispatched four teams from Rocky Point to Kings Park to knock on doors and assess damage.

As of Wednesday, 1,700 residents had made a property damage report through the county's online portal, said county Fire, Rescue and Emergency Services commissioner Rudy Sunderman. So far, 21 homes were determined to have major damage, 143 had minor damage and 30 were classified as affected.

Here are some of the most affected locations and what it will take to repair the damage.

Harbor Road, Stony Brook

Damage seen on Tuesday after flooding rains caused the Mill Pond Dam to come crashing down.

Stony Brook’s Mill Pond was emptied and a portion of nearby Harbor Road destroyed after the heavy rainfall took out a dam underneath the road. Debris from the dam and road laid in the now-drained waterway Tuesday morning as scores of onlookers stopped by to take in the sight.

Estimated damage/timeline to repair: Brookhaven Town officials are working with Ronkonkoma-based Hayduk Engineering LLC to develop a cost estimate to rebuild the dam. Brookhaven Town Highway Superintendent Dan Losquadro estimated the design and permitting process could take a year, with another year for construction.

Harbor Road still remains closed, but local and state officials visited the area and nearby Mill Creek Road Wednesday to assess damage. There is no estimate on when repairs are made. Officials were submitting damage estimates to Suffolk County, seeking to qualify for federal aid.

Michael Shenota, an associate professor of civil engineering technology at Farmingdale State College, said several complicating factors means the restoration could take four to five years, and cost more than $10 million. He estimated $15 million could be possible, with $20 million being an outer limit.

The project is complicated because it involves a dam, a nearby nature preserve, and a road that went over the dam, he said.

“There is a lot of wildlife, a lot of environmental concern,” he said. “Each are going to have to be studied on their own to make sure whatever they construct meets the needs of all three of those things and make sure that one doesn’t negatively impact the others.”

Stony Brook Grist Mill, Stony Brook

The Stony Brook Grist Mill, which is located on Harbor Road near Mill Pond, sustained flooding from the storm.

The grist mill, rebuilt in 1751, sustained flooding in its basement, and its water wheel was under sand.

Estimated damage/timeline to repair: A structural engineer examined the Stony Brook Grist Mill on Monday and determined it was structurally sound.

Work continued at the mill on Wednesday, where fallen trees were cut and removed. Tree branches were also removed from the top of the mill's water wheel while the owners cleaned out mud and debris from the basement.

Blydenburgh County Park, Smithtown

Stump Pond stands almost empty after storms caused a dam to collapse on Monday.

The rainfall destroyed the dam in Stump Pond, draining the waterbody into nearby Nissequogue River. The previously underwater tree stumps that give the pond its name were visible for the first time since 1798, the year the pond was created.

Estimated damage/timeline to repair: County officials vowed to restore the pond, but have not given a timeline or a cost estimate for repairs. Activities such as boating and fishing will not be possible until the dam and pond are restored, and the north end of the park is closed until further notice.

Stony Brook University, Stony Brook

Stony Brook University dealt with flooding at the Mendelsohn Center.

Stony Brook University evacuated scores of students from dorms and postponed the move-in day for others Monday morning following the storm. University officials also were offering students up to $5,000 if they canceled their housing assignment for the academic year.

Estimated damage/timeline to repair: As of Wednesday, all residence halls were reopened except for Ammann and Gray, which will need extensive repairs and cannot be safely occupied, according to Stony Brook University spokeswoman Kelly Drossel. Additional dorms have been temporarily reassigned as triples to accommodate some students.

Those who were expected to move in Monday and Tuesday will now move in Thursday and Friday, respectively. The school did not provide a cost estimate for repairs.

Stony Brook University officials said Wednesday that they are still assessing how many students have been displaced from the two dorms damaged by the storms and it is unclear how long those residence halls with remain out of operation.

They are also working on how many students will be assigned to triple rooms.

The same halls flooded in 2021 during Hurricane Ida and several mitigation efforts - including increased stormwater drainage, pumps to relieve pressure on an adjoining drainage system and a new trench system - had been put into place since, said Kelly Drossel, university spokeswoman.

"The reality is, this storm was much worse than expected for everyone. Without the proactive emergency management plans we have in place, and immediate response, this could have been much worse," she said.

Classes are expected to start on schedule Monday.

Smithtown Public Library

Damage books in the lower level of the Smithtown Library, which had up to 10 feet of water inside, after a buildup of water burst a window in our stairwell. The level lower level houses AV materials, that includes DVDs, Blu-rays, and music CDs. The water destroyed all of that material type but our biggest loss was to our Long Island history room. That room contained not only Smithtown historical material but also of Long Island. Some of the documents inside this room date back to the 1600s and they were severely damaged. Smithtown August 21, 2024

Floodwaters as high as 12 feet caused a window in the library's east stairwell to break and the water poured into the lower level, breaking down walls, offices and an elevator shaft. Water rose at least 10 feet high, almost reaching if not touching the basement's ceiling, said Robert Lusak, the director of Smithtown Library.

Estimated damage/timeline to repair: The storm not only damaged the library's infrastructure on the lower level, but it also caused untold damage to a prized historical collection dating to the 17th century, and destroyed more than 21,000 AV materials that had been stored there.

The Richard Hockman Handley Collection, which is comprised of rare books, documents, manuscripts, and atlases related to Long Island's history, were thought to be safe, stored in a locked room with a weather-protectant door designed to prevent water from breaching. But the flooding was so intense that the water broke through the room’s walls of sheet rock, while the door stayed intact.

Staff had begun to digitize the historic documents, but there is a chance some items may not be salvaged. Adam Lyszczarz, archival specialist with Prism Specialties, said the majority of historic items may not be the same, but will be saved.

The library closed indefinitely on Monday. It will take weeks to reopen its first floor as new electrical panels need to be installed, Lusak said.

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