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North Hempstead to create computer maps to track storm water

Erin Reilley, chief sustainability officer for the Town

Erin Reilley, chief sustainability officer for the Town of North Hempstead, stands by a storm water outfall going into Manhasset Bay in Port Washington during low tide Tuesday, Sept. 27, 2016. Credit: Chuck Fadely

North Hempstead this month will begin creating a computerized regional map of storm water drainage systems in an effort to better trace the sources of pollution in Long Island Sound, Hempstead Harbor and Manhasset Bay.

The town will join several other Long Island municipalities in using geographic information system technology to pinpoint the location of pipes, catch basins and outlets.

The state Department of Environmental Conservation is encouraging such mapping statewide and requiring it for areas bordering waters where contamination makes shellfish unsafe to eat. That includes much of the Long Island coastline.

Without detailed, computerized maps, it can be difficult and time-consuming to find sources of pollution, said Paul DeOrsay, executive director of Friends of the Bay, an Oyster Bay environmental group.

“Accurate, readily accessible maps really make it much easier,” he said.

For example, if a high bacterial level is found near a drainage outlet in Manhasset Bay, officials could determine which pipes may have carried the responsible pollutant and then locate the pollution source, said Erin Reilley, North Hempstead’s chief sustainability officer.

North Hempstead is spearheading an initiative that includes the town, 20 villages and the city of Glen Cove. The agreements between the town and villages were approved earlier this year; the town and Glen Cove each approved their agreement on Tuesday.

Many municipalities already have paper maps of storm water systems, Reilley said. But the maps typically stop at municipalities’ borders. The mapping project includes creating GIS-based versions of paper maps. It also entails sending workers to document catch basins and other storm water infrastructure that may not be in current records, and to verify that records are accurate, Reilley said.

Funding for the project is through a 3-year, $316,250 DEC grant.

Brookhaven began GIS-based mapping in 2007, before state grants were available for it, said town storm water manager Veronica King. It took years to document old piping, by driving down every town road and combing through antiquated records, King said.

“Before that, we had a paper index card system that dated back to the 1950s,” she said.

The map needs constant updating as new catch basins and other infrastructure is added, she said.

Huntington, which began its mapping effort in June, found that some older sections of the storm water system were never recorded even on paper, said town spokesman A.J. Carter.

GIS mapping of storm water drainage also helps in flood control and diversion, said Colin Bell, intergovernmental affairs program coordinator for the Town of Oyster Bay, where state-funded mapping of pipes in Massapequa and Massapequa Park is taking place as part of a larger flood-control effort.


  • Geographic information systems mapping includes scanning and then digitizing paper maps and uploading satellite images into GIS.
  • GIS technology can combine maps of different scales so they use the same scale.

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