The LINAP Embayment Water Exchange Study looked at how water exchange practices could affect the nitrogen impairments in embayments. A water exchange practice changes the amount, speed, or direction of water moving through an area. The results of the study show that water exchange techniques are not effective in large waterbodies like most of Long Island’s embayments. Often, the physical size of the water exchange practice is small compared to the large waterbodies to which they are applied, which means their impact is limited. Water exchange projects may be useful, however, for smaller Long Island waterbodies, where the volume of increased water exchange approaches the volume of the overall waterbody.
The goal of the study was to provide communities with basic information on water exchange practices suitable for Long Island. A Water Exchange Handbook (PDF) and final Technical Report (PDF) were developed that outline the study.
A webinar to present the findings and answer questions about the LINAP Water Exchange Study was held on Tuesday, April 9th at 10:00am. View the recording here.
Background
Nassau and Suffolk County have published Nine Element Watershed Plans to address the excess nitrogen in Long Island waters. Both plans show that nitrogen reduction practices on the land alone, such as wastewater upgrades, will not be effective for meeting the nitrogen reductions needed for some waterbodies and that other technologies need to be evaluated. Water exchange projects are an example of those technologies. As part of the LINAP Scope, LINAP conducted a study to look at if water exchange practices could improve water quality in Long Island embayments.
A public meeting to introduce the project was held in February 2022. A second public meeting was held in August 2022 to present the findings from the study. A public webinar is planned for the spring of 2024 to present the results.
Study Parameters
The handbook summarizes the study results and includes information on types of waterbodies commonly found on Long Island. These include:
- Harbor with a sand spit
- Shallow, open harbor
- Tidal stream
- Coastal lagoon
- Coastal ponds
Different types of water exchange practices were evaluated on the waterbodies. The type of exchange practices included:
- Environmental dredging
- Sand spit removal
- Pipe-and-pump
- Culvert or pipe with tidal flow
- Tide gate
The water exchange technologies were modeled in the waterbodies to determine the effects. The results were analyzed based off a series of criteria that should be considered to determine if a project is successful. The evaluation criteria included water quality and coastal impacts, environmental impacts, cost and constructability, and social acceptance.
Funding for this study was provided by EPA’s Long Island Sound Study.
