Problem– Lake Ontario experienced period-of-record (1918-2017) maximum monthly average water levels during May through July 2017. NOAA lake gages recorded instantaneous peaks-of record, 249.2 at Olcott, 249.1 at Rochester, and 249.0 at Oswego and St. Vincent. These high water levels along with wind-generated waves caused flooding of thousands of residences and businesses and the erosion of miles of shoreline along the southern and eastern shorelines of the Lake. During the second week of July 2017, the USGS installed 14 temporary water-level gages and monitored this flooding through the lake’s recession. This network of water-level gages, in combination with the NOAA sites, provides a dense coverage of the lake water levels. If the USGS gages were continued in operation, they could provide an additional benefit to water-resources managers, emergency responders, and the public. Flood-inundation maps tied to the recorded water levels at each of the gages could be created that would depict the areal extent of flooding that is likely to occur along segments of the lake’s shoreline.
Objective and Scope– The objective of this project is to produce a library of flood-inundation maps (FIMs) at half-foot increments of elevation that would span 245 to 250 feet (North American Vertical Datum of 1988; NAVD 88) or the range in elevation from the year-round average water level to a water level that exceeds the 2017 peak (by almost one foot). FIMs would be divided into shoreline segments extending approximately half-way to the adjacent lake gages and would be tied to the water-surface elevation as recorded by the lake gage located mid-way within a given segment.
Relevance and Benefits – This project will support the USGS Mission Areas of Water and Natural Hazards and will meet the USGS goals of (1) providing water-resources and hazards information that will be used by multiple parties (Federal and State) for planning and operational purposes and will contribute to protection of life and property, and (2) contributing data to national data bases that will be used to advance the understanding of regional and temporal variations in hydrologic conditions. Project data will also be used to support the ongoing efforts under Annex 4 of the Great Lakes Water Quality Agreement (GLWQA).
1. Compile the most recent and highest quality lidar data that is available along the southern and eastern shorelines of Lake Ontario. Lidar elevations are computed based on the North American Vertical Datum of 1988. Merge these data and create a seamless digital elevation model of the terrain in the study area.
2. Create a water-surface grid for each of 11 half-foot increments of elevation from 245 to 250 ft, NAVD 88.
3. Using GIS, subtract the terrain DEM grid values from the water-surface grid values and generate a flood-extent polygon and a water-depth grid for each water-surface elevation. The depth grid will be applicable to those areas of the shoreline for which lidar data is available and will not include areas that are typically submerged, such as embayments and stream mouths. The maps will extend upstream on embayments and streams as far as the available lidar data permits, but no further than the upstream ends of embayments or the stream reaches that are substantially affected by backwater from the lake.
4. Sub-divide the southern and eastern shorelines of the lake into segments that will extend slightly further than half the distance to an adjacent water-level gage. Therefore, each water-level gage will be located at the approximate mid-point of each lake segment. (Although a single flood-extent map and depth grid could be produced for the entire study area, that is, the entire southern and eastern shorelines, for each of the water-surface elevations (resulting in a total of 11 flood maps/depth grids), segmentation of the shoreline is necessary to accommodate the limitations of the USGS Flood-Inundation Mapper, on which the maps will be posted. The Mapper allows for only one gage to be associated with a map library. Therefore, the shoreline needs to be segmented in order to permit display of both the current water levels for a given lake gage as well as the FIMs that are proximal to that gage.)
5. Upload each lake-segment FIM library–the flood-extent maps and depth grids–to the USGS Flood-Inundation Mapper website (https://wimcloud.usgs.gov/apps/FIM/FloodInundationMapper.html). Metadata associated with each set of FIMs will be stored with each library.
6. Write a Scientific Investigations Report (SIR) to describe the process of the FIM production. The “SIR annotated online template” report (at https://water.usgs.gov/osw/flood_inundation/toolbox/preparereport.html) will be used for this purpose.
Products and Deliverables – A library of flood-extent polygons and water-depth grids will be created for each lake shoreline segment. A Scientific Investigations Report will be written to describe the process of the FIM production.
Timeline – The GIS work will be completed within 6 months of the start of the project. A draft report and uploading the FIMs to a review mapper site will be completed within 9 months of the start of the project. The final report will be published and FIMs will be uploaded to the official Flood Mapper website within 18 months of the start of the project.
Personnel – A GS-12 GIS Specialist, will compile lidar data, produce a terrain DEM and water-surface grids, and generate the flood-inundation maps and depth grids. A second hydrologist, with GIS expertise, will assist in these task and also will write the metadata and SIR, shepherd the FIMs through the approval process, and upload the FIMs to the Flood Mapper website.
Communication Plan –
· Project personnel will be in regular contact with the cooperator via email, phone, and in person.
· An initial meeting will be held with the cooperator.
· Periodic updates will be provided to apprise the cooperator of the status of the project and of any unforeseen delays.
· Preliminary FIMs will be presented to the cooperator as soon as they are available.
· A courtesy draft of the report will be shared with the cooperator for input and feedback.
Project Location by County
Orleans County, NY, Monroe County, NY, Genessee County, NY, Wayne County, NY, Oswego County, NY, Livingston County, NY, Seneca County, NY, Jefferson County, NY, Oswego County, NY, Madison County, NY, Onondaga County, NY, Ontario County, NY, Niagara County, NY
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“Lake Ontario gage installation”