Gomez & Sullivan Engineers, P.C.

Memo

To:        Edward Alkiewicz & Jeff Gerlach

From:    Michele Stottler

CC:       Scott Ault

Date:    September 15, 2008

Re:       Water Level Data for Design of Fish Attraction Structures

At the May 28, 2008 Ecological Standing Committee meeting, a question was raised about the water level data used for design of the fish attraction structures.  The structures were designed so that they are in the water deep enough to maintain adequate clearance between the top of the structure and the water surface to avoid creating a boating hazard and to prevent damage by ice scour in the winter.  The top elevation of the shallow-water structure provides 5 feet of clearance and the elevations of the deep-water structures provide between 11 and 16 feet of clearance between the top of the structure and a low water level.  The low water level that was used for design was the absolute minimum hourly water level recorded for the period of record 1991-2002.  There was a concern that this water level was not low enough for conditions when a northeast wind would hold back water from Lake Erie and that the data set was not large enough to be representative.

During relicensing, NYPA conducted a study entitled the Niagara River Water Level and Flow Fluctuation Study in which it compiled a data base of over 5 million records of hourly water level and flow data for gages located in the Niagara River, Lake Erie, and Lake Ontario for the period 1991-2002.  Gages in the database are Buffalo, Fort Erie, Peace Bridge, Frenchmanís Creek, Huntley Station, Black Creek, Tonawanda Island, Slaterís Point, Material Dock, LaSalle, NYPA Intake, American Falls, Ashland Avenue , Lewiston Reservoir, and Port Weller (Lake Ontario).  This network of gages is much more extensive than other rivers because the gages are operated for multiple purposes by multiple entities.  Operators of these gages include the Niagara River Control Center, NYPA, Ontario Power Generation, the National Oceanic Atmospheric Administration, Environment Canada, and the Canadian Hydrographic Service.  This data underwent rigorous review to identify and remove any erroneous or gage malfunction data.

The intent of developing a database with hourly data versus daily data was to capture the range of observed water levels and flows that occur in a given day rather than looking at daily averages. The water level in the Niagara River at any location at any time is a complex function of natural and manmade factors.  Natural factors include flow surges from Lake Erie, wind, ice conditions, and regional and long-term precipitation patterns that affect lake levels, and manmade factors include regulation of the Chippawa-Grass Island Pool to provide flows for Niagara Falls and power plant operation.  In general, the closer a location on the river is to the Chippawa-Grass Island Pool and the farther from Lake Erie, the more influence there is on water levels from manmade regulation and the less influence there is from wind conditions on Lake Erie.

The period of record from 1991 to 2002 was selected because electronic hourly water data was readily available.  The period of record was also representative of both wet and dry periods based on a review of daily flow records for the Niagara River at the USGS Buffalo gage for the period of record 1926 to 2002.  This was determined by a comparison of the mean annual flows (Figure 4.1-1) and flow duration curves (Figure 4.1.2) of the hourly flow data from 1991 to 2002 and daily flow records from 1926 to 2002.  The mean annual flow for years 1991 to 2002 is 212,000 cfs, which is about 3% higher than the long-term average flow of 205,000 cfs for years 1926 to 2002 because the 1930ís and 1960ís droughts lower the average for the longer period of record.  The years 1999 to 2001 are the driest since the mid-1960s.  Years 1997-1998 were among the wettest on record, with 1997 being the third wettest year in 77 years of record. 

The hourly water level data from 1991 to 2002 is representative of long-term river conditions. 

The Niagara Water Level and Flow Fluctuation Study can be found on the NYPA  relicensing website:

http://niagara.nypa.gov/StudyReports/FinalReports.htm