Revising the Historic Monthly Mean Niagara River Flow at Buffalo to Reflect Better Estimates of Maid-of-the-Mist Pool Outflows

Revising the Historic Monthly Mean Niagara River Flow at Buffalo to Reflect Better Estimates of Maid-of-the-Mist Pool Outflows 1961-2007 Background The Niagara River flow at Buffalo is currently computed by summing the flow diverted for hydro-electric power generation at the high head plants at Queenston-Lewiston, the outflow from the Maid-of-the-Mist Pool (MOM), and the diversion through the New York State Barge Canal, and subtracting local inflows and the portion of Welland Canal Diversion returned to the river upstream of the Falls. The outflow from the Maid-of-the- Mist Pool is determined with rating equations using the water level recorded at the Ashland Avenue water level gauge. The equations presently being used were approved in 1981. These equations were revisions of a previous equation approved in 1964. Discharge measurements have been carried out routinely to verify the 1981 rating equations, and it was determined that the 1981 equations were underestimating the flow. In September 2008, the Niagara Board approved a revised rating equation. Prior to 1964, several equations were used to determine the MOM outflow. In 1965, the Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data revised past Niagara River flow estimates using the 1964 Ashland Avenue rating equation for MOM outflow. The Ashland Avenue gauge was installed in 1957, and replaced the Morrison Street gauge for computation of flow out of the MOM. The Coordinating Committee adapted the 1964 Ashland Avenue rating equation to use levels at Morrison Street gauge and re-derived the MOM and Niagara River flows from 1926 to 1957. The 1964 equation was derived using 556 discharge measurements from 1907 to 1962. The measurements before 1952 were made near the head of the river, above Grand Island. The measurements from 1952-62 were made in the lower river, below where the present OPG Beck plants discharge back into the river. The flow out of the MOM at the time of these measurements was determined, as appropriate, by subtracting the Beck plant diversions (or discharges for 1952-62), subtracting the New York State Barge Canal diversion and adding local inflows, to the measured total flow. During these measurements the MOM outflow ranged from 1416 to 6940 cubic meters per second (cms). Most of these measurements were made at MOM outflows well above the flows experienced since OPG s BeckII and NYPA s Robert Moses hydropower plant began pulling water from the river above the falls, in 1955 and 1961 respectively. NYPA s plant was fully operational by 1962. Prior to 1962 the monthly mean outflow from the MOM ranged from about 2940 to about 6700 cms. Since 1962 the range has been from about 1420 to about 3170 cms, only half of what it had been. Beginning in 1973, discharge measurements were made at a new measuring section in the lower river the Cableway Section. This section is upstream of the hydropower plants and measures only the flow out of the MOM pool. After several sets of measurements were made it was decided to revise the Ashland Avenue rating equation using only discharge measurements at the Cableway Section and water levels at Ashland Avenue. The resulting 1981 Ashland Avenue rating equations were based on 70 measurements 1

made between 1973 and 1978. When the 1981 equations were adopted, beginning in April 1981, the historic Niagara River flows prior to April 1981 were not corrected to reflect the revised MOM rating. Continued routine discharge measurements of the outflow from the MOM, particularly those using Acoustic Doppler Current Profilers (ADCP) indicated that the 1981 Ashland Avenue rating equations were underestimating the MOM outflow particularly in the higher flow ranges. The rating was re-evaluated and a new equation determined. With the acceptance of the September 2008 revised Ashland Avenue rating, it became necessary to consider revising historic flows to reflect better estimates of the MOM outflow. Because the 2008 rating equation, like the 1981 equations, was derived using only measured flows in the 1400 to 3700 cms range, it only reflects the MOM outflow since the NYPA plant came on-line. Therefore, only historic flows from 1961 to present will be considered for revision. In this report the term published refers to the historic flows published by the Coordinating Committee in its report, Lake Erie Outflow, 1860-1964, with Addendum 1965-1975, and to flows that continued to be coordinated between the office of the U.S. Army Corps of Engineers (USACE), Detroit and Environment Canada (EC), Burlington. Objective The objective of this study (being done for the International Upper Great Lakes Study (IUGLS)) is to determine revised historic monthly mean Niagara River flows that reflect better estimates of MOM outflow. To do this the difference between the 1981 or 1964 equation estimate and the 2008 equation estimate was determined and applied to the historic/published Niagara River flows from 1961 to 2007. Several methods to determine this difference were evaluated. The availability of historic water level data in digital format was a limiting factor. Analysis There are limits to the amount and kind of historic data that is readily available for recomputing the MOM outflow. Hourly Ashland Avenue water levels are available from the National Oceanic and Atmospheric Administration s (NOAA) website from 1970 to present. For 1962-1969 hourly Ashland Avenue data was obtained directly from Cary Wong of NOAA s National Ocean Service. For 1961, only monthly mean levels were available digitally. Presently, the MOM outflow is determined by a computer program utilized by the USACE, which uses hourly Ashland Avenue water levels and considerations for the transitions in the pool when Falls flows are switched during the tourist season. This program also computes the Niagara River flow at Buffalo, the Lake Erie outflow and the Lake Ontario inflow. The program requires data in addition to Ashland Avenue water 2

levels, such as the hourly diversions for power generation, and much of the older data is not readily available digitally. In the hopes of simplifying the method for determining revised historic Niagara River flows, several alternative approaches to retrofitting the program and obtaining all the past data it requires were tested. They all involved determining the difference between monthly flows computed using the historic MOM outflow equations and those computed using the revised 2008 equation. These differences would be used as the adjustments to the historic monthly mean Niagara River flows. One alternative used hourly Ashland Avenue water level data, another just used monthly mean Ashland Avenue water levels in the rating equations. The goal was to see how well hourly or monthly mean levels could represent the difference between the old and new MOM outflow estimates. Since the best estimates of MOM outflows are obtained using the Lake Erie outflow program, it was used to create a basis of comparison for the other methods. For the current format of the program, data was only available from 2005-2007. The current program was changed to use the revised 2008 Ashland Avenue equation and run for the period 2005-2007. These results were compared to the program results using the 1981 rating equations. The differences between the MOM estimates using the program with the two different ratings became the basis of comparison. These differences were compared to using hourly or just monthly Ashland Avenue water levels and the 1981 and 2008 rating equations, without considering the flow transitions during the tourist season, which the program does. A summary of the results is shown in Table 1. It is important to keep in mind that until 1993 Niagara River flows were coordinated to the nearest thousand cubic feet per second (tcfs) and to the nearest ten cubic meters per second (10 cms), thereafter. Using hourly water levels gives essentially the same monthly average difference between the two MOM estimates (1981 and 2008 rating equations) as using the program. The difference between using the program and using monthly mean water levels is less than 10 cms, but rounds to 10 cms during the summer months. Since hourly Ashland Avenue water levels originally were not readily available before 1970, and at that time the rating equation used for historic flow computation was the 1964 equation, another comparison was performed. This one used both hourly and monthly mean Ashland Avenue water levels for the years 1970-1975 to compute flow differences between the 1964 and 2008 equations, and compared the resulting differences. Table 2 summarizes these comparisons. There seems to be a fairly consistent pattern where the differences are near the same from November through March and about 10 cms different from April through October. Using hourly Ashland Avenue water levels consistently resulted in differences about 10 cms higher than using monthly mean water levels from April to October. The same pattern was seen for the period 1962-1969 once hourly water levels become available. It seems advisable that, if using monthly mean levels to compute the difference between the MOM outflows using the 1964 and 2008 equations, 10 cms should be added to the difference for the months of April to October. This would compensate for having to use monthly mean levels when hourly levels are not available. This effects only the adjustments for 1961, because hourly data was eventually obtained for 1962-1969. 3

Table 1 Differences (in cms) Between MOM Outflow Estimates Computed Using 1981 and 2008 Ashland Ave. Rating Equations 2005 to 2007 Based on Program Based on Hourly WL Based on Monthly WL Program Diff - Hourly Diff Rounded to 10 cms Program Diff - Monthly Diff Rounded to 10 cms 2005 Jan 83 83 86 0 0-3 0 Feb 88 87 89 1 0-1 0 Mar 87 87 88 0 0-1 0 Apr 111 110 114 1 0-3 0 May 107 107 112 0 0-5 -10 Jun 105 104 111 1 0-6 -10 Jul 101 100 107 1 0-6 -10 Aug 100 99 107 1 0-7 -10 Sep 97 97 105 0 0-8 -10 Oct 95 94 102 1 0-7 -10 Nov 60 60 63 0 0-3 0 Dec 53 53 55 0 0-2 0 2006 Jan 57 57 59 0 0-2 0 Feb 77 77 81 0 0-4 0 Mar 70 70 73 0 0-3 0 Apr 106 105 111 1 0-5 0 May 103 102 109 1 0-6 -10 Jun 101 100 107 1 0-6 -10 Jul 104 103 110 1 0-6 -10 Aug 100 100 107 0 0-7 -10 Sep 99 99 106 0 0-7 -10 Oct 102 102 108 0 0-6 -10 Nov 58 58 59 0 0-1 0 Dec 88 90 92-2 0-4 0 2007 Jan 97 97 99 0 0-2 0 Feb 88 88 90 0 0-2 0 Mar 89 89 90 0 0-1 0 Apr 113 112 116 1 0-3 0 May 109 109 113 0 0-4 0 Jun 100 100 108 0 0-8 -10 Jul 98 98 106 0 0-8 -10 Aug 100 100 107 0 0-7 -10 Sep 97 96 104 1 0-7 -10 Oct 93 93 101 0 0-8 -10 Nov 49 49 51 0 0-2 0 Dec 58 58 62 0 0-4 0 4

Table 2 Differences (in cms) Between MOM Outflow Estimates Computed Using 1964 and 2008 Ashland Ave. Rating Equations 1970 to 1975 Year Month Based on Hourly WL Based on Monthly WL Hourly Diff - Monthly Diff Year Month Based on Hourly WL Based on Monthly WL Hourly Diff - Monthly Diff 1970 1973 Jan 128 124 4 Jan 106 101 5 Feb 130 129 1 Feb 105 103 2 Mar 130 129 1 Mar 104 102 2 Apr 116 105 11 Apr 110 104 6 May 115 105 10 May 111 104 7 Jun 115 106 9 Jun 111 105 6 Jul 115 106 9 Jul 110 104 6 Aug 115 106 9 Aug 110 102 8 Sep 116 106 10 Sep 111 101 10 Oct 118 109 9 Oct 112 102 10 Nov 121 118 3 Nov 108 105 3 Dec 117 115 2 Dec 108 107 1 1971 1974 Jan 118 114 4 Jan 108 105 3 Feb 121 119 2 Feb 108 105 3 Mar 116 115 1 Mar 105 102 3 Apr 114 105 9 Apr 113 108 5 May 114 104 10 May 109 105 4 Jun 111 103 8 Jun 109 103 6 Jul 114 106 8 Jul 110 102 8 Aug 114 105 9 Aug 112 102 10 Sep 116 107 9 Sep 113 104 9 Oct 118 108 10 Oct 116 106 10 Nov 124 122 2 Nov 117 114 3 Dec 120 118 2 Dec 111 109 2 1972 1975 Jan 116 114 2 Jan 107 106 1 Feb 121 121 0 Feb 111 104 7 Mar 115 114 1 Mar 108 105 3 Apr 112 103 9 Apr 108 101 7 May 109 102 7 May 110 101 9 Jun 108 101 7 Jun 110 102 8 Jul 109 101 8 Jul 111 102 9 Aug 110 102 8 Aug 113 102 11 Sep 110 102 8 Sep 112 102 10 Oct 110 102 8 Oct 113 103 10 Nov 106 103 3 Nov 111 109 2 Dec 105 102 3 Dec 113 111 2 Hourly Diff - Monthly Diff Rounded to 10 cms 1970 1971 1972 1973 1974 1975 Jan 0 0 0 10 0 0 Feb 0 0 0 0 0 10 Mar 0 0 0 0 0 0 Apr 10 10 10 10 10 10 May 10 10 10 10 0 10 Jun 10 10 10 10 10 10 Jul 10 10 10 10 10 10 Aug 10 10 10 10 10 10 Sep 10 10 10 10 10 10 Oct 10 10 10 10 10 10 Nov 0 0 0 0 0 0 Dec 0 0 0 0 0 0 5

Methods for Determining MOM Outflow Adjustments, 1961-2007 Prior to 1926, the Niagara River flow at Buffalo was not computed using the MOM outflow, so no adjustments are needed for the historical flows. For the period 1926 to 1960, the 1964 rating equation was the best representation of the high MOM outflows of this period. As noted previously, the Coordinating Committee used the 1964 equation to determine the published flows for their report. Only for the period 1961 to present, were adjustments determined and applied to the published Niagara River flows. These adjustments were derived by computing MOM outflow using the revised 2008 rating equation and subtracting the flow computed using the MOM outflow rating equation used in the determination of the published Niagara flow for that time (either the 1981 or 1964 equation). The resulting differences, rounded to the nearest 10 cms, will be applied to the published flows. For some periods, additional adjustments may have also been made, as described below. For the period 1962 to present, hourly Ashland Avenue water levels are available, and were used in the computations. Using hourly water levels and the rating equations to determine the difference between the two estimates of monthly MOM outflow and applying this difference to the published monthly Niagara River flow is about as good as using the Lake Erie Outflow program to determine a revised monthly Niagara River flow. For the period April 1981 to present adjustments were determined from MOM outflows computed using: 1) hourly Ashland Avenue water levels, meters, IGLD 1985; 2) the 1981 Ashland Avenue rating equations, in metric and IGLD 1985; 3) the revised September 2008 Ashland Avenue rating equation. For the period 1962 to March 1981 adjustments were determined from MOM outflows computed using: 4) hourly Ashland Avenue water levels, meters, IGLD 1985; 5) the 1964 Ashland Avenue rating equations, in metric and IGLD 1985; 6) the revised September 2008 Ashland Avenue rating equation. For 1961, hourly Ashland Avenue water levels could not found so monthly mean levels were used. An additional adjustment was applied, depending on the time of year. From the tests done for the period 1970-1975, and comparisons done once hourly levels became available for 1962-1969, it appears reasonable to add an additional 10cms to the rounded differences for the months April through October. To summarize, for 1961 the adjustments were determined from MOM outflows computed using: 1) monthly mean Ashland Avenue water levels, meters, IGLD 1985; 2) the 1964 Ashland Avenue rating equations, in metric and IGLD 1985; 3) the revised September 2008 Ashland Avenue rating equation; and 4) an additional 10 cms applied to the rounded adjustments for the months of April through October. 6

The Equations and Datum Conversions Revised 2008 Ashland Avenue Rating Equation The MOM outflow rating equation approved by the Niagara Board at its meeting in September 2008 is as follows, where Q is MOM outflow in cms and AA is water level at Ashland Avenue gauge in meters on IGLD 1985. 2008 Rating Equation: Q = 0.6429 * (AA -82.814) 3 1981 Ashland Avenue Rating Equation The 1981 Ashland Avenue rating consists of two equations. Which equation to use depends on whether the flow is at or above 1416 cms or below 1416 cms. The original equations were developed in English Standard units, with Ashland Avenue water levels on IGLD 1955: MOM outflows at or above 50,000 cfs: Q = 27135 + 104.372*(AA - 299.394) 2 MOM outflows less than 50,000 cfs: Q = 28.688*(AA - 280.00) 2.113 The 1981 rating equations converted to metric units with water levels on IGLD 1985 are: Flows at or above 1416 m 3 /s: Q = 768 + 31.81*(AA - 91.415) 2 Flows less than 1416 m 3 /s: Q = 10.000*(AA - 85.504) 2.113 1964 Ashland Avenue Rating Equation As reported in Proposed Revision of the Ashland Avenue Gauge Rating Equation for Maid-of-the-Mist Pool Outflow, the 1964 rating equation is: Q= 80.282 * ( AA 55 290.30 ) 2, where Q is in cfs, and AA 55 is the Ashland Avenue level in feet on IGLD 1955. The 1964 rating equation using levels at Ashland Avenue converted to metric and IGLD 1985 is: Q = 24.470 * (AA 85 88.643) 2, where Q is flow in cms, and AA 85 is the level at Ashland Avenue in meters, IGLD85 7

Recommended Revised Niagara River Flow at Buffalo Based on the above detailed procedure, differences between the old and new Ashland Avenue rating equations were determined and used to adjust the published/historic Niagara River flow at Buffalo from 1961 to 2007. Table 3 lists the derived adjustments. Table 4 gives the recommended adjusted monthly mean Niagara River flows at Buffalo for 1961-2007, as well as the coordinated (USACE, Detroit and EC, Burlington) published flows from 1900-1960. The adjustments to MOM outflow are about 4-5% of the total MOM outflow. This is similar to what is seen in recent discharge measurements compared to the 1981 rating equation. Applying the adjustments to the published Niagara River flows increases them about 2%. 8

Table 3 Differences Between MOM Outflow Estimates Computed Using 1964 and 2008 Ashland Ave. Rating Equations To Be Used to Adjust Published Historic Niagara River Flows at Buffalo 1961-2007 (Cubic Meters per Second, rounded to nearest 10 cms) Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1961 120 110 110 130 150 130 120 110 110 110 120 120 1962 120 130 120 110 110 120 120 120 120 120 140 130 1963 130 140 130 120 120 120 120 120 120 120 140 140 1964 130 140 140 120 120 120 120 120 120 120 140 140 1965 140 140 140 120 120 120 120 120 120 120 140 140 1966 140 140 140 120 120 120 120 120 120 120 140 140 1967 140 140 140 120 120 120 120 120 120 120 130 130 1968 130 120 130 110 110 110 110 120 120 120 130 120 1969 130 120 120 110 110 110 110 110 120 120 120 120 1970 130 130 130 120 120 120 120 120 120 120 120 120 1971 120 120 120 110 110 110 110 110 120 120 120 120 1972 120 120 120 110 110 110 110 110 110 110 110 110 1973 110 110 100 110 110 110 110 110 110 110 110 110 1974 110 110 110 110 110 110 110 110 110 120 120 110 1975 110 110 110 110 110 110 110 110 110 110 110 110 1976 110 110 110 110 110 110 110 110 110 110 110 130 1977 120 130 130 110 110 110 120 120 110 120 120 120 1978 120 130 130 110 110 110 120 120 120 120 140 130 1979 120 130 130 110 110 110 110 110 110 110 120 120 1980 120 120 110 110 110 110 110 110 110 110 120 120 1981 130 130 130 110 110 120 110 120 120 110 90 90 1982 80 80 90 120 120 130 110 110 100 100 80 90 1983 90 80 80 110 130 120 120 130 120 110 100 110 1984 80 90 100 120 120 120 120 120 110 100 90 90 1985 110 80 110 150 140 140 120 120 120 110 110 140 1986 100 100 130 140 140 150 140 140 130 130 120 130 1987 130 110 110 130 130 120 130 120 110 110 70 80 1988 80 80 70 110 110 110 100 110 100 100 60 50 1989 60 60 50 110 110 110 110 110 100 100 70 60 1990 50 70 70 110 110 110 100 110 110 100 70 70 1991 100 90 80 110 110 100 100 100 100 90 50 60 1992 60 60 70 110 110 100 100 110 110 100 90 100 1993 110 110 100 130 130 120 120 110 110 100 60 60 1994 80 80 80 110 120 110 110 110 110 100 80 70 1995 90 80 80 110 110 100 110 100 100 100 60 70 1996 70 70 70 110 110 110 110 110 110 110 90 110 1997 120 110 130 150 150 150 150 140 130 120 100 110 1998 120 110 130 140 140 130 130 120 110 100 60 60 1999 70 70 80 110 110 100 110 100 100 100 60 60 2000 50 60 60 110 110 110 110 110 100 100 60 60 2001 60 70 70 110 110 100 100 100 100 100 50 70 2002 70 80 80 110 120 110 110 110 100 100 60 60 2003 70 60 50 110 110 110 110 100 110 100 60 70 2004 80 60 60 110 120 120 110 110 110 100 60 60 2005 80 90 90 120 110 110 110 100 100 100 60 50 2006 60 80 70 110 110 110 110 110 100 110 60 90 2007 100 90 90 120 110 110 100 110 100 100 50 60 Adjustments based on: 1961: 1964 & 2008 MOM rating eq. and monthly mean levels at Ashland Avenue gauge. An extra 10 cms added to April through October 1961-1969 to account for difference in using monthly mean water levels instead of hourly. 1962 Mar 1981: 1964 & 2008 MOM rating eq. and hourly levels at Ashland Avenue gauge. April 1981 2007: 1981 & 2008 rating eq. and hourly levels at Ashland Avenue gauge. 9

Table 4 Recommended Monthly Mean Niagara River Flows at Buffalo 1900-2007 With Flows for 1961-2007 Adjusted to Reflect Better Estimates of Outflow from the Maid-of-the-Mist Pool (Cubic Meters per Second, rounded to nearest 10 cms) Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1900 5350 5240 5410 5550 5800 5830 5720 5690 5580 5350 5490 5470 1901 5350 4840 4810 4870 5100 5380 5380 5320 5380 5270 5210 5210 1902 5130 4730 4870 5180 5470 5610 5950 5920 5720 5830 5690 5640 1903 5550 5300 5610 6000 6170 6170 6090 5920 5920 5800 5640 5640 1904 4930 5040 5440 6060 6400 6540 6370 6230 6090 5970 5800 5720 1905 5350 5010 5100 5350 5860 6200 6310 6200 6090 6000 5780 5890 1906 5720 5440 5320 5550 5800 5920 5920 5860 5720 5750 5830 5920 1907 6140 5780 5660 5890 6170 6290 6400 6170 6090 6060 6000 6000 1908 6060 5690 5860 6230 6540 6460 6310 6200 5950 5660 5660 5610 1909 5210 5210 5380 5490 6170 6230 6170 5950 5750 5550 5410 5660 1910 5100 4900 5240 5440 5950 5920 5780 5610 5440 5550 5470 5320 1911 5040 4810 4930 5070 5490 5490 5380 5210 5100 5210 5520 5380 1912 5210 4840 4870 5520 5920 5890 5750 5800 5830 5720 5830 5750 1913 5750 5890 5780 6600 6770 6650 6460 6170 5860 5750 5860 5830 1914 5580 5380 5130 5550 6090 6140 5920 5780 5690 5520 5580 5300 1915 4930 4930 5100 4960 5300 5380 5470 5660 5640 5610 5580 5350 1916 5550 5550 5350 5720 6140 6310 6170 6000 5800 5660 5550 5550 1917 5320 5070 5270 5720 6200 6510 6630 6480 6260 6260 6230 6120 1918 5490 5240 5610 5470 5690 5830 5780 5750 5830 5690 5860 5660 1919 5830 5610 5690 6000 6510 6510 6260 6200 6000 5780 5860 5640 1920 5010 4620 4760 5100 5640 5780 5800 5720 5660 5640 5610 5800 1921 5490 5300 5440 5780 6090 6000 5920 5660 5610 5410 5270 5640 1922 5240 4870 4930 5660 5920 5970 5800 5660 5550 5470 5380 5100 1923 4930 4700 4870 5040 5380 5520 5320 5240 5100 5010 4960 5210 1924 5440 4870 4900 5150 5690 5660 5690 5520 5410 5380 5300 5150 1925 4560 4470 4790 4870 5100 5070 4930 4870 4810 4840 4930 4870 1926 4130 3960 4330 4670 4730 5130 4960 4930 4980 5380 5580 5270 1927 4900 4810 4840 5150 5490 5610 5520 5410 5300 5130 5150 5750 1928 5470 5070 5070 5180 5470 5830 5920 5780 5640 5490 5610 5640 1929 5440 5320 5720 6340 7020 6910 6820 6570 6290 6090 6340 6090 1930 6290 6060 6310 6140 6650 6650 6400 6060 5950 5720 5610 5470 1931 5240 4930 4700 4980 5180 5180 5180 5100 5010 4900 4900 4930 1932 5350 5470 5130 5180 5380 5380 5300 5100 4900 4810 4730 4810 1933 4930 4620 4500 4790 5490 5490 5180 4980 4840 4730 4620 4470 1934 4390 3990 4050 4390 4500 4470 4360 4390 4360 4330 4190 4280 1935 4190 4050 4160 4300 4620 4730 4670 4760 4590 4470 4420 4390 1936 3990 3280 4360 4790 4870 4980 4810 4670 4560 4670 4760 4470 1937 4980 5210 4960 5210 5640 5690 5860 5640 5350 5130 5070 4900 1938 4470 4560 4960 5380 5550 5520 5470 5580 5350 5180 5210 5180 1939 4810 4700 4960 5150 5580 5660 5520 5520 5300 5240 5070 5150 1940 4590 4500 4640 5150 5350 5640 5520 5300 5350 5150 5270 5300 1941 5240 5100 4900 5010 5130 5130 5100 5010 4930 4840 5010 4810 1942 4560 4530 4840 5270 5580 5660 5640 5660 5580 5470 5610 5610 1943 5210 5410 5440 5490 6260 6740 6570 6480 6260 5950 6000 5890 1944 5380 5300 5320 5720 6170 6260 6060 5860 5750 5580 5410 5520 1945 4960 5070 5550 5830 6140 6230 6200 6170 6030 6370 6120 6060 1946 5830 5490 5640 5830 5890 6140 6060 6000 5720 5550 5640 5580 10

Table 4, Continued Recommended Monthly Mean Niagara River Flows at Buffalo 1900-2007 With Flows for 1961-2007 Adjusted to Reflect Better Estimates of Outflow from the Maid-of-the-Mist Pool (Cubic Meters per Second, rounded to nearest 10 cms) Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1947 5350 5040 5240 5210 6290 6910 6630 6370 6290 5920 5950 5920 1948 5490 5470 5780 6230 6570 6480 6310 6140 5860 5660 5720 5550 1949 5660 5750 5640 5720 5780 5640 5550 5440 5410 5150 5100 5100 1950 5550 5660 5660 5890 6200 6120 5860 5660 5610 5520 5660 5860 1951 5780 5690 5800 6400 6570 6480 6290 6120 6000 5890 6030 6140 1952 6460 6570 6710 6970 7110 6850 6630 6510 6480 6230 6030 6090 1953 6030 6230 6200 6290 6370 6340 6290 6260 6140 5800 5800 6030 1954 5580 5490 5890 6290 6480 6290 6060 6090 5970 6230 6340 6310 1955 6430 6140 6510 6680 6710 6460 6200 6140 5860 5950 6060 5780 1956 5210 5130 5350 5720 6290 6170 6030 6090 6060 5640 5640 5490 1957 5440 5240 5270 5780 5920 5890 6030 5720 5640 5320 5490 5440 1958 5350 4960 4980 5070 5150 5180 5270 5270 5210 5040 5070 4870 1959 4670 4810 5130 5320 5580 5580 5320 5150 4960 5070 5210 5180 1960 5470 5410 5180 5470 5920 6030 5950 5750 5690 5550 5640 5440 1961 5190 5240 5460 5960 6520 6360 6120 6000 5940 5630 5500 5560 1962 5080 4940 5270 5410 5600 5420 5330 5250 5220 5190 5010 5280 1963 4800 4530 5030 5130 5360 5420 5130 5050 4710 4540 4730 4730 1964 4070 4080 4670 4960 5300 5160 4930 4850 4710 4590 4470 4390 1965 4470 4670 4870 4930 5220 5300 5100 4990 4930 5080 5120 5040 1966 5070 5150 5320 5330 5730 5700 5590 5500 5300 5190 5120 5520 1967 5490 5350 5240 5700 5950 5700 5730 5610 5470 5640 5770 5740 1968 5570 6150 5850 5970 6080 6170 6170 6010 5950 5840 5740 6010 1969 5740 5980 5920 6170 6790 6820 6710 6650 6430 6260 6210 6070 1970 5680 5740 5770 6070 6320 6260 6260 6090 6090 5950 6120 6120 1971 6120 5920 6150 6110 6230 6510 6200 6110 6070 6040 5980 6070 1972 6210 5920 6290 6400 6740 6790 6820 6680 6540 6620 6790 7100 1973 7050 6790 7210 7560 7530 7530 7440 7160 6880 6680 6740 6680 1974 6710 6820 7160 7560 7610 7420 7160 6880 6710 6460 6520 6620 1975 6850 6760 6760 7050 7050 7080 6910 6760 6910 6680 6680 6540 1976 6420 6590 7160 7360 7390 7080 7080 6790 6740 6570 6420 5960 1977 5610 5510 5850 6170 6570 6420 6320 6350 6400 6290 6210 6490 1978 6010 5990 6160 6650 6740 6820 6430 6350 6090 6090 5890 6050 1979 5760 5710 5960 6400 6680 6710 6540 6620 6540 6570 6460 6550 1980 6630 6260 6420 6910 6990 6990 6820 6910 6820 6620 6260 6150 1981 5820 5910 6050 6080 6480 6690 6540 6580 6600 6510 6430 6320 1982 6280 5940 6430 6580 6660 6870 6420 6370 6100 5990 6220 6400 1983 6400 6170 6200 6510 6930 6600 6750 6840 6630 6370 6470 6740 1984 6050 6260 6530 6750 6800 6830 6720 6580 6510 6330 6400 6400 1985 6310 5740 6850 7480 7470 7420 7030 6890 6800 6590 6930 7530 1986 6440 6750 7380 7330 7620 7740 7640 7330 7040 7320 7140 7440 1987 7320 6960 6910 7180 7100 6940 7010 6770 6650 6480 6210 6390 1988 6170 6110 6070 6200 6340 6110 5850 5970 5710 5740 5700 5690 1989 5720 5530 5320 5970 6170 6450 6230 6200 5930 5760 5930 5410 1990 5520 5820 5990 6280 6370 6280 6020 6060 6200 6130 5960 6160 1991 6470 6290 6340 6450 6510 6220 6070 5900 5790 5560 5520 5700 1992 5470 5610 5820 6170 6250 5930 6130 6280 6480 6360 6460 6580 1993 6930 6550 6600 7030 6960 6600 6680 6380 6260 6170 6080 6160 11

Comparing the Adjusted Niagara River flows to Flows Computed using the 2001 Buffalo Rating Equation This comparison was only done for May and November, which are usually considered to be open water months. Figure 1 shows a comparison between the Niagara River flows computed using the 2001 Buffalo rating equation and the published Niagara River flows. Figure 2 is the same comparison but with the adjusted published flows. The period of comparison is 1973-2006 because the 2001 Buffalo rating equation is for river conditions since the 1973 Directive changed the operation of the International Control Structure in the Chippawa-Grass Island Pool and consequently the hydraulic slope in the river. Figure 1 Comparison Published & Computed (2001Eq) Niagara River Flow 1973-2006 8000 7500 Published Flow, cms 7000 6500 6000 May Nov 5500 5000 5000 5500 6000 6500 7000 7500 8000 Computed Flow, cms 13

Figure 2 Comparison ADJUSTED Published & Computed (2001Eq) Niagara River Flow 1973-2006 8000 7500 Published Flow, cms 7000 6500 6000 May Nov 5500 5000 5000 5500 6000 6500 7000 7500 8000 Computed Flow, cms 14