Niagara Power Project FERC No. 2216

 

EFFECT OF WATER LEVEL AND FLOW FLUCTUATIONS ON AQUATIC AND TERRESTRIAL HABITAT

 

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Prepared for: New York Power Authority 

Prepared by: Stantec Consulting Services, Inc.; URS Corporation; Gomez and Sullivan Engineers, P.C.; and E/PRO Engineering & Environmental Consulting, LLC

 

August 2005

 

Copyright © 2005 New York Power Authority

 

___________________________________________________

 

EXECUTIVE SUMMARY

STUDY PURPOSE

The Niagara Power Project in Lewiston, Niagara County, New York, is one of the largest non-federal hydroelectric facilities in North America.  In 1957, a 50-year license for operation of the Project was issued by the Federal Power Commission (now the Federal Energy Regulatory Commission, or FERC) to the Power Authority of the State of New York (now the New York Power Authority, or NYPA).  The Project first produced electricity in 1961.  The operating license for the Project expires in August 2007 and NYPA has begun the relicensing process.  As part of the relicensing process, NYPA investigated the potential effects of water level and flow (when used in this report the term “flow” means velocity) fluctuations on aquatic and terrestrial habitat.  The Investigation Area includes U.S. waters of the mainstem upper Niagara River and mainstem lower Niagara River and portions of its tributaries, and associated riparian habitats.  For this report, the upper Niagara River is defined as that part of the United States portion of the Niagara River from the Peace Bridge downstream to the Niagara Power Project intakes.  The lower Niagara River is defined as the United States portion of the Niagara River from the tailrace of the Niagara Power Project downstream to Lake Ontario.  U.S. waters and riparian zones extending from the Project water intakes in the upper river to the tailrace in the lower river are being examined in a separate study and are not discussed in this report.  Stantec Consulting Services, Inc. conducted all fieldwork, preliminary data analysis, wrote habitat descriptions for this report, and provided technical assistance in determining the potential effects of water level and flow fluctuations on aquatic and terrestrial habitats.  Gomez and Sullivan Engineers, P.C. and E/PRO Engineering & Environmental Consulting, LLC completed the final analysis of potential effects on habitats and species that use these habitats.  URS Corporation produced all maps and figures for this report.   

 

STUDY PARAMETERS

            Water Level and Flow Fluctuations

Water level and flow fluctuations in both the upper and lower Niagara River are caused by a number of factors.  Natural factors include flow surges from Lake Erie, wind, ice conditions, and regional and long-term precipitation patterns that affect lake levels, while manmade factors include boat wakes, regulation of Niagara Falls flows per the 1950 Niagara River Water Diversion Treaty, operation of hydroelectric power plants on the Canadian side of the river, and operation of the Niagara Power Project.  The influence of these factors on water levels is interrelated and dynamic.  Because the water level in the Niagara River at any location at any time is a complex function of natural and manmade factors, distinguishing the exact amount of water level fluctuation attributable to each factor is difficult.  In the upper river, the fluctuations were assessed using monthly minimum and maximum water level data from permanent water level gauges for a typical, wet and dry year.  All “significant” storm events were removed from the dataset.  For the lower river, monthly minimum and maximum water levels from temporary gauges in 2002 were used.   For the Lewiston Reservoir, monthly minimum and maximum water levels from 1991-2002 were used.  Even the efforts to remove water level data recorded during significant storm events could not isolate the effects of NYPA and OPG operations on water levels and flow in the upper Niagara River as there are other influencing factors, such as localized environmental conditions on Lake Erie and smaller wind events that were included in the analysis.  Because water level fluctuations are influenced by a number of factors, the approach used for this investigation provides a resource conservative of the potential effects due to NYPA and OPG operations (i.e., resource conservative means that this analysis is likely to overestimate rather than underestimate the effect of NYPA and OPG power operations on habitat in the investigation area). 

            Habitat Characterization

The aquatic habitats in the upper and lower Niagara River, Lewiston Reservoir and the terrestrial habitats near these areas were delineated and classified using a combination of aerial photography, existing literature, and field surveys.  Key habitat features that were mapped included water depth zones, the location and relative extent of areas with little or no current, dominant substrates, the location of submerged aquatic vegetation (SAV) and emergent aquatic vegetation (EAV), and the location of documented large wetland areas.  In 2002, field data collection was completed along 24 representative transects in the upper and lower river and Lewiston Reservoir.  In addition, three cross-sectional transects per tributary (a total of nine) were established in Tonawanda, Cayuga, and Ellicott Creeks.  Elevation control was established at each transect and site-specific aquatic and terrestrial habitat data were collected.  The resulting habitat information was used in assessing habitat availability and distribution in relation to fluctuating water levels. 

Habitats were described by their attributes (e.g., depths, vegetation type, substrate, velocity).  Water level fluctuations in the Niagara River and Lewiston Reservoir were analyzed using water elevation data from 10 permanent gauges in the upper river, four temporary gauges in the lower river, and one permanent gauge in the Lewiston Reservoir.  The potential effect of water level and flow fluctuations on aquatic and terrestrial habitat and the habitat used by representative species was assessed in the upper and lower Niagara River and Lewiston Reservoir.  The was accomplished using (1) minimum and maximum water elevations superimposed on the habitat that exists in a given area to identify the habitat types located in the zone of fluctuation and (2) information in existing scientific literature to make qualitative determinations regarding the potential effect on habitats and representative focus species.

            Focus Species

The potential effects of these water level and flow fluctuations on aquatic and terrestrial habitats and the habitat of representative (focus) species were assessed by examining the timing and magnitude of the fluctuations in relation to the habitats that exist in a given area and how and when these habitats are utilized by these species.  A total of 37 species (19 fish, 15 wildlife, and three macroinvertebrates) were selected by NYPA, USFWS, and NYSDEC.  These were chosen because they are of particular interest (i.e., lake sturgeon), represent the majority of all species that use the various habitats in the investigation area for specific life-stages (i.e., spawning and nesting, overwintering, foraging, etc.), and sufficient literature exists on the habitat requirements for these species.  These species were used as analysis tools for determining the potential effects of water and flow fluctuations on aquatic and terrestrial habitats in the investigation area.  Although the potential effects discussed in this report are focused on the life stage of the 37 representative species, these species are meant to represent similar grouping of species that use habitats influenced by water level and flow fluctuations for similar life stages.

FINDINGS AND CONCLUSIONS

            Aquatic and Terrestrial Habitat

                        Upper Niagara River

In the upper river, water depths affected by water level fluctuations were determined to be within the 0-2-foot zone, and a small component (the first 0.5 feet) of the 2-6-foot depth zones, with the difference in monthly maximum and minimum water elevations being <2 feet for most months and years.   Most areas that were not sheltered from wind or wave action had little or no submerged aquatic vegetation (SAV) in the 0-2-foot depth zone, and SAV was common in 2-20 feet of water, much of it forming dense beds.  Areas that were particularly exposed to southwest winds had little or no vegetation between 0 and 4 feet deep.  Sheltered areas often had SAV and EAV (emergent aquatic vegetation) in the 0-2-foot zone.  This is similar to a survey conducted in 1955, which found SAV in water generally 1.5 – 5.5 feet deep, and in water <1.5 feet deep in sheltered areas; however it was not indicated what the water surface elevation was during the 1955 survey.  A survey conducted in 1928 also found SAV and EAV in the same locations as in 1955 and 2002 (although SAV occurred at depths up to ~20 feet in 2002).  The same species were dominant in all years.  The potential effect of water level fluctuations in the 0-2-foot depth zone is on SAV and EAV distribution.  It is possible that in some areas of the river, water level fluctuations have created conditions for SAV and EAV such that their distribution shifts landward in wet years and towards the center of the channel of the river in dry years.  An indirect effect of these fluctuations is on where wind and wave action may be focused, which has the potential to affect SAV and EAV establishment in nearshore areas. Water level fluctuations potentially affect the extent of areas of little or no velocity in the upper and lower rivers, causing slight decreases in extent as water levels fall and slight increases in extent as water levels rise.

Long-term (e.g., seasonal, yearly) water level fluctuations in the upper river and Grand Island tributaries could result in changes in coastal wetland habitat structure, distribution, and species composition over time.  Many coastal wetlands are dynamic ecosystems that require water level fluctuations and both high and low water levels to maintain habitats and the diversity of plant and animal species.  These long-term fluctuations have varying sources, magnitudes, frequencies, timing, and duration, each with different effects on wetlands, and are important to the maintenance of coastal wetlands.  Short-term (daily) fluctuations resulting from American and Canadian hydroelectric operations likely have a limited direct effect on coastal wetlands because these fluctuations are cyclical, with generally consistent extent and frequency; enabling wetland vegetation to become adapted.  The portion of Buckhorn Marsh that is located between the two weirs is not affected by water level fluctuations and water levels between these water level control structures are relatively stable.  

Regulation of water levels that result in dampening of fluctuations can affect coastal wetlands.  Where water-level regulation has significantly reduced the occurrence of extreme high and low water levels, disruption of the natural fluctuation cycle favors species intolerant of water-depth change and associated stresses, and/or excludes species requiring periodic exposure of fertile substrates, potentially leading to a reduction of species diversity.  For example, the dominance of cattails in many Lake Ontario marshes suggests a trend toward reduced species diversity following a reduction in the amplitude of natural water level fluctuations.

Seasonal and daily fluctuations in water levels may influence the portion of the nearshore zone affected by waves by exposing a wider area of this zone to wave action than if there were no fluctuations.  Energy associated with waves may be an important factor affecting the local extent of EAV in nearshore habitats, physically uprooting and removing EAV and creating bands of coarser substrates in exposed nearshore habitats. 

            Lower Niagara River

In the lower river, monthly differences between maximum and minimum elevations are similar to those of the upper river.  Water depths affected by water level fluctuations were determined to be within the 0-2-foot and a small component (approximately the first 0.5 feet) of the 2-6-foot depth zones.  In the lower river, water level fluctuations affect depth to a greater extent than width, as the river’s sides are very steep.  The distribution of SAV in the nearshore area of the lower river may be affected in the same manner as in the upper river, although the nearshore area in the lower river where SAV could become established is much narrower than in the upper river.  A 1928 survey of the lower river found that SAV was uniformly distributed in the nearshore area at depths of 3-13 feet, which is similar to that found in 2002 (although SAV occurred at depths up to ~20 feet in 2002).  No wetlands and very little EAV were identified in the lower river.  Water level fluctuations potentially affect the extent of areas of little or no velocity in the upper and lower rivers, causing slight decreases in extent as water levels fall and slight increases in extent as water levels rise.

Coastal wetland habitats do not occur in the lower river because of the relatively steep slopes leading down to the water, the lack of shallow water areas with flat bathymetry, coarse substrates, and fast water flows.  These combined factors are not conducive to the development of large, fringe riverine wetlands, and these habitats likely have never existed in the lower river to any great extent. 

            Lewiston Reservoir

The sides of the Lewiston Reservoir are large boulder riprap, which is unsuitable substrate for the establishment of SAV.  Most of the bottom of the reservoir contains substrate suitable for SAV establishment, but extensive SAV establishment is likely precluded by water level fluctuations. 

The steep, riprapped interior walls of Lewiston Reservoir, combined with the extreme weekly water level fluctuations, are not conducive to the development of coastal wetland habitats and none occur there.

Fish and Macroinvertebrate Focus Species

            Upper and Lower Niagara River

Water level and flow fluctuations have the potential to affect the spawning, egg, and larval habitat used by lake sturgeon, lake trout, muskellunge, largemouth bass, smallmouth bass, walleye, yellow perch, bluntnose minnow, northern pike, and crayfish (in both the upper and lower Niagara River), brown bullhead, greater redhorse, burrowing mayfly nymphs and eggs, and giant floater mussels (in the upper Niagara River only), and Chinook salmon and rainbow smelt (in the lower Niagara River only).  Potential effects resulting from the loss of use of shallow water habitats are somewhat mitigated by the fact that suitable habitat exists at greater depths and affords opportunities for these species’ lifestages at depths that are not affected by water level fluctuations.  Northern pike are documented to spawn in shallow (<1.2 feet deep) water on SAV and EAV, but are also documented to spawn over SAV in water up to 16 feet deep.  SAV is common throughout the upper river and along the shorelines of the lower river in water up to ~20 feet deep, and may provide suitable spawning, egg and larval habitat at depths that are not affected by water level fluctuations.  EAV is nearly absent from the lower Niagara River; therefore, northern pike in the lower river may spawn only over SAV, which is generally below the depth affected by water level fluctuations. 

Water level and flow fluctuations in the upper and lower Niagara River also have the potential to affect the spawning, egg and larval habitat used by white sucker.  Of the aquatic focus species, white sucker have the narrowest range of reported spawning depths (0.2 – 1 foot), a range of depths that are fully encompassed by the water level fluctuations in the upper and lower river

The spawning, egg, and larval habitat of emerald shiner are not affected by water level and flow fluctuations in the upper and lower Niagara River, as emerald shiner are pelagic and their spawning, egg and larval habitat is in mid-water.  In addition, water level fluctuations in the lower Niagara River do not affect burrowing mayfly nymphs and eggs, and giant floater mussels.

            Lewiston Reservoir      

The large boulder riprap sides of the Lewiston Reservoir are not suitable substrate for the spawning of smallmouth bass, rock bass, and yellow perch.  The substrate of the bottom of the reservoir (primarily clay, mud, muck and silt) is not suitable for smallmouth bass and rock bass spawning.  Although the substrate of the bottom of the reservoir is suitable for yellow perch spawning, at the time the fieldwork was conducted for this investigation there was little SAV and submerged brush, the preferred habitat for yellow perch spawning.  Similar to the upper and lower river, the spawning, egg, and larval habitat of emerald shiner are not affected by water level fluctuations in Lewiston Reservoir because emerald shiner are pelagic and their spawning, egg and larval habitat is in mid-water. 

Wildlife Focus Species

            Upper and Lower River

The representative wildlife species that potentially lay eggs and hibernate in suitable habitat in areas influenced by water level fluctuations in the upper river and its tributaries include the green frog, northern leopard frog, common mudpuppy, common snapping turtle, and midland painted turtle.  In the lower river these species include the common mudpuppy, green frog, common snapping turtle, and midland painted turtle.  Any potential effects are somewhat mitigated by the presence of suitable habitat in the upper and lower rivers for these species’ lifestages at depths that are not influenced by water level fluctuations.        

Some of the suitable nesting habitat of the Virginia rail, American coot, and spotted sandpiper is located in areas influenced by water level fluctuations in the upper river and its tributaries.  However, water and shorebirds are known to adapt to water level changes by employing various nest building strategies and/or by laying multiple clutches of eggs during the nesting season.  A similar situation exists in the lower river for the nesting lifestage of the spotted sandpiper. 

There is muskrat habitat (for all lifestages) in the upper river that is influenced by water level fluctuations.  However, sufficient food sources exist in the upper river and there is suitable water depth for muskrat below the zone that is influenced by fluctuating water levels.  In addition, literature also indicates that muskrats can build high and low level (elevation) dens and access tunnels in river banks to accommodate fluctuating water levels.  There appears to be suitable habitat available for the muskrat in areas not influenced by water level fluctuations (i.e., between the weirs at Buckhorn Marsh, some of the marsh associated with Burnt Ship Creek west of Interstate 190).  The presence of a muskrat den on Grass Island in the Chippawa-Grass Island Pool east of Woods Creek suggests that water level fluctuations in the upper river may be within tolerances for this species. 

Water level fluctuations can have an overall positive effect on the foraging opportunities of wildlife focus species that feed in nearshore habitats of the upper (and its tributaries) and lower rivers.  Temporal shifting of the water depth zones can increase foraging opportunities for these species by increasing the amount of area available for foraging when the water is low.  Conversely, foraging opportunities can be diminished when water levels are high.

According to literature and review of field data collected in 2002, all other wildlife focus species’ lifestages are mobile or are more likely to occur outside of areas influenced by water level fluctuations during immobile lifestages.

            Lewiston Reservoir

Preferred substrates and hibernacula for the common snapping turtle are absent from Lewiston Reservoir and suitable nesting habitat is found outside the zone of water level fluctuations, and great blue heron, canvasback, and greater scaup do not nest in the reservoir.  Foraging opportunities for the great blue heron and spotted sandpiper would likely be enhanced during low water levels in the reservoir because of the increased availability of forage area and easier access to prey.  Conversely, the foraging efficiency of canvasback is potentially indirectly affected by water level fluctuations because the extreme weekly fluctuations in Lewiston Reservoir preclude the development of extensive SAV beds.  The effects on the foraging efficiency of greater scaup are expected to be minimal because this species forages in a wide range of water depths (similar to those found in the reservoir).  During the time that this species typically occurs on the reservoir to any significant extent (fall and winter), water depths in most areas of the reservoir are at least 10 feet or greater.


ABBREVIATIONS

Agencies

FERC               Federal Energy Regulatory Commission

INBC               International Niagara Board of Control

NYNHP            New York Natural Heritage Program

NYSOPRHP     New York State Office of Parks, Recreation and Historic Preservation

NYSCD            New York State Conservation Department

NYSDEC          New York State Department of Environmental Conservation

NYPA              New York Power Authority

OPG                 Ontario Power Generation

USFWS            United States Fish and Wildlife Service

Units of Measure

C                      Celsius, Centigrade

cfs                    cubic feet per second

cm                   centimeter

EST                  Eastern Standard Time

F                      Fahrenheit

fps                    feet per second

ft                      feet

IGLD 1985       International Great Lakes Datum 1985

in                     inch

m                     meter

mi                    mile

mm                  millimeter

MW                 Megawatt

USLSD             U.S. Lake Survey Datum 1935

Environmental

EAV                 emergent aquatic vegetation

HSI                  habitat suitability index

IBA                  Important Bird Area

SAV                 submerged aquatic vegetation

 


1.0     INTRODUCTION

The New York Power Authority (NYPA) is engaged in the relicensing of the Niagara Power Project (Project) in the Town of Lewiston, Niagara County, New York.  The present operating license of the plant expires in August 2007.  In preparation for the relicensing of the Project, NYPA is developing information related to the ecological, engineering, recreational, cultural, and socioeconomic aspects of the Project.  As part of this information-gathering effort, aquatic and terrestrial habitats were mapped and characterized in relation to documented water levels so that the potential effects of water level and flow fluctuations on these habitats and associated species could be qualitatively evaluated.  

The scope and design of this investigation was prepared by the Niagara Power Project Relicensing Team, which consists of technical and relicensing staff from NYPA; URS Corporation (URS); Gomez and Sullivan Engineers, P.C.; E/PRO Engineering and Environmental Consulting, LLC; and Aquatic Science Associates, Inc.  Stantec Consulting Services, Inc. conducted all fieldwork, preliminary data analysis, wrote habitat descriptions for the report, and provided technical assistance in determining the potential effects of water level and flow fluctuations on aquatic and terrestrial habitats.  Gomez and Sullivan Engineers, P.C. and E/PRO Engineering & Environmental Consulting, LLC completed the final analysis of potential effects on habitats and species that use these habitats.  URS Corporation produced all maps and figures for this report.

The 1,880-MW (firm capacity) Niagara Power Project is one of the largest non-federal hydroelectric facilities in North America.  The Project was licensed to the newly created Power Authority of the State of New York (now the New York Power Authority) in 1957.  Construction of the Project began in 1958, and first electricity was produced in 1961.

The Project has several components.  Twin intakes are located approximately 2.6 miles above Niagara Falls.  Water entering these intakes is routed around the Falls via two large low-head conduits to a 1.8-billion-gallon forebay, lying on an east-west axis about 4 miles downstream of the Falls. The forebay is located on the east bank of the Niagara River.  At the west end of the forebay, between the forebay itself and the river, is the Robert Moses Niagara Power Plant, NYPA’s main generating plant at Niagara.  This plant has 13 turbines that generate electricity from water stored in the forebay.  Head is approximately 300 feet.  At the east end of the forebay is the Lewiston Pump Generating Plant.  Under non-peak-usage conditions (i.e., at night and on weekends), water is pumped from the forebay via the plant’s 12 pumps into the 22-billion-gallon Lewiston Reservoir, which lies east of the plant.  During peak usage conditions (i.e., daytime Monday through Friday), the pumps are reversed for use as generators, and water is allowed to flow back through the plant, producing electricity.  The forebay therefore serves as headwater for the Robert Moses plant and tailwater from the Lewiston Plant.  South of the forebay is a switchyard, which serves as the electrical interface between the Project and its service area.

Approximately 3,600 acres of lands and waters are owned by NYPA in the Village and Town of Lewiston, City of Niagara Falls, and Town of Niagara.  The NYPA-owned lands are managed by NYPA in association with the generation and transmission of electricity at the Niagara Power Project. 

1.1         Physical Description of the Niagara River

The Niagara River, which flows from Lake Erie to Lake Ontario, forms a portion of the boundary between the State of New York and the Province of Ontario.  The river drains four of the five Great Lakes, a drainage area of approximately 263,700 square miles. The difference in surface elevations between the two lakes is about 326 feet, half of this occurring at Niagara Falls. 

The upper Niagara River extends about 22 miles from Lake Erie to the Cascades Rapids, which begin 0.6 miles upstream of the Horseshoe Falls (Canadian side of river).  From Lake Erie to Strawberry Island, a distance of approximately 5 miles, the channel width is greatest at the river’s head (9,000 feet) and least at Squaw Island, just downstream of the Peace Bridge (1,500 feet).  Average channel velocities are approximately 5 to 9 feet per second (fps) in the vicinity of the Peace Bridge.  Between Squaw and Strawberry Islands, the river width is approximately 2,000 feet, with average channel velocities on the order of 4 to 5 fps.

At Grand Island, just downstream of Strawberry Island, the river divides into the west channel, known as the Canadian or Chippawa Channel, and the east channel, known as the American or Tonawanda Channel.  The Chippawa Channel, approximately 11 miles long, varies in width from 2,000 to 4,000 feet.  Average channel velocity is 2-3 fps.  The Chippawa Channel carries approximately 58% of total river flow. The 15-mile-long Tonawanda Channel varies in width from 1,500 to 2,000 feet upstream of Tonawanda Island.  Downstream of this island the channel varies in width from 1,500 to 4,000 feet, with average channel velocities of 2-3 fps.  At the downstream end of Grand Island (i.e., the north end), the channels unite to form the 3 mile-long Chippawa-Grass Island Pool, at the lower end of which is the International Niagara Control Structure.  This linear structure, with 18 sluice gates for control of flow over Niagara Falls, extends perpendicularly from the Canadian shoreline to the approximate midpoint of the river.  The Falls is located about 4,500 feet downstream of the International Niagara Control Structure.  The fall (i.e., change in elevation) from Lake Erie to the Chippawa-Grass Island Pool is approximately 9 feet.  The lower Niagara River emerges from the gorge at Lewiston, New York, subsequently dropping another 5 feet to Lake Ontario, and widening to 2,000 feet.  The lower Niagara River is navigable from the mouth at Lake Ontario to just upstream of the Niagara Power Project tailrace by conventional watercraft, and upstream to the Whirlpool by specialized watercraft.

1.2         Investigation Area

For this report, the upper Niagara River is defined as that part of the United States portion of the Niagara River from the Peace Bridge downstream to the Niagara Power Project intakes.  The lower Niagara River is defined as that part of the United States portion of the Niagara River from the tailrace of the Niagara Power Project downstream to Lake Ontario  (Figure 1.3-1).  The Investigation Area includes U.S. waters of the mainstem upper Niagara River and mainstem lower Niagara River and portions of its tributaries, and associated riparian habitats.  Excluded from this is the area between the upper and lower Niagara River as defined above.  This area is the subject of a separate report.  Discussions in this report focus primarily on the upper Niagara River (including Twomile Creek and several upper Niagara River tributaries on Grand Island) and three mainstem tributaries of the upper river (Tonawanda Creek, Ellicott Creek, and Cayuga Creek), the lower Niagara River, and Lewiston Reservoir. 

1.3         Objectives and Tasks

The objectives of this investigation were to:

1.      Assess the potential effects of water level and flow fluctuations on aquatic and terrestrial habitats in the investigation area.

2.      Describe the outcomes of Objective 1 on specific life stages of representative aquatic and terrestrial focus species that utilize potentially affected habitats.

The tasks used to address the objectives were:

1.      Delineate and classify aquatic and terrestrial habitats in the investigation area.

2.      Characterize aquatic and terrestrial habitats in the investigation area along representative transects.

3.      Describe the potential effects of water level and flow fluctuations on aquatic and terrestrial habitats of the Niagara River, selected tributaries of the river, and Lewiston Reservoir.

4.      Identify representative aquatic and terrestrial species of interest.

5.      Describe how the representative aquatic species use their habitats.

6.      Describe how representative terrestrial species use their habitats.

7.      Identify species and lifestages that may be affected by water level and flow fluctuations.

Habitat mapping across the investigation area provided a general overview of habitat within the upper Niagara River, lower Niagara River, and Lewiston Reservoir.  Detailed habitat characterization along representative transects described the distribution of specific habitat features and provided the basis for evaluations of the potential effects of water level fluctuation on nearshore habitat and associated species.  Qualitative assessments were made primarily using cross-sectional views of representative transects to evaluate relationships between habitats (and associated fish and wildlife) and water level fluctuation patterns documented in the investigation area.  Plan view habitat maps were also consulted to assess habitat availability and distribution. 

Water level and flow data from 1991 to 2002 were analyzed by URS et al. (2005a) to characterize fluctuations and to identify the relative influence of natural and anthropogenic causal factors.  Results of those analyses were used to identify the potential effects of water level and flow fluctuations on aquatic and terrestrial resources.


Figure 1.3-1

Investigation Area

[NIP – General Location Maps]


2.0     WATER LEVEL AND FLOW FLUCTUATIONS

Data on Niagara River and Lewiston Reservoir water level and flow fluctuations are integral to assessing the potential effects of those fluctuations on habitats and species.  This section describes the regulations governing water levels and flow, the results of the water level and flow fluctuation analyses completed in support of NYPA’s relicensing of the Project as they pertain to the subject of this habitat report, and the average Niagara River water velocities.

2.1         Treaty and Regulations Governing Water Levels and Flow

In 1950, the United States and Canada signed the Niagara River Water Diversion Treaty, the purpose of which was to preserve the beauty of Niagara Falls by guaranteeing adequate flow over the Falls, at the same time ensuring the fair use of remaining water for power generation.  Article IV of the treaty provides that no less than 100,000 cubic feet per second (cfs) must be released over Niagara Falls from 8 a.m. to 10 p.m. EST beginning April 1 and ending September 15 each year, and from 8 a.m. to 8 p.m. EST beginning September 16 and ending October 31 each year (i.e., the tourist season).  It also provides that no less than 50,000 cfs must be released over Niagara Falls at any other time.  Article V provides that all water in excess of the mandated flows over Niagara Falls may be diverted for power purposes. 

The 1993 Directive of the International Niagara Board of Control (INBC) requires that the International Niagara Control Structure be operated to ensure an operational long-term average pool level of El. 562.75 feet (IGLD 1985 El. 561.55).  All elevations in this report are referenced to U.S. Lake Survey Datum 1935 (USLSD).  Values for other pertinent datums, such as International Great Lakes Datum 1985 (IGLD 1985), are listed in parentheses.  The Directive also establishes certain tolerances for the pool’s water level as measured at the Material Dock gauge (located on the Canadian side of the river approximately 3 miles upstream of Niagara Falls), permitting up to 1.5 feet fluctuation between daily maximum and minimum levels.  This daily allowable fluctuation must occur within a normal 3-foot range between El. 561.24 to 564.22 feet (IGLD 1985 El. 560.04 to 563.02), as shown in Figure 2.1-1.  Under extreme conditions (e.g., high flow, low flow, ice), the allowable range of Chippawa-Grass Island Pool water level fluctuation is extended to 4 feet.  The Directive establishes the absolute permissible low level in the pool at El. 560.75 feet (IGLD 1985 El. 559.55) and the absolute permissible high water level at El. 564.75 feet (IGLD 1985 El. 563.55). 

2.2         Water Level Fluctuation Analyses

As part of the relicensing process for the Niagara Power Project, URS characterized the fluctuation that occurs within the upper Niagara River, lower Niagara River, and Lewiston Reservoir from 1991 through 2002.  Data were collected from 16 permanent water level gauges in the upper and lower river and Lake Ontario (URS et al. 2005a) and from four temporary water level gauges in the lower river downstream of the Robert Moses tailrace in late October to early November 2001 and during the period June through November 2002.  The locations of these gauges are shown in Figure 2.2-1.  Water levels were also monitored in 2002 in and around Buckhorn Marsh on the northern end of Grand Island (see Section 2.2.1.2).

The URS characterization included a description of: 1) the magnitude, frequency and spatial extent of water level and flow fluctuations in the Niagara River associated with water diversions for power generation at the Niagara Power Project and the Sir Adam Beck Project and 2) the magnitude and frequency of water level fluctuations in Lewiston Reservoir associated with power generation at the Project.  It was known at the investigation’s outset that water level and flow fluctuations in both the upper and lower Niagara River are caused by a number of factors.  Natural factors include flow surges from Lake Erie, wind, ice conditions, and regional and long-term precipitation patterns that affect lake levels, while manmade factors include boat wakes, regulation of Niagara Falls flows for scenic purposes, operation of power plants on the Canadian side of the river, and operation of the Niagara Power Project.  The influence of these factors on water levels is interrelated and dynamic.  Because the water level in the Niagara River at any location at any time is a complex function of natural and manmade factors, distinguishing the exact amount of water level fluctuation attributable to each factor is difficult.  The URS et al. (2005a) report also differentiates the effects of significant wind events (defined as those that caused changes in flow at Fort Erie on the order of 25,000 to 50,000 cfs per day or a change in water level at Fort Erie greater than 2 feet per day) that induced water level fluctuations through a combination of gauge data analysis and empirical calculation of surface wave height and wind setup (see Section 2.2.1.4).

Data were analyzed in various ways to produce a picture of daily fluctuation in the upper and lower river and to establish the upstream extent of such fluctuation in the upper river.  The results are summarized in the following sections.  Complete details are available in the water level study report (URS et al. 2005a). 

2.2.1        Upper Niagara River

Water level fluctuation in the upper Niagara River from all causes, including power production by both U.S. and Canadian plants and natural factors, normally amounts to less than 1.5 feet per day as measured at Material Dock, the official monitoring gauge (Table 2.2.1-1).  A daily water level fluctuation of 1.5 feet is allowed by the 1993 Directive of the INBC.  The portion of upper-river water level changes attributable to power production is the result of varying withdrawals of water by the Power Entities, namely, NYPA and Ontario Power Generation (OPG).  It was found that regulation of the Chippawa-Grass Island Pool water levels has a more pronounced effect during the tourist than the non-tourist period.  The reason for this is that during daylight hours in the tourist season, NYPA and OPG are required to pass more water over Niagara Falls for scenic purposes, making less of the natural flow in the river available for hydropower generation.  This requires NYPA and OPG to use more water from storage in the Chippawa-Grass Island Pool during the tourist season to meet energy demand. 

Lake Erie water levels and natural conditions, such as wind-generated flow surges and ice, influence water levels in the upper Niagara River, especially during the non-tourist season.  Graphs of hourly water level and flow data, duration-distribution analysis of daily fluctuations, and an analysis of the days with the greatest daily fluctuation by URS et al. (2005a) bear this out.

The elevation of Lake Erie also fluctuates on a short-term basis.  Lake Erie is a long, narrow, and relatively shallow lake with its major axis aligned with the prevailing southwesterly winds.  The head of the Niagara River lies at the downwind end of the lake near Buffalo, New York.  Strong southwest winds can greatly increase the lake water level at Buffalo, increasing river flow at the same time.  This increase in water level is called wind set-up, and represents a wind-induced tilting of the lake, called a seiche.

Regulation of Chippawa-Grass Island Pool water levels and river storage diminishes the effect of flow surges from Lake Erie.  During extreme events, water level increases at Fort Erie have reached as high as 10 feet, but the dampening effect along the river has led to a rise in Chippawa-Grass Island Pool surface levels of only one foot.  Wind-generated surface waves may contribute to water level fluctuations in the Chippawa-Grass Island Pool, while wind set-up is more of an influence at Fort Erie (URS et al. 2005a).

To demonstrate the relative contributions to water level fluctuations made by various natural and man-induced factors in the upper reaches compared to the lower reaches of the upper Niagara River, URS et al. (2005a) prepared two cross-sectional views of the upper river (one at Frenchman’s Creek and one at Material Dock) comparing these factors.  These drawings are included as Figures 2.2.1-1 and 2.2.1-2, respectively.  While the ranges for the 5/95% exceedance levels (i.e., water levels occurring greater than 5% but less than 95% of the time) are comparable between the two gauges, the ranges for maximum and minimum are much greater at Frenchman’s Creek (located in the upper reaches of the upper river near Lake Erie) compared to Material Dock (located in the lower reaches near the NYPA intakes).  The amplitudes of surface waves are similar between the two locations, but the amplitudes of potential storm surge event/wind set-up are dramatically different.  A storm surge on Lake Erie can cause a change in water level at Frenchman’s Creek of greater than 5 feet but can be less than the allowable 1.5 feet fluctuation at Material Dock. 

2.2.1.1   Upper Niagara River Tributaries

Water level fluctuations on the upper Niagara River influence water levels in tributaries to the mainstem.  To determine the extent of this influence, an analysis was performed by URS et al. (2005b) using “standard step backwater” hydraulic computations as described by the U.S. Army Corps of Engineers (USACE 2002).  The results illustrating the extent of the influence of the upper Niagara River mainstem influence on tributary water levels are mapped in Figure 2.2.1.1-1.  The habitat analysis for Tonawanda, Cayuga and Ellicott Creeks was conducted to the upstream extent of the model data that was available.  The potential habitat effects associated with water level fluctuations in the mainstem Niagara extend some unknown distance upstream from these boundaries.  The extent of the affected area in these three tributaries and the effect it has on the conclusions of this report will be the subject of a future investigation.

2.2.1.2   Buckhorn Marsh and Grass Island

Due to the interest in evaluating water level fluctuation effects on fish and wildlife resources in Buckhorn Marsh and at Grass Island, URS monitored water levels in those areas in 2002.  Buckhorn Marsh is a large wetland complex associated with Burnt Ship Creek and Woods Creek, near the northern tip of Grand Island.  Most of the portion of the marsh east of Interstate-190 is enclosed by two weirs.  The stoplog crest elevation of the west weir is (USLSD 1935) 564.86 feet and that of the east weir is 564.23 feet (Anderson 1995).  The portion of the marsh west of Interstate-190 includes no water level control structures.  Grass Island is a vegetated shoal located in the Tonawanda Channel of the upper river near the mouth of Woods Creek.  

Six temporary monitoring gauges were installed by URS in Buckhorn Marsh and Grass Island in late March 2002 and were monitored through mid-November 2002.  One gauge was placed in the undiked portion of the marsh west of Interstate-190 (gauge SD-01), two within the diked portion of the marsh east of Interstate-190 (gauges SD-02 and SD-03), one in Woods Creek near its mouth (gauge SD-04), one in Burnt Ship Creek near its mouth (gauge SD-05, and one within the deep emergent marsh that forms Grass Island (gauge SD-06).  The locations of these gauges are shown in Figure 2.2.1.2-1.  Water level graphs for gauges SD-01, SD-02, and SD-05 (i.e., the undiked portion of the marsh west of Interstate-190 and the western end of the diked area) are included in URS et al. 2005a and those for gauges SD-03, SD-04, and SD-06 (i.e., the eastern undiked portion of the marsh bordering Woods Creek, Grass Island, and the eastern end of the diked area) are in URS et al. 2005a.  These areas were graphed and discussed separately so that water level fluctuations in the diked portion of the marsh could be described in relation to the undiked areas immediately to the west and east.

For the west side of Buckhorn Marsh, monthly water levels during the March through November 2002 monitoring period mirrored each other at gauge SD-01 (undiked section of Burnt Ship Creek) and gauge SD-05 (near mouth of Burnt Ship Creek), where daily fluctuation patterns were evident (URS et al. 2005a).  Water levels in Burnt Ship Creek at SD-01 and SD-05 display very similar fluctuation patterns throughout 2002.  Water levels at SD-01 fluctuate daily usually around 0.2-0.3 feet per day during the tourist season of 2002.  This fluctuation can be attributed to the daily water level fluctuations in the Chippawa-Grass Island Pool.  The daily fluctuations were not evident during the first three weeks of November 2002, which corresponds to non-tourist season.  The data from these two gauges are useful in categorizing water level fluctuations, however the data should not be relied upon when analyzing absolute water level elevations due to anomalies described in URS et al. 2005a. 

Water levels at SD-02 display a pattern largely independent of the water levels observed at SD-01, as this gauge is upstream of the west weir.  Water levels in the diked portion of Burnt Ship Creek (gauge SD-02) appear independent of water levels in the Niagara River as the water levels at SD-02 stayed at a consistently higher elevation and varied considerably less throughout the sampling season.  However, from March 28 – April 16, 2002, the water level at SD-02 did fluctuate above the west weir, however after April 16, the water level appears to have stabilized.  The cause of the fluctuations at SD-02 prior to April 16, 2002 is unknown, and these patterns were not observed at SD-03, which was located in the marsh above the east weir.  The difference between water levels at SD-02 and SD-01 was greatest in the spring (March through mid-June) when the water level was typically about 1.0 foot higher in the diked portion of the marsh.  As the year progressed to September and October, the water level differences decreased to about 0.5 feet.

The water level patterns on the east side of Buckhorn Marsh during the 2002 monitoring period followed a generally similar pattern to those presented above, although with more dramatic fluctuations outside the diked portion of the marsh.  Woods Creek (gauge SD-04) and Grass Island (gauge SD-06), which are subjected to Niagara River water level fluctuations, exhibited daily fluctuations of approximately 1.5 feet throughout the monitoring period (URS et al. 2005a).  The water level in the diked portion of the marsh (gauge SD-03) did not exhibit daily fluctuations and was somewhat higher than Woods Creek and Grass Island from April to June and October to November.  However, unlike the west side of the marsh, the summer and early fall water levels outside the control structures were higher, by as much as 0.5 feet (URS et al. 2005a).  Water levels within the diked portion of the marsh fluctuated much less than in Woods Creek or at Grass Island.

In summary, the two weirs impounding Buckhorn Marsh hold the water level fairly constant in the diked portion of the marsh while, downstream of the weirs, the water level in the undiked portion of the marsh and associated tributaries generally tends to follow the fluctuation patterns present in the river (URS et al. 2005a).

2.2.1.3   Annual Duration Analysis Curves

URS et al. (2005a) prepared annual duration analysis curves using 1991-2002 data from permanent gauges.  Water level data from the ten gauges relevant to this habitat investigation are summarized in Table 2.2.1.3-1.  Duration analysis curves show the percentage of time in the period of record that a value of any given magnitude has been equaled or exceeded.  The median value represents the 50th percentile point.  The extreme ends of the distribution curves (high and low percentiles) represent infrequent, large, or small fluctuations due to all factors represented in the data set (URS et al. 2005a).  Maximum, 5% exceedance, median (50% exceedance), 95% exceedance, and minimum water elevations were plotted in conjunction with a variety of habitat data collected in the field along transects (see Section 3.2) to illustrate habitat occurrence relative to fluctuating water levels. 

2.2.1.4   Monthly Non-Storm Water Elevation and Flow Analyses for Upper Niagara River

The 1991-2002 gauge data for the upper river were further analyzed by removing data recorded during “significant” storm events and then identifying maximum and minimum water elevations for each month during typical, wet, and dry years.  These analyses provided an opportunity to evaluate potential effects of water level and flow fluctuations on habitats during any month of the year.  The procedures used to complete these analyses and the results are described below. 

In terms of river flow conditions, 1995 was a comparatively “typical” year, 1997 was a “wet” year, and 2001 was a “dry” year.  Of the 12 years (1991 - 2002) of data that were analyzed in the water level and flow fluctuation report (URS et al. 2005a), the average river flow at Fort Erie was 212,723 cfs.  In 1995, the average hourly flow in the Niagara River at Fort Erie was approximately 212,668 cfs.  In 1997, the average hourly flow was approximately 243,000 cfs, and for 2001 the value was approximately 186,000 cfs.

In order to determine the effect of combined Canadian and NYPA hydroelectric operations on Niagara River water levels, significant wind events were identified and sorted from the data.  Storm events were selected by analyzing wind data at Buffalo Niagara International Airport for 1995, 1997, and 2001 and corroborating those data with flow conditions observed at the Fort Erie gauge.  Identification of the “significant” storm events to exclude was based on engineering judgment of the wind’s effect on water level and stream flow.  Significant wind events were defined as those that caused changes in flow on the order of 25,000 to 50,000 cfs per day or a change in water level at Fort Erie greater than 2 feet per day.  The water level data were then analyzed without the significant storm events to determine the effect of Canadian and NYPA hydroelectric operations and other less significant factors.  This approach to determine the effects of power operations on water levels in the upper Niagara River was considered conservative, as it is not possible to separate other factors that contribute to changes in water levels such as small wind effects, boat waves and local environmental conditions.

It is important to note that it is not possible to completely isolate the effects of power operations on water levels in the upper Niagara River, as there is usually some wind activity on Lake Erie.  The analysis completed by URS et al. (2005a) was a conservative estimate of the effect due to NYPA and OPG power operations.  Tables 2.2.1.4-1, 2.2.1.4-2, and 2.2.1.4-3 were created to show the monthly maximum and minimum water elevations, as well as differences between those elevations, during “non-significant storm” periods at several gauges in the upper Niagara River for 1995, 1997 and 2001, respectively.  Information from these tables was used to characterize water level fluctuation at different locations in the upper Niagara River.  These fluctuations are due to a combination of smaller natural events in the river and Lake Erie as well as NYPA and OPG power generation (URS et al. 2005a). 

At the Material Dock gauge, differences between maximum and minimum water elevations for non-storm events during non-tourist season months (November - March) were mostly <2.0 feet in 1995, 1997, and 2001.  The only exception occurred in March 1995 when the difference was 2.03 feet (Table 2.2.1.4-1).  During tourist season months (April - October), differences between maximum and minimum elevations at the Material Dock gauge during non-storm events frequently exceeded 2.0 feet in 1995 (typical year) and 1997 (wet year), with the differences ranging between 2.17 feet in April 1997 to 2.59 feet in October 1997 (Table 2.2.1.4-2).  During the tourist season, water level fluctuations due to regulation of the Chippawa-Grass Island Pool for power generation were generally less in 1997 (high flow year) compared to 1995 (typical year) due to the availability of more water in the river (URS et al. 2005a).  In 2001 (dry year), differences between maximum and minimum elevations for non-storm events never exceeded 2.0 feet at the Material Dock gauge (Table 2.2.1.4-3). 

At the Frenchman’s Creek gauge, differences between maximum and minimum elevations for non-storm events were almost always <2.0 feet during both non-tourist season and tourist season months.  The only exceptions occurred in January 1995 (Table 2.2.1.4-1) and January 1997 (Table 2.2.1.4-2), when the differences were 2.17 feet and 2.00 feet, respectively.

At the gauges in the middle reaches of the upper river (i.e., LaSalle, Black Creek, Tonawanda Island, and Huntley Station), differences between maximum and minimum elevations for non-storm events during non-tourist season months (November - March) were mostly <2.0 feet in 1995, 1997, and 2001.  The only exceptions occurred in January and February 1995 (Table 2.2.1.4-1) and January 1997 (Table 2.2.1.4-2) when the differences ranged between 2.08 feet and 2.56 feet.  During tourist season months (April - October), differences between maximum and minimum elevations at the middle river gauges during non-storm events also were mostly <2.0 feet in 1995 (typical year) and 1997 (wet year), with the differences ranging between 2.02 feet at the LaSalle gauge in May 1995 to 2.66 feet at the Tonawanda Island gauge in April 1995 (Table 2.2.1.4-1).  In 2001 (dry year), differences between maximum and minimum elevations for non-storm events never exceeded 2.0 feet at the middle river gauges (Table 2.2.1.4-3).

2.2.2        Lower Niagara River

Water level fluctuations in the lower river, measured immediately below the Robert Moses Power Plant tailrace, are much less than those observed above the Robert Moses tailrace (URS et al. 2005a).  The average daily water level fluctuation during the 2002 tourist season at the gauge SG-01A, located 1.4 miles downstream of the Robert Moses tailrace, was approximately 1.5 feet.  The daily fluctuations decrease progressively at the temporary gauges located further downstream.  At the most downstream temporary gauge SG-04A, the average daily fluctuation during the tourist season was 0.6 feet.  From the data collected, it appears that manmade regulation for Treaty flows and Canadian and U.S. hydroelectric generation have an effect on water levels and flows in the lower Niagara River to its mouth at Lake Ontario (URS et al. 2005a). 

The average water levels in the lower Niagara River downstream of the Robert Moses tailrace have a seasonal cycle related to the water level of Lake Ontario.  Lake Ontario water levels are unrelated to Niagara River hydropower operations.  Water levels downstream of the Robert Moses tailrace fluctuate less during the non-tourist season because the Falls flow is constant and because generation flows at the Niagara Power Project and OPG’s Sir Adam Beck Project fluctuate less (URS et al. 2005a).

Gauge data from the 2002 monitoring period showed that the lower river temporary water level gauge readings from near Artpark (gauges SG-01A, SG-01B, and SG-01C) and Lewiston Landing (gauge SG-02A) had similar patterns throughout the monitoring period (URS et al. 2005a).  The most upstream location (Artpark) showed slightly higher water levels than the Lewiston Landing site, but the differences were generally less than a foot.  There was a gradual decline in the water levels from June to November, with more than a 3-foot drop over that period, which is related to the seasonal declines in water levels in Lake Ontario.  Daily fluctuations at both gauges were typically about 1.0-1.3 feet (URS et al. 2005a).

The gauges near Joseph Davis State Park (gauge SG-03A) and Fort Niagara (gauge SG-04A) had synchronous readings during the monitoring period.  The daily fluctuations were noticeably reduced compared to those recorded closer to the Robert Moses tailrace, typically ranging between 0.5 and 0.8 feet (URS et al. 2005a).  The gauge readings at Joseph Davis State Park were consistently higher than at Fort Niagara, but by less than one foot.  The water levels declined at these two locations as the season progressed, similar to the Artpark and Lewiston Landing gauges, with readings over 3.0 feet lower by the end of the monitoring period. 

Table 2.2.2-1 shows lower-river maximum and minimum monthly elevations (over a portion of 2002) in the context of maximum and minimum monthly elevations at Port Weller (Lake Ontario) over the period 1991-2002 and 2002, and in the Lewiston Reservoir over the period 1991-2002.

2.2.3        Lewiston Reservoir

Water levels in the Lewiston Reservoir fluctuate in response to daily demand for energy and Niagara River flow.  All fluctuations are attributable to Project operations, although water level fluctuations are always greater during the tourist season, as the Project’s nighttime share of river water is stored for use during peak demand periods.

Operation of the Niagara Power Project can result in water level fluctuations in the Lewiston Reservoir of 3-18 feet per day, and approximately 11-36 feet per week depending on the season and river flows.  Weekly drawdowns are typically greater (21-36 feet) during the tourist season than the non-tourist season (11-30 feet), when NYPA’s allocated share of water for power generation is reduced during daytime hours to provide higher scenic Falls flow (URS et al. 2005a).

Table 2.2.2-1 shows maximum and minimum monthly elevations of the Lewiston Reservoir over the period 1991-2002.

2.2.4        Flow Fluctuation

Flow duration curves for tourist and non-tourist seasons were developed for the Fort Erie gauge.  Flows are usually higher during the tourist season, with the exception of severe winter storms causing high flow events during the non-tourist season.  Flows in the tourist season range between 190,000 to 245,000 cfs in the upper Niagara River at Fort Erie (URS et al. 2005a).

2.2.5        Water Velocities of the Niagara River

Estimates of average river channel velocities were made for the upper Niagara River between Fort Erie and the NYPA intakes and for the lower Niagara River between NYPA/OPG’s Project tailraces and Lake Ontario.  Since both stream reaches are subject to backwater effects (see Section 1.3 in URS et al. 2005a), the stage-discharge relationship at any given location varies for different downstream water levels.  A range of average channel velocities was, therefore, calculated for a low and high downstream water level condition.  The average stream velocity was determined at each cross-section for a range of flows corresponding to the 10% and 90% exceedance intervals for a high and low water level. Table 2.2.5-1 shows the range in average river velocities.  Locations of the gauges in the table are in Figure 2.2-1.


Table 2.2.1-1

Daily Median Water Level Fluctuations for the Period 1991-2002

 

Tourist Season

Non-Tourist Season

Gauge

(Ft., USLSD 1935)

(Ft., USLSD 1935)

Fort Erie

0.62

0.82

Frenchman's Creek

0.54

0.49

Huntley

0.49

0.45

Black Creek

0.61

0.44

Tonawanda Island

0.55

0.43

LaSalle

1.21

0.45

Slater's Point

1.42

0.45

NYPA Intake

1.47

0.46

Material Dock

1.31

0.45

 


Table 2.2.1.3-1

Water Elevations at Selected Gauges Based on Duration Analyses of 1991-2002 Data

 

Water Elevation (Ft., USLSD 1935)

 

 

 

 

Equaled or Exceeded

 

 

 

 

 

5%

50%

95%

 

Δ

Δ

Gauge

Max.

 

(Median)

 

Min.

max/min

5%/95%

 

 

 

 

 

 

 

 

Fort Erie

581.79

574.46

572.78

571.16

568.67

13.12

3.30

Frenchman's Creek

570.33

567.67

566.62

565.60

563.92

6.41

2.07

Black Creek

568.76

566.24

565.40

564.52

563.17

5.59

1.72

Huntley

570.71

567.54

566.39

565.45

564.00

6.71

2.09

Tonawanda Island

569.23

566.65

565.82

564.92

563.37

5.86

1.73

Slater's Point

565.64

563.74

563.09

562.44

561.67

3.97

1.30

LaSalle

566.01

564.25

563.54

562.87

561.96

4.05

1.38

NYPA Intake

565.47

563.83

563.14

562.44

561.30

4.17

1.39

Material Dock

564.49

563.36

562.77

562.04

561.27

3.22

1.32

Port Weller

249.59

248.26

246.54

245.26

244.40

5.19

3.00

Lewiston Reservoir

658.82

655.26

644.54

630.18

620.16

38.66

25.08

 

 

 

 

 

 

 

 

Notes:

"Defective Reading", "Gauge Malfunction", and "Missing Data" excluded from data analyses.

Fort Erie and Port Weller gauges located outside the investigation area.

 


Table 2.2.1.4-1

Upper Niagara River Monthly Non-Significant Storm Elevations and Flow for 1995, a “Typical” Year (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Jan

High

563.46

563.73

563.46

564.17

566.33

567.16

567.30

567.79

574.63

254,000

Low

561.76

561.95

562.25

562.63

564.48

564.88

565.64

565.62

571.67

188,500

Diff.

1.70

1.78

1.21

1.54

1.85

2.28

1.76

2.17

2.96

65,500

Feb

High

563.48

563.87

563.90

564.36

566.32

566.83

567.45

567.60

574.26

245,500

Low

561.60

561.88

561.97

562.37

564.24

564.77

565.63

565.72

571.67

188,500

Diff.

1.88

1.99

1.93

1.99

2.08

2.06

1.92

1.88

2.59

57,000


Table 2.2.1.4-1 (CONT.)

Upper Niagara River Monthly Non-Significant Storm Elevations and Flow for 1995, a “Typical” Year (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Mar

High

563.64

563.81

563.85

564.17

565.80

566.12

566.75

566.92

573.46

227,300

Low

561.61

561.86

561.94

562.38

564.29

564.71

565.54

565.46

571.49

184,700

Diff.

2.03

1.95

1.91

1.79

1.51

1.41

1.21

1.46

1.97

42,600

Apr

High

563.96

564.09

564.20

564.99

566.33

567.85

567.55

567.74

574.18

243,600

Low

561.59

561.77

561.82

562.42

564.63

565.19

565.90

566.03

571.84

192,100

Diff.

2.37

2.32

2.38

2.57

1.70

2.66

1.65

1.71

2.34

51,500


Table 2.2.1.4-1 (CONT.)

Upper Niagara River Monthly Non-Significant Storm Elevations and Flow for 1995, a “TYPICAL” Year (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

May

High

563.79

564.07

564.06

564.39

565.98

566.47

No Data

567.36

574.16

243,200

Low

561.59

561.73

561.96

562.37

564.80

565.19

No Data

566.03

572.34

202,700

Diff.

2.20

2.34

2.10

2.02

1.18

1.28

No Data

1.33

1.82

40,500

Jun

High

563.46

563.86

563.88

564.18

565.78

566.17

No Data

567.09

573.77

234,300

Low

561.46

561.79

561.89

562.42

564.60

565.07

No Data

565.91

572.52

206,600

Diff.

2.00

2.07

1.99

1.76

1.18

1.10

No Data

1.18

1.25

27,700


Table 2.2.1.4-1 (CONT.)

Upper Niagara River Monthly Non-Significant Storm Elevations and Flow for 1995, a “TYPICAL” Year (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Jul

High

563.62

564.06

563.97

564.42

566.19

566.61

No Data

567.53

574.31

246,600

Low

561.62

561.97

562.00

562.44

564.90

565.33

No Data

566.23

572.50

206,200

Diff.

2.00

2.09

1.97

1.98

1.29

1.28

No Data

1.30

1.81

40,400

Aug

High

563.46

564.07

564.12

564.39

565.96

No Data

No Data

567.21

574.22

244,500

Low

561.27

561.94

562.01

562.45

564.89

No Data

No Data

566.01

571.86

192,500

Diff.

2.19

2.13

2.11

1.94

1.07

No Data

No Data

1.20

2.36

52,000


Table 2.2.1.4-1 (CONT.)

Upper Niagara River Monthly Non-Significant Storm Elevations and Flow for 1995, a “TYPICAL” Year (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Sep

High

563.60

564.08

563.87

564.43

566.02

No Data

No Data

567.09

573.12

219,800

Low

561.61

561.97

564.56

562.57

564.56

No Data

No Data

565.63

571.41

183,000

Diff.

1.99

2.11

1.77

1.86

1.46

No Data

No Data

1.46

1.71

36,800

Oct

High

563.59

564.05

563.91

564.35

565.91

566.24

567.60

567.23

574.22

244,500

Low

561.60

561.85

561.90

562.45

564.57

565.02

565.64

565.83

571.75

190,200

Diff.

1.99

2.20

2.01

1.90

1.34

1.22

1.96

1.40

2.47

54,300


Table 2.2.1.4-1 (CONT.)

Upper Niagara River Monthly Non-Significant Storm Elevations and Flow for 1995, a “TYPICAL” Year (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Nov

High

563.41

563.70

563.66

563.64

565.93

566.35

566.98

567.16

573.53

228,900

Low

561.81

562.04

562.11

562.73

564.51

564.95

565.58

565.72

571.34

181,600

Diff.

1.60

1.66

1.55

0.91

1.42

1.40

1.40

1.44

2.19

47,300

Dec

High

563.51

563.83

563.84

563.85

566.08

566.44

No Data

567.29

573.64

231,400

Low

561.93

562.20

562.26

562.66

564.34

564.72

No Data

565.35

570.60

166,400

Diff.

1.58

1.63

1.58

1.19

1.74

1.72

No Data

1.94

3.04

65,000

Note:  High and low elevations for each gauge exclude the storm events.  The monthly extremes at any given gauge may not occur on the same day.


Table 2.2.1.4-2

Upper Niagara River Monthly Non-Significant Storm Elevations and Flow for 1997, a “Wet” Year (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Jan

High

563.77

564.72

564.59

565.67

567.01

567.60

568.26

568.42

574.63

253,877

Low

561.99

562.65

562.62

563.11

565.18

565.73

566.39

566.42

572.00

195,467

Diff.

1.78

2.07

1.97

2.56

1.83

1.87

1.87

2.00

2.63

58,410

Feb

High

563.40

563.93

563.86

564.06

566.29

566.62

567.44

567.64

574.07

241,023

Low

561.96

562.45

562.62

563.11

565.31

565.47

566.23

566.46

572.03

196,138

Diff.

1.44

1.48

1.24

0.95

0.98

1.15

1.21

1.18

2.04

44,885


Table 2.2.1.4-2 (CONT.)

Upper Niagara River Monthly Non-Significant Storm Elevations and Flow for 1997, a “Wet” Year (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Mar

High

563.40

563.86

563.80

No Data

566.69

567.28

568.13

568.33

575.12

265,390

Low

562.35

562.85

562.81

No Data

565.37

565.67

566.42

566.59

572.76

211,711

Diff.

1.05

1.01

0.99

No Data

1.32

1.61

1.71

1.74

2.36

53,679

Apr

High

564.49

564.72

564.88

565.47

567.18

567.60

568.00

568.72

575.45

273,159

Low

562.32

562.73

562.75

563.40

565.77

566.23

567.05

567.21

573.44

226,967

Diff.

2.17

1.94

2.13

2.07

1.41

1.37

0.95

1.51

2.01

46,192


Table 2.2.1.4-2 (CONT.)

Upper Niagara River Monthly Non-Significant Storm Elevations and Flow for 1997, a “Wet” Year (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

May

High

563.34

563.80

563.80

564.52

566.62

567.08

567.77

568.19

575.58

276,267

Low

561.86

562.45

562.45

563.04

565.57

566.03

567.05

567.01

573.54

229,157

Diff.

1.48

1.35

1.35

1.48

1.05

1.05

0.72

1.18

2.04

47,110

Jun

High

563.31

563.93

563.86

564.39

566.65

567.21

568.13

568.33

575.54

275,490

Low

561.60

562.52

562.35

563.01

565.47

565.93

567.21

567.01

573.61

230,640

Diff.

1.71

1.41

1.51

1.38

1.18

1.28

0.92

1.32

1.93

44,850


Table 2.2.1.4-2 (CONT.)

Upper Niagara River Monthly Non- Significant Storm Elevations and Flow for 1997, a “Wet” Year (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Jul

High

563.34

563.96

563.73

564.52

566.62

566.95

568.00

568.23

575.71

279,410

Low

562.03

562.65

562.58

563.24

565.77

566.29

567.18

567.28

574.10

241,023

Diff.

1.31

1.31

1.15

1.28

0.85

0.66

0.82

0.95

1.61

38,387

Aug

High

563.27

563.96

563.80

564.45

566.59

567.08

No Data

568.23

575.12

265,390

Low

561.53

562.19

562.13

563.01

565.60

566.19

No Data

567.14

573.64

231,382

Diff.

1.74

1.77

1.67

1.44

0.99

0.89

No Data

1.09

1.48

34,008


Table 2.2.1.4-2 (CONT.)

Upper Niagara River Monthly Non- Significant Storm Elevations and Flow for 1997, a “Wet” Year (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Sep

High

563.67

564.26

564.16

564.65

566.36

566.88

No Data

567.93

574.85

259,210

Low

561.27

562.13

562.03

562.85

565.64

566.00

No Data

566.98

573.25

222,553

Diff.

2.40

2.13

2.13

1.80

0.72

0.88

No Data

0.95

1.60

36,657

Oct

High

564.03

564.59

564.42

565.01

566.78

567.14

No Data

568.10

574.92

260,763

Low

561.44

561.90

561.86

562.65

565.11

565.73

No Data

566.49

572.56

207,438

Diff.

2.59

2.69

2.56

2.36

1.67

1.41

No Data

1.61

2.36

53,325


Table 2.2.1.4-2 (CONT.)

Upper Niagara River Monthly Non- Significant Storm Elevations and Flow for 1997, a “Wet” Year (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Nov

High

563.60

564.06

563.93

564.45

566.36

No Data

567.70

567.90

574.69

255,396

Low

562.39

562.75

562.75

563.21

565.24

No Data

566.36

566.52

572.66

209,593

Diff.

1.21

1.31

1.18

1.24

1.12

No Data

1.34

1.38

2.03

45,803

Dec

High

563.54

563.96

563.83

564.39

566.39

No Data

567.67

567.87

574.85

259,210

Low

562.32

562.72

562.68

563.18

565.08

No Data

566.16

566.32

572.49

206,026

Diff.

1.22

1.24

1.15

1.21

1.31

No Data

1.51

1.55

2.36

53,184

Note:  High and low elevations for each gauge exclude the storm events.  The monthly extremes at any given gauge may not occur on the same day.


Table 2.2.1.4-3

Upper Niagara River Monthly Non- Significant Storm Elevations and Flow for 2001, a “Dry” Year  (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Peace Bridge

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Jan

High

563.05

563.26

563.29

No Data

564.88

565.80

566.36

566.42

567.50

572.02

196,138

Low

561.82

562.19

562.20

No Data

564.07

564.47

565.12

565.08

566.16

570.36

161,600

Diff.

1.23

1.07

1.09

No Data

0.81

1.33

1.24

1.34

1.34

1.66

34,538

Feb

High

563.46

563.68

563.66

No Data

565.13

565.84

566.37

566.49

567.70

572.26

201,046

Low

561.94

562.28

562.29

No Data

563.86

564.25

565.16

564.84

565.86

570.00

154,466

Diff.

1.52

1.40

1.37

No Data

1.27

1.59

1.21

1.65

1.84

2.26

46,580


Table 2.2.1.4-3 (CONT.)

Upper Niagara River Monthly Non- Significant Storm Elevations and Flow for 2001, a “Dry” Year    (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Peace Bridge

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Mar

High

563.16

563.31

563.35

No Data

565.00

565.48

566.19

566.25

567.57

572.34

202,459

Low

561.99

562.24

562.29

No Data

564.00

564.42

565.27

565.05

566.16

570.46

163,578

Diff.

1.17

1.07

1.06

No Data

1.00

1.06

0.92

1.20

1.41

1.88

38,881

Apr

High

563.73

564.02

564.02

No Data

565.46

565.66

566.43

566.54

567.83

572.45

205,319

Low

561.77

562.04

561.98

No Data

564.39

564.96

565.41

565.02

566.65

570.79

170,217

Diff.

1.96

1.98

2.04

No Data

1.07

0.70

1.02

1.02

1.18

1.66

35,102


Table 2.2.1.4-3 (CONT.)

Upper Niagara River Monthly Non- Significant Storm Elevations and Flow for 2001, a “Dry” Year    (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Peace Bridge

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

May

High

563.47

563.81

563.86

No Data

565.56

565.97

566.57

566.69

568.10

572.77

211,711

Low

561.91

562.23

562.22

No Data

564.43

564.87

565.42

565.51

566.82

571.10

176,926

Diff.

1.56

1.58

1.64

No Data

1.13

1.10

1.15

1.18

1.28

1.67

34,785

Jun

High

563.58

563.94

563.93

No Data

565.77

566.21

566.80

566.89

568.16

572.91

215,314

Low

561.79

561.96

562.10

No Data

564.69

565.12

565.68

565.80

567.08

571.22

178,939

Diff.

1.79

1.98

1.83

No Data

1.08

1.09

1.12

1.09

1.08

1.69

36,375


Table 2.2.1.4-3 (CONT.)

Upper Niagara River Monthly Non- Significant Storm Elevations and Flow for 2001, a “Dry” Year    (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Peace Bridge

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Jul

High

563.55

563.99

563.98

No Data

565.70

No Data

566.60

566.85

568.19

572.78

212,453

Low

561.80

561.95

562.02

No Data

564.29

No Data

565.42

565.89

566.82

570.86

171,523

Diff.

1.75

2.04

1.96

No Data

1.41

No Data

1.18

0.96

1.38

1.92

40,930

Aug

High

563.64

564.08

563.98

No Data

565.50

566.04

566.52

566.68

568.00

572.55

207,438

Low

561.88

562.14

562.11

No Data

564.32

564.97

565.71

565.83

566.78

570.85

171,523

Diff.

1.76

1.94

1.87

No Data

1.18

1.07

0.81

0.85

1.21

1.70

35,915


Table 2.2.1.4-3 (CONT.)

Upper Niagara River Monthly Non- Significant Storm Elevations and Flow for 2001, a “Dry” Year    (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Peace Bridge

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Sep

High

563.46

563.90

563.94

564.24

565.36

565.91

No Data

566.56

567.83

572.39

203,872

Low

561.70

562.10

562.04

562.70

564.32

564.91

No Data

565.52

566.59

570.57

165,555

Diff.

1.76

1.80

1.90

1.54

1.04

1.00

No Data

1.04

1.25

1.82

38,317

Oct

High

563.48

563.87

563.87

564.29

565.52

566.10

No Data

566.71

567.87

572.18

198,963

Low

561.80

562.10

562.07

562.32

564.40

564.60

No Data

565.23

566.32

570.39

162,271

Diff.

1.68

1.77

1.80

1.97

1.12

1.50

No Data

1.48

1.54

1.79

36,692


Table 2.2.1.4-3 (CONT.)

Upper Niagara River Monthly Non- Significant Storm Elevations and Flow for 2001, a “Dry” Year    (Elevations in 1935 Datum)

Month

Material Dock

(ft)

NYPA Intake

(ft)

Slater’s Point

(ft)

       LaSalle

(ft)

Black Creek

(ft)

Tonawanda Island

(ft)

Huntley Station

(ft)

Frenchman’s Creek

(ft)

Peace Bridge

(ft)

Fort Erie Elevation

(ft)

Fort Erie Flow

(cfs)

Nov

High

563.09

563.46

563.36

563.75

564.92

565.59

566.15

566.41

567.77

572.29

201,753

Low

561.89

562.21

562.17

562.23

564.30

564.54

565.28

565.20

566.32

570.52

164,884

Diff.

1.20

1.25

1.19

1.52

0.62

1.05

0.87

1.21

1.44

1.77

36,869

Dec

High

563.38

563.73

563.60

563.79

565.52

566.07

566.89

566.93

568.59

573.66

232,123

Low

562.14

562.55

562.40

562.33

564.14

564.48

565.22

565.11

566.16

570.17

157,680

Diff.

1.24

1.18

1.20

1.46

1.38

1.59

1.67

1.82

2.43

3.49

74,443

Note:  High and low elevations for each gauge exclude the storm events.  The monthly extremes at any given gauge may not occur on the same day.


Table 2.2.2-1

Lower Niagara River (2002 Data), Port Weller (1991-2002, 2002 Data) and Lewiston Reservoir (1991-2002 Data) Maximum and Minimum Monthly Elevations

 

Month

Artpark       (SG-01)

Lewiston (SG-02)

J. Davis SP (SG-03)

Youngstown (SG-04)

Port Weller (2002)

Port Weller (1991-2002)

Lewiston Reservoir

USLSD 1935 (Ft.)

 

Jan

Max

No Data

No Data

No Data

No Data

246.40

248.21

658.48

Min

No Data

No Data

No Data

No Data

245.46

244.50

624.16

Diff.

No Data

No Data

No Data

No Data

0.94

3.71

34.32

Feb

Max

No Data

No Data

No Data

No Data

246.50

248.18

658.56

Min

No Data

No Data

No Data

No Data

245.09

244.96

624.43

Diff.

No Data

No Data

No Data

No Data

1.41

3.22

34.13

Mar

Max

No Data

No Data

No Data

No Data

246.90

248.21

658.61

Min

No Data

No Data

No Data

No Data

245.54

245.16

627.17

Diff.

No Data

No Data

No Data

No Data

1.36

3.05

31.44

Apr

Max

No Data

No Data

No Data

No Data

247.88

249.46

658.56

Min

No Data

No Data

No Data

No Data

246.55

245.62

621.75

Diff.

No Data

No Data

No Data

No Data

1.33

3.84

36.81

May

Max

No Data

No Data

No Data

No Data

248.36

249.59

658.82

Min

No Data

No Data

No Data

No Data

247.36

246.11

621.27

Diff.

No Data

No Data

No Data

No Data

1.00

3.48

37.55

Jun

Max

250.01

249.61

No Data

248.84

248.53

249.06

658.63

Min

248.08

248.09

No Data

248.11

248.13

246.27

620.63

Diff.

1.93

1.52

No Data

0.73

0.40

2.79

38.00

Jul

Max

249.77

249.38

249.05

248.75

248.30

248.51

658.58

Min

247.22

247.16

247.26

247.01

247.36

246.21

620.49

Diff.

2.55

2.22

1.79

1.74

0.94

2.30

38.09

Aug

Max

No Data

248.73

248.23

248.22

247.53

247.91

658.55

Min

No Data

246.10