Niagara Power Project FERC No. 2216
UPPER
NIAGARA RIVER TRIBUTARY BACKWATER STUDY
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Prepared for: New York Power Authority
Prepared by: URS Corporation; Gomez and Sullivan Engineers, P.C.; and E/PRO Engineering & Environmental Consulting, LLC
August 2005
___________________________________________________
Copyright © 2005 New York Power Authority
Agencies
FEMA Federal Emergency Management Agency
FERC Federal Energy Regulatory Commission
IJC International Joint Commission
INBC International Niagara Board of Control
NOAA National Oceanic and Atmospheric Administration
NYPA New York Power Authority
USACE United States Army Corps of Engineers
USGS United States Geological Survey
Units of Measure
cfs cubic feet per second
El. elevation
fps feet per second
IGLD International Great Lakes Datum
MW megawatt
NGVD National Geodetic Vertical Datum
USLSD U.S. Lake Survey Datum 1935
Miscellaneous
HEC-RAS Hydraulic Engineering Center -
River Analysis System
As part of the relicensing effort for the Niagara Power Project, NYPA conducted an engineering analysis of surface water level and flow fluctuations in the Niagara River and presented the analysis in a report entitled Niagara River Water Level and Flow Fluctuation Study (URS et al. 2005).
The upper Niagara River Tributary Backwater Study is a supplement to URS et al. 2005 and was done to provide additional information on the effect that water levels in the upper Niagara River can have on water levels in tributaries. The study provides an estimate of the tributary reach lengths that could be influenced by water surface elevation fluctuations in the upper Niagara River. It was used to determine the geographic scope of studies for other resources, including habitat, shoreline erosion, and water quality.
Seven tributaries were selected based on field reconnaissance, the availability of existing hydraulic models, and the possible significance of the tributaries to the relicensing process for the Niagara Power Project. The tributaries are Woods Creek, Gun Creek, and Spicer Creek, located on Grand Island, and Cayuga Creek, Bergholtz Creek, Tonawanda Creek, and Ellicott Creek, located on the U.S. mainland (Figure EX-1.).
The study determined the length of each tributary that is influenced by fluctuations in water levels of the upper Niagara River. The results are based on the median annual flow for each tributary and water levels for the upper Niagara River that included the annual minimum and maximum and the 5%, 50% (median), and 95% exceedance values for the period of record (1991- 2002).
The tributary reach lengths influenced by upper Niagara River water levels are considered to be conservative estimates of the effects of U.S./Canadian hydropower generation for a median flow event because water level fluctuations are caused by other factors in addition to U.S./Canadian hydropower generation. These factors include wind, natural flow and ice conditions, regional and long-term precipitation patterns that affect Lake Erie levels, control of the Niagara Falls flow for scenic purposes, and operation of power plants on the Canadian side of the river. Water level fluctuations in the upper Niagara River, from all causes, are generally less than 1.5 feet per day. As stated above, this study investigated a wide range of water levels, from the minimum to the maximum recorded elevations in the upper Niagara River (1991-2002), a difference that can span 4 to 6 feet. Such a range in elevation does not represent a typical upper Niagara River daily water level fluctuation of 1.5 feet, or less. Conditions other than Project operations (i.e., wind on Lake Erie), often drive the Niagara River to the extreme water levels such as the annual maximum and minimum elevations.
Water levels in the upper Niagara River influence water levels in each of the 7 tributaries – Woods Creek, Gun Creek, Spicer Creek, Cayuga Creek, Bergholtz Creek, Tonawanda Creek, and Ellicott Creek. Table EX-1 provides the estimated length of the study tributaries influenced by the Niagara River for the three highest study elevations: the median (50% exceedance), the 5% exceedance and the annual maximum water surface elevations. The median Niagara River water level is representative of daily water levels due to U.S./Canadian hydropower generation. Conversely, the annual maximum Niagara River water level occurred during a storm surge from Lake Erie and is not representative of the range of daily water level fluctuations due to U.S./Canadian hydropower generation. For all of the tributaries studied except Gun Creek, the affected stream length varies depending on the water level of the upper Niagara River (see Table EX-1). A steep profile in Gun Creek between 2,900 feet and 4,200 feet upstream of the mouth limits the upstream influence of Niagara River water level fluctuations on creek water levels. Figure EX-2 illustrates the tributary segments that were found to have water surface elevations influenced by the median upper Niagara River elevations.
Analysis of water levels in Tonawanda and Ellicott Creeks is complicated by the fact that dredging and water diversions, for the purposes of navigation on the Erie (New York State Barge) Canal and flood control, have altered the hydraulics and hydrology in both tributaries and the relationship of these tributaries to the upper Niagara River. An additional factor for Tonawanda Creek is that 11.6 miles of the tributary are part of the Erie (Barge) Canal system where water levels are influenced by canal operations. In order to maintain a uniform canal width and depth and flat slope, the Tonawanda Creek channel has been dredged and maintained. During the canal operational period (generally the first week of May through the last week of October) when the guard lock gate in Lockport is opened, flow in the creek often moves in an upstream (easterly) direction because the level of the Erie (Barge) Canal at Lockport is lower than that of the Niagara River at the City of Tonawanda. Up to 1100 cfs of flow are diverted from the Niagara River for canal operations. Accordingly, water levels in Tonawanda Creek are not solely influenced by upper Niagara River water levels.
For the median Niagara River water level condition, the extent of influence of Niagara River water level was estimated to be 13.7 miles upstream of the mouth of Tonawanda Creek. This estimate seems reasonable as the upstream end of the affected tributary has a more riverine character (as compared to sections of the Erie (Barge) Canal) and is near two riffles. Field observations confirmed that two riffles, located at 13.6 miles and 14.1 miles from the mouth, act as hydraulic controls limiting the upstream influence of Niagara River water level fluctuations due to U.S./Canadian hydropower generation on Tonawanda Creek water levels (Gomez and Sullivan and E/PRO 2005). For the annual maximum Niagara River water level, the extent of influence of Niagara River water levels is nearly 19 miles upstream from the Niagara River based on engineering judgment. (The engineering judgment was made by extending the median and annual maximum water levels of the Niagara River to where they intersect the stream bottom of Tonawanda Creek. The stream bottom profile was obtained from Flood Insurance Studies for towns and communities that are intersected by the creek.)
The analysis of Ellicott Creek found that flood control and dredging operations have also changed the hydraulic and hydrologic characteristics of the creek. Based on engineering judgment, upper Niagara River water levels influence water levels in Ellicott Creek approximately 7 miles upstream of the mouth. This distance coincides with a riffle that extends from 6.9 to 7.1 miles from the mouth, and for which field observations confirmed was a hydraulic control limiting the upstream influence of Niagara River water level fluctuations due to U.S./Canadian hydropower generation on creek water levels (Gomez and Sullivan and E/PRO 2005). (The engineering judgment was made by extending the median and annual maximum water levels of the Niagara River to where they intersect the stream bottom of Ellicott Creek. The stream bottom profile was obtained from Flood Insurance Studies for towns and communities that are intersected by the creek.) To reduce flooding, both the U.S. Army Corps of Engineers (USACE) and local government entities have altered the channel by making it deeper and wider and by building a dam at Island Park near the Village of Williamsville. Regulation occurs today by the seasonal manipulation of that dam and by intermittent pumping from stone quarries into stream.
|
Study Tributary |
Estimated Annual Median Flow (cfs) |
Approximate Study Length of Tributary |
Estimated Length of Tributary Influenced by Upper Niagara River (to nearest 100 feet) |
||
|
At Median Niagara River Water Surface Elevations |
At 5% Exceedance Niagara River Water Surface Elevations |
At Maximum Niagara River Water Surface Elevations |
|||
|
Woods Creek |
5.9 |
16,170 feet |
9,000 feet |
9,000 feet |
11,000 feet |
|
Woods Creek - Tributary 1 |
2.3 |
14,355 feet |
1,300 feet |
1,300 feet |
2,400 feet |
|
Woods Creek -Tributary 3 |
0.3 |
8,920 feet |
No Influence |
No Influence |
No Influence |
|
Spicer Creek |
2.4 |
12,680 feet |
2,600 feet |
2,600 feet |
4,600 feet |
|
Gun Creek |
2.7 |
7,460 feet |
4,100 feet |
4,100 feet |
4,100 feet |
|
Cayuga Creek |
27.5 |
14,690 feet |
8,300 feet |
9,700 feet |
10,100 feet |
|
Bergholtz Creek |
17.7 |
16,420 feet |
9,000 feet |
9,000 feet |
10,900 feet |
|
Ellicott Creek |
77.2 |
11,000 feet |
7.0 miles1 |
7.0 miles1 |
7.1miles 1 |
|
Tonawanda Creek |
408.2 |
10,570 feet |
13.7 miles1 |
18.8 miles1 |
18.9 miles1 |
1Based on engineering judgment from information provided in Flood Insurance Studies on the tributary profiles and the upper Niagara River water surface elevations
Location Plan – Upper Niagara River and Studied Tributaries
Tributary Segments that are Influenced by Upper Niagara River Median Water Levels
The New York Power Authority (NYPA) is engaged in the relicensing of the Niagara Power Project in Lewiston, Niagara County, New York. The 1,880-MW (firm power output) Niagara Power Project is one of the largest non-federal hydroelectric facilities in North America and was licensed to the Power Authority of the State of New York (now the New York Power Authority) in 1957. Construction of the Project began in 1958, and electricity was first produced in 1961.
The present operating license for the plant expires in August 2007. In preparation for the license submittal for the Niagara Project, NYPA is assembling information related to the ecological, engineering, recreational, cultural, and socioeconomic aspects of the Project.
Water level fluctuations in the upper Niagara River are caused by a number of factors in addition to the operation of the Niagara Power Project. These factors include wind, natural flow and ice conditions, regional and long-term precipitation patterns that affect Lake Erie levels, control of the Niagara Falls flow for scenic purposes, and operation of power plants on the Canadian side of the river. Generally, water level fluctuations in the upper Niagara River, from all causes, are less than 1.5 feet per day.
Currently, there are two regulatory constraints on flow and water
level fluctuations – The Niagara River Water Diversion Treaty of 1950 and the
1993 Directive of the International Niagara Board of Control. To balance the need for power with a desire
to preserve the beauty of Niagara Falls, the Treaty provides for the regulation
of the amount of water diverted for hydroelectricity production. On average, more than 200,000 cubic feet per
second (cfs), or 1.5 million gallons of water a second, flows from Lake Erie
into the Niagara River. The Treaty
requires that at least 100,000 cfs of water be allowed to spill over Niagara
Falls during the tourist season daylight hours, defined as April 1 through
October 31. The 100,000 cfs flow may be
reduced to 50,000 cfs at night during this tourist season and throughout the
day the rest of the year. The remaining
Niagara River flow is available for hydroelectric generation by Canada and the
United States and is to be shared equally by the two nations.
Pursuant to the requirements of the 1993 Directive of the International Niagara Board of Control (INBC), water level fluctuations in the Chippawa-Grass Island Pool (in the upper Niagara River, i.e., above Niagara Falls) are limited to 1.5 feet per day within a 3-foot range for normal conditions (Figure 1.0-1). For unusual conditions (high flow, low flow, ice, etc.), the allowable range of Chippawa-Grass Island Pool water levels is extended to 4 feet and the 1.5 feet daily fluctuation tolerance can be waived. The water level fluctuation limits of the 1993 Directive are independent of the seasonal flow limits dictated by the 1950 treaty.
As part of the relicensing effort for the Niagara Power Project, NYPA conducted an engineering analysis of surface water level and flow fluctuations in the Niagara River and presented the analysis in a report entitled Niagara River Water Level and Flow Fluctuation Study (URS et al. 2005).
The Upper Niagara River Tributary Backwater Study is a supplement to the above referenced study and is intended to provide additional information on the effect water levels in the upper Niagara River have on tributary water levels. The study provides conservative estimates of tributary reach lengths that could be influenced by different elevations in the upper Niagara River by U.S./Canadian hydropower generation. The estimates are conservative because water level fluctuations are caused by other factors in addition to U.S./Canadian hydropower generation. Since this information was utilized to determine the geographic scope of studies for other resources such as habitat, shoreline erosion, water quality, etc., the other studies produced “conservative” estimates of impacts.
Seven tributaries were selected for this study on the basis of a field reconnaissance of the tributary, the availability of existing hydraulic models, and possible significance of the tributary relative to the relicensing process for the Niagara Power Project. The locations of the tributaries are shown on Figure 1.0-2 and they are Woods Creek, Gun Creek, and Spicer Creek, which are located on Grand Island, and Cayuga Creek, Bergholtz Creek, Tonawanda Creek, and Ellicott Creek, which are located on the U.S. mainland (eastern Niagara River shore). Bergholtz Creek joins Cayuga Creek approximately 5,600 feet upstream of Cayuga Creek's confluence with the upper Niagara River; Ellicott Creek joins Tonawanda Creek approximately 1,600 feet upstream of Tonawanda Creek's confluence with the upper Niagara River.
Regulation of the Chippawa-Grass Island Pool Water Levels as Specified by the INBC 1993 Directive
Elevation Datum: USLSD 1935. To convert water levels in the upper Niagara River from USLSD 1935 to IGLD 1985 subtract 1.2 feet
Abnormal flow conditions are considered to exist when any four consecutive hourly mean Niagara River flows, as determined from levels at the Fort Erie gauge, are greater than 270,000 cfs or less than 150,000 cfs.
Upper Niagara River and Studied Tributaries
The analysis of the seven tributaries selected for this study (see Section 1.0) began with the establishment of hydrology estimates and the development of hydraulic models for each tributary. The following sections describe the methods used to develop the hydrologic and hydraulic components of this study.
The flow (discharge) of water in a tributary will influence the water surface elevations found at points along the tributary. When the physical nature of the stream channel (i.e., geometry, slope, channel roughness), applicable backwater effects, and the stream discharge are entered into a hydraulic model of the stream reach, the water surface profile for that reach can be determined.
The discharge(s) to apply in the calculation of a water surface elevation should be related to the purpose(s) of the study. For a study of water surface elevations found at locations along a stream during a severe flood, a flood discharge would be developed using statistical analyses of existing gauges and/or empirical models. The calculated flood discharge would then be applied in a hydraulic model to determine the flood water surface elevations.
The purpose of the upper Niagara River Tributary Backwater Study is to provide conservative estimates of the tributary reach lengths that could be influenced by fluctuations in the upper Niagara River. Accordingly, the discharge to apply in this study would be one that is representative of the "normal" conditions found in the tributaries, as opposed to an extreme discharge event that would be applied in a flood study or low-flow application.
For this study, the median annual flow or 50% exceedance flow was selected to be representative of the "normal" discharge conditions in the tributaries. The median annual flow is a statistical value that is useful for describing the central tendency of flow over the year. Thus, the discharge value applied to determine water surface elevations is one that would generally be found in the middle of a list of average daily flow records sorted for the year. That is, one-half of the flows would generally be higher and one-half would generally be lower than the median flow value.
Actual stream discharge records, which are used to determine the median annual flow at a specific locale in the tributary, are often not available and therefore, alternative engineering methods must be employed to estimate the median annual flow. The methodology selection begins by investigating the availability of flow records within a given tributary. If flow data are available for the tributary, such as from records taken by USGS stream flow gauges, and the records are of sufficient length to be representative of the hydrologic changes that can occur annually, those data would be used to determine the median annual flow.
Of the seven tributaries investigated in this study, only two (Tonawanda Creek, Ellicott Creek) have stream flow data recorded by a stream flow gauge on the tributary. The Tonawanda and Ellicott Creek stream flow gauges were located near the area considered for this study, and each have a record of sufficient length (over 25 years) to provide a normal distribution of flow. Therefore, the gauge records were used to estimate the median annual flow for those tributaries. Because the gauges were not located at the exact location of this study, the gauge records required adjustment using a ratio of drainage areas.
The drainage area ratio adjustment method is commonly used to estimate hydrologic conditions. Drainage area is often the primary variable responsible for the quantity of discharge at a stream location in the watershed. Accordingly, the drainage area ratio method employs records from the nearby gauging station and adjusts those records to the location of interest by the proportion of drainage areas:
Flow at Ungauged Location = Ay/Ax * Flow at Gauged Location
Where: Ay
= Drainage area at ungauged location,
Ax =
Drainage area at gauged location.
The results of the median annual flow estimates for Tonawanda and Ellicott Creeks are provided in Section 3.0.
For the five study tributaries without stream discharge records, an alternate engineering method was employed to estimate the annual median flow for each tributary. The method used in this study was one that applied regional relationships of the median annual flow to the physical characteristics (drainage area, annual precipitation, etc.) of watersheds in the western New York region.
The process began with the review of USGS flow gauges in the western New York region. Factors considered when selecting a streamflow gauge included the length of gauge record available, the mean annual precipitation at the gauge, and geographical location. The initial list of gauges was examined further to exclude gauges with a short or spotty gauge record, regulated stream flows, and/or a dissimilarity in watershed characteristics (e.g., unacceptable differences in basin area, percent forested, percent urbanized). The final list of gauges that were used in this study to develop a median annual flow estimate for the five ungauged tributaries is shown in Table 2.1-1. Figure 2.1-1 depicts the location of the gauges used in the analysis.
To reduce the probability for error in the multiple (regression) analysis, it was important that each sample set of regional flow gauge records be of equal size, or period of record. As is shown in Table 2.1-1, the period of record is not common among the thirteen gauges selected in this analysis. Therefore, to accurately develop a relationship to predict gauge flows, it was necessary to acquire missing data and/or extend the gauge records to a common period by developing a cross-correlation of flow between the records. This study used an approach known as maintenance of variance extension (MOVE) to develop the correlations structure of the gauge records (Maidment 1992). Additional information on the MOVE is provided in Appendix A.
The multiple regression analysis was performed on the equally sized gauge records constructed for the 93 year period from January 1909 through December 2001. The regression analysis was predicated with the fact that more than one independent variable was needed to estimate the median annual flow in a tributary. The forward selection of variables found that two variables, drainage area and average annual precipitation, provided an effective model of the median annual tributary flow. The analysis also found that the relationship of these independent variables to the median annual flow was best described with an exponential function of the variables. Several computer models were developed to assess the relationship of these variables and those models found that the median annual flow was best estimated with the following equation:
Q = C * D A
* P B
where: Q =
Estimated Flow
C
= Coefficient of Determination (0.001)
D
= Drainage Area (square miles) of Tributary
P
= Average Annual Precipitation (inches) within Tributary Watershed
A
= Power factor to raise Drainage Area (0.95)
B
= Power factor to raise Average Annual Precipitation (1.88)
The
median annual flows estimated for the five ungauged tributaries are presented
in Section 3.0.
Additional
information on the regression analyses used for the development of hydrology in
ungauged tributaries can be found in Maidment (1992)
and in Appendix A.
The Hydrologic Engineering Center River Analysis System hydraulic program (HEC-RAS, version 3.1.1, May 2003) developed by the U.S. Army Corps of Engineers, Davis, CA, was used to analyze the effects of water levels in the upper Niagara River. The models require, as input, detailed survey information, such as stream cross-sections, bridge and culvert geometry, the type of bridge or culvert, and the longitudinal profile of the streambed. Those data were obtained from Federal Emergency Management Agency (FEMA) flood insurance studies that had been previously completed for the Town and/or City in which the tributary is located. The following is a list of flood insurance studies referenced for the development of the tributary hydraulic models:
· FEMA Flood Insurance Study, Town of Grand Island, NY, July 1979
· FEMA Flood Insurance Study, City of North Tonawanda, NY, July 1981
· FEMA Flood Insurance Study, City of Tonawanda, NY, February 1979
· FEMA Flood Insurance Study, City of Niagara Falls, NY, September 1990
· FEMA Flood Insurance Study, Town of Wheatfield, NY, May 1991
The original FEMA flood insurance studies were completed between 1979 and 1990. Since that time, bridges and other structures were found to have changed from the original surveys. Accordingly, the geometry of several bridges and culverts were checked in October 2002 and August 2003. The modifications found at the structures were noted, and modifications that were considered to be significant in terms of hydraulic influence had the changes incorporated into the HEC-RAS models.
Another parameter needed for hydraulic modeling is a coefficient of channel roughness (Manning's n). The roughness coefficients for this study were taken from the HEC-2 models used in the FEMA studies.
Generally, for each of the tributaries in this study, the channel slope is low gradient. This fact, and the fact that a non-flooding flow (median annual flow) was studied, will result in tributary water surface elevations that are controlled by a downstream water surface elevation (i.e., sub-critical flow). Because the study tributaries discharge into the Niagara River or into a Niagara River tributary near its mouth with the Niagara River, the Niagara River water surface elevations influence the water levels in those tributaries. Therefore, the starting water surface elevation in the hydraulic models for all but two study tributaries is an upper Niagara River water level.
The starting downstream water elevations were determined from duration analyses of hourly water levels at several locations within the upper Niagara River (URS et al. 2005). These water level statistics were utilized in this study to determine water surface elevations for the annual 0% (maximum elevation of record), 5%, 50%, 95%, and 100% (minimum elevation of record) exceedance values at the point where a tributary enters the upper Niagara River. Those elevations were entered into the HEC-RAS models as the starting water surface elevation (Table 2.2-1). For Tonawanda Creek and Spicer Creek, the water level statistics at the Tonawanda gauge were used. For Cayuga Creek, Woods Creek, and Gun Creek, an interpolation between the Tonawanda and LaSalle gauges was used. The starting elevation for Ellicott Creek is the water surface elevation predicted by the HEC-RAS model at the junction with Tonawanda Creek. The starting elevation for Bergholtz Creek is the water surface elevation predicted by the HEC-RAS model at the junction with Cayuga Creek.
The results of the hydraulic model analyses performed on the seven tributaries in this study are provided in Section 3.0.
USGS Stream Gauges in the Western New York Region
|
Gauge Location |