Niagara Power Project FERC No. 2216

SHORELINE EROSION AND SEDIMENTATION ASSESSMENT STUDY UPSTREAM AND DOWNSTREAM OF THE POWER PROJECT

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Prepared for: New York Power Authority

Prepared by: W.F. Baird & Associates Coastal Engineers Ltd.

August 2005

___________________________________________________

Draft Report

Volume 1 – Main Report

New York Power Authority

Niagara Power Project

(FERC NO. 2216)

Draft Report

Volume 1 – Main Report

Shoreline Erosion and Sedimentation Assessment Study Upstream & Downstream of the Power Project

EXECUTIVE SUMMARY

The New York Power Authority (NYPA) is engaged in the relicensing of the Niagara Power Project in Lewiston, Niagara County, New York. The present operating license of the plant expires in August 2007. As part of its preparation for the relicensing of the Niagara Power Project, NYPA is developing background information related to the ecological, engineering, recreational, cultural, and socioeconomic aspects of the Project.

As part of this process, a Scope of Services was prepared to complete a qualitative assessment of erosion and sedimentation areas upstream and downstream of the Niagara Power Project. Baird & Associates was retained in 2002 to perform a comprehensive visual reconnaissance of the upper and lower Niagara River, as well as of select tributaries, as prescribed in the Scope of Services. Baird & Associates was retained in 2003 to address a second Scope of Services that prescribed additional data collection at selected erosion and sedimentation areas, as well as additional visual reconnaissance surveys of other major tributaries of the Niagara River system.

This report includes the combined Study Area of the 2002 and 2003 Scopes of Service. The Study Area includes portions of the American shoreline of the Niagara River, the Gorge, and the major tributaries. The upper Niagara Study Area extended from the Peace Bridge to the NYPA Project intakes, and included the Tonawanda and Chippawa Channels. Major tributaries assessed in the upper Niagara Study Area included Gill Creek, Little Niagara River, Cayuga Creek, Bergholtz Creek, Little River, Tonawanda Creek, Ellicott Creek, Twomile Creek, Big Sixmile Creek, Burnt Ship Creek, Woods Creek, Gun Creek, and Spicer Creek. The lower Niagara Study Area extended from just upstream of the Robert Moses Niagara Power Plant (RMNPP) tailrace to Lake Ontario along the American shoreline. The Gorge Study Area also included the upper river from the NYPA Project Intakes to the Falls and the gorge area extending from the Falls to the Robert Moses Niagara Power Plant tailrace. The only tributary assessed in the Gorge portion of the Study Area was Fish Creek. With the exception of Tonawanda Creek (for reasons described in Section 5.3.4), the upstream limit of the tributaries was determined based on the approximate location where Niagara River water levels cease to have an influence. The upstream limit is approximate or qualitative in most cases and was based on several factors including; (a) limits supplied by NYPA for selected tributaries (based on results of URS et al. 2005a), and (b) GIS analysis of local topographic information relative to water levels on the river.

Field investigations entailed documenting the type of shoreline within the Study Area, performing a preliminary inventory of shoreline protection features, identifying substantial erosion and sedimentation sites, and a number of “points of interest.” Erosion sites are those areas where erosion is presently occurring. For each erosion site, preliminary comment of the causes of erosion is provided. For the detailed erosion areas, additional data was collected for further assessment of the sites. Points of interest are defined as areas that are not presently eroding but that have eroded in the past or that appear susceptible to future erosion. Points of interest also include areas where the shore protection is in an advanced state of deterioration, or locations on tributaries where a small erosion scarp was identified. This scarp is often less than one foot high and is not related to severe bank erosion or slope failures. Rather it is attributed to natural erosion processes in the tributaries, which are, by nature, erosional features. Sedimentation areas are locations where sand, silt and/or clay has “settled out” from the water due to several factors (as described in Section 4.1.5)

The shoreline within the Study Area was documented by:

· taking digital photographs of typical shoreline reaches;

· delineating areas that were “Protected” or “Unprotected”;

· noting different types of protection;

· locating areas of poor or failing protection;

· geophysical surveys to identify surficial characteristics of the riverbed; and,

· topographic and hydrographic surveys at select erosion areas.

Digital photos were taken to document typical shoreline types, and were geo-referenced using GPS equipment. Together with the geo-referenced photos, all classifications (erosion areas, points of interest, sedimentation areas, and protected/unprotected reaches) were incorporated into a GIS to assist in the documentation and analysis of the Study Area.

In summary, on the upper Niagara River, approximately 3 percent of the American shoreline inventoried was identified as actively eroding and 63 percent as protected in some manner. The lower river showed erosion along 14 percent of the shoreline, with 37 percent protected. For the total length of tributaries assessed in the upper river, approximately 4 percent of the creek banks were identified as actively eroding, and 40 percent as protected in some manner. Also, a majority of Tonawanda Creek is completely protected, which has an influence on the total protection value noted above.

The primary driving forces for erosion are wind-generated waves, ship/boat-generated waves and river currents on the upper and lower rivers. For the tributaries, erosion occurs when the bed shear stress generated by river currents exceed the resisting properties of the creek materials. Field observations suggest this condition only occurs during the spring freshet and following severe rainfall events. Summer and fall flow conditions, and any water level fluctuations that occur during these periods (natural or induced by U.S./Canadian power generation), do not appear to accelerate erosion. Many other processes play a secondary role in erosion of the rivers and tributaries, including ice, debris, surface runoff, groundwater flow, and weathering. The influence of these driving forces is modulated to different degrees by water level fluctuations depending on the nearshore profile shape, geology and natural/artificial shore protection characteristics. It is important to note that water level fluctuations in both the upper and lower Niagara River are caused by a number of factors in addition to US/Canadian power generation. These include wind, natural flow variations, ice conditions, the water levels of Lake Erie and Lake Ontario, and control of Niagara Falls flow for scenic purposes.

Water level fluctuations may influence erosion rates along two reaches of Grand Island, each about 3,000 feet long, that feature wide, shallow, nearshore shelves. The shelf is effective at dissipating wave energy at low, and possibly average water levels, but not at high water levels. These two sites were chosen as detailed erosion areas, and additional field data was collected at these sites during the 2003 study. Other possible areas of greater water level influence on erosion include some sections of the upper and lower river where shore protection features have deteriorated or are unsuitable for the local conditions.

A conceptual sediment budget was prepared for the Niagara River, including the tributaries and connecting channels. The sediment sources and sinks in the equation were identified and described in qualitative terms. Side scan sonar was collected for the Tonawanda Channel, between the north and south Grand Island bridges, and was used to document the substrate types for the river bed. Other data sets included in the analysis were existing mapping of the river substrate and habitat transects collected along the shoreline.

Sediment sources include suspended sediment from Lake Erie, river bank erosion, river bed erosion, and sediment from the tributaries and canals. The following sediment sinks within the study area were identified: dredging, river bed deposits, accumulation in the U.S. and Canadian reservoirs, losses to the Welland River, and deposition in Lake Ontario. The side scan data helped to identify potential locations of new sediment (i.e. sources), such as river bed erosion and sediment sinks, such as the Turning Basin at Tonawanda Island and the dredged bay at the Twin Intakes. The daily water level fluctuations in the Niagara River due to U.S./Canadian power generation will have some influence on the various sediment budget variables described above.

1.0 INTRODUCTION

The New York Power Authority (NYPA) is engaged in the relicensing of the Niagara Power Project in Lewiston, Niagara County, New York. The present operating license of the plant expires in August 2007. As part of its preparation for the relicensing of the Niagara Project, NYPA is developing background information related to the ecological, engineering, recreational, cultural, and socioeconomic aspects of the Project. As part of this process, a Scope of Services was prepared to assess erosion and sedimentation areas upstream and downstream of the Niagara Power Project.

Baird & Associates was retained in 2002 to perform a comprehensive visual reconnaissance of the upper and lower Niagara River, as well as of major tributaries on the American side of the river, that may be affected by water level fluctuations. The study involved the following tasks:

· identification and delineation of areas experiencing significant shoreline erosion;

· identification of areas that may be experiencing sedimentation;

· identification, in a qualitative manner, of the most likely causes of shoreline erosion; and

· a preliminary inventory of shoreline protection features.

The Study Area for the previous Shoreline Erosion and Sediment Assessment report prepared by Baird (Baird 2003a) included the American shoreline of the Niagara River and selected tributaries that may be affected by water level fluctuations. The lower Niagara River Study Area extended from just upstream of the Robert Moses Niagara Power Plant tailrace to Lake Ontario. The upper Niagara River Study Area included both the Tonawanda and Chippawa Channels, and extending from the Peace Bridge to the NYPA Project Intakes. Major tributaries in the upstream portion of the Study Area included Little Niagara River, Cayuga Creek, Little River, Tonawanda Creek, and Ellicott Creek. The upstream limits chosen for the tributaries in the previous study was based on two factors; a) a visual assessment in the field that active bank erosion was not present, and b) the physical limitations of the survey boat in narrow and shallow creeks/channels.

In 2003, a Scope of Services was prepared to expand the previous study to include additional tributaries, and to document areas further upstream that were initially visited for the previous investigation. The Scope of Services also prescribed a more detailed survey of selected erosion areas upstream and downstream of the Niagara Power Project, as well as a more detailed assessment of sedimentation areas in the river.

The 2003 Study Area included the following tributaries; Fish Creek, Gill Creek, Cayuga Creek, Bergholtz Creek, Ellicott Creek, Twomile Creek, Big Six Creek, Burnt Ship Creek, Woods Creek, Gun Creek, and Spicer Creek. The upstream study limits of the tributaries was determined based on the location where Niagara River water levels cease to have an influence. With the exception of Tonawanda Creek (for reasons described in Section 5.3.4), the upstream limits of the tributaries were based on several factors including; (a) limits supplied by NYPA for selected tributaries (based on results of URS et al. 2005a), and (b) GIS analysis of local topographic information relative to water levels on the river.

The Study Area also included the upper river from the NYPA Project Intakes to the Falls and the gorge area extending from the Falls to the Robert Moses Niagara Power Plant tailrace. Figure 1.0-1 shows the limits of the Study Area for the combined studies.

The tasks undertaken in the earlier study were repeated in the present study for the expanded Study Area. A more detailed survey of erosion was also undertaken in selected areas of the upper and lower river at locations chosen from the earlier study. The detailed erosion surveys were also performed in selected tributaries of the upper river. In addition, a more detailed sedimentation survey was undertaken for a substantial portion of the Tonawanda Channel of the upper river. All of the data collected was incorporated into a GIS to assist in the documentation and analysis of the Study Area. This report presents the results of the combined studies.

Figure 1.0-1

Study Limits

[NIP – General Location Maps]

2.0 PROJECT DESCRIPTION

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 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 information presented in this section was provided by URS or derived from URS et al. 2005b.

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 and the river, is the Robert Moses Niagara Power Plant (RMNPP), 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 (LPGP). Under non-peak-usage conditions (i.e., at night and on weekends), water is pumped from the forebay via the LPGP’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 receptor of 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.

For purposes of generating electricity from Niagara Falls, two seasons are recognized: tourist season and non-tourist season. As required by international treaty, at least 100,000 cubic feet per second (cfs) must be allowed to flow over Niagara Falls during tourist season (April 1 – October 31) daytime hours, and at least 50,000 cfs at all other times. Canada and the United States are entitled by international treaty to produce hydroelectric power with the remainder.

It is important to note that water level fluctuations in both the upper and lower Niagara River are caused by a number of factors other than the US/Canadian power generation. These include wind, natural flow variations, ice conditions, the water levels of Lake Erie and Lake Ontario, and control of Niagara Falls flow for scenic purposes. Water level fluctuations in the Chippawa-Grass Island Pool are limited by an International Niagara Board of Control (INBC) directive to 1.5 feet per day within a 3-foot range for normal conditions. For unusual conditions (i.e., high flow, low flow, ice, etc.), the allowable range of Chippawa-Grass Island Pool water levels is extended to 4 feet. The effect of ponding in the Chippawa-Grass Island Pool is detectable upstream and varies with river conditions. At most, this backwater influence can extend to somewhere between Frenchman’s Creek and the Peace Bridge.

Water-level fluctuations in the lower Niagara River (upstream of the RMNPP tailrace) from all causes can be as great as 12 feet per day. Most of this daily fluctuation is due to the change in the treaty-mandated control of flow over Niagara Falls. Water level fluctuations downstream of the RMNPP tailrace are much less. The average daily water level fluctuation 1.4 miles downstream of the RMNPP tailrace, during the 2002 tourist season, was approximately 1.5 feet. The daily fluctuations decrease progressively at the temporary gages located further downstream. At the most downstream temporary gage 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.

3.0 BACKGROUND ON EROSION AND SEDIMENTATION PROCESSES

This section presents an overview of erosion processes for the types of shorelines encountered on the upper and lower reaches of the Niagara River. This section also includes a brief discussion of the geology and glacial geomorphology of the Study Area.

Open coast and river shorelines in the Great Lakes Basin may be broadly grouped into three categories:

· sandy shores, including beaches backed by dunes and barrier beach complexes;

· cohesive shores, including consolidated glacial till, lacustrine clay and erodible sedimentary rocks such as dolomite, limestone, sandstone and shale from the Paleozoic era; and

· erosion-resistant bedrock shores, such as the Precambrian granite found in the Thousand Islands Region of the St. Lawrence River.

All eroding shorelines in the Study Area fall into the second category, namely, cohesive shores. The erosion processes associated with cohesive shores are fundamentally different from the erosion of sandy shores. It is essential that these differences be recognized in the implementation of shore stabilization measures. This section discusses erosion and sedimentation processes associated with cohesive shores. This description has been adapted from a chapter on this topic prepared for the new U.S. Army Corps of Engineers (USACE) Coastal Engineering Manual by Dr. R. Nairn of Baird & Associates (CEM Part III, Chapter 5). Many of the technical terms used are explained in the glossary presented in Appendix A of this report.

3.1 Local Geology and Glacial Deposits

The geology, glacial deposits and surficial soils within the study area are described in Chapter 10 of the First-Stage Consultation Report (NYPA 2002). Additional details can also be found in several historical references, including Grabau (1901) on the Paleozoic rocks, Kindle and Taylor (1913) for a description of the glacial history and Johnston (1964) for information on the water bearing characteristics of the bedrock. These references will be summarized briefly below to provide context for the following discussion of erosion processes. The reader should refer to these references for additional details if required.

The underlying bedrock within the Study Area is from the Paleozoic era, dips slightly to the south, and was formed 500 to 350 million years ago (Johnston 1964). North of the Niagara Escarpment, the surficial deposits are underlain by Queenston Shale, which outcrops along the banks of the Niagara River near Lewiston. Above the Escarpment, the final bedrock layer is Lockport Dolomite, which is generally 5 to 15 feet below the glacial deposits and modern soil horizons. Between these two formations are layers of limestone, sandstone, and shale, which can be observed in the Niagara Gorge.

The completion of the Paleozoic era, approximately 300 million years ago, marked the transition to the Quaternary period when the landscape in the Great Lakes Basin was influenced by a glacial epoch known as the Pleistocene. This was followed by the post-glacial Holocene, which began approximately 10,000 years ago, and continues today. During the Pleistocene, several continental glaciers advanced south and retreated north across the Study Area. The final glacial event is known as the Wisconsin, and this period is responsible for the deposition of the cohesive sediments found above the Queenston Shale and Lockport Dolomite within the Study Area.

The deposits related to the Wisconsin Glaciation can be generally grouped into three categories for the purpose of this erosion investigation: 1) glacial till, which consists of varying distributions of clay, silt, sand, cobbles, and pebbles, and is formed under pressure at the base of the glacier, 2) lacustrine clay, which forms at the bottom of temporary lakes located along the ice margin when sediment-laden meltwater is transported to the lakes from the glacier, and 3) isolated deposits of sand and gravel that have been eroded from the till and clay, then sorted and transported by glacial streams from the retreating glacier. In general, the glacial till is found directly on top of the bedrock, then capped by the lacustrine deposits, and occasionally followed by sands and gravels.

3.2 Cohesive Shore Processes

3.2.1 Definition of a Cohesive Shore

A shore is defined as cohesive when the erosion process is directly related to the irreversible removal of a cohesive sediment substratum (i.e., glacial deposits, ancient lagoon peats, tidal flat muds, valley and bay fill muds, lacustrine clays, flood deltas consisting of fine sediments, soft Paleozoic or sedimentary rocks, and other consolidated or over-consolidated deposits). Even when sand beaches are present over cohesive soils, the soils under the sand beach play the most important role in determining how these shores erode and evolve in the long term. This differs fundamentally from sandy shores where erosion (or deposition) is directly related to the net loss (or gain) of unconsolidated sediment (i.e., sand and gravel) from a given surface area. Erosion on a sandy shore is a potentially reversible process while erosion on a consolidated cohesive shore is irreversible.

A further distinction may be made between “mud,” or unconsolidated cohesive sediment that has been recently deposited (‘recently’ may be a matter of several years, for example), and hard or consolidated cohesive sediments. For this study, the eroding cohesive shores consist of consolidated glacial till and lacustrine clay (which, in some areas, will have been softened by subaqueous and sub-aerial erosion processes) observed in the upper Niagara River, and erodible sedimentary rock, such as shale observed in the lower Niagara River.

A thin veneer of sand and gravel, sometimes forming a beach at the shore, usually covers the consolidated or partially consolidated sediments that constitute cohesive shores. Such a shoreline, although sandy in appearance, does not consist of an infinitely thick pile of sand, and, in such instances, conventional coastal engineering principles are often not applicable. Cohesive shorelines may be associated with an eroding bluff or bank face such as Buckhorn Island, or they may consist of a transgressive barrier beach perched over older cohesive sediments (no examples of this shoreline type are found along the Niagara River). The presence of the sand veneer often disguises the underlying consolidated substratum, and therefore, at many locations, cohesive shores are incorrectly assumed to behave as sandy shores. Along the lower Niagara River in the vicinity of Lewiston, the talus slopes at the base of what once would have been high sedimentary rock cliffs constitute a special case of cohesive shore. Because these cliffs generally consist of very weak Queenston Shale, the talus consists of eroded and partially consolidated shale debris.

Cohesive shores are found over a large part of the Great Lakes, Arctic, Atlantic, Pacific, and Gulf coasts of North America, over a large part of the North Sea coast of England, and in sections of coastline along the Baltic and Black Seas. Estimates from the International Joint Commission (IJC) Erosion Processes Task Group Report (1993) suggest that more than 50 percent of the lower Great Lakes and connecting channel shores may be classified as cohesive. As the awareness of this shore type grows, and as sub-bottom investigations become more prevalent, more examples are being identified. As Riggs et al. (1995) note, in many cases, the shore is not just a “thick pile of sand.”

3.2.2 Principles of Erosion on Cohesive Shores

Erosion processes on cohesive shores are distinctly different from those on sandy shores. On consolidated cohesive shores, the erosion process is irreversible because, once eroded in an energetic coastal environment, cohesive sediment cannot be reconstituted in a consolidated form. Furthermore, since the sand and gravel content is usually low in these deposits (often less than 20 percent), the volume eroded is not balanced by the volume of deposition within the littoral zone. The eroded fine sediments (silt and clay) are winnowed, carried offshore, and deposited downstream in deeper water or sheltered bays. Even on the sedimentary-rock shores of the lower Niagara River, much of the Queenston Shale is so weak that it quickly breaks down to clay-sized particles that are lost into deep water. The sand and gravel fraction, on the other hand, usually remains in the shallow littoral zone.

Consolidated cohesive sediment is eroded by at least four mechanisms:

· through abrasion by sand particles entrained in hydraulic flow;

· through pressure fluctuations associated with turbulence generated at various scales, such as wave-breaking-induced turbulence that reaches the riverbed, or large-scale eddies that may develop in the surf zone (the area where wave breaking occurs);

· through chemical and biological influences; or

· through wet/dry and freeze/thaw cycles, when exposed to the atmosphere (desiccation) or in shallow water.

Sand and gravel (or shingle) can also provide a protective cover to the underlying cohesive substratum. However, only when the sand cover is of sufficient thickness to protect the cohesive substratum at all times will the shore revert to a sandy classification (i.e., truly a “thick pile of sand”). This condition likely never develops along the Niagara River. On consolidated cohesive shores, the rate of lake or riverbed downcutting determines the long-term rate at which the bluff or bank retreats at the shoreline. In other words, while sub-aerial geotechnical processes may dictate when and where a slope failure will occur over short periods (1 to 25 years), the rate of shoreline retreat over the long term (>50 years) is determined by the rate at which the nearshore underwater profile is eroded (i.e., the downcutting rate).

3.2.3 Underwater Erosion Processes

An extensive study of nearshore profiles on the north-central shore of Lake Erie, described by Philpott (1984), revealed that the profile shape remained relatively constant over an eighty-year interval despite dramatic shore recession. For this to occur, erosion must be distributed across the full width of the nearshore profile. This led Philpott (1984) to conclude that the controlling process in bluff or cliff recession on cohesive shores is not restricted to wave action at the toe (as proposed by Sunamura (1992) for eroding rocky coasts), but by the erosion of the nearshore profile by waves. Boyd (1992) cites many earlier references that also suggest that nearshore erosion has a controlling influence on shoreline recession. The shoreward shift of the dynamic equilibrium profile implies that erosion or downcutting is proportional to the gradient of the nearshore profile and is, therefore, greatest close to shore. Davidson-Arnott (1986) describes field measurements of downcutting for a till profile (through the deployment of micro-erosion meters across a transect) at a site near Grimsby on Lake Ontario. The results confirm the hypothesis on downcutting, namely, that the rate increases towards the shore in a manner related to the local bed slope, allowing for the preservation of the profile shape as it shifts shoreward with time. The downcutting hypothesis has now been confirmed by many other field investigations, including nine years of profile retreat data at Maumee Bay State Park in Ohio (Fuller 2002). Hutchinson (1986) and Sunamura (1992) also note that the rate of lowering (or downwasting) of the intertidal platform on erodible rocky coasts likely determines the long-term rate of cliff retreat in most instances. The key point is that erosion of a bluff is an effect of the erosion of the nearshore profile. The shore materials and erosion processes found at the above mentioned sites are similar to the Niagara River shoreline and therefore the findings are relevant to this study.

In general, it has also been shown that the underlying cohesive profile, for cases where the properties of the cohesive sediment are uniform, follows an equilibrium profile shape as defined by Dean (1977). The morphology of the nearshore profile is a product of the local wave climate, the water level regime, and the resisting properties of the bottom substrate. The combination of local driving forces and sediment properties at a site will produce an unique profile shape that varies spatially along the shore.

The downcutting process is illustrated in Figure 3.2.3-1 for a cohesive shore site located east of Toronto along the Scarborough Bluffs, on Lake Ontario. The bluff face has retreated approximately 100 feet (30 meters) over a 37-year period, for an average long-term recession rate of 2.7 feet/year (0.8 meters/year). The underlying cohesive profile shape of 1952 is very similar to that of 1989; it has simply shifted shoreward by 100 feet. The long-term bluff or cliff retreat rate is equivalent to the long-term profile retreat rate. This figure also shows that erosion can continue even if there is a significant quantity of sand covering an underlying cohesive sediment profile. The position of the underlying cohesive profile shown in Figure 3.2.3-1 was estimated based on observations that the cohesive sediment is usually exposed or very thinly covered in the troughs between the sandbars. Also, it is known that the till is exposed at the toe of the bluff (i.e., at the back of the beach).