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Geomorphology and Sea-level Rise on one of Canada's Most Sensitive Coasts: Northeast Graham Island, British Columbia Author(s): I.J. Walker and J.V. Barrie Source: Journal of Coastal Research, Special Issue No. 39. Proceedings of the 8th International

Coastal Symposium (ICS 2004), Vol. I (Winter 2006), pp. 220-226 Published by: Coastal Education & Research Foundation, Inc. Stable URL: http://www.jstor.org/stable/25741565 Accessed: 14-10-2015 01:59 UTC

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Journal of Coastal Research SI 39 220-226 ICS 2004 (Proceedings) Brazil ISSN 0749-0208

Geomorphology and Sea-level Rise on one of Canada's Most Sensitive Coasts: Northeast Graham Island, British Columbia

I. J.Walkerf and J.V.BarrieJ

tDepartment of Geography,

University of Victoria

Victoria, British Columbia

V8W 3P5 Canada ij walker@uvic. ca

{Geological Survey of Canada - Pacific,

Institute of Ocean Sciences

Sidney, British Columbia V8L 4B2 Canada [email protected]

ABSTRACT

WALKER, L J., and BARRIE, J.V., 2006. Geomorphology and sea-level rise on one of Canada's most 'sensitive'

coasts: Northeast Graham Island, British Columbia. Journal of Coastal Research, SI 39, (Proceedings of the 8th

International Coastal Symposium), 220 - 226. Itajai, SC, Brazil, ISSN 0749-0208.

This paper documents the geomorphology of one of Canada's most dynamic coastlines, northeast Graham Island,

Queen Charlotte Islands (Haida Gwaii). This area has undergone major sea-level changes (-150 to +16 m) over the

Holocene and is currently rising at +1.6 mm a1. Relict shorelines and recent progradational ridges tell of landscape response to sea-level changes. Given a macrotidal range, energetic wave climate and ongoing erosion, the

Geological Survey of Canada identifies this as one of Canada's most sensitive coasts to future sea-level rise. Retreat

of 1-3 m a1 and tens of metres in extreme years (e.g., El Nino 1997-98) occurs on East Beach, while the dissipative shores of North Beach prograde at 0.3-0.6 m a1. Over 100 km of sandy beach are maintained by strong littoral

transport by tidal currents and storm waves. Northward longshore transport on East Beach heads westward around

Rose Spit to North Beach, particularly during SE storms. Despite a moist climate and dense vegetation, aeolian

activity is high and moves sand onshore into foredunes and driftwood jams that stabilize the backshore against wave

attack. Foredunes migrate on the order of metres per year while larger parabolic dunes migrate slower (metres per

decade). Migrating shore-attached bars feed beach-dune systems while their leading edge is a locus for beach

erosion. Dendrochronological (tree-ring) evidence is explored to provide proxy evidence of past climate changes and geomorphic responses. Instead of landward erosion of the beach and deposition in the nearshore per the Bruun

model, the response of this coast to ongoing sea-level rise involves high onshore sand transfer, accretion and

foredune migration that provide a buffer against wave attack. This preliminary examination sets the geomorphic

stage for a larger, interdisciplinary study on sea-level rise impacts that threaten communities, ecological reserves, cultural sites and critical infrastructure in the region.

ADDITIONAL INDEX WORDS: Climate change, sea-level rise, coastal erosion, Queen Charlotte Islands._

INTRODUCTION

The Queen Charlotte Islands (Haida Gwaii) is an archipelago located 80 km offshore from British Columbia's north coast

(54?N, 132?W, Fig. 1). The northeastern region of Graham

Island, known as the Argonaut Plain or Naikoon peninsula, is

comprised of unconsolidated Quaternary sediments of

glaciofluvial origin (Clague et aL, 1982). This region is distinct in British Columbia in that it experienced limited to no ice cover during the Late Wisconsinan glaciation (ca. 16000 yr

BP) and may have served as a glacial refugium (Warner et aL,

1982). Dramatic fluctuations in relative sea level have occurred

in the northern Pacific margin of Canada over the late

Quaternary. In Hecate Strait, a rapid regression to -150 m

occurred between 14600 - 12400 14C yr BP due to isostatic

rebound followed by transgression to +16 m by 8900 14C yr BP due to combined eustatic rise and subsidence of a glacioisostatic

forebulge (Josenhans et aL, 1997, Barrie and Conway,

2002). Since 3800 14C yr BP, sea level has regressed leaving a series of relict shorelines and prograding beach ridges. Over the

20* century, relative sea level has been rising at a rate of +1.6

mm a1 (Abeysirigunawardena and Walker, 2005). The modern coastal landscape of NE Graham Island consists

of over 100 km of sandy shoreline that is host to a variety of

landforms including low gradient, dissipative beaches backed

by prograding foredunes on North Beach; reflective cuspate cobble beaches with sandy low tide terraces on Rose Spit; and

multiple-barred beaches backed by migrating foredunes and

parabolic dunes on East Beach. This coast experiences 'extreme'

conditions including a macrotidal range, an energetic wave

climate with frequent storm surges and frequent, strong winds

exceeding gale force (65 km hr1). This creates a dynamic coastline that is maintained by northward littoral transport of

sediments along East Beach by strong wave and tidal currents.

This coast is retreating by 1 -3 m a1 and greater during extreme

events such as the 1997-98 El Nino that caused 0.4 m of regional sea-level rise and 12 m of localized retreat (Barrie and

Conway, 2002). In contrast, the dissipative shores of North

Beach are prograding at 0.3 to 0.6 m a1 (harper, 1980). On

both shores, much of the littoral sediment is moved onshore via

aeolian delivery in frequent transporting winds to active,

migrating dune systems despite a moist maritime climate, extensive logjams and dense forest cover.

Given the tidal range, wave regime, erodible sediments and

ongoing rates of sea-level rise and erosion, the Geological

Survey of Canada (GSC) identifies NE Graham Island as one of Canada's most sensitive coastlines to sea-level rise (Shaw et

aL, 1998). In that study of past and modern responses to sea

level rise may portend future impacts, the purpose of this paper is to discuss the late Quaternary and modern geomorphology of

this coast and identify potential responses to sea-level rise. This

examination provides a preliminary physical basis for a larger

interdisciplinary study of the vulnerability of this area to future

sea-level rise. A preliminary integrated conceptual framework

for this larger study appears in a companion paper (Dolan and

Walker, 2006).

PHYSICAL SETTING

Climate

Graham Island experiences a marine west coast cool (Cfb) climate and receives 1398 mm a1 precipitation. Environment

Canada 30 yr climate normals for Sandspit Airport (150 km S) show that 69% of this precipitation falls as rain from September to March though appreciable (300-500 mm), yet short-lived, snowfall occurs from December to March. The moderating influence of the Pacific Ocean on average temperatures is

seasonally pronounced with above freezing daily temperatures

Journal of Coastal Research, Special Issue 39, 2006

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Geomorphology and sea-level rise on one of Canada's most 'sensitive' coasts: Northeast Graham Island, British Columbia 221

Figure 1. Study region on northeastern Graham Island, Haida

Gwaii (Queen Charlotte Islands), British Columbia, Canada. Wind rose and sand drift potential rose are shown.

of 3.2?C in January (high 5.6?C, low 0.7?C) and mild summer temperatures of 15?C in August (high 17.9?C, low 12.1?C).

Wind and Wave Regime Coastal systems in this region of the NE Pacific experience

seasonally opposed winds that are strongest in winter months. In the fall, the Aleutian Low pressure system develops and intensifies causing a counter clockwise circulation of surface

winds. This brings moisture-laden S-SE winds up Hecate Strait

to Haida Gwaii from October through April. Come May, the Aleutian Low declines and retreats to the NW while the North Pacific High expands and intensifies. This shifts the wind regime from a dominant SE mode (winter) to a W-NW mode in summer (Fig. 1). Annual average wind speeds are 8.5 m s1 in

Hecate Strait with less than 1% calm conditions (ElD et al.,

1993). For the period 1995-1999, 67% of winds recorded at the Rose Spit meteorological station were above the accepted sand

transport threshold of 6 m s1 (Fryberger, 1979). Maximum gusts often exceed 160 km hr1 and a maximum wind of 113 km hr1 (storm force) was recorded. These are some of the strongest, most persistent, and most competent recorded winds in Canada.

Hecate Strait is also known for its severe wave conditions.

Annual significant wave height, Hs, for the area is 1.8 m. The

peak (most energetic) period is 10 s with waves of H <3 m being the most frequent. The most active season is from November

/'* Queen Charlotte Islands

/

-1-1-1-1-1-1-1-1-1-1-1-1-1-1? 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Radiocarbon years before present (x 1000)

Figure 2. Generalised sea-level curves for the Queen Charlotte

Islands and for the Northern Hecate Strait modified from Clague et al. (1982), Fedje and Josenhans (2000), Barrie and Conway (1999,2002) and Hetherington et al. (2003).

(H=2.8 m) through January (H=2.6 m) with maximum observed Hs of 14.3 m in December (ElD et aL, 1993). Higher values (H > 3.5 m) occur in the shallower waters of Dogfish Banks along East Beach and prevail for 20-30% of the time during winter months (Thomson, 1981). The dominant wave direction in Hecate Strait is S-SW though SE winds and onshore refraction in shallower waters cause SE waves on East Beach.

On North Beach, NW swell and storm waves are comparatively

infrequent and less energetic.

Tides and Currents

Currents in Hecate Strait and Dixon Entrance are driven

mainly by tidal forcing with coastal topographic effects only locally important (Amos et aL, 1995, Strong et aL 2002). Tides are semi-diurnal mixed and range 5-7 m with HHWMT

exceeding 7 m. Reversing flood-ebb tidal currents occur as

water floods into Hecate Strait around Rose Spit from Dixon

Entrance, then reverses at high tide. Typical flood current

speeds are 0.25-0.5 m s1 near Rose Spit and 0.15 m s1 on the ebb

along East Beach (Amos et aL, 1995). Two gyres exist: a clockwise gyre centred on Rose Spit and a counter-clockwise

gyre centred near Cape Ball. Thus, a current divergence exists on East Beach that shifts S on the ebb while northward currents increase on the northern 20-30 km of the beach. In Dixon

Entrance, the Rose Spit eddy rotates counter-clockwise and

eastward on North Beach (Crawford and Greisman, 1987) at

speeds of 0.06-0.11 m s1 (Flather,1987). River discharge and

winds appear to have minimal effect on tidal currents except

during intense storms when wind-shear currents can approach 0.25 m s1 (Strong et aL, 2002). Amos et aL, (1995) show that storm-enhanced currents transport significant amounts of

sediment from East Beach, around Rose Spit to North Beach.

Sea Level History and Landscape Response A regional sea level regression on the northern Pacific margin

of Canada began after the late Wisconsinan glacial maximum ca. 16000 yr BP. Crustal flexure and rebound due to a

glacioisostatic forebulge caused a rapid sea level regression ca.

14600-12400 14C yr BP to -150 m in southern Hecate Strait (Josenhans et aL 1997) and to as much as -100 m in northern Hecate Strait (Barrie and Conway, 1999, 2002, hetherington et aL, 2003) (Fig. 2). At this time, much of Hecate Strait along East Beach was subaerially exposed and

Figure 3. 1980 airphoto (NAPL #A25613-39) showing relict prograding shorelines of Naikoon Peninsula over the Holocene.

Recent, gradual progradation to the W shown by closer ridges on North Beach. Area of coverage for Figs. 4 and 5 also shown.

Journal of Coastal Research, Special Issue 39, 2006

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222 Walker and Barrie

may have provided a corridor for early human migration

(Josenhans et al, 1995). Following this, eustatic rise and subsidence of the forebulge caused rapid sea level transgression to +16 m by 8900 14C yr BP (Fedje and Josenhans, 2000).

Drowned shorelines, barrier islands and wave cut scarps exist as

much as 100 m below modern sea level (Warner et al, 1984, Barrie and Conway 2002). Since 380014C yr BP sea level has regressed, leaving a series of relict shorelines extending NNW

from Argonaut Hill that demarcate distinct progradational

phases over the late Holocene (Fig. 3). The extent and spacing of the shorelines indicates that a significant amount of sediment

was available for spit platform growth. Gradual isostatic

adjustments, rather than abrupt tectonic motions are thought to

have controlled spacing of the earlier phases (Barrie and Conway 2002). Closer ridges to the W side of Rose Spit indicate a more recent phase that may have began 110014C yr BP

(Clague et al, 1982) due to tectonic uplift (Harper, 1980). However, a transect survey of 7 beach ridges extending 0.4 km

inland at South Beach indicates foredune progradation at a

stable datum. This is an important distinction as the term 'beach

ridge' is poorly defined (Otvos, 2000) and the role of aeolian processes is often understated (Hesp, 1984, 2002). Optical dating of relict shorelines is underway to ascertain the timing and extent of past sea level changes.

Modern Geomorphology and Sediment Dynamics Over 100km of sedimentary shoreline exist on NE Graham

Island that is host to a variety of landforms including: dissipative beaches backed by prograding foredunes on North Beach; reflective cuspate cobble beaches with a sandy low tide terrace on NW Rose Spit; and multiple-barred beaches backed

by migrating foredunes and parabolic dunes on East Beach. The

East Beach coastline is maintained by active littoral transport of

eroded bluff sediments from Capes Ball and Fife by strong wave and tidal currents (Amos et al, 1995). Figure 4 shows nearshore bars, a log drift line demarcating the berm crest, 5-10

m foredunes with blowouts and parabolic dunes migrating NW

Figure 4. a) East Beach looking S from Kumara Lake/Cape Fife region. Treed ridge behind dunes (right) is a former shoreface. b)

Migrating 5-10 m foredunes with blowouts and incipient dune at toe. Seaward, an incipient dune also exists on the driftwood jam.

(Right) up to 1.2 km into muskeg on an old shore platform. Currently, this coast is retreating by 1-3 m a1 (Conway and

Barrie, 1994) and greater during extreme events (e.g., El Nino

1997-98, Barrie and Conway, 2002). However, erosion (i.e., sand loss from the beach) appears to be localized to bluff sections with narrow backshores while accretion (though not

progradation) via aeolian transfer is widespread in areas with

wide backshores and foredunes (Fig. 4b). Nearshore sediments are stored and cycled in shore-parallel

bar systems on East Beach that are maintained by intense swash

action and strong longshore tidal currents. In some areas, beaches are slightly rhythmic with rip currents. Bars are

reworked periodically by storm waves (cf. Anthony and

Orford, 2002) and on northern East Beach are shore-attached.

These bars provide enhanced sand supply to backshore dune

systems (Fig. 5) similar to that observed by Anthony (2000) on the coast of France. Comparison of 1980 and 1997 airphotos shows migration of this bar complex about 5km N toward Cape Fife. On the leading edge of these bars, erosion of beach and bluff systems occurs as wave energy is focused onshore and less

sand is available in the nearshore to dissipate this energy. This,

coupled with erosion by high storm waves, may have led to the drainage of Kumara Lake between 1980 and 1994 (Conway and Barrie 1994). Interestingly, 1954 and 1966 photos also show the lake drained without bars present suggesting that dune growth and subsequent erosion during extreme storms may be a

recurring process in lake maintenance.

In contrast to the eroding shores of East Beach, the

dissipative shores of North Beach are prograding at 0.3-0.6 m a1

(Harper, 1980). Much of this sediment originates from East Beach rather than offshore from Dixon Entrance (Amos et aL,

1995). During SE storms, northward alongshore transport on

East Beach is funneled through a nearshore channel westward

around Rose Spit. Sand is then worked onshore to North Beach

by NW waves and winds.

The convergence of North Beach and East Beach forms one of

Canada's most spectacular coastal landscapes, Rose Spit (Fig.

6), that is known for its ecological and cultural significance. Rose Point extends several kilometres north into Dixon

Entrance as a flat cobble-gravel plain capped by aeolian sands.

It is bounded on East Beach by 1-5 m foredunes that grade to wave cut scarps toward the end of the plain. Beyond this, Rose

Spit proper extends another 3 km as a steep-faced intertidal

cobble beach where sediment-rich currents from East Beach

collide with the waters of Dixon Entrance. During SE storms, currents flow westward to North Beach as reflected in the

western curve of the spit. On the NW side, beaches are coarser

a) 1980

b)1997

Cape Fife Kumara Lake (drained)

Figure 5. Comparison of 1980 (a) and 1997 (b) airphotos showing shore-attached bars on East Beach. Bar system has

migrated northward 5 km and Kumara Lake has drained over

this period._

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Geomorphology and sea-level rise on one of Canada's most 'sensitive' coasts: Northeast Graham Island, British Columbia 223

Figure 6. 1980 airphoto of Rose Spit (NAPL #A25558-116, inset) and oblique photo showing mixing of sediment-rich

waters from East Beach (left) under NW swell. Rose Bar shown

in forefront.

and more reflective with a distinct sandy low tide terrace. A

scarped, cuspate cobble berm formed at spring tide is evident with one to two smaller terraces formed at lower tide stages. Terraces diminish westward on North Beach as the system becomes more dissipative. This transition is distinct and may demarcate the eastern extent of onshore sand delivery from East

Beach. There appears to be little alongshore transport on North

Beach eastward to Rose Spit, which would explain the high accretion rates and sediment coarsening toward the spit.

Impacts of Driftwood on Beach-dune Systems

Driftwood, mostly felled timber, litters backshore environments along East and North Beach (Fig. 7). By providing a major store for sediment in the backshore, logjams serve three important geomorphic functions. First, logjams act

as 'accretion anchors' that fortify the backshore by storing

significant amounts of aeolian sand. In some areas, rapid accretion and/or complete burial of the drift jam have occurred.

This stabilizes the beach by providing a store of sand and debris that is reworked as a buffer during wave attack. Foredune scarps behind drift jams indicate that complete removal could occur

during high storms. Once re-deposited however, accretion

would resume and logjams would fortify the beach between significant storms. The role of such backshore storage

components and onshore aeolian delivery in general is often

overlooked in assessments of coastal sedimentary dynamics. The second function of driftwood is as nuclei for incipient

dune formation. Windblown sand from the beach is deposited as

shadow dunes within the drift matrix and, provided deposition continues in the absence of wave erosion, the matrix fills and

vegetation establishes. Dune establishment may take several

seasons in areas with wide, log-jammed backshores and

requires high onshore sand transport and low frequency of

destructive wave surges. On North Beach where driftwood is

less dense and the backshore is less exposed to wave attack, dune development is more continuous. Unlike vegetated

incipient foredunes (Hesp, 1984,1989), sizable incipient dunes can develop in driftwood jams before vegetation colonization

occurs. Figure 7b shows an incipient driftwood dune seaward of an established foredune vegetated with dunegrass (Elymus mollis). Generations of Sitka spruce (Picea sitchensis) have

colonized older dunes and provide a chronology of beach

progradation. Dune development via this process is key to the

progradation and stabilization of this coast.

The third impact of driftwood is to dam river discharge and/or preserve backshore swales. The resulting lakes are common at

the base of foredunes along East Beach (Fig. 4a). Aeolian accretion appears to be key in the development of these features

and, in some areas, sand has subsequently filled backshore

lakes. Rapid drainage by channel incision or wave erosion and

rupture of the drift jam is common. High onshore sand transport,

Figure 7. Driftwood jams act as accretion anchors and stabilize

backshore environments along East Beach near Rose Spit (a). On North Beach, logs act as nuclei for incipient foredune

growth (b).

Coupled with shifting nearshore bars causes deranged drainage on East Beach.

Aeolian Activity Much of the littoral sediment transported along the shores of

Graham Island is moved landward by strong winds into active dune systems; this despite a wet climate and dense forest cover.

The wind regime is highly energetic with transporting winds occurring 67% of the time for the period 1995-99. To assess sand drift potential, the Fryberger, (1979) model was used

with wind data for this period from the Rose Spit meteorological station. Resulting DP values (in vector units,

VU) are plotted as a drift rose (Fig. 1). The total drift potential for the region of 4566 VU is well above those documented for desert regions (80-489, Fryberger, 1979) or for the Canadian prairies (300-1600, Wolfe and Lemmen, 1999) and surpasses those for the Netherlands coast (1700-4000, Tsoar, 2000). The resultant drift potential vector (RDP) is 2967 VU to 316 (NW) which reflects the dominant SE winds in the regime. This is slightly less than an average dune alignment of 336

? 8?

(determined from airphoto analysis of 94 parabolic dunes on the coast) which may reflect steering from a secondary (W-NW)

mode in the regime from summer winds. Foredune migration rates are on the order of metres per year while parabolic dunes

move slower (metres per decade). Wolfe and Lemmen, (1999) suggest that in high-energy

prairie environments sand supply, not wind, is the limiting factor for dune migration. Most prairie dunes are 'closed' to new

inputs and rely largely on reworked sand eroded locally from stabilized dunes for maintenance. On NE Graham Island

however, dunes receive high sand supply moved onshore via

frequent competent winds. Instead soil moisture, which limits

sand transport at low concentrations (Namikas and Sherman,

1995), and vegetation cover may be more important at limiting aeolian activity, especially beyond the backshore environment.

Dendroclimatology and dendrogeomorphology

Dendrochronological (tree-ring) records provide high resolution accounts of past climate. For instance, Mountain

hemlock (Tsuga mertensiana) at treeline on southern Graham

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224 Walker and Barrie

Island is sensitive to June-July temperature and coastal Shore

pine (Pinus contorta) is very sensitive to seasonal precipitation

(Smith 1999). This latter record shows notable droughts in the late 1940s and early 1950s. These preliminary reconstructions

emphasize the dynamic nature of climate in Haida Gwaii and, while there is great variability in the controls of forest growth, it

is likely that climate variations are reflected in existing forest

structure.

Next to temperature and precipitation, no other climatic

factor has a greater impact on tree growth than wind

(Schweingruber, 1996). Aeolian processes impact trees via

abrasion, burial or deflation and application of wind stress and

sediment loads. This produces distinct physiological responses that include tilting, flagging, bark removal, adventitious roots, reduced and/or contorted growth, and death. Impacts are

widespread on NE Graham Island including: dwarf krummholz

Sitka spruce, tilted and buried trees on foredunes, 'ghost forests'

killed by dune migration, exhumed adventitious roots formed

by rapid accretion and subsequent deflation, prop root

buttressing, and abraded trunks. Dendrogeomorphic techniques are being applied to identify periods of dune activity and migration (cfi marin and FlLlON, 1992). This, with dendroclimatological evidence, can provide proxy records of

coastal landscape responses to climate variability that could

extend back several hundreds of years.

A 'SENSITIVE' COAST

The Geological Survey of Canada (GSC) defines 'sensitivity' as the degree to which a rise in sea level would initiate or

accelerate coastal geomorphic changes given local conditions

and other climate change effects (e.g., increased storminess)

(Shaw et al 1998). Admittedly, this definition overlooks ecological and socio-economic factors such as the capacity of

impacted communities to adjust and adapt (cfi LuiTZEN et al 1992, Smit and PlLlFOSOVA, 2003). Identified impacts include

increasing tidal inundation, storm surge flooding, coastal

retreat, erosion and accretion. All of these affect coastal form

and function and in some areas are changing at geologically

rapid rates. Recognizing potential hazards to coastal

communities and ecosystems, the GSC mapped a 'sensitivity index' for the entire Canadian coastline (Shaw et al, 1998). The

index is a function of: rock type, relief, landforms present, sea

level change, wave height, tidal range and shoreline change. Most of the Canadian coast (67%) has a low sensitivity, 30% is moderately sensitive and 3% is highly sensitive. The coast of

British Columbia (10.5% of the Canadian coast) has a moderate-low sensitivity due to a prevalence of steep, rocky shores. Exceptions include the Fraser Delta, Vancouver and NE

Graham Island, which has a mean sensitivity value of 13 (low 3.2, high 25) and ranks among the most highly sensitive in Canada.

Climate Change and Potential Sea-level Rise

Impacts

The northeast Pacific experiences dramatic variability in

climate driven, in part, by two large-scale modes of variability: the El Nino/Southern Oscillation (ENSO) and the Pacific Interdecadal Oscillation (PDO). The warm phase of the PDO is characterized by an enhanced wintertime Aleutian Low and

warmer water along the west coast of North America (Zhang et

al 1997). The cool phase is approximately opposite and transitions between phases are abrupt and occur approximately every 25 years (Gedalof and Smith, 2001). The extratropical

expression of ENSO is similar, with El Nino events resembling the warm phase of the PDO. Strong ENSO events recur every 3

to 7 years and rarely last longer than one year (Yarnal and

Diaz, 1986). Recent ENSO events (1982-83, 1997-98) produced enhanced storm waves and winds that caused intense

erosion along the Pacific coast from California to Washington

(Storlazzi et al, 2000, Dingler and Reiss, 2001, Allan and

Komar, 2002). To date, little is known about the impacts of

such modes of variability on the shores of Graham Island.

During El Nino 1997-98, Barrie and Conway, (2002) observed a regional sea-level rise of 0.4 m, and enhanced storm

waves and winds that caused 12 m of retreat. Though storms

were more intense this season due to the enhanced Aleutian

Low, it is uncertain as to whether they occurred more frequently. Because the effects of PDO and ENSO are additive (Gershunov and Barnett, 1998) and the PDO may have been in the cold phase (Hare and Mantua, 2000), it is possible that future events may have greater impact, especially if

superimposed on a rising sea level. Furthermore, some models

predict future scenarios with a semi-permanent ENSO-like

state (TlMMERMANN et al, 1999), which would entail more

frequent impacts. The dominant view on how coastlines will respond to sea

level rise has been framed by the Bruun, (1962) model, which suggests that shorelines will undergo landward retreat due to

wave erosion of the upper beach and consequent deposition of

sediment in the nearshore to a depth that is equal to the increase

in sea level (S). As such, shoreline retreat is simply a function of

beach slope and rise in sea level and is in the range of 50-100S

for most beaches (Scor Working Group 89, 1991). Davidson-arnott, (2005) challenges the assumptions of the

Bruun model and proposes a model that considers onshore sand

transfer to beach-dune systems with no net transfer to the

nearshore. By way of sand delivery to the backshore, this model

shows preservation and landward migration of foredunes as a

response to sea-level rise. This appears to be the case on East

Beach where, under sea-level rise of 1.6 mm a"1, periodic wave

scarping andnet shoreline retreat of 1 -3 m a"1, high onshore sand

transfer is able to rapidly replenish backshore storage, restore

and maintain actively accreting and migrating foredunes (Fig.

4b). Thus, 'erosion' in the broadest sense per the Bruun model

(i.e., coastline retreat and sand loss from the beach) does not

seem to be the current response of this coastline to ongoing sea

level rise. Rather, erosion is localized to bluffs with narrow

backshores while sand accretion in log jammed backshores and

migrating foredunes is widespread. What remains to be seen is

how potential increases in storm frequency and magnitude and

rates of sea-level rise would affect this response.

CONCLUSIONS

This paper documents the coastal geomorphology of one of

Canada's most dynamic coastlines: NE Graham Island, Queen Charlotte Islands (Haida Gwaii). This area has undergone

significant sea-level changes (-150 to +16 m) over the Holocene

and is currently rising at +1.6 mm a1. Relict shorelines and

progradational ridges indicate landscape response to former sea

levels. Given a macrotidal range, energetic wave climate and

ongoing erosion, the Geological Survey of Canada identifies

this as one of Canada's most sensitive coasts to future sea-level

rise.

Over 100 km of sedimentary beach systems are maintained

by strong littoral transport by waves and tidal currents.

Northward longshore transport on East Beach heads westward

around Rose Spit to North Beach, particularly during SE

storms. Retreat of 1-3 m a1 and tens of metres in extreme years

(e.g., 1997-98 El Nino) occur on East Beach, which provides sand to shore-attached bars that migrate northward and enhance

both onshore sand supply to beach-dune systems at low tide

stages, as well as beach erosion on their leading edge due to a

lack of available sand and focus of wave energy. Reflective

cuspate terraces on NW Rose Spit diminish westward on North

Beach as the system becomes more dissipative and sand

accretion predominates. This transition is distinct and may demarcate the extent of sand delivery from East Beach.

Eastward longshore transport toward Rose Spit is minimal.

Despite a moist climate and dense vegetation, aeolian activity is high and sand is moved onshore by frequent transporting

winds into foredunes and driftwood dunes that stabilize the

backshore. Foredunes migrate on the order of metres per year while large parabolic dunes (up to 1.2km long) move slower

Journal of Coastal Research, Special Issue 39, 2006

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Geomorphology and sea-level rise on one of Canada's most 'sensitive' coasts: Northeast Graham Island, British Columbia 225

(metres per decade). Dune alignment (336 ? 8) is skewed to the resultant drift vector (316?) perhaps due to reworking by summer winds. Dendrochronological geomorphic evidence

shows the impact of aeolian processes on trees including tilting,

flagging, burial, 1xunk scarring, exhumed adventitious roots, dwarf growth and ghost forests killed by dune migration.

Dendrochronological evidence is being used to provide insight into climate variability and landscape responses over the past several hundred years.

Contrary to the Bruun model (i.e., landward erosion of the

beach-dune system and nearshore deposition), this region is

responding to ongoing erosion and sea-level rise by retreating on East Beach whilst maintaining high onshore aeolian sand

transfer and accretion in driftwood jams and migrating foredunes that stabilize the shore against wave erosion. The

dissipative shores of North beach continue to prograde rapidly at0.3-0.6ma1.

The preliminary assessment provided in this paper sets the

geomorphic background for larger, interdisciplinary study of

the vulnerability of this coast to climate change and sea-level

rise impacts that threatens communities, cultural sites, resources, ecological reserves, and critical infrastructure in the

region.

ACKNOWLEDGEMENTS

This project is facilitated with financial support from NSERC and the Government of Canada's Climate Change Action Fund to IJW and contributes to Natural Resources

Canada's Climate Change program. Impacts and Adaptations Field assistance from K. Pearce, J. Axelson, J.Anderson andW.

Zantvoort is appreciated, as is logistical support from BC Parks

and the Council of the Haida Nation. Contributions by Drs.

Stephen Wolfe (GSC-Ottawa) and Dan J. Smith and Ze'ev

Gedalof (UVic Tree Ring Laboratory) are also recognized.

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