Geomorphic changes of North

Beach Barrier Island during a

mild year in the Chatham

Harbor/ North Beach Barrier

Island Estuary

By Nam Le

1

ABSTRACT

The dramatic changes on North Beach Barrier Island epitomizes the geologic instability

of the Chatham Harbor/North Beach Barrier Island Estuary. Previous studies conducted by

Graham Giese and other coastal geologists observed the barrier island over several years after

North Inlet’s formation; however, their research has not examined the dramatic seasonal changes

that took place. Amassed literature and collected data show North Beach Barrier Island

extending southward and widening. A combination of mechanisms including longshore drift,

tidal currents, and the tidal prism are potentially responsible for the occurring geomorphic

changes. As longshore drift transports sediment southward and tidal currents affect the exchange

of seawater in the Chatham Harbor/North Beach Barrier Island Estuary, the functionality and

significance of South Inlet become jeopardized.

INTRODUCTION

Cape Cod has been known for its dynamic environment where thunderous waves and

turbulent tides shape its coastlines every day. However, the southeastern elbow of the Cape is

most geologically significant in terms of coastal change. From tidal hydraulic changes and

storm-driven longshore drift, the Nauset Barrier Beach Island System formed two inlets over the

past several decades. Because of these two breaches, the barrier island known as North Beach

Barrier Island was created and has since been the center of geomorphic observation.

This study’s main focus is in the Chatham Harbor/ North Beach Barrier Island Estuary in

the Nauset Barrier Beach Island System (Figure 1). In this system, the different coastal

landforms originated from outwash deposits produced from glacial meltwaters of the retreating

Pleistocene continental ice sheet, and those glacial deposits subsequently eroded by wave action

and transported by waves, currents, and eolian processes (Giese, 1988). Over time, Nauset Beach

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broke into three different barrier islands from the formation of South Inlet in 1987 and North

Inlet in 2007: North Beach, North Beach Barrier Island, and South Beach (Aubrey and Robertson

1998).

Due to dynamic conditions where turbulent wave action and tide cycles presents,

Chatham, Massachusetts regularly undergoes coastline and barrier island changes. In 2009, many

real estate owners lost significant beachfront after a few moderate storms came through the coast

Figure 1. Google Earth Image of Chatham’s barrier islands in 2013. South Inlet separates North Beach

Island and South Beach and North Inlet separates North Beach and North Beach Barrier Island. (from

NASA Earth Observatory, 2013).

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(MacQuarrie, 2009). The Chatham Harbor/North Beach Barrier Island Estuary is a system driven

by tidal inlets, tidal-driven passages between sea and estuary (Giese et al., 2009). Referring to

Figure 1, South Inlet transfers water through Chatham Harbor into Pleasant Bay and Little

Pleasant Bay. Here, concepts like tidal prism and hydraulic efficiency are important because they

characterize the quality and quantity of seawater exchange between ocean and basin (Giese et al.,

2009). Tidal prism is the volume of water exchanged between ocean and basin, while hydraulic

efficiency measures the ocean-basin’s ability to exchange sea water (Giese et al., 2009).

North Beach Barrier Island continues to change, its southern tip extending due to

longshore drift and an ebb-dominated South Inlet (Pendleton and Fitzgerald, 2005). Because of

these processes, South Inlet displays significant shoaling, becoming less efficient for commercial

and recreational boat navigation. As shown in Figure 2, the South Inlet has gotten shallower and

narrower since 2009.

Because of this geologic phenomenon, thorough observation was conducted during the

summer of 2016 to investigate the geomorphic changes by season. A combination of photo

collections, tidal analysis, and geologic interpretation comprised this overall study. Final

observations taken in January of 2017 will show the geomorphic changes occurring on North

Beach Barrier Island, continuing the trend predicted decades ago by Graham Giese and other

experts (Giese et al., 2009).

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Figure 2. Aerial comparison of North Beach Barrier Island in 2009 (A) and 2015 (B). Emphasized by the

red circle in photo A and central feature in photo B, the southern tip of the island has extended

tremendously. Another observation is the distinct narrowing of Chatham Harbor that separates the barrier

island and the inland coast. The green circle in photo B illustrates the shoaling and narrowing of South Inlet.

(after Giese and Kennedy, 2015)

A B

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CHATHAM HARBOR/NORTH BEACH BARRIER ISLAND ESTUARY

South Inlet

History and Formation

On January 2nd 1987, Nauset Beach was breached, forming an inlet in the Nauset Barrier

Beach Island System. The formation occurred due to four factors: a nor’easter extratropical

storm, distorted tidal conditions and phase lags, shoreline trends, and bay bathymetry (Fitzgerald

and Pendleton, 2002). One day after the new inlet had formed, storm waves broke the opening to

100 m wide. By 1988, the inlet became 2.0 km wide due to an increase in Pleasant Bay and Little

Pleasant Bay’s tidal prism.

This over time has become the most important navigation passage to the Chatham

Harbor/North Beach Barrier Island Estuary (Giese et al., 2009). Commercial and fishing boats

were able to move from Pleasant Bay and the Fish Pier to the ocean and vice versa. As shown in

Figure 3, South Inlet becomes a very important navigation inlet because it is much easier than

maneuvering past South Beach Island. But ever since North Inlet formed in 2007, shoaling has

impeded traveling through the estuary.

North Inlet

History and Formation

Twenty years after South Inlet formed in 1987, Nauset Beach breached offshore of

Minister’s Point in North Chatham in 2007, forming North Inlet (Figure 4). It was on April 15th

2007 when a nor’easter storm hit Cape Cod, bringing in high winds and extreme tidal distortions

(Adams and Giese, 2010). Because of this breach, the Nauset Barrier Beach Island System is

now a multiple-inlet system (Giese et al., 2009).

Concerns were later raised about the breach because more sediment was brought into

Chatham Harbor and Pleasant Bay, ultimately impacting navigation through South Inlet from a

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decrease in water velocity (Giese, 2012). As seen in Figure 5, the 2007 break augmented the

longshore drift on the Atlantic side of North Beach Barrier Island, causing more sediment

deposition towards the southern tip/southeastern portion. Thus, ever since North Inlet formed,

navigation safety of South Inlet has been jeopardized by extreme shoaling (Adams and Giese,

2010).

Figure 3. Google Earth Imagery of Chatham’s barrier islands in 1987. This was taken nine months after

South Inlet formed. The red circle indicates South Inlet. The red arrows illustrate the newly formed

navigation passage for boats. (after NASA, Earth Observatory, 1987)

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Impacts on North Beach Barrier Island

The formation of both inlets created North Beach Barrier Island by splitting the barrier

island from North Beach and South Beach (Figure 4). Being the bigger and older of the two,

South Inlet has always been an important entrance to the Chatham Harbor/North Beach Estuary;

however, North Inlet’s development has distorted normal sediment transport, increased beach

erosion, and altered tide cycles (Adams and Giese, 2010).

Figure 4. Google Earth Image of Chatham’s barrier islands in 2007. This was taken four months after

North Inlet formed. The red circle illustrates North Inlet. Because there are two inlets, the barrier island

system is a multiple inlet system. (after NASA, Earth Observatory, 2007)

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9

Tidal Hydraulics

From observational studies conducted by Graham Giese and other scientists, North Beach

Barrier Island has grown larger. With longshore drift accompanying the movement of eroded

sediments, North Inlet has grown larger and South Inlet has started built up with sediments.

Consequently, areas around North Inlet have experienced increased wave activity due to greater

sediment-transporting waves, which tend to narrow inlets. Because of this trend, South Inlet will

become too shallow and too narrow to stay as a major navigational inlet to the estuary (Figure 6).

Figure 6. Photo sequence of North Beach Barrier Island (2006-2015). The red ovals illustrate the gradual

sediment build up along the inner shores of North Beach Barrier Island as well as the narrowing of South

Inlet. The hooks that started to form in 2012 are caused by the flood-dominated system, where the

ingoing tide is significantly stronger than the outgoing tide in the estuary. (after Giese and Kennedy,

2015)

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North Beach Barrier Island is seen as a formation in an inlet/estuary system, where the

exchange of sea water between ocean and lagoon basin occurs. Prior to 2007, South Inlet

transferred sea water through a channel, characterized by Chatham Harbor, into a semi-

permanent basin, represented by Pleasant Bay and Little Pleasant Bay (Figure 7). Here, the

system’s tidal prism was primarily determined by the tides passing through the inlet and waves

transporting sediment along the outer shores of North Beach Barrier Island (Giese et al., 2009).

Figure 7. Aerial image of North Beach Barrier Island in 2009. Pleasant Bay

and Little Pleasant Bay are the semi-permanent basins. Chatham Harbor is

the channel connecting basin to ocean. (after Giese and Kennedy, 2015)

BASIN

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After North Inlet formed, prior tidal dynamics were altered. North Inlet brought in more

waves than usual, which in turn transported more sediment into Chatham harbor (Adams and

Giese, 2010). Because North Inlet is flood-dominated rather than ebb-dominated, more sediment

came into the estuary than actually came out of it (Fitzgerald and Pendleton, 2002) (Figure 6).

Subsequently, heavy shoaling occurred in South Inlet and sediment deposited along the inner

shores of North Beach Barrier Island, ultimately narrowing the southern entrance to the estuary.

With more sediment deposition in the harbor, water velocity and hydraulic efficiency

have decreased (Giese et al., 2009). In return, with less ability for sea water exchange between

ocean and basin, sediment movement continues to be halted. Over time, as seen in Figure 8,

sediment built up on the inner shores of North Beach Barrier Island, extending the southern tip

and narrowing the harbor and inlet. Thus, the current geomorphic growth seen on the island was

primarily initiated by the formation of both North and South Inlets.

A

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METHODS

Data Collection

Location and resources used

Photographs of North Beach Barrier Island were taken from across Chatham Harbor, in

the overlook parking lot in front of Chatham Lighthouse. The overlook parking lot was chosen as

the stationary position because it was the most elevated and accessible location to enable photos

to thoroughly capture the southern tip of North Beach Barrier Island and South Inlet. One spot on

the left end and one spot on the right end of the overlook were chosen for the two reference data-

collecting positions (Figure 9).

Figure 8. Photo comparison of North Beach Barrier Island in 2007(A) and in 2016 (B). Red circles

indicate the southward growth of the barrier island over time. Heavy sediment deposition can be seen in the

2016 photograph, with the bottom hook thickly developed. (after NASA, Earth Observatory, 2007 and

2016)

B

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An 8-megapixel digital camera in the iPhone 5S was used to collect the data points. A

combined use of panorama and normal photo frame documented the photo-sequence compilation

of the study site. The low-tide predictions publicized by NOAA/COPS/CO-OPS-ODIN MAP

were closely followed to schedule when photographs were to be taken. During photograph days,

close attention to weather forecast was also necessary to characterize the atmosphere and predict

photo quality.

A

B

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C

Figure 9. A). Left spot in the overlook parking lot. B). Right spot in the overlook parking lot. C). Aerial

image of North Beach Barrier Island in 2015. Labels (left as A and right as B) and arrows illustrate what

each spot captured. (Figure 9C. is after Giese and Kennedy, 2015).

A

B

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Work Plan

A photo sequence was compiled over a six week study that started on June 28th and ended

on August 10th. In each week, photographs were taken over two days, each day collecting four

photos during predicted low tide. The two days differed for some weeks due to storms and

unavailability for data collection. Taking photos during low tide truly encapsulated the changes,

with the retreating tide substantially exposing North Beach Barrier Island. This compilation

collected the majority of the required data points, documenting the geomorphic changes on North

Beach Barrier Island over a mild summer in Chatham. The final photographs were taken on

January 10th of 2017 to briefly illustrate geomorphic changes over the fall and winter.

The work schedule included recording lowest tide times and their respective water levels:

Because both the actual times and tide levels were documented, any tide distortions and

anomalies were displayed. In addition, sharp changes in water levels can justify unusual changes

in the photos.

Week Date(s) and Times Low Tide Levels

1 06/28/2016: 1:48pm

06/29/2016: 2:42pm

06/28/2016: 0.682 ft

06/29/2016: 0.823 ft

2 07/12/2016: 1:42pm

07/13/2016: 2:18pm

07/12/2016: 1.02 ft

07/13/2016: 1.11 ft

3 07/21/2016: 8:20pm

07/22/2016: 9:24pm

07/21/2016: 1.09 ft

07/22/2016: 1.11 ft

4 07/26/2016: 12:30pm

07/27/2016: 1:24pm

07/26/2016: 1.11 ft

07/27/2016: 1.16 ft

5 08/02/2016: 7:12pm

08/03/2016: 8:12pm

08/02/2016: 1.10 ft

08/03/2016: 1.06 ft (photo not taken)

6 08/09/2016: 12:06pm

08/10/2016: 12:42pm

08/09/2016: 1.12 ft

08/10/2016: 1.09 ft

Final 01/10/2017: 5:48pm 01/10/2017: 1.21 ft

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RESULTS

Photo Sequence

Week 2

Week 4

Week 1

Week 3

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Interpretation

Visible changes

Although Cape Cod had a very mild summer in 2016, its dynamic environment still

undergoes coastal change. But because there were no big nor’easter storms since last spring,

Week 5

Week 6

Week Final

Figure 10. Overall photo sequence of the southern tip of North Beach Barrier Island (June 28th-August

10th, January 10th). Due to the different low tide times, lighting in the photos are not consistent. The red

circles indicate a small break in the lower hooks of the barrier island. The small break can be seen filling up

and then breaking down over the course of six weeks. The red ovals illustrate the growth and development

of the southern tip, with a potential new hook forming. This also implies the narrowing of South Inlet.

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North Beach Barrier Island has yet to experience dramatic damage or changes. Nevertheless,

Figure 10 illustrates the continuous changes the barrier island goes through over a season. After

gathering the photographs taken this summer and in January, the only parts of the island

exhibiting visible changes were the bottom two hooks and the miniature pond at the southern tip

(See Figure 11). Ergo, the photo sequence in Figure 10 focused on that particular region of the

island.

The bottom hook over time has heavily deposited with sediment, forming a small

ephemeral pond that floods during high tide. In Weeks 1, 2, and 5, the same sliver in the inner

shore was breached, opening the pond to Chatham Harbor (See Figures 10 and 11). However,

when comparing Week 5 to Weeks 6 and Final, the breach is more enclosed and the pond gets

visibly smaller. In addition, the small opening shifted north (in the photograph, to the left), which

implies the influx of sediment deposition coming from South Inlet. This gradual sediment build

up can be seen when comparing Weeks 1 and 2 to Weeks 6 and Final.

As predicted and modeled by Graham Giese and other experts, North Beach Barrier

Island’s southward growth is causing South Inlet to migrate (Adams and Giese, 2010). As

captured by the photo sequence, the southern tip in Week 6 compared to Week Final is visibly

different. This illustrates that the five months in between August 10th and January 10th have

caused significant sediment build up. The shape of the tip in Week 6 is much rounder and well-

deposited, while Week Final exhibits longer shape with more recent deposition. Due to the

elongation and growth of the North Beach Barrier Island’s southern tip, South Inlet passage

narrows and migrates southward (See Figure 11).

Causing mechanisms

The seasonal changes occurring at the southern tip of North Beach Barrier Island are a

result of intense longshore drift, tidal currents, and decreased hydraulic efficiency in a multiple-

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inlet system. The inner and outer shores of the barrier island since 2015 have significantly

widened and extended (Figures 10 and 11). The buildup on the outer shores are caused by

longshore drift transporting sediment from the North Inlet’s ebb delta southward, depositing

along the outer shores of the barrier island from angled swash and backwash (Figure 12).

Figure 11. Aerial comparison of North Beach Barrier

Island in 2015 and 2016. The red circle indicates the

substantial deposition of the bottom hook, ultimately

forming the small pond seen in the 2016 photo. The little

green circle in 2016 photo displays the sliver breach in the

pond. It also reflects what the photo sequence in Figure 10

captured. (2015 is after Giese and Kennedy, 2015) (2016 is

after Ted Keon, Town of Chatham, 2016)

2015 2016

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The buildup on the inner shores are due to a decrease in the system’s ability to exchange

seawater from Pleasant Bay/Little Pleasant Bay to the ocean and vice versa. As seen in Figure

12, North Inlet is more flood-dominated than ebb-dominated because of the large flood delta

(shoaling) in the basin and small ebb delta right at the mouth. Due to the shoaling around North

Inlet, hydraulic efficiency is impeded, causing water to move southward towards Chatham

Harbor. The southward-moving tidal currents transport sediments eroded from the barrier’s

upper inner shore through Chatham Harbor, depositing them along the inner shore as the current

moves towards South Inlet.

This can also explain the formation of the hooks on the southern tip of the island (Figures

10 and 11). The repetition of the hooks imply some type of positive and negative feedback

mechanism because the geologic shape is created by a dual-directional process. It is plausible

that the tidal currents depositing sediment along the inner shore and the longshore drift moving

transporting sand southward are both responsible for the widening and extension of North Beach

Barrier Island. Deposition on the inner shore is augmented by the amount of sediment brought in

by the tidal currents from Pleasant Bay and North Inlet. Sediment transport capacity is heavily

determined by storms and their movement direction. For that, the frequent nor’easter storms on

Cape Cod strike the barrier island system from the northeast, causing the barrier islands to

migrate southwest.

Referring back to Figure 10, the sandbar enclosing the small pond was significantly

larger in Week 5 than in Weeks 1 and 2. The potential cause for this change was a small storm

that occurred two days prior to the photo being taken. A combination of wind gusts, intensified

tidal currents, and increased water levels initiated enough force to breach the inner shores of

North Beach Barrier Island (Maio et al., 2014). Interestingly enough, the sandbar in Weeks 6 and

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Figure 12. Zoomed in version of North Beach Barrier Island in 2016 from Figure 11. Green arrows

indicate longshore drift along the outer shore of North Beach Barrier Island. Blue arrows indicate the

direction of the incoming tide current when passing through North and South Inlets. Orange arrows

indicate the direction of the outgoing tide current. The blue arrows are bigger than the orange arrows in

North Inlet because it’s more flood-dominated, while South Inlet is more ebb-dominated. (after Ted Keon,

Town of Chatham, 2016)

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Final significantly closed up, returning to normative conditions where continuously eroded

sediment is transported from the upper inner shore down to the lower inner shore and southern

tip of North Beach Barrier Island (See Figure 10).

In terms of the southern growth seen in Week Final, many processes in combination can

be responsible. Because the time difference between Week 6 and Week Final was five months,

North Beach Barrier Island went through over a season of storms, gusting winds, and tidal

waves. Over the month of December and beginning of January, Chatham experienced several

small nor’easter storms that directly affected the estuary. The growth and new formation of

another hook is in progress because of storm-driven longshore drift along the outer shores,

wrapping around the southern tip and depositing eroded sediment in South Inlet’s ebb-delta (See

Figure 12). Because North Inlet is flood-dominated, South Inlet becomes ebb-dominated,

shoaling more intensely around the entrance of the estuary. And when storms went through the

system, regardless of how big they were, rigorous shoaling led to heavy sediment buildup. Thus,

months of scattered storms exacerbated the continuous trend present on North Beach Barrier

Island.

These changes bring into question the potential degree of damage and change during a

more intense season than 2016. As North Beach Barrier Island continues to grow, South Inlet

continues to migrate southward, becoming narrower and shallower for navigation. As bigger

storms come in, tidal currents transport more and more sediment to the southern tip of North

Beach Barrier Island, ultimately augmenting the size of South Inlet’s ebb-delta. In addition, inlet

migration and narrowing causes further tidal distortion when predicting high and low tide times

(Giese and Kennedy, 2015).

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SUMMARY

Aerial imagery and photograph observation have provided coastal geologists visual

understanding of North Beach Barrier Island’s continuous changes. Ever since North Inlet

formed in 2007, the Chatham Harbor/ North Beach Barrier Island Estuary have experienced

significant geomorphic changes. These changes include the extension and widening of the

southern tip, primarily caused by longshore drift, tidal currents, and hydraulic inefficiency.

However, geologists have predominantly observed the barrier island year by year, not

considering potential dramatic changes over one season.

After examining North Beach Barrier Island over a six-week summer study and a final

January observation, visible changes mainly centered on the southern tip. The buildup on the

inner shore, forming sand hooks and ephemeral ponds, is a concerning progression initiated by

strong tidal currents transporting eroded sediment from upper inner shore down towards the

lower inner shore. This is also due to North Inlet’s flood-delta decreasing the exchange of water

from Pleasant Bay back to the ocean, forcing water flow down Chatham Harbor and out of South

Inlet’s ebb-delta. And over time, the heavy shoaling in the ebb-delta have built up along the

bottom shores of North Beach Barrier Island, continuously narrowing and shallowing South

Inlet.

This will become a center of future coastal study as dramatic changes will continue to

take place over seasons, months, perhaps days. Despite the mild conditions of summer 2016,

visible changes continue to reinforce the trends predicted by Graham Giese and other experts.

Thus, the seasonal geomorphic study of North Beach Barrier Island illustrated the dynamic

environment of Cape Cod, proving the geologic volatility of the Chatham Harbor/North Beach

Barrier Island Estuary.

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REFERENCES CITED

Adams, M. and G. S., Giese, 2010: Monitoring a Nauset Beach Breach and Inlet Formation,

2007-2008 on Cape Cod, Chatham, Massachusetts: U.S. Department of the Interior,

Natural Resources Report NPS/NER/NRR 2010/144, 18 pp.

Aubrey, D. G. and W. V. Robertson, 1998: Beach Changes and Management Options for Nauset

Barrier Beach and Orleans Town Beach, Cape Cod, MA: Report to the Town of Orleans.

Technical Report, Woods Hole Oceanog. Inst. Tech. Rept., WHOI-98-10.

Fitzgerald, D. M. and E. Pendleton, 2002: Inlet Formation and Evolution of the Sediment

Bypassing System: New Inlet, Cape Cod, Massachusetts. Journal of Coastal Research,

Special Issue no. 36, p. 290-299.

Giese, G. S., 1988: Cyclical behavior of the tidal inlet at Nauset Beach, Chatham, Massachusetts.

Hydrodynamics and Sediment Dynamics of Tidal Inlets, p. 269-283.

Giese, G. S., 2012: Analysis of tidal data from Meetinghouse Pond, Chatham Fish Pier and

Boston: with application to management. The Pleasant Bay Resource Management

Alliance, 18 pp.

Giese, G. S. and C. G. Kennedy, 2015: Analysis of tidal data from Meetinghouse Pond, Chatham

Fish Pier and Boston: January 2012-June 2015. The Pleasant Bay Resource Management

Alliance, 11 pp.

Giese, G. S., S. T. Mague, and S. S. Rogers, 2009: A Geomorphological Analysis of Nauset

Beach/ Pleasant Bay/ Chatham Harbor For the Purpose of Estimating Future

Configurations and Conditions. The Pleasant Bay Resource Management Alliance, 32 pp.

MacQuarrie, B., 2009: In Chatham, an austere utopia yields to a relentless tide, at

http://archive.boston.com/news/local/massachusetts/articles/2009/06/25/in_chatham_an_

austere_utopia_yields_to_a_relentless_tide/ (accessed 20 January, 2017).

Maio, C. V., A. M. Gontz, R. M. Sullivan, S. M. Madsen, C. R. Weidman, and J. P. Donnelly,

2014: Subsurface Evidence of Storm-Driven Breaching along a Transgressing Barrier

System, Cape Cod, U.S.A. Journal of Coastal Research, v.32, Issue 2, p. 264-279.

Pendleton, E. and D. M. Fitzgerald, 2005: Comparison of the hydrodynamic character of three

tidal inlet systems. High Resolution Morphodynamics and Sedimentary Evolution of

Estuaries, v. 8, p. 83-100.