Recent shoreline erosion rates along Black River Bay, Jamaica: Erosion and recovery after Hurricane Ivan in 2004

Karen Zelzer Missouri State University, Dr. Robert Pavlowsky Missouri State University

AbstractRising sea level is threatening coastal areas, particularly those in the Caribbean which rely heavily on tourism and marine resources to support its economy. The purpose of this study is to analyze shoreline position along the south coast of Jamaica to determine the locations and rates of coastal change. IKONOS satellite imagery sets for 2003, 2007 and 2012 were used to monitor land use and shoreline changes along Black River Bay, including Galleon Beach Fish Sanctuary, in St. Elizabeth, Jamaica. In particular, the effect of Hurricane Ivan in 2004 on shoreline changes was evaluated. Erosion rates were significantly higher during 2003-2007, the period including Hurricane Ivan (-0.90 m/yr), with reduced erosion rates and some recovery by deposition observed during the post-hurricane period (0.21 m/yr). Little to no changes were observed along limestone headlands and mangrove swamps with highest rates on sandy beaches lacking offshore coral reef protection and exposed to storm waves. Overall, shoreline recession averaged -0.31 m/yr during the study period with a peak erosion rate of -1.13 m/yr at Parrottee Point. Within the next 10 to 30 years, an expected 9 km of mangrove swamps and over 100 buildings are at risk due to sea level rise and shoreline erosion.

Introduction

Study Area Black River Bay (Figure 3) is one of Jamaica’s oldest towns and has a population of over 5,000. The bay is located along the Southwest coast of Jamaica with a mix of sandy beaches, mangroves and limestone headlands (Figure 4 & 5). Most of the land surrounding the bay is ≤ 3 m elevation and composed of alluvium and/or marine deposits. Urban development is located around the mouth of the Black River and some property damage due to SLR has already been observed (Figure 6). The main beaches are located at Malcolm Bay, Black River East, Parrottee Pond and at Parrottee Point. 55% of the shoreline has some level of reef protection and 51% of the shoreline is composed of mangrove forests located within 100 m from the shore.

Objectives(1) Geospatially determine patterns of shoreline erosion and

accretion rates for 30 km of shoreline over the past 10 years including the effects of Hurricane Ivan in 2004

(2) Determine the relationships between erosion patterns and shoreline orientation, geology, vegetation, and beach composition

(3) Identify coastal areas and related land uses at risk due to future shoreline erosion.

Methods(1) Acquired QuickBird and GeoEye satellite imagery from Digital Globe for the years

2003, 2007 and 2012. Spatial resolution ranged from 0.6 m to 2.4 m.(2) Images mosaicked, rectified using GCPs and projected to UT _WGS 84, zone 18N.(3) Digitized vegetation and waterline for each year at a 1:1,250 scale and created transects spaced at 50 m intervals. (4) Measured change between each digitized vegetation and waterline. (5) Determined rates of change for the storm period (2003-2007), post-storm period (2007-2012) and overall (2003-2012). (6) Use rates and SLR rate to predict land loss along Black River Bay for the next 10 to 30

years.

The sandy beaches of Jamaica are important in supporting the county’s economy through tourism, coastal resources, and marine resources (Cambers, 2009). Sandy beaches are being threatened by storm events, sea level rise (SLR) and shoreline erosion. Shoreline changes are generally related to: natural processes associated with long-tern geomorphic evolution; hurricanes and other wind-producing systems; human modifications of the shoreline and sediment budget; and sea-level change related to climate variability (Zhang et al., 2004)

Hurricane Ivan in 2004 was a category 5 hurricane that occurred 32 km from the south coast of Jamaica (Figure 1). Winds reached up to 180 km/hr producing swells between 2 and 8 meters in height (Economic Commissions for Latin America and the Caribbean, 2004).

SLR as well as human interaction with the coast influence the rate at which shorelines are changing. Sea level has gradually increased since the last glacial maximum (Robinson and Hendry, 2012); however rates have accelerated within the last 100 years due to climate change. Global mean sea level (GMSL) is currently at 3 mm/yr (National Geographic, 2014; IPCC, 2014). The IPCC projects SLR to increase to 0.18 m to 0.59 m by the year 2100 (Figure 2).

Figure 1. Hurricane Ivan in 2004. This Category 5 storm traveled within 32 km of the Southwest coast of Jamaica and produced 180 km/hr winds (NOAA, 2004). Figure 2. IPCC projections for global SLR. Rates are

expected to increase to 0.18 m/yr to 0.59 m/yr by 2100 (IPCC, 2013).

Table 1. Rates of shoreline change along Black River Bay.

Conclusions(1) Overall rate of erosion of -0.31 m/yr observed for the either Black River Bay. Increased erosion rates observed during the storm period (-0.90 m/yr) and recovery observed during the post-storm period (+0.21 m/yr). (2) Hot spots experience higher erosion rates and are expected to experience greater shoreline loss over the next 10 to 30 years which put mangrove swamps and urban structures at risk. (3) Cold spots experienced little to no change since these areas are mainly resistant shorelines with little to no sandy beaches present. CS 2 is the main area where accretion is observed. Cold spots are expected to remain stable or accrete over the next 10 to 30 years.

Figure 3. Black River Bay. The bay has a 30 km shoreline with the main sandy beaches located at Malcolm Bay, south of the Black River, and Parrottee Point.

ResultsOverall rate of -0.31 m/yr over the 9 year period with increased rates along Malcolm Bay, Parrottee Pond and Parrottee Point and decreased rates along Hunts and Hodges Bay. Accretion was observed in zone 6, south of the Black River(Table 1 & 2). For this study, negative values represent erosion and positive values represent accretion.

Figure 4. Sandy beach along Parrottee Point

• Erosion Rates were highest during the storm period (2003-07) and an overall rate of -0.90 m/yr was observed.

• Recovery was observed in most areas during the post-storm period (2007-12) at an average rate of 0.21 m/yr.

• Areas with the highest rates of erosion, or hot spots, were observed downshore from Fonthill (HS 1), at Malcolm Bay (HS2), Parrottee Bay (HS 3) and Parrottee Point (HS 4).

• Areas that experienced little to no change or accreted over the study period are considered cold spots. These were observed at Hunts and Hodges Bay (CS 1), Black River East (CS 2) and Starve Gut Bay (CS 3).

LabelRate of Change

(m/yr)

HS 1 -1.4

HS 2 -1.1

HS 3 -1.7

HS -4.7

CS 1 0

CS 2 +1.8

CS 3 0

Table 2. Rates at hot spots and cold spots.

Figure 7. Vegetation changes from 2003 to 2012. (a) The storm period (2003-07) experienced overall erosion. (b) The post-storm period (2007-12) experienced mainly recovery. (c) the net vegetation change from 2003-2012 shows the overall erosion that occurred along Black River Bay.

Figure 8. Examples of hot spots and cold spots. HS 4 is located at Parrottee point and experienced an average loss of -4.7 m/yr with a maximum change of -77 m.

• Parrottee Point (HS 4) is a sand spit (Figure 8). This explains the high rate of change that occurred at this location.

• Other areas where hot spots are observed are where sandy shorelines are located. Cold spots are mainly resistant shorelines with little to no sandy beaches present. CS 3 (Figure 9) is where the most accretion occurs likely due to the calm environment and discharge from the Black River.

Figure 10. Predicted shoreline loss. (a) Malcolm Bay (b) Buildings at risk located at Parrottee Pond.

(b)(a)Zone Estimated Annual Rate

(m/yr)Change in 10 years (m)

Change in 30

years (m)

Whole Bay -0.31 -6 -181 -0.42 -8 -222 -0.37 -7 -203 -0.03 -3 -94 -0.22 -5 165 -0.05 -4 -106 +0.47 +8 +237 -0.25 -6 -178 -0.67 -10 -299 -1.13 -14 -43

10 -0.44 -7 -22HS 1 -1.4 -17 -51HS 2 -1.1 -14 -42HS 3 -1.7 -20 -60HS 4 -4.7 -50 -150CS 1 0 -3 -9CS 2 +1.8 +21 +63CS 3 0 -3 -9

Table 3. Predicted shoreline loss.

CS 2 CS 3

Figure 9. CS 2 is located at Hunts bay and Hodges Bay where little sand is found and most of the shoreline is mangrove swamps.

Figure 5. Mangroves along Hunts Bay Figure 6. Property damage due to SLR.

• Predicted shoreline loss (Table 4) is expected to be the highest in hot spot areas and lowest in cold spot areas. Malcolm Bay (Figure 10a) could experience a loss of -14 m in the next 10 years and -42 m in the next 30 years. Buildings along Black River Bay are at risk (Figure 10b).

Cambers, G. (2009). Caribbean beach changes and climate change adaptation. Aquatic Ecosystem Health & Management, 12(2), 168-176. doi:10.1080/14634980902907987Cubasch, U., D. Wuebbles, D. Chen, M.C. Facchini, D. Frame, N. Mahowald, and J.-G. Winther, 2013: Introduction. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USAZhang, K., Douglas, B C., & Leatherman, S. P. (2004). Global warming and coastal erosion. Climatic Change, 64, 41-58.

References:

Geographic Zone Transects 2003-07 Rates

(m/yr)2007-12 Rates

(m/yr)2003-2012 Rates

(m/yr)Recovery Rates

(m/yr) Numb Name (n) Mean Min Max Mean Min Max Mean Min Max Mean

1 Fonthill 87 -0.72 -0.34 0.30 -0.16 -2.70 0.0 -0.42 -2.90 0.29 0.562 Malcolm Bay 72 -0.66 -1.90 0.01 -0.12 -0.70 0.50 -0.37 -1.90 0.01 0.543 Hunt Bay 33 -0.10 -1.00 1.13 0.03 0.0 0.40 -0.03 -1.04 1.13 0.134 Hodgens Bay 40 -0.55 -1.50 0.0 0.08 -0.25 0.80 -0.22 -1.30 0.22 0.63

5 Black River Bay West 39 -0.44 -0.79 0.0 0.29 0.0 1.75 -0.05 -0.80 1.75 0.736 Black River Bay East 88 -0.20 -1.70 1.23 1.06 -0.30 3.20 0.47 -1.70 3.15 0.807 Parrottee Pond 170 -0.75 -1.50 0.56 0.20 -0.60 1.00 -0.25 -1.70 0.97 0.958 Parrottee Bay 38 -1.31 -1.90 0.0 -0.10 -1.40 1.20 -0.67 -2.92 1.24 1.219 Parrottee Point 54 -2.88 -7.90 1.20 0.44 -1.20 2.40 -1.13 -8.09 2.03 3.32

10 Starve Gut Bay 78 -1.38 -2.70 0.0 0.40 -0.30 1.04 -0.44 -2.98 0.28 1.78 Annual Rate (m/yr) -0.90 0.21 -0.31 1.07