Sea Level Change and Erosion
While many island communities are worried about sea level rise, post-glacial (isostatic) rebound will outpace the rising waters at least through the end of the century, depending on how quickly the ocean rises. While Hoonah and the rest of the northern panhandle will gain land in the coming years, the reshaping of the shorelines will still affect where tribal members can harvest shellfish and intertidal vegetation and impact salmon runs in important streams. Erosion, while primarily a focus in the western part of the state, is likely to increase over the next decade as severe weather events become more frequent.
Figure 3 As sea level rise and post-glacial rebound battle it out, the southern half of the panhandle is likely to look land while the northern half (including Hoonah) is likely to keep gaining land under all emissions models. Figure from the Pacific Northwest Research Station/ Johnson and Kruger.
POST-GLACIAL REBOUND IS EXPECTED TO DROP THE SEA LEVEL BETWEEN 4 AND 43 INCHES BY THE END OF THE CENTURY DEPENDING ON HOW FAST HUMANS CURB GREENHOUSE GAS EMISSIONS.
While sea level rise will therefore be less of an issue than for many other islands, sea level and rebound will still dramatically reshape Southeast Alaska’s coastlines. Clam and eelgrass beds, currently staples of the shallow intertidal region, are likely to face significant shifts over the next 80 years due to this change. Regions that are currently intertidal are likely to become meadows and no longer support seagrass, shellfish, normal fish, or crabs, while newly exposed regions are likely to fill that gap. Since eelgrass stabilizes sediments, areas that lose their grasses are more likely to face difficulties with erosion and loss of sediments. While the areas that support eelgrasses and shellfish are likely to change, the overall area is predicted to stay the same.
SEA LEVEL CHANGES ARE LIKELY TO BE WORSENED BY INCREASING EROSION, DRIVEN BY SEVERE WEATHER EVENTS. The US Army Corps of Engineers has been monitoring erosion near the Mendenhall River in Juneau and is attributed to heavy rainfall events and melting of the Mendenhall Glacier. Given that heavy rainfalls and extreme weather are likely to increase in the future, it is likely that shoreline erosion will become more of an issue in Hoonah in the next few decades. Erosion can block salmon streams, damage intertidal vegetation and shellfish beds, and increase the amount of sediment in the water which negatively impacts fish.
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