HISTORICAL SHORELINE CHANGE AND SEA LEVEL RISE IMPACT ASSESSMENTS IN TOYAMA PREFECTURE

抄録

 The Toyama coastal regions have experienced a significant impact from severe erosion. This degradation can be attributed to a combination of factors such as insufficient quantity of sediment supply from the Kurobe dam to the coastal area. In this study, we used Digital Shoreline Analysis System (DSAS) to identify historical shoreline changes with notable change rates. We calculated shoreline change rates from 1985-2024 by leveraging historical shoreline positions derived from google earth images. Shoreline recession was observed on many beaches, especially Nyuzen and Asahi beaches experienced significant erosion when compared to other beaches. However, from 2014 to 2024 shorelines have been regenerating by a gradual increase in sediment deposition along all beaches except Iwasehama beach. Furthermore, we employed Bruun Rule method to project future shoreline retreat projection based on Toyama beach characteristics, sediment size, historical wave characteristics and Regional Mean Sea Level Rise (RMSLR) projections. This study identified that under different scenarios of sea level rise, certain beaches in Toyama Prefecture could experience significant loss rates. Iwasehama beach could lose 14% of its beach under SSP1-2.6 scenario, while near future the Amaharashi beach in 2070 is 93% under SSP5-8.5, and for Himi beach in 2100 it is 46% under SSP2-4.5. The results show the beaches located at Himi and Amaharashi beaches are at risk of disappearing sooner than other beaches. These findings show that coastal areas are always changing, and it is important to keep monitoring them and adjusting management strategies accordingly. This research findings will help stakeholders identify the most effective measures to combat shoreline retreat caused by sea level rise.