Presentation Information
[O12-P56]Comparison of Color and Composition of River Sand Flowing into the Chirihama Coast
*Yuria Minamidani1, Yuuna Sakaguchi1, Teruki Matsuo1, Sawa Okabe1 (1. Ishikawa Prefectural Nanao High School SSC)
Keywords:
Chirihama Coast,Coastal erosion,Sand supply,Environmental analysis,Elemental analysis,Cluster analysis
[Motivation and Objectives]
The Chirihama Coast in Ishikawa Prefecture is famous for the "Chirihama Nagisa Driveway," the only beach in Japan where motor vehicles can be driven. In recent years, however, the narrowing of the beach due to coastal erosion has become a serious issue. One of the primary causes is considered to be a "shortage of sand supply." While many studies have focused on the sand supply from the Tedori River, the largest source in the region, there has been little research on the contribution of smaller rivers that flow directly into the Chirihama Coast. This study aims to clarify the contribution of these local rivers to the sand supply by comparing the color (ratio of colored to colorless rock fragments) and elemental composition of sand collected from multiple rivers and coastal points.
[Methods and Data Analysis]
The research was conducted in three stages.
In [Survey 1], sand samples were collected from the mouths of five rivers (Hakui, Aimi, Hodatsu, Maeda, and Omika) and compared with samples from three points along the Chirihama Coast and the mouth of the Tedori River. We used microscopic photography to calculate the ratio of colored to colorless rock fragments.
In [Survey 2], to trace the origin of the sand, we collected samples from the upstream, midstream, and downstream sections of the Hakui, Hodatsu, and Omika river systems and analyzed the transition of rock fragment ratios.
In [Survey 3], we conducted elemental analysis using an X-ray fluorescence (XRF) spectrometer to accurately identify the source of the sand. Cluster analysis was applied to the elemental data to evaluate the similarities between the river mouth samples and the Tedori River samples.
[Results]
Survey 1 revealed that the Tedori River has a significantly higher ratio of colored rock fragments than the other rivers. Interestingly, the ratios at the Chirihama coastal sites did not match the Tedori River, suggesting an influence from local rivers.
Survey 2 showed that in the Hakui and Omika Rivers, the colored rock fragment ratio increased at the river mouths compared to upstream, approaching the values of the Tedori River. In contrast, the Hodatsu River showed little change from upstream to downstream, indicating a potential independent supply of sand.
Survey 3's cluster analysis showed that the elemental compositions of the river mouths were generally distinct from the Tedori River. However, the colorless rock fragments at the Hakui River mouth showed high similarity to those of the Tedori River. Furthermore, the mismatch between the upstream and downstream clusters of the Hakui River suggests that external sand is being deposited at its mouth.
[Conclusion and Future Challenges]
Our results suggest that the Hodatsu and Omika Rivers likely contribute to the sand supply of the Chirihama Coast due to the consistency of their sand composition from upstream to the river mouth. Conversely, the Hakui River's contribution appears low, as its mouth is dominated by external sand, likely transported from the Tedori River via ocean currents.
Future research should involve continuous monitoring that accounts for seasonal sand movement and wave-induced littoral drift. By using the "sand fingerprints" (elemental compositions) identified in this study, we aim to quantitatively evaluate the contribution of each river to the overall sediment distribution of Chirihama, providing a scientific basis for effective beach nourishment and erosion control measures.
The Chirihama Coast in Ishikawa Prefecture is famous for the "Chirihama Nagisa Driveway," the only beach in Japan where motor vehicles can be driven. In recent years, however, the narrowing of the beach due to coastal erosion has become a serious issue. One of the primary causes is considered to be a "shortage of sand supply." While many studies have focused on the sand supply from the Tedori River, the largest source in the region, there has been little research on the contribution of smaller rivers that flow directly into the Chirihama Coast. This study aims to clarify the contribution of these local rivers to the sand supply by comparing the color (ratio of colored to colorless rock fragments) and elemental composition of sand collected from multiple rivers and coastal points.
[Methods and Data Analysis]
The research was conducted in three stages.
In [Survey 1], sand samples were collected from the mouths of five rivers (Hakui, Aimi, Hodatsu, Maeda, and Omika) and compared with samples from three points along the Chirihama Coast and the mouth of the Tedori River. We used microscopic photography to calculate the ratio of colored to colorless rock fragments.
In [Survey 2], to trace the origin of the sand, we collected samples from the upstream, midstream, and downstream sections of the Hakui, Hodatsu, and Omika river systems and analyzed the transition of rock fragment ratios.
In [Survey 3], we conducted elemental analysis using an X-ray fluorescence (XRF) spectrometer to accurately identify the source of the sand. Cluster analysis was applied to the elemental data to evaluate the similarities between the river mouth samples and the Tedori River samples.
[Results]
Survey 1 revealed that the Tedori River has a significantly higher ratio of colored rock fragments than the other rivers. Interestingly, the ratios at the Chirihama coastal sites did not match the Tedori River, suggesting an influence from local rivers.
Survey 2 showed that in the Hakui and Omika Rivers, the colored rock fragment ratio increased at the river mouths compared to upstream, approaching the values of the Tedori River. In contrast, the Hodatsu River showed little change from upstream to downstream, indicating a potential independent supply of sand.
Survey 3's cluster analysis showed that the elemental compositions of the river mouths were generally distinct from the Tedori River. However, the colorless rock fragments at the Hakui River mouth showed high similarity to those of the Tedori River. Furthermore, the mismatch between the upstream and downstream clusters of the Hakui River suggests that external sand is being deposited at its mouth.
[Conclusion and Future Challenges]
Our results suggest that the Hodatsu and Omika Rivers likely contribute to the sand supply of the Chirihama Coast due to the consistency of their sand composition from upstream to the river mouth. Conversely, the Hakui River's contribution appears low, as its mouth is dominated by external sand, likely transported from the Tedori River via ocean currents.
Future research should involve continuous monitoring that accounts for seasonal sand movement and wave-induced littoral drift. By using the "sand fingerprints" (elemental compositions) identified in this study, we aim to quantitatively evaluate the contribution of each river to the overall sediment distribution of Chirihama, providing a scientific basis for effective beach nourishment and erosion control measures.