GROUNDWATER RESPONSE TO TIDES ON A SANDY BEACH
DOI:
https://doi.org/10.11113/aej.v14.20740Keywords:
sandy beach, water table, tides, morphology, wavesAbstract
Beach profile formation and morphology have been widely studied in recent years. A key point of understanding the dynamics of sandy beaches is the knowledge of the interactions between tides and groundwater with the beach profile, despite the challenges of conducting high-quality measurements. This study aims to clarify the response of groundwater levels to tides during two fieldworks: inter-monsoon (2017) and Southwest monsoon (2018) at Desaru Beach. Four monitoring wells were installed perpendicular to the beach, alongside a tide gauge, a wave buoy, and an underwater current meter. The findings showed that the water table was generally not flat but fluctuated with time following the tidal pattern at a tangent. Lag times observed in all wells ranged from 3 hours 20 minutes to no lag times during the spring and from about 4 hours 40 minutes to no lag times during the neap. The groundwater closest to the sea indicated a shorter lag time at high tides than low tides during the inter-monsoon and Southwest monsoon. This study indicated that the beach groundwater filled up faster than it drained between rising and falling tides. The time lags of groundwater levels established in this study can be utilised in coastal flood forecasting for similar beach conditions.
Keywords: Sandy beach, water table, tides, morphology, waves
Kajian mengenai pembentukan dan morfologi profil pantai dijalankan secara meluas sejak kebelakangan ini. Satu perkara penting dalam memahami dinamik pantai berpasir adalah pengetahuan tentang interaksi antara pasang surut dan air bumi terhadap profil pantai, meskipun terdapat kesukaran dalam melakukan pengukuran berkualiti tinggi. Kajian ini bertujuan untuk menjelaskan respons paras air bumi terhadap pasang surut semasa dua kerja lapangan dijalankan iaitu antara-musim (2017) dan musim barat daya (2018). Empat perigi pemantauan dipasang secara serenjang dengan pantai, bersama-sama dengan tolok pasang surut, boya gelombang dan meter arus. Hasil kajian menunjukkan aras air secara umumnya tidak rata tetapi berubah mengikut corak pasang surut dengan tangen. Air bumi yang terdekat dengan laut menunjukkan masa lengah yang dicerap dalam semua perigi berjulat antara 12 minit hingga 3 jam 35 minit semasa pasang surut perbani dan dari 5 minit hingga 3 jam 55 minit semasa pasang anak. Air bumi yang terdekat dengan laut menunjukkan masa lengah yang lebih pendek semasa pasang tinggi berbanding pasang surut semasa antara-musim, sementara keadaan tersebut kekal relatif konsisten semasa musim barat daya. Kajian ini menunjukkan bahawa air bumi memenuhi dengan lebih cepat daripada mengalir keluar antara pasang naik dan pasang surut. Masa lengah paras air bumi yang ditetapkan dalam kajian ini boleh digunakan dalam meramal banjir pantai untuk keadaan pantai yang serupa.
Kata kunci: Pantai berpasir, aras air, pasang surut, morfologi, gelombang
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