Trend hujan jangkamasa panjang dan pengaruhnya terhadap hakisan permukaan: Implikasinya kepada tapak kampus baru Sultan Azlan Shah, Tanjong Malim (Long-term rainfall trends and their effects on surface erosion: Implications for the Sultan Azlan Shah new campus site, Tanjong Malim)

Abstract

Hujan merupakan salah satu elemen penting dalam proses dan perubahan bentuk bumi. Penganalisisan terhadap data hujan akan dapat menentukan pelbagai impak yang berlaku di atas permukaan bumi seperti kadar luahan, aliran permukaan, air dalam tanah, hakisan tanih, meramalkan dan menetukan kejadian banjir. Trend jangka panjang dan juga intensiti sering dikaitkan sebagai penyumbang kepada peningkatan kadar hakisan permukaan di kawasan yang dibangunkan. Dalam penulisan ini, fokus diberikan kepada tindakan hujan terhadap masalah hakisan tanih yang berlaku di tapak kampus baharu UPSI yang sedang dibangunkan. Penelitian terhadap ciri hujan, pengaruh angin monsun, trend hujan jangkamasa panjang serta perkaitan hujan dengan kejadian hakisan dilakukan. Hasil kajian menunjukkan trend hujan jangkamasa panjang di Tanjong Malim adalah meningkat dan sentiasa melebihi 2400 mm setiap tahun. Kawasan kajian sedang dibangunkan terletak di kaki bukit dan Banjaran Titiwangsa sentiasa menerima hujan lebat dengan jumlah yang tinggi dari jenis hujan bukit dan hujan perolakan. Selain itu, didapati bulan November dan April merupakan bulan-bulan yang mempunyai purata hujan bulanan yang tinggi. Jumlah hujan yang
tinggi dan kerap menyumbang kepada kadar hakisan permukaan yang tinggi, menyebabkan banyak alur sungai semulajadi tertimbus, terbentuk alur-alur baharu seperti galir dan galur serta berlakunya proses pemendapan di kawasan sungai dan tasik. Analisis ciri-ciri hujan adalah sangat penting dalam menyediakan maklumat asas tentang potensi hakisan serta pengekalan paras air dalam kawasan tadahan serta membantu pihak-pihak yang bertanggungjawab dalam pembukaan kawasan tanah secara besar-besaran di kawasan ini. Ciri dan trend hujan yang ditunjukkan dapat memberi gambaran tentang bagaimana aktiviti pembangunan yang ingin dijalankan perlu dirancang terlebih dahulu agar kesan negatif seperti hakisan tanih dapat dikurangkan.

Katakunci: hakisan permukaan, langkah mitigasi hakisan, pemendapan, pengurusan cerun, saliran tiruan, trend
hujan

Rain is an important element in the course of terrain changes. Analyses of rainfall data would determine the various impacts that occur on the earth surface such as the rate of discharge, surface flow, water in the soil, soil erosion, and flood forecasts and determination. Long-term rainfall trends and intensities often contribute to increases in the rate of surface erosion in areas undergoing development. In this paper, the focus is on the effects of rainfall on soil erosion at the site of the UPSI new campus which was being developed. The study area was located at the foothills of the Titiwangsa Mountain Range which had always received heavy orographic and convectional rainfalls. November and April were the months with the higher average of monthly rainfall. The rainfall characteristics, the monsoons influences, the long-term rainfall trends and the connection between rainfall and occurrence of erosion were examined. The findings revealed that there was an increasing long-term rainfall trend in Tanjong Malim amounting to more than 2400 mm per year. Soil erosion was serious here because adequate mitigation measures were not adopted by the parties responsible for the earlier site development of the Proton City resulting in severe siltation of local rivers and lakes. The situation would have been greatly helped had artificial drainage and sediment traps been constructed, slope management practised, and soil protection vegetation planted.

Keywords: artificial drainage, erosion mitigation measures, rainfall trends, sedimentation, slope management,surface erosion