Penilaian Degradasi Lahan dan Dampak Sedimentasi terhadap Perencanaan Bangungan Air di Daerah Aliran Sungai Wai Ruhu, Kota Ambon

Land degradation is the reduction in the ability of land to generate benefits from certain land uses under special treatment from land management. Land degradation usually indicates deterioration in the production capacity of the land either temporarily or permanently. A further consequence of the land degradation process is the emergence of unproductive areas called critical lands. Quantitative and qualitative determination of erosion in a watershed area could be identified through observation of real damage indicators that had occurred in the field. This is based on this study results combined with the method of determining soil degradation in the field, namely the Field Assessment Tools, indicators of soil damage due to erosion obtained in the area of this this study area. These included pedestals, exposed plant roots / tree roots and exposed building foundations as an indication of land degradation due to sheet erosion, channel indicators as channel erosion and trench indicators as trench erosion. The classification of land degradation due to erosion found in the Wai Ruhu watershed showed that the level of land degradation could be classified as light erosion, moderate erosion, heavy erosion and very heavy erosion, with the range of erosion varying from 4.40 tons/ha/year to 675,62 tons/ha/year. Meanwhile, from the results of direct measurements, the overall average sediment concentration was 98,06 mg/L. During the rainy season, the average sediment concentration produced was 107,43 mg/L, higher than during the dry season of 88.69 mg/L. The Wai Ruhu watershed had a fairly large discharge. Although during the dry season the river was not dry completely, the discharge was very small. The basic material found along the Wai Ruhu watershed indicated that there had been intensive degradation processes in the upstream area. Excessive deposition along the river would result in reduced capacity of the river channel. Keywords: Ambon, discharge, land degradation, sedimentation, Wai Ruhu Watershed ABSTRAK Degradasi lahan adalah berkurangnya kemampuan lahan untuk menghasilkan manfaat dan keuntungan dari penggunaan lahan tertentu di bawah perlakuan khusus dari pengelolaan lahan kerusakan lahan biasanya menandakan kemunduran kapasitas produksi dari lahan baik secara temporer maupun secara permanen. Akibat lanjut dari proses degradasi lahan adalah timbulnya areal-areal yang tidak produktif yang disebut lahan kritis. Penentuan besar erosi secara kuantitatif dan kualitatif pada suatu wilayah DAS dapat diidentifikasi melalui pengamatan terhadap indikator-indikator kerusakan yang nyata terjadi di lapangan. Berdasarkan hasil penelitian yang telah dilakukan ini, yang dipadukan dengan metode penentuan degradasi tanah di lapangan berupa Field Assessment Tools, maka indikator-indikator kerusakan tanah akibat erosi yang didapatkan di daerah penelitian. Itu terdiri dari pedestal, akar tanaman/akar pohon terekspos dan fondasi bangunan terekspos sebagai indikasi degradasi lahan akibat erosi lembar, indikator alur sebagai erosi alur dan indikator parit sebagai erosi parit. Klasifikasi degradasi lahan akibat erosi yang ditemukan di DAS Wai Ruhu menunjukkan bahwa tingkat degradasi lahan tergolong erosi ringan, erosi sedang, erosi berat dan erosi sangat berat, dengan kisaran besar erosi yang bervariasi antara 4,40 ton/ha/tahun sampai 675,62 ton/ha/tahun. Sedangkan dari hasil pengukuran langsung secara keseluruhan konsentrasi sedimen rata-rata adalah sebesar 98,06 mg/L. Untuk saat hujan konsentrasi sedimen rata-rata yang dihasilkan adalah sebesar 107,43 mg/L, lebih tinggi daripada saat kemarau sebesar 88,69 mg/L. DAS Wai Ruhu mempunyai debit yang cukup besar. Meskipun pada saat kemarau aliran sungai tidak kering sama sekali, tetapi debitnya sangat kecil. Material dasar yang terdapat di sepanjang saluran DAS Wai Ruhu menggambarkan bahwa telah terjadi proses-proses degradasi yang intensif di daerah hulu. Pengendapan yang berlebih di sepanjang sungai akan akan mengakibatkan berkurangnya kapasitas saluran sungai. Kata kunci: Ambon, DAS Wai Ruhu, debit air, degradasi lahan, sedimentasi