The Effect of Changes in Land Cover on Total Sediment Yield in Peusangan Watershed, Aceh Province

The watershed is an area above or higher than a river whose topographical boundaries cause water to flow into the same river. The river flow carries sediment particles that potentially cause silting of the estuary area. The sediment carried by the river flows from the erosion process that occurs in the watershed. Changes in land cover potentially affect the rate of sediment export to rivers due to changes in surface roughness and water infiltration rate to the ground. This study aims to identify the effect of the land cover change on the total sediment yield from the Peusangan Watershed, Aceh Province. The sediment yield is calculated from the erosion rate and the sediment delivery ratio. The erosion rate is modeled using the revised universal soil loss equation, while the sediment delivery ratio is calculated based on the function of the watershed area. From the results of the calculation, in general, the rate of erosion is at a very level where the average erosion rate in 1995 is 26,715 tons/ha/year, in 2005 it is 26,886 tons/ha/year, in 2015 it is 24,959 tons/ha/year and in 2018 amounted to 26,771 tons/ha/year. With a sediment delivery ratio value of 0.180, The total sediment yield was 1,083,148.20 tons in 1995, 1,090,047.94 tons in 2005, 1,011,920.71 tons in 2015, and 1,085,398.35 tons in 2018. The identification results show that the changes in land cover affect the total sediment yield that comes out of the watershed.

Analisa Pendugaan Laju Erosi Dengan Menggunakan Model Agricultural Non Point Source Pollution (AGNPS) Di Sub Das Lesti Kabupaten Malang

Perubahan tata guna lahan dan bentuk topografi yang berombakbergelombang dan berbukit bergunung dengan kemiringan lereng 8-45 %, serta besarnya intensitas curah hujan berdampak pada tingginya laju erosi di wilayah Sub DAS Lesti. Erosi lahan yang terus menerus terjadi menyebabkan pendangkalan pada sungai di Sub DAS Lesti. Oleh karena itu dilakukan analisa dan melakukan pemetaan tentang kondisi eksisting besarnya laju erosi dan sedimentasi beserta tingkat bahaya erosi pada Sub DAS Lesti dan juga upaya konservasi lahan guna untuk mengurangi dampak dari laju erosi tersebut. Perhitungan menggunakan model Agricultural Non-Point Source Pollution (AGNPS) diperoleh laju erosi ratarata DAS sebesar 163,119 ton/ha/tahun. Hasil analisis tingkat bahaya erosi berdasarkan Indeks Bahaya Erosi oleh Hammer (1981) diperoleh indeks dengan tingkat rendah (indeks 10) seluas 14,623 km2 , tingkat tinggi (indeks 4-10) seluas 16,342 km2 . Berdasarkan hasil perhitungan sediment delivery ratio (SDR), didapatkan hasil perkiraan sedimen sebesar 144.820,54 ton/tahun atau 120.683,96 m3 /tahun. Upaya konservasi lahan guna untuk mengurangi besarnya laju erosi dilakukan dengan beberapa cara baik dengan menggunakan metode vegetatif maupun metode mekanik.

A Study of Sediment Yield in the Deji Reservoir Watershed Using Risk Analysis

<p>Deji Reservoir Watershed was used as a sample site to understand the sediment yield using risk analysis. The historic typhoon and/or torrential storm events were collected to estimate the excessive runoff for each event. The distribution of SCS-CN is obtained by combining the maps of land use and soil texture, and the excess rainfall (Pe) and the maximum water storage (S) for each event were then calculated according to SCS-CN. Regression analysis shows that there is a good relationship between estimated runoff (x) and measured runoff (y); y=0.9561x+3*10<sup>6</sup>, R<sup>2</sup>= 0.9414. Topographic wetness index (TWI) and sediment delivery ratio (SDR) were derived from DEM. The risk model developed to assess the sediment yield is calculated from the multiplication of hazard (Pe), vulnerability (TWI), and exposure (SDR). The total siltation amount of Deji Reservoir from 2009 to 2017 was taken as the measured value, and the estimated amount of sediment yield was calculated from the aforementioned formula  to obtain the potential index of sediment yield. The results show that there is also a good relationship between estimated sediment yield (x') and measured sediment yield (y') annually; y'=10<sup>-11</sup>x'<sup>2</sup>-0.0223x'+9*10<sup>6</sup> , R<sup>2</sup>= 0.74.</p><p>Keywords: Risk Analysis, Curve Number, Sediment Delivery Ratio</p>

KAJIAN EROSI LAHAN DI KAWASAN AIR STRIP RUNWAY 2600 BANDARA DEPATI AMIR (PGK) BERDASARKAN TATA GUNA LAHAN MASTERPLAN ULTIMATE

Standar permintaan engineering pesawat agar desain bangunan infrastruktur di area Air Strip Runway 2600 yang ada dapat mempunyai fungsi lain. Sedangkan kondisi lain sangat menentukan keselamatan karena lahan di sekitar Air Strip Runway 2600 Bandara Depati Amir (PGK) jika tidak ditutupi vegetasi seperti rumput, kondisi lain lahan yang belum ditutupi vegetasi di sekitar Air Strip Runway 2600 berpotensi akan mengalami erosi lahan, kemudian hasil erosi lahan ini akan terbawa oleh aliran air sehingga akan masuk ke saluran drainase yang akan menyebabkan sedimentasi pada saluran drainase tersebut, akhirnya akan berkurang efektifitas kinerja saluran drainase tersebut. Metode yang digunakan untuk memprediksi laju rata-rata erosi di area Air Strip Runway 2600 dengan memperhitungkan faktor erosivitas hujan, erodibilitas tanah, kemiringan lereng atau panjang lereng, pengelolaan tanaman dan konservasi tanah, yang masing masing tata guna lahan tersebut mengacu pada Masterplan Ultimate Bandara Depati Amir (PGK). Perhitungan dilakukan menggunakan persamaan USLE (Universal Soil Loss Equation) yang dikembangkan oleh Wischmeier dan Smith (1965, 1978), kemudian Sediment Delivery Ratio (SDR) dan Sediment Yield.Hasil penelitian ini, prediksi laju erosi permukaan pada area Air Strip Runway 2600 Bandara Depati Amir (PGK) tahun pertama yang mencapai 5,60 mm/tahun atau 100,76 Ton/Ha/tahun, laju erosi tahun kedua mencapai 3,38 mm/tahun atau 60,84 Ton/Ha/tahun dapat diklasifikasikan ke dalam kelas bahaya erosi sedang (kelas III) dan nilai SDR adalah sebesar 56,3%, nilai sediment yield (SR) pada tahun pertama sebesar 5.887,59 Ton/Tahun, pada tahun kedua ketika rumput pada area Air Strip telah tumbuh dengan sempurna terjadi penurunan hasil sediment yield yaitu nilai SR sebesar 3.554,85 Ton/Tahun.