SETIAWAN, Hendri and Rudiarto, Iwan and Hidayat, Jafron Wasiq (2021) PERMODELAN PENGGUNAAN LAHAN DAN DAMPAKNYA TERHADAP LAJU SEDIMENTASI PADA DAS WAY SEPUTIH PROVINSI LAMPUNG. Masters thesis, School of Postgraduate Studies.

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Abstract

DAS Way Seputih merupakan salah satu prioritas pengelolaan DAS di Provinsi Lampung. Kondisi DAS menunjukkan adanya perubahan penggunaan dan tutupan lahan yang memiliki dampak pada peningkatan rata-rata debit sungai (16,3 m3/detik menjadi 17,1 m3/detik) sehingga berisiko terjadinya banjir dan bencana alam lainnya. Risiko tersebut didukung dengan adanya lahan kritis di DASS Way Seputih mencapai 7,8% dan lahan berpotensi kritis mencapai 66,43%. Tujuan penelitian ini adalah menganalisis perubahan penggunaan dan tutupan lahan pada DAS Way Seputih dan penerapan model SWAT untuk menghasilkan skenario penggunaan dan tutupan lahan yang optimal. Penelitian ini dilakukan pada bulan Juni sampai November 2020 yang berlokasi di DAS Way Seputih Lampung. Model yang digunakan dalam memprediksi dan mengevaluasi kondisi hidrologi yaitu model SWAT. Software yang digunakan meliputi ArcGIS 10.4.1, SWAT-CUP, ArcSWAT, dan Microsoft Office. Hasil penelitian menunjukkan adanya perubahan tutupan lahan DAS Way Seputih pada tahun 2011-2018. Adanya peningkatan luas pertanian lahan kering bercampur semak (160%), sawah (909%), semak belukar rawa (28%), tubuh air/sungai (10%), fasilitas transportasi (100%), tanah terbuka (100%), pertambangan (100%), sedangkan pengurangan luas hutan lahan kering sekunder (8%), hutan rawa sekunder (39%), pertanian lahan kering (34%), perkebunan (31%), rawa (90%), semak belukar (86%), dan pemukiman (2%). Permodelan Hidrologi SWAT menghasilkan 4 skenario penggunaan lahan. Penyusunan skenario 1 (penambahan lahan hutan menjadi 20%) dapat meningkatkan rata-rata debit aliran DAS terhadap kondisi existing sebesar 0,13%, menurunkan sedimen sebesar 51,67%. Penyusunan skenario 2 (penambahan pertanian lahan kering menjadi 50%) menunjukkan adanya peningkatan rata-rata debit aliran terhadap kondisi existing sebesar 2,63% dan dapat meningkatkan nilai sedimen sebesar 8,95%. Pada skenario 3 (penambahan perkebunan menjadi 15%) dapat menurunkan rata-rata debit aliran sebesar 3,02% terhadap kondisi existing dan menurunkan hasil sedimen sebesar 39,39%. Sedangkan skenario 4 (penambahan lahan pemukiman menjadi 20%) menunjukkan adanya peningkatan rata-rata debit aliran sebesar 0,65% terhadap kondisi existing dan menurunkan hasil sedimen sebesar 0,21%. Hasil skenario 1 memiliki keadaan paling ideal berdasarkan kondisi existing dibandingkan skenario lainnya, karena mampu menurunkan sedimen paling besar sehingga dapat mengurangi risiko terjadinya bencana banjir, meningkatkan kualitas air, kuantitas air (hidrologi), dan mendukung kehidupan ekosistem DAS.
Kata Kunci : DAS Way Seputih, SWAT, Skenario, Sedimentasi

The Way Seputih watershed is one of the priority watershed management in Lampung Province. Watershed conditions indicate changes in land use and cover which have an impact on increasing the average river discharge (16.3 m3 / second to 17.1 m3 / second) so that the risk of flooding and other natural disasters. This risk is supported by the existence of critical land in Way Seputih Watershed reaching 7.8% and potentially critical land reaching 66.43%. The purpose of this study was to analyze changes in land use and cover in the Way Seputih Watershed and the application of the SWAT model to produce optimal land use and cover scenarios. This research was conducted from June to November 2020 which is located in the Way Seputih Lampung Watershed. The model used in predicting and evaluating hydrological conditions is the SWAT model. The software used includes ArcGIS 10.4.1, SWAT-CUP, ArcSWAT, and Microsoft Office. The results showed that there was a change in the land cover of the Way Seputih Watershed in 2011-2018. There was an increase in the area of dry land mixed with shrubs (160%), rice fields (909%), swamp scrub (28%), water/river bodies (10%), transportation facilities (100%), open land (100%), mining (100%) while reducing the area of secondary dryland forest (8%), secondary swamp forest (39%), dryland agriculture (34%), plantations (31%), swamps (90%), scrub (86 %), and settlements (2%). SWAT Hydrological Modeling resulted in 4 land-use scenarios. Preparation of scenario 1 (additional forest land to 20%) can increase the average watershed flow rate to the existing conditions by 0.13%, reduce sediment by 51.67%. The preparation of scenario 2 (addition of dryland farming to 50%) shows an increase in the average flow rate to the existing conditions by 2.63% and can increase the sediment value by 8.95%. In scenario 3 (the addition of plantations to 15%) can reduce the average flow rate by 3.02% against the existing conditions and reduce the sediment yield by 39.39%. Meanwhile, scenario 4 (addition of residential land to 20%) shows an increase in the average flow rate of 0.65% to the existing conditions and a decrease in sediment yield by 0.21%. The results of scenario 1 have the most ideal condition based on existing conditions compared to other scenarios because they can reduce the greatest amount of sediment so that it can reduce the risk of floods, improve water quality, water quantity (hydrology), and support the life of the watershed ecosystem.
Keywords: Way Seputih Watershed, SWAT, Scenario, Sedimentation

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