Judul: Planned Flood Discharge Analysis and Efforts to Reduce Runoff in Ciherang Sub-watershed, Cisadane Watershed
Abstrak: Sub-DAS Ciherang memiliki tutupan lahan yang didominasi oleh sawah dan perkebunan yaitu sebesar 539.2 ha dan 464.18 ha serta curah hujan bulanan yang tinggi pada bulan November sampai dengan Maret. Penelitian ini bertujuan untuk melakukan analisis curah hujan rencana pada Sub-DAS Ciherang, menganalisis debit banjir rencana dan besarnya limpasan, serta menganalisis upaya-upaya apa saja yang dapat dilakukan untuk mencegah terjadinya banjir. Pengukuran debit puncak dan limpasan dilakukan dengan analisis hidrologi dimana dalam pengukuran curah hujan rencana digunakan metode Log-Pearson III dan dalam pengukuran debit puncak digunakan metode hidrograf satuan sintesis Nakayasu. Sub-DAS Ciherang memiliki rata-rata curah hujan harian maksimum sebesar 103.18 mm/tahun dengan curah hujan rencana yang dihitung berdasarkan metode Log-Pearson III dengan periode ulang 2, 5, 10, 25, 50, dan 100 tahun sebesar 93.33, 124.11, 148.17, 182.99, 212.44, dan 245.02 mm. Sub-DAS Ciherang memiliki debit puncak dengan periode ulang yang sama yaitu sebesar 41.38, 55.03, 65.69, 81.13, 94.19, dan 108.63 m3/detik. Besarnya rasio DRO (direct runoff) dengan curah hujan pada 2 kejadian hujan sebesar 16.8% dan 19.3%. Besarnya DRO tersebut menyebabkan ancaman banjir pada daerah hilir cukup besar sehingga diperlukan upaya untuk mencegah terjadinya banjir. Upaya-upaya pencegahan banjir dapat dilakukan dengan konservasi tanah dan air yang dapat dibagi menjadi tiga metode, yaitu secara mekanik, vegetatif, dan kimiawi. Kata kunci : analisis hidrologi, , debit puncak, limpasan, pencegahan banjir, The Ciherang sub-watershed has land cover which is dominated by rice fields and plantations, namely 539.2 ha and 464.18 ha as well as high monthly rainfall from November to March. This study aims to analyze the planned rainfall in the Ciherang sub-watershed, analyze the planned flood discharge and runoff size, and analyze the efforts that can be made to prevent flooding. Measurement of peak discharge and runoff is carried out by hydrological analysis where the Log- Pearson III method is used in the planned rainfall measurement and the hydrograph method of the Nakayasu synthesis unit is used in the measurement of peak discharge. The Ciherang sub-watershed has a maximum daily average rainfall of 103.18 mm / year with a planned rainfall calculated based on the Log- Pearson III method with a return period of 2, 5, 10, 25, 50, and 100 years of 93.33, 124.11, 148.17, 182.99, 212.44, and 245.02 mm. The Ciherang sub-watershed has a peak discharge with the same return period, namely 41.38, 55.03, 65.69, 81.13, 94.19, and 108.63 m3/s. The magnitude of the DRO (direct runoff) ratio with rainfall in 2 rain events is 16.8% and 19.3%. The amount of DRO threatens the threat of flooding in the downstream area which is quite large so that efforts are needed to prevent flooding. Flood prevention efforts can be carried out by conserving soil and water which can be divided into three methods, namely mechanical, vegetative, and chemical. Keywords: flood preventing, hidrology analysis, peak discharge, runoff
Keyword: flood preventing, hidrology analysis, peak discharge, runoff

Judul: Analysis of Surface Runoff in Citarum Watershed
Abstrak: Beberapa DAS di Indonesia telah mengalami kerusakan, salah satunya adalah DAS Citarum. Kerusakan yang terjadi pada DAS menunjukkan masih lemahnya sistem pengelolaan yang ada. Sistem pengelolaan DAS yang lemah terjadi karena kurang terdeteksinya kerusakan DAS secara dini dan periodik. Kerusakan DAS dapat diidentifikasi menggunakan pemodelan hidrologi, antara lain dengan analisis aliran permukaan (surface run off) menggunakan metode Soil Conservation Service berbasis curve number (SCS-CN). Penelitian ini bertujuan untuk menentukan dan memetakan nilai CN dan aliran permukaan di DAS Citarum. Nilai aliran permukaan diprediksi dengan model SCS berdasarkan nilai CN setiap unit lahan. Data yang digunakan pada penelitian ini yaitu data tekstur tanah, curah hujan dan jenis tutupan lahan untuk menentukan nilai CN. Nilai CN diolah untuk menentukan nilai aliran permukaan. Nilai CN yang tinggi berpotensi menghasilkan aliran permukaan yang tinggi. Selanjutnya, nilai aliran permukaan dipetakan pada seluruh wilayah DAS Citarum. Hasil penelitian menunjukkan nilai CN tertinggi terdapat pada satuan lahan terbangun dan terendah terdapat pada satuan lahan bervegetasi. Nilai aliran permukaan tertinggi terdapat pada subDAS Cigundul sebesar 731 mm/tahun dan terendah di subDAS Citarum Hulu sebesar 356,22 mm/tahun. Curah hujan yang menjadi aliran permukaan tertinggi sebesar 34% terjadi di subDAS Citarum Hilir dan terendah sebesar 20% terjadi di subDAS Citarum Hulu., Several watersheds in Indonesia have been degraded, one of which is the Citarum watershed. The degradation of the watershed indicates that the existing management system is still weak. Poor watershed management system occurs due to lack of early and regular detection of watersheds degradation. Watershed degradation can be identified using hydrological modeling, including the analysis of surface runoff using the curve number-based on Soil Conservation Service (SCS-CN) method. This study aims to determine and mapping the value of CN and surface runoff in the Citarum watershed. The surface runoff value was predicted using the SCS model based on the CN value of each land unit. The data used in this study are data on soil texture, rainfall, and land cover types to determine the CN value. The CN value is processed to determine the surface runoff value. High CN values have the potential to produce high surface runoff. Furthermore, the surface runoff value was mapped over the entire Citarum watershed area. The results show that the highest CN value is found in the built- up area and the lowest is in the vegetated area. The highest surface runoff value are found in the Cigundul sub-watershed at 731 mm/year while the lowest in the Citarum Hulu sub-watershed at 356.22 mm/year. The highest percentage of rainfall that became surface runoff was occured in the Citarum Hilir sub- watershed (34%) and the lowest is in the Citarum Hulu sub-watershed (20%).
Keyword: curve number, runoff mapping, SCS-CN

Judul: Penentuan Nilai Eigen dan Vektor Eigen dari Matriks Tridiagonal 2-Toeplitz dengan Pendekatan Polinomial Chebyshev
Abstrak: The eigenvalues and eigenvectors of a matrix can be determined by finding its characteristic polynomials. The characteristic polynomials of a tridiagonal 2-Toeplitz matrix is shown to be closely connected to polynomials which satisfy the Chebyshev recurrence relationship. If the order of the matrix is odd, then the eigenvalues are found explicitly in terms of the Chebyshev zeros and the eigenvectors are found in terms of the polynomials satisfying the recurrence relationship. For even ordered matrices, the situation is more complicated. The problem in these cases is that although the Chebyshev recurrence formula is still applied, its initial values are not generating Chebyshev polynomials
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