Hidayati, Indah Kusuma and Dr. Eng. Donny Harisuseno,, ST,MT. and Ir. Agus Suharyanto,, M.Eng.,Ph.D. (2022) Model Parameter Abstraksi Awal (Ia) pada Limpasan Permukaan yang Dipengaruhi Waktu Penggenangan (Ponding Time, tp),. Doktor thesis, Universitas Brawijaya.
Abstract
Soil Conservation Service-Curve Number (SCS-CN) adalah salah satu pendekatan empiris yang paling banyak diterapkan untuk memperkirakan curah hujan efektif yang berkontribusi terhadap limpasan permukaan. Namun dalam penggunaannya, metode SCS- CN memiliki beberapa keterbatasan yaitu estimasi total limpasan permukaan berasal dari curah hujan, tetapi tidak memperhitungkan intensitas hujan dan durasi hujan di dalam perhitungannya. Nilai abstraksi awal (Ia) dalam metode SCS-CN tidak terkait dengan sifat infiltrasi tanah sehingga penggunaan SCS-CN rentan terhadap kesalahan yang relatif besar di dalam DAS yang kecil. Abstraksi awal (Ia) merupakan fungsi dari parameter abstraksi awalِ (λ)ِ danِ retensiِ potensialِ maksimumِ (S).ِ Saatِ ini,ِmetodeِ SCS -CN mengasumsikan parameterِabstraksiِ awalِ (λ)ِ samaِ denganِ 0,2,ِ namunِ demikianِ parameterِِ Sِ danِλِ dariِ persamaan SCS-CN dapat berasal dari data infiltrasi yang diamati di lapangan. Penelitian ini mengamati laju infiltrasi dan waktu penggenangan (tp) di lapangan, yang dipengaruhi jenis tanah dan tata guna lahan. Parameter infiltrasi ini selanjutnya akan digunakan untuk membentuk model abstraksi awal (Ia) yang digunakan untuk memodifikasi model SCS-CN agar lebih sesuai untuk diterapkan di Indonesia. Penelitian dilakukan di salah satu DAS di Wilayah Sungai Brantas yaitu DAS Lesti, Kabupaten Malang, pada musim kemarau, yaitu mulai Juli sampai dengan Agustus 2020. Pengukuran laju infiltrasi dengan metode flooding, menggunakan alat Double Ring Infiltrometer. Dari hasil pengamatan, didapatkan parameter laju infiltrasi metode Horton yang terdiri dari f0 = laju infiltrasi awal, fc = laju infiltrasi akhir, dan k = koefisien Horton. Selain itu, didapatkan juga waktu penggenangan (tp) dan abstraksi awal (Ia). Nilai abstraksi awal dan waktu penggenangan dari data observasi ini selanjutnya dibandingkan dengan nilai abstraksi awal dan waktu penggenangan hasil perhitungan empiris, yaitu melalui overlay antara kurva intensitas curah hujan (i) dan laju infiltrasi (f). Berdasarkan hasil analisis keandalan menunjukkan bahwa didapatkan hubungan kuat antara Iaobs dan Iaemp, serta tpobs dan tpemp. Penelitian ini menghasilkan model parameter abstraksi awal (Ia)yang merupakan fungsi laju infiltrasi konstan (fc) dan waktu penggenangan (tp), dengan model Ia = fc.tp. Pendekatan model S dinyatakan fungsi laju infiltrasi konstan (fc) dan parameter Horton (k), dengan model S=fc/k. Model SCS-Ia modifikasi dengan menggunakan parameter infiltrasi Ia = fc.tp dan S = fc/k lebih sesuai diaplikasikan dalam perhitungan hujan efektif atau limpasan permukaan dibandingkan rumus SCS-CN original.
English Abstract
Soil Conservation Service-Curve Number (SCS-CN) is one of the most widely applied empirical approaches to estimate the effective rainfall that contributing to surface runoff. However, in the use of The SCS-CN method has several limitations that are the estimation of total surface runoff comes from rainfall, but does not count rain intensity and rain duration in its calculations. The initial abstraction value (Ia) in the SCS-CN method is not related to properties of soil infiltration so that the use of the SCS-CN is prone to having large errors in small watersheds. The initial abstraction (Ia) is a function of the initial abstraction parameter (λ) and the maximum potential retention (S). Currently, the SCS-CN method assumes an initial abstraction parameter (λ) equal to 0.2, however, the S and λ parameters of the SCS-CN equation that can be obtained from observed data in the field. This study observed infiltration rate and ponding time (tp) in the field, which were influenced by soil type and land use. These infiltration parameters then will be used to form an initial abstraction model (Ia) which is used to modify the SCS-CN model that's more suitable for application in Indonesia. The research was conducted in one of the watersheds in the Brantas River Basin, that is Lesti Watershed, Malang Regency, during the dry season, from July to August 2020. Measurement of infiltration rate by flooding method, using a Double Ring Infiltrometer. From the observations, the infiltration rate parameter obtained by the Horton method consists of f0 = initial infiltration rate, fc = constant infiltration rate, and k = Horton's coefficient. In addition, the ponding time (tp) and initial abstraction (Ia) were also obtained. The initial abstraction values and ponding time from these observational data are then compared with the initial abstraction values and ponding time results from empirical calculations, that is through an overlay between the rainfall intensity curve (i) and infiltration rate (f). Based on the results of the reliability analysis shows that there is a strong relationship between Iaobs and Iaemp, also tpobs and tpemp. This study resulted an initial abstraction parameter model (Ia) which is a function of constant infiltration rate (fc) and ponding time (tp), with the model Ia = fc.tp. The S model approach is expressed as a function of the constant infiltration rate (fc) and the Horton parameter (k), with the model S=fc/k. The modified SCS-Ia model using the infiltration parameters Ia = fc.tp and S = fc/k is more suitable to be applied in calculating effective rainfall or surface runoff than the original SCS-CN model.
| Item Type: | Thesis (Doktor) |
|---|---|
| Identification Number: | 0622070011 |
| Uncontrolled Keywords: | Hujan Efektif, Abstraksi Awal, Laju Infiltrasi, Waktu Penggenangan .- Effective Rainfall, Initial Abstraction, Infiltration Rate, Ponding Time |
| Subjects: | 600 Technology (Applied sciences) > 624 Civil engineering |
| Divisions: | S2/S3 > Doktor Teknik Sipil, Fakultas Teknik |
| Depositing User: | PKN 02 UB |
| Date Deposited: | 08 Jun 2023 01:47 |
| Last Modified: | 08 Jun 2023 01:47 |
| URI: | http://repository.ub.ac.id/id/eprint/201122 |
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