Time of concentration, Tc, is defined as time elapsed from the beginning of rainfall infiltrated into soil layer until it reaches a constant infiltration rate (fc) which is indicated an equilibrium subsurface flow rate. In hydrological view, time of concentration plays a significant role in elaboration of transformation of rainfall into runoff in a watershed. The aims of this research are to define influence of soil density and soil water content in determining time of concentration using infiltration concept based on water balance theory, and to find out the effect of land slope this time. Watershed laboratory experiment using rainfall simulator was employed to examine time of concentration associated with infiltration process under different slope, soil density and soil water content based on water balance concept. The steady rainfall intensity was simulated using sprinklers which produced 2 dm3∙min−1. Rainfall, runoff and infiltration analysis were carried out at laboratory experiment on soil media with varied of soil density (d) and soil water content (w), where variation of land slopes (s) were designed in three land slopes 2, 3 and 4%. The results show that relationship between soil density and land slope to time of concentration showed a quadratic positive relationship where the higher the soil density address to the longer time of concentration. Moreover, time of concentration had an inverse relationship with soil water content and land slope that means time of concentration decreased when the soil water content increased.

Drought monitoring, including its severity, spatial, and duration is essential to enhance resilience towards drought, particularly for overcoming drought risk management and mitigation plan. The present study has an objective to examine the suitability of the Standardized Precipitation Index (SPI) and Percent of Normal Index (PN) on assessing drought event by analyzing their relationship with the Southern Oscillation Index (SOI). The monthly rainfall data over twenty years of the observation period were used as a basis for data input in the drought index calculation. The statistical association analyses, included the Pearson Correlation (r), Kendal tau (τ), and Spearman rho (rs) used to assess the relationship between the monthly drought indexes and SOI. The present study confirmed that the SPI showed a more consistent and regular pattern relationship with SOI basis which was indicated by a moderately high determination coefficient (R2) of 0.74 and the magnitude of r, τ, and rs that were of 0.861, 0.736, and 0.896, respectively. Accordingly, the SPI showed better compatibility than the PN for estimating drought characteristics. The study also revealed that the SOI data could be used as a variable to determine the reliability of drought index results.

Intensitas hujan yang tinggi akan menyebabkan limpasan permukaan yang besar dan dapat berdampak negatif. Kurva IDF mempermudah perhitungan debit banjir rencana. Tujuan penelitian ini adalah menentukan metode empiris intensitas hujan dan IDF yang cocok untuk lokasi penelitian. Metode yang digunakan adalah Talbot, Mononobe, Hasper Der Weduwen, dan Van Breen. Hasil perhitungan menunjukkan bahwa Metode Talbot yang paling sesuai digunakan di lokasi penelitian. Metode Talbot memiliki nilai Deviasi Rata-rata 1.49; Kesalahan Relatif (Kr) rata-rata sebesar 8.64% dan Koefisien Nash Sutcliffe (ENS) rata-rata sebesar 0.98. Kemudian dilakukan validasi metode terpilih menggunakan kala ulang 2 tahun dan 5 tahun dengan membandingkan intensitas hujan metode empiris dan intensitas hujan pengamatan dengan hasil nilai Deviasi Rata-rata sebesar 2.22; nilai Kesalahan Relatif (Kr) rata-rata sebesar 15.11%, dan Koefisien Nash Sutcliffe (ENS) rata-rata sebesar 0.93.

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Legend Genangan pada saluran Gambar 4. Evaluasi saluran drainase eksisting (hujan 5 th, tata guna lahan 2010)