Abstract:A comparison between commonly used techniques for hydrograph recession analysis, namely the semi-logarithmic plot of a single recession segment, the master recession and a relatively new approach based on wavelet transform was carried out. These methods were applied to a number of flood hydrograph events of two catchments in West Java, Indonesia. The results show that all the methods tested produce reasonable and comparable results. However, problems arise in the semi-logarithmic plot and the master recession, i.e. determining the recession parameter K is not an easy task especially where the plotted data on a semi-logarithmic plot is not a linear but a curved line. On a curved line, the end of direct flow or starting point of baseflow is not clear and it is quite difficult to identify. Hence, the best line as a basis for computing the recession parameter K becomes uncertain. The wavelet transform approach, however, produces promising results and minimizes a number of problems associated with hydrograph recession analysis. The end of direct flow and the location of the baseflow component are easily determined through the wavelet maps.
Peatland wildfires, especially in tropical ecosystems, are often caused by drought, and lead to smoke and other related problems in all aspects of community life in Indonesia, especially in Central Kalimantan. Drought is worsened by the number of dry days in the dry season, known as the El Niño phenomenon, and the drainage system in a peatland. Additionally, drought decreases the water table and increases the probability of occurrence of wildfires in peatland areas. This study aims to modify the numerical formula of the drought factor (DFt) in the Keetch–Byram drought index (KBDI) based on tropical peatland wildfire conditions in Central Kalimantan during the El Niño phenomenon in 2015. Furthermore, it applies a revised peatland water table reference of 400 mm below the ground surface, based on previous research and the Government regulation on peatland ecosystem protection and management in Indonesia. These El Niño conditions caused a rain decline of approximately 35% in Block A, Ex-Mega Rice Project, Mantangai sub-District, Kapuas District, Central Kalimantan Province. The modified KBDI is compared with the Number of Fire Alerts (NFA) using NASA’s Active Fire Data in 2015. The analysis results demonstrate that the modified DFt under tropical peatland conditions leads to an increase in the drought index value, beginning on the driest days between July and November 2015. The value of the KBDI drought index increases from the high to the extreme index from September to November 2015, when as many as 61 extreme drought indices became indicators for peatland wildfire risk assessment. The extreme KBDI is directly proportional to the NFA recorded during 2015, and the highest number of fire alerts is observed for October 2015, with 1746 fire alerts within 31 days and extreme drought indices from 27 days. Hence, this modified formula is suitable for wildfire conditions on this peatland in Central Kalimantan. Overall, the modified DFt can be successfully applied to the El Niño phenomenon in 2015.
Rice grows well under certain condition and environment including soil, water and nutrients. Some researches have shown that traditional method with continues flooding need tremendeous amount of water for rice cultivation and gives low water productivity. To increase the water productivity, number of water saving irigation techniques have been studied and applied. Study on effect of number of water irrigation treatments on water productivity of rice was carried out. Eight irrigation treatments were conducted for growing rice in pot experiment i.e. shallow intermittent irrigation (SII), alternate wetting and drying (AWD1, AWD2, AWD3 and AWD4), shallow water depth with wetting and drying (SWD1 and SWD2), and semi-dry cultivation (SDC). The performance of those treatments in terms of agronomic and water parameters was compared to the shallow intermittent irrigation as a control method. The study reveals that the shallow intermittent irrigation needs the highest amount of water compare with other treatments. The lowest amount of water was achieved under the semi-dry cultivation. It could save water up to 18.4% compare to the control treatment. By using the alternate wetting and drying and the shallow water depth with wetting and drying treatments, irrigated water can be reduced up to 13.1% and 5.4%, respectively. The highest grain was obtained by alternate wetting and drying (AWD4) and the semi-dry cultivation yielded the smalest grain. On average the alternate wetting and drying and shallow water depth with wetting and drying increased the grain yield by 22.9% and 17.9%, whereas the semi-dry cultivation reduced the yield up to 14% compare to the shallow water depth treatment. The alternate wetting and drying treatments have significantly improved the water productivity by 41.6%, shallow water depth with wetting and drying increased by 24.2% relative to the shallow intermittent irrigation treatment, whereas the most saving water treatment i.e. the semidry cultivation performed quite similar with the shallow water depth treatment, as a result of low grain yields under the treatment.
Unit hydrograph is a popular method for predicting flood caused by rainfall in a catchment. This method has little flexibility to different storm, consequently the unit hydrographs produced differ considerably from storm to storm. This is partially due to the unit hydrograph method ignores the influence of antecedent soil moisture condition (AMC) on runoff generating processes. This paper presents the research result on the influence of AMC to peak discharge of observed unit hydrograph (q p-obs ). In this research the AMC is approached by parameter of soil moisture deficit (SMD) which has opposite meaning with the AMC. The SMD was represented by a variable of S c (storage capacity) that is the space volume remaining the soil moisture evaporated. The research was conducted using hydrologic data (rainfall, discharge, and evaporation) assembled from 4 upper basin surrounding Mount Merapi and Mount Rinjani. The research experiments were performed by deriving unit hydrographs using two methods, namely conventional method (Collins) producing observed unit hydrograph (HSobs) and simulation method using tank model of Yue and Hashino producing simulated unit hydrograph (HS sim ). The impact of Sc to the q p-obs was analyzed using peak discharge of HS obs and peak discharge of HS sim . The research result are concluded that: (1) the relationship between Sc and peak discharge of unit hydrograph showed that if the Sc increases (AMC decreases) then the peak discharge of HS obs decreases, (2) The formula of correction has exponential form of eksponensial (, with q p-obs-kor is peak discharge of corrected observed unit hydrograph (3) The average corrected observed unit hydrograph has the highest peak discharge than the peak discharge of Synthetic Unit Hydrograph of Nakayasu and the peak discharge of Synthetic Unit Hydrograph of Gama1.Keywords: AMC, observed unit hydrograph, tank model, corrected observed unit hydrograph Abstrak: Hidrograf satuan adalah salah satu cara untuk memperkirakan besarnya banjir di sungai akibat hujan pada suatu DAS. Hidrograf satuan sangat populer dan dipakai secara luas di dunia. Metode ini mempunyai fleksibilitas yang rendah terhadap hujan yang berbeda, sehingga hidrograf yang dihasilkan berbeda-beda pada setiap hujan. Hal ini diduga disebabkan antara lain karena teori hidrograf satuan mengabaikan pengaruh kondisi awal kelengasan tanah (antecedent soil moisture condition, AMC) pada proses penurunan hidrograf satuan. Tulisan ini menyajikan hasil penelitian tentang pengaruh AMC terhadap debit puncak hidrograf satuan observasi (q p-obs ). Dalam penelitian ini variabel AMC didekati dengan besaran defisit kelengasan tanah (soil moisture deficit, SMD) yang mempunyai makna berlawanan dengan AMC. SMD direpresentasikan dengan variabel Sc (storage capacity) yakni volume udara di dalam pori tanah yang ditinggalkan air karena terevapotranspirasi keluar. Penelitian dilaksanakan dengan menggunakan data hidrologi (hujan, debit aliran, dan evaporasi) yang dikumpulkan dari 3 DAS hulu (upper catchment) di k...
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