A phenomenon that often occurs in Indonesia which is also an annual disaster that hit several areas is drought. Drought is a condition in which an area, land, or community experiences a shortage of water so that it cannot meet their needs. Drought can be caused because an area does not experience rain or is dry for a long period of time or the rainfall is below normal, so that the water content in the soil is reduced or even non-existent. The areas to be analyzed are the Hidirasa watershed, the Rontu watershed, and the Jangka watershed in Bima Regency, West Nusa Tenggara. The analysis drought aims to determine the deficit, drought duration, drought criteria based on deficits and surpluses that occur by analogy to Oldeman's criteria, hydrological drought index analysis, and hydrological drought distribution maps. In this study, data were used for the Tawali watershed in the Hidirasa watershed, the Sari watershed for the Jangka and the Kumbe water for the Rontu watershed to determine the Q50 and Q80 thresholds using the method Flow Duration Curve (FDC) to obtain hydrological drought characteristics. In the analysis of hydrological drought in several watersheds in Bima Regency, the results show that the maximum deficit in the Hidirasa, Term and Rontu watersheds was 1.09 m³/s, 0.14 m³/s, 0.49 m³/s which occurred in 2001, 1995, and 2001. From the deficit, it was found that the average drought period occurred 8-9 months from May to December and even some until January which indicated that the drought criteria were in zone 2 according to Oldeman. The largest hydrological drought index is the Hidirasa watershed, the Jangka Watershed and the Rontu watershed, respectively, -0.45, -1.00, -1.00, with a very strong drought category.
The biggest water demand is in the agricultural sector. This great need is caused by the irrigation system with continuous inundation (conventional). One of the water-saving irrigation methods is the System of Rice Intensification (SRI) method. The SRI method of giving water is done intermittently. One of the obstacles to the application of the SRI method is a continuous water source. The dam is one of the water sources whose water availability is relatively easy to manage, making it suitable for irrigation applications using the SRI method. This study aims to analyze the provision of irrigation water for SRI and conventional systems at the Meninting Dam and its effect on the area of irrigation services. In this study, an analysis of water availability was carried out using awlr data, an analysis of irrigation water requirements using the conventional method and the SRI method. Reservoir simulation analysis is used to determine the area that can be irrigated, planting intensity and reservoir reliability. The results for the conventional method of irrigated area that can be served are 1,559 ha with a planting intensity of 300% and a reservoir reliability of 95.83%. At the same intensity and reliability as the conventional method, the SRI method can irrigate 1,980 ha of irrigation area, so using the SRI method can increase the service area by 421 ha or can increase the service area by 27%.
Determining the rain pattern distribution is believed to affect the design flood. Providing hourly rainfall observations can be obtained, and the distribution patterns can be determined. However, in areas that do not have one, flood discharge calculations are carried out by distributing daily rainfall using empirical methods. This study distributes daily rainfall into hourly rainfall in the Jangkok watershed using ABM and Mononobe methods and calculates the flood hydrograph using the Nakayasu model. The synthetic unit hydrograph obtained from the actual rain distribution is then compared with the unit hydrograph generated from the empirical distribution, then the deviation is measured. The results showed that the Mononobe and ABM rain distribution gave the same hydrograph shape as the observation one, only for 2 hours of rain duration. As long as the rain lasts 3-6 hours, the peak flood discharge (Qp) tends to be lower, 7-20% for Mononobe and 2-7% for ABM. Then the Qp becomes overestimated (5-12%) for a rain duration of >6 hours. Mononobe gives the same flood peak time (Tp) as observation rain for 1-5 hours rain duration and becomes 1 hour earlier for >6 hours. In contrast, ABM produces peak times 1 hour longer than hydrographs with observation rain. Generally, the two methods provide a more significant hydrograph deviation for a longer duration of rain.
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