Perubahan tutupan lahan yang terjadi berdampak pada kondisi hidrologi disuatu DAS. Kondisi hidrologi yang dimaksud dengan besaran keluaran DAS adalah debit yang menggambarkan besaran air. Penelitian ini bertujuan untuk mengetahui pengaruh perubahan tutupan lahan terhadap aliran sungai di DAS Pangkajene. Data dianalisis dengan menggunakan analisis hidrologi dan perubahan tata guna lahan. Hasil penelitian menunjukkan bahwa terjadi peningkatan debit banjir rancangan sebesar ±18,83 m³/det pada masing-masing kala ulang. Perubahan tata guna lahan yang terjadi adalah luas area sawah, tambak, dan pemukiman bertambah sedangkan luas area hutan menjadi berkurang. Meningkatnya nilai debit banjir tidak signifikan dikarenakan perubahan tata guna lahan juga tidak berubah cukup banyak.
Natural dam on Way Ela river was a landslide formation of Ulakhatu mount located at Negeri lima village, Distric Leihutu, Ambon island on 13th July 2012. The natural dam blockage the valley for 300 m wide and 200 m height with total 1,000 m dam area and providing 87 million m3 volume of water storage. Slope failure trigger by slide area on the deeper surface structure leading to landslide. High risk landside increased by the high rainfall intensity of 432 mm/day and causing the failure of natural dam Way Ela. This study aimed to analyse debris flow velocity of the landslide of natural dam. Analysis performed based on debris during using geometric slope with empirical model system. PMF Syndrer-Alexeyev and GAMA-1 method and PMP frequency analysis equation method demonstrated that rainfall intensity data along with recurrent period of 100 years of Qpeak resulting debit volume of 448.85 m3/d. Furthermore, velocity estimation also showed that on 215.66 elevation high, allowable slope degree of (i) 0,005 %, average width of Way Ela river of 79.97 m and Manning’s grain roughness of 0.004 μm would resulting debris flow velocity of 10.98 m/s, and distance from the landslide centre point to the river mouth was 2.5 km. Those data leading to achieve arrival flow time to the residential area of 3.8 minutes. This study results potential as a base data for disaster mitigation due to high risk of debris flow velocity presented by Way Ela river.
Tallo River has the potential to pose a threat of flooding because it is strongly influenced tide. Regulation Ponds are flood control structures built upstream from areas that will be protected from flood hazards. Storage Capacity Analysis of Nipa regulation pond using Ripple method. Flood routing results obtained a maximum of 3.395.116,79 m3, while topographic conditions obtained a maximum of 3.583.270,96 m3 then optimization analysis based on the Ripple Method obtained with volume accommodated during 1980-1984 is 2.508.330,462 m3, during 1985-1989 is 2.158.594,429 m3, during 1990-1994 is 1.721.928,984 m3, during 1995-1999 is 2.072.035,680 m3, the volume accommodated during 2000-2004 is 2.526.941,033 m3, volume accommodated during 2005-2009 is 1.996.205,351 m3 and volume accommodated during 2010-2014 is 1.913.798,405 m3. This shows that storage capacity of regulation Pond can serve to reduce flood in Tallo River. Based on the cumulative storage analysis, a maximum storage of 10.592.032,714 m3 obtained from the inflow and outflow analysis, indicating that the Nipa regulation pond was able to reduce flood in amount of 38,07 % i.e. 4.032.440,62 m3.
Way Ruhu has a river with the slope of the land is steep. The heavy rains that often occur in the city of Ambon resulted in floods and landslides in several places thus to give a big loss to the people in the city of Ambon both the loss of property and lives. This study was conducted with the aim to determine the magnitude and time of flooding in the Way Ruhu watershed, the modeling results will be applied in android so that people can evacuate early because information can be received more quickly and the Government can prepare better mitigation programs. Modeling methods are carried out using 2D software HEC-RAS 5.0.7 which requires hydrological and topographical data as the main inputs. The output from HEC-RAS is a flood map, flood height, and duration of the flood. The results of this study indicate that the time between the upstream river rise and the arrival of floodwater in the downstream is less than one hour, with flood characteristics as high as 1-5 meters and receding within 4 to 11 hours.
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