Paving blocks have been widely known as an alternative technology for reducing runoff discharge due to their infiltration performance and capability of retarding the flow. Surface configuration of the different paving blocks types and the openings area play important role in decreasing the runoff velocity. In this study, we investigated the surface runoff velocity on two types of paving blocks layers, and a smooth pavement as comparison. The paving blocks type were rectangular blocks, which have 3.2% openings ratio and hexagonal blocks, which have 6.5% openings ratio. We used a tilted plot covering area of 2 × 6 m, equipped by a rainfall simulator to accommodate the variation of surface slope and rainfall intensity. We measured the velocity by using modification of dye tracer and buoyancy method. The data were then tabulated and graphed based on the paving types and the surface slopes. Generally, the velocity-slope relationship has demonstrated that the increase in surface slope leads to the increase in velocity. In this study, the result showed that slope and rainfall intensity simultaneously influenced the velocity (F = 19.91 > F_table = 5.14; P < 0.05). However, the findings of this study showed a weak relationship between the changes of surface slope and the changes of runoff velocity on the rectangular blocks (R² = 0.38). The greater slope did not always invariably lead to the greater runoff velocity. It was likely that there was other predictor variable that was not identified before, and need to be further investigated.

Debris flow is a devastating phenomenon that happens in hilly and mountainous regions and has a serious impact on affected areas. It causes casualties and serious damage to the environment and society. Therefore, a susceptible assessment is necessary to prevent, mitigate, and raise awareness of the impact of debris flows. This paper focuses on evaluating the deposition area along the deposition board. The methodology involved an experiment on a physical model by demonstrating the debris flow based on the steepness of the flume slope at 15°, 20°, and 25° angles. The limestone particles with a total volume of 2.5 × 10⁶ mm³ acted as debris and were released with water from the tank to the deposition board with an area of 10 × 10⁵ mm². The volume, area, and length of particle distribution carried from the flume to the deposition board were then determined. Based on the experimental results, the deposition board is covered with particles of about 696.19 × 10³ mm³, 748.29 × 10³ mm³, and 505.19 × 10³ mm³ volume for each 15°, 20°, and 25° angle, respectively. In actual situations, debris flow is capable of causing significant risk to the affected area. This study can be deemed useful for a risk assessment approach, to help develop guidelines, and to mitigate the regions where debris flows are most probable to occur.

Kajian Pengembangan Sistem Penyediaan Air Bersih Pada Daerah Rawan Air Di Desa Sumbersih Kecamatan Panggungrejo Kabupaten Blitar

Jakarta is a large city with a population of around 10 million who still suffer flooding during the rainy season. A program that is being implemented to reduce flooding that occurs every year is called “Total Solution for Ciliwung”. One of the programs is to build 3 (three) diversion channels on the Ciliwung River located in Kalibata, Kebon Baru, and Kampung Melayu respectively. This paper only discusses the problem of flooding in Jakarta in the aspect of hydraulics. This research was conducted with the aim of analyzing the character of floods in the Ciliwung River based on variations in the choice of diversion channel locations. Analysis of flood characteristics using the HEC-RAS 4.1 Program. The results of the analysis provide conclusions, that variation 7 (seven) provides the most optimal reduction in flooding. The main result is, the water level profile in point 260, the water flow is sub-critical which the water level at +18.50 m or decreases by 0.5 m from the existing condition at +19.00 m. While the inundation area become of 2,414 km² is reduced by 0.60 km² or by 20% from the existing condition 3,018 km².

PDAM of the City of Buntok is the supplier of clean water needs for the areas of Buntok Kota, Hilirsper, and Jelapat Hamlets and Pamait Village. Population growth, water loss and utilization of discharge that has not been optimal have become obstacles in service. The aim of the research is to evaluate the existing distribution network and development plan until 2038 as viewed from the aspect of hydraulics and water quality using WaterCAD v8i software, as well as economic analysis to determine water prices. The available discharge is 10, 000 l/s. Simulation of the existing condition produces pressure and headloss gradient that meet technical requirements, while velocity did not meet technical criteria. Water requirements for 2038 need an additional Water Treatment Plant with capacities of 30 l/s and 20 l/s. The simulation of development results met the technical requirements, being 0.3-4.5 m/s, a headloss gradient 0-15 m/km, and pressure of 0.5-8 atm. Further, the hydraulic model was used to analyse the concentration of residual chlorine. Injection at the tank inlet amounted to a constant 0.4 mg/l. Simulation of produced residual chlorine met the requirements from 0.383-0.395 mg/l. Economic analysis resulted in a water price of Rp. 6, 100.00/m3, BCR 1.23, IRR 12.14 %, and BEP of 11 years. Based on the willingness to pay being Rp. 4, 200.00/m3, the value of required government subsidies is Rp. 13, 905, 747, 800.