ANALISIS DEBIT PUNCAK PADA DAS AIR MANNA BAGIAN HILIR MENGGUNAKAN PENDEKATAN METODE HIDROGRAF SATUAN SINTETIS (HSS) SNYDER DAN HEC-RAS 5.0.7

Floods is a disaster which is one of the causes of failure of watershed managemen. High rainfall is also a factor in flooding. As a result the river cross section is not able to accommodate the flow of water and cause the river to overflow. This research was conducted to determine the amount of peak discharge Sub-DAS Air Manna Bagian Hilir and identify areas prone to flooding. This study uses a synthetic unit hydrograph (HSS) Snyder and HEC-RAS 5.0.7. Hydrological analysis results obtained from the peak discharge at Sub-DAS Rindu Hati using HSS Snyder for a return period of 2, 5, 10, 25, 50 and 100 yearsthat is 743,627 m3/sec, 839,491 m3/sec, 897,761 m3/sec, 962,599 m3/sec, 1008,717 m3/sec, and 1052,800 m3/sec with a peak time of 5,915 hours. After analysis using software HEC-RAS 5.0.7, DAS Air Manna no longer able to accommodate flow rates occur.

Minimisation of Overestimation of River Flows in 1D- Hydrodynamic Modeling

One-dimensional hydrodynamic models overestimate river cross-section derived from freely available SRTM DEMs. The present study aims to minimize the overestimation of river flow. DEM-extracted cross-sections obtained from 30 m and 90 m resolutions show higher elevation values than the actual river cross sections of Krishna and Bhima rivers, India. To minimize the overestimation of the river flow, DEM-extracted cross-sections are modified using known cross-section of the river. The corrections for cross sections extracted from DEM, are obtained by subtracting the DEM-derived cross-sections from a known cross-section of the river. Monsoons flows that occurred in years 2006 and 2009 in Krishna and Bhimariver have been used for modeling. The MIKE HYDRO River model performance with modified DEM-extracted cross-sections of river improves as the correlation coefficient, root mean square error, index of agreement, Nash Sutcliffe efficiency & Percentage deviation in peak (%) values are improved.

A Review of Numerical Simulations of Secondary Flows in River Bends

River bends are one of the common elements in most natural rivers, and secondary flow is one of the most important flow features in the bends. The secondary flow is perpendicular to the main flow and has a helical path moving towards the outer bank at the upper part of the river cross-section, and towards the inner bank at the lower part of the river cross-section. The secondary flow causes a redistribution in the main flow. Accordingly, this redistribution and sediment transport by the secondary flow may lead to the formation of a typical pattern of river bend profile. It is important to study and understand the flow pattern in order to predict the profile and the position of the bend in the river. However, there are a lack of comprehensive reviews on the advances in numerical modeling of bend secondary flow in the literature. Therefore, this study comprehensively reviews the fundamentals of secondary flow, the governing equations and boundary conditions for numerical simulations, and previous numerical studies on river bend flows. Most importantly, it reviews various numerical simulation strategies and performance of various turbulence models in simulating the flow in river bends and concludes that the main problem is finding the appropriate model for each case of turbulent flow. The present review summarizes the recent advances in numerical modeling of secondary flow and points out the key challenges, which can provide useful information for future studies.

Case Study: Influence of Three Gorges Reservoir Impoundment on Hydrological Regime of the Acipenser sinensis Spawning Ground, Yangtze River, China

After the construction of the Three Gorges Dam (TGD) in China, the downstream has been affected by the reduction in sediment discharge and regulation of flow processes, which have resulted in severe scouring and changes hydrological regime. Consequently, the spawning ground of Chinese sturgeon distributed along the downstream Yichang reach could be affected. This study examined the effects of TGD on the streamflow, sediment load and channel morphology downstream based on in situ measured data. Results showed that, after the impoundment of the TGD, sediment load at the downstream Yichang hydrological station decreased significantly, and the Yichang reach continued to be scoured. The distribution of erosion was uneven, and the scouring mainly occurred in the branching channels. The channel gradient and riverbed roughness increased with the erosion of the river cross section. After more than 10 years of erosion, the riverbed scouring and armouring in the Yichang reach was basically completed, thus we expected that the spawning grounds of Chinese sturgeon could be retain as the riverbed tends to be stable. The findings in this work have implications in the protection of the critically endangered Chinese sturgeon.

PENGARUH DEBIT ALIRAN TERHADAP SEDIMENTASI DI SUNGAI LEMATANG KABUPATEN LAHAT

Sedimentation that occurred in the Lematang River in Lahat Regency was caused by river bank erosion, construction activities, and household waste brought by the flow discharge. The flow of the Lematang river will certainly affect the amount of sedimentation that will occur in the Lematang river.Based on the test results of the analysis of sediment sample filters, the results obtained d50 = 0.425 mm, and the results of research on the river cross-section with the aim to calculate the volume of base sediment sediment / bed load that occurs by flowing Lematang river flow obtained H = 0.41 m, B = 0 , 41 m, V = 2,650 m / sec.Based on the results of the analysis of the influence of flow discharge on sedimentation in the Lematang River, Lahat Regency, it is known that the type of bed load sediment in the Lematang River is poorly graded sand with large sediment transport carried by the flow discharge in the study segment of 0.022 (m3 / sec) with the duboy's method and 0.0000004 (kg / sec / m) with the shield's method, so the sediment volume for the next one year is 693,792 (m3 / sec) m for the duboy's method and 126,144 (kg / sec / m) for the shield's method .

Solving Inverse Problems of Unknown Contaminant Source in Groundwater-River Integrated Systems Using a Surrogate Transport Model Based Optimization

The paper presents a new approach to identify the unknown characteristics (release history and location) of contaminant sources in groundwater, starting from a few concentration observations at monitoring points. An inverse method that combines the forward model and an optimization algorithm is presented. To speed up the computation, the transfer function theory is applied to create a surrogate transport forward model. The performance of the developed approach is evaluated on two case studies (literature and a new one) under different scenarios and measurement error conditions. The literature case study regards a heterogeneous confined aquifer, while the proposed case study was never investigated before, it involves an aquifer-river integrated flow and transport system. In this case, the groundwater contaminant originated from a damaged tank, migrates to a river through the aquifer. The approach, starting from few concentration observations monitored at a downstream river cross-section, accurately estimates the release history at a groundwater contaminant source, even in presence of noise on observations. Moreover, the results show that the methodology is very fast, and can solve the inverse problem in much less computation time in comparison with other existing approaches.