Kevin Filindo Tawalujan, Tiny Mananoma, Jeffry Swingly Frans Sumarauw
In 2020, flooding occurred in the village of Molibagu, causing damage and losses for the residents who live and work around the Molibagu River. One of the causes of this flood was heavy rainfall, which triggered an increase in the flow discharge of the Molibagu River. Therefore, an analysis of the flood discharge and water level in the Molibagu River is needed to minimize the potential risk of flooding and to determine effective control strategies based on developed scenarios. The objective of this research was to identify effective scenarios from several alternatives, including normalization and the addition of embankments on the left and right sides of the river, to control flooding. The Molibagu Watershed has an area of 38.7 km². Secondary data in the form of rainfall data was obtained from the Sulawesi I River Basin Office (BWSS-I). The rainfall stations ARR-MRG Kosinggolan Matayangan and MRG Bolangaso Molibagu are the sources of maximum daily rainfall data, which will be analyzed over the period from 2008 to 2022. To obtain the parameters needed to determine the peak discharge of 17.5 m³/s, the HEC-HMS software is used. After obtaining the calibrated parameters, the analysis will continue to determine the design flood discharge for various return periods using the HEC-HMS software. The design flood discharge for the return periods will then be input into the HEC-RAS software to obtain the inundation area and water surface elevation of the Molibagu River. As a form of flood control, three flood control scenarios are applied: normalization, embankments, and a combination of normalization and embankments, using RAS Mapper to model and show the extent of the inundated areas. Based on the simulation results obtained, the second scenario, which involves handling with normalization at the same elevation and based on existing flood discharge, is more effective in reducing water level height and mitigating flood overflow better than handling with levees. However, in this scenario, the river cross-section is not able to reduce the flood discharge at the 50 and 100 year return periods, so a combination of the first and second scenarios is needed to reduce the flood and there is no more inundation.
<p>In recent years, urban flood disasters in China have become increasingly serious. In mid-June 2022, the northern part of Guangdong Province was affected by continuous rainfall, and floods occurred in many rivers in the upper and middle reaches of the Beijiang River in the Pearl River Basin, causing serious floods in many cities, villages, and towns in the basin. Based on the rain and flood processes of these flood disasters and analyses of the specific disaster situations of three typical cities, this paper deeply analyzes the urban water system, vertical topography, etc. The main and secondary causes of flood disasters in the three cities are studied, and the deficiencies in the expansion of cities under different natural geographical conditions are explored through comparisons to address flood disasters. This work provides a basis for the cities to establish flood control systems that are integrated, systematic, and adapted to local conditions.</p>
AbstractIncorporating 50 years of flood data for the Manas River Kenswat Hydrological Station from 1957 to 2006, the Pettitt test and Mann–Kendall trend test are used to analyse non‐stationarity of the flood characteristic sequences. Moreover, the Pearson type‐III (P‐III) distribution, the mixed distribution (MD) and conditional probability distribution (CPD) models are employed to analyse frequency and to calculate the design flood process line. The results showed that the annual maximum peak discharge and the annual maximum flood volume are most likely to change in 1993. The MD model considering the non‐stationarity of the flood sequence is more accurate than the CPD model and the traditional P‐III distribution model. There are significant differences in the design flood process lines of the 1996 typical flood process obtained by the three methods using the same frequency scaling method. In addition, under different design standards, the design value of the MD model is 20–53% smaller than the design value approved in 2008 (approved by China Renewable Energy Engineering Institute) and 4–48% higher than the traditional P‐III distribution design value. The results can provide a new reference for the management of non‐stationary floods in Manas River.
Kondwani G. Munthali, Brian J. Irvine, Yuji Murayama
Severe watershed degradation continues to occur in the tropical regions of southern Africa. This has raised interest to harness and manipulate the potential of the watershed resources for human benefit as the populations grow. Songwe River is one such degrading watershed causing biennial flooding among other problems. In this study, climatic, land use, topographic and physiographic properties were assembled for this watershed and used in a process-based Geographical Information System (GIS) with the aim of determining the hydrological sediment potential of Songwe River watershed and quantifying possibilities of reservoir sedimentation. The study further aimed at determining the critical sediment generating areas for prioritized conservation management and the relationship between the increasing flood events in the floodplains and the rainfall trends. Based on hydrological runoff processes using the Pan-European Soil Erosion Risk Assessment (PESERA) model, the estimated amount of sediment transported downstream is potentially huge. Most of the sediment generation was established to be occurring in the upper sub-basin and specifically from built up village and degraded natural land. These trends have not only caused the increased flooding events in the lower sub-basin, but also pose a great sustainability risk of sedimentation to the proposed reservoir.
Hydro-technical constructions are very important in diminishing flooded areas and associated damage in the event of a flood. The case study for the Miletin River in the Moldavian Plateau (Eastern Romania) focusses on the historical floods of June 1985. The floods recorded at the Miletin River hydrometric stations are: 106 m3/s for Nicolae Balcescu station and 204 m3/s for Şipote station. Our analysis involves a series of simulations of a flood flow constant using the hydrological data associated with the 1985 flood. The mathematical modelling base is the high-grade terrain model (LiDAR raster type). Two flood scenarios have been carried out: the first one was based on the running of a constant flow considering the present hydro-technical constructions and works; the second scenario implied running the same flow, but without hydro-technical constructions. Bands of flooding associated to the two scenarios were generated. Flooded areas and damages were determined considering the modification of the bed by these works. Comparative analysis of flooded areas scenarios reveals, in the case of the same amount of precipitation, a downward trend in flood flows due to the presence of the hydro-technical constructions.