100-year Return Period Research Articles

Analysis and Flood Mapping of Pekalen Watershed of Probolinggo Regency Using HEC-RAS Application

Flooding is one of the natural disasters that needs attention, especially in the Pekalen watershed, Probolinggo Regency. The purpose of this research is to analyze the design flood discharge and mapping of the area potentially affected by inundation. The research stages began with arithmetic area average rainfall analysis, log pearson type III design rainfall analysis, chi squared and smirnov-kolmogorov distribution fit test, mononobe rainfall intensity, HSS Nakayasu design flood discharge analysis, and flood mapping with HEC-RAS 2D flood modeling. The design flood discharge of Pekalen watershed at 10-year return period is 421.4 m³/s, 25-year return period is 455.12 m³/s, and 50-year return period is 479 m³/s. The areas potentially affected by inundation at 25 years return periods are Sukomulyo, Sukokerto, Pajarakankulon, Kradenan, Tanjung, Karangbong, Temenggungan, Karanggeger, Ketompen, Petemon, Selogudigwetan, Selogudigkulon, Puspan, Braniwetan, Branilor, Sumbersecang, Satreyan, Maronkidul, Gerongan, Brabe, Condong, Racek, Pesawaran, Ranugedang, Jangkang, Segaran, Ranuagung, Tiris, Andungsari, Andungbiru, and Sumberaren.

Confined and mined: anthropogenic river modification as a driver of flood risk change

Rivers are often confined by structures and subjected to aggregate mining. In dynamic rivers, these interventions cause changes to riverbed and bank topography that potentially cause changes in hydraulics and flood risk. Repeat, system-scale, high-resolution topographic surveys of the gravel-bed Bislak River, the Philippines, are used to quantify annual morphological change and, using two-dimensional hydraulic modelling, to simulate changes to flood risk. Aggregate mining exports sediment and creates pitted topography, and embankments cause both deeper channels and disconnect the river from its floodplain. The consequently increased channel capacity reduces flood risk, with up to a 5% decrease in inundated areas for 10- to 100-year return periods. Sediment deprivation also increases bed shear stress that can induce scour, infrastructure damage and increased flood impacts. Rising global floodplain populations and increasing demand for aggregate ensure that sustainably managing geomorphologically dynamic rivers to support floodplain development and mitigate flood impacts remains a pertinent challenge.

A new approach on design and verification of integrated sustainable urban drainage systems for stormwater management in urban areas.

Stormwater runoff control is often a concern due to urbanization and extreme rainfall events. Sustainable urban drainage systems can support traditional hydraulic networks in rainwater management by providing local runoff disposal and reuse of collected stormwater. The objective of the study is based on an innovative analytical-probabilistic approach for evaluating the functioning of rainwater tanks in stormwater management with the potential for using collected water for non-potable purposes. A pilot case of a rainwater tank integrated with an infiltration system was considered within the framework of the Polisocial Award 2023at the Off-Campus Cascina Nosedo of Politecnico di Milano (Italy). The performances of the rainwater tank in satisfying irrigation were evaluated through a new version of an analytical probabilistic approach, whose validation confirmed it is promising and offers excellent perspectives in the field of stormwater management. The probabilistic equation developed in this study relates the probability of rainwater reuse to the main parameters involved in the process (i.e., storage volume, irrigation area, rainfall depth, etc.), enabling to define the management rules of the storage for the optimization of the stormwater management. In the application, to consider an irrigation area lower than 30m2, ensures the fully meeting of the requirements by the system in the rainiest year, and to avoid falling below the 50% (2-year return period) during the driest year.

ANALISIS PENGARUH PERUBAHAN TATA GUNA LAHAN MENGGUNAKAN EPA-SWMM DI DAS KRUKUT

Flooding in Jakarta, a lowland area traversed by several rivers, has become a recurring challenge due to increased development, business activities, and land-use changes. This study aims to calculate the design flood discharge for various return periods and analyze the impact of land-use changes on flooding in the Krukut River Basin. The analysis utilized ArcGIS for land-use changes and EPA-SWMM for hydrological and hydraulic simulations. Results indicate that changes in land cover have led to an increase in flood discharge, for instance, in the 2-year return period from 106.01 m³/s (2006) to 108.25 m³/s (2017), and in the 100-year return period from 204.61 m³/s (2006) to 208.93 m³/s (2017). Mitigation efforts, such as the implementation of infiltration wells, were effective in reducing flood discharge, with EPA-SWMM simulations showing a reduction in the 100-year return period from 208.93 m³/s to 186.22 m³/s. This study recommends the implementation of infiltration wells and the enforcement of spatial planning regulations (RTRW) as conservation strategies to mitigate flood risks in the Krukut River Basin.

Multidimensional Urban Waterlogging Risk Assessment Based on a Refined Inundation Model

To enhance the scientific and accurate assessment methods for urban waterlogging risk in City B and to promote sustainable urban development, this paper conducts a detailed evaluation of waterlogging risk from three dimensions: pedestrian safety, road traffic, and waterlogging-prone areas. After considering existing monitoring technologies and the constructed waterlogging model, the paper identifies standing water depth, standing water duration, and standing water velocity as the key indicators for waterlogging risk assessment and utilizes scenario simulation methods to evaluate waterlogging risk across these dimensions. Additionally, the paper employs boundary conditions of 2-h short-duration rainfall with a 5-year return period and 24-h long-duration rainfall with a 50-year return period for the assessment. The evaluation results indicate that, for pedestrian safety, under both short and long-duration rainfall conditions, low-risk areas represent the largest proportion of risk areas, reaching 6.36% and 10.83% of the total area, respectively. In the road traffic assessment, the proportions of severely congested roads under short- and long-duration rainfall conditions are 27.06% and 57.15%, respectively. In the evaluation of waterlogging-prone areas, high-risk areas account for the largest proportion of risk areas under both short- and long-duration rainfall conditions, reaching 0.64% and 1.42% of the total area, respectively.

Redesigning the Fuse Plug, Emergency Spillway, and Flood Warning System: An Application of Flood Management

According to the World Health Organization (WHO), floods are one of the most important natural disasters in the world, resulting in the severe loss of human lives and intense destruction of infrastructure. The frequent floods in recent decades have caused most parts of Iran to be affected by periodic and destructive floods. Consequently, the casualties and financial losses of floods have increased significantly. The present study aims to investigate redesigning the fuse plug, emergency overflow, and flood system at Ramshir Dam, Iran. In this regard, using a two-dimensional mathematical model, floods with a return period of 10 and 100 years with different scenarios have been investigated. Four scenarios were analyzed, including the current situation, flood channel dredging scenario, flood channel overhaul scenario, and flood channel overhaul scenario with reservoir dredging. The results show the following: (1) The flood channel in its current state cannot even discharge flows lower than the design, i.e., 1400 m3/s, and the flow overflows from the embankments on its sides. (2) Also, the reservoir dredging prevents the failure of the second fuse plug in the 100-year return period (flow rate 4370 m3/s). (3) Discharge more than 2400 m3/s cubic meters led to the activation of the first fuse plug. (4) The present research findings are of particular and essential importance in flood management. (5) The results of this research were based on the rehabilitation and simulation of the diversion dam facilities in the control and conveyance of flood and on three factors of spillway, flood channel, and flood plain, and the correct function of the fuse plug was reviewed.

Flood analysis using the HEC-RAS software for Antakya Altınçay Creek

Flood is one of the most important disasters in the world. Floods, common in our country, are the second disaster after the earthquake in terms of loss of life and property caused by natural disasters and the first among climatic disasters. The district of Antakya is located where streamflow has a high flow coefficient. Because of flooding in Altınçay Creek which flows through the center of Antakya into the Orontes River, flood studies need to be carried out and the necessary precautions taken to prevent flooding. In this study, peak discharges for 2, 5, 10, 25, 50, and 100-year return periods of Altınçay Creek passing through residential areas in Antakya were determined by SCS and DSI synthetic methods. Using these estimated peak discharges the water profile along the Altınçay Creek route has been simulated using HEC-RAS software, and the flood risk areas were determined on cross-sections basis. As a result, flood risk was not observed in peak discharge for return periods of 2, 5 and 10 years. However, flood events were observed at 16, 51, and 73 different cross sections in peak discharges for return periods of 25, 50, and 100 years respectively. To reduce flood damage, it was suggested that the cross-sectional areas having flood risk must be increased.

Research on optimal scheduling of minor and moderate floods for cascade reservoirs in the lower reaches of the jinsha river considering power generation

The comprehensive cascade reservoir system is extensively used for flood control and power generation. Traditional reservoir scheduling often treats these tasks as competing objectives, prioritizing flood control during the flood season and neglecting power generation benefits. This approach, primarily applied to large floods, leads to hydraulic resource wastage and power generation loss during minor and moderate floods. The lower Jinsha River cascade reservoirs have significant flood control storage capacity, allowing part of the capacity to be used for maintaining higher water levels without compromising safety under minor and moderate floods within a 20-year return period. This paper proposes an optimal scheduling model that considers both flood control and power generation tasks for the lower Jinsha River cascade reservoirs. The Multi-objective Particle Swarm Optimization (MOPSO) algorithm was used to find non-inferior solution sets. An evaluation index system was developed to select optimal solutions under different flood frequencies, using the Minimum Discriminant Information Principle and VIKOR model. The results indicate that the optimal scheduling scheme under 20-year, 10-year, and 5-year return period floods can enhance power generation by 1.64, 1.71, and 1.35 billion kWh, respectively, compared to conventional scheduling. This approach supports coordinated flood control and power generation scheduling, contributing to the high-quality development of the Yangtze River Economic Belt.

PENGENDALIAN BANJIR SUNGAI BENGKANG UNTUK MENDUKUNG KAWASAN EKONOMI KHUSUS MANDALIKA

Changes in land use that have occurred over a period of several years in the Kuta area have resulted in a lack of water catchment areas. The impacts caused by the lack of catchment areas are flooding and reduced water quality in rivers. The flood disaster in the Bengkang River caused damage to bridge infrastructure and people’s homes. The Bengkang river basin is divided into 3 sub – basins with a total area of 10,45 km2. Based on the results of the design flood analysis using the Nakayasu synthetic unit hydrograph method, the largest flood discharge value was obtained, namely 32,859 m3/second for a return period of 25 years. Hydraulic modeling was carried out to determine the water level and the ability of the river section to receive flow using HEC-RAS 6.1 software. Based on the simulation results with a return period of 5 years, it is known that flooding occurs in the middle and lower reaches of the Bengkang River, so structural mitigation is needed, namely normalization and repair of embankments. A 25-year return period flow simulation was carried out using a cross – section of the channel plan and no runoff was obtained in the Bengkang River.

Variations in Present and Future Hourly Extreme Rainfall: Insights from High-Resolution Data and Novel Temporal Disaggregation Model

Extreme rainfall-induced events adversely affect agriculture, infrastructure, and socioeconomic development in a region. Therefore, a comprehensive understanding of their occurrences and past and future variability in the context of global warming is imperative, especially at the fine temporal (sub-daily) and spatial (local to regional) scales for better contextualizing inferences from a policymaking perspective. This study provides a detailed analysis of global warming’s impacts on extreme rainfall in Jiangsu Province, utilizing the latest high-resolution ERA5-Land reanalysis data and the latest climate models. A novel temporal disaggregation model was developed to predict future hourly extreme rainfall. The results show that the bias-corrected model reduced the overestimation of extremes by as much as ~7.4% for the location parameter and accurately reproduced the spatial variability of rainfall. Projections from eight climate models indicate a future increase in rainfall intensity by an average of over 7%. Moreover, the projections indicate two contrasting trends for different event durations: short-duration events (e.g., 1 h) show a 7.1% increase at the 5-year return period and a more pronounced 8.9% increase at the 50-year return period. Conversely, long-duration events (e.g., 24 h) experience an 8.4% increase at the 5-year return period and a smaller 6.0% increase at the 50-year return period. This suggests that rarer, short-duration events are expected to increase more than less rare ones, while rarer, long-duration events show a smaller increase than their less rare counterparts. Addressing spatial heterogeneity in extreme rainfall patterns provides actionable insights for climate adaptation and mitigation, supporting initiatives like the ‘Jiangsu Province Climate Change Adaptation Action Plan’. This study underscores the need for policy-driven, community-led climate actions to mitigate flood risks and enhance resilience in a region vulnerable to flooding amidst global warming and increasing human interventions.

Normalization of Suak Ujong Kalak estuary as a flood reduction effort for Meulaboh city

Abstract Meulaboh City frequently experiences flooding, with runoff flowing into the Suak Ujong Kalak Estuary, a natural outlet for the city’s drainage system. Currently, the estuary is unable to effectively accommodate the runoff, exacerbating the flood risk. This study aims to evaluate the existing condition of the Suak Ujong Kalak Estuary and propose a normalization plan to improve flood control. The research employs a descriptive-quantitative methodology, involving field surveys, data collection, and hydrological and hydraulic analyses. The hydrological analysis includes rainfall frequency analysis, chi-square testing, and rainfall intensity calculation using the Mononobe method. Flood discharge estimation is based on the Rational method for a 25-year return period. Hydraulic analysis is conducted using HEC-RAS 6.3.1 software. The results show that the estuary receives an inflow of 79.33 m3/second, which exceeds its current capacity. Hydraulic analysis reveals that the estuary cannot accommodate the discharge, causing overflow with an average height of 0.6 meters and a storage capacity of 40,798.43 m3. To address this, the study recommends a normalization effort, involving excavation with an average depth of 1 meter, to improve the estuary’s capacity and reduce flooding in Meulaboh City.

Joint Probability Distribution of Extreme Wind Speed and Air Density Based on the Copula Function to Evaluate Basic Wind Pressure

To investigate an appropriate wind load design for buildings considering dynamic air density changes, classical extreme value and copula theories were utilized. Using wind speed, air temperature, and air pressure data from 123 meteorological stations in Shandong Province from 2004 to 2017, a joint probability distribution model was established for extreme wind speed and air density. The basic wind pressure was calculated for various conditional return periods. The results indicated that the Gumbel and Gaussian mixture model distributions performed well in extreme wind speed and air density fitting, respectively. The joint extreme wind speed and air density distribution exhibited a distinct bimodal pattern. The higher the wind speed was, the greater the air density for the same return conditional period. For the 10-year return period, the air density surpassed the standard air density, exceeding 1.30 kg/m3. The basic wind pressures under the different conditional return periods were more than 10% greater than those calculated from standard codes. Applying the air density based on the conditional return period in engineering design could enhance structural safety regionally.

Probabilistic assessment of peak discharge and debris flow concentration in the Surma River using Monte Carlo simulation

ABSTRACT Rivers, vital for household and industrial needs, vary in size due to erosion and sedimentation and are significantly impacted by climate variations. Accurate estimation of river characteristics like discharge and debris flow concentration is essential for designing hydraulic systems in flood-prone areas. This study assesses these factors in the Surma River, located in Sylhet, Bangladesh, by using Monte Carlo simulation to reduce uncertainty. The simulation optimized the time of concentration against water level height. Peak discharge results for 5, 10, 25, 50, and 100-year return periods were 1,904.66, 2,174.77, 2,543.63, 2,846.72, and 3,124.25 m3/s, with corresponding debris flow concentrations (Cv) of 0.5499989, 0.5499976, 0.5499967, 0.5499940, and 0.5499147. During the monsoon season, the maximum peak discharge reached 5,095.58 m3/s with a Cv of 0.7886368. Model validation using the F test and R2 test demonstrated high accuracy, indicated by low mean squared error (MSE), mean absolute error (MAE), and root mean square error (RMSE), along with a coefficient of determination (R2) of 0.7097. The p-value from the F test (0.197852) indicated strong alignment between predicted and observed discharges. This study enhances understanding of flow dynamics, improves prediction precision, and underscores the importance of historical data in flood risk assessment.

Pesisir Barat Lampung Wave Characteristic Comparative Study

The need for ocean data is important to increase the utilization of ocean areas. A facility, development, system, or structure in the ocean cannot be planned properly without data in that ocean. One of the important data in water areas is ocean waves. In the offshore area of Pesisir Barat, wave characteristic data is still very hard to find. Knowledge of the ocean characteristics of the Pesisir Barat waters is needed, one of which is in the form of wave characteristics. To obtain more comprehensive information, two satellite reanalysis data sources were analyzed. The average height of significant wave height in the Perisir Barat is 1.75 to 2.25 m from BMKG and only 0.25 to 1.00 m from ECMWF. Based on the wave direction, the ocean waves in the Pesisir Barat move North to Northwest (NW), perpendicular to the coastline. The distribution of the annual maximum significant wave height matches the theoretical Log-normal distribution. Extreme significant wave height is obtained with a value of 4.10 to 4.29 m for a 100-year return period and 3.09 to 3.39 m for a 1-year return period. In terms of design or study of maritime potential in the western waters of Lampung, these values can be a benchmark as a basic study of wave characteristic data.

Identifying homogeneous hydrological zones for flood prediction using multivariable statistical methods and machine learning

One method for estimating floods in areas lacking statistical data is the use of regional frequency analysis based on machine learning. In this study, statistical and clustering-based approaches were evaluated for flood estimation in the Karkheh watershed. The hydrological homogeneity of the obtained zones was then assessed using linear moments and heterogeneity adjustment methods proposed by Hosking and Wallis. Then, the ZDIST statistic was used to calculate the three-parameter distributions for stations within each hydrologically homogeneous cluster. These parameters were computed using linear moments, and floods with different return periods at each station were estimated using regional relationships. The results indicated the creation of two clusters in this area, with five stations in cluster one and 11 stations in cluster two. The statistical homogeneity values for clusters one and two were calculated as 0.33 and 0.17, respectively, indicating the homogeneity of each region. Generalized Pearson type III and generalized extreme value distributions were selected as the best regional distributions for clusters 1 and 2, respectively. The results also showed that floods could be estimated for return periods of 2, 5, 25 years, and more. The highest estimated flood is predicted at the Jelugir-e Majin station, where the flood with a 2-year return period reaches 1034 m3 s−1. This increases to 5360 m3 s−1 for a 100-year return period. The approach presented in this study is recommended for similar regions lacking complete information.

A novel SPM wind-wave-aquaculture system: Concept design and fully coupled dynamic analysis

A fully-coupled aero-hydro-net-mooring time-domain model is constructed by coupling AQWA and FAST with open-source code F2A, initially used for preliminary analysis of a turret-moored deep-sea aquaculture vessel powered by wind energy. Due to wind-wave complementarity at the site, an optimal point absorber is employed to suppress motion around energetic wave periods, particularly near the vessel's heave and pitch natural periods. A framework for detailed analysis of the deep-sea aquaculture vessel with hybrid wind-wave power generation is then established in the time domain, with results compared to preliminary frequency domain findings. Fifteen environmental conditions, including steady and turbulent winds, regular and irregular waves, and extreme scenarios representing 50- and 100-year return periods in the Northern Bohai Sea, are considered. The study verifies the rationality of the internal turret mooring system and the point absorber, providing detailed guidance for mooring design by analyzing mooring dynamics. This research focuses on deep-sea aquaculture vessels and hybrid wind-wave energy systems, emphasizing the complex coupling effects between them.

A probabilistic approach to combine sea level rise, tide and storm surge into representative return periods of extreme total water levels: Application to the Portuguese coastal areas

Coastal hazard and vulnerability assessments in the context of climate change usually rely on the estimation of total water levels (TWLs) through a deterministic approach, consisting on the simple summation of its components: mean or median sea level rise projections, maximum tide values, and extreme storm surge projections based on return periods (usually of 100 years). However, such methodology yields TWLs compatible with return periods much greater than the commonly used ones in hazard, vulnerability and risk assessments, occasionally by more than one order of magnitude (thousands of years). Deterministic approaches also neglect uncertainties in TWL components, or other sources of variability, as random variables with known probability density functions. Here, we present, validate, evaluate and apply a methodology to provide a numerical solution for the estimation of representative return periods of extreme TWLs, for any coastal area, to which the three cumulative density functions of SLR, tide and storm surge are given. The use of representative TWLs is crucial for accurate hydrodynamical modelling of coastal flooding, both along inland waters and coastlines facing the open ocean, as well as to coastal vulnerability and risk assessments. Using two dynamic ensembles, the projected 4-, 25- and 100-year representative TWL return periods are estimated across five vulnerable areas along the Portuguese coastline and compared with deterministic TWLs. Our results show that the methodology can accurately reproduce the observed TWL distributions and return values associated with extreme events, these being generally lower than the deterministic ones, undergoing, nevertheless, greater changes towards the end of the 21st century. We provide a baseline for future studies to delve into more accurate and realistic translation of physical, anthropogenic-driven climate change effects into socioeconomic impacts along the coastal areas.

Assessing the characteristics of extreme floods in Nepal

Abstract. This study examines the characteristics (magnitudes, trends, and frequency of occurrences) of extreme floods in Nepal, a country that is at significant risk from floods. Daily discharge data from 1980 to 2015 of three gauging stations (Chisapani of Karnali Basin, Devghat of Narayani Basin, and Chatara of Koshi Basin) were used to assess the largest 1 % of flows, the annual top five high flows, and floods of different return periods (2-, 5-, 10-, 20-, and 100-year). In addition, temporal trend analysis of the flood peaks was carried out using the Mann–Kendall test and Sen's slope estimates. Results show that the magnitudes of the largest 1 % flows range from 6310 to 17 900, from 6967 to 12 100, and from 6080 to 9610 m3 s−1 at Chisapani, Devghat, and Chatara, respectively. The monsoon, especially from mid-June to early September, consistently witnesses over 90 % of 1 % extreme flows, with August registering more than 51 % of these occurrences. July and August combine for 81 % of the top five flow events, predominantly in August. Despite insignificant flow changes at a 95 % confidence level, extreme floods (2-, 5-, 10-, 20-, and 100-year return periods) are concentrated heavily in July and August, with August's second fortnight recording the most flood events. This assessment emphasizes July and August as critical months for extreme floods, aiding Nepalese authorities in planning dynamic resource allocation, disaster response, and effective flood management.

Probabilistic fault displacement Hazard analysis in an extensional setting: Application to a strategic Dam and methodological implications

We present a Probabilistic Fault Displacement Hazard Analysis (PFDHA) for a strategic dam located in the Upper Tiber Valley (Northern Apennines of Italy) claimed to be sited on a supposed capable fault (Montedoglio fault). We verify the seismic capability of the Montedoglio fault through detailed geological and geophysical analyses. We find no evidence for considering the Montedoglio fault as an active and capable structure, the fault being constituted by a system of discontinuous parallel faults, apparently inactive since more than 56 ± 3 ka, and likely unable to nucleate strong surface rupturing earthquakes. Since the dam lies on the hanging wall of the closest major active fault of the area (Anghiari normal fault, ∼1.5 km away), we investigate the likelihood of having distributed faulting at the dam's site in case of a strong surface-rupturing earthquake occurring on the Anghiari fault. We apply a probabilistic approach to obtain hazard curves of exceedance of vertical displacement at the dam's site for different rupture scenarios. We show that the mean hazard curve is always below an annual frequency of exceedance of 1 × 10−5, corresponding to displacement values below 1 cm over 100,000 years of return period. The study highlights several weaknesses and uncertainties in using PFDHA with state-of-the-art models, suggesting the need for improvements to enhance their applicability in earthquake engineering geology practice.

ANALISIS DEBIT RENCANA UNTUK PERENCANAAN BANGUNAN PENGENDALI BANJIR DI DAS WAI RUATA KABUPATEN MALUKU TENGAH

The high rainfall, rapid urbanization, and the presence of impermeable surfaces have drastically increased surface runoff, overwhelming river systems with high water volumes. Changes in land use and rapid population growth further escalate flood risks. Analyzing planned discharge rates and flood control building planning becomes urgent to mitigate losses and risks caused by floods in the Wai Ruata watershed. Calculations indicate that for the Q100 Log Normal (2475.17 m3/s, the channel height is 2.50302 m, closely approximating public information (2.5 m), with a difference of 0.00302 m or 0.302 cm. This suggests that the calculated maximum flood water level based on planned discharge analysis using the rational method for Log Normal probability of 2.503 m is reasonably accurate. It can serve as a reference for flood control building design heights, potentially lasting around 100 years in the Wai Ruata watershed. Planned flood discharges in the Wai Ruata watershed are as follows: for a 2-year return period, 505.80 m3/s (Gumbel), 449.27 m3/s (Log Normal), 462.56 m3/s (Log-Pearson Type III); for a 50-year return period, 1868.80 m3/s (Gumbel), 2016.26 m3/s (Log-Normal), and 1837.18 m3/s (Log-Pearson); and for a 100-year return period, 2137.98 m3/s (Gumbel), 2475.17 m3/s (Log-Normal), 2166.93 m3/s (Log-Pearson). Gumbel planned flood discharge data can be used for a 25-year lifespan of water structures, whereas for a 100-year lifespan, Log-Normal planned flood discharge is more suitable.