Design Flood Level Research Articles

Evaluating Design Flood Levels Using a Machine Learning-based Costal Compound Flood Level Model

Coastal floods, a type of compound disaster, results from the interactions between rainfall and tides. However, in Korea, the design flood level for coastal areas typically relies on the average water level according to the tide, ignoring this interaction. This study aimed to address this gap by developing a machine learning-based compound flood level model that incorporates the interactions between rainfall and tides. It also evaluated the adequacy of the design water level in the Taehwa River basin, a representative tidal river. Before developing the model, Discrete Wavelet Transformation (DWT) was used to identify the components of the compound flood level. The DWT results indicated that the compound flood level comprised three elements: rainfall-runoff, tides, and noise. A Long Short-Term Memory (LSTM) model was then created using these elements as input to estimate the compound flood level for a 200-year frequency, which is the design frequency of the Taehwa River. The compound flood level calculated by the model was 6.15 m, which is higher than the established design flood level of the Taehwa river (5.79 m). This discrepancy indicates that the current flood measurements for the Taehwa River are inadequate in accounting for compound flooding. Based on these findings, we recommend incorporating the compound flood concept when calculating the design water levels in coastal areas.

Numerical calculation of seepage field and stability analysis of dam body of closed tailings pond

Abstract In this study, taking a certain iron ore tailings pond as the research object, a closed pond engineering design was conducted to ensure its sustained and stable operation. Firstly, installation of a flood drainage system (spillway) and closure of the existing overflow tower and drainage pipe are suggested. Secondly, numerical analysis is conducted on the seepage field of the dam body to determine the position of the saturation line of the dam body under normal water storage level and design flood level. Subsequently, the stability of the dam body under various working conditions is assessed using the limit equilibrium method.

Water Hammer Characteristics and Component Fatigue Analysis of the Essential Service Water System in Nuclear Power Plants

Due to the operation conditions and system characteristics of the essential service water system of nuclear power plants, water hammer pressure fluctuates in each transient process. In order to further analyze the characteristics of the water hammer and the harm this can cause to system equipment, this paper uses one-dimensional transient computing software to simulate the water hammer characteristics of the system under different operating conditions and at different water levels. The instantaneous pressure data of water hammer in the essential service water system were used as input conditions for fatigue analysis of components, and the fatigue damage of at-risk parts was calculated. The results show that the pressure fluctuation due to single pump outage is greater than that due to single pump start-up and the start-up of double pumps. The maximum pressure of the system under the design flood level is greater than that of other water levels, and the maximum pressure of the system under each working condition is 3.87 MPa. The most at-risk part of the system pressure fluctuation is the return valve, followed by the valve after a bend in a pipe and the tee pipe fitting. In the whole system, the joint of the main branch of a tee pipe experiences the greatest fatigue damage, and the theoretical fatigue life is 127.55 years.

Two‐dimensional morphological model for prediction of erosion of a reach of Brahmaputra River using MIKE 21C software with hydrodynamics and river morphology modules

AbstractUnderstanding the morphological dynamics in highly braided rivers, like the Brahmaputra, is crucial for effective river management. To gain this understanding, data is essential for mathematical modeling, enabling short and medium‐term predictions of morphological changes. Our study focused on the Palasbari‐Gumi stretch of the Brahmaputra River, utilizing a two‐dimensional morphological model (MIKE‐21C). Our objectives were to predict erosion patterns, plan protective measures, and anticipate morphological changes. Author conducted multiple models runs under various hydrological scenarios. For coarse sand, the model projected an annual sediment load of 257 Mt/year in 2021, with a bankfull discharge of 314 Mt/year. Historical records noted 400 Mt/year sediment load in the Brahmaputra. Importantly, our model's predictions closely matched empirical data, especially regarding ADCP velocities, design flood levels, and annual sediment load. Peak model velocities deviated by less than 9% from ADCP measurements, predominantly within acceptable limits. Predicted flood levels for bankfull discharge conditions achieved nearly 96% accuracy at the Gumi site. This study highlights the role of predictive modeling in guiding river training measures, especially in dynamic braided river systems like the Brahmaputra, over a two‐3 year horizon.

Assessment of the impact of climate change and flooding on bridges and surrounding area

Climate change has the potential to significantly impact transportation infrastructure performance. Bridges crossing rivers are designed to withstand a maximum flood level (design flood) considering the expected frequencies and magnitudes of floods in the area. The design flood level ensures the safety of the bridge without being damaged against historical flooding levels. However, flood magnitude and/or frequency are expected to increase in some regions due to climate change, and therefore, bridges may not be able to maintain their serviceability and safety, resulting in significant risk to users and economic losses. This problem is approached in this paper by investigating the effects of flooding and climate change on bridges crossing rivers and surrounding areas. The input of the proposed methodology is the river flow for various climate change scenarios as well as the topography and bridge characteristics. Flood frequency analysis is used to provide information about the magnitude and frequency of annual maximum river discharges under a changing climate. Afterwards, several risk assessment indicators are computed for the bridge and its surrounding area. In addition, stochastic Poisson process is integrated to account for the randomness of floods arrivals and to investigate stochastically the probability of exceeding the design flood level. The proposed methodology is illustrated with a case study in the United Kingdom. The results indicate that the risk of flooding, and associated consequences, would increase for the case study when considering more pessimistic climate change scenarios. Findings from this study can be used to inform decision making for improving bridges’ resilience.

Non-stationarity in extreme rainfalls across Australia

Future flooding is likely to exceed current design flood levels which are based on historical extreme rainfall characteristics. The Clausius-Clapeyron relationship explains the intensification of extreme rainfalls as approximately 7% per one degree warming as atmospheric water holding capacity increases with temperature. Therefore, to prepare for a future warmer climate, we need to develop methodologies to project future rainfall intensities across the range of durations and exceedance probabilities used in engineering design. However, the studies that have investigated changes in extreme rainfalls across Australia have had disparate results and are not spatially or temporally comprehensive – hampering our understanding of changes in extreme rainfalls across different durations and exceedance probabilities.This study investigates the impact of climate change on rainfalls from the annual maximum to the 1 in 100-year rainfall across a range of storm durations for the continent of Australia. We find increases in short duration (<1 h) annual maximum rainfall are greater than increases in long duration (>1 h) annual maxima across Australia from 1967 to 2021. These results are consistent regardless of the data period or data set chosen for analysis. We estimate events rarer than the annual maxima through fitting non-stationary Generalize Extreme Value models. We find that events of rarer severity have increased more than frequent events. Further, we identify the parameterisation of a model with non-stationary location and scale parameters to capture the changes in historic design quantiles that are consistent with our physical understanding of rainfall intensification, empirical quantile changes, and historical trends. We conclude that trends in annual maxima are best represented by non-stationary models that incorporate changes in both location and scale parameters, not by solely varying either location or scale parameters.

Analysis of flood control risk in floodwater utilization considering the uncertainty of flood volume and peak

Introduction: A design flood is a hypothetical flood used for the design of reservoirs and other hydrologic engineering infrastructures. Among many hydrological properties of a design flood, flood volume and peak can significantly affect the safety of reservoir operation. However, the uncertainty of flood volume and peak has rarely been considered in the risk analysis of reservoir operation regarding floodwater utilization.Methods: In this paper, a general risk analysis framework that integrates the Monte Carlo sampling method and the most likely event selection method is proposed to calculate the risk of operating a single reservoir. By generating a large amount of stochastic bivariate flood data, the most likely design values were selected for a given return period. The probability of the maximum water level exceeding the current design flood level was calculated based on the simulation of flood control operation under various floodwater utilization schemes.Results: The model is applied to the Shagou reservoir in the Shuhe River basin, China. The results show that the design flood volume and flood peak obtained by the bivariate joint return are 7.59% and 8.22% higher than those from univariate frequency analysis, respectively; the joint return period of bivariate design value spans from 10a to 1000a compared to the historical data; and the flood control risk at Shagou reservoir is 0.29 under current flood control operations based on the uncertainty of flood volume and peak.Discussion: Moreover, the marginal benefit may contain floodwater utilization and a transmission risk effect between different node projects in the flood control system.

Stability analysis of slopes based on cloud model-Monte Carlo coupling

Risk analysis of dam slopes is crucial for ensuring the safety and stability of hydraulic engineering. To improve the accuracy and reliability of risk analysis, we adopt the cloud theory approach and conduct a study on the distribution types of soil shear strength indicators based on indoor geotechnical tests. We propose a “cloud model-Monte Carlo” coupling model that uses the cloud model to describe the uncertainty of risk factors and determine the probability distribution types of shear strength parameters, while the Monte Carlo method is used to simulate random variables in the model. The effectiveness of the proposed model is validated through a risk analysis of a slope of an earth-rock dam, with results showing significantly greater accuracy and reliability compared to traditional methods. The calculation results show that the risk probability corresponding to the design flood level of the dam is 9.01×10-6, exceeding its allowable risk standard of 0.5×10-6, hence the need for reinforcement treatment. The proposed model can accurately evaluate the risk of dams and provide the scientific basis for decision-making in dam safety management.

Assessment of reservoir response to flood conditions to optimize hydropower operations – Isimba HPP Uganda

Lake Victoria is the largest tropical lake in the world and the source of river Nile, the longest river in the world. Due to prolonged precipitation above the average over the past two years, the lake water levels have increased surpassing the highest ever recorded of 13.41m in 1964. To mitigate the negative impacts on the people, navigation and developments in the flood zones, lake outflows were gradually increased from 1000cumecs to 2400cumecs. Isimba Hydropower Plant (HPP) with a reservoir capacity of 170 million cubic meters is the fourth hydropower plant along the upper Nile cascade with a design flood level of 1055m above sea level. Reservoir operation is constrained by the bridge construction and ferry operation works downstream which are affected by the increased discharges. There is also uncertainty of the incoming discharge magnitude and travel time due to lack of an upstream gauging station. This paper seeks to assess the reservoir response to the increasing flood conditions using Hydrologic Engineering software for flood routing and to model an operation water level (OWL) that optimizes power production and flood control whilst ensuring public safety of the downstream activities through real-time forecasts in the short term.

Developing a Rainfall Impact Forecasting Model for Disaster Mitigation around the River

Impact forecasting has been applied to estimate flood damage in many different countries based on accurate weather forecasts. This study develops a model forecasting the impact of rainfall on riverside flood risks in the Busan Metropolitan City. The rainfall impact forecasting equations were obtained on a 1km x 1km grid with respect to water levels and critical rainfall thresholds. Critical rainfall was determined based on the end point of river and the discharge-water level relationship between design flood discharge and design flood level by analyzing water-rainfall in 3-hour critical rainfall. Model verification was performed using a heavy rain event with a total of 283.3 mm from July 22 to 24, 2020. According to the rainfall impact forecasting, 60 to 70% of the design flood level (“MEDIUM” alert) was issued on rivers between 10-11pm on July 23. In the rivers where the rainfall impact alert was issued, actual damages were found such as flooded roads and floodplain, which confirmed the appropriateness of the model. The high model accuracy was also validated by comparing the alert standard for water level with forecasted rainfall impact at the water level station in Suyeong River.

Flood Risk Assessment for Coastal Cities Considering Sea Level Rise due to Climate Change

The purpose of this study was to present disaster prevention performance targets for Korean coastal cities, given the rise in sea level due to climate change. The disaster prevention performance targets for coastal cities are used to assess flood risk caused by increased sea levels. The proposed disaster prevention performance targets give additional consideration for design tide level or design flood level, which are design factors for hydraulic structures located along the coast. The rate of sea level rise in the West Sea was 0.61 ㎝/year. It was the fastest rise rate of all of Korea's seas. The sea level rise rate in the East Sea was calculated at 0.58 ㎝/year. This study also quantitatively confirmed that flood damage increases according to sea level rise using the United States' Environmental Protection Agency-Storm Water Management Model (EPA-SWMM). This study suggested a method for setting the disaster prevention performance targets of expected flood damage in coastal cities. Therefore, suggested disaster prevention performance targets should be highly specialized for coastal cities. However, sea level rise and rainfall are key factors that cause floods. Therefore, further research on disaster prevention in coastal cities should be carried out to consider the combined effects of sea level rise and rainfall.

The Joint Effect of River Flow and Tides on the Determination of Design Flood Levels in the Han River

Li, L. and Jun, K.S., 2020. The joint effect of river flow and tides on the determination of design flood levels in the Han River. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 257–261. Coconut Creek (Florida), ISSN 0749-0208.In tidal rivers, flood water levels are driven by a joint effect of upstream river discharge and downstream tidal level. Design flood level, which is used to design structures for flood protection, is usually determined by a steady-state flow model using constant values of upstream river discharge and downstream water level as inputs. However, the approach applying a steady-state flow model can overestimate water levels in tidal rivers because flood wave attenuation and the joint effect of river flow and tides are not taken into consideration. In this study, to investigate the effect of river-tide interaction on water levels along tidal rivers, a time series of design flood flow at the upstream boundary and a large number of tide scenarios at the downstream boundary are forced into a one-dimensional hydrodynamic model of the Han River, resulting in peak water levels along the river. Design flood levels are determined through a statistical analysis of the obtained peak water levels. The design water levels estimated by the proposed approach tend to be lower than that determined by a steady-state flow model. Moreover, a significant difference in the estimated peak water levels is observed near the downstream boundary due to different tide scenarios.

Seasonality in a tidal reach: Existence, impact and a possible approach for design flood level estimation

Heterogeneity caused by seasonality could lead to the estimation error of the design flood level (DFL). This research intended to examine the existence of seasonality in the extreme water levels in a tidal reach and to quantify its impact on the DFL estimation. The mixed-distribution, a commonly used method for design value estimation with heterogeneous samples, was tested. A case study was carried out in the Pearl River Delta, South China. Results showed that a significant seasonality existed in the extreme water levels that were generated from the flood-tide interactions in the delta. If the DFL was estimated with a single distribution, the DFL with a return period smaller than 1.1 years would be underestimated and more information of the non-flood season would be lost. The mixed-distribution was superior in its consideration of seasonality, however, when the return period was over 10 years or smaller than 5 years, the DFL estimation results of this approach were only shifted by <1% from that of a single distribution.

A general framework of design flood estimation for cascade reservoirs in operation period

The hydrological regimes of downstream reservoirs have been significantly altered due to the operation and regulation of upstream cascade reservoirs. The original design flood quantiles, namely “design flood in construction period”, do not consider anthropogenic impacts in reservoir operation period, and have led to enormous conflicts between flood control and conservation. In this study, the “design flood and flood limited water level in operation period” are defined for practical application. We establish a general framework to measure the spatiotemporal pattern of streamflow and to estimate design floods of cascade reservoirs in operation period. The multivariate t-copula and a genetic algorithm strategy are proposed to solve the curse of dimensionality encountered in the derivation of most likely regional composition. The Jinsha River and Yalong River cascade reservoir system in China, which consists of 13 large reservoirs with the total storage capacity of 74.06 billion m3 and hydropower capacity of 71.47 GW, is selected as a case study. Results indicate that: (1) The curse of dimensionality can be well addressed by applying multivariate t-copula to build high dimensional joint distribution and using the genetic algorithm to achieve the most likely regional composition. (2) Compared with the design floods in construction period, the design floods of downstream reservoirs in operation period have been significantly reduced due to the upstream reservoir regulation. The 1000-year design peak flood discharge, 3-day, 7-day and 30-day flood volumes of Xiangjiaba reservoir decrease by 38.7%, 37.4%, 34.2% and 13.8%, respectively. (3) The flood limited water level of these reservoirs can be raised without increasing flood control risks in operation period. The cascade reservoirs in the Jinsha River and Yalong River can generate 3.28 billion kW h more hydropower (or increase 4.3%) annually during flood season.

Improving Practice of Flood Shelter Implementation in Alluvial River Floodplain With Hydro-Morphological Analysis

Flood shelter is widely used as a flood-proofing measure in floodplain areas. However, the practice of flood shelter implementation lacks proper planning, design, and construction. This study was undertaken to identify such gaps and bridge them through a case study and pilot of selected shelters in Bangladesh. An interdisciplinary approach comprising both quantitative hydrologic-hydraulic analysis and qualitative participatory social appraisal was followed in the study. The findings revealed that design flood levels were under-estimated, macro-stability of shelter sites were not assessed, and water velocity was not considered in shelter implementation. Based on an assessment of macro-stability of the chars, flood frequency and flow velocity through hydro-dynamic simulation with the HEC-RAS model, two shelters were redesigned and promoted as model shelters which performed well in a subsequent flood. The approach followed in this study can be replicated for shelter implementation in any riverine char environment for better outcome.

Design Flood Estimation: Exploring the Potentials and Limitations of Two Alternative Approaches

The design of flood defence structures requires the estimation of flood water levels corresponding to a given probability of exceedance, or return period. In river flood management, this estimation is often done by statistically analysing the frequency of flood discharge peaks. This typically requires three main steps. First, direct measurements of annual maximum water levels at a river cross-section are converted into annual maximum flows by using a rating curve. Second, a probability distribution function is fitted to these annual maximum flows to derive the design peak flow corresponding to a given return period. Third, the design peak flow is used as input to a hydraulic model to derive the corresponding design flood level. Each of these three steps is associated with significant uncertainty that affects the accuracy of estimated design flood levels. Here, we propose a simulation framework to compare this common approach (based on the frequency analysis of annual maximum flows) with an alternative approach based on the frequency analysis of annual maximum water levels. The rationale behind this study is that high water levels are directly measured, and they often come along with less uncertainty than river flows. While this alternative approach is common for storm surge and coastal flooding, the potential of this approach in the context of river flooding has not been sufficiently explored. Our framework is based on the generation of synthetic data to perform a numerical experiment and compare the accuracy and precision of estimated design flood levels based on either annual maximum river flows (common approach) or annual maximum water levels (alternative approach).

Flooding in Delta Areas under Changing Climate: Response of Design Flood Level to Non-Stationarity in Both Inflow Floods and High Tides in South China

Climate change has led to non-stationarity in recorded floods all over the world. Although previous studies have widely discussed the design error caused by non-stationarity, most of them explored basins with closed catchment areas. The response of flood level to nonstationary inflow floods and high tidal levels in deltas with a dense river network has hardly been mentioned. Delta areas are extremely vulnerable to floods. To establish reliable standards for flood protection in delta areas, it is crucial to investigate the response of flood level to nonstationary inflow floods and high tidal levels. Pearl River Delta (PRD), the largest delta in South China, was selected as the study area. A theoretical framework was developed to quantify the response of flood level to nonstationary inflow floods and the tidal level. When the non-stationarity was ignored, error up to 18% was found in 100-year design inflow floods and up to 14% in 100-year design tidal level. Meanwhile, flood level in areas that were ≤22 km away from the outlets mainly responded to the nonstationary tidal level, and that ≥45 km to the nonstationary inflow floods. This study will support research on the non-stationarity of floods in delta areas.

无资料感潮河段设计洪水位计算

感潮河段的洪水过程由于既受上游河道径流和下游潮汐的双重作用，使感潮河段的水文情势尤为复杂。本文针对无资料感潮河段设计洪水位计算，提出根据短期潮位对比观测，通过准同步比较，将长期潮位观测站逐年实测潮位资料转引至工程海域后，对逐年的极端高潮位采用PIII型频率曲线进行适线计算，得到不同频率设计高潮位，从而解决不同频率潮位计算问题；针对河流洪水计算，由于缺乏实测河流流量资料，采用水库最大下泄流量加区间流量作为上游流量边界，采用一般大潮高潮位作为下游水位边界，同时对河口地形根据不同时期影像资料进行了适当假定，采用水动力模型进行了河流洪水计算，得到满足工程需要的设计洪水位；上述所述方法对无资料感潮河段设计洪水位计算提供了重要参考。 The hydrological regime of the tidal reach is complicated because it’s influenced by both the upstream runoff and the downstream tide. This paper focuses on the design water level calculation for tidal river in ungauged basin based on the short-term tidal level observation, the long term tidal observation and short term tidal level observation relationship. After the quasi-synchronous comparison, the tidal level data of long-term tide observation stations are transferred to the engineering sea area. By using the P-III frequency curve, the extreme tidal level of each year is estimated for different design tide levels. As a result, the problem of different frequency tide calculation is solved. As to the river flood design water level calculation, because the lack of observation river flow data, the maximum reservoir discharge flow and interval flow is used as the upstream flow boundary conditions, the average high tidal level is used as the downstream water level conditions. Besides, based on different time of the remote sense image at the estuary, the rational assumptions of estuarine topography is put forward using the hydrodynamics model, the design water level satisfied the project need is calculated. The above-mentioned methods provide an important reference for the calculation of the design flood level of tidal reach inungauged basins.

Reconsideration of evaluating design flood level at Imjin River estuary

본 연구에서는 조석의 영향을 주기적으로 받는 임진강 하류부의 계획홍수위를 보다 합리적으로 산정하는 방안을 검토해 보았다. 우선 감조하천의 특성을 감안할 수 있는 부정류모의를 수행하여 홍수위의 변동을 살펴보았고, 수위 계산에 민감한 매개변수인 조도계수를 해당지역의 특성에 맞게 현실화하여 홍수위 변화를 분석하였다. 그 결과를 2011년 임진강하천기본계획보고서에서 고시한 임진강 하구 계획홍수위와 비교하고, 감조구간 에서 홍수위 산정시 유의해야 할 점들을 정리하였다. 참고로 2011년에 고시된 계획홍수위는 대규모 하상 준설 단면을 입력자료로 하여 부등류모 의를 통해 산정된 바 있다. 본 연구의 결과, 임진강 하구의 경우 홍수위 산정에 있어서 조도계수를 한강하구와 동일한 값으로 할당하고, 하구 조위를 감안할 수 있는 부정류 모의를 수행하면 하상 준설을 하지 않더라도 홍수위가 제방 여유고를 만족함을 알 수 있었다.

A composite dowel bridge in the Czech Republic

AbstractThe floods in the Czech Republic in the last few decades have resulted in a significant number of bridges having to be rebuilt. Unfortunately, the work meant long‐term traffic closures for railway bridges, coupled with significant costs for renovation and for providing alternative transport services. As a result, the minimum clear headroom above the design flood level required for new bridges and for reconstructing existing bridges has been increased. This initiated a search for new approaches to designing individual parts of bridge crossings, aiming to comply with the stricter conditions. The research aims to decrease costs in comparison with the costs of raising the finished grade level of the railway, especially at places where adjacent sections such as railway stations etc. are connected.