Design Rainfall Research Articles

Flood Risk Assessment to Enable Improved Decision-Making for Climate Change Adaptation Strategies by Central and Local Governments

This study assessed the flood risk in the Republic of Korea, considering representative concentration pathway (RCP) climate change scenarios, after applying the concept of “risk” as proposed by the Intergovernmental Panel on Climate Change. For the hazard assessment, hazard indicators were constructed utilizing design rainfall standards, which represented the local flood protection capability, as a flood threshold. We constructed high-resolution spatial images from data of buildings, roads, agriculture areas, and the population that have suffered significant flood damage in the Republic of Korea. We also calculated flood exposure levels by analyzing the scales of the targets in low-lying areas. Environmental and anthropogenic conditions that can directly increase or decrease river flooding and urban flooding were set as indicators and utilized as proxy variables. As a result of the risk assessment, we found 43 risk areas in the historical period, accounting for 19% of the total administrative districts, 42 in the projected period under RCP 4.5 (18%), and 51 in the projected period under RCP 8.5 (22%). This study’s results can be utilized by the central government to determine flood risk priority areas in various administrative districts and by the local government to select priority areas to install flood reduction facilities.

Comparison of Assessments of Urban Areas Using the Flood Vulnerability and Potential Flood Damage Methods

Recently, urban flood damage has rapidly increased due to climate change, rapid urbanization, and frequent guerrilla heavy rains. Therefore, a quantitative flood damage analysis technique is required for effective policy regarding flooding in urban areas. In this study, the flood vulnerability and potential flood damage (PFD) methods, which are representative methods for analyzing the degree of flood damage in urban areas, were applied. In addition, the results of each analysis method were compared and analyzed using the flood prevention capacity-damage (PCD) matrix technique, which intuitively shows that even if many existing flood protection facilities are built, flood damage can be large when there is insufficient management or heavy rainfall exceeding the design rainfall occurs. The two existing flood damage techniques estimated Seocho-gu to have low flood vulnerability due to high financial independence and many flood damage protection facilities. However, application of the PCD matrix resulted in classifying Seocho-gu as highly vulnerable to flooding. These conflicting results thus demonstrate that a more detailed review and analysis are necessary when establishing a flood protection policy.

Calibration-free approach to reactive real-time control of stormwater storages

Stormwater systems will likely require major upgrades due to increases in peak flows caused by the combined effects of urbanization, densification (urban infill) and climate change. Recently, the real-time control (RTC) of storages has been considered as a means to reduce peak flows and potentially avoid major infrastructure upgrades. This paper introduces a RTC approach, the Target Flow Control (TFC) approach, which is able to maintain system outflows at or below specified target flows (e.g., existing system capacity). The key features of the approach are that it does not require calibration to catchment specific data, as is the case for existing approaches and is only based on storage level information measured in real-time during rainfall events. This makes the approach generally applicable to different catchments and able to respond to future changes in rainfall due to land use and/or climate change. The TFC approach is tested on a simple two-storage system for 750 design rainfall events from a range of climates, event durations, rainfall intensities and temporal patterns using a practically achievable control time step of 30 s. Results show that the TFC approach can achieve the desired target flows effectively, with 95% of the experiments having less than 10% errors in target flows. This is an exciting achievement, given the TFC approach does not require calibration and only requires measurable storage level information. The outcomes highlight the potential of the TFC approach as a practical RTC approach that can maximize the effectiveness of existing stormwater conveyance systems by maintaining stormwater system outflows at desired target flows, thereby potentially avoiding stormwater infrastructure upgrades due to land use and climate change.

Analisis Debit Banjir Untuk Perencanaan Bendung Malunda Kabupaten Majene

This study aims to analyze the flood discharge of the Malunda Weir design. This research can be used as a reference for similar research. Due to the earthquake in Palu, the dam cracked in several parts, then collapsed due to flooding. Planning for flood control, river security, and other water structures can be carried out properly if the planned flood discharge in the river is known. Regional average rainfall is calculated by the Algebraic Average method. Then analyzed by calculating the design rainfall using the Gumbel method, Log Pearson Type III and Log Normal. Then determine the flood discharge using the HSS Nakayasu and HSS Gama I methods with return periods of 25, 50, and 100 years. Based on the calculation results of the Nakayasu HSS method, the flood discharge for a period of 25 years = 791.570 m3/second; 50 years = 903.575 m3/second ; and 100 years = 1014, 533 m3/sec. In the HSS Gama I method, the flood discharge for a period of 25 years = 860,794 m3/second; 50 years = 1005.687 m3/second ; and 100 years = 1149, 507 m3/sec. From the calculation of the 2 HSS methods, it can be concluded that the closest Synthetic Unit Hydrograph is the Synthetic Unit Hydrograph. From the calculation of the 2 HSS methods, it can be concluded that the closest Synthetic Unit Hydrograph is the Synthetic Unit Hydrograph.

Comparison of Regionalisation Techniques for Peak Streamflow Estimation in Small Catchments in the Pilbara, Australia

Arid and semi-arid regions typically lack high-resolution river gauging data causing difficulties in understanding rainfall-runoff patterns. A common predictive method for discharge estimation within ungauged catchments is regional flood frequency estimation (RFFE), deriving peak discharge estimates from similar, gauged catchments and applying them to the catchment of interest. The majority of RFFE equations are developed for larger catchments where flow events may be larger and of greater interest. We test a series of RFFE methods derived for the Pilbara region, applying them to new ungauged small catchments under 10 km2. Rainfall values are derived from a guideline Australian design rainfall database, Australian Rainfall and Runoff 2019 (ARR2019) which was recently updated with an additional 30 years of rainfall data. RFFE equations are compared to a direct rainfall model to evaluate their performance within small catchments, identifying key limitations and considerations when modelling small headwater catchments.

THE ESTIMATION OF FLOOD-AFFECTED AREA IN THE DOWNSTREAM OF CODE RIVER, YOGYAKARTA, INDONESIA

The rapid development of settlements and sediment deposition has increasingly narrowed the drainage in the Code River. This condition causes floods and wider distribution of the affected areas. This research aims to estimate the maximum amount of rain, predict the probability of flood, and predict flood-prone areas in the Code River. Data were collected by observation, remote sensing image interpretations, literature studies, and documentation. Data analysis was performed using Log Pearson Type III for design rainfall analysis, Weibull formula for flood probability analysis, and rational method for planning maximum discharge analysis. Flood modeling is carried out by the iteration method. The results show: (1) the maximum amount of rain based on the calculated design rainfall with a return period of 5 to 40 years is R5 = 106.83 mm, R10 = 116.67 mm, R20 = 127.30 mm, R40 = 134.25 mm, (2) the probability of flood that is predicted from the maximum discharge caused by the design rainfall at each return period is Q5 = 82.45 m3/sec, Q10 = 89.42 m3/sec, Q20 = 96.95 m3/sec, Q40 = 101.86 m3/sec. (3) Inundation of the flood target area in the 5-year return period covers an area of 0.4456 km2, the 10-year return period covers 0.5209 km2, the 20-year return period covers 0.6023 km2, the 40-year return period covers 0.6555 km2. This paper presents information on the potential for a flood at various return periods to increase preparedness and reduce risks due to flood disasters.Keywords: Disaster, Floods, Estimated Flood-Affected Areas, Code River, Yogyakarta

극한강우 발생에 따른 소규모 댐 위험도 분석

The local heavy rains that didn't happen in the past, super typhoon and local torrential rainfall, generates more rainfall than the design rainfall applied to the design of the hydraulic structure this raises the anxiety about safety from natural disasters. In this study, the risk was analyzed extreme rainfall for a small dam belonging to a relatively large-scale structure among hydraulic structures and The target of analysis is the Cheongsong pumped storage plant in Cheongsong, Gyeongsangbuk-do. In Korea, extreme rainfall occurs mainly in the Jirisan area of the south coast and the east coast area. Therefore, in this study, the extreme rainfall that occurred in the eastern coastal area near the Cheongsong pumped-water power plant was selected and used for analysis. The maximum daily rainfall since 2000 in the east coast area was Typhoon Mitag in 2019, which caused a lot of rainfall in the east coast areas such as Pohang, Yeongdeok, and Uljin. In this study, it was assumed that rainfall such as typhoon Mitak occurred in the basin of the Cheongsong pumped storage plant, and the effect of dam outflow according to power generation on the downstream area was analyzed.

A SYNTHETIC PRECIPITATION MODEL TO DETERMINE THE USAGE OF THE DISTRIBUTION OF RAIN AS A DATA INPUT IN CALCULATING THE DESIGN FLOOD

In calculating the design-flood discharge, engineers often use the frequency-distribution analysis of rainfall data as the basis for obtaining the magnitude of the design flood. The distribution of rain stations is an important factor in determining the distribution of regional rainfall; however, not all catchments have sufficient rain stations to represent the distribution of precipitation in a watershed. This results in a flood hydrograph—obtained using a rainfall–runoff model that is based on the calculation of the estimated rainfall—with a low level of correlation with the observed hydrograph. This research aims to set up a synthetic rain station that corrects the difference between the simulated hydrograph and observed hydrograph to achieve a better correlation level. Usually, researchers use the available rain stations for analyzing the design rainfall and design flood; however, in this research, a synthetic rain station has been built. Rainfall–runoff modeling methods for ungauged catchments (UCs), i.e., watersheds without observation stations, are widely available. Each method has different parameters to determine the unit hydrograph in a watershed. During the development of rainfall–runoff models at UCs, the precipitation in the upstream of a watershed is often assumed to be uniform, but it is not the case. The methodology used in this study collects hourly rainfall data from the ARR and hourly flood-discharge data from the AWLR in one catchment, then calculates the Thiessen coefficient before and after the set up of the synthetic rain station, and finally, calculates the rainfall at the synthetic rain station by trial and error. From the results of the synthetic rainfall modeling, the equation for the synthetic rainfall is obtained:ArRR=(-0.127A-0.260FB-0.307Re+1.227Q+0.51)/(C.K_Thiessen ) with a correlation coefficient of R = 0.818 in a watershed area below 300 km2.

Evaluating the Effect of the Location and Design of Retention Ponds on Flooding in a Peri-Urban River Catchment

In order to reduce the flooding risk in urban and peri-urban river catchments, retention ponds or wet detention ponds are often used. However, there has been little work that uses distributed hydrological modeling to consider their optimum location and design in order to reduce the flood risk in a river catchment. This work considers two existing and two potential ponds in the 22.8 km2 Braid Burn catchment, Edinburgh, Scotland. Using the Shetran physically based distributed hydrological model, the effect of these ponds on the river discharges for eight measured rainfall events and two design rainfall events is considered. The results show the larger Blackford pond is best at reducing the peak discharge at the catchment outlet. The other three ponds are designed to be almost the same. The potential pond in the upper part of the catchment reduces the peak discharge at the outlet; the pond in the middle at Oxgangs makes little difference to the peak discharge, while the potential pond in the lower part of the catchment increases the peak discharge at the outlet. These results show that when considering flood risk, the location of a retention pond within a river catchment is important, and it can make the flooding worse at the outlet if it is located in the wrong location. This work suggests the pond should be located in the upper part of the catchment, although the ideal location will depend on the catchment’s shape and lag time.

EVALUASI GENANGAN PADA LAPANGAN SEPAK BOLA DI STADION SULTAN AGUNG KABUPATEN BANTUL

Sultan Agung Stadium is one of Indonesia's premier league stadiums and international standards with a subsurface drainage system. Subsurface drainage is considered to be very efficient compared to surface drainage. However, during heavy rains, there are still some puddles on the surface of the football field. The presence of puddles is a massive problem in a football match because it can block the flow of the ball. The purpose of this study was to evaluate the drainage system of the Sultan Agung Stadium football field in terms of the diameter, depth, and distance between the subdrain pipes. The data analyzed include soil, rainfall, and drainage dimension data. Soil data was used to analyze the infiltration test, soil porosity, and permeability. Rainfall data is used for hydrological analysis by determining the design rainfall at 2, 5, and 10-year return periods, and drainage dimension data is used for hydraulics analysis by determining the pipe capacity and drain layer. Based on the results of this study, a pipe with a diameter of 6 inches with a distance of 5 m cannot overcome inundation during the 10-year return period. Variations in depth and distance between drainage pipes are known to have an effect on inundation that occurs in the field. By reducing the distance to 4m, the inundation that occurs can be resolved

Understanding nutrient dynamics for effective stormwater treatment design

Current stormwater quality modelling tools lack robust mathematical replication of nutrient entrainment in runoff. This makes it challenging to design effective stormwater treatment systems such as nature based solutions with adequate resilience to future changes in nutrient inputs in urban environments. Consequently, poorly treated stormwater can be discharged into receiving waters, leading to nutrient enrichment and in turn, environmental and human health impacts. This study integrated empirically based with statistical modelling techniques to incorporate nutrient dynamics into commonly used Intensity-Frequency-Duration (IFD) distributions of design rainfall. Field based nutrient wash-off experiments were conducted to understand nutrient behaviour during a runoff event. New mathematical formulations were derived to describe the decay (wash-off) of nutrients. Rainfall intensity, duration and initially accumulated pollutant load exert positive influence on the decay of nitrogen and phosphorous, while organic carbon has a negative impact on phosphorus decay. It was also evident that nitrogen species would decay at a similar rate, while phosphorus species may decay at different rates. Compared to nitrogen species, phosphorous species were found more likely to be washed-off during a rainfall event. Using the mathematical formulations developed, wash-off of nitrogen and phosphorous was simulated for 435 very frequent and frequent/infrequent design rainfall events leading to the creation of Intensity-Frequency-Duration-Wash-off (IFDW) curves. Analysis of uncertainty associated with IFDW indicated that total phosphorous could be completely washed-off during most of the design rainfall events, while total nitrogen would only be completely washed-off by very few events that are rarer than 10 % AEP (annual exceedance probability). IFDW can act as a tool for supporting effective stormwater treatment design in order to promote sustainable stormwater management and reuse.

Developing Intensity-Duration-Frequency (IDF) Curves Based on Rainfall Cumulative Distribution Frequency (CDF) for Can Tho City, Vietnam

Information on the relationship between rainfall intensity, duration and accumulation frequency or return period (IDF) is commonly utilized in the design and management of urban drainage systems. Can Tho City, located in the Vietnamese Mekong Delta, is a city which has recently invested heavily in upgrading its stormwater drainage systems in the hope of preventing reoccurring flood events. Yet, much of these works were designed based on obsolete and outdated IDF rainfall curves. This paper presents an updated IDF curve for design rainfall for Can Tho City. For each duration and designated return period, a cumulative distribution function (CDF) was developed using the Pearson III, Log-Pearson III, and Log-Normal distribution functions. In order to choose the best IDF rainfall curve for Can Tho City, the CDF rainfall curve and empirical formulas used in Vietnam and Asia (Vietnamese standard 7957:2008, Department of Hydrology, Ministry of Transportation, Talbot, Kimijima, and Bermard) were compared. The goodness of fit between the IDF relationship generated by the frequency analysis (CDF curve), and that predicted by the IDF empirical formulas was assessed using the efficiency index (EI), and the root mean squared error (RMSE). The IDF built from Vietnam’s standard TCVN 7957:2008 with new parameters (A = 9594, C = 0.5, b = 26, n = 0.96) showed the best performance, with the highest values of EI (0.84 ≤EI≤ 0.93) and the lowest values of RMSE (2.5 ≤RMSE≤ 3.2), when compared to the other remnants.

Flow-Type Landslides Analysis in Arid Zones: Application in La Chimba Basin in Antofagasta, Atacama Desert (Chile)

In the world, the hazards of intense rainfall are recurrent and increasing. In addition, they are one of the natural hazards that cause the most severe damage to infrastructure and even cause deaths every year. Flow-type landslides are capable of develop in areas with different geomorphological, geological and climatic characteristics. In hyper-arid zones such as the Atacama Desert, these hazards are capable of develop in a timely manner, causing catastrophes. This study analyzes the flow-type landslide in a hyper-arid mountainous area in La Chimba basin of Antofagasta city (Chile). For this, a hydrometeorological analysis is carried out through a pluviometric analysis, statistical analysis of frequencies through the Gumbel probabilistic method of extreme values and determination of maximum flows by obtaining IDF (intensity-duration-frequency) curves and design rainfall intensity as a function of concentration time. To obtain the maximum flows of liquid runoff and debris, for different return periods, the rational method was used with the method proposed by O’Brien. For the determination in the impact zone, the modeling software HEC-RAS (Hydrologic Engineering Center’s River Analysis System) and RAMMS (Rapid Mass Movements). Hydrographs are used for a return period of about 200 years, considered the most unfavorable scenario with the Voellmy–Salm model. To validate the modeling, a morphometric, sedimentological and comparative analysis is carried out between real impact zones of 1991 event and those generated in this study. It is concluded that the sedimentological and morphometric characteristics indicate that the type of flow that it can originate would have a rapid response to rainfall events of great intensity or duration. The modeling provided by HEC-RAS represents a fluvial-type flow, while the RAMMS modeling is closer to the consistency of a flow-type landslide, which is estimated to be closer to reality. The results show that despite being in a hyper-arid zone, the rainfall factor is capable of landslides triggering in mountainous areas.

FIELD DATA ANALYSIS OF HOME-BASED STORMWATER ON-SITE DETENTION SYSTEM

This paper describes the field test of a stormwater detention system which is a system designed to hold a specific volume of water and release it slowly over time, in this test case precast concrete modular units are assembled in a residential car porch and connected to a partial roof catchment via a downpipe. Stormwater is held and stored temporarily within the chambers created by the precast concrete pieces. Rainfall and flow data associated with the detention system in terms of the inflow, outflow and water levels data are collected and verification process are performed by comparing the collected data to design data for the intended system. Analyses of five storm events confirm that the estimated design inflow, outflow and water levels in response to 5- and 10-minute 10-year Average Recurrent Intervals (ARI) design rainfall are safe against the actual rainfall and actual detention and discharge performances.

Estimation of Daily Design Rainfall in Argentina from Satellite-Derived Data

Estimation of Daily Design Rainfall in Argentina from Satellite-Derived Data

Real-time model predictive and rule-based control with green infrastructures to reduce combined sewer overflows

The impact of integrating large-scale distribution of green infrastructures (GIs) with different real-time control strategies on combined sewer overflows (CSOs) is assessed for the southern area of the City of Montreal's combined sewer system (Canada). An iterative process involving a synthetic design rainfall event and model predictive control (MPC) of the sewer system is developed to distribute GIs according to cost-efficiency and spatial analysis criteria. The distributed GIs are alternatively integrated with static, rule-based control (RBC) and MPC, for which model simulations are performed for a two-month period. The performance of the three strategies is compared in terms of CSO volume and frequency reductions, fulfillment of the outfall environmental priorities and transfer of runoff capture to CSO volume reduction. A gradual increase in GI implementation levels and an alternative scenario of GIs distribution are also considered to assess the performance of the two real-time control (RTC) strategies. By comparing the scenarios where GIs are uniformly distributed with those where no GIs are implemented and omitting the most extreme rainfall event, average CSO volume reduction is about 65%, 82% and 92%, respectively, for static control, RBC and MPC. Moreover, the scenario integrating GIs with MPC is the only one permitting to avoid almost all CSO events and the fulfilment of the outfall environmental priorities. GIs efficiency performance (the transferability between global runoff capture and CSO volume reduction) is also the highest under MPC, even when considering varying GI implementation levels and spatial distribution schemes.

Illinois State Water Survey Bulletin 75: New Precipitation Frequency Study for Illinois

ABSTRACTStorm frequency estimates and their temporal distributions are important in determining estimates of runoff or peak flow rates in many engineering and hydrological problems. Illinois State Water Survey Bulletin 70 has been serving as the design rainfall standard in Illinois since its publication in 1989. Although Bulletin 70 represented the best available data at the time of its publication, the standards needed to be reevaluated and updated after more than three decades and with the growing evidence of the nonstationary nature of heavy precipitation. The trends in heavy precipitation in Illinois prompted the creation of a new frequency study named Bulletin 75, providing precipitation frequencies for event durations ranging from 5 min to 10 days and for recurrence intervals ranging from 2 months to 500 years. The results are presented for the same 10 geographic sections in Illinois as in Bulletin 70 to maintain the continuity of hydrologic studies and compatibility with regulations. The primary goal of this paper is to outline some of the key methodological issues and challenges, to compare the results with the previous sources, and to highlight the effects of the changing precipitation standards on the development of amendments to existing ordinances. Lake County in Illinois, as one of the most affected urban areas with the highest change in heavy precipitation, was selected to illustrate issues related to the application of modified precipitation standards.

The Response of Runoff Pollution Control to Initial Runoff Volume Capture in Sponge City Construction Using SWMM

Source facilities can manage stormwater runoff pollutants while also limiting runoff volume in China’s sponge city construction. However, there is no apparent link between source volume control and runoff pollution reduction. This research uses SWMM to develop a model based on the basic data of a city’s catchment zone in northern China in order to statistically examine the response relationship between the initial runoff volume capture of sponge city construction and the reduction effect of stormwater runoff pollution. Based on the dimensionless constant of the runoff pollution control curve, we suggested a novel approach for evaluating runoff pollution control effectiveness. This method was used to examine the response relationship between runoff volume control and runoff pollution control in three typical initial runoff volume capture facilities in the study area, namely bioretention, permeable pavement, rain barrels, and terminal storage tanks, under various design rainfall conditions. The dimensionless constant (Dc) has good practical application value and can quantitatively quantify the control effect of various facilities on stormwater runoff pollution. The Dc value of the source facilities is higher than that of the terminal control facilities, indicating that the source facilities have a higher ability to reduce rainwater runoff pollution than the terminal facilities, particularly the infiltration facilities. The research ideas and evaluation methods proposed in this paper provide an alternative approach for selecting and optimizing facilities during the planning and designing stages of sponge city construction, which can also be used in the monitoring and evaluation stage after completion to carry out a more effective evaluation of sponge facilities’ effects.

Design flood computation at ungauged catchments of Baitarani River Basin using scaling concept and probabilistic time distribution of design rainfall

ABSTRACT Short-duration rainfall data are basic inputs to many rainfall-runoff models for generating the flood hydrographs. But these data are scarce in comparison to daily data, which is abundantly available, but cannot be directly used unless disaggregated to a shorter duration. This paper adopts a simple scaling approach for disaggregation of daily design precipitation into the desired duration and the time distribution of precipitation based on 3p Beta distribution herein referred to as the scaled 3p-Beta approach. The rainfall quantiles and their temporal distribution, when used as an input to the rainfall-runoff model, generate the design flood hydrograph at the ungauged location. The Upper Baitarani Basin under Mahanadi Sub-zone (3d) of India has been selected as the test catchment. The efficacy of the proposed scaled 3p-Beta approach, and also the rational approach coupled with CWC-2p Gamma UH was verified in the test catchment for design flood computation. The findings reveal that the methodology ensures encouraging results directly derivable from the abundantly available daily rainfall data and can be applied in any ungauged catchment in a region.

Estimation of design precipitation in Beijing–Tianjin–Hebei region under a changing climate

ABSTRACT Under changing environments, conventional methods based on an assumption of stationarity can lead to unreliable estimates of design rainfall quantiles. In this study, the trend of six extreme precipitation indices in the Beijing–Tianjin–Hebei region was analysed using different methods. Nonstationary models were established for annual maximum one-day precipitation (RX1d) and annual total precipitation when daily precipitation is greater than 95% of daily precipitation in a year (R95p) exhibiting significant trend, while stationary models were established for the two indices showing no significant trend. Finally, the nonstationary and stationary design precipitation were estimated using the average design life level method and the stationary method, respectively. The results indicated that for some stations in the east and south, a significant decreasing trend was observed for RX1d and R95p. This resulted in the overestimation of their design precipitation using the stationary methods and altering the spatial distribution of precipitation extremes for future period near these stations.