Flood Simulation Utilizing HEC-HMS and HEC-RAS

본 논문의 목적은 1차원 수리모형인 HEC-RAS(Hydrologic Engineering Center's River Analysis System)를 통해 강우의 시간적 분포를 적용한 홍수위를 산정하고, 산정한 홍수위 값과 대상유역의 정밀한 지형데이터를 활용하여 홍수위에 따른 범람영역을 GIS기반의 사용자 정의 모델을 통해 자동 생성하는데 있다. 하천의 범람영역 분석은 지형데이터의 정확성에 따라 결과가 달라지므로 대상유역 지형 데이터의 정밀성이 최우선이다. 따라서 GIS기반의 홍수범람 영역을 자동생성하기 위해 UIS(Urban Information System)와 하천 관련 보고서, 수문학 정보 등을 기반으로 공간 및 속성 데이터의 구축방법을 제시하고, 대상 유역에 제시한 모델을 적용하여 GIS기반의 분석 결과를 표출시스템을 통해 제공한다. The goal of this paper is to calculate flood elevation by applying temporal distribution of rainfall through HEC-RAS(Hydrologic Engineering Center's River Analysis System) and to automatically create areas of flooding by a user-defined spatial model based on GIS using calculated values of flood elevation and detailed data of topography. Accuracy of topographic data is the most important factor because of deeply changing analysis results of flooding areas of a river. Therefore, this paper suggests a method of attributive and spatial data construction based on the GIS using UIS(Urban Information System, river-related reports, and hydrologic information. Also, we implement an expression system to provide analysis results extracted from the proposed model.

The Hydrologic Engineering Center – River Analysis System (HEC-RAS) is one of the most famous software for hydraulic engineering modeling in river systems. One of the key capabilities of this program is floodway modeling which is based on an iterative process and good engineering judgments. The iterative process should be implemented in such a way that the water surface elevation does not exceed a designated height (1.0 feet) which is also called a surcharge. In order to keep this restriction, steady-state modeling based on a 100-year flood (base flood) is implemented in HEC-RAS and then multiple profiles based on surcharges are created. This procedure can be done using encroachment analysis in HEC-RAS. The graphical visualization of input and output data in HEC-RAS and also GIS mapping tools provide a simple and useful floodway modeling process.

In the studies presented here, we demonstrate the latest simulation capabilities of two-dimensional (2D) free-surface flow modeling through specific case studies. In hydrodynamic investigations, it is often necessary to use coupled one-dimensional (1D) and two-dimensional (2D) modeling. For the unsteady 1D–2D tasks at hand, we employed the widely accepted HEC-RAS (Hydrologic Engineering Center's River Analysis System) and HEC-HMS (Hydrologic Modeling System) simulation software. In one case study, a one-kilometer urban reach of a stream flowing through the outskirts of a major city was analyzed in connection with plans to improve water quality in recreationally impounded lakes. The hydrodynamic assessment of the planned lake conditions was carried out using 2D modeling. The spatial resolution of the model enabled the identification of potential sediment deposition zones and the verification of the proper operation of the weir and outlet structures. In another case, we analyzed surface runoff generated by precipitation falling on the site of a planned solar power plant located within a small riverside town. The results helped assess the need for and potential design of a stormwater drainage system. The spatial resolution of the 2D model allowed for an accurate determination of both the quantity and extent of surface runoff accumulation. Keywords: HEC-HMS, HEC-RAS, hydrodynamic, runoff, distributed model

Flood inundation mapping is an important tool for municipal and urban growth planning, emergency action plans, flood insurance rates and ecological studies. Mapping a floodplain requires a forecasting of the behavior of the stream in question for various recurrence interval storm events and the ability to translate the forecasted results into a plan-view extent of flooding. The Hydrologic Engineering Center's River Analysis System (HEC-RAS) has the ability to model flood events and produce water surface profiles over the length of the modeled stream. With the companion GIS utility, HEC-GeoRAS, those water surface profiles can easily be converted to flood inundation maps. This paper will address the steps required to perform a flood inundation mapping study using HEC-RAS and will present a case study, demonstrating the capabilities of HEC-RAS and HEC-GeoRAS.

This study investigates the effects of changes in land-use on the hydrology of the Swan Creek watershed in Lucas County, Ohio, over a thirty-year period. The study presents the GIS based runoff models and the HEC-RAS Flood analysis for the watershed. The runoff modeling was performed using a modification of the rational formula first proposed by Rossmiller in 1980. The C factor (land use) in the rational equation (Q = CIA) is modified to account for land use, soil type and slope factors. Four model runs for each of the land-use coverages were created based on the statistical precipitation recurrence intervals: P 10 , P 25 , P 50 , P 100 (a total of 12 model runs). The models differed only in the basic land-use classifications for each decade of interest. The runoff analysis predicts that increased runoff volumes in the watershed are directly related to increasing urbanization. The study showed that runoff volumes of a P 100 storm in 1973 of certain sub-basins has the equivalent runoff of a P 10 storm in 1995. The flood modeling was performed in the Army Corps of Engineer's Hydrologic Engineering Center's River Analysis System (HEC-RAS). Twelve model runs were also created in HEC-RAS to evaluate the effect of the land-use changes in each of the time periods for each of the storms. The study showed that flood extent of a P 50 storm in 1973 across the watershed has the equivalent flood extent of a P 10 storm in 1995. The flood modeling predicts that the Swan Creek hydrologic system responds more quickly and severely today to events that would have been smaller in the past.

Evaluating SWOT water level information using a large scale hydrology simulator: A case study over India

Hydraulics and hydrodynamics tools, along with remote sensing data, are used for flood modeling. Flood models rely on reliable ground data for calibration and validation purposes since factors contributing to floods are complex and affect the accuracy of models. Hydrologic Engineering Center's River Analysis System (HEC-RAS) is one of the most used 1D and 2D flood modeling software. GeoHECRAS is the latest modified tool for flood modeling that uses HEC-RAS on its backend with a user-friendly interface that speeds up the process. This study used GeoHECRAS to simulate water levels downstream of the Guddu barrage on the Indus River (Pakistan). For calibration and validation of the model, water levels observed from the in-situ gauge downstream of the Guddu barrage were used. For calibrated model, the difference between simulated and observed water levels ranges from -0.1718 m to +0.1521 m. For the validated model, it was from -0.232 m to 0.138 m.

Hydraulic simulation models are critical tools for analysing the hydraulic properties of a river’s system flow. The work focuses on the simulation of a river flow in a Kelantan basin using the one-dimensional (1D) Hydrologic Engineering Center - River Analysis System (HECRAS). In the present study, cross-sections from survey data were utilised into the RAS Mapper provided in HEC-RAS 5.0 to simulate the river flow in the region. This study highlights the modelling methodology with a focus on data collection and its importance during the calibration and validation process. The model was used to discover the expected peak flood levels based on historical flood events. Simulated flows were utilised to examine the potential of the model during the model development procedure. The simulation outcomes reveal that the simulated flows are in excellent agreement during the model development as the obtained R2 value was between 0.95 to 1.0 during both model calibration and validation. This demonstrates the applicability of the HEC-RAS 1D model in simulating precise river flow, especially for flood events.

Wetlands are among the most unique and biologically diverse ecosystems on the planet, playing critical roles in water filtration, carbon sequestration, and supporting rich biodiversity. However, these ecosystems are increasingly under threat from a combination of climate change and anthropogenic pressures. To safeguard these vital systems and ensure their sustainable functioning, the Ramsar Convention, an international treaty for wetland conservation, was adopted by 172 countries. The Anzali Wetland, situated in northern Iran, is one such Ramsar site and represents a significant ecological and hydrological resource. This wetland receives freshwater inputs from over 11 rivers and maintains a dynamic connection with the Caspian Sea. However, a confluence of challenges, including climate change-induced flooding, agricultural and wastewater runoff, declining Caspian Sea levels, and accelerated sediment deposition, has severely threatened the wetland’s integrity and functionality.Addressing these challenges requires comprehensive management strategies informed by robust scientific understanding. Decision-makers and stakeholders need accurate tools to predict the outcomes of various interventions and develop targeted restoration plans. Hydrological and hydraulic models have become essential tools in this context, providing insights into complex ecosystem dynamics and helping evaluate the effectiveness of proposed management measures before their implementation.In this study, the HEC-RAS (Hydrologic Engineering Center's River Analysis System) model, a computational fluid dynamics (CFD)-based software, was employed to simulate the hydraulic behavior of the rivers flowing into the Anzali Wetland. This model is particularly well-suited for assessing open-channel hydraulics and has been tailored to represent the unique characteristics of the Anzali Wetland. Given that the wetland’s water levels are predominantly influenced by seasonal river inflows rather than Caspian Sea fluctuations, the model emphasizes the critical role of river hydrology in sustaining wetland productivity, including vegetation health and biodiversity.The HEC-RAS model was calibrated and validated to cover the vast region and major inflows of the Anzali Wetland. It aimed to assess the effectiveness of existing flood control infrastructure, analyze contamination pathways and their impacts on water quality, and identify areas within the wetland prone to excessive sediment deposition. The model results also provide valuable insights into the interplay between hydrology, sediment transport, and water quality within the wetland. For example, the model highlights areas with severe sediment accumulation, threatening to disrupt aquatic habitats and navigation. Additionally, it identifies critical zones where agricultural and urban runoff introduce contaminants, adversely affecting water quality and wetland health.The outcomes of this modeling effort serve as a vital decision-support tool for wetland managers and policymakers. By simulating different restoration scenarios, such as improved flood control measures, sediment management strategies, and contamination mitigation efforts, the model enables stakeholders to prioritize actions that will have the most significant impact on preserving and restoring the Anzali Wetland. This study underscores the importance of integrating advanced hydraulic modeling with ecosystem management to safeguard vulnerable wetlands like Anzali, ensuring their ecological, cultural, and economic functions for future generations.

ABSTRACTOne of the most essential inputs in flood inundation mapping is the geometric description of the floodplains and river channel that often derives from the digital elevation models (DEMs). By increasing the satellite-based technologies during the past 30 years, several DEM sources ranging from fine-resolution and accurate, but costly, to low-cost and low-resolution have been developed. In most parts of the world, especially developing countries and data sparse regions, the coarse resolution DEMs is the only available data set for hydraulic modelling and flood inundation mapping. This research addressed the usefulness and efficiency of the recently released Advanced Land Observing Satellite (ALOS) DEM in flood inundation mapping using 1D Hydrologic Engineering Centre- River Analysis System (HEC-RAS) model. In addition, other DEM sources such as Shuttle Radar Topography Mission (SRTM-90 m), SRTM-30 m, and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER-30 m) are used to carry out a comprehensive evaluation of remotely sensed DEMs for flood inundation mapping. Findings indicate that using ALOS-30m for hydraulic simulation approximately leads to the similar results as well as ground-based DEM (GDEM). For example, the Mean Absolute Percentage Error (MAPE) in simulating mean Water Surface Elevation (WSE) and mean inundated extents based on this dataset, within the cross-sections, is lower than 8% and 13% for SojasRood river, respectively, while for Sarbaz river these values are 9% and 2%. Moreover, in both rivers, SRTM-30 m relative to ASTER-30 m and SRTM-90 m DEMs presents better results in deriving the geometric model and hydraulic simulation. Also, Hydraulic modelling based on ASTER-30 m, even relative to SRTM-90 m as a coarser resolution DEM, shows a significant discrepancy compared to GDEM. Moreover, in both rivers, the MAPE in predicting inundated extents, within the reaches, is higher than 38%.

Glacial Lake Outburst Flood Modelling of the Tikip Lake, Sikkim Himalaya, India

Flooding is one of the extreme hydrological phenomena. It is a recurring natural disaster that causes loss of life and property in many parts of the world, particularly during the monsoon season. It is important to address such issues for local government and policymakers to manage the flood properly. One such flood management activity is to develop a flood-prone area that depicts the spatial and temporal extent of flood accurately. The integration of the Hydrologic Engineering Centre - River Analysis System (HEC-RAS) model and geospatial tools have emerged as a crucial approach for identifying and mapping flood-prone areas. The successful application of the HEC-RAS model generally depends on the topographical data, which represents the channel and floodplain geometry. In floodplain geometry, discrete cross-sections play a vital role to develop the floodplain map, particularly in the flat topographical region. To extract these data it needs a high-quality digital elevation model (DEM), such as light detection and ranging (LiDAR). However, due to a lack of high-resolution topographical data, flood hazard mapping in developing countries is rare. In common practice, the centerline of the river is considered the flow path for the channel. The orientation of the cross-sections is perpendicular to this line and extends to reach the limits of the floodplain. But, it is difficult to define the limits and it may depend on the magnitude of the flood. Hence, in this study, the HEC RAS model coupled with ArcGIS has been applied to the Ganga River, which traverses through the Bihar state of India to study the effect of cross-sectional width to define the floodplain. The Bihar state is facing substantial hardships from annual flooding events with approximately 16.5% of India’s flood-prone area. The extreme flood values for 5, 10, and 25 years of return period have been determined and the influence of the three different cross-sectional widths to mapping the floodplain has been investigated. This novel perspective adds dimension to the understanding of flood dynamics and its implications for flood risk assessment. In this analysis, it has been observed that, with an increase in the width of the cross-section, the floodplain area also getting increased. In this topographical region, keeping a fixed flow path will underestimate the flood-prone area. The width of the flow path depends on the topography of the region and the river flow. The outcomes of this analysis provide valuable insights into the flood-inundated areas for the specified return periods, enabling the identification and prioritization of flood-prone zones.

Problems and prospects in long and medium range weather forecasting

Karachi, the biggest city of Pakistan, has undergone various urban sprawls due to its continuously growing population that has severely affected its natural drainage pattern. The city had an extensive natural drainage system which has now lost its original form. This study investigated the blockages and their causes during the last two decades in one of the city’s riverbeds—Malir. Moreover, the extent of floods identifying the vulnerability of the watershed’s urban area after major rainfall events was modeled. The geospatial techniques and satellite images of Landsat 5, 7, and 8 were used to analyze the changes in land use and land cover (LULC) of the Malir Basin. The Shuttle Radar Topographic Mission (SRTM) Digital Elevation Model and topographic sheets of 1975 were utilized to delineate the natural drainage network and streambeds of the basin using geographical information system (GIS) tools. Historical rainfall data from 1985 to 2014 were acquired from the Pakistan Meteorological Department (PMD) to simulate runoff using the US Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS and HEC-GeoHMS). The flood modeling was done using the River Analysis System (HEC-RAS and GeoRAS). Rainfall-runoff simulations and flood extent and depth of five major rainfall events—1992, 2003, 2007, 2009, and 2013—were modeled in this study. GIS overlay analysis combined the LULC, riverbed, and drainage line layers to identify the blocked area and to quantify the specific LULCs that were causing blockages in the riverbed. Several maps, which are prepared in this study, show the parts of the river with altered drainage patterns in 2013 from what existed back in 1975.

ABSTRACTFloods are frequent natural disasters, and the management of floods involves predicting flood hydrographs and inundation maps. However, the uncertainty associated with these predictions is a significant challenge in flood management. This study focuses on the uncertainty associated with the selection of mathematical models to estimate flood hydrographs and their impact on inundation map predictions. The study involved setting up 27 hydrological models using different mathematical models for the loss, transform, and routing methods within the Hydrologic Engineering center – Hydrologic Modelling system (HEC-HMS) model. The results showed that the peak flow estimation depends on the models adopted for predicting the flood hydrograph. This uncertainty was translated to the flood inundation maps, where the inundated area varied across different flood events. The study also found that the hydrological conditions prior to the start of the event impact the hydrological model predictive uncertainty, and ensemble predictions by Bayesian model averaging can reduce the uncertainty.