Assessment of inundation risk in urban floods using HEC RAS 2D

ASEAN Engineering Journal, 2022

Floods are natural disasters which if occurred produce damage to property and human life. The study of floods is important for protection of properties and human life risk. This study focuses on flooding characteristics in the flood plain of Tikurwha river catchment using two-dimensional (2D) hydrodynamic modeling. The flood inundation map of the flood prone areas is carried out using HEC-RAS 2D models with incorporation of Arc-GIS tools. Hence, using the magnitude of the flood at 2, 10, 50- and 100-year return period with a respective value of 72, 98.69, 123 and 135 (m3/s). The output of flood hazard inundation maps are carried out in 2D HEC-RAS Mapper in which the flood area at a respective return period’s flood magnitude are 75 ha, 102 ha, 108 ha, and 122 ha respectively. Based on the obtained flood inundation area, the economic impact of the flood at the specified return periods are estimated as 1791.99, 2436.89, 2589.45, and 2914.861 quintals of crop production were damaged due...

Journal of The Institution of Engineers (India): Series A, 2018

Urban floods are self-invited disasters which are responsible for huge property loss and in some cases loss of lives, self-invited in the sense man's desire for more and more land, and uncontrolled infrastructure development is altering natural land use, land cover and stream flow paths. Thus, high-intensity rainfall for shorter time period is producing high peak runoff from altered/urbanized catchment. The urban flood events in India have been increasing in past few years, affecting major cities, and the frequency of floods continues to grow in future. It is beyond our capabilities to prevent these events from occurring; therefore, it is very important to develop a strategy to combat such events so that losses in terms of human lives and property can be minimized. This paper explains a framework developed for flood modeling on regional scale combining GIS with a rainfall-runoff model (HEC-HMS) and a hydrologic model (HEC-RAS). Hyderabad city of India is considered as a pilot study area as it is a region of frequent occurrences of severe flash floods. Three major flood events, viz. July 1989, August 2000 and August 2008, that occurred in Hyderabad are selected as cases to examine the modeling framework, and flood inundation maps are prepared representing area at risk and delineate the regions where the flooding is likely to occur. The study represents the importance of 2D modeling of flood problems to develop management strategies to tackle the probable future events by employing flood risk reduction measures.

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences

Space for water is now becoming guiding principle of urban planning because urban flooding is the major problem facing by most of the cities in India. Urban development in developing countries like India usually occurs with high population concentrating in small areas, with poor drainage conditions. People occupy floodplain areas in low flood years and when larger flood occurs it causes high damage. The origin for urban floods is floodplains encroachment and unplanned drainage systems. Complexities in the urban environment and drainage infrastructure have an inherent influence on surface runoff. This runoff generates urban flooding which poses challenges to modeling urban flood hazard and risk. As like in river flooding satellite images are not available for unban flooding scenario. So better modelling provides minimizing loss of life and property. The present study focuses on recognizing the highly effected areas which are liable to flooding when extreme rainfall occurs for part of Hyderabad city (Zone XIII). The entire Hyderabad city is divided into 16 zones and each zone having details of existing drain network. A coupled 1D-2D flood modelling approach is used to identify flood prone areas and develop flood inundation and flood risk maps. 1D model for pilot area is developed using storm water management model (SWMM) and coupled with 2D PCSWMM. A web based GIS platform INPPINS is used to geo reference the existing network details and exported to 1D SWMM model. The model is simulated for extreme flood event occurred in past. The simulation run results identifies overflowing drainage nodes and flood inundation maps and risk maps prepared. The flood risk maps identify the low lying areas which need immediate attention in case of emergency. The overflowing nodes suggest the need of improvement of drainage in the area to safely dispose of the storm water and minimize the flooding.

Water

Floods are brutal, catastrophic natural hazards which affect most human beings in terms of economy and life loss, especially in the large river basins worldwide. The Indus River basin is considered as one of the world’s large river basins, comprising several major tributaries, and has experienced severe floods in its history. There is currently no proper early flood warning system for the Indus River which can help administrative authorities cope with such natural hazards. Hence, it is necessary to develop an early flood warning system by integrating a hydrodynamic model, in situ information, and satellite imagery. This study used Hydrologic Engineering Center–River Analysis System (HEC–RAS) to predict river dynamics under extreme flow events and inundation modeling. The calibration and validation of the HEC–RAS v5 model was performed for 2010 and 2015 flood events, respectively. Manning’s roughness coefficient (n) values were extracted using the land use information of the rivers a...

Odisha state witnessed severe flooding in the years 2003, 2008, 2009 and 2011 which affected major districts like Cuttack, Khurdha, Jagatsinghpur, Puri and Kendrapada. HEC-RAS 2D is a hydraulic model which is used to simulate water flowing through rivers and open channels. In addition, the model also provides the depth of water, velocity and water surface elevation with respect to time. Using this model, part of Mahanadi River stretch from Tikarpara to Mundali was taken as the study area for simulating floods during September 2008. Inputs to the model like CARTO DEM at 10 m posting, discharge data, roughness coefficient were provided and flood inundation was simulated. The flood extent from the model was validated with the satellite derived flood extent obtained from RADARSAT satellite. Model performance was evaluated based on the parameters F1 and F2 where, F1 and F2 are measures of fit which range from 0 to 1 and −1 to 1 respectively. If the fit value is closer to 1, it indicates that the model performance is better. Sensitivity analysis is carried out to investigate the model performance for

Remote Sensing

One-dimensional (1D) hydraulic models have been extensively used to conduct flood simulations for investigating flood depth and extent maps. However, the 1D models cannot simulate many other flood characteristics, such as flood velocity, duration, arrival time and recession time when the flow is not restricted within the channel. These flood characteristics cannot be disregarded as they play an important role in developing flood mitigation and evacuation strategies. This study formulates a two-dimensional (2D) hydrodynamic model combined with remote sensing (RS) and geographic information system (GIS) approach to generate additional flood characteristic maps that cannot be produced with 1D models. The model was applied to a transboundary river of Deg Nullah in Pakistan to simulate an extreme flood event experience in 2014. The flood extent images from the moderate resolution imaging spectroradiometer (MODIS) and observed flood extents were used to evaluate the model performance. Mor...

Journal of water management modeling, 2024

Conducting a flood frequency analysis and mapping of the inundated area in rivers are important for river flow modeling. The main purpose of this research is to estimate the peak flow, model the inundated area using HEC-RAS, and conduct an analytical hierarchy process for the upper Baro Akobo basin in Ethiopia. The inundation area and river depth for 25, 50 and 100 years are considered while contemplating several factors which contribute to flooding. The downstream of the basin has experienced numerous floods that occurred in 2006, 2007, 2010, 2011, and 2012. Flood frequency analysis with stream flow data from 1990-2009 at the Baro-Gambella gauging station was carried out to estimate the expected peak floods of the watershed. The analysis was conducted using the Gumbel, Normal, and Log Pearson Type III distribution methods. The peak floods with return periods of 25, 50, and 100 years with a minimum statistical value calculated using the Normal distribution method resulted in 1739.586 m 3 /s, 1820.872 m 3 /s and 1893.974 m 3 /s, respectively. The HEC-RAS model results indicated that the flood inundation areas under different land use changes for 25-, 50-, and 100-year return periods were 446.2 km 2 (annual crop cover), 404.4 km 2 (built area cover), 323.3 km 2 (flooded vegetation), and 93.58 km 2 (forest area), respectively, whereas the inundation depth ranged from 0-2.6 m, 0-2.9 m, and 0-3.2 m depth at the upstream and downstream of the river, respectively. The outcome of this study could be used to reduce temporal and permanent flood risk.

Water

Fluvial floods are one of the primary natural hazards to our society, and the associated flood risk should always be evaluated for present and future conditions. The European Union’s (EU) Floods Directive highlights the importance of flood mapping as a key stage for detecting vulnerable areas, assessing floods’ impacts, and identifying damages and compensation plans. The implementation of the EU Flood Directive in Greece is challenging because of its geophysical and climatic variability and diverse hydrologic and hydraulic conditions. This study addressed this challenge by modeling of design rainfall at the sub-watershed level and subsequent estimation of flood design hydrographs using the Natural Resources Conservation Service (NRCS) Unit Hydrograph Procedure. The HEC-RAS 2D model was used for flood routing, estimation of flood attributes (i.e., water depths and flow velocities), and mapping of inundated areas. The modeling approach was applied at two complex and ungauged represent...

Global Journal of Environmental Science and Management, 2019

Flooding is one of the most occurring natural hazards every year risking the lives and properties of the affected communities, especially in Philippine context. To visualize the extent and mitigate the impacts of flood hazard in Malingon River in Valencia City, Bukidnon, this paper presents the combination of Geographic Information System, high-resolution Digital Elevation Model, land cover, soil, observed hydro-meteorological data; and the combined Hydrologic Engineering Center-Hydrologic Modeling System and River Analysis System models. The hydrologic model determines the precipitation-runoff relationships of the watershed and the hydraulic model calculates the flood depth and flow pattern in the floodplain area. The overall performance of hydrologic model during calibration was “very good fit” based on the criterion of Nash-Sutcliffe Coefficient of Model Efficiency, Percentage Bias and Root Mean Square Error – Observations Standard Deviation Ratio with the values of 0.87, -8.62 a...

Current Science, 2021

The present study looks into the Hyderabad urban floods of October 2020 from a geospatial perspective. The spatial extent and severity of the flooding event for a part of the urban catchment (Zone-12) of Hyderabad city are modelled using HEC-RAS 1D-2D considering 13 October 2020 rainfall event. The study compares the present flooding to the previous flooding incidence which impacted Hyderabad, almost a decade back on 24 August 2000. The study shows that rapid unplanned urbanization ignoring the regional and local hydrological landscape has aggravated the flooding severity. The study highlights the fact that rapid, uncontrolled urbanization (16.5% increase) over the last two decades have substantially influenced the urban hydrology producing higher flood volumes for comparatively small rainfall event. Thus regulating urbanization, providing enhanced drain capacity, rejuvenating the water bodies and streams is need of an hour to check and reduce the spatial flooding extent.