Dam Break Analysis of Khadakwasla Dam by Using HEC-RAS

Abstract

A dam is a structure constructed across river which stores water and supplies water for various purposes. Though the dams have many benefits, there is always a threat of dam break floods which are devastating in nature. Hence, it becomes essential to analyze and simulate dam failure scenarios to understand the severity of dam break flood and identify areas under threat which helps in land use planning and developing emergency response plans. This study attempts to carry out dam break/breach analysis for the Khadakwasla dam using a one-dimensional hydraulic model called Hydraulic Engineering Center’s River Analysis System (HEC-RAS). HEC-RAS tool is utilized to determine the breach outflow hydrograph and hydraulic conditions at critical downstream locations. Further, the breach outflow hydrographs are routed using dynamic flood wave routing. Further, HEC-RAS model is simulated for breach parameters derived from five different empirical methods, and the results are compared.

Introduction

I. INTRODUCTION

Dams are man-made or artificial barriers usually constructed across a stream channel to impound water. Dams are typically provided with spillway systems to safely pass a broad range of flows over, around or through the dam. A dam failure or dam burst is a catastrophic type of structural failure characterized by the sudden, rapid, and uncontrolled release of impounded water or the likelihood of such an uncontrolled release. Between the years 2000 and 2009 more than 200 notable dam failures happened worldwide. Dam failures can range from fairly minor to catastrophic, and can possibly harm human life and property downstream from the failure. Dam failures can be extremely harmful, especially because dams are considered "installations containing dangerous forces" under International Humanitarian law. This is because of the immense destruction that can occur with a dam breach. Throughout history, a large number of dam failures have caused immense property damage when floodwaters destroy infrastructure. In addition, ecosystems and habitats are destroyed as a result of waters flooding them. Along with this, dam failures over the years have taken thousands of lives. The older that dams get, the more potential exists for catastrophic dam failures.

The Khadakwasla Dam is a critical infrastructure component serving the city of Pune. A dam break scenario, though unlikely, could have catastrophic consequences. This project aims to utilize HEC-RAS software to simulate a dam break event at Khadakwasla dam and assess the potential downstream impacts. This project will provide valuable insights into the potential consequences of a dam break at Khadakwasla Dam.

The results can be used for:

1. Emergency planning and preparedness for dam safety.
2. Identifying vulnerable areas downstream and prioritizing mitigation strategies.
3. Informing evacuation plans and public awareness campaigns.
4. Guiding future dam safety assessments and potential dam improvement works.

By analyzing a hypothetical dam break scenario, this project aims to contribute to the safety and well-being of downstream communities.

II. LITERATURE REVIEW

Several research papers were reviewed to study how the HEC-RAS can be used for its applications. Reviewing papers helped in determining and limitation and the scope of the study. In literature study, the results forecasted in the research papers were also compared with the real incidents that had happened in recent years, ascertaining the accuracy of the software. The results in research paper on Dam Break Analysis of Khadakwasla dam using HEC RAS found matching to recent reports of C.W.P.R.S. shared to us.

III. METHODOLOGY

The two primary tasks in the analysis of Dam Break Studies are the prediction of the dam break flood hydrograph and the routing of that hydrograph through the downstream valley. Predicting the outflow hydrograph can be further subdivided into predicting the breach characteristics (e.g., shape, depth, width, rate of breach formation) and routing the reservoir storage and inflow through the breach. The routing tasks through the breach and through the downstream valley are handled in most of the widely used computer models with various one-dimensional routing methods. However, the programs differ widely in their treatment of the breach simulation process. Many models do not directly simulate the breach; rather, the user determines the breach characteristics independently and provides that information as input to the routing model. Following methodology has been adopted in the present study:

1. Study and understand the problem, review information about dam operation and other details.
2. Review of salient features of all the four dams in the Mutha River System i.e., Khadakwasla dam.
3. Estimation of breach parametersDam Break Analysis and flood routing with dam at FRL (Level Pool Routing) impinched over and above full reservoir levels of dam using 1-Dimensional mathematical model.
4. Estimation of inundation levels at different locations at downstream of dams for different scenarios of breaching using estimated water surface profile.
5. Preparation of inundation map which can be used for preparation of Emergency Action Plan.

A. Dam Break Analysis of Khadakwasla Dam:

Khadakwasla dam was constructed on River Mutha in the year 1880. It is a gravity dam with capacity of 86 Mm it was partially breached in the year 1961 to form safe passage for flood generated due to breaching of Panshet dam. The breached part was reconstructed in the year 1973 Ogee spillway with 11 numbers of radial gates is provided for the outflow discharge on the left side of the dam. The breaching section with earthen material is also constructed next to spillway unit on the left side of the dam for providing safe passage to floods without damaging dam structure under emergency situations. Dam Break study for Khadakwasla dam was carried out by developing 1-D mathematical model using HEC-RAS under level pool scenario. The breaching of earthen part of the dam due to overtopping was considered for the studies. The routing of dam break flood was carried out through the downstream reach of river Mutha upto the Navi Peth. The breach parameters for the present study were estimated as per the guidelines given in the manual of HEC-RAS for Dam Break Analysis. The details of the breach parameters considered are mentioned in the table 1.

Conclusion

Dam Break analysis of Khadakwasla dam was carried out for overtopping of Khadakwasla reservoir. The cross sections of the study reach of river Mutha were extracted from DEM of the study area. The breach parameters considered for the present study are estimated based on guidelines given in HEC-RAS software manual. The dam break flood hydrograph was routed through downstream river channel using HEC-RAS and water surface profile has been estimated. It is subsequently used for the preparation of inundation map as an input for emergency action planning. The following conclusions were arrived at after Dam Break analysis for Khadakwasla Irrigation System: 1) The region affected by the breaching of dam can cause severe damage to human life. Hence, HEC-RAS is beneficial to identify these areas. 2) The HEC-RAS software provided us the overall analysis of flood occurred by dam breaching, including its affected area, inundation maps and total water coverage. 3) This analyzed data and maps can help us to create an action plan to control the living non-living life damage before the actual breaching/flooding happens. 4) The analysis of HEC-RAS also can be modified according to different weather conditions, storage capacity, river flow etc. 5) The purpose of this analysis is to create a pre plan. Also, the detailed specifications of the affected region help us implement necessary actions to each specific part.

References

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Copyright

Copyright © 2024 Shubham Nigale, Prof. Avadhoot Kadu, Shree Pagare, Moreshwar Devapure, Baba Bandagar, Sanskruti Deokar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.