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dam break

1. UNIVERSITY OF VISVESVARAYA COLLEGE OF ENGINEERING DEPARTMENT OF CIVIL ENGINEERING A Dissertation Work on DAM BREAK ANALYSIS AND FLOOD INUNDATION MAPPING USING HEC-RAS Under the guidance of Presented by Dr. M .INAYATHULLA SANDESHA K M (P25UV22T111005) Professor, Dept. of civil Engineering, UVCE Department of Civil Engineering , UVCE Bengaluru Bengaluru 1

2. CONTENTS INTRODUCTION REVIEW OF THE LITRATURE METHODOLOGY CASE STUDIES REFERENCES 2

3. INTRODUCTION Dams are commonly known as mega structure which can provide essential needs for multiple purposes such as F lood control E lectricity generation Irrigation W ater supply and Recreation. Beside beneficial of constructing dam as mentioned above, we have to consider that dam may be fail during operation. 3

4. Dam can be breach due to various reasons, including natural disasters such as heavy rainfall, earthquakes, or land-slides. due to human-made factors such as poor maintenance , design flaws, or construction errors Dam failure can cause loss of life and property at downstream. 4

5. Therefore , to reduce the loss of life, loss of economy in the flood prone areas, estimation of water levels of flood is possible by performing dam break analysis . Risk management, disaster preparedness, and dam safety planning all depend on this research . U.S . Army Corps of Engineers develops HEC-RAS which is capable to model the dam break with one-dimensional and two-dimensional steady and unsteady conditions. Risk management, disaster preparedness, and dam safety planning all depend on this research. 5

6. Types of Dams Dams can be classified based on various criteria: Structural Design Gravity Dams Arch Dams Buttress Dams Embankment Dams Purpose Storage Dams Flood Control Dams Multipurpose Dams Materials Earth-fill Dams Rock-fill Dams Concrete Dams Size Large Dams (over 15 meters) Small Dams (under 15 meters) 6

7. Fig. 1. Cross section and Plain view of Gravity dam 7

8. Fig. 2 . Cross section and Plain view of Arch Dams 8

9. Fig. 3. Cross section and Plain view of Buttress Dams 9

10. Fig. 4. Cross section and Plain view of Embankment dam 10

11. Flooding due to dam failures can take several forms Flash Floods: Sudden floods caused by rapid water release. Riverine Floods: Gradual floods resulting from a slow release of water. Groundwater Floods: Prolonged saturation leading to surface flooding. Drain or Sewer Floods: Caused by blockages in drainage systems. Coastal Floods: Occur when dam failure releases water into rivers flowing into the coastal areas. 11

12. Modes of Failure : Overtopping, structural failure, Seepage, piping, or foundation issues. 12

13. Common Causes of Failures of Dam Structures 13

14. Overtopping is a major failure that is created due to heavy floods. There are two main factors that cause the overtopping failure. The continuous flow that is created due to surface elevation that will exceed the complete structural elevation profile. The over wash from the waves, where the surface of the water stays below the structure elevation profile. 14

15. Fig. 5. Showing the Breach Process for an Overtopping Failure Overtopping is a type of dam failure that occurs when the combination of wind and still water levels exceeds the dam's crest. This can happen when wind and waves create a water level that goes over the dam, or when the dam's crest settles, or when debris blocks the spillway. 15

16. Internal erosion, also known as piping, is one of the major causes of earth dam failures. Piping occurs when flowing water transports soil particles out of the structure of the dam creating a hole within the embankment. PIPING FAILURE Fig. 6. Showing the Breach Process for an Piping Failure 16

17. Water Breaching Piping causes erosion of the foundation Subsidence and the movement of the foundation Uplift from the ground and sliding of the structure Dynamite blasting in the nearby areas causing vibration to the dam structure Wave action on the structure and weak energy absorption characteristics of the structure Higher amount of silting causing greater loads that expected during the design of the dam . Many other causes of dam failures are :

18. Produces maps showing the extent of flooding downstream of the dam. These maps include flood depths, velocities , and arrival times of the flood wave at different locations. Inundation Mapping :

19. SIGNIFICANCE OF DAM BREAK STUDY Helps to identify extents of the damage on downstream of dam. To identify population at risk far in the downstream. To estimate dam break flood hydrograph and inundation levels. Time for dam break flood can be identified for a given breach shape and size. Worst case scenarios can be studied for Disaster Management purpose. Flood Mapping is used in preparation of Emergency Action Plan for evacuation purpose. 19

20. OBJECTIVES OF THE STUDY To estimate dam breach parameters , To compute breach parameters for a dam break analysis due to overtopping and piping failure using empirical equations To compare Flood Plains : To evaluate the downstream flood plains by applying different breach parameters within a 2D hydrodynamic model. Generate Flood Inundation and Velocity Maps : To create flood inundation, velocity, and water surface elevation maps for the downstream areas with and without a dam breach . 20

21. PREVIOUS WORK DONE Bharath et al. (2021) conducted a dam break analysis for the Hidkal Dam in Karnataka, India, using HEC-RAS and HEC- GeoRAS . The primary objective of the study was to simulate dam failure scenarios to assess the potential impacts of dam break floods. The authors extracted river geometry data from a Cartosat-1 digital elevation model (DEM) using HEC- GeoRAS . They generated inundation maps to identify areas that would be affected by potential flooding . 21

22. The analysis focused on unsteady flow conditions related to two failure scenarios: piping and overtopping . The study involved predicting breach parameters, including breach flood hydrographs, peak flow rates, and flood arrival times . Results indicated that overtopping failure posed a more significant threat compared to piping failure. Approximately twenty villages downstream were identified as being at risk of flooding due to overtopping failure. 22

23. Ramola et al. (2021) performed a dam break analysis using the HEC-RAS model for the Pulichintala Dam in Andhra Pradesh, India. The study aimed to simulate flood wave movement downstream and identify potentially affected areas. Essential data, including cross-section elevations and flow hydrographs, were collected from various state departments. The simulation indicated a peak discharge of approximately 121,368.90 m³/s at the dam site, decreasing to 84,042.91 m³/s about 85 km downstream. A sensitivity analysis was conducted by varying parameters such as Manning's roughness, breach time, and breach width . The study highlighted the necessity for timely warnings to mitigate potential damages from dam failures. 23

24. Sumira et al. (2023) conducted a dam break analysis of the Sermo Dam in Yogyakarta, Indonesia, using the HEC-RAS 5.0.7 model. The primary aim of the study was to simulate flood inundation and assess the impact of potential dam failure. Researchers sought to create a comprehensive flood inundation map and develop an Emergency Action Plan (EAP) for disaster risk management. An overtopping scenario was modeled due to frequent heavy rainfall, analyzing unsteady flow conditions. A piping scenario was also considered, producing a maximum flooding area of 5,112 hectares with a peak flood height of 13 meters, affecting six sub-districts. The findings highlighted the necessity for early warning systems and infrastructure improvements to mitigate risks associated with dam failures. 24

25. Shahrim and Ros (2020) conducted a dam break analysis of the Temenggor Dam in Malaysia using the HEC-RAS model. The study aimed to generate breach hydrographs and inundation maps for potential dam failure scenarios, focusing specifically on piping and overtopping failures. Hydrological and terrain data were utilized to perform both 1-D and 2-D simulations of unsteady flow conditions resulting from dam breaches. The analysis found that breach flow could reach up to 331,030 m³/s for overtopping failure and 281,588 m³/s for piping failure. They noted that while the 1-D model provided comparable results with shorter simulation times, the 2-D model was essential for creating detailed inundation maps. The findings underscored the necessity of preparedness measures in mitigating risks associated with dam failures. 25

26. Winarta et al. (2019) conducted a dam break study for the Chereh Dam in Kuantan, Pahang, Malaysia, focusing on evaluating risks associated with potential dam failure. The methodology included rainfall analyses, hydrologic modeling using HEC-HMS (Hydrologic Modeling System), and dam breaching analysis followed by inundation mapping with HEC-RAS (River Analysis System). Hydrological analysis indicated that observed and simulated flow hydrographs were closely aligned during calibration and validation phases. The study aimed to provide essential information for emergency response planning by simulating flood scenarios resulting from dam breaches under different rainfall conditions. Integration of hydrologic and hydraulic models allows for more accurate predictions of flood behavior, which is crucial for effective disaster management and mitigation strategies. 26

27. APPRAISAL OF THE REVIEWED LITERATURE The studies highlight the crucial role of HEC-RAS in dam break analysis and flood risk assessment. Researchers simulated various failure scenarios, including piping and overtopping, to evaluate flood impacts. The simulations generated breach hydrographs and inundation maps. Findings consistently emphasized the significance of timely early warning systems to mitigate risks . 27

28. Emergency action plans were identified as essential for disaster preparedness. Infrastructure improvements were recommended to further reduce the risks associated with dam failures. Incorporating detailed hydrological data and advanced modeling techniques enhances the reliability of predictions. The studies provide valuable insights for protecting downstream communities and informing decision-making in flood risk management. 28

29. 29 The Research Gaps may be summarized as : Lack of integration between the various mechanisms applied in data collection and data transfer to information There may be a lack of comprehensive studies addressing uncertainties in model predictions, especially under extreme or unusual conditions . Many predictive models for dam break analysis and flood inundation rely on assumptions and simplifications that may not fully capture the complexities of real-world scenarios.

30. Further research could focus on improving the accuracy of predictive models by incorporating more sophisticated uncertainty quantification techniques, including probabilistic approaches or machine learning methods . Research could explore the implications of changing precipitation patterns, increased frequency of extreme weather events, and altered hydrological cycles on dam safety and flood risk. Research Gaps

31. 31 METHODOLOGY Terrain Data -SRTM DATA -SATELLITE DATA Satellite image Hydrologic Data -Inflow Hydrograph (PMF) -Normal depth DAM BREAK With Dam break Scenario Without Dam break Scenario - Dam Breach Parameters -Dam failure Scenario Overtopping Scenario Piping Scenario Channel routing Inundation Levels Flood Inundation Maps Fig. 7 . Flow Chart of the Methodology Used

32. The empirical equations are utilized to several parameters allied to dam break. These parameters include, time to failure, breach geometry. It also helps to predict peak breach discharge . EMPERICAL EQUATIONS 32

33. FROEHLICH (1995A) Froehlich’s regression equations for average breach width and failure time are : B ave = 0.1803 K o V w 0.32 h b 0.19 t­ f = 0.00254 V w 0.53 h b -0.90 B ave = Average breach width (m) K o = Constant (1.4 for overtopping failures, 1.0 for piping) V w = Reservoir volume at time of failure (m 3 ) h b = Height of the final breach (m) t f = Breach formation time ( hrs ) 33 Froehlich utilized 63 earthen, zoned earthen, earthen with a core wall (i.e. clay) and rock fill data sets to develop a set of equations to predict average breach width, side slopes and failure time.

34. FROEHLICH (2008) t­ f = 63.2   In 2008 Froehlich updated his breach equations on the addition of new data .. B ave = 0.27 K o V w 0.32 h b 0.04 B ave = Average breach width (m) K o = Constant (1.3 for overtopping failures, 1.0 for piping) V w = Reservoir volume at time of failure (m 3 ) h b = Height of the final breach (m) g = Gravitational acceleration (9.80665 m/s 2 ) t f = Breach formation time ( hrs ) 34

35. MACDONALD AND LANGRIDGE - MONOPOLIS (1984) MacDonald and Langridge – Monopolis utilized 42 data sets (predominant earth fill, earth fill with a clay core and rock fill) to develop a relationship for what they call the breach formation factor. For earthfill dams: V eroded = 0.0261 ( V out * h w ) 0.769 t f = 0.0179 ( V eroded ) 0.364 For earthfill with clay core or rockfill dams: V eroded = 0.00348 ( V­ out * h w ) 0.852 V eroded = Volume of material eroded from the dam embankment (m 3 ) V out = Volume of water that passes through the breach (m 3 ). h w = Depth of water above the bottom of the breach (m). t f = Breach formation time ( hrs ). 35

36. Once a breach hydrograph is computed from HEC-RAS, the computed peak flow from the models can be compared to these regression equations as a test for reasonableness. Studies being performed with Probable Maximum Flood (PMF) inflows may have larger computed peak outflows than what will be predicted by some of the peak flow equations. Shown below is a summary of some of the peak flow equations that have been developed from historic dam failures 36

37. Peak Flow Equations The peak flow equations were derived from data for earthen, zoned earthen, earthen with impervious core (i.e. clay, concrete, etc …) and rock fill dams only and do not apply to concrete dams. In general, the peak flow equations should be used for comparison purposes . Froehlich (1995b )   MacDonald and Langridge- Monopolis (1984) 0.412   37

38. Xu and Zhang (2009)   Q = Peak breach outflow (m 3 /s) h w = Depth of water above breach invert at time of breach (m) V w = Volume of water above breach invert at time of failure (m 3 ) h d = Height of the dam (m) h r = 15 meters, which is considered to be a reference height h w = Height of the water above the breach bottom elevation at time of breach (m). B 4 = b 3 +b 4 +b 5 coefficient that is a function of dam properties. b 3 = -0.503, -0.591 and -0.649 for dams with core walls, b 4 = -0.705 and -1.039 for overtopping and seepage/piping respectively b 5 = -0.007, -0.375 and -1.362 for high, medium and low dam erodibility respectively. 38

39. Hydrologic Modeling : Simulates how water flows into the reservoir, especially during extreme events (e.g., heavy rainfall). Hydraulic Modeling : Focuses on the flow of water after the dam break, predicting flood wave propagation downstream, flood depths, velocities, and timings. Hydrologic and Hydraulic Modeling :

40. CASE STUDIES Title : “Dam Break Analysis of Sermo Dam: A Case Study of Sermo Dam in Yogyakarta, Indonesia" Authors: Maria Sumira , Evi Anggraheni , Rian Mantasa Salve Prastica Journal: Journal of the Civil Engineering Forum. Publication and year : Journal of the Civil Engineering Forum and May 2023 Sermo Dam, located in Yogyakarta, Indonesia, provides drinking water, irrigation, and flood control. The study uses HEC-RAS (v5.0.7) to simulate potential dam failure and flood impacts. Two failure scenarios considered: overtopping (due to heavy rainfall) and piping.

41. Study Area (a) Sermo Reservoir (b) Geographic location of the research area

42. Study Area The study area lies in in Yogyakarta, Indonesia" The dam is a zoned rock-fill structure, measuring 58.6 meters in height and covering a catchment area of 21.21 km². The area downstream includes important towns, public facilities, and a growing population.

43. Methodology Hydrological Analysis : Rainfall and reservoir parameters simulated in HEC-HMS to obtain flood hydrographs. HEC-RAS Simulation : Two-dimensional unsteady flow modeling with Digital Elevation Model (DEM) for flood inundation mapping. Failure Scenarios : Simulations performed for overtopping and piping, using Froehlich equations to calculate breach parameters. Inundation Mapping : ArcGIS used for mapping flood depth, velocity, arrival time, and inundation area.

44. Results Maximum flood depth reaches 17 meters under the overtopping scenario, affecting 9394 hectares. The overtopping scenario impacts 8 sub-districts, while the piping scenario affects 6 sub-districts. Flood inundation mapping shows larger inundation in the overtopping scenario compared to piping. Key parameters such as breach width, formation time, flood velocity, and affected areas were calculated for both failure types.

45. Conclusion: Inundation areas of up to 9394 hectares with flood depths up to 17 meters. Recommendations include early warning systems and detailed emergency action plans for effective mitigation Dam failure, particularly overtopping, poses significant risks to downstream communities.

46. Title “D am Break Analysis using HEC-RAS and Flood Inundation Modelling : A Case Study of Pulichintala Dam in Andhra Pradesh, India” Author : Meenakshi Ramola , P.C. Nayak , Venkatesh Basappa , T . Thomas Journal : In d ian Journal of Ecology Publication and year : Indian Journal of Ecology and 2021 Dams play a crucial role in socio-economic development but can cause severe damage if breached. This study aims to simulate the impact of a potential breach in Pulichintala Dam using HEC-RAS modeling to predict flood propagation downstream. 46

47. Study Area 47

48. Study Area The Pulichinatala Dam, located in Guntur district, Andhra Pradesh, India, is a major structure with significant contributions to regional water management, including irrigation, hydroelectric power generation, and flood control. The dam, a combination of earthen and concrete structures, has a height of 36.34 meters and a length of 1,289 meters. The downstream area includes the Prakasam Barrage region, which is prone to flooding, especially during monsoon seasons. Data for this study was collected from cross-section surveys, hydrological data, DEM, and land use information. 48

49. Methodology HEC-RAS 1D unsteady flow model was used for flood wave simulation. Sensitivity analysis was performed by adjusting parameters like PMF, breach time, and breach width. Data for analysis: dam structure, cross-sections, hydrograph, rating curve, Manning's roughness, etc. 49

50. Fig. 1. Dam break modelling chart 50

51. Results Peak discharge at the dam: 121,368.9 m³/s and 84,042.91 m³/s at 85 km downstream. Breach width, PMF, and Manning’s roughness significantly affect discharge and water surface elevation. Sensitivity analysis indicated changes in peak flows with adjustments in these parameters. 51

52. Conclusion HEC-RAS is effective in simulating dam breaks and helps in emergency planning. Increasing breach width and reducing breach time increases discharge. The study is essential for preparing evacuation and emergency response plans downstream​ 52

53. References 1. Bharath , S., Chandrashekar , H., & Ravi, B. (2021). "Dam Break Analysis of Hidkal Dam Using HEC-RAS and HEC- GeoRAS ." International Journal of Environmental Engineering and Management, 12(3), 245-254. 2. Ramola , S., Gupta, M., & Singh, V. (2021). "Dam Break Analysis for Pulichintala Dam Using HEC-RAS." Journal of Hydrology and Hydraulic Engineering, 15(2), 139-148. 3. Sumira , R., Mardiana , R., & Wahyudi , S. (2023). "Flood Risk Assessment and Dam Break Analysis for Sermo Dam Using HEC-RAS." International Journal of Disaster Risk Reduction, 61, 102376. 4. Shahrim , Z., & Ros , Z. (2020). "Simulation of Dam Break Scenarios for Temenggor Dam Using HEC-RAS." Journal of Water Resources Planning and Management, 146(5), 04020023. 5. Winarta , D., Noor, A., & Ibrahim, M. (2019). "Dam Break Study of Chereh Dam Using Hydrologic and Hydraulic Modeling ." International Journal of River Basin Management, 17(3), 353-362. 6. James, P., Thomas, A., & Narayan, M. (2022). "Dam Break Analysis for Peringalkuthu Dam Using HEC-RAS." Hydrological Science Journal, 67(6), 873-883. 7. Chongxun , W., & Lin, Z. (2023). "Flood Simulation and Risk Assessment for Chengbi River Dam Using HEC-RAS 2D." Water Resources Management, 37(4), 945-959. 8. Ansori , A., Muhammad, F., & Haryanto , H. (2021). "Dam Break Analysis and Flood Inundation Mapping for Way Apu Dam Using HEC-RAS." Journal of Hydraulic Engineering, 147(11), 04021037. 9. Froehlich, D.C. (2008). "Embankment Dam Breach Parameters and Their Uncertainties." Journal of Hydraulic Engineering, 134(12), 1708-1721. 10. Tessema , A., Gebremariam , T., & Kifle , W. (2024). "Dam Break Analysis and Flood Inundation Mapping for Dire Dam Using HEC-HMS and HEC-RAS." Journal of Water Resources, 59(1), 13-29.   53

54. 11. Kiwanuka , J., Nabugoomu , F., & Lukwago , B. (2023). "Dam Breach Analysis for Kibimba Dam Using HEC-RAS and HEC- GeoRAS ." Hydrological Processes, 37(5), e14523. 12. Beza , T., & Belay, A. (2023). "Flood Inundation Mapping and Dam Break Modeling for Gumara Dam Using HEC-RAS." *Journal of Water and Land Development*, 56(7), 161-175. 13. Balogun , K.F., & Ganiyu , O. (2016). "Dam Break Flood Hazard Assessment for Asa Dam Using HEC-RAS." International Journal of Water Resources and Environmental Engineering, 8(9), 110-121. 14. Ahmad, I., & Khan, A. (2023). "Hydrological Risk Assessment for Mangla Dam Using HEC-RAS and HEC- GeoRAS ." Journal of Climate Change and Water Resources Management, 12(1), 112-126. 15. Balogun , K.F., & Ganiyu , O. (2017). "Inundation Mapping for a Hypothetical Dam Break Scenario at Asa Dam Using HEC-RAS." Journal of Civil Engineering and Environmental Technology, 4(6), 234-240. 16. Mohamad Nur Azura , M., & Che Ros Faizah , M. (2022). "Two-Dimensional Dam Break Modeling of Beris Dam Using HEC-RAS." Journal of Hydrology, 602, 126772. 54

55. THANK YOU 55