DAM BREAK ANALYSIS USING HEC-RAS MODEL

PROJECT TEAM TEAM MEMBERS Hari Prasath. V (91710103012) Jeya Vignesh. J (91710103014) Moses Prawin Paul. S (91710103031) Muthu Kumar. M (91710103032) TEAM GUIDER Ms. D. Chella Meena., M.E.

Need for Analysis: Dams are built for water supply, hydro-power generation, flood control, etc., However, dams may cause catastrophic damage to human life and property if they collapse. With the help of the dam failure model, the failure modes of the dam can be predicted in advance.

Objective: To identify the dam break conditions under various scenario To identify the flood inundated area in the event of a dam break, using hydrologic software HEC-RAS. To protect against the loss of life and property damage, flood control measures are suggested

INTRODUCTION Damages to property, human sufferings and loss of life resulting from floods have been increasing annually despite decades of effort and huge expenditure for flood control. floods alone can cause heavy damages to mankind then the damages due to dam failure will be manifold and catastrophic because of the indiscriminate development of settlement and industries in the flood plain. There is an old Chinese proverb – “The Great Levee is ruined by ant nest”. For reduction of flood damages, both structural and non- structural methods are employed

STUDY AREA – VAIGAI BASIN The Dam is located at the latitude 10°03´ N and at the longitude 77°35´ E. The spillway portion had been constructed with masonry in cement mortar. The masonry dam is flanked on both the sides by earthen dams. The Perranai canal prevents seepage and pilferage loss from the River. This canal comes into operation from the year 1995-1996 irrigation seasons.

EARTHERN DAM Length of Dam in Left Flank : 542.544 m Length of Dam in Right Flank : 2700.528 m Maximum height of Dam : 25.908 m Bottom width of Dam : 152.400 m Top width of Dam : 7.620 m Top level of Dam : + 278.900 m

Vaigai River: The River Vaigai originates on the Eastern slopes of the Western ghats in Varushanadu Hills in Aundipatty Taluk of Theni District. The total length of the river is 258kms. The river flows along FIVE districts 1. Theni 2. Dindigul 3. Madurai 4. Sivagangai and 5. Ramanathapuram

Vaigai river basin:

Vaigai Dam: Vaigai Reservoir scheme had been taken up for execution during 2nd Five Year Plan Period and completed in 1958 at a distance 34km upstream of Peranai Regulator. VAIGAI DAM was constructed to store Periyar water and balancing the flood from Vaigai river during North East Monsoon. The Storage Capacity of Vaigai reservoir is 6879 Mcft

LITREATURE REVIEW Cameron T. Ackerman et al (2007) have made an attempt in the analysis of dam failure models by providing a scenario generating tool for identifying the resulting hazards. finally discussed the process for gathering and preparing data, creating an unsteady- flow model in HEC-RAS, entry of dam breach parameters, performing a dam failure analysis, and mapping of the flood progression.

Ludvig Bjerke et al(2007) simulated results showed a peak discharge of respectively 625 m3/s and 4350 m³/s. The travel time of the flood wave from the Aparan dam to Ashtarak was 1 hour. Yi (Frank) Xiong(2008) firstly described the dam break in the aspects of theories and models. Break parameters prediction, the understanding of dam break mechanics, peak outflow prediction were shown as the essential for the dam break analysis, and eventually determined the loss of the damages.

Sam Crampton(2007) describes that the potential flood risk caused by dam failure is often more severe and can behave very different to that of natural flooding events. His models have enabled flood inundation maps which include peak elevation, flood wave arrival time and flood wave time to the peak for both sunny day and storm in progress failures Dr. Melvin G. Schaefer(2010) some applications are Downstream Hazard Classification. Inundation mapping for use in developing Emergency Action Plans. Aid in the selection of Design/Performance Levels for Critical Project Elements. Incremental Damage Analysis - an alternative procedure for sizing emergency spillways.

Methodology Data Collection Hydrological Data geometric data, cross section data Dam Details HEC-RAS MODELLING Simulations Results Flood Damage Assessment

Salient features of Vaigai Dam: Type : Masonry Cum Earthen Dam Maximum Height : 33.83 m (111 ft) Earthen dam Length : 3199.00 m Masonry Dam Length : 316.00 m Catchment Area : 2253.3 sq.km Water Spread Area at FRL : 24.20 Sq.Km FRL : (MWL (+) 916.00 ft Capacity at FRL : 194.78 Mcum

Spill Way 7 Nos of size 12.19 m x 4.57 m (40’ x 15’) Type : Lift Gates Discharging Capacity : 62978 Cusecs River Sluice 7 Nos. of size1.52 m x 2.74 m (5’ x 9’) Discharging Capacity : 15412 Cusecs Drainage Gallery 1 Number of Size : 1.52 m x 2.29 m (5’ x 7’6”)

Dam failure scenarios: Sliding Piping Overtopping Poor maintenance Cracking Internal erosion

COLLECTED DATA FROM VAIGAI DAM 1) Dam Details Type of dam masonry spillway with earth dam flanks either side Total length of dam 3,559 m Length of masonry spillway 315.468 m. Length of earth dam on the right side 2,700.528 m. Length of earth dam on left side 5442.544 m. Top level of the dam +278.900 m.

2) Spillway Details shape of spillway ogee crest of spillway +271.280 m. length of spillway 7 nos. of 12.192 x 4.572 m. 3) Breach Information Maximum water level reached +279.205 m. Lowest elevation that bottom breach reaches +254.210 m. Final breach width 75 m.  Side slope of breach 0.03. Time of breach development 1 hr.

DERIVATION OF ONE HOUR HYDROGRAPH FROM 13-15 NOV.1992 STORM rate time hour Total run off ordinate in cumec Base flow ordinate in cumecs Direct run off ordinate(3-4) cumecs Unit Hydrograph ordinate 5/net in cumecs Time from beginning of surface run off hour 11.92 10.00 95   11.00 104 69 35 20 1 12.00 756 73 683 386 2 13.00 1461 76 1385 782 3 14.00 1453 79 1374 776 4 15.00 1313 83 1230 695 5 16.00 1223 86 1137 642 6 17.00 1133 89 1044 590 7 18.00 921 93 828 468 8 19.00 543 96 447 253 9 20.00 402 99 303 171 10 21.00 103 299 169 11 22.00 106 296 167 12 23.00 109 293 166 13 24.00 398 112 286 162 14 1.00 259 115 144 81 15 2.00 250 118 132 74 16

  3.00 250 121 129 72 17 4.00 247 124 123 69 18 5.00 127 120 67 19 6.00 131 116 65 20 7.00 134 113 64 21 8.00 137 110 62 22 9.00 141 106 60 23 10.00 144 103 58 24 11.00 147 100 56 25 12.00 151 96 34 26 13.00 214 154 5 27 14.00 166 157 9 3 28 15.00 160 6 29 16.00 163 2 30 17.00 31 EDRO 11,110 Pnet = 11110 x 1x 60 x 60/ 2255.30 x 106 = 0.0177 M ( or ) 1.77 cm.

ANNUAL PEAK INFLOW SERIES OF VAIGAI DAM Year Annual peak inflow in 100 cumecs Order number 7.3.84 18.55 1 14.11.92 14.61 2 19.11.79 13.98 3 8.11.77 9.93 4 17.12.71 7.61 5 12.11.60 7.30 6 9.11.93 7.10 7 8.1.90 4.64 8 5.12.61 4.11 9 9.12.63 3.59 10 17.11.66 3.13 11 29.12.73 2.64 12 26.11.78 2.63 13 9.11.72 2.44 14 22.11.80 2.41 15 10.11.59 2.31 16 30.10.87 2.04 17 19.11.76 1.94 18 4.11.67 1.878 19

1.11.64 1.74 20 19.12.68 1.69 21 25.10.81 1.68 22 18.9.75 1.66 23 26.10.89 1.56 24 7.11.83 1.55 25 8.11.85 1.43 26 19.10.70 1.35 27 22.10.62 1.27 28 24.11.74 1.21 29 3.12.65 1.14 30 23.10.91 1.05 31 1.11.86 1.01 32 21.8.69 0.95 33 5.12.82 34 8.11.88 0.84 35

Average Unit Hydrograph

The Hydraulic Model (HEC-RAS): HEC- RAS is a computer program for modeling water flowing through systems of open channels and water surface profiles. The basic computational procedure of HEC-RAS is based on the solution of the one-dimensional energy equation. Energy losses are evaluated by friction and contraction/expansion. The momentum equation may be used in situations where the water surface profile is rapidly varied.

HEC-RAS MODELLING Water quality analysis. Movable boundary sediment transport computations Unsteady flow simulation Steady flow water surface profile computations

OVER TOPPING PIPING HEC-RAS USED TO MODEL

CROSS SECTION DETAILS Cross section Elevation 245.9 825 244.925 1720 245.9 825 244.925 1720 242.285 2320 340.895 3000 239.3 4000 238.36 4950 236.36 6000 234.395 7000 233.325 8050 230.325 9000 229.375 10000 225.275 11200 223.075 12400 221.865 13900 220.195 15260 217.815 17000 215.415 18500 214.355 20000 212.36 21700 209.465 23940 203.59 26000 199.565 28000 196.8 30150 193.97 32050 192.59 34100 190.105 34760 188.96

HEC-RAS geometric data

HEC-RAS cross section data

HEC-RAS cross section graph

General profile plot

HEC-RAS flow profile data

flow hydrograph

OUTPUT DATA

CONCLUSION The HEC-RAS results show that the flood can inundate to the range of 1.67 Sq km. HEC-RAS and DAM BRK results are approximately equal . If the dam breaks the flood will reach the Madurai within 6 hours To minimise the damages following remedial measures can be initiated. Existing important installations may be shifted outside the flood zone in a phased programme The people living inside the flood zone can be evacuated well in advance to avoid human loss of life.

Reference “GUIDELINES FOR DAM BREACH ANALYSIS” State of Colorado, Department of Natural Resources, Division of Water Resources. “Dam Break Analysis for Aparan Reservoir, Armenia” Per Ludvig Bjerke. “Dam failure Analysis using HEC-RAS &HEC-GeoRAS” Cameron T. Ackerman, P.E. & Gary W. Brunner, P.E. Hydraulic Engineering Center, Davis, CA 95616. “A Dam Break Analysis using HEC-RAS” Yi(frank) Xiong Department of Civil & Environmental Engineering, Mississippi State University, MS.

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