HEC-RAS FLOW ANALYSIS IN THE RIVER TAPI

E-proceedings of the 37th IAHR World Congress August 13 – 18, 2017, Kuala Lumpur, Malaysia HEC-RAS FLOW ANALYSIS IN THE RIVER TAPI (1) DARSHAN J. MEHTA , DR. S. M. YADAV (1) (2) (3) & MRS. SAHITA I. WAIKHOM Sardar Vallabhbhai National Institute of Technology, Surat, Gujarat, India darshanmehta2490@gmail.com (2) Sardar Vallabhbhai National Institute of Technology, Surat, Gujarat, India shivnam27@gmail.com (3) Dr. S & S. S. Ghandhy Government Engineering College, Surat, Gujarat, India siwgecs@gmail.com ABSTRACT Floods are natural disaster; they cause the losses and damages to lives, properties and the nature. The main objective of this study is to integrate science of meteorology, hydrology and hydraulics by using an appropriate and effective method in flood management. 1-D Hydrodynamic model is used to evaluate geomorphic effectiveness of floods on lower Tapi river basin. In this present study, geometry of lower Tapi River, flood plain of Surat City and past observed flood data have been used to develop 1-D integrated hydrodynamic model of the lower Tapi River, India. After collecting the entire data using 1-D hydrodynamic model to simulate the flood of year 1944, 1945, 1968, 2006, 2007, 2012 and 2013. As Surat city has faced many floods since long back. Major flood event occurred in the year 1883, 1884, 1942, 1944, 1945, 1949, 1959, 1968, 1978, 1979, 1990, 1994, 1998, 2002, 2006, 2007, 2012 and 2013. The carrying capacity of river is approximately about 4.5 lakhs cusecs (12753 cumecs) at present. The river network and cross sections for the present study were extracted from the field surveyed contour map of the river Tapi River. In this, stability of a segment of lower reach of Tapi river approximately 9 km length between Weir cum causeway and Kapodra (Uttran Bridge) is evaluated for its carrying capacity and geomorphic effectiveness. The study reach consists of 36 cross-sections. The model is used to evaluate steady flow analysis, flood conveyance performance and uniform flow analysis. The study area selected is highly affected by the flood and it is necessary to develop flood reduction plan for the study area which will helps to control a big disaster in future. The recommendations are done based on this study either to increase height of the retaining wall or construct a retaining wall at certain sections along study reach. The present study also recommends improving carrying capacity of Tapi river so that it will minimize the flood in surrounding area of Surat City. Keywords: Flood Event, HEC-RAS, Steady Flow, Tapi River, Uniform Flow computations 1 INTRODUCTION Rivers play a major role in the human civilization as they are the major source of fresh water, transportation, and resources. However, some times this relationship is often “troubled” because change in river discharge which leads to flood or drought. Floods has been considered as one of the most devastating natural hazards/disasters causes huge immediate damage and long term loss on human activity, economic development of a society as well as on the environment. River Tapi is originating from a Multai Hills (Gavilgadh hill ranges of Satpura) and flowing through three states Maharastra, Madya Pradesh and Gujarat having length of 725 Kms. The flow of water and water level in the river Tapi is controlled at Ukai dam which is 100 kms away from Surat city. The foundation of dam is resting on Dolerite dykes (Basalt). It is constructed for irrigation purpose mainly and also served the purpose of flood control, generation of hydropower and supply of industrial and drinking water. The average rainfall in the catchment area is about 785 mm and average yearly run off is 17,226 MCM. The area of Surat city situated at delta stage of the river is 326.51 sq.km. and population is about 40 lakhs. The city is having 60,000 Shops & Establishment in trading activity. The city is also famous for diamond industry. The Major industries like Essar Steel, Reliance, ONGC, L & T, Gail, Kribhco, Shell, NTPC, GSPC, Torrent Power etc. are situated in the city. A flood is an unusually high stage in a river normally the level at which the river overflows its banks and inundates the adjoining area. As Surat city has faced many floods since long back. Major flood event occurred in the year 1883, 1884, 1942, 1944, 1945, 1949, 1959, 1968, 1978, 1979, 1990, 1994, 1998, 2002, 2006, 2007, 2012 and 2013. With rapid advancement in computer technology and research in numerical techniques, various 1-D hydrodynamic models, based on hydraulic routing, have been developed in the past for flood forecasting and inundation mapping. In this study, one dimensional hydrodynamic model HEC-RAS has been developed using geometric and past flood data of the lower Tapi River. The discharge (past flood data) and river stage (stations and elevations) were chosen as the variables in practical application of flood warning. The developed model has been utilized to simulate the flood of year 1959, 1968 and 2006 for uniform flow computation. Many practicing Engineers already have established HEC-RAS models for floodplain analysis. Thus, this single terrain is usable for both hydrologic and hydraulic modeling. Tapi is main source of water in Surat and other region surrounded it. In Tapi river mostly flood occur due to upstream raining and therefore it is necessary to forecast flood and prepare flood mitigation plan. 1 E-proceedings of the 37th IAHR World Congress August 13 – 18, 2017 - Kuala Lumpur, Malaysia With rapid advancement in computational technology and research in numerical techniques, various one dimensional (1D) hydrodynamic models, based on hydraulic routing, have been developed, calibrated, validated and successfully applied for flood forecasting and inundation mapping. Hydrodynamic models that reproduce the hydraulic behavior of river channels have been proven to be effective tools in floodplain management (Timbadiya et. al, 2001). Floods are occurring in river Tapi time to time, due to which major portion of the city is submerged creating a lot of damage in residential as well as industrial areas. There is a need of reducing the effect of flood. In this paper, the flood water levels along the Tapi River in Surat were simulated using the HEC-RAS 1-D hydrodynamic model to prepare the people to survive during floods with minimum damages 2 OBJECTIVES The flood affects human lives, destroying their home and livelihood, moreover affecting the country‟s business, economy and industry. As the research and development continues to overcome this vulnerability, the study made in this project tries to focus on use of HEC- RAS. The objectives of the study is to analyze the stability of a segment of lower Tapi river reach between Weir cum causeway and Kapodra (Uttran Bridge) by evaluating its carrying capacity in response to peak discharge and slopes. 3 STUDY AREA Surat is situated between latitude 21° 06ʹ to 21°15ʹ N and longitude 72°45ʹ to 72°54ʹ E, on the bank of river Tapi and having coastline of Arabian Sea on its west. Surat falls in Survey of India map number 46C/15, 16.The Tapi River receives several tributaries on both the banks and there are 14 major tributaries having length more than 50 km. On the right bank, 4 tributaries namely Vaki, Gomai, Arunavati and Aner join the Tapi River. On the left bank, 10 important tributaries namely the Nesu, Amaravati, Buray, Panjhra, Bori, Girna, Waghur, Purna, Mona and Sipna drain into the main river channel. The drainage system on the left bank of the Tapi river is, therefore, more extensive as compared to the right bank area. The Purna and Girna, the two important left bank tributaries, together account for nearly 45 % of the total catchment area of the Tapi River. The Tapi river, the second largest west flowing river in India, originates from Multai (Betul district) in Madhya Pradesh (M.P.) at an elevation of 752 m having length of 724 km and falls in to the Arabian Sea at little 2 2 beyond the Surat city. The total drainage area of Tapi is 65,145 km out of which 9804 km lies in Madhya 2 2 Pradesh, 51,504 km lies in Maharastra and 3837 km lies in Gujarat. The Tapi river basin is divided in three sub-basins namely, upper Tapi basin (up to Hathnur), middle Tapi basin (Hathnur to Gighade) and lower Tapi basin (Gighade to the sea). The Surat city is located at the delta region of the Tapi river. Surat city lies at a bend of the river Tapi, where its course swerves suddenly from the south-east to south-west. From the right bank of the river, ground rises slightly towards the north but the height above Mean Sea Level (MSL) is 13 m. River Tapi flows through the city and meets the Arabian Sea at about 16 km from Surat. Surat is 90 km in downstream of Ukai Dam over river Tapi. At present the most challenging problem the city faces, is the frequently occurring floods in the river of Tapi. The city of Surat and its economy have been hit by a number of floods over the past few decades which were mainly during 1944, 1945, 1949, 1959, 1968, 1979, 1990, 1994, 1998, 2006, 2007, 2012 and 2013. Floods are occurring in river Tapi time to time, due to which major portion of the city is submerged creating lot of damage in residential as well as industrial areas. There is a need of reducing the effect of flood. In this paper the aspects of river channel modification are also considered for enhancing the carrying capacity and reducing the effect of flood in the city. Figure 1 - Study area with cross-sectional details 2 E-proceedings of the 37th IAHR World Congress August 13 – 18, 2017 - Kuala Lumpur, Malaysia Due to encroachment, silting and scouring, depth and width are reducing day by day. By reducing carrying capacity on adjoining areas and modifying the channel it will helpful in the preparation of flood mitigation plan for Surat city as a curative measure for the control of flood in the river Tapi. Thus, the modification of river channel is done to increase the carrying capacity of river Tapi and thus reducing the effect of flood in Surat city and surrounding region. Figure 1 shows the study area from Weir cum Causeway to Kapodra Bridge. The details of the study reach are: Total numbers of cross-sections are 36 (CS-1 to CS-36), River reach length is 9kms i.e. (9000 metres), Red line indicates cross-sections in river reach, Average interval between crosssections to cross-sections is 250 metres, Upstream: Weir cum causeway Downstream: Kapodra Bridge 4 HEC-RAS OVERVIEW Originally designed in 1995, the United States Army Corps of Engineers Hydraulic Engineering Center‟s River Analysis System (HEC-RAS) is “software that allows you to perform one-dimensional steady and unsteady flow river hydraulics calculations, sediment transport-mobile bed modeling, and water temperature analysis.” The program solves the mass conservation and momentum conservation equations with an implicit linearized system of equations using Preissmann‟s second order box finite difference scheme (Subramanya et. al.). In a cross-section, the overbank and channel are assumed to have the same water surface, though the overbank volume and conveyance are separate from the channel volume and conveyance in the implementation of the conservation of mass and momentum equations (Hong et. al. 2011). HEC-RAS was first released in 1995 and since that time there have been several major versions of HEC-RAS of which 4.1 is the latest version released in 2010. In this paper, version 4.1 of HEC-RAS was used. The development of the program (HEC-RAS) was done at the Hydrologic Engineering Centre (HEC), which is a part of the Institute for Water Resources (IWR), U.S. Army Corps of Engineers. HEC-RAS has the ability to make the calculations of water surface profiles for steady and gradually varied flow as well as for subcritical, super critical, and mixed flow regime. In addition to this, HEC-RAS is capable to do modeling for sediment transport, which is notoriously difficult. Therefore, modeling sediment transport is based on assumptions and empirical theory that is sensitive to several physical variables (Beaver, 2004). 5 DATA REQUIRED IN HEC-RAS The data‟s required for carrying out 1-D hydrodynamic modeling using HEC-RAS are Manning „n‟ value, Slope of a river bed, Detailed cross sections of river (Geometric Data), Map of Study area, Past flood data or peak discharge data (Table 1), R.L of both banks i.e. Left side and Right side bank of the Study reach Table 1 Flood History of Surat City Sr. No. Year Discharge at Kakrapar weir (Cumecs) Discharge at Kakrapar weir (Lakh cusecs) 1 1876 20530 07.25 2 1883 28456 10.05 3 1894 22682 08.01 4 1942 24352 08.60 5 1944 33552 11.85 6 1945 29018 10.25 7 1949 23843 08.42 8 1959 36670 12.95 9 1968 43924 15.51 10 1969 24239 08.56 11 1998 19017 06.73 12 2006 25788 09.10 13 2012 9508 03.35 14 2013 13092 04.62 Source: Flood Cell, Surat 5.1 Geometric Data The basic geometric data consists of establishing how the various river reaches are connected (River System Schematic); cross section data; reach lengths; energy loss coefficients (friction losses, contraction and expansion losses); and stream junction information (John et. al. 2009). Surat Municipal Corporation (SMC) has provided the geometric data of the reach for present study as contour map in Auto CAD (.dwg file) format. The cross-section data at different locations were extracted from aforesaid map for the river under consideration. The effect of meandering has been neglected as there is no reasonable curvature seen in study reach by providing expansion and contraction coefficient as 0.3 and 0.1 respectively. Total 36 cross3 E-proceedings of the 37th IAHR World Congress August 13 – 18, 2017 - Kuala Lumpur, Malaysia sections at various important locations on the river have been used. The detailed configuration of study reach was respectively collected from Surat Municipal Corporation (SMC) and Surat Irrigation Circle (SIC), Govt. of Gujarat, India in the hard map format. All stations should be entered from left to right looking upstream. Data such as Manning‟s n values, bank stations, reach lengths, and expansion/contraction coefficients are required for each cross-section. Manning‟s n values are used primarily for calibration purposes. 5.2 Cross sectional Data Usually, the average cross section of a channel does not change under natural conditions over a period of years. Boundary geometry for the analysis of flow in natural streams is specified in terms of ground surface profiles (cross sections) and the measured distances between them (reach lengths). Cross sections should be perpendicular to the anticipated flow lines and extend across the entire flood plain. Cross sections are requires at locations where changes occur in discharge, slope, shape or roughness; at locations where levees begin or end and at bridges or control structures such as weirs. Each cross section is identified by a Reach and River Station label. (Agnihotri et. al. 2011). The cross section is described by entering the station and elevations (x-y data) from left to right, with respect to looking in the downstream direction. 5.3 Reach Length The reach length (distance between cross sections) should be measured along the anticipated path of the center of mass of the left and right over bank and the center of the channel (these distances may be curved). 6 FLOOD CONVEYANCE PERFORMANCE For evaluation of flood performance, past flood data collected from the Surat Irrigation Circle, Surat and also Flood Cell, Surat were used. The flood frequency analysis results were based on data which coincides with the upstream limit of the project reach. Major flood events took place in the year 1883, 1884, 1942, 1944, 1945, 1949, 1959, 1968, 1994, 1998, 2002, 2006, 2007 and 2013. The summary of the floods is given in the Table 1. 7 METHODOLOGY The input data require for 1-D analysis for carrying capacity of study reach, data collected from Surat Municipal Corporation are entered in HEC-RAS software. The study reach consists of 36 cross sections. The details like station number, elevation, Manning‟s roughness coefficient (Garde et. al.) were entered in geometric data window of HEC-RAS software. After entering geometric data the necessary steady flow data can be entered. Steady flow data consists of number of profiles to be computed, flow data and the river system boundary conditions. To access the carrying capacity of particular section using hydraulic design function and uniform flow condition, input discharge of specific year in the software. Additionally, discharge can be changed at any location within the river system. Discharge must be entered for all profiles. A boundary condition must be established at the most downstream cross section for a subcritical flow profile and at the most upstream cross section for a supercritical flow profile. Based on this input data HEC RAS will compute section. The computed section is sufficient to carry input discharge if F.S.L is within the bank heights. If computed section is insufficient to carry input discharge software will develop levees on that bank which is overtopped by the input discharge. The above procedure is repeated for all the 36 sections. 8 RESULT AND RESULT DISCUSSIONS In this study sufficiency of existing sections are accessed using two major flood events of historical floods. The section were classified as highly critical (where depth of water above existing bank is more than 0.7m), moderately critical (where depth of water above existing bank is between 0.4 to 0.7m) and critical (where depth of water above existing bank is up to 0.4m). Figures present computed sections using HEC-RAS software and past flood data. Figure shows the graph between station (Chainage in m) and elevation (Bed level in m). Fig. 2 to Fig. 9 shows the critical sections computed using flood discharge of 25788 cumecs (2006), 33552 cumecs (1944), 43294 cumecs (1968) and 36670 cumecs (1959). Table 2 shows the summary result of flood events 1968, 2006, 1959 and 1944 year. Figure 3 - Detail of Computed CS - 4 Figure 2 - Detail of Computed CS - 1 4 E-proceedings of the 37th IAHR World Congress August 13 – 18, 2017 - Kuala Lumpur, Malaysia Figure 4 - Detail of Computed CS - 14 Figure 5 - Detail of Computed CS - 15 Figure 6 - Detail of Computed CS - 22 Figure 7 - Detail of Computed CS - 25 Figure 8 - Detail of Computed CS - 30 Figure 9 - Detailed of Computed CS - 36 In flood event 1968 having discharge 43924cumecs, 9 sections are highly critical, 19 sections are moderately critical and 8 sections are critical thus it is strongly recommended to construct levees or retaining wall on the particular cross sections. In flood event 2006 having discharge 25788cumecs, 8 sections are highly critical, 10 sections are moderately critical and 18 sections are critical in which 18 sections are common as that in flood event of 1968, thus it is strongly recommended to raise the level of levees or retaining wall at particular cross sections and also suggest to construct the retaining wall or levees at particular sections. In flood event 1959 having discharge 36670cumecs, 8 sections are highly critical, 9 sections are moderately critical and 19 sections are critical. In flood event 1944 having discharge 33552cumecs, 4 sections are highly critical, 13 sections are moderately critical and 19 sections are critical. Table 2 Classification of study reaches cross sections based on HEC RAS analysis Sr. No. 1 Flood Event 1968 (43924 cumecs) Highly Critical Moderately Critical Critical CS-10, CS-13, CS-14, CS15, CS-24, CS-32, CS-33, CS-34, CS - 36 CS-2, CS-3, CS-4, CS-5, CS-6, CS-7, CS-8, CS-9, CS-12, CS-18, CS-20, CS-21, CS-22, CS-23, CS-26, CS-28, CS-29, CS-30, CS-31 CS-1, CS-11, CS-16, CS-17, CS19, CS-25, CS-27, CS-35 5 E-proceedings of the 37th IAHR World Congress August 13 – 18, 2017 - Kuala Lumpur, Malaysia 2 2006 (25788 cumecs) CS-11, CS-13, CS-14, CS15, CS-24, CS-32, CS-33, CS-34 CS-6, CS-8, CS-9, CS-10, CS-18, CS-20, CS-21, CS-25, CS-26, CS-27 3 1959 (36670 cumecs) CS-2, CS-3, CS-10, CS-11, CS-13, CS-14, CS-15, CS24 CS-5, CS-7, CS-9, CS-12, CS-20, CS-21, CS-32, CS-33, CS - 34 4 1944 (33552 cumecs) CS-2, CS-3, CS-10, CS-24 CS-5, CS-7, CS-9, CS-12, CS-11, CS-13, CS-14, CS-15, CS-20, CS-21, CS-32, CS-33, CS - 34 CS-1, CS-2, CS-3, CS-4, CS-5, CS-7, CS-12, CS-16, CS-17, CS19, CS-22, CS-23, CS-28, CS-29, CS-30, CS-31 CS-35, CS-36 CS-1, CS-4, CS-6, CS-8, CS-16, CS-17, CS-18, CS-19, CS-22, CS23, CS- 25, CS-26, CS- 27, CS28, CS-29, CS-30, CS-31, CS-35, CS-36 CS-1, CS-4, CS-6, CS-8, CS-16, CS-17, CS-18, CS-19, CS-22, CS23, CS- 25, CS-26, CS- 27, CS28, CS-29, CS-30, CS-31, CS-35, CS-36 9 CONCLUSIONS It is strongly recommended that the sections, at which water overtop the existing level, embankment or retaining wall need to be raised. It is recommended that the storm drain outlets should be provided with flood gates to prevent entry of flood water in the study area. It is strongly recommended that the width of the river in no case be encroached as already sections are sensitive to high floods, encroachment will result in flooding of study region. It is strongly recommended that no new construction be allowed in flood plain area. REFERENCES Agnihotri PG and Patel JN (2011). Modification of channel of Surat city over Tapi river using HEC- RAS software. International Journal of Advanced Engineering Technology, 2, 231-238. Anthony LF., Chester W., and Brian PB. (2000). Stable Channel Design for Mobile Gravel Bed Rivers, Journal of Water Resource and Protection, 10, 1-9. Beaver (1994). Hydraulic modelling of river channels using GIS based tools named HEC, 2, 45-55. Frantisek K. (2007). On the Determination of the Stable Bed Slope of a Channel Using Mathematical Model, Journal of Soil and water Resource, 3, 104-111. 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