GEOMORPHIC EFECTIVENESS OF FLOODS ON LOWER TAPI RIVER BASIN USING 1-D HYDRODYNAMIC MODEL,HEC-RAS Darshan Mehta 1, Raju Karkar 2, Lalji Ahir 3 Assistant Professor, CED, S.S.A.S.I.T, Surat, Gujarat, India 1 UG Student, CED, S.S.A.S.I.T, Surat, Gujarat, India 2 UG Student, CED, S.S.A.S.I.T, Surat, Gujarat, India 3 Abstract: Floods are natural disaster they cause the losses and damages to lives, properties and the nature. The main objective of this paper 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 paper, 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 i.e. HEC-RAS and using peak flood discharge of year 1968, 1959 and 2006. The carrying capacity of river is approximately about 4.5 lakhs cusecs (12753 cumecs) at present. Thus for this present study we have selected our study area from Weir cum causeway to Kapodra Bridge. Approximately 10 km length between Weir cum causeway and Kapodra Bridge is evaluated for its carrying capacity and geomorphic effectiveness. The study reach consists of 40 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: Cross-section, Flood, Flood conveyance performance, Geomorphic Channel. INTRODUCTION Life, both animal and plant, is impossible without water. The importance of water as a resource is abnormal. River is the main source of water and it s been need to construct dam and other structure on river to collect useful water for population. 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, All rights reserved by www.ijaresm.net ISSN : 2394-1766 1
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. For this present study we have selected our study area from Weir cum causeway to Kapodra Bridge in which there are 40 cross-sections and length of study reach is 10km. The hydraulic models like HEC-RAS are used for evaluate flood conveyance performance and uniform flow computation by Mehta Darshan J. (2014). HEC-RAS was also used in the preparation of Flood Mitigation Plan for Surat city as a curative measure for the control of flood in the river Tapi. John Shelley and A. David Parr (2009) had done the river analysis with the Copeland method. The Copeland method for designing geomorphologically stable channels has been included in the Army Corps of Engineers Hydraulic Engineering Circular River Analysis System (HEC-RAS). OBJECTIVES The objectives of the study are: To carry out uniform steady flow analysis using HEC-RAS software. To determine adequacy of existing sections to carry floods of various magnitude. To identifying critical cross-sections of study reach. To develop flood reduction plan for the study area which will helps to control a big disaster in future. STUDY AREA Surat is a port city situated on the banks of the Tapi river. Big water resources projects like Ukai Dam, Kakrapar weir are near the Surat. As mentioned earlier Surat has been blessed by the flow of Tapi however, it has also suffered a lot because of floods in Tapi since historic time. Flood occurs at Surat city frequently due to sudden release of water from Ukai dam in river Tapi. The river reach selected for present study is extremely important as 80% of total population of Surat is settled on the either side of the bank. Major business centers for diamond industries, textile industries and industrial area of Hazira are within few km radius of the study reach. Fig. 1 shows the study area with cross-sections details. Total no. of cross sections is 40. Total distance of Study reach is 10km (10000m). Distance between cross-sections to cross-sections is 250m. Red line indicates cross sections. Upstream reach is Weir cum causeway and downstream reach is Kapodra Bridge. All rights reserved by www.ijaresm.net ISSN : 2394-1766 2
Figure 1: Study area with Cross-sections Source: Google Maps 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. In a crosssection, 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. 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. DATA REQUIRED IN HEC-RAS The following data are required for carrying out 1-D hydrodynamic modelling using HEC- RAS. 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 All rights reserved by www.ijaresm.net ISSN : 2394-1766 3
Sr. No. Year IJARESM Discharge at Kakrapar weir (Cumecs) Discharge at Kakrapar weir (Lakh 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 Table 1: Flood History of Surat City Source: Flood Cell, Surat METHODOLOGY Following are the steps are required for uniform flow computations: Step 1: Create a new HEC-RAS project. Step 2: Create a new river and reach in the geometry editor window. River Name: Tapi Reach Name: Weir cum causeway to Kapodra Bridge Step 3: Enter the geometric data i.e. station and elevation data. Step 4: After adding all data we get geometric cross-section in HEC-RAS software which is Step 5: Enter the Manning s value for upstream reach. In this paper, value of n is taken as 0.022. The value of n can be taken according to bed material of the river reach. Step 6: Enter steady flow data for different flood peak discharge. Once the geometric data is entered, the necessary flow data can be entered Steady flow data consists: the number of profiles the flow data and the river system boundary conditions Step 7: Open Run windows. Click on Hydraulic design function and select, uniform flow. Step 8: In Uniform flow window input the peak flood discharge of specific year to a selected section. Step 9: In the same window, Input slope to a selected cross-section. Here, slope can be calculated from cross-section to cross-section In our present project we obtained slope S = 0.00031 Repeat this procedure for 40 cross-sections. Step 11: Repeat steps 8 to steps 10 for all cross sections of study reach i.e. 40 cross sections. RESULT ANALYSIS Data Analysis is the key tool in understanding the behavior of the river cross-sections under the effect of various flood events. After collecting all data of study reach, input all data All rights reserved by www.ijaresm.net ISSN : 2394-1766 4
for designing of river reach section in uniform flow and simulation is carried out using HEC- RAS and past flood event. The flood events of 1959, 1968, and 2006 were considered for steady flow analysis of Tapi river for a reach of 10 km. The study of behavior of river crosssections under various flood discharges along with tidal condition is carried out. The carrying capacity of study reach section is accessed for three flood events. Following are the finding from the above study is summarized as below: 1. At cross-section 1, for flow of 36670 and 25788 cumecs the cross-section is sufficient to carry flow but when the flow is of 43924 cumecs, the section is not capable of carrying the flow. 2. At cross-section 14, for flow of 25788 cumecs the cross-section is sufficient to carry flow but when the flow is of 36670, and 43924 cumecs, the section is not capable of carrying the flow. 3. At cross-section 22, for flow of 25788, 36670, and 43924 cumecs the cross-section is not capable to carrying the flow. 4. At cross-section 25, for flow of 25788, 36670, and 43924 cumecs the cross-section is not capable of carrying the flow. All rights reserved by www.ijaresm.net ISSN : 2394-1766 5
5. At cross-section 30, for flow of 25788 cumecs the cross-section is sufficient to carry flow but when the flow is of 36670 and 43924 cumecs, the section is not capable of carrying the flow. 6. At cross-section 40, for flow of 25788 and 36670 cumecs the cross-section is sufficient to carry flow but when the flow is of 43924 cumecs, the section is not capable of carrying the flow. CONCLUSION The study area is highly affected by the flood and it is necessary to develop flood reduction plan for the study area which helps to control big disaster in future. As the slope of river increases, the velocity of water also increases and hence the discharge carrying capacity of river also increases. The width of bank of study reach has reduced considerably from 1080m to 900m only as a result of encroachment on the bank. By considering the past flood events, it is strongly recommended to improve the carrying capacity of Tapi River, so that it will minimize the flood in surrounding area of Surat City. From the analysis of Flood event 2006, it shows that West zone and South-west zone is highly Flood prone while East zone is least. About 90-95% Surat city was under water in hazardous 2006 flood event. It is strongly recommended that the sections, which water overtops over the existing embankment or retaining wall need to be raised. Due to urbanization, some natural drainage is blocked by constructions such as Airport and Shipyard. If such constructions are must to be build up then alternate routes must be provided for natural drainages to flow. It is strongly recommended to provide the flood gates on remaining storm drain to prevent entry of flood water in the study reach. ACKNOWLEDGMENT Authors are thankful to Principal and Director, Shree Swami Atmanand Saraswati Institute of Technology, Surat. The authors are also grateful to Surat Municipal Corporation and Surat Irrigation circle for providing data for present study. REFERENCES [01] Timbadiya P.V., Patel P.L. and Porey P.D. (2014).. One-dimensional hydrodynamic modelling of flooding and stage hydrographs in the lower Tapi River in India. CURRENT SCIENCE, VOL. 106, NO. 5, 10 MARCH 2014. [02] Mehta Darshan J. (2014). The hydraulic model, HEC-RAS is employed to evaluate flood conveyance performance and also uniform flow computation is carried out. [03] Mehta Darshan, Dr.S.M.Yadav and Waikhom Sahita (2014). 1-D hydrodynamic a. modelling of flooding in the lower tapi river basin in surat, Gujarat. National Conference on Recent Advances in Civil and Structural Engineering, (RACSE-'14). [04] Mehta Darshan, Ramani Manthan and Joshi Maulik (2014). Application of 1-D HEC- RAS models in design of channels.international Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163 Volume 1 Issue 7 (August 2014). All rights reserved by www.ijaresm.net ISSN : 2394-1766 6
[05] Mehta Darshan, Dr.S.M.Yadav and Waikhom Sahita (2013). Geomorphic Channel Design and Analysis Using HEC-RAS Hydraulic Design Functions Global Research Analysis, Paripex. [06] Agnihotri P.G and Patel J.N (2011). Improving carrying capacity of river tapi (Surat, India) by channel modification, International journal of Advance Engineering Technology. [07] John Shelley and A. David Parr (2009). Using HEC-RAS Hydraulic Design Functions for Geomorphic Channel Design and Analysis, World Environmental and Water Resources Congress 2009: Great Rivers 2009 ASCE [08] Krovak Frantisek (2007). Irregularity of the gradient, accompanied by heavy bed-load experiencing abrupt changes of the flow as a result of heavy rainfalls of short duration and high intensity. [09] Vincent S. Neary, and NicKorte (2002). Preliminary Channel Design: Blue River Reach Enhancement in Kansas City. Global Solutions for Urban Drainage [10] Andrew J. Miller (1988). Flood Hydrology and Geomorphic Effectiveness. Earth surface Processes and Landforms, VOL. 15, 119-134 (1990). [11] Lisa L. Ely, Kale Vishwas, YehoudaEnzel and Victor R. Baker (1994). Geomorphic and hydrologic aspects of monsoon floods on the Narmada and Tapi Rivers in central India. Geomorphology 10 (1994) 157-168. All rights reserved by www.ijaresm.net ISSN : 2394-1766 7