International Journal of Advanced Engineering Technology E-ISSN 0976-3945

Research Article IMPROVING CARRYING CAPACITY OF RIVER TAPI (, INDIA) BY CHANNEL MODIFICATION Agnihotri P.G a and Patel J.N. b Address for Correspondence a. Associate Professor b. Professor Civil Engineering Department, S.V. National Institute of Technology, Ichchhanath, Surat – 395 007 (INDIA). ABSTRACT Surat city is situated at the bank of river Tapi (India) near its delta region. The flow of water and water level in the river Tapi is controlled by dam which is 100 kms away from Surat city. The city has faced many floods since long. The aspects of channel modification of river Tapi using geospatial technologies are proposed in this research paper. This is helpful in the preparation of Flood Mitigation Plan for Surat city as a curative measure for the control of flood in the river Tapi. For channel modification, software HEC-RAS is used. The flood inundation map of Surat city is prepared in Arc GIS using software HEC- Geo RAS. INTRODUCTION summary of the flood is given in the Table No. 1. The River Tapi is originating from a Multai Hills Surat city and surrounding villages are part of flood (Gavilgadh hill ranges of Satpura) and flowing drainage of Tapi River. The carrying capacity of river through three states Maharastra, Madya Pradesh and was about 6 Lacs cusecs. Since 1883 floods are having length of 725 Kms. The flow of water recorded in the month of August and September. and water level in the river Tapi is controlled at Ukai Major flood event took place in the year 1883, 1944, dam which is 100 kms away from Surat city. The 1959, 1968, 1998 and 2006. The effective waterway foundation of dam is resting on Dolerite dykes of river Tapi is reducing day by day with respect to (Basalt). It is constructed for irrigation purpose width and depth due to silting, which affect the mainly and also served the purpose of flood control, carrying capacity of the river. The dredging of river generation of hydropower and supply of industrial in certain reaches can be carried out by conducting its and drinking water. The average rainfall in the feasibility project. The computation for channel catchment area is about 785 mm and average yearly modification of river Tapi has been carried out and run off is 17,226 MCM. The area of Surat city the enhanced cross section of river Tapi is suggested. situated at delta stage of the river is 326.51 sq.km. The channel modification is suggested in the reach of and population is about 40 lacs. The city is having river Tapi between Kathor to Magdalla. The 60,000 Shops & Establishment in trading activity. modification of river channel is done to increase the The city is also famous for diamond industry. The carrying capacity of river Tapi and thus reducing the Major industries like Essar Steel, Reliance, ONGC, L effect of flood in Surat city and surrounding region. & T, Gail, Kribhco, Shell, NTPC, GSPC, Torrent CHANNEL MODIFICATION METHODS Power etc. are situated in the city. The study area is Most widely used methods for channel modification shown in Fig. No.1. Floods are occurring in river are discused below. Tapi time to time, due to which major portion of the Levees city is submerged creating lot of damage in Levees are seldom equated with a channel residential as well as industrial areas. There is a need modification because, in most cases, they are of reducing the effect of flood. In this paper the constructed well away from the channel. However, a aspects of river channel modification are considered levee on one or both sides of a stream represents a for enhancing the carrying capacity and reducing the new and higher channel bankline for flood flows. effect of flood in the city. Levees confine the flood to a smaller cross section of NECESSITY OF CHANNEL MODIFICATION the floodplain and thus serve to channel flood flows Flood occurs at Surat city frequently due to sudden downstream. The benefits of levees are that they have release of water from Ukai dam in river Tapi. At the the least impact on the stream environment of any of time of floods in river Tapi, Surat city and the structural flood reduction alternatives, and they surrounding regions are most affected. The city has are nearly always the most effective and least faced many floods since long back. There was a flood expensive method of reducing flooding to the in the Surat in 1959, 1968, 1998 and 2006. The protected area.

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International Journal of Advanced Engineering Technology E-ISSN 0976-3945

Fig. 1 River Basin Map of India Table 1: Flood History at Surat Discharge Water Level at Sr. No. Flood Event Period (Lac Cusecs) Hop Bridge(m) 1 1883 10.05 11.05 July 2 1884 8.46 10.05 September 3 1894 8.01 10.33 July 4 1942 8.60 10.56 August 5 1944 11.84 11.32 August 6 1945 10.24 11.09 August 7 1949 8.42 10.49 September 8 1959 12.94 11.55 September 9 1968 15.5 12.08 August 10 1994 5.25 10.10 Aug.-Sep. 11 1998 7.00 11.40 September 12 2006 9.09 12.40 August

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International Journal of Advanced Engineering Technology E-ISSN 0976-3945

High-Flow Diversion Channel and Weir and clearing of part of the channel. The same A high-flow diversion channel and weir refers to a environmental negatives and potential problems exist formal control structure that diverts some amount of for this solution as for the clearing and snagging and flow (can vary from a portion to most of the higher compound channel options, but only for one side of flows) out of the river and into a separate channel, the channel. This solution is modeled in HEC-RAS usually moving the diverted flow along a different by adjusting both the geometry and the n value. flow path or to a different watershed. The diversion Widening the Upper Channel and Using the of flow results in increased flood protection for land Original Channel for Low Flow and communities downstream of the flow split. The Widening the upper channel and using the original diverted flow often rejoins the existing stream farther channel for low flow involves clearing and enlarging downstream. The benefits of using this method are both sides of the existing channel. The lowest that no modifications are made to the river channel, (deepest) portion of the existing channel is left as and the diversion often takes place well upstream undisturbed as possible to act as a low flow channel from the protected area, improving visual aesthetics during regular small events. Sedimentation in the cut (as opposed to when a levee or channel modification areas along with vegetative growth will make is constructed to protect the area). maintaining the new capacity of the modification High-Flow Cutoff/Diversion Channel difficult. This can be modeled in HEC-RAS similarly A high-flow cutoff/diversion channel differs from a to clearing and enlarging one side of the channel. high-flow diversion channel/weir in that a gated weir Realigning the Channel structure is not needed at the diversion channel When a channel is realigned, portions of the original entrance; the diversion channel is smaller, and the channel may be abandoned, as the modified portions diversion flow path is shorter-often just the distance follow a new flow path for at least part of the reach. across the neck of a meander loop. During higher If the total modified channel length is shorter than the flows, the diversion channel allows a portion of the original channel length, a steeper invert slope will flow to follow a shorter, more efficient flow path. occur. This will ultimately result in faster velocities, The advantages are that the existing channel remains and may significantly increase scour and deposition unaffected and additional capacity is provided during problems along the realigned reach. One or more higher flows. As with the previous channel erosion control structures are usually necessary for modification types, the disadvantages are the land this method. Realigned channels can be modeled in costs required for the diversion channel, the loss of HEC-RAS by locating the centerline station for the this land for other purposes, and the need for erosion new channel and adjusting the channel and overbank control structures at the upstream and downstream reach lengths. The realignment may also include diversion boundary increased cross-sectional area and a reduced n value. Clearing and Snagging HYDRAULIC DESIGN OF RIVER CHANNEL Clearing and snagging involve removing vegetation The channel modification of River Tapi is done from from the channel sides and along the bankline Kathor to Magdalla using concept of Most Efficient (clearing) and removing trees, debris, and stumps sections. The channel is designed for carrying from the channel (snagging). The channel geometry different discharge of water using theory of practical and alignment usually remain unchanged with this lined channel sections. solution, with the modification simply resulting in a Design Procedure lower Manning's n value. Clearing and snagging is The data given: therefore modeled in HEC-RAS by reducing the Discharge Q, Bed Slope of Channel S, Rugosity channel n value. However, significant environmental Coefficient n, Maximum permissible velocity V and Side effects may result from this solution. Fish habitat and slope of Channel m (m Horizontal to 1 Vertical) cover are removed, the shade given by vegetation is To be evaluated: lost, and bottom sediments are resuspended by the Hydraulic Mean radius R, cross section area A, snagging. wetted perimeter P, Bed width b and Depth of Clearing and Enlarging One Side of the Channel water h This technique combines clearing and snagging with Equations used: cutting, but only on one side of the existing channel. 1. Continuity Equation Q = A*V Additional capacity is gained from the enlargement

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International Journal of Advanced Engineering Technology E-ISSN 0976-3945

1 2. K = θ + Cot(θ) 2. Maning’s Equation V = R 3/2 S 2/1 n K = 0.321751 + 3 = 3.321751 3. Area of Cross section Design Steps A = 850/2.35 = 6024.86 m 2 1. Area of cross section 4. Hydraulic Mean Radius 2 A = bh + h θ + cotθ 2/3 ( )  .0225 × .2 35  2. Perimeter of cross section R =   = 6.11 m  .0 000225  P = bh + 2h(θ + cotθ ) 5. Wetted Perimeter 3. Hydraulic mean radius of cross section P = A/R bh + h2 (θ + cotθ ) P = 6155.83/5.92 = 985.20 m R = bh + 2h()θ + cotθ 6. Put the values of K,A and P in Quadratic Where, b = Bed width of Canal (m) Equation shown in step-7, 2 h = Depth of Water in Canal (m) 3.321751h – 985.20h + 6024.86 = 0 θ = Inclination of Side of Canal with Solving the quadratic equation, Horizontal at Top h = 6.24 m (The other root h = 290.34 m 4. P = A/R will give negative value of b) From step 2 and 3 7. The bed width of canal b 5. bh + 2h(θ + cotθ ) = A / R = 6024.86 / 6.11 − 2 * 6.24 * 3.321751 b = 943.70 m Say b = 944 m b = A / R − 2 h (θ + cot θ ) In the Triangle ABC (Fig. 2) From step 1 and 5 Angle C = 90°, Angle A = θ and 6. A = (A / R − 2h(θ + cotθ ))h + Angle B = 90° - θ 8. b1 = h * Sin(θ) h 2 + (θ + cot θ ) b1 = 6.24 * Sin (0.321751) = 1.97 m 2 9. b = m * 6.24 * Cos (θ) 7. A = (Ah / R −)h (θ + cotθ ) 2 b2 = 3 * 5.413025 * Cos (0.321751) 2 h (θ + cotθ ) − (A / R)h + A = 0 = 17.78 m Kh 2 − Ph + A = 0 10. y = h – h * Cos (θ) Where K = θ + Cot(θ), P = A/R y = 6.24 - 6.24 * Cos (0.321751) 8. In the above equation, value of A, R and P is = 0.32 m evaluated as follow: 11. The top width of canal T A = Q/V T = b+2b 1+2b2 2/3 T = 943.70 +(2 * 1.97) + (2 * 17.78) n × v  R =   T = 983.2 m  s  In case a larger or smaller depth is needed, some P = A/R adjustment can be made with the slope since the 9. The Equation shown in step-7 is Quadratic given value is only the average slope of the terrain Equation. Solving the equation and taking the and minor changes are always possible. relevant root (the other root gives a negative For Discharge 500000 Cusecs ( 14158.42 Cumecs) value); the value of h can be evaluated. Data Given Sample Calculation Rugosity Coefficient n = 0.0225 Data given Side Slope 1in m = 3 Discharge Q (Cumecs.) = 14158.42 (5,00,000 Bed Slope of Channel S = 0.00025 Cusecs) Velocity of Flow V (m/Sec.) = 2.3 Rugosity Coefficient n = 0.0225 Calculated Quantities Side Slope 1in m, m = 3 Area of Cross Section A = 6024.86 m 2 Bed Slope of Channel S = 0.00025 Hydraulic Mean Radius R = 6.11 m Velocity of Flow V (m/Sec.) = 2.35 Wetted Perimeter P = 985.2 m Cot (θ) = 3 1. Here cotθ = 3and θ = 0.321751 radian ( ) Value of θ in radian = 0.321751

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International Journal of Advanced Engineering Technology E-ISSN 0976-3945

Factor K = 3.321751 general, these tools are used for planning studies, but

Depth of Water h 1 = 290.34 m (Not considered) it can also be used for hydraulic design of flood Depth of Water h 2 = 6.24 m control channels. In the present study, three different Bottom Width = 944 m modifications of river channel for three value of b1 = 1.97 m discharge is discussed. The design parameters for b2 = 17.78 m three different alternatives are mentioned in Table y = 0.32 m No. 2. The modification of existing River section is Top Width = 983.2m carried out using software HEC RAS 4.0. The sample Design of River Channel for different discharge is details of modification of river cross-section are shown in Table No. 2. shown in Table 3. A typical modified river cross- MODIFICATION OF RIVER CHANNEL section is shown in Fig. 3. The flood inundation map The channel design/modification tools in HEC-RAS is prepared in ArcGIS 9.2 along with HES-Geo RAS allow the user to perform a series of trapezoidal cuts for all the three alternatives of channel modifications. into the existing channel geometry or to create new channel geometry. The current version of HEC-RAS has two tools for performing channel modifications. These tools are available from the Tools menu of the Geometric Data editor and are labeled Channel Design/Modification and Channel Modification (original). The tool labeled Channel Design/Modification is a new tool for HEC-RAS version 4.0. The tool labeled Channel Modification (original) is the original channel modification tool developed for HEC- RAS. The original channel modification tool has been left in HEC-RAS for those Fig. 2 Designed Practical Section of Trapezoidal user’s who may prefer this tool to the new one. In Channel

Original Cross-Section

Modified Cross-Section Elevation (m) Elevation

Distance (m)

Figure 3 Existing and Modified Channel Section of River Tapi for flow of 500000 cusecs

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International Journal of Advanced Engineering Technology E-ISSN 0976-3945

Table 2 Channel Design for Different Alternatives Sr. Discharge Bottom Depth of Top Width b (m) b (m) y (m) No. (Cusecs) Width (m) Water (m) (m) 1 2 1 500000 944 6.24 983.2 1.97 17.78 0.32 2 450000 846 6.26 884.7 1.98 17.82 0.32 3 400000 746 6.28 786.2 1.99 17.88 0.32

Table 3 Channel Modification Details

FLOOD SUBMERGENCE preparation of flood inundation map is also done Flood submergence map of the city is prepared using using HECGeo-RAS. The model comprises of three software HEC-RAS, HECGeo-RAS and ArcGIS 9.2. stages Pre-processing of the modeling including preparation 1. Pre-processing of geometric data is done in ArcGIS 9.2. Further 2. Running the model editing of Geometric data and assigning of Flow data 3. Post-processing is accomplished in software HEC-RAS. The model is Flood inundation map for flood event of also run in HEC-RAS. The flood inundation map is 2006 (9.1 Lac Cusecs) is shown in the Fig. 4. For the prepared in ArcGIS 9.2. The software HECGeo-RAS same area flood inundation map is prepared after is working as a link between the ArcGIS 9.2 and modifying the section of river Tapi for different HEC-RAS. It displays in the window of ArcGIS 9.2 alternatives for flow of 9.1 Lac Cusecs and shown in as a special toolbar. It is used for the creation of Fig. 5 to Fig. 7. The reduction in flood submergence different themes (Layers) for modeling as part of due to proposed modification is shown in Table 4. Pre-processing. The Post-processing of model for the

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International Journal of Advanced Engineering Technology E-ISSN 0976-3945

Table 4 Comparison of Inundated Area after Channel Modification for Flow of 9.1 Lac Cusecs Total Area Modified Area of Area of Area of Area of Area of of Carrying Inundation Inundation Inundation Inundation Inundation Inundation Capacity < 2 m (% ) 2 - 5 m (% ) 5 - 8 m (% ) 8 - 11 m (% ) > 11 m (% ) (% ) Existing 100 19.54 58.09 12.58 4.71 5.08 400000 Cusecs 87.51 35.27 36.12 7.64 4.65 3.82 450000 Cusecs 81.03 32.64 33.35 6.83 4.66 3.56 500000 Cusecs 78.30 31.77 32.34 6.22 4.61 3.35

Fig. No. 4 Flood Depth Map of Surat City for 9.1 Lac Cusecs Flow before modification of River Channel

Fig. No. 5 Flood Depth Map of Surat City for 9.1 Lac Cusecs Flow after modification of River Channel (Modified Carrying Capacity 400000 Cusecs)

Fig. No. 5 Flood Depth Map of Surat City for 9.1 Lac Cusecs Flow after modification of River Channel (Modified Carrying Capacity 450000 Cusecs)

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International Journal of Advanced Engineering Technology E-ISSN 0976-3945

Fig. No. 5 Flood Depth Map of Surat City for 9.1 Lac Cusecs Flow after modification of River Channel (Modified Carrying Capacity 500000 Cusecs) CONCLUSION 4. Agnihotri P.G. and Patel J.N (2008). “ Study of The study area (Surat City, INDIA) is highly affected Flood at Surat City and Its Remedial Measures” The 3rd IASME / WSEAS International by the flood and it is necessary to develop flood Conference on Water Resources, Hydraulics & reduction plan for the study area which helps to Hydrology , (WHH'08) University of Cambridge, control big disaster in future. As apart of flood Cambridge, UK, during February 23-25, 2008 5. H.M. Raghunath (2005), “Hydrology: Principles, reduction plan, modification in the cross section of Analysis, Design”, New age International river Tapi is proposed in this paper. Different Publishers, New Delhi alternatives of river channel modification are 6. Handerson F.M. (1966), ” Open Channel Flow” The Mac Millan Company, New York considered. The hydraulic design of the river section 7. Patel J.N. “Flood management over region of is carried out and reduction in area of submergence river Tapi using GPS” Journal of Geospatial for modified river section is calculated using Today, Vol-I, Issue – 4, October-November, 2002. geospatial technologies. The total inundation area for 8. Subramanya K. (1991), “Flow in Open the flood of 9.1 lacs cusecs reduced to 87.51 %, Channels”, Tata McGraw-Hill, New Delhi. 81.03 % and 78.30 % for modified carrying capacity 9. S.N. Ghosh (1986), “Flood Control and Drainage Engineering”, Oxford and IBH Publishing Co. of river 400000 cusecs, 450000 lacs cusecs and Pvt. Ltd., New Delhi 500000 cusecs respectively. REFERENCES 1. AjayKumar (1995), “Flood Control and Settlement Planning” Mohit Publication, New Delhi. 2. Akash Acharya, Biswaroop Das, Kiran Pandya et al (2006), “Surat 2006 Floods: A Citizens’ Report“Centre for Social Studies (CSS) Surat and Department of Human Resource Development (DHRD), Veer Narmad South Gujarat University, Surat. 3. Agnihotri P.G. and Patel J.N (2008), “Preparation of Flood Reduction Plan for Surat City and Surrounding Region (India)” International Journal on Transactions on Fluid Mechanics ; Issue 2 Volume 3 ; 116-125 ; WSEAS

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