Follow Us

----------------------------------------------------------

Monday, 26 March 2018

“EFFECTIVNESS OF RCC PORCUPINE SYSTEN IN PROTECTING RIVERBANK USING A 2D FLUME MODEL STUDY”


Ms. Utkarsha A.  Dubey
Mrs. V. S. Limaye
Mrs. A. V. Deshpande
M. E. (Hydraulics) 2nd Year,
Associate Professor,
Assistant Professor
Dept. of Civil Engg.
Dept. of Civil Engg.
Dept. of Civil Engg.
Sinhgad College of Engineering, Pune
Sinhgad College of Engineering, Pune
Sinhgad College of Engineering, Pune
55dubeyutkarsha@gmail.com
vslimaye.scoe@sinhgad.edu
Avdeshpande.scoe@sinhgad.edu

ABSTRACT:
The effect of porcupines on the reduction in velocity of flow near the banks and their ability to induce sedimentation has been investigated experimentally by various fraternities. An attempt has been made to access the pattern of deposition caused by various configurations of Porcupine field, the alignment of porcupine units, relationship between the Manning’s roughness coefficient (‘n’ value) and the quantum of porcupine units, etc.in an two dimensional Flume model at CWPRS, Pune for the present study. The main objective of this study is to propose a suitable methodology in terms of the placement, quantum, and orientation of porcupine units to increase the resistance in the erosion prone reaches of a channel. The basic principle of porcupine placing near the river bank is to offer resistance to flow thereby reducing velocity and inducing sedimentation near the erosion prone banks. This will in turn build the river banks resulting in shifting of channel course away from the banks. The main advantage of RCC porcupine units are its flexibility and also will be always in defense, if the river banks are attacked by the channel migration in future.
Various attempts have been made to overcome excessive erosion by constructing river training works. Porcupine systems are one of the novel techniques which have been adopted as a cost-effective method of river training. The effect of porcupines on the velocity of flow and their ability to capture sediment has been investigated experimentally. Also, an attempt has been made to logically study the pattern of deposition caused by various configurations of Porcupine field and hence to propose a preliminary design methodology.


Key Words: RCC Porcupine systems; river training; 2 D flume; cost-effective; riverbank protection.




I. INTRODUCTION

Rivers in alluvial plans are highly variable in their behavior and it is often unpredictable. A stream, which is quite trouble free during low flow, may attain a threatening condition during high stages. It may develop unforeseen meander, break through embankment, attack town, and important structures, outflank bridges and in general may create havoc. Therefore, whenever any hydraulic structure is built across an alluvial stream, adequate measures in form of  river-training works must be taken to establish the river course along a cretin alignment with a predetermined cross-section, all there works which are constructed to train the river are known as river-training works.
River training’ refers to the structural measures which are taken to improve a river and its banks. River training is an important component in the prevention and mitigation of floods and general flood control, as well as in other activities such as ensuring safe passage of a flood under hydraulic structure. For flash flood mitigation, the main aim is to control the water discharge regime in the watercourse by limiting its dynamic energy, thereby controlling the morphological evolution of the watercourse (Colombo et al. 2002). River training measures also manages sediment transportation and thus minimize bed and bank erosion. Many river training structures are implemented in combination with bioengineering techniques to lessen the negative effects on environment and landscape. There are a number of types of river training structure. The selection and design of the most appropriate structure depends largely on the site conditions.
River training is necessary in those reaches of the river where the river encounters excessive erosion of bed or banks. Braiding, meandering, breaching of embankments, damages of hydraulic structures, roads and railways, etc. are some of the consequences of an untrained river. Various river training measures which are commonly deployed include spurs/groynes (permeable and impermeable), submerged vanes, bank pitching, guide vanes, bundling etc. Details about planning, layout, design, and maintenance of permeable and impermeable type spurs are covered in IRC: 89 (1997) & IS: 8408(1994). Porcupine Systems have also been installed in big rivers in India like Brahmaputra and Ganga and have yielded fairly good results. After Repeated failures of earthen spurs upstream and downstream of the Farakka Barrage on the Ganga River (India), Central Water Commission (CWC) Used RCC To protect the erosion of left bank. It is reported that the porcupines were very effective and helped in siltation of the bank. Aamir and Sharma (2015) have developed a rational design methodology for riverbank protection using RCC Porcupines.    
             RCC Porcupines have also been deployed at Majuli Island, Assam, India and they have been found quite effective in reducing the intensity of the river Brahmaputra. A Porcupine is a unit of the system which comprises six members of RCC which are jointed together with the help of or on nuts and bolts to form a tetrahedral frame. Each member is 2-4 m in length, depending upon the requirements. At the time of concreting of members, holes are kept in the RCC poles for the bolts. Generally, RCC poles of 3 m length are used having a cross section of 15 cm × 15 cm. reinforcement is given using 4 Nos. of MS bars of 6 mm diameter, with stirrups at 15cm c/c. larger porcupines may also be used with greater cross section and heavier reinforcement as per the requirement. Bolts are normally 12-15 mm dimeter. Check nuts are to be provided for better grip. Washers are required at both ends for better grip with the RCC members. RCC porcupines should be connected together by wire rope and properly placed on the ground to avoid any disturbance caused by the intensity of flow. Figure 1 shows a three dimensional sketch of a typical RCC Porcupine unit.