Bridge cum Bandhara

     In most parts of the country, the streams run dry after only a short period after the end of monsoon. The water table is getting lower and lower due to more and more bore wells being dug and exploited.  Drinking water for cattle becomes scarce. Recent developments in material engineering have resulted in achievement of higher Strength with reduction in the Volume or Weight of materials. 

Ferrocement Ungated weir

Reinforcement

Construction stage

Construction Stage

Ungated weirs about 3 meter height Arch type ferrocement weir, Principle used is Strength Through Shape, For retaining structures Strength is not only criteria, Stability of structure is also important. So even if we are using materials having high Strength/Weight ratio Storage capacity (Height of Structure gets limited) has limitations. To overcome this problem Bridge Cum Bandhara (BcB) is dual problem solution as it can serve dual purpose of crossing as well as a water storage structure. 

   Concept

        Taking advantage of the number of bridges that will be built. Post monsoon flow is blocked at the upstream edge of the bridge and a small storage is created at low cost. 

The following materials for the gates can be used-

1. Steel
2. Fibre Reinforced Plastic
3. FRC gates

Advantages of B-C-B

1. No additional land acquisition is required. 
2. Additional ground water recharge can be made with the help of BCB. 
3. Existing Bridge can be converted to BCB to store excess water during monsoon and can be used for irrigation purpose during summer. To tap post monsoon flow to create storage up to 4.0 m. The storage is created by fixing needles/gates between bandhara piers to tap last flow. 
4. Stored water is used for drinking and irrigation by converting bridges into BCB. It enhances the ground water which then is available for irrigation as well as for drinking water. 
5. Surplus percolated water out of irrigation activity again joins the river which is tapped and reused for irrigation. Such stored water can be used for artificial recharging the nearby bore wells as well as open well to augment ground water.

Components of B-C-B

•       Weir

•       Bandhara Pier with footing

•       Bridge Pier with footing

•       Superstructure

•       Gates/needle plates

•       Energy dissipaters

Considerations for BCB

•       Rock foundation shall be available at shallow depth (< 3 m)

•       Bridge proper and bandhara can be constructed separately.

•       Max Water Storage height 4.0 m

•       Provision of ogee spillway for excess flow

•       With Gates. (Earlier needle plates)

Design Consideration

•       BCB structure is recommended for water way upto 60-80 m but can be used for even larger length.

•       FTL as per storage requirement but 1 m below the bank level (to contain afflux)

•       Sill level = 0.3 m + GL

•        sill level may be stepped

•       The gross percentage obstruction (bridge + bandhara) shall not exceed to an extent that will generate undesirable afflux and velocity. (25%&30%)

•       The gross percentage obstruction (bridge + bandhara) shall not exceed to an extent that will generate undesirable afflux and velocity.

•       10% more than 25% & 30%

•       For High Level and High-level submersible bridge Vertical Clearance (V.C.) (Soffit-FTL) =2m.

•       For Submersible bridge V.C. Not less than 1.5m.

•       Weir foundation = 1.5 in exposed/SR, 0.6 into HR

•       Minimum height of weir > 1.5 m

•       Top of Bandhara Pier = FTL+0.5

•       Ogee overflow sections at suitable locations

•        Pier oriented along current directions.

•       Designed for v= 3.0m/s top of Bandhara pier, and 4.5 m up to RTL of Submersible bridge

Materials 

•       For Pier M-30 RCC.

•       Reinforcement = Fe 500 D

•       Weir PCC M-20.

•       Structural steel Rolled sections and plates as per IS226 and IS 816

Construction and planning

•       Bridge proper and bandhara can be constructed separately.

•       Main bridge pier with SS to be completed before onset of monsoon

•       if not possible then?

•       Restrict height of pier and bandhara pier to 1 m above sill level.

•       foundation = 1.5 in exposed/SR, 0.6 into HR

•       Minimum ht of weir > 1.5 m

•       Top of Bandhara Pier = FTL+0.5

•       Ogee overflow sections at suitable locations

•        Pier oriented along current directions

Operation

•       Removal and fixing gates so adjusted that water level is not more than FSL

•       Gates to be inserted at commencement of fair-weather season and must be removed before beginning of monsoon.

•       Arrangement to remove and placing gates to be provided

Where to Propose

•       Impervious Rock foundation is available at shallow depth (< 3 m)

•       Velocity of river considered 4.5 m/s at RTL

•       Water scarce Area

Do not Propose

•       National Highways or Railway affected area

•       Forest area or area in the downstream side of forest

•       Very high bridges (height above GL > 7m) as operation of BCB will be difficult

•       River in meandering stretch

•       Rock not available at reasonable depth

Gates for BCB

•       Water can be stored by conventional needles.

•       Automatic gates are also available in market.

•       The removal and fixing of needles should be so adjusted that the water level does not exceed designed full tank level use of simple mechanical equipment such as hydraulic crane / simple crane.

Automatic Radial Gate

•       The automatic radial gate is specifically developed for BCB.

•       When u/s water level is below FRL, gates can also be operated by means of a trolley mounted manual hoist supported on a monorail gantry.  No Separate Hoist Bridge is required.

•       No electricity, no operating staff, no monitoring of water level is required for gate operation.

•       Lower cost, Lower maintenance.