Why is the intake floor placed 1.0-1.5 m or more above the undersluice crest or river bed?

So that bed load rolls past below the intake instead of entering

So that floating debris is trapped on the sill

To increase the head across the trash rack

To let sand settle inside the canal

What are the undersluice (scouring sluice) and the divide wall for?

The sluice is opened in floods to flush deposits in front of the intake; the divide wall separates the intake from the sluice

The sluice stores water for the dry season; the wall supports the rack

The sluice passes the turbine discharge; the wall reduces seepage

The sluice traps floating logs; the wall raises the sill

Where is the intake best located on a river bend?

On the outer bank, because secondary flow carries bed load to the inner bank

On the inner bank, where flow is slow and sediment settles

On the straight reach far downstream of the weir

At the middle of the river on the bed

How do the trash boom and the low rack velocity (0.6-1.0 m/s) control floating debris?

The angled boom deflects logs and trash towards the weir spill or sluice, and low velocity stops debris from holding on the bars

The boom stores the debris permanently, and low velocity helps sand to settle

The boom lifts debris into the canal, and high velocity cleans the bars

The boom stops bed load, and low velocity increases head loss

2069 Chaitra · 6 marks

Control of bed load and floating debris at intake

Short answer

Bed load is excluded by placing the intake sill 1.0–1.5 m above the river bed, an undersluice with divide wall to flush gravel, and a gravel trap. Floating debris is controlled by an angled trash boom, a trash rack with 50–100 mm spacing, and low approach velocity (0.6–1.0 m/s) to prevent clogging.

How is the control of bed load and floating debris in a ROR intake done? Explain with appropriate plan and sectional drawings of the system.

In a RoR plant on a steep Himalayan river, bed load (gravel, boulders) and floating debris (logs, leaves, trash) must be kept out of the intake. This is done by the arrangement shown below.

PLAN
 river ====================================>
        scour sluice (undersluice)  ||||||| weir
   +---+====================+
   |  flood   divide wall    |
   |  wall   --> gravel trap |--> canal to
   | rack|gate               |    settling basin
   +---------------------------+
   trash boom o-o-o-o (angled)

SECTION (through intake)
 pond ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   boom o   | rack |gate|
            |###\  |    |==> canal
   sill 1.0-1.5 m above undersluice floor
 //// undersluice floor (low) ////  --> flushing

Control of bed load

High intake sill: the intake floor is placed 1.0-1.5 m (or more) above the undersluice crest or river bed, so the bed load rolls past.
Undersluice (scouring sluice) next to the intake, with gates, creates a flushing channel in front of it; it is opened during floods to scour deposits, and the divide wall separates the intake from the sluice.
Intake location on the outer bank of the bend, where the secondary flow moves bed load to the inner bank.
Curtain (skimming) wall or bed-load excluder: only the upper clear water is drawn.
Gravel trap after the intake with flushing arrangement, and a settling basin for sand.
Guide bunds and training walls keep a stable flow line near the intake.

Control of floating debris

Trash boom (floating or fixed), set at an angle to the flow, deflects logs and trash towards the weir spill or sluice.
Trash rack (clear spacing about 50-100 mm) with an automatic or manual rake, inclined at about 75°.
Skimming walls and a surface spillway pass the floating material over the weir.
Low velocity at the rack (0.6-1.0 m/s) so the debris does not hold on the bars.
Periodic inspection and cleaning in the monsoon.

✓ Answer checked by Claude Opus 5.5 (high effort)

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