Tamil Nadu PSC Agricultural Drainage Engineering: practice questions

Question 1 · medium

In an arid irrigated plain, a shallow water table causes secondary salinisation mainly because:

1. Rainfall dissolves salt from the atmosphere and deposits it in the soil faster than it can be leached
2. Irrigation water is always saline in arid areas
3. Drains carry salt from neighbouring fields into the root zone
4. Groundwater rises by capillarity to the surface, evaporates and leaves its salts behind

Question 2 · easy

A field has scattered isolated depressions on otherwise gently sloping land. Which surface drainage system is most suitable?

1. Parallel field drains at close spacing
2. Bedding of the whole field
3. Deep relief wells
4. Random field drains connecting the depressions

Question 3 · medium

When designing a collector ditch that receives subsurface lateral outlets, which hydraulic condition must be met at design flow?

1. The collector must flow at critical depth so that the outlets discharge freely
2. The collector velocity must exceed 3 m/s to keep sediment moving
3. The water level in the collector must be below the lateral outlets
4. The collector bed must be level

Question 4 · medium

What is the primary drainage purpose of land grading?

1. To lower the water table below the root zone across the whole field by gravity
2. To give the field a uniform slope so that excess surface water runs off without ponding
3. To increase the drainable porosity of the subsoil so that water percolates to depth faster
4. To intercept seepage from a neighbouring canal

Question 5 · easy

Which is a function of a drain envelope?

1. Keeping soil out of the pipe
2. Raising the pH of drainage water
3. Increasing the drainable porosity of the whole field between drains
4. Preventing roots from using groundwater

Question 6 · easy

In a composite subsurface drainage system:

1. Each lateral discharges directly into an open ditch
2. There are no laterals, only wells
3. Laterals feed a buried collector
4. Water is removed only by surface grading

Question 7 · easy

Vertical drainage means:

1. Draining water vertically through the soil into drains
2. Removing surface water through vertical inlets
3. Installing drains at vertical spacing
4. Lowering the water table by pumping groundwater from wells

Question 8 · medium

The Salinity Control and Reclamation Projects (SCARPs), a large-scale programme of public drainage tubewells begun in the early 1960s, were implemented in:

1. Uzbekistan
2. Pakistan
3. Australia
4. the Netherlands

Question 9 · easy

Bio-drainage lowers the water table by:

1. Transpiration of groundwater by trees or perennial plants with high water use
2. Microbial breakdown of water into gases
3. Roots physically opening channels through which water flows by gravity to deep drains
4. Plant uptake of salts from the groundwater

Question 10 · easy

The osmotic effect of soil salinity on crops:

1. Makes soil water more available to plants because dissolved salts draw water into the roots
2. Is caused only by boron
3. Lowers soil-water potential so plants take up water with more difficulty, as in drought
4. Occurs only when ESP exceeds 15