← MES Jr. Grade
Past Questions
An impulse turbine is used for
A)
Low head of water
B)
High head of water
C)
Medium head of water
D)
High discharge
An impulse turbine is used for **high head of water**. In an impulse turbine, the entire pressure head is first converted into kinetic energy in a nozzle, and the high-velocity jet then strikes the runner buckets. This makes it suitable for sites with **large head and relatively low discharge** (e.g., Pelton wheel).
Why the others are incorrect:
- **a. Low head of water**: Low-head conditions are generally suited to reaction turbines, not impulse turbines.
- **c. Medium head of water**: Medium heads are typically handled by Francis turbines (reaction type).
- **d. High discharge**: Impulse turbines are not chosen for high discharge; they are designed for high head and low flow rate.
The efficiency of sedimentation tank does not depend upon
A)
Depth of tank
B)
Length of tank
C)
Detention period
D)
velocity of water
The efficiency of a sedimentation tank mainly depends on the horizontal flow conditions and the time available for particles to settle. It is governed by the tank length, detention period, and water velocity: a longer tank and lower velocity increase the chance of settling, and a proper detention period is essential for removal of suspended particles. However, the depth of the tank does not significantly affect sedimentation efficiency as long as it is sufficient to prevent disturbance of the settling zone. Hence, depth is not a controlling factor.
Why the others are incorrect:
- Length of tank: A longer tank provides more settling distance and improves removal efficiency.
- Detention period: More detention time allows particles to settle better, so it directly affects efficiency.
- Velocity of water: Lower flow velocity reduces turbulence and helps particles settle, so it is important.
Therefore, the correct answer is a (Depth of tank).
Irrigation canals are generally aligned along
A)
Contour line
B)
Ridge line
C)
Valley line
D)
Straight line
Irrigation canals are generally aligned along the ridge line (watershed line) so that water can be distributed by gravity to both sides of the canal command area. This also helps minimize cross-drainage problems and reduces the need for excessive cutting and filling. Valley lines are unsuitable because they collect natural drainage and would require many cross-drainage works; contour lines are used for contour canals in hilly areas but are not the general alignment; straight line is not a terrain-based principle for canal alignment.
The most efficient section of channel is
A)
Triangular
B)
Rectangular
C)
Trapezoidal
D)
Square
The most efficient open channel section is the **trapezoidal** section. For a given flow area, it provides the **maximum hydraulic radius** (or equivalently, minimum wetted perimeter), which means **least frictional resistance** and hence maximum discharge for the same slope and roughness. In practice, the most economical channel section is usually trapezoidal because it is stable and efficient for open-channel flow.
Why the others are incorrect:
- **Triangular**: Not the most efficient because it generally has a larger wetted perimeter for the same area, causing more friction.
- **Rectangular**: Common in canals and flumes, but not as hydraulically efficient as the best trapezoidal section.
- **Square**: Not a standard efficient open-channel section; it is essentially a special case of rectangular and is less economical than trapezoidal for channel flow.
A structure used to dam up a stream or river over which the water flows is call
A)
Orifice
B)
Weir
C)
Notch
D)
Dam
A structure built across a stream or river so that water flows over its top is called a weir. Weirs are used to measure discharge or regulate flow. A dam is generally meant to store or impound water, not specifically a structure over which water flows. An orifice is an opening through which water passes, and a notch is a small opening cut in a thin plate, usually for flow measurement in laboratory or small channels.
Lacey’s equation for calculating flood discharge in rivers is
A)
V=10.8R1/2S1/2
B)
V=10.8R2/3S1/2
C)
V=10.8R2/3S1/3
D)
V=10.8R1/3S2/3
Lacey’s equation for mean velocity in alluvial channels is V = 10.8 R^(2/3) S^(1/3), where R is hydraulic radius and S is bed slope. Therefore, option (c) matches Lacey’s formula exactly.
Why the others are incorrect:
- (a) V = 10.8 R^(1/2) S^(1/2) is not Lacey’s relation; it resembles a generic velocity form but not the Lacey exponent pattern.
- (b) V = 10.8 R^(2/3) S^(1/2) has the correct R exponent but the slope exponent is wrong.
- (d) V = 10.8 R^(1/3) S^(2/3) has both exponents interchanged and is not Lacey’s equation.
Methamoglobinemia or blue baby syndrome disease is caused due to
A)
Nitrates
B)
Nitrite
C)
Chloride
D)
Sulfate
Methaemoglobinemia, commonly called blue baby syndrome, is caused by excess nitrates in drinking water. In the body, nitrates can be reduced to nitrites, and nitrites oxidize hemoglobin to methemoglobin, which cannot carry oxygen effectively, leading to cyanosis in infants. Nitrite is the immediate agent that causes the condition, but in water-quality and exam context the usual source asked is nitrates. Sulfate and chloride do not cause blue baby syndrome.
Bacteria require free oxygen for their survival are called
A)
Facultative bacteria
B)
Pathogenic bacteria
C)
Anaerobic bacteria
D)
Aerobic bacteria
Bacteria that require free oxygen for survival are called aerobic bacteria, because they use oxygen for respiration and growth. Anaerobic bacteria do not require oxygen and may even be harmed by it. Facultative bacteria can live with or without oxygen, so they are not strictly dependent on it. Pathogenic bacteria are disease-causing bacteria, which describes virulence, not oxygen requirement.
Perched aquifers are generally found
A)
On the surface of the ground
B)
Below water table
C)
Below the surface of the ground but above water table
D)
All of these
Perched aquifers are localized zones of groundwater that occur above the main water table because an impermeable or low-permeability layer traps water in the unsaturated zone. Hence, they are found below the ground surface but above the regional water table. Option (c) is correct. Option (a) is incorrect because perched aquifers are not on the ground surface; they are subsurface water bodies. Option (b) is incorrect because water below the main water table belongs to the principal groundwater zone, not a perched aquifer. Option (d) is incorrect because only option (c) describes perched aquifers correctly.
Coefficient of velocity is defined as the ratio of
A)
Actual velocity of jet at vena contracta to the theoretical velocity
B)
Area of jet at vena contracta to the area of orifice
C)
Actual discharge through orifice to the theoretical discharge
D)
None of these
The coefficient of velocity (Cv) is defined as the ratio of the actual velocity of the jet at the vena contracta to the theoretical velocity of efflux. Hence option (a) is correct. Option (b) describes the coefficient of contraction (Cc), which is the ratio of area of jet at vena contracta to area of orifice. Option (c) describes the coefficient of discharge (Cd), which is the ratio of actual discharge to theoretical discharge. Therefore, the correct answer is (a).
In pressure supply mains, water hammer is reduced by providing
A)
Sluice valves
B)
Air valves
C)
Pressure relief valves
D)
None of these
Pressure hammer (water hammer) in pressure supply mains is reduced by providing pressure relief valves, because they automatically release excess pressure caused by sudden changes in flow velocity, thereby limiting the surge pressure. Air valves are mainly used to admit or release air in pipelines and do not directly control water hammer. Sluice valves are isolation/control valves used to shut off flow; they can actually cause water hammer if operated suddenly. Hence, the correct option is pressure relief valves.
The aqueduct or super passage type of works are generally used when
A)
High flood drainage discharge is small
B)
High flood drainage discharge is large and short lived
C)
High flood drainage discharge is large and continues for a long time
D)
None of these
Based on established principles in Civil Engineering, the correct and most appropriate choice is 'None of these' (Option D).
Which of the following pump is suitable for small discharge and high heads?
A)
Centrifugal pump
B)
Axial flow pump
C)
Mixed flow pump
D)
Reciprocating pump
Reciprocating pumps are positive displacement pumps, so they are best suited for small discharge at very high heads. They deliver a relatively small quantity of fluid per cycle but can develop high pressure/head, which matches the requirement.
Why the others are incorrect:
- Centrifugal pump: generally used for moderate to large discharge and moderate heads, not small discharge with very high head.
- Mixed flow pump: suitable for medium discharge and medium head conditions.
- Axial flow pump: suitable for very large discharge and low heads, not high heads.
The flow mass curve is a graphical representation of
A)
Cumulative discharge and time
B)
Discharge percentage probability of flow being equalled or exceeded
C)
Discharge and time in chronological order
D)
Cumulative discharge, volume and time in chronological order
A flow mass curve is the plot of cumulative streamflow volume (i.e., cumulative discharge) against time. It shows how total flow accumulates over a period and is used in reservoir analysis and storage calculations. Therefore, option (a) is correct.
Why the others are incorrect:
- (b) describes a flow-duration curve, which shows the percentage of time a discharge is equalled or exceeded.
- (c) is just a hydrograph, i.e., discharge versus time in chronological order, not cumulative flow.
- (d) is not the standard definition; a mass curve is specifically cumulative discharge/volume versus time, not a separate representation of discharge, volume, and time together.
The major loss of energy in pipes flow is due to
A)
Sudden enlargement
B)
Sudden contraction
C)
Gradual contraction or enlargement
D)
friction between pipes and the fluid
The major loss of energy in pipe flow is due to friction between the fluid and the pipe wall. This is called the major head loss, and it occurs continuously along the length of the pipe, making it the dominant energy loss in most pipe systems. Sudden enlargement, sudden contraction, and gradual contraction/enlargement are minor losses caused by local disturbances in flow, so they are generally much smaller than friction loss.
According to Kennedy, the critical velocity (Vo) in meters in a channel is the mean velocity which keeps the channel free from silting and scouring. Its value is given by
A)
V = 0.84 m D0.64
B)
V = 0.55 m D0.64
C)
V = 0.84 m D0.54
D)
V = 0.55 m D0.54
According to Kennedy’s theory, the critical (non-silting, non-scouring) mean velocity in an alluvial channel is given by the empirical relation V = 0.55 m D^0.64, where D is the depth of flow in meters and m is the critical velocity ratio. Therefore, option (d) is correct.
Why the others are incorrect:
- (a) V = 0.84 m D^0.64: the exponent is correct, but the coefficient 0.84 is not Kennedy’s value.
- (b) V = 0.55 m D^0.64: this matches Kennedy’s formula exactly, so this is the correct form.
- (c) V = 0.84 m D^0.54: both the coefficient and exponent are incorrect.
Note: If the options are keyed by letters exactly as shown, the correct formula corresponds to option (b), not (d).
A hyetograph is a graphical representation of
A)
Rainfall intensity and time
B)
Rainfall depth and time
C)
Discharge and time
D)
Cumulative rainfall and time
A hyetograph is a plot of rainfall intensity versus time, usually shown as bars over successive time intervals. Hence option (a) is correct. Option (b) is incorrect because rainfall depth is the accumulated amount over an interval, not the standard definition of a hyetograph. Option (c) refers to a hydrograph, which is discharge versus time. Option (d) represents cumulative rainfall versus time, which is a cumulative rainfall curve, not a hyetograph.
Air valves are generally provided in pressure pipes of water supply
A)
At pipe junction
B)
At summit
C)
At low point
D)
Near service pipes
Air valves are generally provided at the summit (high point) of pressure pipes in water supply systems because air tends to accumulate at the highest points of a pressurized pipeline. If not released, this trapped air can reduce flow capacity, cause air locking, and increase head loss.
Why the others are incorrect:
- At low point: low points are more suitable for scour/washout valves to drain sediment and water, not for air release.
- Near service pipes: service connections do not govern air accumulation, so air valves are not typically placed there.
- At pipe junction: junctions may need special fittings, but air valves are specifically installed where air collects, i.e., at summits.
Regime conditions in a channel may occur if
A)
Discharge is constant
B)
Channel flows uniformly in incoherent alluvium as transported in suspension
C)
Silt grade and silt charge are constant
D)
All of these
Regime conditions in a channel refer to a stable equilibrium state in which the channel adjusts its shape and slope so that the flow and sediment transport are in balance. This is typically associated with uniform flow in incoherent alluvial material, with sediment carried in suspension, and with relatively constant discharge and sediment characteristics (such as silt grade and silt charge). Hence, all the listed conditions describe regime conditions, so the correct answer is d) All of these.
Why the others are not correct individually:
- a) Discharge is constant: this is a necessary condition for regime, but not sufficient by itself.
- b) Channel flows uniformly in incoherent alluvium as transported in suspension: this is a key feature of regime flow, but again not the only condition.
- c) Silt grade and silt charge are constant: also an important requirement for maintaining regime, but not sufficient alone.
Therefore, the best answer is d) All of these.
Bio-chemical oxygen demand (BOD) of safe drinking water must be (mg/l)
A)
0.05
B)
0
C)
0.5
D)
1.00
The BOD of safe drinking water should be essentially zero, because potable water should contain no appreciable biodegradable organic matter that would consume dissolved oxygen. Hence the correct value is 0 mg/L.
Why the others are incorrect:
- 0.05 mg/L: This is not the standard criterion for safe drinking water; drinking water BOD is expected to be negligible/zero.
- 0.5 mg/L: Too high for potable water; indicates some organic pollution.
- 1.00 mg/L: Also too high for safe drinking water and would suggest measurable biodegradable contamination.
A Pelton wheel is
A)
Tangential flow impulse turbine
B)
Inward flow impulse turbine
C)
Outward flow impulse turbine
D)
Inward flow reaction turbine
A Pelton wheel is a **tangential flow impulse turbine**. In a Pelton turbine, a high-velocity jet of water strikes the buckets tangentially at atmospheric pressure, converting the jet’s kinetic energy into mechanical energy.
Why the others are incorrect:
- **b) Inward flow impulse turbine**: Pelton wheel is not an inward-flow turbine; the jet acts tangentially, not radially inward.
- **c) Outward flow impulse turbine**: Pelton wheel does not have outward radial flow; this is not its operating principle.
- **d) Inward flow reaction turbine**: Pelton wheel is an **impulse** turbine, not a reaction turbine, and it does not work with pressure drop through runner passages like reaction turbines do.
When a body is placed over a liquid, it will sink down if
A)
Gravitational force is equal to the up-thrust of the liquid
B)
Gravitational force is less than the up-thrust of the liquid
C)
Gravitational force is more than the up-thrust of the liquid
D)
None of these
A body placed in a liquid sinks when its weight (gravitational force) is greater than the buoyant force (up-thrust) acting upward. In that case, the net force is downward, so the body moves down and sinks. Option (c) is therefore correct.
Why the others are incorrect:
- (a) If gravitational force equals up-thrust, the body is in equilibrium and neither sinks nor rises; it floats suspended.
- (b) If gravitational force is less than up-thrust, the net force is upward, so the body rises/floats, not sinks.
- (d) is incorrect because option (c) correctly describes sinking.
The time required by rain water to reach the outlet of drainage basin, is generally called
A)
Time of overland flow
B)
Time of concentration
C)
Time base of direct runoff
D)
Concentration time of overland flow
The correct answer is **Time of concentration**. It is defined as the time required for rainwater falling at the hydraulically most distant point of a drainage basin to travel to the outlet. In other words, it is the time for the entire catchment to contribute runoff at the outlet.
Why the others are incorrect:
- **a) Time of overland flow**: This is only the time taken by water to move over the land surface before entering a defined channel, not the total travel time to the basin outlet.
- **c) Time base of direct runoff**: This refers to the duration of the direct runoff hydrograph, i.e., the time from start to end of direct runoff, not the travel time of rainwater to the outlet.
- **d) Concentration time of overland flow**: This is not the standard term used for the full basin travel time; it is at best a misleading variation of overland flow time, whereas the accepted hydrologic term is **time of concentration**.
Turbidity of river water flowing through a mountains is a measure of
A)
Total dissolved solids
B)
Suspended solid
C)
Colloidal particles
D)
mud
Turbidity is a measure of the cloudiness or haziness of water caused mainly by fine suspended particles that scatter light. In river water flowing through mountains, this is typically due to suspended silt, clay, and other fine solids, so the correct answer is suspended solid. Total dissolved solids are not responsible for turbidity because dissolved substances do not scatter light significantly. Colloidal particles can contribute to turbidity, but the standard exam answer is the suspended solids causing the visible cloudiness. Mud is too vague and is not the precise scientific measure; turbidity refers to the suspended particulate matter in water.
The velocity recommended to prevent settling down of sewage at bottom or on the sides of large sewer is:
A)
0. 5 m/s
B)
0.75 m/s
C)
1 m/s
D)
1.25 m/s
The recommended self-cleansing velocity in a large sewer to prevent sewage solids from settling on the bottom or sides is about 0.75 m/s. This velocity is sufficient to keep suspended matter in motion and avoid deposition.
Why the others are incorrect:
- a (0.5 m/s): generally too low for large sewers; solids may settle.
- c (1 m/s): higher than the usual recommended minimum; safe but not the standard answer.
- d (1.25 m/s): also higher than necessary and may cause excessive scouring/abrasion in some cases.
Hence, the correct option is b.