← MES Jr. Grade
Past Questions — 2014
In linear reservoir, storage varies linearly with
A)
Time
B)
Outflow rate
C)
Inflow rate
D)
None of these
In a linear reservoir, the storage-discharge relationship is linear, i.e., storage S is directly proportional to outflow O: S = kO. Therefore, storage varies linearly with the outflow rate. It does not vary linearly with time or inflow rate in the basic definition.
Probability of a 10 year flood to occur at least once in the next 4 year is
A)
25 %
B)
35 %
C)
50 %
D)
65 %
For a 10-year flood, the annual probability of occurrence is p = 1/10 = 0.1. The probability of at least one such flood in 4 years is:
1 - (1 - p)^4 = 1 - (0.9)^4 = 1 - 0.6561 = 0.3439 ≈ 34.4%.
However, in standard hydrology MCQs, this question is often interpreted using the simpler approximation for recurrence interval problems, and among the given options the intended answer is 25% only if the question is asking for the probability over 4 years as 4/16? That is not correct statistically. The exact probability is about 34%, which matches 35%.
So the correct option is (b) 35%.
Most of the turbidity meters work on the scattering principle. The turbidity value so obtained is expressed in
A)
CFU
B)
FTU
C)
JTU
D)
NTU
Turbidity meters based on the light scattering principle report turbidity in Nephelometric Turbidity Units (NTU). 'Nephelometric' refers to measurement of scattered light. CFU is for colony-forming units in microbiology, FTU is Formazin Turbidity Unit, and JTU is Jackson Turbidity Unit (used with older visual methods), not the standard for scattering-based meters.
Detention time in a “flocculator” is
A)
10 sec to 20 sec
B)
20 min to 30 min
C)
1 hour to 8 hour
D)
2 hour to 3 hour
A flocculator is designed to provide gentle mixing so that small particles collide and form flocs. The detention time is therefore much longer than in rapid mixing units, typically about 20 to 30 minutes. Option (a) is too short for flocculation, while options (c) and (d) are excessively long and are not standard flocculator detention times.
The specific speed of a pump is defined as the speed of a unit
A)
Of unit size with unit discharge at unit head
B)
Of such a size that it requires unit power at unit head
C)
Of such a size that it delivers unit discharge at unit head
D)
Of such a size that it delivers unit discharge at unit power.
The specific speed of a pump is defined as the speed of a geometrically similar pump which would deliver unit discharge against unit head. This is the standard pump-specific-speed definition used in fluid machinery. Hence option (c) is correct. Option (a) is incorrect because it adds "unit size" and is not the definition; option (b) describes power, which is not the pump specific speed definition; option (d) is incorrect because specific speed is not defined at unit power.
The hydraulic gradient line indicates the variation of which of the following?
A)
Velocity head in flow direction
B)
Piezometric head in the direction of flow
C)
Total energy of flow in the direction of flow
D)
None of these
The hydraulic gradient line (HGL) represents the variation of piezometric head, i.e., pressure head plus elevation head, along the direction of flow. It does not show velocity head; that is represented by the difference between the energy grade line and the hydraulic gradient line. The total energy of flow is represented by the energy grade line, not the HGL.
Water logging is the state of soil where
A)
the water table is brought very nearer to the ground surface
B)
the water table is at deeper depth
C)
the moisture in the soil is beyond the reach of plant roots
D)
none of these
Water logging means the soil becomes saturated due to a rise in the groundwater table close to the ground surface. In such conditions, air spaces in the soil are reduced, harming plant growth. Option (b) is the opposite condition, and (c) describes excess moisture but not the standard definition of water logging.
The pressure rise due to water hammer, when valve is closed gradually is equal to
A)
ρLV
B)
ρLV/t
C)
ρt
D)
VL LVt
For gradual closure of a valve, the water hammer pressure rise is given by Δp = ρLV/t, where ρ is the density of water, L is the pipe length, V is the flow velocity, and t is the time of closure. This is the standard formula for gradual valve closure. The other options are incorrect because ρLV is missing the closure time, ρt has wrong dimensions, and the last option is not a valid expression.
Ultra violet rays are highly effective for disinfection for
A)
hard water
B)
highly turbid water
C)
water rich in suspended solids
D)
clear water
Ultraviolet (UV) disinfection works best when water is clear, because UV rays must penetrate the water to inactivate microorganisms. Turbidity, suspended solids, and hardness can shield microbes from UV exposure and reduce effectiveness. Therefore, UV rays are highly effective for disinfection of clear water.
In open channels, gradually varied flow is caused
A)
When the channel slope is equal to the normal slope
B)
When the pressure forces and the change of momentum are different from each other
C)
When the force causing the flow is not equal to the resistance force
D)
When there is an equilibrium between the forces causing the flow and those opposing it
Gradually varied flow (GVF) occurs in open channels when the flow depth changes slowly along the channel length because the driving force and resisting force are not in equilibrium. In other words, the component of gravity causing flow is not exactly balanced by boundary resistance.
Option (d) describes uniform flow, where forces are in equilibrium. Option (a) refers to normal flow conditions, not the cause of GVF. Option (b) is not the standard criterion for GVF in open-channel flow.
Mach’s number is defined as the square root of the ratio of
A)
Inertia force to the pressure force
B)
Inertia force to the surface tension force
C)
Inertia force to the elastic force
D)
None of these
Mach number is the ratio of flow velocity to the speed of sound. In fluid mechanics, it can be expressed as the square root of the ratio of inertia force to elastic force (compressibility effect). Therefore, the correct option is (c). Option (a) corresponds to Euler number, and option (b) corresponds to Weber number.
Two primary air pollutants are
A)
sulphur oxide and ozone
B)
nitrogen oxide and peroxyacetylnitrate
C)
sulphur dioxide and hydrocarbon
D)
ozone and peroxyacetylnitrate
Primary air pollutants are those emitted directly from a source into the atmosphere. Sulphur dioxide and hydrocarbons are directly released from combustion and industrial processes, so they are primary pollutants. Ozone and peroxyacetylnitrate are secondary pollutants because they are formed in the atmosphere by photochemical reactions. Nitrogen oxides are primary pollutants, but peroxyacetylnitrate is secondary, so option (b) is incorrect.
A sanitary sewer is expected to run
A)
full
B)
half full
C)
2/3 full
D)
90% full
A sanitary sewer is generally designed to run partially full, not full, so that there is adequate ventilation and room for fluctuations in flow. In standard sewer design, the usual expected flow condition is about half full. Hence, option (b) is correct. The other options are less appropriate because a sewer running full or nearly full would reduce ventilation and may cause pressure flow, which is not desirable in sanitary sewer systems.
In a pipe flow, the head loss due to friction is 6 m. If the power transmitted through the pipe has to be the maximum, then the total head at the inlet of the pipe will have to be maintained at
A)
36 m
B)
30 m
C)
24 m
D)
18 m
For maximum power transmission through a pipe, the condition is that the head loss due to friction should be one-third of the total head at the inlet.
Given head loss due to friction = 6 m.
So, total inlet head = 3 × 6 = 18 m? Wait, that would be if friction loss were one-third of total head. But for maximum power transmitted in a pipe, the friction head loss equals one-fourth of the total head available, so total head = 4 × 6 = 24 m? Let's verify the standard result: maximum power occurs when discharge head = 1/3 of total head and friction head = 2/3? Actually for pipe power transmission, power delivered at outlet is proportional to Q(H - h_f), with h_f ∝ Q^2. Maximizing gives h_f = H/3, hence H = 3h_f. Therefore H = 3 × 6 = 18 m.
Thus the correct option is (d) 18 m.
Why others are incorrect:
- 36 m and 30 m do not satisfy the maximum power condition.
- 24 m would correspond to a different assumed ratio, not the standard maximum power condition.
Draft tube is used for discharging water from the exit of
A)
an impulse turbine
B)
a Francis turbine
C)
a Pelton wheel
D)
all of these
A draft tube is a gradually expanding tube fitted at the exit of a reaction turbine to recover kinetic energy and discharge water to the tailrace. It is used with a Francis turbine (and other reaction turbines), not with an impulse turbine like the Pelton wheel. In an impulse turbine, the jet acts in air and there is no pressure at the runner exit, so a draft tube is not used.
The most common coagulant is
A)
magnesium sulphate
B)
alum
C)
chlorine
D)
bleaching powder
In water treatment, the most commonly used coagulant is alum (aluminium sulphate). It helps destabilize suspended particles so they can form flocs and settle. Magnesium sulphate is not a standard common coagulant, while chlorine and bleaching powder are disinfectants, not coagulants.
A water borne virus infection is
A)
cholera
B)
swimmer’s itch
C)
jaundice
D)
cancer
Water-borne viral infections are commonly associated with hepatitis viruses, which can cause jaundice. Cholera is a bacterial disease, swimmer’s itch is caused by parasitic larvae, and cancer is not an infectious water-borne disease.
Φ index is defined as
A)
The difference between maximum and minimum infiltration capacities
B)
The difference between the total rainfall and the total runoff divided by the duration of the storm
C)
The rainfall intensity above which the rainfall volume equals the observed runoff volume
D)
The minimum infiltration rate during the storm
The Φ-index is a constant infiltration rate assumed for a storm such that the rainfall in excess of this rate equals the observed direct runoff. In other words, it is the rainfall intensity above which the rainfall volume becomes equal to the runoff volume. Option (d) describes the W-index more closely in some contexts, while (a) and (b) are not the definition of Φ-index.
Water present in the soil which cannot be removed except by heating is called
A)
gravity water
B)
capillary water
C)
hygroscopic water
D)
free water
Water held very tightly by soil particles as a thin film is called hygroscopic water. It cannot be removed by ordinary drainage or plant uptake and is removed only by heating. Gravity water and free water drain under gravity, while capillary water is held in soil pores and is available to plants.
Unit of runoff in M.K.S. system is
A)
Cubic meter / Sec
B)
Meter / Sec
C)
Cubic meter
D)
Square meter
Runoff is the volume of water flowing out per unit time. In the M.K.S. system, discharge/runoff is expressed as volume per second, i.e., cubic meter per second (m³/s). Option (b) is velocity, (c) is only volume, and (d) is area.
For irrigation purpose, the pH value of water should be
A)
Between 3 and 6
B)
Between 6 and 8.5
C)
Between 8.5 and 11
D)
More than 11
Irrigation water should be near neutral to slightly alkaline for safe use by crops and soils. A pH in the range of about 6 to 8.5 is generally considered suitable. Water that is too acidic (below 6) can harm plants and soil chemistry, while highly alkaline water (above 8.5) may create soil problems and reduce nutrient availability. Hence, option (b) is correct.
The S-curve hydrograph is
A)
the summation of the unit hydrograph
B)
the summation of the total runoff hydrograph
C)
the summation of the rainfall hyetograph
D)
all of these
An S-curve hydrograph (also called a summation hydrograph) is obtained by adding successive unit hydrographs of equal duration, each lagged by one unit time. Hence it represents the summation of the unit hydrograph. It is not the summation of the total runoff hydrograph or rainfall hyetograph, so options (b) and (c) are incorrect, and therefore (d) is also incorrect.
Total Energy Line (T.E.L.) represents the sum of
A)
pressure head and kinetic head
B)
datum head and kinetic head
C)
pressure head and datum head
D)
pressure head, kinetic head and datum head
The Total Energy Line (TEL) represents the total mechanical energy per unit weight of fluid at a section. It is the sum of: (1) pressure head, (2) velocity or kinetic head, and (3) datum or elevation head. Hence, TEL = pressure head + kinetic head + datum head. The other options mention only two of these three components, so they are incomplete.
The co-efficient of friction for laminar flow through a circular pipe is given by
A)
f = 0.079 / Re^1/4
B)
f = 16 / Re
C)
f = 64 / Re
D)
none of these
For laminar flow in a circular pipe, the Darcy friction factor is given by f = 64/Re. This is the standard result from Hagen–Poiseuille flow. Option (a) is the Blasius equation for turbulent flow in smooth pipes, and option (b) is not the Darcy friction factor for a circular pipe in laminar flow.
Net irrigation requirement of a crop is given by
A)
Consumptive use + field losses
B)
Consumptive use + conveyance losses
C)
Consumptive use + field losses + conveyance losses
D)
Consumptive use – effective rainfall
Net irrigation requirement is the amount of water that must be supplied by irrigation after accounting for the water already available from rainfall. It is therefore given by consumptive use minus effective rainfall. Options (a), (b), and (c) include losses, which relate more to gross irrigation requirement, not net irrigation requirement.