Hydrology MCQ Quiz - Objective Question with Answer for Hydrology - Download Free PDF

Concept:

Hydrograph

It is used to measure runoff discharge. The area under the discharge and time curve gives the volume of runoff.

Calculation:

Catchment Area = 777.6 km² = 777.6 x 10⁶ m²

Total volume of water = Area of Hydrograph

Total volume = 0.5 x 72 x 60 x 3600 = 7776000 m³

Runoff = Volume / Area = 

Runoff = 0.01 m = 1 cm

Explanation:

• The Blaney–Criddle equation is widely used in India for estimating consumptive use (evapotranspiration) of crops due to its simplicity and reliance on readily available climate data like temperature and crop coefficients.

• Data Required: Only temperature and daylight hours, which are easily available.

• Advantages: Simple, practical, cost-effective.

• Limitations: Less accurate in extreme climates or non-standard crop conditions.

• Suitability: Preferred in Indian irrigation projects and rural planning.

Additional InformationPenman's equation

• Type: Physically based method (semi-theoretical).

• Formula Basis: Combines energy balance and aerodynamic terms.

• Parameters Used:

  • Temperature

  • Solar radiation

  • Humidity

  • Wind speed

• Advantages:

  • More accurate and scientific

  • Useful in precision agriculture or academic research

• Limitations:

  • Requires multiple climate data inputs

  • Complex calculations

• Suitability: Used in research, high-accuracy modeling, and where detailed meteorological data is available.

Tanks and Lysimeter

a) Lysimeter:

• Description: A device used to measure the actual evapotranspiration by isolating a soil volume and monitoring water inputs/outputs.

• Advantages:

  • Direct measurement

  • Highly accurate

• Limitations:

  • Expensive

  • Requires controlled setup and long-term monitoring

• Suitability: Used in research stations for calibration of empirical formulas.

b) Tanks (Class A Evaporation Pan, etc.):

• Description: Evaporation pans are used to measure evaporation losses; crop coefficient is applied to estimate consumptive use.

• Advantages:

  • Simple equipment

  • Easy to operate

• Limitations:

  • Indirect method for consumptive use

  • Influenced by pan location and wind

• Suitability: Supplementary tool for estimating evaporation, not commonly used alone for consumptive use.

Explanation:

• Urbanization increases impervious surfaces like roads and buildings, reducing infiltration.

• This leads to faster runoff, causing the storm runoff hydrograph to have a shorter duration (time base).

• Peak discharge usually increases, and time to peak decreases because runoff reaches the outlet quicker.

• Overall, the volume of runoff may increase or remain similar, but the flow is more rapid and intense.

 Additional InformationA hydrograph is a graph that shows how the flow rate (discharge) of a river or stream varies over time at a specific location, usually in response to a rainfall event.

Components of a Hydrograph:

1. Base Flow:

   • The portion of the streamflow that is sustained between rainfall events, mainly fed by groundwater seepage.

   • It represents the normal, everyday flow in the river before any rainstorm influence.

2. Rising Limb (Ascending Limb):

   • The portion of the hydrograph where the discharge increases due to runoff from rainfall.

   • It reflects how quickly the watershed responds to rainfall.

3. Peak Discharge:

   • The highest point on the hydrograph indicating the maximum flow rate during the storm event.

   • It is critical for designing flood control measures.

4. Time to Peak:

   • The time interval between the start of rainfall or runoff and the peak discharge.

   • It indicates the speed of watershed response.

5. Recession Limb (Falling Limb):

   • The portion after the peak where the discharge decreases as runoff diminishes and base flow conditions are restored.

   • Usually slopes more gently than the rising limb.

6. Lag Time:

   • The time delay between the peak rainfall and peak discharge.

   • Influenced by watershed size, slope, land use, and soil type.

7. Storm Duration:

   • The total time period over which rainfall occurs that influences the hydrograph.

8. Runoff Volume:

   • The area under the hydrograph curve above the base flow line, representing the total volume of water contributed by the storm.

Explanation:

Thornthwaite equation

• Used to estimate potential evapotranspiration (PET) based on temperature and day length.

• It is a climatological method useful in water balance studies and irrigation planning.

• Suitable for regions with limited climatic data.

Hazen-Williams equation

• Used to estimate head loss due to friction in pressurized water flow through pipes.

• It is empirical and applicable mainly for water supply systems.

• Not related to evapotranspiration or atmospheric processes.

Chezy's equation

• Used in open channel flow to calculate flow velocity based on slope and hydraulic radius.

• It is a fundamental hydraulic equation, not related to PET.

• Mainly applied in river engineering and channel design.

Manning's equation

• Also for open channel flow, used to determine the velocity of water.

• Considers channel roughness, slope, and shape.

Explanation:​

• A detention basin is designed to temporarily store stormwater runoff and release it at a controlled rate, helping to reduce peak flow and prevent flooding downstream.

• Therefore, it must be equipped with:

  • Controlled outlets to regulate the discharge of stored water.

  • Spillways (also controlled or auxiliary) to safely handle excess water during extreme events.

Explanation:

Isochrones:

Isochrones is a line on the map which connects points having an equal time of travel of the surface runoff to the catchment outlet. These are some properties of Isochrones:

• Isochrones vary with time, It's most commonly used to depict travel times, such as drawing a 30-minute travel time perimeter around a start location. The isochrone below joins up all points within a 45-minute drive from the origin. 
• Isochrones depict the variation of the pore water pressure along with the depth of the soil sample.
• Isochrones are mainly used for transport planning, property search, sales territory planning, etc. ​

Important Points

Concept:

ϕ_index =  and W_index = 

Where,

P_e = effective rainfall causing runoff, R = runoff, 

t_e = duration of effective rainfall, P = total rainfall and t_r = total duration of rainfall

Calculation:

Given,

ϕ_index = 35 mm/hr

∵  We know that,  runoff occurs when the intensity of rainfall (i) >  ϕ_index 

∴ From rainfall intensity data, the intensity of 30 mm/hr index. 

⇒ P_e = (36 + 40 + 120 + 85 + 45 + 45) × 0.5

⇒ Pe = 185.5 mm and t_e = 3 hr

∵ We know that, ϕindex = 

⇒ 35 =  

⇒ R = 80.5 mm

Now, P = (36 + 40 + 120 + 85 + 45 + 45 + 30) × (30/60)

⇒ P = 200.5 mm and t_r = 3.5 hr

∵ We know that, Windex = 

⇒ Windex = 

⇒ W_index = 34.28 mm/hr

Concept:

Hydrograph:

• A hydrograph is a plot between discharge and time at any given section of a river, channel, etc. 

• It is a response of a given catchment to the rainfall input.

• The shape of the rising limb of a hydrograph depends on both catchment characteristics and rainfall characteristics.

• The shape of the falling or recession limb of a hydrograph depends only on catchment characteristics.
• The inflation point on the falling limb is often assumed to be the point where direct runoff ends.
• Time of Concentration is the time required by the entire drainage area to contribute to the runoff is called the time of concentration or time required by the most extreme point in the drainage to reach the point of interest.
   

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Concept

While selecting the site for rain gauge stations the following points should be considered:

• The site should be on level ground and on open space. It should never be on sloping ground.
• The site should be such that the distance between the gauge station and the objects (like a tree, building, etc) should be at least twice the height of the objects.
• In the hilly area, where level ground is not available, the site should be so selected that the station may be well shielded from high wind.
• The site should be easily accessible to the observer.
• The site should be well protected from cattle by wire fencing.

Concept:

The volume of water evaporated (V) = E × L × B

Where, E = Evaporation measured per day, L = Stretch of evaporation  & B = Average surface width

Calculation:

Given, L = 80 km = 8 × 10⁴ m 

B = 15 m

Evaporation = 0.5 cm / day

Pan co-efficient = 0.7

Total volume of evaporation (V) = 8 × 10⁴ × 15 × 0.5 x 10^-2 × 0.7 × 30 m³

Explanation

∵ We know that,

Runoff coefficient = Runoff/Rainfall

Given,

Runoff = 150 Mm3

Rainfall depth = 750 mm

Area = 500 km2

Rainfall depth in terms of volume = 0.75 × 500 = 375 Mm3 (1 million-m = 106 m)

Runoff coefficient = 150/375

= 0.4

Concept:

Precipitation- It is the fall of water in various forms on the earth from the clouds.

The usual forms of precipitation are as follows:

Note:

Explanation

Concept:

The ϕ – index is a rate of infiltration in which, the rate of infiltration exceeds the value at which volume of runoff become equals to the volume of rainfall.

\( {ϕ_{\left( {index} \right)}} = \frac{{{P_{total}} - Q}}{{Total\;time}}\)

where

PTotal = Total precipitation

Q = Runoff

Calculation:

ϕ - index = 7.5 cm/hr

ϕ - index is the average rate of rainfall such that the volume of rainfall in excess of that rate is equal to the volume of surface runoff

So runoff (R) in cm is,

R 

R 

R 

∴ R = 7.5 cm

Concept:

Form factor: This is defined as the ratio of average width of the basin to the axial length

Form factor 

Form factor 

Calculation:

Given:

Area of catchment = 62.5 mm2

axial length of catchment = 10 mm

Form factor 

∴ Form factor = 0.625