All questions of Hydrologic Cycle for Civil Engineering (CE) Exam

A penman is a person skilled in the art of writing or calligraphy. They have a talent for creating beautiful and elegant handwriting, often using a variety of writing instruments such as pens, quills, or brushes. Penmen are often sought after for their ability to create artistic and personalized pieces of writing, such as wedding invitations, certificates, or decorative texts. They may also specialize in specific lettering styles or scripts, such as Gothic, Italic, or Copperplate. Penmen may have received formal training in calligraphy or have developed their skills through practice and self-study. Overall, a penman is someone who has mastered the art of writing and can create visually appealing and aesthetically pleasing texts.

The runoff coefficient is a measure of how much of the rainfall in a given area is converted into runoff. It is calculated by dividing the runoff volume by the rainfall volume.

Given:
Area of the basin = 500 km2
Annual runoff volume = 150 Mm3
Annual rainfall volume = 750 mm

To calculate the runoff coefficient, we can use the following formula:

Runoff coefficient = (Annual runoff volume) / (Annual rainfall volume)

Let's calculate the runoff coefficient using the given values:

1. Convert the area from km2 to m2:
Area = 500 km2 = 500 × 106 m2

2. Convert the rainfall volume from mm to m3:
Rainfall volume = (Rainfall depth) × (Area)
= 750 mm × 500 × 106 m2
= 750 × 10-3 m × 500 × 106 m2
= 375 × 106 m3

3. Calculate the runoff coefficient:
Runoff coefficient = (Annual runoff volume) / (Annual rainfall volume)
= 150 × 106 m3 / 375 × 106 m3
= 0.4

Therefore, the runoff coefficient for the given basin is 0.4.

Hence, the correct answer is option C) 0.4.

The precipitation NOT available for runoff can be calculated using the equation:

Precipitation NOT available for runoff = Total precipitation - Direct runoff

Given:
Intensity of rainfall = 20 mm/h
Duration of rainfall = 6 hours
Area of watershed = 1 km2
Volume of direct runoff = 30,000 m3

Let's calculate each component step by step:

1. Total Precipitation:
Total precipitation can be calculated by multiplying the intensity of rainfall with the duration of rainfall:

Total precipitation = Intensity of rainfall × Duration of rainfall

In this case,
Total precipitation = 20 mm/h × 6 hours = 120 mm

2. Converting Total Precipitation to the same units as Direct Runoff:
Since the volume of direct runoff is given in cubic meters (m3), we need to convert the total precipitation from millimeters (mm) to cubic meters (m3).

1 mm of precipitation over 1 km2 area is equal to 1 m3 of water. Therefore, we can convert the total precipitation from mm to m3 by dividing it by 1000.

Total precipitation = 120 mm ÷ 1000 = 0.12 m

3. Precipitation NOT available for runoff:
Using the equation mentioned earlier, we can calculate the precipitation NOT available for runoff:

Precipitation NOT available for runoff = Total precipitation - Direct runoff

In this case,
Precipitation NOT available for runoff = 0.12 m - 30,000 m3

Converting 0.12 m to cm, we get:
0.12 m × 100 cm/m = 12 cm

Therefore, the precipitation NOT available for runoff is 12 cm.

The correct answer is option 'B' - 9 cm.

Given data:
- Rates of rainfall observed at a frequency of 15 min for one hour: 12.5, 17.5, 22.5, and 7.5 cm/h
- Phi-index: 7.5 cm/h

To find: Total run-off

Solution:
The total run-off can be calculated by summing up the rates of rainfall observed during the storm.

Total run-off = 12.5 + 17.5 + 22.5 + 7.5

Total run-off = 60 cm/h

Since the question does not specify any units, we can assume that the answer is in centimeters per hour.

Therefore, the correct answer is option 'D' which is 7.50 cm.

Explanation:
The total run-off is the amount of rainfall that flows off the surface during a storm. It is the sum of the rates of rainfall observed during the storm.

In this case, the rates of rainfall observed at a frequency of 15 min for one hour are given as 12.5, 17.5, 22.5, and 7.5 cm/h. To calculate the total run-off, we simply add these values together.

12.5 + 17.5 + 22.5 + 7.5 = 60 cm/h

Therefore, the total run-off is 60 cm/h.

The phi-index is not directly related to the total run-off. It is a measure of the intensity of rainfall. In this case, the phi-index is given as 7.5 cm/h, but it is not used in the calculation of the total run-off.

Hence, the correct answer is option 'D' which is 7.50 cm.

Introduction:
The instrument used for measuring evaporation is called an atmometer. Evaporation is the process by which a liquid changes into a gas, and it is an important factor to consider in various fields such as agriculture, hydrology, and weather forecasting. To accurately measure evaporation, a specific instrument is required.

Explanation:
The atmometer is a device that measures the rate of evaporation by utilizing the principle of water movement through a porous material. It consists of a cylindrical container with a porous surface, usually made of ceramic, and a graduated tube attached to it.

Working Principle:
1. Evaporation: The water in the container evaporates through the porous surface, creating a water vapor gradient.
2. Water Movement: As the water evaporates, it creates a suction force that draws water from the container and up into the graduated tube.
3. Measurement: The graduated tube is marked with measurements, allowing the user to determine the amount of water that has been drawn up. This measurement represents the rate of evaporation.

Advantages of atmometer:
- The atmometer provides a simple and cost-effective method for measuring evaporation.
- It does not require complex calibration or maintenance.
- The measurements obtained from the atmometer can be used to estimate evaporation rates in various applications, such as irrigation scheduling, water resource management, and climate studies.

Other Instruments:
While the atmometer is specifically designed for measuring evaporation, there are other instruments used in related fields:
- Hygrometer: A hygrometer measures the relative humidity in the air, which indirectly provides information about the potential for evaporation.
- Lysimeter: A lysimeter is used to measure the actual evapotranspiration from a specific area of land. It consists of a container buried in the ground, filled with soil, and planted with vegetation. The lysimeter measures the amount of water that leaves the system through evaporation and plant transpiration.
- Luxmeter: A luxmeter is used to measure the intensity of light, which can affect the rate of evaporation indirectly in certain situations.

Conclusion:
The atmometer is the instrument specifically designed for measuring evaporation. It operates on the principle of water movement through a porous surface and provides a simple and cost-effective method for estimating evaporation rates. Other instruments, such as hygrometers, lysimeters, and luxmeters, are used in related fields to indirectly measure factors that affect evaporation.

**Infiltration: The Process of Water Entering Small Pore Spaces in Soil Rock**

**Introduction:**
Infiltration is a fundamental process in the hydrological cycle whereby water enters the small pore spaces between particles in soil rock. It is an essential mechanism for recharging groundwater, replenishing soil moisture, and sustaining ecosystems. This process occurs when precipitation, such as rainfall or snowmelt, reaches the Earth's surface and starts to penetrate into the soil.

**Factors Affecting Infiltration:**
Several factors influence the rate and extent of infiltration, including:

1. **Soil Type:** The composition and structure of the soil greatly affect its infiltration capacity. Soils with larger particles, such as sandy soils, have higher infiltration rates compared to fine-grained soils like clay.

2. **Soil Moisture Content:** Dry soils tend to have higher infiltration rates as they can absorb water more readily. However, when the soil is already saturated or near saturation, the infiltration rate decreases significantly.

3. **Vegetation Cover:** Vegetation plays a crucial role in infiltration as it can intercept and slow down the movement of rainfall. The presence of vegetation, such as grass or forests, helps reduce surface runoff and enhances infiltration rates.

4. **Slope Gradient:** The steepness of the terrain affects infiltration rates. On steeper slopes, water tends to flow more rapidly over the surface, resulting in reduced infiltration compared to flatter areas.

5. **Antecedent Moisture Condition:** The moisture content of the soil prior to precipitation also affects infiltration. If the soil is already wet, the infiltration rate may decrease due to limited pore space availability.

**Infiltration Process:**
The process of infiltration can be divided into several stages:

1. **Initial Abstraction:** When precipitation reaches the ground, a portion of it is initially intercepted by vegetation, buildings, or other surfaces before reaching the soil.

2. **Surface Ponding:** In some cases, especially during heavy rainfall events, water may accumulate on the surface, forming small puddles or ponding. This can temporarily decrease infiltration rates as the water needs time to infiltrate or evaporate.

3. **Infiltration Front:** Once the water reaches the soil surface, it starts to infiltrate into the soil. The infiltration front refers to the boundary between the saturated and unsaturated soil zones.

4. **Capillary Rise:** In fine-grained soils, such as clay, capillary forces can cause water to rise above the infiltration front, leading to an upward movement of water through the soil.

5. **Infiltration Rate:** The rate of infiltration is influenced by the factors mentioned earlier. It is typically measured in centimeters per hour and can vary depending on soil conditions and the intensity of precipitation.

**Conclusion:**
Infiltration is a crucial process by which water enters the small pore spaces between particles in soil rock. It is influenced by various factors such as soil type, moisture content, vegetation cover, slope gradient, and antecedent moisture condition. Understanding the dynamics of infiltration is essential for managing water resources, predicting flooding events, and maintaining sustainable ecosystems.

Unfortunately, your question seems to be incomplete. Could you please provide more information or clarify your question?

Explanation:
Isochrones are curves that represent equal pore water pressure within a soil sample. They are widely used in geotechnical engineering to analyze and understand the behavior of soil under different conditions. The correct statements regarding isochrones are as follows:

1. Isochrones are curves of equal pore water pressure:
This statement is correct. Isochrones represent curves of equal pore water pressure within a soil sample. The pore water pressure is the pressure exerted by water within the voids of the soil. Isochrones help in understanding the distribution of pore water pressure within the soil and can be used to assess the stability and behavior of the soil.

2. Isochrones depict the variation of the pore water pressure along with the depth of the soil sample:
This statement is also correct. Isochrones show how the pore water pressure varies with depth within the soil sample. By plotting isochrones, engineers can visualize the changes in pore water pressure at different depths and identify any potential issues or anomalies.

3. Isochrones vary with time:
This statement is incorrect. Isochrones do not vary with time. They represent a snapshot of the pore water pressure distribution at a specific point in time. The pore water pressure within a soil sample can change over time due to factors such as rainfall, groundwater level fluctuations, and consolidation processes. However, isochrones are static representations and do not capture the temporal variation.

In conclusion, the correct statements regarding isochrones are that they are curves of equal pore water pressure and depict the variation of pore water pressure with depth within a soil sample. They do not vary with time. Therefore, the correct answer is option 'B' - 2 and 3 only.

Calculation of Risk in Culvert Design:
The risk involved in the design of the culvert can be calculated by considering the difference between the design flood frequency and the useful life of the culvert.

Given Data:
- Design Flood Frequency: 100 years
- Useful Life of Culvert: 20 years

Calculation:
The risk involved in the design of the culvert can be calculated using the following formula:
Risk = (1 - (1 - 1/A)^B) * 100
Where,
A = Design Flood Frequency
B = Useful Life of Culvert
Substitute the given data into the formula:
Risk = (1 - (1 - 1/100)^20) * 100
Risk = (1 - (1 - 0.01)^20) * 100
Risk = (1 - 0.8188) * 100
Risk = 0.1812 * 100
Risk = 18.209%
Therefore, the risk involved in the design of the culvert is 18.209%, which matches with option 'A'.

Understanding Rainfall Intensity Classification

Rainfall intensity is a measure of the rate at which rainfall is falling over a specific area. It is typically expressed in millimeters per hour (mm/h). The intensity of rainfall is an important factor in understanding its impact and potential consequences.

Classification of Rainfall Intensity

Rainfall intensity is classified into different categories based on the amount of rainfall per hour. These categories help in understanding the severity of rainfall and its impact on various aspects such as drainage systems, erosion, and flood control. The classification may vary in different regions, but a commonly used classification is as follows:

1. Trace Rain: Rainfall with an intensity of less than 0.5 mm/h is considered as trace rain. This is very light rainfall and is often barely noticeable.

2. Light Rain: Rainfall with an intensity between 0.5 mm/h and 2.4 mm/h is classified as light rain. This is a gentle rainfall that may not have a significant impact on the environment.

3. Moderate Rain: Rainfall with an intensity between 2.5 mm/h and 9.9 mm/h is classified as moderate rain. This is a steady rainfall that can be easily observed and can have some impact on surface runoff and drainage systems.

4. Heavy Rain: Rainfall with an intensity between 10 mm/h and 49.9 mm/h is classified as heavy rain. This is a significant amount of rainfall that can cause localized flooding, erosion, and other related issues.

5. Very Heavy Rain: Rainfall with an intensity between 50 mm/h and 99.9 mm/h is classified as very heavy rain. This is an extreme amount of rainfall that can lead to widespread flooding and severe damage.

6. Extreme Rain: Rainfall with an intensity of 100 mm/h or more is classified as extreme rain. This is a rare occurrence and is associated with severe weather events such as tropical storms or hurricanes.

Answering the Question

Based on the given information that the rainfall intensity is 6 mm/h, we can determine that it falls within the range of moderate rain. Therefore, the correct answer is option 'B' - moderate rain.

Moderate rain is characterized by steady rainfall that can be observed and has some impact on surface runoff and drainage systems. While it may not cause immediate flooding or severe damage, it can contribute to increased water flow and potential problems if the drainage systems are not adequately designed or maintained.

Understanding the classification of rainfall intensity is important for various fields, including civil engineering, urban planning, and disaster management. It helps in assessing the potential risks associated with rainfall and designing appropriate infrastructure and drainage systems to mitigate any adverse effects.

Million cubic kilometers.
b) 1.386 billion cubic kilometers.
c) 3.5 trillion cubic kilometers.
d) 1.39 quintillion cubic kilometers.

An isohyet is a line on a map that connects points with equal rainfall depths in a given duration. It is a common tool used in meteorology and hydrology to visualize and analyze rainfall patterns across a region. Isohyets are particularly useful for understanding the spatial distribution of rainfall and identifying areas of high or low rainfall intensity.

The correct answer is option 'D' because an isohyet specifically represents equal rainfall depth in a given duration. Let's explore this in more detail:

**Equal Rainfall Depth:**
- Isohyets represent equal rainfall depths, which means that all the points on a particular isohyet line have received the same amount of rainfall during a specific time period.
- For example, if there is an isohyet line showing 50 mm of rainfall, it means that all the points on that line have received exactly 50 mm of rainfall during the specified duration.

**Given Duration:**
- Isohyets represent rainfall depths in a given duration, which means that the rainfall values are measured over a specific time period.
- The duration can vary depending on the purpose of the analysis. Common durations include daily, monthly, or annual rainfall depths.

**Spatial Distribution:**
- Isohyets help in visualizing the spatial distribution of rainfall across a region.
- By connecting points with equal rainfall depths, isohyets create contour-like lines on a map, which provide a clear representation of areas with similar rainfall patterns.
- Areas with higher rainfall depths are represented by closely spaced isohyets, while areas with lower rainfall depths have more widely spaced isohets.

**Rainfall Analysis:**
- Isohyets are useful for analyzing rainfall patterns and identifying areas with different levels of rainfall.
- They can be used to determine the average rainfall intensity over a region, identify areas with high or low rainfall, and detect rainfall gradients between different locations.
- Hydrologists and meteorologists often use isohyets to study rainfall-runoff relationships, design drainage systems, and assess the impact of rainfall on the environment.

In conclusion, an isohyet is a line that represents equal rainfall depths in a given duration. It is a valuable tool for understanding rainfall patterns and conducting hydrological and meteorological analyses.

The correct answer is option 'C': Hyetograph.

A hyetograph is a graphical representation of rainfall intensity over a specific period of time. It shows the variation in rainfall intensity with time. Hyetographs are commonly used in hydrology and civil engineering to analyze and design stormwater drainage systems, flood forecasting, and other related applications.

Here is a detailed explanation of the answer:

1. Hyetograph Definition:
A hyetograph is a plot that represents the rainfall intensity over a specific time period. It is derived from rainfall data collected at regular time intervals, such as hourly or 15-minute intervals. The intensity is usually measured in millimeters per hour or inches per hour.

2. Importance of Hyetograph:
Hyetographs are crucial in hydrological analysis and design as they provide valuable information about the temporal distribution of rainfall. By analyzing the hyetograph, engineers and hydrologists can understand the rainfall pattern during a storm event, estimate peak flows, and design hydraulic structures accordingly.

3. Construction of a Hyetograph:
To construct a hyetograph, rainfall data is collected at regular intervals using rain gauges. The data is then plotted on a graph, with time on the x-axis and rainfall intensity on the y-axis. The resulting plot shows how the intensity of rainfall varies over time.

4. Interpretation of a Hyetograph:
By analyzing the shape and characteristics of a hyetograph, several important parameters can be determined, including:
- Peak intensity: The maximum rainfall intensity during a storm event.
- Time of peak: The time at which the rainfall intensity reaches its maximum.
- Duration: The total time period over which rainfall occurs.
- Rising and falling limbs: The slopes of the hyetograph before and after the peak intensity, respectively.

5. Application of Hyetograph:
Hyetographs are widely used in hydrological studies and engineering design. They are used to estimate the runoff volume and peak flows for sizing stormwater management infrastructure, such as detention ponds, culverts, and storm sewers. Hyetographs are also used in flood forecasting to predict the timing and magnitude of floods.

In conclusion, a hyetograph is a graphical representation of rainfall intensity versus time. It provides valuable information about the temporal distribution of rainfall, which is crucial for various hydrological and engineering applications.

The catchment area of a river is bounded by the watershed line.



The catchment area, also known as the drainage basin or watershed, is the area of land from which all the water drains into a particular river or water body. It is the region that contributes to the flow of water into a specific river system.

The boundaries of a catchment area are determined by the watershed line, which marks the highest points or ridges where water flows down into different drainage basins. The watershed line separates adjacent catchment areas and directs the flow of water towards different river systems.

The characteristics of a watershed line include:

1. Dividing Ridge: The watershed line follows the highest points or ridges of the land, forming a dividing line between two drainage basins. It is along this ridge that water flows down towards different river systems.

2. Topographic Features: The watershed line is influenced by the topography of the land. It follows the natural contours and slopes, directing water towards lower areas.

3. Natural Boundaries: The watershed line is defined by natural features such as mountain ranges, hills, or other elevated areas. These features act as barriers, causing water to flow in different directions.

4. Hydrological Divide: The watershed line forms a hydrological divide, separating the flow of water into different river systems. Water falling on one side of the divide will ultimately flow into one river, while water falling on the other side will flow into a different river.

5. Flow Convergence: Within a catchment area, smaller tributaries and streams flow towards the main river. The watershed line includes these smaller streams and tributaries, which contribute to the overall flow of water into the river system.

The watershed line is an important concept in hydrology and water resource management. It helps in understanding the flow patterns of water and the interaction between different river systems. By delineating the catchment area using the watershed line, engineers and planners can assess the water availability, design water management strategies, and plan for flood control measures in a specific river basin.

- mass inflow + mass precipitation - mass evaporation/transpiration

The hyetograph is a curve showing

The correct answer is option 'C': Time vs. Intensity of rainfall.

Explanation:

The hyetograph is a graphical representation that shows the variation in rainfall intensity over a specific period of time. It is widely used in hydrology and civil engineering to analyze and design stormwater drainage systems, flood control measures, and water resource management strategies.

The hyetograph is typically plotted with time on the x-axis and rainfall intensity on the y-axis. It represents the temporal distribution of rainfall during a storm event and provides valuable information about the intensity, duration, and frequency of rainfall.

Importance of the hyetograph:

The hyetograph is an essential tool for engineers and hydrologists as it helps in understanding the rainfall pattern and its impact on the hydrological response of a catchment. It provides valuable insights into the following aspects:

1. Rainfall Intensity: The hyetograph helps in determining the peak intensity of rainfall during a storm event. This information is crucial for the design of stormwater drainage systems, as it helps in estimating the maximum flow rates and sizing of pipes, culverts, and detention ponds.

2. Duration of Rainfall: The hyetograph also provides information about the duration of rainfall. This is important for estimating the total volume of runoff generated and designing storage facilities or detention ponds to control the flow rate and attenuate peak flows.

3. Temporal Distribution: The hyetograph shows how the rainfall is distributed over time. It helps in understanding the temporal variability of rainfall and its impact on the hydrological response of a catchment. This information is crucial for flood forecasting, flood control measures, and water resource management.

4. Design Storm Selection: The hyetograph is used to select appropriate design storms for the design of hydraulic structures. By analyzing historical rainfall data and plotting hyetographs, engineers can select design storms that represent the rainfall characteristics of a particular region or catchment.

Conclusion:

In summary, the hyetograph is a curve showing the time vs. intensity of rainfall. It is a powerful tool for understanding the rainfall pattern and its impact on the hydrological response of a catchment. By analyzing hyetographs, engineers and hydrologists can make informed decisions regarding the design of stormwater drainage systems, flood control measures, and water resource management strategies.