Hydrology Unit Hydrograph Quiz

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Questions and Answers

What is the total flow at hour 12 in the 3hr unit hydrograph from the given data?

  • 132 cu.meter/second
  • 75 cu.meter/second
  • 210 cu.meter/second
  • 180 cu.meter/second (correct)

How much additional flow does a 4 cm excess rainfall contribute at hour 6, assuming a base flow of 15 cu.meter/second?

  • 105 cu.meter/second
  • 90 cu.meter/second
  • 75 cu.meter/second (correct)
  • 60 cu.meter/second

Which hour shows a decrease in the flow rate from the previous hour for the 3hr unit hydrograph?

  • 15 hours
  • 12 hours
  • 21 hours
  • 18 hours (correct)

What is the flow rate at hour 45 in the 3hr unit hydrograph based on the provided data?

<p>33 cu.meter/second (A)</p> Signup and view all the answers

What is the base flow amount that must be added to derive the DRH for the given excess rainfall?

<p>15 cu.meter/second (D)</p> Signup and view all the answers

Which group has the highest runoff potential?

<p>Group D (A)</p> Signup and view all the answers

Which of the following is NOT a factor considered in determining hydrologic condition?

<p>Amount of precipitation (C)</p> Signup and view all the answers

What is the range of runoff potential for a watershed with a moderately low runoff potential?

<p>0.15 – 0.30 in/hr (D)</p> Signup and view all the answers

What is the primary focus of 'land treatment' in the context of watershed management?

<p>Managing agricultural land to reduce runoff and improve infiltration (D)</p> Signup and view all the answers

Which of the following factors would likely contribute to a poor hydrologic condition?

<p>Presence of impervious surfaces like roads (B)</p> Signup and view all the answers

What does the observed hydrograph represent in this context?

<p>Flood response of the basin to rainfall (D)</p> Signup and view all the answers

What is the purpose of deriving a unit hydrograph from a direct runoff hydrograph?

<p>To analyze flood characteristics independent of rainfall (B)</p> Signup and view all the answers

How is the direct runoff hydrograph (DRH) calculated?

<p>By subtracting base flow from the observed hydrograph (C)</p> Signup and view all the answers

What does the base flow represent in the derivation process?

<p>The portion of flow not attributed to direct runoff (B)</p> Signup and view all the answers

What is indicated by the ordinates of the unit hydrograph?

<p>The excess runoff per unit of effective rainfall (B)</p> Signup and view all the answers

At what time does the observed hydrograph peak according to the data?

<p>24 hours (C)</p> Signup and view all the answers

What happens to the ordinates of the unit hydrograph as time progresses following the peak?

<p>They gradually decrease (D)</p> Signup and view all the answers

What is the purpose of dividing the ordinates of the direct runoff hydrograph by excess rainfall?

<p>To derive the unit hydrograph (A)</p> Signup and view all the answers

What is the primary purpose of the 'rising limb' of a hydrograph?

<p>To represent the period of increasing discharge due to rainfall infiltration. (B)</p> Signup and view all the answers

What is the significance of the 'peak discharge' in a hydrograph?

<p>It marks the highest rate of flow during a rainfall event, often used for design purposes. (A)</p> Signup and view all the answers

What does the 'recession limb' of a hydrograph primarily depict?

<p>The gradual decrease in discharge after a rainfall event. (B)</p> Signup and view all the answers

What is a hydrograph?

<p>A graph showing the rate of flow (discharge) versus time at a specific point in a river. (A)</p> Signup and view all the answers

What type of information is conveyed by a hydrograph?

<p>The rate of flow (discharge) of water over time at a specific point. (C)</p> Signup and view all the answers

Which of the following is NOT a topic discussed in the context of rainfall-runoff relation?

<p>Precipitation Intensity (C)</p> Signup and view all the answers

What is the goal of 'hydrograph separation'?

<p>Differentiating between surface runoff and baseflow in the hydrograph. (C)</p> Signup and view all the answers

Which methods are mentioned in the text for estimating runoff?

<p>Rational Method and SCS Curve Method (B)</p> Signup and view all the answers

What does the curve number (CN) represent in hydrology?

<p>A dimensionless number reflecting soil and cover conditions (A)</p> Signup and view all the answers

Which of the following is NOT an advantage of the SCS Curve Method?

<p>High computational demand (C)</p> Signup and view all the answers

What factor is NOT considered when evaluating the hydraulic condition for SCS Runoff?

<p>Soil temperature (B)</p> Signup and view all the answers

In the SCS Curve method formula, what does 'S' represent?

<p>Potential maximum retention after runoff begins (D)</p> Signup and view all the answers

Which land surface characteristics contribute to a good Curve Number assessment?

<p>More than 75% ground cover with light grazing (C)</p> Signup and view all the answers

What is the range of values for the Curve Number?

<p>0 to 100 (D)</p> Signup and view all the answers

Which of the following statements about the hydrologic soil groups is TRUE?

<p>There are four distinct hydrologic soil groups (B)</p> Signup and view all the answers

What does the term 'impervious surfaces' refer to in regard to the Curve Number?

<p>Surfaces that do not allow water to penetrate (C)</p> Signup and view all the answers

What does the abbreviation "ER" most likely represent in the table and graph?

<p>Effective Rainfall (D)</p> Signup and view all the answers

What is the relationship between the "meter / second" values and the "DRH" curves in the graph?

<p>The 'meter / second' values represent the peak flow rates in the DRH curves. (C)</p> Signup and view all the answers

Assuming the values in the table represent flow rates, what is the likely unit for the numbers under columns "(2) * ER", "(3) * ER", and "(4) * ER"?

<p>Cubic meters per second (C)</p> Signup and view all the answers

Based on the data shown, what is the approximate peak flow rate for a 2 cm ER event?

<p>600 meters/second (A)</p> Signup and view all the answers

Based on the data presented, what is the general trend observed in the flow rate as the ER value increases?

<p>The flow rate increases proportionally to the ER. (D)</p> Signup and view all the answers

According to the table, which time interval experiences the most significant change in flow rate during the 4 cm ER event?

<p>12-15 hours (D)</p> Signup and view all the answers

What information is likely to be most useful for accurately predicting a DRH curve for an ER event?

<p>All of the above (D)</p> Signup and view all the answers

The Rational Method, mentioned in the text, is likely used for what purpose in the context of the provided data?

<p>To estimate the peak flow rate for a specific ER event. (C)</p> Signup and view all the answers

Flashcards

Hydrology

The study of water movement and distribution on Earth.

Hydrologic Cycle

The continuous movement of water through evaporation, condensation, and precipitation.

Hydrograph

A graph showing the flow rate of water over time at a specific location.

Discharge

The volume of water flowing per unit time at a specific point.

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Rising Limb

The part of the hydrograph that shows increasing discharge after a rain event.

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Peak Discharge

The maximum rate of flow in a hydrograph.

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Recession Limb

The portion of the hydrograph after peak discharge where flow decreases.

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Runoff Estimation Methods

Techniques like the rational method and SCS Curve Method to predict runoff.

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Unit Hydrograph (UH)

A hydrograph representing the response of a watershed to a unit of rainfall excess.

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Direct Runoff Hydrograph (DRH)

A hydrograph that shows direct runoff from excess rainfall, excluding base flow.

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Base Flow

The sustained flow in a stream or river, resulting from groundwater seepage.

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Excess Rainfall

Rainfall amount that exceeds the initial abstraction and contributes to runoff.

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Cubic Meters per Second (cu.m/sec)

A unit of measurement for flow rate representing cubic meters of water flowing per second.

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Runoff Hydrograph

Graph showing water flow from a basin over time following rainfall.

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DRH (Direct Run-off Hydrograph)

The portion of the hydrograph representing direct runoff after subtracting base flow.

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Ordinates of Hydrograph

Values on the hydrograph that indicate flow rates at specific times.

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6-Hour Unit Hydrograph

Unit hydrograph derived from direct runoff over a 6-hour period.

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Direct Run-off Hydrograph Calculation

Calculating direct runoff by subtracting base flow from the observed hydrograph.

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Meter / Second

A unit of measurement for velocity, indicating distance traveled in meters per second.

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ER (Effective Rainfall)

The amount of rainfall that contributes to surface runoff after absorption and evaporation losses.

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Rational Method

A technique used to estimate peak surface runoff for drainage structure design.

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Peak Surface Runoff Rate

The maximum rate at which water flows over land after rainfall.

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Drainage Structure

Built systems designed to manage water runoff, including sewers and ponds.

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Storm Water Detention Pond

A pond designed to temporarily hold stormwater runoff and release it slowly.

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Surface Runoff

Water that flows over the land surface after precipitation.

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Design of Drainage Structures

The process of creating systems to manage stormwater effectively, ensuring safety and functionality.

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SCS Curve Method

A method to estimate runoff using rainfall and soil retention data.

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Runoff (Q)

The amount of water that runs off the surface after rainfall.

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Rainfall (P)

The depth of rain that falls over a period, also in inches.

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Potential Maximum Retention (S)

The maximum amount of water a soil can retain after runoff starts.

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Curve Number (CN)

A dimensionless number that reflects soil and land cover conditions for runoff.

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Hydrologic Soil Groups

Classification of soils based on their runoff-producing properties.

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Advantages of SCS Method

Reliable, efficient, and uses readily available input data.

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Composite CN

A combined runoff curve number for different land cover types.

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Runoff Potential A

Lowest runoff potential greater than 0.30 in/hr.

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Runoff Potential B

Moderately low runoff potential between 0.15 – 0.30 in/hr.

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Runoff Potential C

Moderately high runoff potential between 0.05 – 0.15 in/hr.

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Runoff Potential D

Highest runoff potential between 0 – 0.05 in/hr.

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Hydrologic Condition Factors

Factors affecting infiltration and runoff include vegetation, cover, and roughness.

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Study Notes

Preface

  • This module aims to provide a detailed presentation of hydrology theory and application.
  • It covers the hydrologic cycle and processes like precipitation, evaporation, infiltration, overland flow, groundwater flow, and surface runoff generation.
  • The module's development accounted for feedback from a peer reviewer and other faculty members to ensure quality.

Unit 7: Rainfall-Runoff Relation

Intended Learning Outcomes

  • Define and describe basic principles related to rainfall-runoff relationships.
  • Solve problems related to rainfall-runoff relationships.

Introduction

  • The chapter discusses rainfall-runoff relations, including hydrographs, hydrograph separation, unit hydrographs, rational methods, and SCS curve methods.

Topics

Definition of Hydrograph

  • A hydrograph is a graph that displays the rate of flow (discharge) over time at a specific point in a river, channel, or conduit.

  • The rate of flow is typically measured in cubic meters per second (cms) or cubic feet per second (cfs).

  • Hydrographs are vital in designing sewage and surface water systems.

  • Components of Hydrograph:

    • Discharge: the rate of flow at a specific location in a water body.
    • Rising limb: the part of the hydrograph where discharge increases due to rainfall.
    • Peak discharge: the maximum discharge rate during a rainfall event.

Hydrograph Separation

  • Methods:
    • Simple method: draw a line tangential to both limbs at their lower portions.
    • Extended method: extend the recession curve prior to the storm up to the peak of the hydrograph.

Runoff Coefficient, C

  • Represents the fraction of rainfall converted into runoff.
  • This value varies based on the watershed's nature (e.g., impervious surfaces, clay soil, etc.).

The Design Rainfall Intensity

  • The intensity needed to estimate peak runoff rate for design.
  • Determined from intensity-duration-frequency data.

SCS Curve Method

  • Equation: Q = (P − 0.2S)²/(P + 0.8S), where:
    • Q: Runoff
    • P: Rainfall
    • S: Potential maximum retention before runoff begins
    • CN: Curve number
  • Curve numbers (CN) reflect soil and land cover conditions. Values can be found in tables.

Assessment (Test I & II)

  • Test I: Questions covering components, types, separation, and unit hydrographs of hydrographs.
  • Test II: Solving problems using the concepts described.
  • Includes time-based data to calculate values with the appropriate equations.

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