Watershed Concepts and Rainfall-Runoff Analysis
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Questions and Answers

Which land cover type has the highest coefficient of runoff?

  • Roofed Area
  • Water/Pond (correct)
  • Industrial
  • Residential
  • The coefficient of runoff for open spaces is generally higher than that for gravel surfaces.

    False

    What is the coefficient of runoff for a residential area?

    0.63

    The coefficient of runoff for water/pond is __________.

    <p>0.75</p> Signup and view all the answers

    Match the land cover types with their respective coefficients of runoff:

    <p>Residential = 0.63 Industrial = 0.65 Open Spaces = 0.25 Water/Pond = 0.75</p> Signup and view all the answers

    Considering the areal average runoff coefficient, what is the average coefficient for open spaces?

    <p>0.4</p> Signup and view all the answers

    Name one area where the coefficient of runoff is 0.8.

    <p>Roofed Area</p> Signup and view all the answers

    Gravel surfaces have a higher coefficient of runoff than residential areas.

    <p>True</p> Signup and view all the answers

    What is the primary focus of the discussed topics?

    <p>Watershed concepts</p> Signup and view all the answers

    The Rational Method is used for calculating runoff from a watershed.

    <p>True</p> Signup and view all the answers

    What does the term 'design rainfall intensity (I)' refer to?

    <p>The ratio of total amount of rainfall to time in mm/hr.</p> Signup and view all the answers

    The _____ Method is a variation of the Rational Method used for runoff analysis.

    <p>Modified Rational</p> Signup and view all the answers

    Match the following methods to their descriptions:

    <p>Rational Method = Estimates peak runoff from small watersheds Modified Rational Method = Refines the calculations by accounting for storage and infiltration SCS Curve Number Method = Utilizes land use, soil type, and hydrologic conditions</p> Signup and view all the answers

    What is the highest rainfall intensity recorded for a return period of 100 years over a duration of 1 hour?

    <p>203.3 mm/hr</p> Signup and view all the answers

    The overland flow time (To) is calculated using 107 times the number of years of rainfall.

    <p>False</p> Signup and view all the answers

    Which of the following is NOT a topic discussed in the content?

    <p>Flood management strategies</p> Signup and view all the answers

    Design rainfall intensity is measured in cubic meters per square meter.

    <p>False</p> Signup and view all the answers

    What does Tc represent in stormwater management?

    <p>Time of Concentration</p> Signup and view all the answers

    List one application of the rainfall-runoff analysis.

    <p>Urban drainage planning or flood forecasting.</p> Signup and view all the answers

    The formula for calculating travel time through channels and pipes is __________.

    <p>Tch = L/V</p> Signup and view all the answers

    Match the following return periods with their corresponding rainfall intensities for a 30-minute duration:

    <p>2 years = 72.6 mm/hr 10 years = 130.8 mm/hr 20 years = 153.0 mm/hr 50 years = 181.7 mm/hr</p> Signup and view all the answers

    What is the minimum velocity stated for Vmin in Manning’s Equation?

    <p>0.8 m/s</p> Signup and view all the answers

    A rolling hill area flooded after 15 minutes of rainfall supports the estimation of the time of concentration.

    <p>True</p> Signup and view all the answers

    In the formula V = (1/n) R2/3 S1/2, R represents the __________ of the watershed.

    <p>hydraulic radius</p> Signup and view all the answers

    Study Notes

    Watershed Concepts

    • A watershed is a contiguous area where rainfall or runoff drains to a common outlet.
    • Basin, watershed, and catchment are synonymous terms for a geographical area.
    • Surface runoff is the portion of precipitation that runs over the land surface and not into the soil.

    Rainfall-Runoff Analysis

    • Rational Method: A simple method for estimating peak flow, Qp = CiA, where:

      • C = runoff coefficient (based on land use)
      • i = rainfall intensity (for a duration equal to time of concentration)
      • A = watershed area
    • Time of Concentration (Tc): Time for water to travel from the most distant point in the watershed to the outlet. Methods for estimating Tc include:

      • Kirpich equation
      • Izzard equation
      • Kerby-Hathaway equation
      • FAA English & SI methods
      • Van Sickle.
    • SCS Velocity Method: Estimating concentration time by total travel time calculated by dividing into segments.

    SCS Curve Number Method

    • SCS Curve Number (CN) method estimates direct runoff from rainfall.

    • The CN is calculated based on soil characteristics, land cover, and antecedent moisture conditions

      • S = 25400/CN - 254 (millimeters). Other calculations may use inches.
      • Ia=0.2S
    • Rainfall-runoff relationships are based on empirical observations.

    • Composite Runoff Coefficient: A method for calculating a single CN for watersheds with diverse land use types.

      • Weighted averaging, using area proportions of each land use category.

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    Description

    This quiz covers key concepts in watershed management, including definitions, runoff analysis methods, and time of concentration calculations. You'll explore various methods for estimating peak flow and travel time within a watershed, focusing on practical applications and formulas. Test your knowledge on watershed dynamics and analysis techniques.

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