Hydrology Unit 5: Evaporation
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Why is it important to have a jug that holds more than 2 liters of water?

  • To prevent the jug from overflowing when adding water to the pan.
  • To ensure the jug can hold enough water to refill the pan after heavy rain.
  • To make it easier to measure small amounts of evaporation.
  • To allow for the evaporation of water from the pan during the measurement process. (correct)
  • How is the measuring jug scaled to measure less than 2 mm of evaporation?

  • The jug is filled with a known amount of water and the volume is marked.
  • The jug is weighed and the weight of the water is used to determine the volume and corresponding evaporation.
  • The distance from the top marker to the bottom of the jug is divided by 20 and marked with increments of 0.1 mm. (correct)
  • The jug is filled to the top mark and the water level is observed after a specific time period.
  • What is the purpose of the PVC pipe supporting the pointer during evaporation measurement?

  • To help maintain a constant water level in the pan.
  • To ensure that the pointer is always submerged in the water.
  • To reduce wave motion in the pan, allowing for a more accurate measurement. (correct)
  • To prevent the pointer from being moved by wind.
  • When rainfall exceeds the pan's capacity, what should be done to ensure accurate evaporation measurement?

    <p>Empty the pan and refill it to the pointer level before adding water from the jug. (A)</p> Signup and view all the answers

    In the text, how is evaporation calculated when rainfall occurs before evaporation measurement?

    <p>The amount of rainfall is subtracted from the total water removed from the pan to determine evaporation. (B)</p> Signup and view all the answers

    If 5 mm of rainfall occurs and 2 mm of water are added to the pan with the measuring jug, what is the evaporation measurement?

    <p>7 mm (C)</p> Signup and view all the answers

    What is the primary purpose of measuring both rainfall and evaporation?

    <p>To assess the impact of weather conditions on water levels. (C)</p> Signup and view all the answers

    What is the recommended time for performing evaporation measurements?

    <p>9:00 am, when the day has just started. (B)</p> Signup and view all the answers

    Which condition is essential for the appearance of subsurface flows?

    <p>The hydraulic lateral conductivity is superior to the vertical conductivity. (C)</p> Signup and view all the answers

    How does the drainage capacity of subsurface flows compare to superficial and groundwater flows?

    <p>Faster than superficial flows but slower than groundwater flows. (C)</p> Signup and view all the answers

    What type of flow occurs when infiltrated effective rainfall circulates in the superior soil layer?

    <p>Subsurface flow (B)</p> Signup and view all the answers

    In which regions is subsurface flow dominant?

    <p>Humid regions with vegetal covering and well-drained soils (B)</p> Signup and view all the answers

    What historical term was used to refer to subsurface flow?

    <p>Hypodermic flow (D)</p> Signup and view all the answers

    What does the term $H_n$ represent in the energy balance equation?

    <p>Net heat energy received by the water surface (C)</p> Signup and view all the answers

    Which of the following terms can be neglected when time periods are short?

    <p>Net heat conducted out of the system by water flow (B), Heat stored in the water body (C)</p> Signup and view all the answers

    How is the sensible heat term $H_a$ estimated?

    <p>Through Bowen's ratio calculation (D)</p> Signup and view all the answers

    In the context of evaporation estimation, which factor contributes to the latent heat of evaporation?

    <p>Density of the water (B)</p> Signup and view all the answers

    What is the purpose of the Mass-Transfer Method?

    <p>To calculate mass water vapor transfer to the atmosphere (D)</p> Signup and view all the answers

    Which variable is NOT included in the Bowen's ratio equation?

    <p>Density of water (D)</p> Signup and view all the answers

    What is the significance of the errors being around 5% in evaporation estimation?

    <p>Reflects satisfactory results for short-term assessments (B)</p> Signup and view all the answers

    What does the latent heat of evaporation formula depend on?

    <p>Density of water times evaporation amount (A)</p> Signup and view all the answers

    What is the recommended percentage open area for a well screen to prevent incrustation and corrosion?

    <p>15 to 18% (D)</p> Signup and view all the answers

    Which of the following is NOT one of the assumptions of Dupuit's equations?

    <p>The aquifer has variable thickness. (D)</p> Signup and view all the answers

    Which condition can lead to unsteady flow in a well?

    <p>Prolonged pumping with no nearby recharge. (A)</p> Signup and view all the answers

    What does the Theis equation assume about the water being pumped from a well?

    <p>It is immediately released from the aquifer's storage. (D)</p> Signup and view all the answers

    What does Dupuit's equation assume about well efficiency?

    <p>It is assumed to be 100%. (A)</p> Signup and view all the answers

    Which of the following characteristics of flow around a well is assumed in Dupuit's derivation?

    <p>Laminar and radial flow. (D)</p> Signup and view all the answers

    Under what circumstance can drawdowns in a well increase with prolonged pumping?

    <p>When there is no natural recharge available. (A)</p> Signup and view all the answers

    Which investigators contributed to the study of hydraulics of wells in unsteady flow conditions?

    <p>Theis, Jacob, Chow, and others. (C)</p> Signup and view all the answers

    Which geological formations serve as effective aquifers?

    <p>Unconsolidated gravels and sandstones (A), Limestones with cavities and glacial deposits (C)</p> Signup and view all the answers

    What is an aquiclude?

    <p>A formation that cannot transmit significant amounts of water (A)</p> Signup and view all the answers

    What characterizes an aquifuge?

    <p>It can neither absorb nor transmit water. (C)</p> Signup and view all the answers

    How is specific yield defined?

    <p>The percentage of water that drains by gravity from a saturated aquifer. (D)</p> Signup and view all the answers

    Which of the following best describes a confined aquifer?

    <p>It is capped with an impermeable layer beneath a homogeneous porous layer. (A)</p> Signup and view all the answers

    What is the formula relating porosity, specific yield, and specific retention?

    <p>porosity = specific yield + specific retention (C)</p> Signup and view all the answers

    What does specific retention refer to?

    <p>Percentage volume of water that cannot drain by gravity. (B)</p> Signup and view all the answers

    What is a key factor influencing specific yield in aquifers?

    <p>Grain size, shape, and distribution of pores. (A)</p> Signup and view all the answers

    Which of the following is NOT a factor that affects pan evaporation?

    <p>Soil type (C)</p> Signup and view all the answers

    What is the main advantage of large weighable lysimeters over smaller ones?

    <p>They provide more precise measurements of evapotranspiration. (C)</p> Signup and view all the answers

    Why is it important to use the same type of pan in measuring evaporation?

    <p>Different pan types affect the evaporation rate differently. (B)</p> Signup and view all the answers

    Which of these is NOT a technique used in hydraulic weighing systems for lysimeters?

    <p>Magnetic resonance imaging (A)</p> Signup and view all the answers

    What is the primary use of micro lysimeters?

    <p>Measuring soil evaporation (C)</p> Signup and view all the answers

    According to the passage, which of the following techniques would be most appropriate for accurate measurement of evapotranspiration in a research center?

    <p>Large weighable lysimeters with load cells (A)</p> Signup and view all the answers

    How can pan evaporation measurements be used in agriculture?

    <p>Estimating the amount of water required for irrigation (A)</p> Signup and view all the answers

    What is the main difference between weighable lysimeters used for short-term and long-term measurements?

    <p>The size and design of the lysimeter (D)</p> Signup and view all the answers

    Study Notes

    Preface

    • This hydrology module aims to detail the theory and application of hydrology.
    • The course covers the hydrologic cycle and related processes such as precipitation, evaporation, infiltration, overland flow, groundwater flow, and surface runoff generation.
    • The module development was influenced by COVID-19 pandemic comments and peer reviewer feedback, alongside faculty input intended to ensure quality module distribution.

    Unit 5: Evaporation

    • Definitions: Evaporation is the process of a liquid changing to a gas below boiling point due to heat transfer.
    • Factors Affecting Evaporation:
      • Vapor Pressure: The rate is proportional to the difference between saturation vapor pressure (at the temperature) and actual vapor pressure in the air.
      • Temperature: A higher water temperature results in a faster evaporation rate.
      • Wind: Increased wind removes evaporated water vapor, increasing evaporation rate up to a critical wind speed.
      • Atmospheric Pressure: Lower pressure generally leads to faster evaporation.
      • Soluble Salts: The presence of salts in water lowers the evaporation rate.
      • Heat Storage: Deep water bodies store more heat, affecting seasonal evaporation patterns compared to shallow bodies.

    Unit 5: Evaporation (Continued)

    • Measurement:
      • Lysimeters: Measure evapotranspiration by recording precipitation and water loss in soil-filled containers, used for long-term measurements of plants, often crops or trees.
      • Evaporation Pans: Standardised pans such as the Class A pan used for measuring evaporation from free water surfaces.

    Unit 6: Basic Subsurface Flow

    • Introduction: Subsurface flow is the horizontal movement of infiltrated water. It's affected by the presence of an impermeable layer.
    • Darcy's Law: The velocity of groundwater flow is proportional to the hydraulic gradient. The equation is V = ki, where V is velocity, k is hydraulic conductivity and i is the hydraulic gradient.
    • Aquifers: Formations that transmit water efficiently.
      • Unconfined Aquifers: Water table aquifers, where the water level is at the top of the saturated zone.
      • Confined Aquifers: Artesian aquifers, where pressure forces water to rise above the water table.
    • Transmissibility: The flow capacity of an aquifer per unit width under a unit hydraulic gradient, and is equal to the product of permeability times the saturated thickness of the aquifer.
    • Water Conditions:
      • Steady radial flow into a well.
      • Steady state conditions; pumping has been continuous long enough to reach equilibrium.

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    Description

    This quiz focuses on Unit 5 of the Hydrology module, emphasizing the important processes and factors affecting evaporation. Explore key concepts such as vapor pressure, temperature effects, and the role of wind in evaporation rates. Perfect for students looking to deepen their understanding of hydrological processes.

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