Introduction to Physical Hydrology
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Questions and Answers

What is the primary purpose of defining a watershed?

  • To measure atmospheric pressure
  • To analyze the hydrological cycle (correct)
  • To classify vegetation types
  • To determine soil composition

How does the shape of a watershed influence hydrograph behavior?

  • Round shapes have no impact on flow
  • Long shapes result in slower flows (correct)
  • Long shapes lead to faster flows
  • Shape does not affect hydrograph behavior

Which factor does NOT affect snowmelt rates in watersheds?

  • Proximity to the equator
  • Average slope (correct)
  • Watershed orientation
  • Watershed shape

What does Gravelius's index (KG) measure?

<p>Watershed shape (A)</p> Signup and view all the answers

In hydrography, Strahler's classification categorizes which aspect?

<p>Stream orders (C)</p> Signup and view all the answers

Which of the following factors does NOT contribute to water infiltration in a watershed?

<p>Average temperature (C)</p> Signup and view all the answers

What does the hypsographical curve illustrate in a watershed?

<p>Elevation distribution (B)</p> Signup and view all the answers

Which characteristic is used to indicate a watershed's reaction to rainfall?

<p>Average slope (D)</p> Signup and view all the answers

What does the Form Factor measure in hydrology?

<p>Basin area to the square of axial length (C)</p> Signup and view all the answers

Which mechanism of precipitation involves warm air rising over cold fronts?

<p>Frontal lifting (A)</p> Signup and view all the answers

What is the primary process that drives the hydrologic cycle?

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

Which of the following affects flow velocity in rivers?

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

What type of instrument is used to measure precipitation continuously over time?

<p>Tipping bucket rain gauge (A)</p> Signup and view all the answers

What key variable describes the decrease in infiltration capacity over time?

<p>Soil saturation (A)</p> Signup and view all the answers

Which equation describes infiltration capacity over time?

<p>Horton Equation (D)</p> Signup and view all the answers

What does drainage density indicate about a watershed?

<p>Closeness of streams within the basin (B)</p> Signup and view all the answers

What causes surface runoff?

<p>Precipitation exceeding soil infiltration (C)</p> Signup and view all the answers

Which method utilizes current meters for measuring stream velocity?

<p>Direct Methods (A)</p> Signup and view all the answers

What do hydrographs primarily display?

<p>Variations in water flow over time (A)</p> Signup and view all the answers

Which factor is NOT commonly associated with watershed characteristics affecting hydrographs?

<p>Altitude of surrounding mountains (B)</p> Signup and view all the answers

Which method is suitable for measuring discharge at bridge sites?

<p>Contracted-Opening Method (A)</p> Signup and view all the answers

What type of hydrologic measurement is useful for predicting flood frequencies?

<p>Statistical analysis (C)</p> Signup and view all the answers

Which of the following is a component of a hydrograph?

<p>Rising limb (D)</p> Signup and view all the answers

What technique involves using sound signals to measure stream velocity?

<p>Ultrasonic Meters (C)</p> Signup and view all the answers

What is the main function of the Penman Equation in hydrology?

<p>To calculate potential evapotranspiration using climate data (A)</p> Signup and view all the answers

What type of runoff is primarily generated from rainfall events?

<p>Surface runoff (A)</p> Signup and view all the answers

Which factor is NOT considered when estimating runoff using runoff coefficients?

<p>Wind speed (C)</p> Signup and view all the answers

How does urban runoff typically differ from natural runoff?

<p>Urban runoff results in quicker flow and higher peaks (A)</p> Signup and view all the answers

What is the primary purpose of Intensity-Duration-Frequency (IDF) curves in hydrology?

<p>To aid in predicting extreme precipitation events (B)</p> Signup and view all the answers

Which of the following types of precipitation has droplets greater than 0.5 mm in diameter?

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

Which of the following statements about the challenges in hydrological measurements is accurate?

<p>Both precipitation and discharge data can have errors of 1-20% (B)</p> Signup and view all the answers

What role does moist air supply play in the formation of precipitation?

<p>It maintains the intensity of precipitation events (A)</p> Signup and view all the answers

What does a T-year event signify in hydrology?

<p>It is an event with a return period of T years. (D)</p> Signup and view all the answers

How is the annual probability of a T-year event calculated?

<p>PT = 1/T (D)</p> Signup and view all the answers

Which probability distribution is generally considered unsuitable for flood data?

<p>Normal Distribution (D)</p> Signup and view all the answers

What aspect of data does skewness indicate?

<p>The symmetry or asymmetry in data distribution. (B)</p> Signup and view all the answers

Which statistical parameter is NOT used to describe data distributions?

<p>Coefficient of correlation (B)</p> Signup and view all the answers

What is the primary role of vegetation in relation to runoff?

<p>It reduces extreme runoff but has limited drought/flood resilience. (C)</p> Signup and view all the answers

What does the term 'concentration time' refer to in hydrology?

<p>The time for water to reach the watershed outlet after rainfall. (A)</p> Signup and view all the answers

In risk analysis, what happens to risk if the return periods are shorter?

<p>Risk increases. (A)</p> Signup and view all the answers

Which data analysis approach utilizes only peak flow data for each year?

<p>Annual Series (A)</p> Signup and view all the answers

Which watershed type is characterized by high infiltration and erosion due to cultivation?

<p>Agricultural watershed. (D)</p> Signup and view all the answers

What do isochrones represent in hydrological analysis?

<p>Contour lines joining points of equal concentration time. (C)</p> Signup and view all the answers

What is the purpose of frequency factors (K) in hydrology?

<p>To estimate event magnitudes for various return periods. (D)</p> Signup and view all the answers

Which type of watershed is most likely to have increased runoff and reduced infiltration?

<p>Urban watershed. (C)</p> Signup and view all the answers

How does the slope of a basin influence hydrological characteristics?

<p>It reflects runoff velocity and erosion potential. (D)</p> Signup and view all the answers

Which characteristic is not mentioned as affecting hydrological analysis of a watershed?

<p>Temperature. (C)</p> Signup and view all the answers

What feature characterizes a coastal watershed?

<p>Influence by tidal actions and flood susceptibility. (C)</p> Signup and view all the answers

Flashcards

Hydrograph

A graph showing the discharge (amount of water flowing) of a river over time, especially after a rainfall event.

Concentration Time

The time it takes for water from the furthest point in a watershed to reach the outlet (like a river's mouth).

Isochrones

Lines on a map that connect points with the same concentration time. They show how fast water flows in different parts of a watershed.

Watershed

A geographical area where all the water that falls on it drains to a common point.

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Small Watershed

A watershed with an area less than 2500 sq. km, where the storage of water within the channels dominates.

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Urban Watershed

A watershed dominated by urban land use, leading to increased runoff and flooding.

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Basin Area

The total surface area of a watershed.

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Basin Shape

The shape of a watershed, influencing how fast water flows and concentrates.

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Pan Evaporimeter

A device used to measure evaporation rates. It is a simple, but often overestimates actual evaporation.

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Penman Equation

A mathematical formula that calculates potential evapotranspiration based on climate data like temperature, humidity, wind speed, and solar radiation.

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Direct Runoff

Water that flows directly into streams, lakes, or oceans from rainfall events.

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Baseflow

The sustained flow of water in a stream or river that comes from groundwater sources.

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Intensity-Duration-Frequency (IDF) Curve

A graphical representation of the relationship between rainfall intensity, duration, and frequency. Used to predict extreme precipitation events.

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Runoff Coefficient

A factor that helps determine the amount of runoff from precipitation. It's typically calculated for a specific area and considers factors like soil type and impervious surfaces.

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Thiessen Polygon

A method for weighting rainfall measurements across an area based on the proximity of rain gauges to a point of interest.

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Hydrograph Analysis

The study of flow variations in a river or stream over time. It helps to understand the water balance and identify contributing factors.

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What is a watershed?

A watershed is an area where all water drains to a common point, like a river or lake. It's like a giant bowl that collects rainwater and directs it to a single outlet.

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How do we define a watershed?

Watersheds are typically defined by the area that contributes water to a specific stream or river at a certain cross-section.

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Geomorphology and watershed shape

The shape of a watershed influences how water flows through it. Long and narrow watersheds tend to have slower drainage compared to round ones.

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Gravelius's Index (KG)

A measure of watershed shape that relates its perimeter to its equivalent circular area. It helps us understand how elongated or compact a watershed is.

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Watershed orientation and snowmelt

The direction a watershed faces can affect how quickly snow melts. North-facing slopes tend to melt slower than south-facing ones.

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Hypsographical Curve

A graph that shows the distribution of elevations within a watershed. It helps us understand the overall terrain.

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Strahler's Classification

A system for organizing streams within a watershed based on their order. Higher order streams are formed by the joining of lower order ones.

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Agro-Pedo-Geological Factors

The type of soil, vegetation, and underlying geology significantly influence how water infiltrates, is retained, and flows off the land.

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Horton-Strahler System

A method for classifying streams into different orders based on their branching hierarchy. Higher order streams represent larger, more complex systems.

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Horton's Law of Lengths

States that the average length of streams in a river network increases geometrically with increasing order.

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Form Factor

A measure of a basin's shape, calculated as the ratio of its area to the square of its axial length. A high form factor indicates a rounder basin.

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Circularity Ratio

Compares the area of a basin to the area of a circle with the same perimeter. A higher ratio implies a more circular basin.

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Elongation Ratio

Represents the ratio of the diameter of a circle with the same area as the basin to the basin's length. A lower ratio indicates a more elongated basin.

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Evapotranspiration

The combined loss of water from a surface through evaporation and transpiration by plants.

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Infiltration Capacity

The maximum rate at which water can infiltrate into the soil. It decreases over time as the soil becomes saturated.

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Ring Infiltrometer

A device used to measure infiltration rate by creating a flooded area and observing the rate of water level decline.

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Surface Runoff

Water flowing over the land surface, occurring when precipitation exceeds soil infiltration or saturation.

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Stream Flow

The total volume of water flowing through a stream, comprising surface runoff, interflow, and groundwater flow.

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Current Meter

A device used to measure water velocity at specific points in a stream, commonly used with direct methods for discharge measurement.

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Moving-Boat Method

A method for measuring stream discharge in large streams by combining stream velocity with the boat's velocity while traversing a cross-section.

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Rising Limb

The upward portion of a hydrograph, indicating increasing water flow, often due to rainfall or snowmelt.

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Recession Limb

The downward portion of a hydrograph, indicating decreasing water flow, as runoff recedes.

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T-year Event

An event with a return period of 'T' years, meaning it's expected to occur once every 'T' years on average. For example, a 100-year flood has a 1% chance of happening in any given year.

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Return Period

The average time interval between occurrences of events of similar magnitude. For example, a 100-year flood has a return period of 100 years.

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Probability of T-year Event

The chance of a T-year event happening in a given year. Calculated as 1/T. For example, the probability of a 100-year flood in any given year is 1/100 or 1%.

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Risk of Exceedance

The likelihood of a flood event exceeding a certain design capacity. For example, a levee designed for a 100-year flood has a 1% risk of being exceeded in any given year.

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Annual Series

Uses the highest recorded flow for each year to analyze flood frequency. Useful for getting a general idea of the flood risk.

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Partial Duration Series

Uses all peak flows exceeding a specified threshold (minimum flow), providing more detailed information about frequency of smaller floods.

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Lognormal Distribution

A statistical distribution often used for flood frequency analysis, as it can handle skewed data (where the data is not symmetrically distributed).

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Extreme Value Type I (EVI)

A statistical distribution commonly used in hydrology for analyzing the maximum values of data, like flood peaks.

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Study Notes

Introduction to Physical Hydrology

  • Focuses on the occurrence, movement, and physical properties of water on and below the Earth's surface, excluding oceanic water
  • Major water types include atmospheric water (vapor, liquid, solid), surface water (rivers, lakes, ponds), soil water (above the water table), and groundwater (below the water table)
  • Freshwater makes up only 2.5% of Earth's water, with 69% in polar ice, 30% in groundwater, and 1% in surface water, soil water, and atmospheric water; a significant portion of groundwater is brackish or saline.

The Hydrological Cycle

  • Describes the continuous movement of water through evaporation, condensation, precipitation, and flow
  • Key processes include evaporation (purifying water and leaving salts in oceans), condensation (forming water droplets in clouds), precipitation (rain, snow, hail falling to Earth), and runoff and flow (water moving overland, through soil, and to groundwater flows to surface water bodies)
  • Residence times for different water sources vary, with oceans having thousands of years, the atmosphere ~10 days, and groundwater ~20,000 years.

Drainage Basins

  • Geographical areas draining into a river or reservoir, often delineated by the highest landscape points for surface water
  • Groundwater boundaries may differ due to variations in permeability
  • Key processes within a drainage basin include precipitation (gross and net), interception, infiltration, percolation, and overland flow

Water Balance Equation

  • Represents the balance of water inputs (e.g., precipitation) and outputs (e.g., evaporation, runoff) within an area.
  • Crucial for understanding the effects of land-use and climate changes, where long-term average values for storage can be set to zero
  • Applications include understanding effects of land-use and climate changes.

Watershed Characteristics

  • A geographical unit for analyzing the hydrological cycle.
  • Delineation (defining the boundaries) may differ for different types of watersheds (e.g., karst areas)
  • Physical characteristics including surface shape, influencing hydrograph behaviour, orientation affecting snowmelt rates, and topography are crucial
  • Importance of geomorphology and hypsographical curves are stressed
  • Altitudes, slope, and hydrography characteristics are key
  • Agro-Pedo-Geological factors impacting runoff are significant (including soil, vegetation, and geological substrate).

Watershed Planning and Management

  • A geographical unit that includes surface and subsurface features, climate, soils, vegetation, and land use for hydrological analysis
  • Water flows from precipitation through soil, groundwater, and streams to larger water bodies
  • Watersheds are classified by size, with implications for management practices and specific characteristics impacting runoff behaviour (e.g, sensitivity to high-intensity short-duration rainfalls, ease of management, and the relative importance of channel vs. overland flow).

Elements of the Hydrologic Cycle

  • Components include precipitation, interception, infiltration, percolation, evaporation, transpiration, and runoff
  • Key points are that water undergoes crucial processes like infiltration and evaporation before contributing to runoff or discharge.

Precipitation Mechanisms

  • Condensation forms water droplets on condensation nuclei.
  • Convection, frontal, and orographic lifting influence precipitation
  • Measurement involves standard precipitation gauges and tipping bucket rain gauges
  • Error analysis accounts for gauge type, wind, location, and systematic errors

Infiltration

  • Water infiltrates the soil and percolates into groundwater or evaporates.
  • Measurement using ring infiltrometers (measures infiltration under ponded conditions) and the Horton equation ( describes infiltration capacity over time).
  • Initial infiltration is high, but it decreases over time as soil saturates.

Evaporation and Evaporation

  • Combination of evaporation and transpiration
  • Affected by factors like energy availability, soil type, temperature, wind and water availability
  • Measured using pan evaporimeters and Penman equation

Runoff

  • Surface runoff, direct runoff, baseflow
  • Runoff processes and techniques are described
  • Methods include using current meters, float method, dilution method, indirect methods such as slope-area and contracted-opening method

Hydrological Measurements

  • Measuring water levels, discharge rates and other hydrological processes such as soil moisture and subsurface water
  • Continuous measurements are key, via conventional gaging stations and advanced techniques
  • Methods include ultrasonic meters, electromagnetic meters.
  • Challenges include wind-induced errors that affect accuracy, systematic errors in historical data, and the need for caution in interpreting measurements.

Hydrologic Measurement systems

  • Includes rain gauges, flow sensors, and microprocessor-based data logging
  • Real-time systems for monitoring rainfall, runoff, water quality
  • Flood early warning systems (using remote sensors, pressure transducers, and radio communications )
  • For larger river systems, real-time data acquisition networks provide flood forecasts

Hydrologic Frequency Analysis

  • Used to predict hydrologic events (e.g., floods)
  • Includes concepts of return periods, probability of occurrence, risk analysis, and different data analysis approaches (e.g. employing long flow records, short records, records from analogous catchments)
  • Probability distributions can be used (e.g., normal distribution, lognormal distribution, extreme value type 1, log pearson type 3)

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