Infiltration and Surface Runoff Quiz
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Questions and Answers

What is the primary factor influenced by the antecedent moisture condition (AMC) during a rainfall-runoff event?

  • Initial abstraction and infiltration (correct)
  • Plant growth rates
  • Soil compaction
  • Evapotranspiration rates

Which statement accurately describes AMC-I?

  • Soils have received significant rainfall.
  • No cultivation has taken place.
  • Soils are wet and saturated.
  • Soils are dry but not to wilting point. (correct)

During the growing season, what amount of rainfall characterizes an AMC-II condition?

  • 36 to 53 mm (correct)
  • More than 53 mm
  • 13 to 28 mm
  • Less than 20 mm

What condition is represented by AMC-III?

<p>Saturated soil conditions prevail from sufficient rainfall. (B)</p> Signup and view all the answers

What standard value for lambda (𝜆) has been adopted by SCS based on measurements from small size catchments?

<p>0.2 (C)</p> Signup and view all the answers

What is the purpose of separating base flow from a storm hydrograph?

<p>To obtain the surface flow hydrograph (D)</p> Signup and view all the answers

Which method of base flow separation involves extending the recession curve backwards?

<p>Method III (A)</p> Signup and view all the answers

What is the hydrograph obtained after base flow separation called?

<p>Direct runoff hydrograph (C)</p> Signup and view all the answers

What factor influences the choice of method for base flow separation?

<p>Local practice (A)</p> Signup and view all the answers

Which component is typically considered as part of the surface flow?

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

What does the rising limb of a hydrograph represent?

<p>The accumulation of storage causing an increase in discharge (D)</p> Signup and view all the answers

Which segment of a hydrograph contains the peak flow?

<p>Crest segment (B)</p> Signup and view all the answers

What is indicated by point A on a hydrograph?

<p>Start of surface runoff (B)</p> Signup and view all the answers

How is base flow separation achieved using Method I?

<p>By connecting the start of surface runoff to point B with a straight line (C)</p> Signup and view all the answers

What is the infiltration capacity?

<p>The maximum rate at which the ground can absorb water. (C)</p> Signup and view all the answers

What does point B represent in the context of a hydrograph?

<p>The end of direct runoff (A)</p> Signup and view all the answers

Which element is NOT significantly influenced by infiltration?

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

Which method involves extending the base flow curve until it intersects the ordinate at the peak?

<p>Method II (A)</p> Signup and view all the answers

What characterizes Zone 3 in the soil structure?

<p>Moisture content is higher than field capacity but unsaturated. (C)</p> Signup and view all the answers

What is generally challenging to pinpoint in a hydrograph analysis?

<p>Point B (A)</p> Signup and view all the answers

Which zone's moisture content is at or close to field capacity?

<p>Zone 4 (B)</p> Signup and view all the answers

In the context of hydrographs, what does the recession limb represent?

<p>The withdrawal of stored water from the basin (A)</p> Signup and view all the answers

What happens after an infiltration event regarding the infiltrated water?

<p>It is redistributed within the soil layers. (D)</p> Signup and view all the answers

Which zone acts as the transition between the saturated top layer and lower zones?

<p>Zone 2 (C)</p> Signup and view all the answers

What classifies a stream as a perennial stream?

<p>It flows continuously all year round. (A)</p> Signup and view all the answers

What is the function of the wetting front?

<p>It separates saturated and unsaturated soil layers. (C)</p> Signup and view all the answers

Which of the following is NOT a factor that affects the relationship between rainfall and runoff?

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

What is a common way to estimate runoff accurately?

<p>Correlating seasonal or annual runoff with rainfall values. (D)</p> Signup and view all the answers

Which type of rainfall leads to an increase in soil moisture and potential groundwater contribution?

<p>Continuous low intensity rainfall (D)</p> Signup and view all the answers

What defines an intermittent stream?

<p>It has baseflow on average once a year or more. (C)</p> Signup and view all the answers

Why are perennial streams important to ecosystems?

<p>They support a variety of plants and animals. (D)</p> Signup and view all the answers

Which of the following statements about annual hydrographs is true?

<p>They enable the classification of streams like perennial, intermittent, and ephemeral. (A)</p> Signup and view all the answers

What is the typical source of water for perennial streams?

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

Which method is used to compute the coefficient of correlation in hydrology?

<p>A statistical method involving paired data. (D)</p> Signup and view all the answers

What is the primary purpose of the double ring infiltrometer?

<p>To overcome the limitations of tube infiltrometers (B)</p> Signup and view all the answers

What factors must be considered before runoff begins?

<p>Evapotranspiration, initial loss, infiltration, and detention storage (C)</p> Signup and view all the answers

How does overland flow relate to runoff in watershed management?

<p>It entails the accumulation of water above the surface before draining (A)</p> Signup and view all the answers

What is the typical regime of overland flow?

<p>Laminar with modest lengths and depths (C)</p> Signup and view all the answers

In a rainfall simulator, what is the height from which raindrops fall?

<p>2 meters (C)</p> Signup and view all the answers

What is the primary function of the outer rings in the double ring infiltrometer?

<p>To prevent the spreading of water from the inner ring (C)</p> Signup and view all the answers

What type of flow does surface runoff create?

<p>Overland flow moving through small channels (C)</p> Signup and view all the answers

Which characteristic is NOT associated with the double ring infiltrometer?

<p>Measurement of evaporation rates (C)</p> Signup and view all the answers

Flashcards

Infiltration Capacity

The maximum rate at which the ground can absorb water.

Field Capacity

The maximum volume of water that the ground can hold.

Zone 1 (Saturated Zone)

A thin layer of saturated soil forms at the top during infiltration.

Zone 2 (Transition Zone)

Beneath Zone 1, a zone where soil moisture is increasing as infiltrated water moves downward.

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Zone 3 (Transmission Zone)

This zone has higher moisture content than field capacity, but isn't fully saturated. Water moves downward.

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Zone 4 (Wetting Zone)

The bottom zone where soil moisture is close to field capacity, becoming less saturated as you go deeper.

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Infiltration Event

An occurrence where water is absorbed into the ground, like during rainfall.

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Percolation

The downward movement of infiltrated water through the soil.

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Double Ring Infiltrometer

A device used to measure infiltration rate by creating a controlled area of water infiltration. It uses two concentric rings to prevent lateral water movement and maintain a constant depth.

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Infiltration

The process by which water enters the soil from the surface.

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Overland Flow

Water flowing across the land surface before entering a channel.

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Channel Flow

Water flowing within a defined channel, like a stream or river.

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Surface Runoff

The total water flow across the land surface, including both overland flow and channel flow.

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Rainfall Simulator

A device designed to mimic rainfall conditions in a controlled experiment. It uses nozzles to produce artificial raindrops of various intensities.

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Rainfall Intensity

The rate at which rainfall occurs, measured as millimeters per hour (mm/hr) or inches per hour (in/hr).

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Runoff

The water flow that occurs when precipitation exceeds infiltration and storage capacity.

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Antecedent Moisture Condition (AMC)

The amount of moisture present in the soil before a rainfall event. It significantly affects how much water infiltrates the ground and how much runs off.

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AMC Types

There are three AMC types: I, II, and III. They describe how dry or wet the soil is at the start of a rainfall event. AMC-I is the driest, AMC-III is the wettest.

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AMC-I

The soil is relatively dry, but not completely wilted. It has been cultivated, meaning it's loose and can absorb more water.

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AMC-III

The soil is saturated, meaning it's very wet and has absorbed as much water as it can. This occurs after a period of heavy rainfall.

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CNII Value

The Curve Number (CN) is a measure of the soil runoff potential depending on the Antecedent Moisture Condition (AMC). CNII is specifically used when the AMC is II (average).

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Runoff Correlation

The relationship between rainfall and the amount of water flowing in a river or stream.

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Perennial Stream

A stream that flows continuously throughout the year, even during dry seasons.

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Intermittent Stream

A stream that flows only during certain times of the year, usually during periods of rainfall.

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Ephemeral Stream

A stream that flows only for a short period after rainfall, often only during the rainy season.

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Hydrograph

A graph that shows the flow rate of a river or stream over time.

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Baseflow

The sustained flow of water in a stream that is not directly from rainfall, typically from groundwater.

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Coefficient of Correlation

A statistical measure that indicates the strength and direction of the relationship between two variables, like rainfall and runoff.

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Annual Hydrographs

Graphs showing the flow rate of a river or stream over an entire year.

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What is base flow?

Base flow is the portion of a stream's flow that comes from groundwater seepage. It's the sustained, slow flow that doesn't depend on recent rainfall. It's like a constant drip, replenished by underground sources.

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What is surface runoff?

Surface runoff is the water that flows over the land, not through the ground, after rainfall. It's the initial surge you see during a storm, flowing quickly over the surface.

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What is direct runoff hydrograph (DRH)?

The DRH is a graph showing the volume of water flowing in a stream after the base flow has been removed. It represents the direct effect of rainfall on the stream's flow.

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How is base flow separated?

Base flow is separated from the total storm hydrograph to isolate the surface runoff. It's done using different methods, like extending the recession curve of the base flow until it intersects the ordinate at the point of inflection.

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Interflow vs. surface flow

Interflow is a type of subsurface flow that moves through the upper soil layers and reaches the stream quickly, making it considered part of the surface flow. It's essentially a faster groundwater flow.

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Hydrograph's Rising Limb

The initial part of a hydrograph which shows how the discharge rises due to water accumulating in channels and across a catchment area.

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Hydrograph's Crest Segment

The part of the hydrograph containing the peak flow, where all the runoff reaches the basin outlet simultaneously.

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Hydrograph's Recession Limb

This represents the decrease in flow as the water stored during the event drains out.

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Base Flow Separation (Method I)

A method of separating the surface runoff from the base flow on a hydrograph by drawing a straight line from the start of direct runoff to a point on the recession limb.

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Point A (Hydrograph)

The point on a hydrograph that marks the start of surface runoff, recognizable by an abrupt change in flow rate.

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Point B (Hydrograph)

The point on a hydrograph where the direct runoff ends and the recession limb begins.

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Base Flow Separation (Method II)

This method separates base flow by extending the pre-runoff base flow line until it intersects with a vertical line through the peak flow.

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Study Notes

Infiltration, Surface Runoff

  • Infiltration is the process of water entering the soil, due to irrigation or rainfall. It involves water moving through the soil by percolation.
  • Infiltration rate is the actual rate at which water moves through soil during a storm. It either matches the rainfall rate or the infiltration capacity, whichever is lower.
  • Infiltration capacity is the maximum rate at which a soil can absorb water.
  • Surface runoff, evapotranspiration, soil erosion, groundwater recharge, and chemical transport in surface and subsurface waters are all greatly affected by infiltration and percolation.
  • A wetting zone forms at the top of the soil, which marks a boundary and can range from centimeters to meters in length.
  • Soil changes from its initial state, to newly wetted soil, to show the wetting zone's boundary. The change depends on infiltration rate and soil properties.
  • The procedure for representing infiltration can be shown in a figure comparing low intensity and high intensity rainfall. This is because infiltrated water can affect soil moisture and contribute to groundwater, if water flows through.
  • Zone 1: A thin layer of saturated soil, at the top.
  • Zone 2: A transition zone below Zone 1.
  • Zone 3: A transmission zone, where moisture moves down. The moisture content is higher than field capacity but not saturated.
  • Zone 4: The wetting zone, where soil moisture is at or close to field capacity. Moisture content gradually decreases with depth.

Measurement of Infiltration

  • Flooding type infiltrometers: Experimental devices to determine how infiltration capacity changes over time. Two types are tube and double ring.
  • Simple (Tube Type) Infiltrometer: A metal cylinder, driven into the ground. Water is added and infiltration rate is calculated by timing and measuring added water volume.
  • Double Ring Infiltrometer: Two rings of different sizes, to overcome the limitations of the tube type. Water is applied to both and infiltration of inner ring is monitored.
  • Rainfall Simulator: A plot of land with nozzles that produce various rainfall intensities. Surface runoff rate and volume are measured for analysis.

Hydrograph Analysis

  • Runoff is precipitation that leaves a catchment area and enters a surface channel. It represents the catchment's output for a specific time period.
  • Before runoff can occur, certain conditions must be met: evapotranspiration, initial loss, infiltration, and detention storage.
  • Initial abstraction (Ia) is a fraction of maximum retention (S), where Q = Ia/S.
  • Curve Number (CN): Soil, vegetation, land use, and antecedent soil moisture define potential maximum retention (S) in a watershed. CN ranges from 0 to 100.
  • CN = 100 means zero potential retention and CN = 0 represents an infinitely abstracting catchment.
  • Hydrological Soil Classification: Helps determine CN values based on soil characteristics. This includes soil depth, effective clay content, and permeability.

Runoff

  • Runoff is the term used to describe how precipitation moves and leaves a catchment area.

Runoff-Classification

  • Direct Runoff: Precipitation that enters streams immediately after rainfall. Includes surface runoff, immediate interflow, and direct rainfall on stream surface.
  • Base Flow: Delayed flow, acting like groundwater flow and reaching a stream. Also includes time-delayed interflow.

Estimation of Runoff Volume

  • Soil Conservation Service (SCS)-CN Method: Conceptual method to estimate direct runoff depth.
  • Based on storm rainfall depth and antecedent soil moisture condition. Simple, predictable and useful.

Runoff Characteristics of Stream

  • Perennial Streams: Flow throughout the year (due to springs, groundwater, and steady rainfall).
  • Intermittent Streams: Have a flow for part of the year, usually driven by high water table during winter or spring.
  • Ephemeral Streams: Only flow during or immediately after rainfall events.

Elements of Hydrographs

  • Rising Limb: Shows how the accumulated storage increases the discharge.
  • Crest Segment: Contains peak flow.
  • Recession/Falling Limb: Describes water from storage, being withdrawn in earlier phases of the hydrograph.
  • Base Flow Separation: Identifying base flow from surface runoff on a hydrograph. Three methods are commonly used.

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Infiltration, Surface Runoff PDF

Description

Test your understanding of the processes of infiltration and surface runoff as they relate to soil and water movement. This quiz covers key concepts such as infiltration rate, capacity, and the formation of wetting zones. Enhance your knowledge of water's behavior in soil and its environmental impacts.

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