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?

Saturated soil conditions prevail from sufficient rainfall. Signup and view all the answers

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

0.2 Signup and view all the answers

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

To obtain the surface flow hydrograph Signup and view all the answers

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

Method III Signup and view all the answers

What is the hydrograph obtained after base flow separation called?

Direct runoff hydrograph Signup and view all the answers

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

Local practice Signup and view all the answers

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

Interflow Signup and view all the answers

What does the rising limb of a hydrograph represent?

The accumulation of storage causing an increase in discharge Signup and view all the answers

Which segment of a hydrograph contains the peak flow?

Crest segment Signup and view all the answers

What is indicated by point A on a hydrograph?

Start of surface runoff Signup and view all the answers

How is base flow separation achieved using Method I?

By connecting the start of surface runoff to point B with a straight line Signup and view all the answers

What is the infiltration capacity?

The maximum rate at which the ground can absorb water. Signup and view all the answers

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

The end of direct runoff Signup and view all the answers

Which element is NOT significantly influenced by infiltration?

Air temperature Signup and view all the answers

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

Method II Signup and view all the answers

What characterizes Zone 3 in the soil structure?

Moisture content is higher than field capacity but unsaturated. Signup and view all the answers

What is generally challenging to pinpoint in a hydrograph analysis?

Point B Signup and view all the answers

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

Zone 4 Signup and view all the answers

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

The withdrawal of stored water from the basin Signup and view all the answers

What happens after an infiltration event regarding the infiltrated water?

It is redistributed within the soil layers. Signup and view all the answers

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

Zone 2 Signup and view all the answers

What classifies a stream as a perennial stream?

It flows continuously all year round. Signup and view all the answers

What is the function of the wetting front?

It separates saturated and unsaturated soil layers. Signup and view all the answers

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

Wind speed Signup and view all the answers

What is a common way to estimate runoff accurately?

Correlating seasonal or annual runoff with rainfall values. Signup and view all the answers

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

Continuous low intensity rainfall Signup and view all the answers

What defines an intermittent stream?

It has baseflow on average once a year or more. Signup and view all the answers

Why are perennial streams important to ecosystems?

They support a variety of plants and animals. Signup and view all the answers

Which of the following statements about annual hydrographs is true?

They enable the classification of streams like perennial, intermittent, and ephemeral. Signup and view all the answers

What is the typical source of water for perennial streams?

Springs and groundwater. Signup and view all the answers

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

A statistical method involving paired data. Signup and view all the answers

What is the primary purpose of the double ring infiltrometer?

To overcome the limitations of tube infiltrometers Signup and view all the answers

What factors must be considered before runoff begins?

Evapotranspiration, initial loss, infiltration, and detention storage Signup and view all the answers

How does overland flow relate to runoff in watershed management?

It entails the accumulation of water above the surface before draining Signup and view all the answers

What is the typical regime of overland flow?

Laminar with modest lengths and depths Signup and view all the answers

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

2 meters Signup and view all the answers

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

To prevent the spreading of water from the inner ring Signup and view all the answers

What type of flow does surface runoff create?

Overland flow moving through small channels Signup and view all the answers

Which characteristic is NOT associated with the double ring infiltrometer?

Measurement of evaporation rates Signup and view all the answers

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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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.