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Questions and Answers
Which of the following best describes the interflow component of runoff formation?
Which of the following best describes the interflow component of runoff formation?
- Water that flows within the upper crusts of the soil, eventually returning to the surface. (correct)
- Water that flows deeply below the soil surface and contributes to stream flow.
- The direct precipitation that lands directly into the stream channel.
- Water that flows above the soil surface before entering a stream channel.
What distinguishes 'direct runoff' from 'base flow' in the classification of runoff categories?
What distinguishes 'direct runoff' from 'base flow' in the classification of runoff categories?
- Direct runoff contributes chemicals to the streams and rivers, while base flow dilutes the concentration of chemicals.
- Direct runoff occurs during dry periods, while base flow occurs after precipitation events.
- Direct runoff is the portion of runoff that enters the stream with a significant time delay, while base flow enters immediately.
- Direct runoff is the portion of runoff that enters the stream immediately after rainfall, while base flow is the delayed flow from groundwater. (correct)
If a catchment area's storage characteristics are altered by adding artificial storage, what is the likely effect on peak runoff?
If a catchment area's storage characteristics are altered by adding artificial storage, what is the likely effect on peak runoff?
- The peak runoff rate will remain the same as storage characteristics have no effect.
- The peak runoff rate will decrease due to increased storage capacity. (correct)
- The peak runoff rate will fluctuate unpredictably due to the complexity of storage dynamics.
- The peak runoff rate will increase due to reduced evaporation.
In the Rational Method formula, $q = \frac{CiA}{360}$, what does the variable 'i' represent?
In the Rational Method formula, $q = \frac{CiA}{360}$, what does the variable 'i' represent?
According to the Rational Method, how does land use affect the peak rate of runoff?
According to the Rational Method, how does land use affect the peak rate of runoff?
When applying the Rational Method to a watershed with multiple land uses, how is the composite runoff coefficient (C) determined?
When applying the Rational Method to a watershed with multiple land uses, how is the composite runoff coefficient (C) determined?
What does the 'time of concentration' represent in the context of storm runoff?
What does the 'time of concentration' represent in the context of storm runoff?
Consider two identical watersheds with the same rainfall event. Watershed A has a higher proportion of forest cover, while Watershed B has more urbanization. How will the peak runoff rates likely differ?
Consider two identical watersheds with the same rainfall event. Watershed A has a higher proportion of forest cover, while Watershed B has more urbanization. How will the peak runoff rates likely differ?
According to the table of conversion factors to convert runoff coefficient of soil group B to other soil groups, which land use has the LOWEST conversion factor for soil group A?
According to the table of conversion factors to convert runoff coefficient of soil group B to other soil groups, which land use has the LOWEST conversion factor for soil group A?
Using the formula $T_c = 0.0195 * L^{0.77} * H^{-0.385}$, if the length of the main channel (L) is doubled, and the elevation difference (H) remains constant, how will the time of concentration ($T_c$) change?
Using the formula $T_c = 0.0195 * L^{0.77} * H^{-0.385}$, if the length of the main channel (L) is doubled, and the elevation difference (H) remains constant, how will the time of concentration ($T_c$) change?
Flashcards
What is Runoff?
What is Runoff?
Water flowing off a catchment area through surface channels into a stream.
Overland Flow
Overland Flow
Flow above the soil surface.
Interflow
Interflow
Flow within the upper soil crust that returns to the surface.
Groundwater Flow
Groundwater Flow
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Direct Runoff
Direct Runoff
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Base Flow
Base Flow
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Rational Method
Rational Method
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Runoff Coefficient
Runoff Coefficient
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Time of Concentration
Time of Concentration
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Study Notes
- Runoff is a phenomenon where precipitation drains or flows from a catchment area through surface channels into a stream channel
- Runoff represents the output from a catchment in a specific unit of time
Runoff Formation
- Runoff consists of three components
- Overland flow that is above the soil
- Interflow beneath the upper soil crusts
- Groundwater flow is deep below the soil
Runoff Classification
- Runoff classifies into two categories based on the time delay between precipitation and runoff
- Direct runoff that enters the stream immediately after rainfall
- Base flow which is a delayed flow that reaches a stream as groundwater flow
Runoff Factors
- Precipitation characteristics like types, duration, and intensity affect runoff
- Land use and land coverage impacts runoff
- Topography influences surface condition, slope, and land features
- Geological characteristics include surface and sub-surface soil types, moisture, rock, and rock permeability
- Meteorological characteristics include temperature and humidity
- Catchment shape and size affect runoff
- Storage characteristics affect runoff because artificial and natural storage reduces peak flow due to the rising evaporation rate
- The Rational Method is used to calculate the peak storm water runoff rate from a drainage area
Rational Method
- A simple way to estimate peak flow of runoff and is used for flood estimation on small rural watersheds (≤5000 ha) and for urban drainage design
- The formula to calculate peak flow is: q = (CiA) / 360
- A is the watershed area in hectares
- i represents rainfall intensity in mm/hr for a duration equals the time concentration (Tc)
- q represents the peak flow rate in cubic meters per second
Runoff Coefficient
- Represents the combined effects of infiltration, evaporation, retention, flow routing, and interception, which impact the peak rate of runoff
- The coefficient (C) changes with rainfall rate, land use, cultivation practices, and hydrologic soil groups
Time of Concentration
- The Rational method uses rainfall intensity for a duration equals to the time of concentration
- The time lag to reach the generated runoff at the remotest point of the watershed to the outlet
- The equation to find the time of concentration is: T = 0.0195 * L^0.77 (L / H)^0.385
- Tc represents the time of concentration in minutes
- L represents the length of the main channel
- H represents the elevation difference between the outlet and the remotest point in the watershed
- Runoff coefficient for composite land use is the weighted average over the area
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