9.2 - Uses
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Interactive Audio Lesson
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Understanding Runoff
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Today, we will learn about runoff. Runoff is essentially the portion of rainwater that flows into rivers and streams. Can anyone tell me the different types of runoff?
Isn't there surface runoff and subsurface runoff?
I think base flow is also a part of runoff.
That's correct! Surface runoff flows directly over land, subsurface runoff seeps in and then emerges, and base flow is the contribution from groundwater during dry periods. A great way to remember this is the acronym 'SSB' - Surface, Subsurface, and Base.
What impacts the amount of runoff?
Good question! The amount of rainfall, soil type, and vegetation all play critical roles. Higher intensity rainfall often leads to increase in surface runoff. Let's keep this in mind as we move forward.
Estimating Runoff Volume
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Next, let's discuss how we can estimate runoff volumes. One widely used method is the SCS Curve Number method. Can anyone explain what this involves?
Isn't it about using land type and moisture conditions to predict runoff?
Exactly! The SCS Curve Number assigns a number between 30 and 100 based on land use and soil types. A higher number indicates less infiltration. Why do you think this matters?
It's important for flood forecasting and resource management, right?
Yes! Remember: 'High Number, High Runoff, Low Infiltration!'
Understanding Hydrographs
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Now let's look at hydrographs, which plot streamflow over time. Who can tell me the main components of a hydrograph?
There's the rising limb, peak discharge, falling limb, and base flow!
Great job! The rising limb shows how the flow increases during a storm, while the falling limb indicates how it decreases afterwards. Can anyone guess how we can separate base flow from direct runoff?
Is there a method to graphically separate them?
Yes! Methods vary; some use straight-line methods while others might apply recession curves. Itβs essential to analyze these components for effective water management.
Flow-Duration and Flow-Mass Curves
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Letβs dive into the Flow-Duration Curve. It's important in predicting water availability. What do we observe on this curve?
It shows the percentage of time a certain flow is equaled or exceeded, right?
Exactly! A steeper curve indicates high variability, while a flatter curve suggests stability. In what situations do you think this information is crucial?
Itβs crucial for managing water supply and environmental flows!
Absolutely! And the Flow-Mass Curve helps in reservoir design by showing cumulative flow over time. Remember: Duration equals reliability!
Effective Rainfall and Environmental Flows
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Lastly, letβs talk about effective rainfall. What do we mean when we say 'effective rainfall'?
It's the part of rainfall that causes runoff after excluding initial losses!
Exactly! Itβs essential for creating unit hydrographs. Speaking of which, why are environmental flows important?
They maintain ecosystem health by providing necessary water flows for habitats!
Exactly right! Understanding and managing these flows is critical for both human and environmental sustainability.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
In this section, we explore runoff and its significance in hydrology, discussing the types of runoff, methods to estimate runoff volume, and key graphical representations like Hydrographs and Flow-Duration Curves. Understanding these concepts is essential for effective water resources management and ecological balance.
Detailed
Detailed Summary
Runoff is the water that flows over land into bodies of water after precipitation. It is categorized into surface runoff, subsurface runoff, and base flow. The volume of runoff is influenced by various factors, including the amount of precipitation and losses due to infiltration and evaporation. The SCS Curve Number method provides a way to estimate runoff by considering land use, soil type, and moisture conditions.
The Flow-Duration Curve (FDC) is instrumental in plotting flow rates to assess flow reliability across time, while Flow-Mass Curves offer cumulative data useful for understanding storage needs in reservoirs. Hydrographs provide a temporal view of streamflow, highlighting peak discharge and normal flow levels. Factors like rainfall intensity, soil type, and topography significantly affect runoff and hydrograph shapes. This knowledge is crucial for managing rivers, flood forecasting, and preserving environmental flows.
Key Concepts
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Runoff: The water that flows over land after precipitation.
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SCS Curve Number: A method for estimating runoff based on various factors like land use and soil type.
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Flow-Duration Curve: A plot that shows how often certain flow rates are equaled or exceeded.
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Hydrograph: A diagram representing streamflow over time.
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Effective Rainfall: The part of rainfall that contributes to runoff.
Examples & Applications
After a rainfall event, water that does not infiltrate the soil flows into nearby streams, constituting surface runoff.
In an urban area with impervious surfaces, runoff may increase significantly compared to a forested area.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
When rain falls down and flows away, Surface runoff is here to stay.
Stories
Imagine a forest after rain. Some water seeps into the ground, called subsurface runoff, while others rush down the slopes into a stream, creating surface runoff. The groundwater stays steady, contributing to base flow, forming a triangle of water!
Memory Tools
To remember the types of runoff, think 'Silly Students Become Friends' - Surface, Subsurface, Base.
Acronyms
Use 'F.E.A.R.' to remember factors affecting runoff
Frequency of rain
Evaporation rates
Area of watershed
and Rainfall intensity.
Flash Cards
Glossary
- Runoff
The part of precipitation that flows over the land surface into water bodies.
- Surface Runoff
Water that flows directly over land to streams.
- Subsurface Runoff
Water that infiltrates the ground and then emerges into streams.
- Base Flow
Groundwater contribution to streamflow during dry periods.
- SCS Curve Number
A method used to estimate direct runoff based on land use, soil type, and moisture conditions.
- FlowDuration Curve
A graphical representation showing the percentage of time a certain flow rate is equaled or exceeded.
- Hydrograph
A plot of streamflow versus time for a specific point in a river.
- Effective Rainfall
The portion of rainfall that generates direct runoff, excluding initial losses.
- Environmental Flows
The quantity, timing, and quality of water flows required to sustain freshwater and estuarine ecosystems.
Reference links
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