biology

Return flow

Return flow is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Return flow rather than just read about it. In short: Return flow is surface water and groundwater that leaves the field following application of irrigation water. While irrigation return flows are point sources, in the United States they are expressly exempted from discharge permit requirements under the Clean Water Act.

Key takeaways

Return flow belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Return flow to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Return flow from memory before moving on to harder problems.

Reference excerpt

Return flow is surface water and groundwater that leaves the field following application of irrigation water. While irrigation return flows are point sources, in the United States they are expressly exempted from discharge permit requirements under the Clean Water Act. Return flows generally return to the irrigation centre after a period of about three to four weeks; due to this, the farmers usually need to pour bleach into the water to kill off any organisms that have entered the stream. If this is not taken care of, diseases such as typhoid fever or cholera could enter the irrigation and pose a risk of epidemic disease to surrounding towns and cities. The return flows in irrigation is nearly 50% of the water supplied in silty clay soil type in tropical countries. The salinity of the return flow water increases with the decrease in percentage of return flow quantity. The rest of the water supplied to irrigation evaporates into atmosphere due to evapotranspiration. When ground water is extracted for irrigation and other uses, most of the return flows seep back into the ground instead of joining the nearby surface stream. When ground water is used in excess of recharge from rainfall or precipitation, the quality of groundwater deteriorates over a period of time and becomes unfit for irrigation use.

References

This article incorporates public domain material from Jasper Womach. Report for Congress: Agriculture: A Glossary of Terms, Programs, and Laws, 2005 Edition (PDF). Congressional Research Service.

Worked examples

Example 1 — a first encounter with Return flow

Start with the simplest possible case. Write down what Return flow claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Return flow before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Return flow ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Return flow

In research: Return flow appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Return flow in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Return flow is common in secondary-school and first-year university syllabi. It links to neighbouring topics Agriculture stubs, Ecology stubs, United States Department of Agriculture, so understanding it makes those chapters shorter.
In everyday life: Look for Return flow outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Return flow in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Return flow means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Return flow out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Return flow in simple terms?

Why does Return flow matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Return flow?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Return flow.