“Blocking Water"

Topic Sentence:

  • an optional sentence created by the writer to tell the reader what the paragraph will be about
  • it may be the first sentence, the second sentence, a sentence in the middle, the last sentence or the writer may have chosen not to write a topic sentence

Main Idea sentence:

  • a sentence created by the reader when reading the paragraph
  • it is “perfect” topic sentence (topic + controlling idea [umbrella idea])
  • when readers create their own main idea sentence for a paragraph, it helps them better understand the paragraph, especially when the writer’s actual topic sentence may not be very clear

To write a main idea sentences for a paragraph:

1. Think of the most general topic (one word) of the paragraph.

2. Then, think of the more specific ideas that express the controlling idea (umbrella word) of the supporting ideas.

4. Do NOT include details that are not common for all the supporting ideas.

5. Make sure that your main idea does not copy more than 3 words in a row from the paragraph; use synonyms and different word order to avoid plagiarism.

Summary Sentencefor a paragraph or section = topic + main supporting ideas

Paragraph 1:

General topic / Supporting ideas / Umbrella word for supporting ideas
dams /
  • home, protection, food
/ good things, benefits, help

Words/ideas for the main idea sentence:

dambeaversbuild/helpbenefits/reasons

Main idea sentences:

  • Beavers build dams for several reasons.
  • Dams give beavers some benefits.
  • Dams help beavers in a couple of ways.
  • Building dams can provide several benefits to beavers.
  • There are several reasons why beavers build dams.

Summary sentence = main idea + support

  • [how beavers use dams]
  • Beavers build dams to make a home, provide protection and supply food.
  • Building dams gives beavers a home, protection and food.
  • Dams can protect beavers, give them a home, and help them with food.

Paragraph 2:

General topic / Supporting ideas / Umbrella word for supporting ideas
dams / sequence (history), so one of the perfect tenses would be good / farming/food

Words/ideas for the main idea sentence:

humans/people dambuild(present perfect progressive) long time/1000s of years

irrigate/grow food

Main idea sentences:

  • Humans have been building dams for a long time for growing food.
  • Dams have been built for a long time by humans to irrigate crops.
  • People have built/have been building dams for a long time for farming/food.
  • Dams have been built for a long time by people to help them farm.
  • Humans have been constructing dams since ancient times for farming.
  • People have built dams for over 5000 years for farming.

Summary sentence = main idea + support

  • Humans have been building dams for 1000s of years beginning in the Middle East to give them water to help them grow crops.

Paragraph 3:

General topic / Supporting ideas / Umbrella word for supporting ideas
dams /
  • drinking water
  • live where there is little water
  • Lake Mead gives water to millions of people
/ places lacking water

Words/ideas for the main idea sentence:

dampeoplewaterplaces lacking provide/live

Main idea sentences:

  • Dams provide water for people in places that lack water.
  • Dams allow people to live in very dry places.
  • Because of dams, people can live in places that don’t have enough water

Summary sentence = main idea + support

  • Dams provide drinking water for cities and town that lack water. An example of this is Lake Mead, which is a large lake created by a dam in a dry area of the US.

Summary sentencefor paragraphs 2 and 3= main idea + support

  • [How people use dams in dry places]
  • People have been building dams for 1000s of years in dry areas of the world in order to provide water for growing food and also water for drinking. A modern example of a large lake made by a dam for these reasons is Lake Mead in a dry area of the US.
  • People have been building dams for 1000s of years in dry areas of the world. The dams provide water for growing food and also water for drinking. A modern example of a large lake made by a dam for these reasons is Lake Mead in a dry area of the US.

Paragraph 4:

General topic / Supporting ideas / Umbrella word for supporting ideas
dams /
  • navigate shallow rivers
  • canals
  • locks because of high ground

Words/ideas for the main idea sentence:

damsshipsnavigate/travelriversshallow/not deep enough

Main idea sentences:

  • Dams help ships travel on difficult rivers.

Summary sentence = main idea + support

Paragraph 5:

General topic / Supporting ideas / Umbrella word for supporting ideas
lock /
  • filled with water to raise boat
  • drained to lower boat
  • series of locks
Pattern: sequence / level of boat

Words/ideas for the main idea sentence:

locklevel of boatcontrols process

Main idea sentences:

  • Locks of dams control the process of changing the level of boats in water.

Summary sentencefor paragraphs 4 and 5 = main idea + support

  • [how dams help ships]
  • Dams help ships travel on difficult rivers. To go around the dams, they use canals and a series of locks, which raise the level of the boats by filling with water and lower the levels by draining the water.

Paragraph 6:

General topic / Supporting ideas / Umbrella word for supporting ideas
dams /
  • make electricity
  • Three Gorges Dam (largest)-ex
  • control flooding
Pattern: listing / manage, control, harness

Words/ideas for the main idea sentence:

damscontrol/managewater

Main idea sentences:

  • Dams can be used to control flooding and make electricity. [summary sentence]
  • Some dams are used to control the flow of water.
  • The movement of the water can be managed by dams.

Summary sentence = main idea + support

Paragraph 7:

General topic / Supporting ideas / Umbrella word for supporting ideas
dams /
  • change environment
  • negatively affect fish
  • make people move
Pattern: listing / negative (adj), hurt (v), impact (v,n), issues (n)

Words/ideas for the main idea sentence:

dams[some negative word: negative/bad/problems/impact/issues]cause/create/make

Main idea sentences:

  • Dams create some negative aspects.
  • Dams have some serious impacts.
  • Dams create some issues.

Summary sentencefor paragraphs 6 and 7 [compare/contrast] = main idea + support

  • [the benefits and problems of big dams]
  • Very large dams, like the Three Gorges Dam in China, have both good and bad points. They are good because they can create electricity and control flooding, but they can also be bad because they impact the environment, cause problems for fish, and make people move from their homes.

Summary:

In the article “Blocking Water”, the author describes (1) how beavers use dams, (2) how people have used dams in dry areas, (3) how dams help ships, and (4) the good and bad points of very big dams.

[how beavers use dams] Beavers build dams to make a home, provide protection and supply food.

[How people use dams in dry places] People have been building dams for 1000s of years in dry areas of the world in order to provide water for growing food and also water for drinking. A modern example of a large lake made by a dam for these reasons is Lake Mead in a dry area of the US.

[how dams help ships] Dams help ships travel on difficult rivers. To go around the dams, they use canals and a series of locks, which raise the level of the boats by filling with water and lower the levels by draining the water.

[the benefits and problems of big dams] Very large dams, like the Three Gorges Dam in China, have both good and bad points. They are good because they can create electricity and control flooding, but they can also be bad because they impact the environment, cause problems for fish, and make people move from their homes.