Answer:
The concept of Flood was used as a symbol for signifying the sad overtone of the novel, for representing migration of people and a reference to the Flood of Noah.
Explanation:
In the first part of the Novel the Joad Family was suffering from a drought which caused many families to search for employment elsewhere, leaving their current land (such as the Joads)
. California, at that time, was the place said to have an ample amount of opportunities. Therefore, the Joads, like many others, moved to California to survive. However, in the end of the Novel, severe rain began and caused a Flood.
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<em>"The rain began with gusty showers, pauses and downpours; and then gradually it settled to a single tempo, small drops and a steady beat, rain that was gray to see through, rain that cut midday light to evening. And at first the dry earth sucked the moisture down and blackened. For two days the earth drank the rain, until the earth was full." </em>(Chapter 29)
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The earth consumed the rain, until it could no more. Once it was full, the flooding began
. This is a symbol for workers moving to California to find jobs
. However, this migration ended up causing California to become full of people. Consequently, there were more people than jobs available and issues started to rise again.
Furthermore, Steinbeck's use of Flood also shades light over the tragic theme of the Novel and as the apocalyptic nature of the flood was used as a reference to the Noah's Ark.