Here's a sentence: "The volume of resources invested is clearly evident."
Is this redundant?
Yes, it is redundant.
The volume of resources invested is clear.
means the same thing basically as:
The volume of resources invested is evident.
However, redundancies can be (and are) used for strengthening an expression.
According to Wikipedia:
the term "redundancy" tends to have a negative connotation and may be perceived as improper because of its use of duplicative or unnecessary wording... however, it remains a linguistically valid way of placing emphasis on some expressed idea. Through the use of repetition of certain concepts, redundancy increases the odds of predictability of a message's meaning and understanding to others.
It goes on to give commonly used examples: a variety of different items, an added bonus, to over-exaggerate, end result, free gift", future plans, unconfirmed rumor, past history (one memorialized in medicine as "Past Medical History"), safe haven, potential hazard, completely surrounded, false pretense, and so on.
So though it's redundant, it does not mean it's not a useful and acceptable way to express an idea more clearly.
The Latin roots suggest that something which is evident should always be able to be seen clearly ("obvious to the eye or mind"). In the example sentence given, the word "clearly" is redundant, but in a comparison one conclusion could be more clearly evident than another.
That being said, the phrase "clearly evident" does have some usage.
That specific word choice does appear redundant, however, people who use that phrase don't intend to say the same thing twice, but rather put a qualifier on the word evident.
People who use this phrase likely mean something more like "abundantly evident" or "abundantly clear".
Wanting to be literal about the phrase "clearly evident," perhaps someone actually means to say that not only is the item evident, but the fact that it is evident is clear. It would be like saying "It was made obvious on purpose and that can be easily seen."
Either way, the message is the same: "There can be no mistake except by negligence."
Answering OP's question:
In linguistics, redundancy refers to information that is expressed more than once.
The majority of dictionary definitions stress that 'evident' primarily means 'that is plain / clear to see'
So it is unarguable that this is an example of redundancy.
However, people are rushing to the defence of the expression. With no need:
Often, redundancies occur in speech unintentionally, but redundant phrases can also be deliberately constructed for emphasis, to reduce the chance that a phrase will be misinterpreted. In rhetoric, the term "redundancy" tends to have a negative connotation and may be perceived as improper because of its use of duplicative or unnecessary wording (and some people expand the definition to include self-contradictory wording, similar to double negation); however, it remains a linguistically valid way of placing emphasis on some expressed idea.
[Wikipedia; op cit]
Summing up what I have seen here and what I have personally observed:
By most dictionary definitions, "clearly evident" is literally redundant. A number of writers believe this to be true.
Even given most dictionary definitions, there are some that feel "clearly" can be used to add emphasis, to mean "particularly evident" or "more evident than is typically the case".
And for some of us, "evident" does not simply mean plain or obvious. It means "something that can be derived, learned, or understood; based on evidence." While none of the definitions cited so far are so worded, definitions like "that can be seen" and "clear to the mind" do not imply trivially so.
As an example, if at the end of a long mathematical proof I say "Therefore it is evident that the hypothesis is correct" -- I believe this is an appropriate use of the word evident, but illustrates something that is not "clearly evident", because it required rigor to demonstrate. In fact I have often heard 'evident' used this way.
From the example, and the definitions that do not preclude it, I claim that "clearly evident" is arguably correct and meaningful usage.