retaining wall/irrigation question

Due to the fact my GC was an idiot, I have a drainage isseue on one side of my house. The slope is excessive, and when it rains the water just sits.
The easy answer is to change the elevation using dirt, but that would result in piling 2' of dirt up against a wood fence, which would lead to premature rotting. Other issue is that irrigation lines are trenched parallel to the fence. So, need to raise elevation without impacting fence or irrigation lines.
Only answer I can think of is to build retaining wall length of lot line, and backfill with dirt to change elevation. Then drive 1/2' rebar down 24' or so into the ground on each end of the base line of timbers (4x8 pt posts). To avoid hitting irrigation lines, I would not be able to trench the first course of timbers more than 3' or so under grade.
Questions: Do i need to put any kind of footing under the first level of timbers, like sand? It will probably take 3-4 courses of timbers to get the elevation up high enough to channel the water correctly. I know a base will make it more level but is it necessary for stability?
I am afraid the rebar will puncture the irrigation lines. Except for exposing the lines, is there a way to determine exactly where the lines are? Forget calling the people that installed them - we had to go to court to get them to back up their other work...grrrrrrrr..
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