I'm wanting to lay concrete pavers on a walkway sloped towards a timber retaining wall. The question I have is how close to the timber retaining wall should I lay the pavers. Laid immediately up to the timber wall wont allow any water flow through the drainflow coil situated inside the retaining wall, and will likely allow any water to run over the retaining wall which may result in erosion of the wall's piles. I'm thinking a gap between where the pavers end and where the retaining wall timber starts will require a mortar haunching to bind the sand and base course under the pavers, preventing those layers from washing away. Then by filling the gap between the mortar haunching and the retaining wall timber with gravel/pebbles should allow for any water runoff to access the drainflow coil. Any thoughts on this process? Heading in the right direction? I've been looking online for a video of a similar paving/retaining example but not found one yet.
Insert a drain channel.
Go to store in the gutter or roofing department. Find a 1 inch or larger U shape. (probably galvanized or aluminum)
Set it between pawers and retainer wall. Try to install it slightly sloped so the water runs off.
As added on bonus:
Wrap mosquito net (the aluminum type) around it before installing it, to stop rocks and sand falling in it.
The primary purpose of a retaining wall, whether stone or timber, is to provide a path for water to pour over the wall, not to be be absorbed behind the wall. That will rot the timbers faster than pouring over them.
Runoff is the #1 defense... find ways to aid that. Take your pavers right up to the timbers, and if possible tuck them beneath.
What you're describing as a haunch sounds like more of a water trap, which will quicken the rot. Same as any water trapped behind the timbers in your fill (there's an obsession with water drainage behind retaining walls... it's a last resort... way, way, way less effective than surface drainage). Get your pavers and substrate under the timbers if you can.
A backdrain system is part of the system, but it's not the key part. You chose timbers, and can sustain them with various chemicals, but should enjoy their 30-year decay as part of your choice... there's no way to keep them structurally pristine. Aging and decaying timber is awesome.
In the meantime, get water pouring over them and not behind them.