Since rock is shallow, it appears that Dcat's ideas will not be applied. That is good. I'm what they call a geotechnical engineer. My Master's Degree thesis project at Cornell U. was checking the efficiency of sub-drains under highways. I also checked out and verified the value of the recommendations of the US Army Corps of Engineers's determinations for filters (1938) in sub-drain installations.
Having spent the last 60 years preaching to architects and contractors that if you try to collect seepage or surface water with a so called "French Drain", you have to think about filtering the fines out of the water. If you use clear rock, or even pea gravel as the collecting medium you run the risk of it plugging up with mud. I've seen many a house perimeter footing drain clog up the first year, as well as French drains installed with rock backfill.
OK,, what is the best filter so you don't get plugging? It is the coarse concrete sand used for making concrete, sometimes called torpedo sand. If you are familiar with ASTM Specifications it is Fine Aggregate in standard C-33. Yes it is not as permeable as single size stones, but it usually is more porous than the soil from which the water seeps. How do you keep that sand out of the pipe? Use a pipe with 1/16" slots or very common plastic pipe used for footing drains, or have that pipe wrapped with a filter cloth. If you use solid pipe, drill a few rows of 3/16" diameter holes ON THE BOTTOM. Armco Steel used to sell corrugated steel pipe with those holes specifically for sub-drains under roadways. You might get a few sand grains in the pipe, but the coarser sands then bridge over the holes. Of the many jobs I have called for using this method, never has a single one failed. I still run into building inspectors that need education on this.
Sorry but while the rock idea sounds good, with a significant flow of water those French Drains usually fail in time.