I'll take your word for that...
I am not aware of any such dedicated drainage system, but old hwy 80 is elevated relative to swampy low ground on either side of the roadway.https://proaudiodesignforum.com/images/ ... 00_geo.pdf (Due to the size of the pdf it takes awhile to render at any zoom level.)
Your water goes out onto the Hwy 80 drainage system?
There is a huge culvert going under old hwy 80 a few hundred yards west of me that handles the flow from my "good" draining front ditch system. There are smaller culverts east of me under old hwy 80 and less effective rain ditch systems south of old 80.
Driving several miles east or west on old hwy 80 from hwy 503 intersection ( road I live on), after large rain events reveals massive bodies of standing flood water often on both sides of the roadway.
My perspective from decades driving on old hwy 80, It appears more like a dam separating two swamps. The natural water runoff appears north to south, the road runs east/west.It looks like if it weren't for Hwy 80 your water would have no place to go.
Your topo shows meandering creeks south of me moving east/west sort of, but my sense is that water escapes South, especially from my immediate yard.
A topo showing several miles east or west of me should reveal a lot of low ground on either side of old 80. My speculation is that these swampy low ground areas serve as reservoirs to prevent more severe flooding downstream after major rain events.
[update... there are serious flood warning for a few counties south of me, and 50-60 miles west of me Jackson/Pearl river. I'm OK /update]