I am trying to map hydrologic capture zones (HCZ). HCZ's are contributing areas upslope of any potential capture feature (i.e. road, pipeline path, railroad line), that would alter/impact the natural drainage pattern in a watershed. A simplified example is show here (yellow area is HCZ, which lies partially in basin- the pink area):
I am having a lot of trouble coming up with a good method to map areas upslope and downslope of roads. My current methodology is based on @nagib's post:
This method may have promise, but details in those steps are sparse, especially for the all important and complex second step- path distance allocation. When I tried to mimic nagib's method, I didn't get a very intuitive result. Not surprising, because I am not very familiar with calculating upslope/downslope using path distance allocation. The result looked like:
In mapping HCZs it seems to me that accurately defining upslope and downslope areas of roads is a critical first step. Any resources or thoughts on a very accurate methodology for getting these areas right? Using ArcMap 10.4 primarily, but have access to QGIS and Whitebox GAT.
Per @nagib's request here is a third pic showing second pic with contours (white lines):
Also, here is a pic combining upslope/downslope areas, contours, pour point(orange point) at intersection of road(black line) and river(blue line), and the resulting subshed (white area) from that pour point: