downstream ID

[nmizukami]

Current assumption on outlet of basin: if downstream ID is less than zero, it is outlet of the basin. kwt_routine use this assumption. This might not be good assumption based on downIndex routine in network_topo.f90. However, downstreamID can be any number and if the routine does not find segment ID matching with downstream ID, downstream index get missing. Also reach with downstreamID <=0 also get missing downstream Index. missing downIndex indicate outlet of the basin.

For MPI version, tributary basin (which connected to mainstem) preserve downstream ID from the entire network data and downstream index get missingVal during augmentation process. For this reason, kwt_routine cannot use downIndex <0 (or =missingVal) for outlet reach identification because outlet of tributary basin routine in task is not really outlet for the entire network. The KWT routine can use downstream ID (<=0 condition) to identify outlet within the tributary basin in task and outlet of the entire networks, but this relies on current downstream ID assumption.

To alleviate potential error in identifying outlet (tributary basin in task and entire network), downstream ID for entire network need to be set to missing. This way, tributary basin outlet in task still holds downstream ID.