How can the NHD be used to support modeling?
We say that NHD is a ‘framework’ for modeling. This framework consists of two basic components. First, there are permanent features (reaches) with permanent, public identifiers (reach code) that support the linear referencing (reach route system) of attributes to the stream network. Second, the reaches have flow relationships (RFlow table) that enable you to programmatically walk up and down the network encountering the information that you have linked to the network through linear referencing. To perform meaningful modeling, you’ll have to link additional information on the NHD network. For example, if you wanted to perform impact analysis, you might link pollution events to the network (through linear referencing) and then navigate downstream (with the flow table) to see what streams would be affected by the events. If you want to do dilution modeling, you’ll need lots of additional information such as flow volume, velocity, travel time, etc. for NHD reaches. So the NHD provides the
