I thought users might be interested in how to represent islands in Raven. It requires a little trickiness with the :FlowDiversion command.
Here, we have a simple 4 subbasin system with a main branch (subbasin 1-3) and a secondary branch (the flow around the island should be routed through basin 4. We initially set up the :SubBasins-:EndSubbasin block as if 4 is a headwater basin that drains into 3, i.e., the network order is 1->2, 2->3, 4->3, and 3->out of the system (-1).
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:SubBasins
:Attributes, NAME, DOWNSTREAM_ID, PROFILE, REACH_LENGTH, GAUGED
:Units , none, none, none, km, none
1, B1, 2, PROF_1, 3.0, 1
2, B2, 3, PROF_1, 4.0, 1
3, B3, -1, PROF_1, 3.0, 1
4, Div, 3, PROF_2, 4.0, 1
:EndSubBasins
We then (in the .rvt file) add a NULL Basin Inflow Hydrograph to subbasin 4 so that Raven no longer treats subbasin 4 as a headwater basin and the channel routing is explicitly simulated (NOTE: this step will not be required in Raven versions after v3.0.1):
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:BasinInflowHydrograph 4
:AnnualCycle 0 0 0 0 0 0 0 0 0 0 0 0
:EndBasinInflowHydrograph
Note the use of the :AnnualCycle command to keep this short and sweet. The last step is to add a flow diversion (also in the .rvt file):
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:FlowDiversion 1 4 0.30 0.0
This indicates that we will route 30% (0.30) of the outflow from basin 1 to basin 4, and that there is no minimum flow criterion (i.e., we always divert 30% of flow regardless of the outflow from 1). If you wanted to get more rigorous about this, you can implement the :FlowDiversionLookupTable command instead, such that the diverted flow is dependent upon the magnitude of flow from basin 1.
This approach can be used in much more complicated flow networks. For instance, you could easily split basins 2 and 4 into multiple basins. You could have multiple islands. This is supported even if there is a lake/reservoir in basin 1 where the splitting of flow occurs.