small island in the stream-split flow?

[Uzy]

Hi,

I need to model brook that has couple split low-flows around small islands. typical example attached. Since this is just small island (100ft) during low flow, do I need to model split flow junction and creating two river centerline around island? Or, what I think will do, just pick one centerline (probably the side of the island that carries the most flow) and do XS to cover second flow line around island, something as shown in attached photo.

I believe this is too small split to model two river centerline and split-flow optimization. Please advise if this is appropriate method based on your experience.

Thank you for you help,
Uzy

[Lonnie A]

In the picture below I would model as one reach. The island is small enough that the WSE left and right of it isn’t going to vary enough to worry about. Depending on the WSE upstream of the island can you see that flow has the ability to enter the area to the right of the island? If it doesn’t put ineffective flow in that area. You can also look at what the flow is computed to be in the right overbank of the XS just before the island and then look at what the flow is computed in the two section that cover the island to see if there is a relative continuity of flow and then play with ineffective station to get a relative agreement. For example if the U/S XS shows 2000 cfs in right overbank and the 2 next DS show 3000 cfs add ineffective in the right overbank to have a closer agreement on those 2 XS. You might need to adjust your bank station to be on the island and inline with it to figure out this continuity and then after a few iterations move the bank stations back to where they belong.

[Anonymous]

Thank you Lonnie! I had the same approach except didn’t think about moving the bank stations to island and back to figure out the split flow. Thanks again.

Uzy

[Author]

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