Ineffective flow area

[neighbor_ttl]

Aloha to all

I am trying to determine the capacity of the bridge or channel of a small stream.
The modeled upstream boundary situation is like
this:


Left Bank Right Bank
-------- -------
\ WS / \ WS
\========/ \=========
\ / \---------------
\ /
\ /
\ /
--------

Even the water surface inside the channel is lower than the right
bank, there is some water overflow to right. The right water surface is equal to the water surface inside the channel.

so I set up the area beyond left and right bank as normal ineffective flow area. The profile showed that the water was still overbank but marked as ineffective flow. Now the problem is with the flow distribution in Standard Table 2.
QLeft QChannel QRight

200.00
400.00
800.00
1000.00
1200.00
1400.00
1600.00
1800.00
2000.00
2200.00
1.71 2398.29
4.13 344.54 2251.33
5.56 463.81 3030.63
8.73 728.84 4762.42

How can the Q Channel is as little as 344.54 when the total runoff is 2600?
Did I do something wrong when modeling?

Thanks and Regards,
Hong