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Q: In ESTRY is it possible to apply a QH rating in the channel. Not as a downstream boundary, but in the middle of a reach to act as a control representing a structure in the channel? A: In regards to QH ratings in channels, there are two different methods: • M Channel (section 5.8.1 of the 2016 Manual) The M channel uses a matrix of QH relationships to define the mechanics. You can also read the description in the manual but I’ve coloured up my example csv for easy reading below. There are a few rules with the flow values: the matrix must be square, it must have the centre line of diagonals and it must be negative (or zero) below the diagonal and positive (or zero) above. • Q Channel (Section 5.8.2 of the 2016 Manual) This uses a Depth Discharge curve, like you would for a pit inlet. The H values in this case are for the upstream end of the culvert. In deciding between the two of them, I’d have a look at the culvert and the flow regimes you expect. If you think that the culvert will have significant downstream control, then an M channel is the better option. If it’s pretty much always upstream controlled, then you may be able to get away with just a Q channel.