HEC-6 questions

Fellow modellers,

we are currently trying to model the sediment transport in a large river and have to overcome some strange behaviour in HEC-6, v4.1

The instabilities at the beginning and at the end of a reach can be adjusted with the input volume and, if necessary an extension of the reach a couple of X-sections downstream (fictional if necessary), I presume ?

Varying most of the available parameters yields the expected effects, besides ...

when the actual grain size distribution (PF cards) comes into play, we discovered that this does NOT affect the total sediment transport.

e.g.: Test actual grain sizes:
100 % between 16 and 32 mm yields the SAME sediment transport as
100 % between 30 and 32 mm.

This is obviously not what all the textbooks say.

Thus HEC-6 seems to take into account only the mean grain size(s) calculated from the fraction boundaries, not from the actual grain sizes.

And: Did anybody check the effect of the way HEC-6 calculates the total sediment transport in all grain size classes, in the way that at first the transport volume is calculated as if one class would cover 100 % of the movable bed, and THEN multiply this fictional value by the fraction the class actually consists of, summing up the fraction volumes afterwards?

we would appreciate any input to resolve this questions. Maybe we are stuck in a kind of deadlock misinterpreting some of the input values?

Thanks in advance for your help,
Peter Hanisch
ph@donauconsult.co.at

PS.: Besides: hows about the trick with the expansion and contraction factors: the output says different values than we used in the input (same in the sample files!!). But this is only hydraulics ...

PPS: Any idea of a textbook or practical guide through the pitfalls of HEC-6 ?

PPPS: is there a similar piece of software floating around, which might be a bit more up to date concerning the (G)UI and which can deal with METRIC values, please?