Sediment Transportation (Flow Series Boundary Information)

[Anonymous]

I am working with the sediment transportation function for the first time. I am trying to determine the maximum “scour” within a dry mountain channel adjacent to our project as we are installing rip-rap revetment along the channel’s side and will be required to take the revetment to the maximum scour depth. I started to have trouble entering the “Boundary Conditions-Flow Series” as I am not confident what information needs to be input in this area (i.e. flow duration, computation increment, flow). In looking at several examples it appears that the data entered in this field constituted multiple events over a large course of time. For my project I do not have this data, however I can generate a synthetic unit hydrograph for the tributary area to the channel. Can sediment transport analysis be conducted with just one event (i.e. unit hydrograph)? In my mind the answer would be yes and no (i.e the program will calculate scour for that event, but the results will not determine a “maximum” scour depth, which happens over many events). Sorry if my question seem trivial. Thank you.

[Anonymous]

Hi,

You can use a synthetic hydrograph to model one event but your result will obvisouly be limited. I did a similar project but I had a full years worth of hourly flow data so I could look at max scour depth. You would really need this

However, you might be able to find a similar donor catchment that has a long ger record as per FEH methodology that you could substitute into your model instead although that is a lot of work, especially if you don’t know the Flood Estimation Handbook methodology.

Do you have a flow duration curve for the site? If so you might be able to create a years worth of data from that, ie Q1% for 1% of the time, Q2% for 1% of time ……….Q99% for 1% of the time.
It may not be totally accurate as some extreme events will be truncated but given the lack of any other data, it may be the best that can be achieved.

Anyway the flow file requires:
FLOW SERIES for upstream boundary condition
– Period durations, typically I use 8760 rows of data for one year of hourly data.
– Comp. increment, I use a global CI of 0.5 and then do sensitivity analysis by changing it to 0.1 and if results are same, 0.5 figure is good enough. Smaller CI more accurate but takes a long time to run. You can use automatic but that takes some time to set up, it is more time efficient and I don’t use it as my models run quick enough.
– Tempt data: just specify the average annual temp for the region for duration of 8760 hours unless you have any other data.

NORMAL DEPTH for downstream boundary.
-enter a friction slope. This will be the average slope between the first three or four cross sections. enter it as a decimal, ie 4% slope is 0.04

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