modeling uneven sediment buildup in culvert

[Anonymous]

I am using RAS to model a tidal situation through a culvert.

The downstream end of the culvert is blocked with sediment to a depth of one-foot. But given the culvert slope, the upstream end of the culvert isn’t really blocked at all (the sediment elevation doesn’t change form the bottom elevation).

If I use a one-foot depth of blockage, it applies that uniformly to the entire culvert length which would over mute the tides on the upstream end. Is there a way to more correctly model this situation but having a one-foot blockage on the DS end and really no blockage on the upstream end?

I would figure this is a common situation so has anyone developed a work around. In this case, getting the tides thought the culvert is critical since I am trying to assess the feasibility of the upstream site for tidal marsh restoration and need to know the tidal signal into the site proposed for restoration to tides.

Thanks for any thoughts, Roger

[Anonymous]

You could do a series of culverts that are connected end-to-end and that had different depths of sediment.

However, the easiest thing to do would probably be to model the culvert as a series of cross sections with lids. Where the shape of the cross section with the lid matches the shape of the culvert (where the station/elevation of the cross section has been adjusted for the amount of sediment at that location). Cross sections with lids will give simimlar results as culverts operating under outlet/energy control. It does not give the same results for culverts operating under inlet control, but inlet control is not that common.

If any part of the cross section with lid flows full, you will want to use the Priessmann’s slot option.

[Author]

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