TUFLOW Forum

# Richard Hughes

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1. ## M channel matrix

I have an in channel structure that consists of two large gabion baskets which are designed to build head to spill over a side spill weir. There is no top to the baskets ie no soffit or deck and last year, flow did pass over the top of the gabions. We have tried to model this as an M channel using a flow matrix. The strucure has been modelled in HEC RAS to derive an upstream and downstream depth ( from which the head loss can be calculated). I have attached an attachment of this. I am confused how to input this data into the flow matrix as the manual states that the u/s and d/s depths must be the same - I am confused how the relationship derived from HEC RAS can be maintained if this is the case? I have also attached a photo of the structure if anyone has better ideas of how to model it ( flow direction is from the left to right) I hope this makes sense.
2. ## M channel matrix

I have an in channel structure that consists of two large gabion baskets which are designed to build head to spill over a side spill weir. There is no top to the baskets ie no soffit or deck and last year, flow did pass over the top of the gabions. We have tried to model this as an M channel using a flow matrix. The strucure has been modelled in HEC RAS to derive an upstream and downstream depth ( from which the head loss can be calculated). I have attached an attachment of this. I am confused how to input this data into the flow matrix as the manual states that the u/s and d/s depths must be the same - I am confused how the relationship derived from HEC RAS can be maintained if this is the case? I have also attached a photo of the structure if anyone has better ideas of how to model it ( flow direction is from the left to right) I hope this makes sense.
3. ## Modelling reservoir dam spillways in 2D

I am currently modelling a reservoir entirely within the 2D domain. However, once water spills over the reservoir dam crest, there is a vertical 25 metre drop. We have tried modelling it via an SX link across the dam wall, which is connected to a short 1D channel at the base of the dam, which in turn connects back into the 2D domain via another SX link. This has not worked, with instability as soon as the dam spills. The mechnanism with which the water spills over the dam is not important , as all we need is the correct spill volume continuing within the downstream channel. Is there a way of transferring a spill volume from the top of the dam to the bottom of the dam with a 25 metre drop in elevation? Regards Rich
4. ## Reservoir Operating Rules

I am currently building a purely 2D model for a reservoir, however, the reservoir releases are in response to an initial trigger level and stabilisation of the reservoir level. A release is started when the reservoir level reaches a certain level, which i can model using the trigger SA function. After the intial release, the release is increased every hour, until the reservoir level stabilises or reduces. At this point, the releases are reduced every hour. I can specify the releases and hourly increase through naming a hydrograph. Where i am struggling to find a solution is how to stop and reduce the releases based on the reservoir level, as the reduction in flow is based upon the reservoir level not increasing rather than a specific level. I'm guessing some form of logic would be required, but seing PHA's response in 2008 to a similar query, it didnt appear that a solution, in ESTRY TUFLOW, was possible. Is there a solution to specifying flow in response to levels, but also stopping or reducing flow based upon the level increase rate rather than a specific level? I hope this makes sense! Thanks Rich
5. ## z line elevation points

A quick question. I have a very detailed survey in which many survey points are very close together. In some instances, there are 6 survey points within a single grid cell. In this instance, if the data is read in as elevation points in a zln layer, how would TUFLOW interpret the data. I realise that manual filtering of the survey would need to occur to remove unesessary points, but if TUFLOW was run with mutliple elevation points within a single grid cell, what would happen? Would an avarage elevation be taken for the cell, or is there a default ie, take the highest/lowest elevation? Cheers Rich
6. ## Cross scetion representation

I am currently reviewing a TUFLOW model, however, the cross sections have been entered in a way that i am not familiar with. The surveyed cross sections have been entered as CS lines, type XZ. The CS lines (cross scetions) have been placed at the centre of 1d_nwk sections. Upstream and downstream inverts have been manually entered for each 1d_nwk section in the attributes table. Am i right in thinking that the channel 'shape' described by a CS line is applied to the whole 1d_nwk section ( albeit with elevation changes to meet the specified invert levels). If this is correct, how does ESTRY interpolate between channel shape, if a channel shape is applied to a whole 1d_nwk section. If consecutive cross sections vary greatly in shape, will there be a sudden channel shape change at the 1d_nwk section break? Regards Richard
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