Designing pipes for no flood criteria

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for drainage designs to be valid. They first have to meet the no surcharge criteria

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and then they must meet the no flood criteria.

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In this example, the no surcharge criteria have already been designed

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and the pipes have been sized adequately for no surcharge.

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First

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edit the rainfall data so that you are using a longer period storm

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on the ribbon rainfall slash pollutants tab rainfall panel,

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click rainfall manager to open the rainfall manager.

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The design dot rainfall dot I D R X file is already active

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in the tree view,

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expand the design storms node and expand the F S R node and select rain one to edit it

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The Rain one Parameters appear,

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click the return periods tab.

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Currently

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there is a two year period set up,

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click add to add another return period

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Under return period years,

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enter 30,

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Then

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enable the use option for the new 30-year storm and

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then disable the two year storm to deactivate it.

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Click the storm durations tab

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here, leave all nine of these storms active,

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return to the return periods tab to ensure the 30 year storm is active.

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And then click the parameters tab here, leave both summer and winter active,

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which multiplied by the nine active storms gives you an

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click save and then exit the rainfall manager.

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Keep in mind that the no flood criteria

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are quite different from the no surcharge criteria.

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The no flood considers a much longer period of time

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as well as the extreme changes to the rainfall amounts,

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whereas the no surcharge criteria took into account

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a steady state or steady flow of runoff.

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Now that the rainfall criteria have been set,

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you can configure the analysis criteria

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on the ribbon,

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click the analysis tab and then in the criteria panel click analysis criteria.

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The analysis criteria, dialog opens

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here, you stipulate which storms you will run the analysis with.

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In this case there is only one storm,

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so click the checkbox next to rain one to select it

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As soon as you do,

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you can see the method number of storms and the maximum runtime values

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appear as FS are the 18 storms 2880 minutes of runtime respectively.

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Notice the output interval value set to one minute.

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This indicates that the program is reporting a calculated result every minute.

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It is actually performing the calculations every few seconds.

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But for the purposes of the graphing and table tools, it is reported once per minute,

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expand the time step drop down.

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This affects how often the program performs the calculations,

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you can set it to default

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reduced or shortest.

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Essentially this option helps you set the

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balance for creating a stable hydrology model

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in which you can trust the calculations are correct

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info drainage uses S W M M

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a very well understood

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stable calculation model.

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If you were to set this to shortest,

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it would take longer for the calculations to complete.

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In addition,

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it is best to use when you have a more complicated system

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that has storage areas or any constrictions to the flow.

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But since this model is just one line of pipes running downhill,

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you can keep the time step set to default.

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The next parameter urban creep is used to take into

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account that over time the pimp value will increase.

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Property owners may install additional structures or

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they may add a paved parking area,

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all of which would increase the percentage impervious value.

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This can be set to use a global value or

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it can be added to each subcategory within the model

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For this exercise.

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Leave it set to apply global value and leave the percentage set to zero

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the junction flood risk margin is whether the water has come within a certain

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distance of the cover levels in times that it has flooded or nearly flooded.

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This is set to 300

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by default, but you can change this if you need to

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leave the perform no discharge analysis option d selected

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as it is not a normal part of the no flood criteria

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and will not be needed for this exercise.

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Click ok

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with the design criteria set.

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It is time to validate the calculation model

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on the ribbon analysis tab analysis panel, click validate

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the validate. Dialogue opens showing that the site is okay

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if there were any errors such as a pipe that did not have a

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length specified or a manhole that did not have a cover level specified.

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They would appear here under the site node.

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You would be able to click on them to see where in the model the error was

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and the relevant dialog box would open

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so that you could fix the error.

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This is a simple model, however, so no errors occurred.

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Keep in mind that this validation tool checks to

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make sure all the necessary data is there,

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It does not check to make sure the data makes sense.

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For example, if you had an oversized or undersized pipe,

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it would not recognize that here,

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but if those values were completely missing, it would list the error,

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click cancel.