|Click to download the METRIC model files.|
We are going to size our pipes in line with the Sewers for Adoption (SfA) UK guidance specifications. To meet these requirements we need to make sure that our network will not surcharge for a 1:2 year event and will not flood for a 1:30 year event. We can either do this by manually altering pipes individually, or we can use the Pipe Sizing Wizard found within the Preliminary Sizing Ribbon.
The Pipe Sizing Wizard works by using an Intensity Duration Frequency (IDF) curve for a particular storm event, for a particular area. We will specify this using FSR data. The Pipe Sizing Wizard reads the IDF curve for the time of concentration of an individual pipe and then a rainfall intensity is generated. This rainfall intensity generates the expected flow the pipe will have to deal with (in the UK this is done using the Modified Rational Method). The connection is then sized accordingly. This is related to the Wallingford Procedure for the UK, and enables pipes to meet the Sewers for Adoption criteria or similar guidance documents in other countries on pipe surcharging and flooding for various events, as stated above.
The second stage of the Pipe Sizing Wizard allows us to enter the Pipe Sizing Criteria, within here are a variety of conditions that can be specified for our pipes to be designed to. We will be using the (UK) Modified Rational Method (as mentioned above), combined with the FSR 2 Rainfall Source, the two-year return period FSR data from Oxford (UK) as the basis for our pipe design.
New s/shot here
The third stage of the Pipe Sizing Wizard allows us to enter the Pipe Sizing Criteria. Click on the ellipses next to the Pipe Size Library and then select Default. You will be asked if you want to save existing dat, select No and the default sizes will be entered. Click OK to close the form. We want to use the Lock drop down menu to maintain our slopes by selecting Slopes. We also want to tick on Min. Cover Depth and Synchronise Manhole Invert Levels. Update s/shot
Note: There is surcharging in the lower pipe for the 1:2 year critical storm, is due to the water depth in the pond being greater than the soffit of the pipe (as can be seen in profile view).
Now that we have resized our pipes we want to alter our Dry Pond so that we are meeting the same discharge flow rate as the existing site. As we saw from our phases report for the developed site we are discharging at higher rates than the existing site. To successfully decrease the flow rates we will alter the outflow control and also the pond size, as reducing the flow rate will lead to a higher storage volume required.
You can carry on from the previous Chapter or open XP_Tutorial6.xpdx and switch to the Completed Design phase by selecting from the drop-down list on the left Tree View panel if you have not already done so.
More information on the Export Pipe Function can be on Export Pipe Network.