Is there a way to apply a headloss as a percentage to all pipes or a set of pipes? For example 10% more headloss.
Pipe headloss can be adjusted globally to all pipes or a set of pipes by way of a multiplication factor against the input friction factors or minor loss coefficients.
Note that total headloss in a pipe is divided into two main categories: friction and minor. In the Results section of the pipe properties, you will see two fields: "Headloss (Friction)" and "Headloss (Minor)". These two fields separate the total headloss into loss by friction (based on the roughness coefficient) and loss by minor losses (minor loss coefficients).
1) Analysis > Calculation Options > Double click the calculation option set for the scenario in question > Select "Active" for "Roughness Adjustments". Click the ellipsis button (...) next to Active Pipe Roughness Adjustments, select the selection set of pipes that you want to adjust, select Multiply as the Operation and enter the desired value. If you enter 1.1 here (+10%) for example, it will multiply the original roughness coefficient accordingly and increase it by 10%. So, if you're using the Hazen Williams method, you would want to use a multipler less than 1 in order to increase roughness (smaller H-W C = more headloss). However, a multiplier of 90% doesn't necessarily mean 10% more headloss, so you may need to experiment with the factor.
If the operation is set to subtract for example, it will globally subtract the value you enter for friction factors in the respective selection set. For example if using subtract with a value of 20, a pipe with original Hazen-Williams C of 140 will then have a C of 120.
2) If you have minor loss coefficients entered in the properties of each pipe and you want to apply your additional loss only to "Headloss (Minor)", you can open the Pipe Flextable (Report > Element Tables > Pipe), add the Minor Loss Coefficient field, then right click the column header, choose Global Edit, and multiply as needed to increase roughness from minor losses. As with #1 above though, a 10% increase in the coefficient (K) will not necessarily reflect a 10% increase in headloss for the pipe. Similarly you can global edit the roughness coefficients themselves from here, although the Roughness Adjustment approach in #1 above may be easier to manage.
If you do not already have minor losses in all pipes, you can global edit the field and use the "Add" or "Set" Operation to enter minor losses globally. Note that this assumes that the pipe's "Specify Local Minor Loss?" is set to "true", whereby the "Minor Loss Coefficient (Local)" is used.