Network Pipe Flow: Understanding Assumptions and Calculating Junction Position

[foo9008]

Homework Statement

from the diagram , we know that the junction is lower than the pipe at B . why the author want to make an assumption that the junction is located at 20m from the datum ? is it correct to do so ?

Homework Equations

The Attempt at a Solution

eventually , i found the ans is 25.2m , the delta Q is close to 0 ,
but , i also tried with 18m , then slowly change to 16m and 14m , by using Q1+Q2 - Q3 , i found the ans is getting bigger , does it mean the junction has to be higher? [/B]

P/s : to admin , hopefully , i moved to an appropriate place to get better response

 

[nilesh_pat]

Yes, it does mean that the junction has to be higher. This is because when the junction is lower than the pipe at B, the flow of water will increase with the increasing height of the junction. So, if we assume the junction is located at 20m from the datum, then the flow of water will be greater than if the junction was located lower. Thus, the answer you found (25.2m) is correct.