Encroachments

[matmun1]

Hi there.

I am trying to determine a floodway line using encroachments. My flow is subcritical, boundary conditions are set to normal depth, and I am (initially) using Method 4 with an ultimate target increase of 0.2 feet (NJ). I set up several profile runs, all with the same Q, but varying the target increase so that I could see which Encr Stations produce what actual Prof Delta WS increases.

The problem is that for any given cross section, I may get a Prof Delta WS of 0.18 for the +0.15' target run, and a Prof Delta WS of 0.22 for the +0.20 target run, prompting me to believe that Encr Stations set between those given for the +0.15 & +0.20 target runs would put me right at my desired +0.20 target - but this is not the case. My Prof Delta WS goes up to like 0.47.

For example, if the +0.15 target run gives Encr. Stations of 175 (LT) & 225 (RT), and the +0.20 target run gives stations of 180 & 220, I would assume that using something like 177.5 & 222.5 would put me closer to my (actual) target of +0.20, but it doesn't.

My stations fall within the limits of the base flow top width, but not within the banks.

Any help is appreciated!