Very Small Negative Water Surface Elevation Change for Encroachment Analyses

[szheng]

In my floodplain encroachment analyses, there is a negative (-0.03 ft) water surface change between the natural 100-year profile and the encroached profile. I tried numerious combinations of encroachement station placement for the affected cross section, a few cross sections upstream and downstream. Even I placed the all encroachemnt stations at the 100-year water surface left and right stations for those cross sections, the negative number still cannot be eliminated.

Have any of you run into this kind of problems before? Do you know the causes and how to solve the problem?

Thank you very much!

Shuhai

[Debajit Basu Ray]

Hi,

There shouldn't be any negative water surface change while doing floodplain encroachment. The negative change in water surface means that you squeeze too much on the water. The velocity of water will increase and water surface will drop and will be going towards supercritical flow.

You have to encroach the water by lesser amount as you did in your current project. If you encroach by lesser amount the problem you faced will be solved.

Thanks,

Debajit Basu Ray
debajit@bossintl.com