Flood analysis using Hecras

Question

Hi every one i am performing the basic Hecgeo-ras Tutorial when i exported the geometry in Hec-ras and computed the Steady Flow Analysis in hec-ras it gives me this error 'a horizontal manning n value needs to be specified on first station' Can any one help me about this.

Answer 1

When using HEC-GeoRAS, it is the user's responsibility to assign Manning's n coefficients to each cross section. That is, unless you first created a LandUse feature class in the map document. If you created an empty LandUse feature class then the "N_Value" fields will be blank and since the calculations in the program start at the first station, you will see an error just as you stated.

From the Purdue University Tutorial: To assign Manning’s n to cross-sections, click on RAS Geometry->Manning’s n Values->Extract n Values. Confirm LandUse for Land Use, choose N_Value for Manning Field, XSCutLines for XS Cut Lines, leave the default name Manning for XS Manning Table, and click OK.