GEOPAK Junction Loss Methodology

Method 1 is Chows Modern Sewer Design and Method 2 is AASHTO. The main difference would be the loss coefficients. They are different for each method.

Beebe,

I found the following two paragraphs in the StormCAD help file. It states that AASHTO has dropped their own method in favor of the HEC-22 method. Does GEOPAK plan on adding a "Method 3" (HEC-22) to the calculation options?

Thanks,
Josh

Manhole Head Loss Equations (AASHTO/HEC-2 Overview)
The `HEC-22' headloss method used in StormCAD V8i is based on the FHWA's Urban Drainage Design Manual, Hydraulic Engineering Circular No. 22 (HEC-22) energy-loss methodology. This method computes an adjusted headloss coefficient by multiplying the initial headloss coefficient by correction factors for diameter, flow depth, relative flow, plunging flow and benching (Structure Headloss). This adjusted headloss coefficient is then multiplied by the velocity head in the outlet pipe to determine the total junction headloss. This is the method outlined in the current edition of the HEC-22 document (HEC-22, Second Edition, August 2001).

The `AASHTO' headloss method used in StormCAD V8i was originally implemented based on the 1991 version of the AASHTO Model Drainage Manual. This method determines the total junction headloss by adding the contraction, bend and expansion losses at a junction, then applying correction factors for non-piped flow and shaping if applicable (Headloss - AASHTO Method). More recently, the AASHTO Model Drainage Manual has dropped this method in favor of the method described in HEC-22, Second Edition (August 2001). However for compatibility with earlier versions of StormCAD V8i, and also with the various state and regional drainage authorities who continue to use the original AASHTO headloss method, the `AASHTO' headloss method in StormCAD V8i is still based on the 1991 version of the AASHTO Model Drainage Manual.

GEOPAK will not be adding a different method. As one moves forward to the SUDA products that will be offered soon that method (HEC-22) will be available.