Product(s):	StormCAD, CivilStorm, SewerGEMS
Version(s):	08.11.XX.XX and 10.00.XX.XX
Area:	Calculations

Problem

In StormCAD (GVF-Rational Solver), how is the conduit property "System CA" computed?

Solution

When using the Rational runoff method, the conduit property "System CA" is the sum of the upstream "Catchment CA" and catch basin "External CA" values.

For Example:

Catchment (Upstream)

Runoff Coefficient = 0.9
Area (unified) = 2 acres
Catchment CA = 0.9 * 2 = 1.8 acres

Catch Basin (Upstream)

External CA = 1 acre

Conduit (Upstream)

System CA = Catchment CA + External CA = 1.8 + 1 = 2.8 acres

Catchment (Downstream)

Runoff Coefficient = 0.8
Area (unified) = 3 acres
Catchment CA = 0.8 * 3 acres = 2.4 acres

Catch Basin (Upstream)

External CA = 1.5 acres

Conduit (Downstream):

System CA = 1.8 + 1 + 2.4 + 1.5 = 6.7 acres

See Also

System CA results for a catch basin are lower than the CA results for the upstream catchment