|
Hydraulic calculations shall be performed by using the U.S. Army Corps of Engineers
HEC-RAS "River Analysis System" computer models. Normal depth channel calculations
are permissible for constructed open channels with a uniform geometric cross section
where 1) there is no potential for the water surface elevations to be controlled by
backwater and 2) the channel is not in a FEMA floodplain.
Certain watersheds have hydrologic and hydraulic models that are available through
the San Antonio River Authority website, Digital Data & Modeling Repository (D2MR).
Developments proposed within the limits of these watersheds must have the models updated
by the design engineer to reflect changes in flow, channel configuration (including
alterations to vegetation) and channel structures. The design engineer's models must
use the same computer program that was used in the existing model e.g. HEC-RAS or
FEMA latest accepted models. The updated models shall be submitted to the Director
of TCI.
The influence of gravity on fluid motion in an open channel flow can be expressed
in a dimensionless quantity called a Froude Number (Fr). The Froude Number is expressed
in the following equation.
(Equation 9.2)
V
= Mean velocity (fps)
g
= Acceleration of gravity = 32.2 ft/s
d
= Hydraulic depth (ft.)
The hydraulic depth is defined as the cross sectional area of the channel perpendicular
to the flow divided by the free water surface.
|
|
|
