# RE: Retaining Wall

• To: seaint(--nospam--at)seaint.org
• Subject: RE: Retaining Wall
• From: "Lutz,James" <JLUTZ(--nospam--at)earthtech.com>
• Date: Tue, 11 Jul 2000 11:42:27 -0700
Q=AV is a continuity equation. It applies for both closed conduit and open
channel flow.

For a V shaped ditch (triangular channel), following are some formulas from
Chow's "Open Channel Hydraulics" you can use to determine the flow rate Q
for a given water depth "y", channel invert slope "s", side slope "z"
horizontal to 1 vertical, and Manning roughness coefficient "n", which might
be on the order of .03 to .05 for a grass lined ditch, but can vary
dramatically depending on channel conditions. The problem usually consists
of playing with trial values of "y", "z", and "s" until your dimensions
match the required Q, and then adding some freeboard for a safety factor.
It's pretty simple to set up on a spreadsheet for a trial and error
solution.

A=zy^2

R=zy/(2(1+z)^.5)

V=1.49(R^.67)(S^.5)/n

z and y are in feet. Q is in cfs. n and s are dimensionless.

These equations are for normal depth assuming steady flow conditions and a
constant bottom slope.

-----Original Message-----
From: SDGSE(--nospam--at)aol.com [mailto:SDGSE(--nospam--at)aol.com]
Sent: Tuesday, July 11, 2000 11:00 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Retaining Wall

In a message dated 7/11/00 7:52:03 AM Pacific Daylight Time,
smithegr(--nospam--at)bellsouth.net writes:

<< Q = V*A.  In order to determine V, you must know the area, A.  Area is a
function of the depth, so as you will quickly find out, there are infinite
combinations of V and A for every Q. >>

I hate do disagree, but isn't Q=AV for flow in a pipe under pressure rather
than an open channel.

Oshin Tosounian, S.E.
Los Angeles, CA

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