HomeMy WebLinkAboutPE 2.87.41; POINSETTIA VILLAGE; HYDROLOGY AND HYDRAULIC CALCULATIONS; 1988-06-27.1
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This plate applies onV when the grate Is loasted In a low, poIat or
sump where the wAie'r will pond at the grate.
The capacity of the grate. depends upon the area of the openings and
the depth, of water at the vate. Recent aVeriments have deteroLned that
a grate will act as, a weir and follow the weir for=Ll& for deptho (heads)
on the grate up to 0.4 ft. lt will act as an orifice and follow the o4-
fice fonula for heads of 1.4 ft. 00 over. For himmob betwean. 0.41t.
and 1.4 ft. the aperatlon Is ladetWto beemos ot ve M-aft ad sddkw
over the gmte.
In the usual problem, the following are givent
A particular desian of grate with dimensions.
A denigi discharge (Q) or inforiestion as to drainags &roap
rainfall Intensities and,, rwWt ocefftoleSs trm WMA a
discharge ass be satinated.
Compute the perimeter of the grate openinS (P) Ignoring Us
bars and omitting &sW side over which tbe water does not .
enter,, suab as when ons side is against the f&" of a eafte
Divide the result by 2. This allows-for partial GUS" at
the grate by asaumLM that on4 half at Wo perinalm WU
be effective.
Cuff4mte the Q/P ratio.
Compute the total area of clear opening (A), excludLag am
taken up by bars, &ad divide by 2. This iallowe for paftial
clog&tng of the vat* by assuniag that, aaW hW 0 Me &M
will be effective.
Con"te this WA ratio.
Enter the charL 4A the bottom scale uainS Line (a) with the
Q(P value and lins (b) with the Q/A v&UW &A read, tW M-
quired head in feet at the left imargin.
If the roqkLLred head falls below 0.4 ft.* (a) QrJ1 %tU SPOW, This is the usual *cass.
If the'requLred head falls above 1.4 ft.,0 (b) on.4 will aVW.
If the required head, fall* bet"wen 0.4 fL-'wW 1.4 ft. the
actual head my be anywhere between (a) md (b). Use the
value that f
w
vas the moist conservative resultj, beift wAre to
use line (a ith Q/P and line (b) with Q/A.
If the InIst, is a combination type with gmto. and curb opeb-
in& the recommsnded procedure is the smo " with a grate
&lone except the perimeter and Area an not avidsid by 2.
72ws reason for this is that the curb opening will SIMMS as a
relief In event the Smte become clogged. With the pmate
"rating freell it is questionable w1wLber wAah water w1lX
got to the curb opening until the 41eGlArp-19
submerp the entire grate.
It the grate has an appreciable aro&& &UPS so the &I& way
from the curb is Motor than that imucL to the Gaft the 10nM
over the side should be 4eLeratned " r from gut 0~
the ends. Uss the depth at the oLddla of UW gate for 04
inflow and depth at e4p aw%y &= UW Mb tW " UnWe
INLET CAPACITY OF GRATE AT SAO
Plate 2.6 - 0658
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