Evening star. [volume] (Washington, D.C.) 1854-1972, 1893-01-07

above suggested. and I therefore conclude That
ample provision is made" u. r. Francis.
quoted BY A. Fecley, y. IS Boston Water
Works, Additional supply. Boston. iss2)
CAPACITY or THE OVERFLOW.
Az TO the capacity Of the overflow. 10 40
necessary 10 depart from prcceslents on .c-
count Of the extent % the watershed. aud IN.
comparatively heavy rainfalls tina, occasionally
occur IN the Croton basin. Judging from ths
possibilities OF rain or thaw in This and neigh
boring watersheds, the flowing cApacitv Of a..
overflow should not be less than equivalent %
the fow, In twenty-four hours. uf a volume %
water represented bv a uniform thickness OF an
inches over the whole watershed.
IL is true that no such flow Is on record and
Tie SEXUAL flow NAV never, IL IL hoped. come 70
that figure. but a combination OF adverse cir
eOmstances, such as an exceptionally heavy
rainfall. occurring at q time when the reservoir
II already full and when the ground l. covered
win snow can bring about such q condition OF
things, and II l. Wise TO be prepared for a. Ia
can be 90 much more readily done that an in
crease IN the length Of the overflow can be OBJ
tained at comparatively small cost
lhe writer having had occasion 60 design the
o'ernoN OF several dams on an equivalent ossis.
may be allowed 70 state that on he occurrence
OF ireshet which produced a fow somewhat
less than one-half Of the quantity lust men
TONED. he should not hut feel In accorianc.
with The sentiment Of the people living lover
NeNA an AHt NallcN. tlAt the channels Of dis
charge were none too large
The length OF overflow corresponding N
these conditions IL about 800 feet
Report OF A Fteley. consulting engineer on
the proposed Quaker Bridge dam see rage
~ report OF Aduednct Commissioner city Of
New York. for lss9.)
RAINFALL TO RI PROVIDED ron.
On mature consideration Of all the condi-
tons that occur 70 Us. but without undert.k-
ing TO provide FOR remote possibilities. We are
OF the opinion that a rainfall Of twelve inch..
IN t"enty-four hours. or the equivalent in ram.
melted snow AMI ice should be provided for
The proportion Of Thu. that would aow Of in
the stream during the same time depend.
largely upon the condition o. the valley. In its
present condition probably not more than one
quarter OF the whole amount woula reach tha
lower end OF the valley: the large mart OF the
remainder would be held back in the meadow.
and other low places TO dow Of gradually "a in
the flood Of February. lSs6 lmprovemants
Will no doubt be made az an early date 20 t,re-
vent tnls'and OF course proportionately larger
| quantity VIII How Of IN n given time As the
land becomes occupied by buildings and as
sumes an urban character. with houses close
together aud with paved streets or even IL the
surface be lald out as park with drivewavs
ana suOsoh drains. a snll larger portion will
| How on IN 2 given time until ultimately n
the city continues 10 grow in that direction a.
1t has done. we estimate that in a rainfall such
as we are considering the maximum flow in the
stream would be about three-quarters Of the
| rainfall during the same length OF time
The How In the stream would not be syn
chronOus with the rainfall but later and a. ,he
storm progressed the tendency would be for the
| rate OF How TO approach the rate Of the min
fall, and If the raia continued 20 fall indefinitely
| at a uniform rate the flow IN tho stream aud
rainfall would after a certain interval be nearly
| the same.
Twelve inches OF rain in twenty-four bours IN
| the watershed of Stony brook is at the rate 81
| 4,lOl cubic feet per second. In the present
| condition OF the stream above the pvnchou
street culvert we are of the opinion that tho
MAXIMUM Hood Al that point would correspond
TO about one-fourth OF that rate. say about 600
cubic feet per second. and when the channels of
stony brook and tributaries above the culvert
4 are improved 10 an extent 20 relieve the
\ meadows from being flooded we estimate that
| the maximum flow in the stream would l,e
about one-half the rate of the rainfall or say
| 1000 cnbic feet per second. aud ultimately
when the valley is all closely built upon ia.
rate of flow would be equal 20 three-fourths Of
the rainfall, or about 5000 cubic feet per sec
| ond. (Report of commission on the prevention
OF foods in the valley Of stony brook; PIP. IL
and 49,
MEMORANDA
In an appendix Capt LUX saws tina, in the
absence of actual gaugings Of the Rock creek
/
| approximate limits between which. a. n prob-
| able maximum and minimum. the discharge
due TO a rainfall OF exceptional severity and
extent may be supposed 10 lie.
| AS to the probable lower limit he saws Il Il
| not unreasonable to provide against si, inches
| OF rainfall uniformly discharged in twenty -four
hours from the whole OF so much of the water-
shed rs is rural in character and is likely 10 re-
main SO for a considerable period. A. this a. .
basis he calculates that the total discharge for
the basin Is 0.227 plus 4,674, or a. s0l cubic
| feet per second.
To fix the higher limit he has supposed the
| basin. 49,36i.2 acres, to be divided into five
areas. equal in size, built upon and paved and
similar IN slope and surface conditions. The
result is 5,l2s cubic feet per second for each
OF the smaller areas, or 25.6iO cubic feet per
second for the whole. lie has no doubt that
this result is larger than any discharge that can
be expected to take place. except under con-
ditions which he cannot possibly foresee.