HomeMy WebLinkAbout1969 Lozier NE and Cayuga Heights Stormwater Drainage Study REPORT
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STORMWATER DRAINAGE STUDY
FOR
NORTHEAST" AREA
EXTENDED TO INCLUDE THE
VILLAGE OF CAYUGA HEIGHT'S
TOWN OF ITHACA
TOMP INS COUNTY NEW YGRI
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November, 1969 10 Gibbs Street
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Rochester, New `fork 14M
REPORT ON
STORM WATER DRAINAGE STUDY
FOR
NORTHEAST AREA
EXTENDED TO INCLUDE THE
VILLAGE OF CAYUGA HEIGHTS
TOWN OF TTHACA TOMPKINS COUNTY.2 NEW YORK
This report is concerned with further considera-
tion of stormwator drainage problems as they occur in the
northeast area of the Town of Ithaca and continue westward
downstream into and through a portion of the Village of
Cayuga Heights .
The areas involved comprise the Renwick Brook
watershed including a north and a south branch to the main
stream .
Suburban development is causing and will continue
to cause increased stormwater runoff on the watershed in
two ways . First, new structures with impervious roofs ,
parking lots and driveways tend to shed more andmore water
downhill as building development replaces vacant farmland .
Second , as this increased runoff becomes more prevalent and
apparent, the need for improved waterways becomes more
prevalent and apparent. Improved waterways expedite the
shedding of more runoff downstream. Hence , the cure enhances
the problem. In June of ,this year , our studies suggested
improvements to cure drainage problems, created by increased
building construction in the northeast area . These improve-
ments tended to shift the problems downhill 'into the Village
of Cayuga Heights .
Lozmn ENGINEERS,INC
2 .
In accordance with a request of the Town Board ,
we have n,iade an additional study of the Renwick Brook
watershed downhill from the north branch . Our findings
are reported herewith .
Renwick Brook makes eleven culvert crossings in
the Village of Cayuga Heights betwten the Village Line and
Cayuga Lake ; seven are under Town roads , two are under
New York State Highways and two are under Lehigh Valley
Railroad tracks . Exhibit "B" included herewith shows the
relative location of these facili'ties . Examination of
the Plan and Profile reveals two important characteristics
of the drainage area . The mushroom-type "PI an" of the
drainage area and its plateau-type "Profile" combine to
create a "waterfall " or " rapids " effect near Highgate
Road . Even on the plateau , runoff is quite rapid. In
fact, one of the questions to be evaluated in this study
is practically eliminated by these physical features .
The question raised pertained to an evaluation of the
problems created by improvement of the north branch drainage
faci 1 i ties al one as compared wi th improvement of the whole
watershed. The criteria for making this evaluation is
" time of travel " or velocity of stream flow. The profile
is steep enough at 25 feet pet, thousand feet on the plateau
that the difference in time of travel between unimproved
channels taken at 3 feet per second and improved channels
taken at 10 feet per second is not sufficient to make a
significant difference in the quantity of, s tormwater to be'
Lozrrn ENoINEEHS,INC.
3 .
designed for. For example , see footnotes ( 1 ) and ( 2) in
Table 1 . There is not sufficient difference between
300 cfs . and 375 cfs . or between 471 cfs . and 593 cfs . to
pose a change in ditch or culvert sizing .
There are several reasons for this interpretation
which it may be well to review before considering capacity
of the existing facilities .
First, capacity of hydraulic structures in storm-
water work is not a rigid quantity . This is nicely illus -
trated by two existing culverts : One in Reach 8 at 7 foot
diameter and the other in Reach 10 at 9 foot diameter are
both located to handle substantially the same flow . The
7 foot culvert has a capacity of approximately 1800 cfs .
with a velocity of 45 fps . The 9 foot culvert has a
capacity of approximately 2100 cfs . with a velocity of
33 fps . What capacity the designers of these structures
had in mind is not known , but both are adequate for a
10 year storm"jwhich we estimate will result in a peak
runoff of approximately 600 cfs . At this rate , both
culverts will flow part full . The 9 foot culvert will
carry a stream of water 3-1 /2 feet deep at a velocity of
23 feet per second , for example .
Thus , it can be seen that capacity is not a
rigid consideration ; there are others .
LozaiR ENGINEERS"INC.
4 .
Hydraulic structures are frequently enlarged to
p�rovide for passage of floating timbers and ice when swift
open streanis are involved . This subject is a matter of
experience and judgment.
Hydraulic structures are generally designed for
a maximurn velocity of approximately 10 feet per second
according to a rule-of-thumb . On one hand , higher velo-
cities like 23 fps . may not be harmful on a 10 year return
period basis . On the other hand , another consideration is
involved ; that is , that s for mwater facilities are an
insurance proposition .
An economic appraisal of a proposed stormwater
project should rightfully include an estimate of the total
cost of repairing all damage and claims during the life
( bond retirement) of proposed facilities . The risk of high
velocity erosion someday attended by cost of washout
repairs may- be less than the cost of a concrete liner for .
velocity or erosion control in the State's case , for
example . In our case , it might be advisable to consider
the prospects of buying out a fdw houses in the flood plain .
A house or two on Triphammer Road and one with window sills
below Winthrop Place are examples . The whole question of
responsibility for flood plain damage is debatable , Physical
damage to a few basements could be considerably less costly
than culvert improvements . These thoughts are well known ,
but economic and, legal considerations are not a controlling
Lozinri ENoINEERS,IXC
5 .
criteria either. There are intangible considerations as
well .
A flooded gas heater in 'the basement is an
•explosion hazard. .i, 'M washed out culvert which gives way
suddenly under pressure with high velocities could cause
a freak accident with children at play. The 5 .foot by
5 foot box culvert partially 'bl ocked by boulders is a
candidate -for this sort of tragedy. It should at least
be cleaned -out.' The capacity of this structure must be
listed at 600 cfs . because of- its location in a 20 foot
gorge . This capacity .would be effected if a 3- foot. deep
stream dashed through at, 40 feet e'r second,: which, i t.
could do on the, existing. 110• foot pe r 1000 -foot 'slope. '
Such.. velocities * are Unheard of Exactly. yih,at'. .might
happen is unknown'. . .'A w*as h'o u t, co u 1 d a va' I an ch d' down H i.1'1*:'
causing only, a .few thods'an*d Aol lais* worth of p*hysical,
amage or- it 'could create - a''.-freak accident- .l..", N 6 e'd le s t.
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say , all of these considerations are confusin.g unless
they are kept in perspective.
Flood dam,a'ge involves collection and pas'sa.ge
of waterin sufficient quantities to overburden channels
and culverts . Small ditches and culverts tend to retard
runoff so that upstream facilities protect downstream faci -
lities in a way. The 42 inch culvert at Winthrop Place
protects the' 4 frot box culvert at Highgate , for example.
Increasing the capacity of the culvert at Winthrop from
Lozmn Exoixmms,INC.
'�A.6ti 4*4 150 "IVA
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150 cfs ( 42") to 400 cfs . (new bridge ) relieves the
danger of flooding cellars at Winthrop and creates the
danger of an avalanche at Highgate . Without the change ,
Highgate is secure .
This consideration leads to the subject of
check dams " which serve to hold back peak runoff LUItil
storm',is subside . Thus , we have two choices for solution
of the problem .
The first choice includes five new culverts at
Winthrop , Triphanimer , ' Highgate , Remington and Cayuga
Heights . We say bridges advisably in lieu of circular
or box culverts to suggest that the shape of the underpass
should match the shape of the channel ; that is , it should
be wide and shallow to pass swift streams without obstruc-
tion . Channels are frequently, made with 2 to I side slopes
on an 8 foot bottom. The 8 foot width is selected to
accommodate a bulldozer blade for maintenance . We estimate
that the cost of providing five new culverts will be
$140 ,000 . This does not include any allowance for channel
widening .
Channel velocities will generally be in the order
of 10 fps . because of the slope of the watershed. This
means that some form of lining will be required where rock
is not prevalent . Where rock is prevalent , rock excavation
will be required , In other words , the cost of channel
improvements may be prohibitive . This coupled with the
Lozrnrz E1VG1NEER8,1N(-
cost of new culverts leads us to conclude that our second
choice may be the better answer.
The second choice includes a check dam with a
diversion structure . For estimating purposes , we cal -
culated the requi red volume at the " south junction " to be
3 ,000 ,000 cubic feet . On 'this basis , constructi on costs
for providing storage at this location will be approximately
$95 ,000 . Realization that one check dam will be less
expensive than five culverts coupled with an understanding
that costs for veloci,ty control All be a factor led to
our conclusion . This is why check dams are frequently
employed in flood control work . However, the problem is
not entirely solved because utilization of one check dam
will involve some channel improvement and a few culverts ;
Winthrop Place and Triphammer on Renwick Brook and Trip-
hammer on the south branch , for example . The answer will
depend upon the cost and extent of necessary channel improve-
ments and availability of land for one or more check dams
together with an appraisal of upstream facilities which has
been beyond the scope of the report.
The purpose of this study was to make a preliminary
investigation and report on the downstream effects of improve-
ments proposed in a previous study for the north branch .
LOZIEIz E*xarN-ImRS INC.
Our investigation shows that there are eleven
streani crossings ., Of these , only twqo are adequate to
pass a 10 year runoff without tangible daniage ; two will
cause flooding ; four are candidates for intangible
damage , and three are of questionable concern . T h e s e
are located at Cayuga Heights and Route 13 , at Winthrop
Place and Triphammer Road , at Highgate , Highland , Reniington ,
and North Sunset Drive and at East Shore Drive respectively .
There is evidence that continued building develop-
ment and stream improvement may soon create a co=1011
drainage problem for the Town of Ithaca and the Village of
Cayuga Heights . The magnitude of their joint problem in
ternis of cost will be somewhere between $140 ,000 . znd
$220 ,000 . Further, appraisal of this aspect requires an
instrument survey and test borings . Other aspects include
local tributary improvements which are not accounted for
herein . Also , acquisition of land for dam sites and cost
of easements for rights-of-way should be investigated .
Inquiries concerning the possibility that Federal or State
Aid may be available have not been made .
Lozri,:u INC,
g .
Authority to undertake a 'flood control project
is divided. Creation of a joint drainage district is
feasible . Village and Terra Planning Reprus ntatly s an
the illag and Town Boards should be consulted .
Respectfully submitted ,
LOZIER ENGINEERS , INC.
J . C. Dunlap
R. W . Cutler
R 'B : JCD: cag
TABLE NO . 1 - SUKHARY OF DESIGN CONSIDERATIONS IN STUDY AREA
;each Description of Drainage P . M . * Exist . Propose
Number Reach Location Vrep (fSIjI) jja,ft . SjEJ Struc . Structu
I Headwaters to N.Junction 305 365 None Bridge
and 81
Channel
2 N . Junction to Village Line 400 375 ( 1 ) None
3 Village Line to Winthrop PI . 440 400 42" Dia ,
4 Winthrop Pl . to Triphammer 450 406 36" and
4 2"
5 Triphammer to Munition 736 5: 93 ( 2 ) None Channel
( 480) Widenin
6 S . Junction to Highgate 760 610 444 ' Bridge
and 8 '
Channel
7 Highgate to Remington 770 616 On X6 %
8 Remington to Cayuga Heights 780 620 7 ' Dia . None
9 Cayuga Hts . to N . Sunset Dr. 790 625 5IX51 60 S . f.
NO 9 ' Dia . None
10 N . Sunset Dr. to Cayuga Lake 300 630 41h X81w None
( 1 . 25 mi . )
P . D. F. Designates project design flood to approximate design
rquirements . I
( 1 ) 375 c . f. s . with ' improvements compared to 300 without improvements .
( 2 ) 593 c . f. s . with improvements compared to 471 without improvVents
Trapezoidal culvert simulating bridge and channel with 2 " freeboard
ROB : sli
November 5 , 1969
Lonym ENGINUERS,IXC
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