HYDROLOGIC AND HYDRAULIC ANALYSIS

BOWMAN A VENUE DAM PROJECT STUDY FOR RESIZING

Tllg UPPER POND RESERVOIR

BLI;-.10 BROOK, CITY OF RYE

PHEPARED FOR:

WSP-SELLS /1/UAI?CUFF MA.VOR, NEW YORK

PAUL C. RIZZO ENGINEERING- NEW YORK, PLLC 51:!0 WIIITE IJI. ,\I NS RUAU, SUITE~25

l'Aiut\'TOWN, NEW YORK 1059 l

PROJECT No. 11-4626 SEPTE:\IBER 21, 2012

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TABLE OF CONTENTS

PAGE

LIST OF TABLES ......................................................................................................................... iii

LIST OF FIGURES ....................................................................................................................... iii

1.0 PURPOSE .......................................................................................................................... I

2.0 REFERENCES .................................................................................................................. 1

3.0 METHODOLOGY ............................................................................................................ 2

4.0 HYDROLOGIC ANALYSIS ............................................................................................ 3

4.1 Water Delineation and Area of Study .................................................................... 3

4.2 Storm Detennination .............................................................................................. 3

4.3 Runoff Model ......................................................................................................... 5

4.4 Transforn1 Method ................................................................................................. 6

4.5 Hydrologic Analysis Results .................................................................................. ?

5.0 HYDRAULIC ANALYSIS ............................................................................................... 7

5.1 Model Data and Geon1ctry ..................................................................................... 7

5.1.1 1\-todel Data ................................................................................................. 7

5.1.2 Model Geornetry ........................................................................................ 8

5.2 Manning Roughness Coefficient (n) ...................................................................... 8

5.3 Inflow Hydrographs and Boundary Conditions ..................................................... 9

5.4 Scenarios Analyzed ................................................................................................ IO

6.0 RESULTS AND FINDINGS ............................................................................................. 1 I

7.0 COMPARISON BETWEEN RIZZO AND WSP-SELLS ANALYSIS ............................ I5

7.1 Discharge Flow Values .......................................................................................... 15

7.2 Model Geometries .................................................................................................. I?

7.3 Steady Versus Unsteady Analyses ......................................................................... I?

7.4 Sluice Gate OptiJnization ....................................................................................... l8

7.5 Flow Dynamics through the 1-95 Culvert .............................................................. 18

APPENDICES

R I 11-462MI2

~

LIST OF APPENDICES

"""' APPENDIX TITLE

0"")

APPENDIX A SITE INSPECTION PHOTOGRAPHS

, APPENDIX B APPROXIMATE GEOGRAPHIC BOUNDARIES FOR NRCS (SCS)

RAINFALL DISTRIBUTIONS (FROM REFERENCE 9)

APPENDIX C BLIND BROOK WATERSHED- PHYSICAL PARAMETERS r'"'>

APPENDIX D RESIZED UPPER POND ALTERNATIVES

APPENDIX E PLAN VIEW OF BOTH THE 2006 FEMA HEC-RAS MODEL AND

RIZZO HEC-RAS MODEL WITH ORTHOIMAGERY

APPENDIX F GIS DATA

APPENDIX G RIZZO HEC-HMS MODEL

r.'!r.l APPENDIX H RIZZO HEC-RAS MODEL

R I ll--l6:!W 12 II

TABLE NO.

TABLE I

TABLE2

TABLE 3

TABLE4

TABLES

TABLE6

TABLE 7

TABLES

TABLE 9

FIGURE NO.

FIGURE L

FrGURE 2

FIGURE 3

R I I 1-4626/ 12

LIST OF TABLES

TITLE

SUBW ATERSHEDS VERSUS AREAS

PREClPITATION DEPTHS FOR 24 HOUR RAINFALL

COMPOSITE CN NUMBERS

CLARK METHOD PARAMETERS

HYDROGRAPHS PEAK FLOW VALUES lN CFS

IN FLOW HYDROGRJ\PH S AND BOUN DARY CONDITIONS

SUMMARY OF RESU LTS SHOWING S RFACE EL. AN D WATER

LEVEL DTFFERENTIJ\L FOR THE 5 ANALYZED CASES

DISCHARGES FLOW V /\LUES COMPARISON

RIZZO UPDATED PROBAB ILITY PEAK FLOW ANALYSIS

LIST OF FIGURES

TITLE

CROSS SECTION GEOMETRY COM PARISON DOWNSTREAM OF HIGHLAND ROAD AND UPSTREAM OF TH E I-95 CULVERT

COMPARISON BETWEEN UNSTEADY AND STEADY FLOW MODELING

REPRESENTATION OF HYDRAU LIC CONDITIONS AT THE 1-95 CULVERT FOR Til E 50-YEAR FLOOD

Ill

~ Pau l C. Riu.o ;\s~m:iatcs. Inc. ~ <_ CO:--<SCLTANTS

By A E Date 09/ 13/ 12 Checked by GMS Date 09/20/12

Subject Bowman A venue Dam Hydrolo!!ic and Hydrau lic Studv for RcsiLitH.! the Upper Pond Rescrvni r

AC = A\la& ~S'LI v (:j L£ I

bi1S = t;ff() /1. f:l~/fv-

1.0 PURPOSE

0 Sheet f\io._J _of 19 Project No. Il-4626

The City of Rye is located in Westchester County, New Yt)rk. approximately 7 milt:s north of the New York City line. It is bounded on the south and east by the Long Is land Sound. o n the west by the Village of Mamaroneck, on the north by the Village of Rye Brook. to the northwe<.;t by the Tuwn/Yi llage of Harrison, and on the northeast by rhe Village of Port Chester. The Ci ty shares three watersheds wi th

these other communities: Blind Brook, Beaver Swamp Brook, and coasta l Long bland Sound.

As a resu lt of its po!" ition on the coast and at the base of two watersheds. Rye ex perience:-. ch ronic llooding and wind damage from coast<:ll and inland storms. Pre,·ious studies (Reference 2&.:1 ) show that overall flooding problems \\'ithin the watershed arc cau .... ed by a narrow channel width. obstructed tlows. vegetative growth in stream hanks. constricted bridge openings. IO\\ banks. scd imcnt ~ll inn in tidal

reaches, years of wetland Iii ling and lloodplain encroachment. Over the pa:-.t severa l years. certain area of the Blind Brook watershed have experienced ex treme rlood ing and wind damage rr(lm inland and

coastal storm events. Flooding causes repeti ti ve property losses. The C ity o f Rye has developed and implemented tlood mitigation solutions to decrease ri -;ks re lated to fl ooding.

Paul C. Rizzo Engineering - New York, PLLC (RI ZZO) \\'as retained b) 'v\'SP Sclh tu pcrf'orm a Hydrologic and Hydraulic (H& H) analysis to determine the potent ial benefits or n:: .... it.ing the Upper Pond in order to increa!-.C temporary storage capacity du ring signil~ cant storm events. The intention is to

re time storm water tlow in order to decrease wa ter surface prollle!-. within the Blind Brook Ri ve r

between Interstates 1-287 and 1-95 . RIZZO was also asked to consider optimi7i ng the sluice gate operation to increase poten tial benefits from the new sluice ga te.

2.0 R EFERENCES

I. Unired States Geological Survey. 20 II. "LBCD 2006 Lnnd Co\ e r". ht ed .. http://www .mrlc .!!.OV/n kJ2006.php.

2. U.S. Am1y Corps of Engineers. March 2009, Blind 13rno~ Watershed Manage rncnt Plan .

3. United States Geological Survey (USGS), 2009, " I /3 -Arc Second National Elc vat ion Dataset'', SDE

Digital Data, avai lab le: http://seamless.us!:!!U.!.l>V .

4. WS P Sells. March 20mL Flood Mitigation Study- Bnwman A ,·enue Dam S ite.

~ Paul C. Riuo Associalc ·. Inc. ~ <__ CONSt:LTANTS 0 By AE Date 09/13112 Checked by GMS Date 09/20112

Subject Bowman Avenue Dam Sheet 1'\o._L.of 19 Hydrologic and Hydraulic Studv for Resizin g: Project No. I I -4626 the Upper Pond Reservoi r

5. WSP Sell s, August 2007, Hydrologic Report on the Blind Brook Watc r~hccl .

6. Natural Resources Conservation Service. 2006, "Digi tal General Soil Map of U.S." . NY and CT, US Depanment of Agriculture, http ://so i ldaLaman . nrc~.usda. !!O \'.

7. U.S. Geological Survey, 2000, Equations for Es timating Clark Un it-Hycl rograph Parameters for Small Rural Watersheds in Ill inois.

8. NYSDEC, 1989, Guidelines for Design of Dams. Revised Version.

9. Chow, Maiclment & Mays. l988, Applied Hydrology.

I 0. Natural Resources Conservation Service (NRCS ). June 1986. Urban ll ycl rology for Small

Watersheds TR 55.

II. Federal Emergency Management Agency (FEMA), 1979. r:J ood Insurance Study.

12. U.S. Department of Commerce, January 1963, Technical Paper No..+O (TP--t0): "Rainfall Frequency Atlas of the United States for Durations from 30 Minutes to 2-t I lours and Return Periods from I to 100 Years''.

3.0 METHODOLOGY

In order to determine the impacts o r proposed resized Upper Pond alternati ves on water surface prori les between Interstates l-287 and 1-95 and optimized the sluice gate operat ion ~equcnci n g. RIZZO performed a comprehensive hydrologic and hydraul ic analysis of the ent ire Blind Brook Watcr!-.hed . RIZZO utilized the most current data ava ilable to perform its sLUdy. This includes:

• Additional large storm events, which occurred subsequent to WSP Sell s 200K study (Reference 4):

• Light Detect ion and Ranging (LIDAR) data which represents the mnsl current and highest resolution available topographic data; and,

• State-of-the-practice analytical techniques.

Precipitation events with 2. 5, 10. 25.50 and 100-year ~ t orm return periods \\ Crc considered in this analysis for comparison to the 2008 WSP Sells Study. Prec ipitation \vas determined using the methodology presented in the National Weather Service's Technical Paper No. -tO (TP -tO) (Reference 12 ).

~ Paul C. Riu.o A:-;sociatcs. lnc.:. ~ ......(_ CONSLILTAN I'S

By AE Date 09/13/12 Checked by GMS Date 09/20/12

Subject Bowman Avenue Dam H vdro lo!lic and Hvtlraulic St ud v lur Re~i1.inu

the Upper Pond Resen'L)ir

0 Sheer No._3_ of _1_2 Project No. 1 1-4626

In flo,,· hydrograph events were compured as the runoff from the precipitat it'n C\ t:n t ~ Je:.cribed above using

the Hydro logic M oueling System computer software HEC-Hi\11S (vcr:-.iun .).3) de\c lnped by the United

States A rmy Corps of Engineers (USACE).

The Geographic Information System (G IS) software A rcG IS wa~ u:-.cd to 111anage and analyze the rnost

current topographic and hydrologic data avai lable in order to create the III :C-IItvl S. A rc-Hyd ro tools

(ArcG IS A pplication) were used to delineate the watershed.

The U.S. Department of A griculture-Natural Resources Conservation Service (N RCS)- Curve N umber

(CN) anti the Snyder Transform Methods were respecti ve ly used to n1utk l the hydrologic loss and to

transform the rainfal l cxce:.s into runoff hyclrographs.

Finally. in !low hydrographs obtained from HEC-HMS for the di rrc rcnt ~ tnnll CVC IIh ..;e r \'e as input into the

HEC-RAS model. The analyt ical model stans in the vici nity of Crawford Park and end~ approximately 800

feet downstream of 1-95. This is an unsteady tlow HEC-RAS 111\ldcl. '' llich u~l.!-. the rull dynamic, Sai nt­

Yenant equation wi th an implic it. tinite difference method to calcu late equal inn ~ulutio n :-. . This approach

allows storm event llood wa\'CS to be routed within ri ver -. \\'hilc model ing hydrug.raph~ variation in space.

time. and fl ood wave auenuation. The results represent a very an.:u ratt.' nHKkling or real llooding

phenomena.

4 H YDRO LOG IC r\~,\L\'S IS

4. 1 Watershed Delineation a nd Area of Study

The Blind Brook Watershed, which originates in the v ic init y o r the Westchester County A irport,

drains an area or approximately I 0.9 square mi les into the Long l s lt~nd Snund. The area

en<.:Ompasscs several mun icipal ities including the City o r Rye. Vi !I age ur Rye Brook, Vi llage of

Port Chester. and Town/Village of Harrison. A second tributary w tile ea~t joins the main branch

south or the Bowman Avenue Dam in the Vil lage o f Rye Bru11k. Fmn) the dttm. the brook flows

south, under Interstate I -287 and through the City bus inc~~ di~trict to Miltun Harbor.

Prineipallancl uses in the Upper B l ind Brook Watcr..; hed arc the airpurt. largl.! campu~ offices, golf

courses. forests, wetlands and res idential areas. Within the City of Rye. :ts de.;cribed in Reference

2, the \Vatershed is dominated by low and medium density rc.;i dcn tial dc,elopment. institutional

and recreational uses, open space. and a smal l central hu.-. inc."" di-.trict. The area along the brook is

highly developed. with many residences. businesse-. and public building-. adjacelll to the

watercourse. Photographs taken during site in spection~ arc U\ ailahk in t\ ppendix ,-L

~ Pau l C. Ri1.1.o Associates, Inc. ~ <_ CONSULT:\i\TS

By AE Date 09/13/1 2 Checked by GM S Date 09/20/ 12

Subj ect B owman A venue Dam H ydrologic and Hydraulic Study for Rcs izin2 the Upper Pond Reservoir

0 Sheet No._..1_of J.2 Proj ect No. I 1-4616

For integrat ion into the HEC-HMS model. the Bli nd Brook Watershed was subdivided into six

sub-watersheds according to topographic and hydro logic (i .e. stream and ponds topology)

conditions. Sub-watersheds areas are provided in Tahle I .

T ABLE I SUBWATERSHEDS VERSUS AREAS

Sub-watersheds A reas I mi2J

Blind Brook Country Club (SW I ) 2.1 0

Lincoln A venue (SW2) ].28

Bowman Avenue (SW3 ) 1.46

1-287 (S W4) 1.1 0

Purchase Street (SWS) 0.6t<

1-95 (SW6) 0.44 Total 9. 15

4.2 Storm Determination

ationa1 Weather Service's Technical Paper No.-lO (TP-·W - R eference 12 ), which has publ ished

data for estimating hypotheti cal frequency-based swrms. was used in this sLUdy. The rain fall

frequency (isopluvial ) maps presented in TP-40 arc for .;;elected durations of time. A 24-hour

rain fa ll duration was se lected for the Blind Brook Watershed, which adequately exceeds the time of

concentration for the watershed.

As the intensity of rainfall varies considerabl y during a storm, as we ll as for various geographic

regions or the United States, NRCS developed rour syntheti c 24-hour rainfall distributions (f, fA , fl

nnd Ill) from available National W eather Service (NWS) dura tion frequency data (Hersh field 1961 ;

Frederi ck et al. , 1977) or local storm data (Reference I 0 ). T he appro.x imate geographic boundaries

for NRCS (SCS) rainfall distributions are given in Appendix 13. A type Ill d ist ribution.

corresponding to the location of the Blind Brook Watershed, was selec ted for this analysis. For

example. in Table 2. a 100-year flood/24 hours duration. a conservati ve va lue of7.2 inches ofrain

was considered and implemented into the HEC-H MS Model.

~ Paul C. Rin.o Associa tes. Inc. ~ '<_ C<>;-.JSlJLTA:\TS

By AE Date 09/ 1311 2 Checked by GMS Date 09/20/12

Subject Bowman A venue Dam HvdroloQic and Hydraulic Studv for Rcs iz.in Q the Upper Pond Reservoir

TABLE 2

PRECIPITATION DEPTHS FOR 24 HOUR RAINFALL

0 Sheet No._2_of J..2 Project No. 11-4626

Storm Event Prec i[)itation Depth [inches]

2- years 3.3

5-years 4.3

I 0-yc~us 5. 1

25-ycars 5.7

50 years 6.4

100 years 7.'2.

Suu rcc: l?eference 12

4.3 Runofl' Model

Runoff i" simulated in HEC-HMS using mathematical methods describing the rainfall -runoff

relations for a drainage basin. The input component!:> include basin model, meteorological model.

time series data. paired data. and conrrol speci fication. Runorr for the watershed \\'Us estimated

using the Natural Resources Conservation Service (NRCS). Runorr Curve Number (CN) method

available in HEC-HMS.

The CN Number is an empirica l parameter used for pred icting direct runo ff from rainfall excess.

Th is method i:-. wide ly used and has been proven efficient to determine the approx imate amount or

clin.:c t runorr from a rainfall event in a particular area. CN Numbers arc based on the area·s

hydrologic soil group. land use and land cover. Blind Brook Watershed characteri sti cs were

determined using Geographic Information System (GIS) clat ;.t. ArcG IS, a slate-o f-the-an GIS

sort ware program. was used to treat and analyze both Digita l Elevation M odel (USGS 2009-

Reference 3 ). Land Cover Data (USGS 20 I I - Reference I) and Soi I Data (N RCS 2006-

Reference 6). Appendix C presents thi s informat ion. Table 3 presents the compos ite CN Numbers

for the different sub watersheds considered. Input fi les arc includes on the C D provided in

;-\ ppendix F.

~ Paul C. Rizzo Associa1cs, Inc. ~ < CONSL"LTANTS 0 By AE Date 09/13112 Checked by GMS Date 09/20/12

Subject Bowman A venue Dam Hydrologic and Hydraulic Study for Resizing the Upper Pond Reservoir

Sheet No._6_of ..1.2 Project No. 11-4626

TABLE3 COMPOSITE CN NUMBERS

Sub-watersheds Composite CN Numbers

Blind Brook Country Club (SW I) 75

Lincoln A venue (SW2) 73

Bowman Avenue (SW3) 74

1-287 (SW4) 75

Purchase Street (SW5) 67

1-95 (SW6) 62

4.4 Transform Method

The NRCS Curve Number method described above has been applied to determine runoff from

initial rainfall. The method transforms excess precipitation into a simulated discharge hydrograph at the outlet of the watershed.

The Clark Unit Hydrograph method has been used in HEC-HMS for the Blind Brook watershed

hydrographs development (Reference 7). This method has been shown to provide accurate results

when used for small watersheds. The Clark Method requires three parameters to calculate

hydrographs: Tc. the time of concentration for the basin, R. a storage coefticient, and a time-area

curve. The time-area curve is used to develop the translation hydrograph resulting from a

precipitation event and is input into HEC-HMS. The Tc and R calculations are presented here in

Table 4.

TABLE4 CLARK METHOD PARAMETERS

Time of Storage Sub-watersheds Concentration Coefficient

(hours) (hours)

Blind Brook Country Club (SW I) 3.01 1.24

Lincoln Avenue (SW2) 2.51 0.89

Bowman Avenue (SW3) 1.4 0.56

1-287 (SW4) 1.89 0.99

Purchase Street (SW5) 1.16 0.63

1-95 (SW6) 0.77 0.43

~ Paul C. Rizzo Associates, Inc. ~ <_ CONSULTANTS 0 By AE Date 09/13/12 Checked by GMS Date 09/20/12

Subject Bowman A venue Dam Hydrologic and H ydraulic Study for Res izing the Upper Pond Reservoir

Sheet No._7_or 19 Project 1 o. I 1-4626

4.5 Hydrologic Ana lysis R esults

Output from the hydrologic analysis consists o f hydrographs obtained for the si x sub-watersheds

composing the Blind Brook Watershed Basin. The hydrographs arc used as input data for the

hydraulic analys is described in thi s report. Table 5 presents the hydrograph peak flows for storm

events ranging from 2 to 100 year peri od or return.

TABLES HYDROGRAPll PEAK FLOW VALUES IN CFS

Blind Brook & Bowman 1-287 Purchase 1-95

Storm Event Lincoln Av. A venue (SW-+) Street (SW6)

(SW l &SW2) (S W3) (SW5 )

2-years 1054.2 540.9 336.4 22 1.3 163.9

5-years 1602.8 790.6 49 1.3 32H 2-W.l

I 0-years 2073.2 100 1.9 622.2 420.1 3 14.1

25-years 2539.7 1165.2 723.2 492.2 369.3

50 years 3023 .6 1359.7 843.5 57R.9 436. 1

100 years 3560.7 1585 .9 983.3 680.8 5 15.1

Complete hydrographs are avajlable on the CD provided in Appendix G .

5 HYDRAULIC ANALYSIS

5. 1 Model Data and Geometry

5.1.1 Model Data

LIDAR data thal was used to build the HEC-RAS Model o f the Blind Brook, was downloaded

from Westchester County. LJDAR data was used to ex tract cross-section geometric dated for the

hydraulic model. This data. acqu ired in 200lJ. was processed in ArcG IS. For the proposed resized

Upper Pond A lternati ves, RIZZO processed topographi c data obtained by WSP Sells from a field

survey performed on April 201 2 and merged the topographic information into the general model.

The HEC-GeoRAS extension versions 4. 1 for A rcG IS 9.3 was used to delineate, ex tract, and

import the cross sections into the H EC-RAS model.

~ Paul C. Rizzo Associates, Inc. ~ "'<._ CONSIJI.TA:'\TS 0 By AE Date 09/13112 Checked by GMS Date 09/20112

Subject Bowman A venue Dam Sheet t\o._8_of ..12 Hvdrolo£ic and Hvdraulic Studv for Resizin2 Project No. ll-4626 the Upper Pond Reservoir

5.1.2 Model Geometry

The analyzed portion of the Blind Brook was con. tructecl as a single reach in the model. The model

struts in the vicinity of Crawford Park and ends approximately 800 feet downstream of I-95 for a

total length of 3 miles (see Appendix E- Figure E-2). The model includes bridges, ponds and the

Bowman Avenue Dam structme. Bridge geometries were taken both from the 2006 FEMA Model

(Reference 2) provided by WSP Sells and RIZZO field investigations performed in February and

May 2012. Areas for the Upper and Lower Pond were modeled into HEC-RAS using topographic

survey data provided by WSP Sells. Proposed pond resizing alternative geometries were provided

by WSP Sells and imported into HEC-RAS. Bowman Avenue Dam was also incorporated into the

model along with the gate operation sequence. Bowman Dam and Spillway was modeled into

HEC-RAS as an inline structure. The dam sluice 2ate wm; coded in the inline structure alon2 with ~ ~

the bottom opening located at the invert of the dam.

Cros sec tions required to develop the model were chosen at representative locations throughout

the Brook and at locations where changes occur in discharge. slope, shape and roughness. Cross­

sections were cut from the LIDAR Data to define the creek ( ee Appendix E- Figure E-2 ).

Afterward, cross section extrapolations were performed within the creek in order to reach a density

of one cross-section for each 40 ft. of creek for a total number of 387 cross sections. Areas of the

Upper and Lower Pond were modeled using more closely spaced cross-sections at 25 to 50 feet

intervals so that HEC-RAS performs fully dynamic unsteady flow routing through the ponds and

downstream or the Bowman Dam. This was also clone for the resized pond alternatives. Appendix D presents the plan views of the resized pond alternatives.

5.2 lVIanning Roughness Coefficient (n)

Manning's roughness coefficients for the streambed, and overbanks were selected from the 2006 FEMA HEC-RAS model supported by engineering judgment. The original Manning's n-values

reponed in the old FEMA model were adjusted where necessary in the hydraulic modeling phase

on a cross ection by cross section basis. Values ranging rrom 0.045 to 0.065 were used for the

stream and the overbanks areas. For numerical stabi lity of the I IEC-RAS model the higher

manning values (i.e. 0.065) were used during low flow . imulations.

~ Paul C. Ri ZLo A:-.:-.nt.:ia1~:s. Inc. ~ <_ CONSULTt\:\TS

Subject Bowman A \·cnue Dam

0 By AE Date 09/13/12 Checked by GMS Date 09/20/12 Hvdrolo2ic and Hydraulic Studv for Resizin!l

the Upper Pond Reservoir

Sheet No._9_of J.2 Project No. I 1-4626

5.3 lntlow Hydrographs and Boundary Conditions

The unsteady HEC-RAS model was developed for the selected study limits. As discussed in section

4.1, the hydrologic software HEC-HMS was used to develop storm inflow hyurographs for input

into the unsteady flow model. These hydrographs were funher used to conduct the hydraulic

modeling with HEC-RAS.

Within the unsteady HEC-RAS model , the inflow hydrographs were used as inputs into the model.

The locations of the boundary condit ions arc l isted in Table 6. Boundary conditions al low HEC­

RAS to initiate its ca lcu lation (i.e. solving the St. Vcnant equation)

TABLE(, INFLOW HYDROG RAPHS AND fi OUNDARY CONDITIONS

HEC-RAS Ri ver Station Reference L ocation Boundary Condition 4603.397 Li nco In A vcn uc lnflow hydrograph 3556.227 Inflow to Upper Pond at Latera l In tlow

Westchester A venue 2796.049 IS Bowman A venue Dam Internal boundary (i.e., gate

operation using HEC-RAS Rule Operations)

2630.106 Tributary tn Lower Pond at Lateral inllow hyclrograph Bowman I\ venue confluence with East Branch Blind Brook

2108.907 - l-t32. 194 Between 1-287 and Purchase Uniform lateral innow Street

1432. 194-3 I .82327 Between Purchase Street and Uniform lateral intlow downstream of 1-95

13.8377 1 Downstream of 1-95 Normal depth

Local intlows were modeled as lateral inllows in the HEC-RAS model. Table 61ists the point of

lateral inOow and the corresponding HEC-RAS eros-; sec tions are presented bclmv:

• Local drainage from Blind Brook and Lincoln A venue sub-watershed is modeled as

upstream inllow hydrograph at cross-section -t603 .397.

• L ocal drainage from Bowman A venue Dam sub-watershed is modeled as lateral in tlow to

Upper Pond at Westchester Avenue at cross-sect ion 3556.2'27.

• Local drainage from 1-287 sub-watershed is rnocle lecl as lateral inflow to Lower Pond at

Bowman A venue ar cross-sec tion 2630. I 06.

~ Paul C. Rizzo Associates. Inc. ~ <_ CONSULTANTS 0 By AE Date 09/13/12 Checked by GMS Date 09/20/ 12

Subject Bowman Avenue Dam Sheet No._I_O_of J..2 Hydrolo2ic and Hydraulic Study for Resizing Project No. 11-4626 the Upper Pond Reservoir

• Local drainage from Purchase Street sub-watershed is modeled as uniform inflow between

I-287 and Purchase Street between cross sections 2108.907 and l 432.194.

• Local drainage from I-95 sub-watershed is modeled as uniform inflow Between Purchase

Street to downstream of J-95 between cross-sections 1432.194 and 3 J .82327.

For all scenarios, the normal depth method was used for the downstream boundary condition. The

gradient was estimated between the last few downstream cross-sections of the river reach , to be

approximately 0.002 ft/ft.

When there is an inline structure in HEC-RAS, no cross-section in the model can go dry, therefore ,

a constant base now of 200 cfs was set as the minimum ilow throughout the Blind Brook River at

all times for numerical stability at low flow within the HEC-RAS environment.

5.4 Scenarios Analyzed

The analysis aims to determine the potential impacts o r the proposed resized Upper Pond

Alternatives on water surface profiles between Interstates 1-287 and l-95. lt also considers an

optimized sluice gate operating sequence. Water levels corresponding to the 2-year, 5-year, I 0-

year, 25-year, 50-year and 100-year return s torm events were determined.

The following scenarios were analyzed:

• Case A: Existing Condition

• Case B: Sluice GaLe lnstallation

• Case C: Proposed Resized Upper Pond

• Case D: Proposed Maximized Resized Upper Pond

• Case E: Combination Resized Upper Pond and Sluice Gate\

Case A consists of the existing condition with the timber logs installed at the dam bottom and the IS­feet wide by 2.5-foot high orifice opening at the dam invert. Water su1·face elevations for Case A were

used to establish the baseline hydraulic characteristics or the Blind Brook River between Interstates I-287 and 1-95.

Case B represents RIZZO's proposed optimized gate sequence operation consisUng or keeping the

gate closed for the 5-year storm, adopting the WSP-Se lls gate operation procedure for return period

ranging from 5 to 10 years and setting the gate fully open for rloods greater than 10 years.

~ Paul C. Rizzo Assnciarcs. Inc. ~ "<._ CONSULTANTS

By AE Date 09113/12 Checked by GMS Date 09/20/12

Subject Bowman A venue Dam Hvdrologic and Hydraulic Studv for Resi zing the Upper Pond Reservoi r

0 Sheet No._l_l_of J...2 Project No. I 1-4626

Case C consists on resizing the Upper Pond by excavating I 0-LOOO cubic yards of material (i.e.

96,000 cubic yards of soil and 14,000 cubic yards of rock). CaseD is a maximized resized alternative

aimi ng to remove approximately 130,000 cubic yards of material (i. e. 109,000 cubic yards of soil and

2 1 ,000 cubic yards of rock).

Case Eisa combination o f the Cases A and C consisting or a simulation with the Resized Upper Pond

and the Sluice Gate Installed.

6.0 R ESULTS A.~D Fl :--I D~GS

A summary of anticipated wate r surface e levations t'or the 5 cases are presented in Table 7. To

compm·c the different cases with each other, summary results arc presented for five representative

cross-sections. The locations are:

• Downstream of 1-2!)7

• Purchase Street

• Mendota A venue

• High land Road

• Upstream of I-95

Results of this study show a potential reduction in downstream water elevations resulting from the

s luice gate install ation for large storm events (i.e. fl oods with retu rn periods between 25 and I 00

years). Overall , water elevat ions are projected to be approximately 6 inches lower after s luice gate

installation for the 50 and I 00 return period floods.

Results also show that between the two resized pond alternatives. Cases C and 0 , the incremental

benefit gajned with the maximized resized altemativc (Case C) is insignificant. By implementing the

smaller resized pond alternati ve (Case D). potential water elevations are between 8 and 10 inches

lower for the smal ler storm events (i.e. 2 to I 0 year period of return storms) and around 4 or 5 inches

lower for the large r storm events ( i.e. 50 and 100 year period of return).

Case E, wh ich models the smaller resized pond alternative with the sluice gate insta lled, shows

overall potential water surface leve l decrease of I 0 to 15 inches between 1-287 and 1-95 during large r

storm events.

G fS Fi les, HEC-HMS and HEC-RAS models used and all the pertinent data arc placed on C Os and

are provided in Appendix F, G and H.

~ Paul C. Ri11o Assnl"iatcs, Inc. ~ <._ CONSU l.TAN'J S

B y AE Date 09/13112 Chc~.:kcd hy GMS Date 09/20/12

Subject Bowman A v~nue Dam Hydrolo!!iC and Hydraulic Study for Resizing the Upper Pond Reservo ir

TABLE 7

0 Sheet No._!1_of .J.2 Project No. I 1-4626

SUMMAUY OF RESULT SHOWING SURFA CE ELEVATIONS AND WATER LEVEL DIFFERENTIAL FOR TUE 5 ANALYZED CASES

DiiTt:renc..:e ( Inches)

Flood Sluice Gate Resized

1\ lax. Upper Resized Upper (Period or Locations

Existing Cond. Jnsl.

Upper Pond-Pond - Alt. Pond - Alt 2 &

Case Case Case

Return ) (CASE A)

(CASE B) Alt. 2 (Case

I (Case D) SG (Case El A& B A&C A& O

C)

DIS of 1-287 :n.s :n.8 33.2 33.1 :n.2 () -7 -8 -Pun.:hase Stn.:c.:t 28.3 28.3 27.7 27 .(1 27.7 0 -7 -8

2 Year Mel!llota A wnue 2-L9 24.lJ 24.-l 24.3 24.-l () - () -7

Hi ghland Roat..l 2-1.5 2-L) 23.l'! 23.7 23.8 () -X -9

U/S 1-95 23 .-1 23.-l 22.9 :22.9 21.9 0 -5 -6

DIS of 1-287 J-+.5 * 34.1 3-LO 3-LO * -5 -6

Pun:ha!->e Street 29.8 * 29.0 2X.S 28.8 * - 10 -12

5 Year :Vkndota A'c nue 26.6 * 25.7 25.5 25.5 * I - II - 13

Hi 1rhland Road 26.5 * 25.5 25.3 25 .. 1 * -12 - I-I

U/S 1-95 2-1.7 * 23.H 2).7 2:. .7 ~ - I 0 - II

DIS of 1-287 35. 1 * 34.9 34.9 34.9 * -2 -3 -

Purchase Street 3 1.0 * 30.6 305 ~0.5 * -5 -6

10 Year Mendota A Vt: 11 uc 27.8 * 27.3 27.3 27 . .1 * - (J -6 . Hi).!hland Roau ?.7.7 * 17.:. 27.2 27.2 * - () -7

U/S 1-95 26. 1 * 25 . .'\ 25.4 2.'\.4 * -H -9

DIS of 1-287 J:'i.5 35.-1 35 .-1 35.-l 35.3 -2 - I - I

15 Year Purchase Strt:et 3 1.7 3 1.6 3 1.5 3 1.4 31.4 -2 -3 -4

Mendota A \'cnue 28.7 28.6 28.2 28.2 2H.3 - I -5 -6

Case A&E

-7

-7

-6

-8

-5

*

* * * * * * * *

* ,

-.)

-4

-+

~ Paul C. Ri zzo Assm:ialcs. Inc. ~ <._ CONSULTANTS

Subject Bowman A venue Dam By AE Date 09/ 13/12 Checked by GMS Date 09/20/ 12 Hydrologic and Hydraulic Study for Resizing

the Upper Pond Reservoi r

Highland Road 28.6 28 .5 28.2

U/S 1-95 27.3 27.2 26.R

DIS of 1-287 35.9 35.7 35.9

Purchase Street 32.5 32. 1 32.3

50 Year tvkndota A venue 29.8 2~ . .+ 29.-+

I-Ii }!h land Road 29.8 29.3 29.4

U/S 1-95 2S.7 28.2 28.2

DIS of 1-287 36.3 36. 1 36.2

Purchase Street 33.2 33.0 33. 1 100 Year Mendota A venue 3 1.2 30.8 30.8

High land Road 3 1.2 30.7 30.8

U/S 1-95 30.2 1lJ. 7 29.7

* Refer to WSP-Sdls gate operation sequence (Reference 4)

0 Sbe~.: t No._ 1_3_of _!.2 Project No. I l--l626

28. 1 28.3

26.7 26.9

35.9 J'i .S

11.3 3 1.9

29.4 2lJ.O

29.3 28.9

28.2 27 .7

36.2 35.9

33.1 3'J .6

30.8 30.1

30.7 30.0

29.7 28.9

-I

-I

-3

-5

-6

-6

-6

-2

-3

-5

-5

-6

1

-5 -6 -4

-6 -7 -5

- I -I -5

-2 -3 -8

-5 -6 - 10

-5 -6 - 10

-5 -6 -I I

-I -I -5

-2 -2 -S

-4 -5 -14

-5 -5 -14

-5 -6 - 15

~ Pau.l C. Riz~o Associates, Inc. ~ <._ CONSULTAN I S

By AE Date 09/13/1 2 Checked by GMS Date 09/20/12

Subject Bowman A venue D am H ydrologic and Hydraulic Study for Resizing the Upper Pond Reservoir

7.0 COMPARISON BETWEEN RIZZO AND 2008 WSP SELT~S ANALYSIS

7.1 DISCHARGE FLOW VAL UES

0 Sheet No. _ _l1 __ of .1.2 Project No. I 1-4626

Table 8 presents a comparison of discharge flow values from the present study and the 2008 WSP-Sclls

study (Reference 4).

TABLES DISCHARGE FLOW VALUES COMPARISON

Storm Event Peak Discharge (cfs) Return Periods Location*

(years) WSP-Sells RIZZO

D/S of 1-287 781 1023

2 Purchase St 781 1036

U/S of 1-95 928 1024

0/S of 1-287 1275 2098

5 Purchase St 1275 2143

U/S of 1-95 1534 2057

0/ S of 1-287 1663 2829

10 Purchase St 1663 2883

U/S of 1-95 1982 2780

0/5 of 1-287 2292 3346

25 Purchase St 2292 3429

U/S of 1-95 2594 3300

0/S of 1-287 2767 3995

so Purchase St 2767 4084

U/5 of 1-95 3078 3849

D/S of 1-287 3346 4633

100 Purchase St 3346 4673

U/5 of 1-95 3583 4389

*Comparisons between WSP Sd ls model and RIZ7.0 mmlL:I arc approximate d ue

to differences in model geometry and cross sections.

WSP-Sells used discharge flow values from its August 2007 Hydrologic study for the Blind Brook

Watershed (Ref erence 4 ). This study used peak flow data from USGS Gage 0 1300000 located

downstream of the 1-95 cui vert to calculate peak discharge rates or various return periods.

,...,

~ l'aul C. Ri!.ZP/\ssociates. Inc. ~ "<_ CONSULTA:-:TS

By AE Date 09/13/12 Checked by GMS Date 09/20112

Subject Bowman Avenue Dam Hvdrolo!!ic and Hydraulic Study for Resizing the Upper Pond Reservoir

0 Sheet No.___l2_of .1.2 Projec t No. 1 J -4626

The discharges reported in Table 8 were computed using a probabilistic approach (i.e . Log-Pearson

Type ill method) using annual peak discharges recorded between I Y'-1-J. and 1990. In order to account for

recent development in the watershed, only the la.<; t 20 years of records were used lo r the analys is.

Discharge ll0w values obtained by RIZZO were computed using a deterministic approach to model

[)hys ical processes (e.g., surface runoff, infiltral ion, evapotranspiration, and channel flow) in response to

rainfall events within a hydrologic model (I IEC-HMS) and routing these tlows downstream in a

hydraulic model (HEC-RAS). The HEC-HMS anti HEC-RAS models were developed using the most

current topograptl ic and hydrologic data avai I ab le for the watershed. T his data re flects watershed

conditions present within the last ri ve years.

By way of compari son, RIZZO also performed a probab ili ~tic analys is on the USGS Stream Gage

0 1300000 data using a Log Pearson T ype Il l distribution. However, the data were supplemented by

estimating discharge rates of two :-> ignifican t lloods that occurred in the last 5 years (i.e. in 2007 and

20 II ). By incorporat ing these new data. the estimated peak discharge rates for tloOlls of different return

rcriocls went up signiricantly. Summary or results are presented in Tahle 9 below. Due w the

uncertainty surrounding the probabilistic estimates. the HEC-RAS modeling was done using the

deterministic analyses discussed ahove.

TABLE9

RIZZO UPDAT ED PROBAiliLlTY PEAK FLOW ANAL YS lS

Storm Event Peak Di scharge

Return Periods Location* (years)

(cfs)

2 1024

5 1893

10 D/5 of 1-95

2639

25 3793

50 4817

100 5992

~ Paul C. Rizw Associa te~ . Inc. ~ <._ CONSULTANTS

Subject Bowman A venue Dam

0 By AE Date 09/13/12 Checked by GMS Date 09/20/12 Hvclrolmdc and 1-lvdrau lic Study for Re-; izing

the Upper Pond Reservoir

Sheet No._ l_6_ of 19 Projec t No. 11-4626

7.2 MODEL GEOMETRY

The model geometry between the RlZZO model and the WSP Sells mode l is different. The WSP Sells model utilized geometry from the FEMA Flood Insurance Study (FIS) model, which was developed using Digital Elevation Model (OEM) data. The vertical accuracy of th is data is approximutely 2 feet.

The RIZZO model makes usc or more recentl y <mtilable LIDAR data, \\'hich has a hori zontal resolution of 9 feet and a vertical accuracy of 7 inches. Whi le this data is more accurate than the topographic data from the FEMA FIS, it does not necessarily indicate that the newer topography yields signil'icantly more accurate results. For comparison, a sample cross section is shown below that highlights topographical differences between the model geometries.

60 55

50

~ 45 .:: '-" 40 c .Sl 35

~ 30 ~ w 2 5

20

15

10 0 50 100 1 50

--L IDAR Data- RIZZO

----- DEM Data - WSP Sells

200 250 300 350 400 450

S"tation (ft)

Figure 1: Cross Section Geometry Comparison Downstream of Highland Road and Upstream of the 1-95 Culvert

Additionally, RLZZO model is composed of 387 cro. s-sections (average spacing of 40 reel) versus 39 cross-sections for the 2006 FEMA HEC-RAS model (See both model plan view in Appendix E ) which was used in the WSP-Sell s 2008 Study (Reference J ).This eli tlcrcnt level of accuracy between the two models leads to differences in water leve ls.

7.3 STEADY VERSliS U NSTEA DY A:'-~A LYSES

The HEC-RAS model used by WSP Sells is a steady flow model. The peak flow from the flood hydrograph released from Bowman Avenue Dam was used in the HEC-RAS model as a con rant value. This peak discharge value was tempora ll y and spatiall y constant. Therefore. at every cross

~ Paul C. Riu.o Associates, In ~,;. ~ "<_ CONSULTANTS 0 By A E Date 09/ 13/ 12 Checked hy GMS Date 091101 12

Subject Bowman Avenue Dam Sheet No._ l_7_ of 19 Hydrolo£ic and Hvdraulic Studv for Rcsiz in!! Project No. 11-4626 the Upper Pond Reservoir

section the tlow rate is a constant value. The only variability i~ the cross sectional area of the now and the tlow veloc it y. Alte rnative ly. RlZZO's HEC-RAS model is an unsteady flow mouel.

The flood hydrograph is routed through the reach so the llood di scharge changes with time and space. An unsteady now regime allows the noocl hydrograph to attenuate as it moves downstream

(See Figure 2 ). The output from an unsteady now model is more rcpre"entat ive of the way water levels rise and fall during a nood. An unsteady fl ow model allov;s for storage. spatial. and temporal changes in the water levels as the flood \vave propagates dO\vnstrearn.

RIZZO Un<le>dy Flow ~Jodd

WSP-SELLS Steady F1ow 1\lo•l cl

Figure 2: Comparison bet·wccn Unsteady and Steady Flow Modeling

7.4 SLUICE GATE OPTJ~IIZr\TlOl\

Part of the RIZzo·s scope of work was to consider ways to optimize the sluice gate operation. The

purpose of this was to determine if adjustments in gate operation settings could lead to an additional decrease in water levels downst ream of the Bowman Avenue Dam. Along with the other poims mentioned above. the different mode of gate (lpe ration between RIZZO and the WSP-Selb models

did lead to differen t water levels within the downstream area of interest.

7.5 FLOW 0 Y:SA,Il CS THROUGH THE 1-95 C UL VERT

A significant difference between the WSP-Sells and RIZZO HEC-RAS models is the predicted flood levels for the 50-year tlood (See Figure 3). In the WSP Sell s model, the effect of the sluice gate operation on the 50-year tlood levels is sign ilicant, lowering the tlood levels by as much as 4.15 ft upstream of the 1-95 culvert. With the RIZZO model, the benefit is signilicantly smaller (0.5 ft). Making a direct compari son between these result s is not easy clue m the diflerences di scussed above. Multip le variables changed between the two analyses.

~ Paul C. Rizzo AssPt:iatcs, lnt:. ~ <_ CONSU LTANTS

By AE Date 0911 3/ 11 Checked by GMS Date 09/20/12

Subject Bowman A venue Dam H yd ro lo!!ic and ll yd raulic Study for Res izinrr the Upper Pond Reservoir

0 Sheet. ·o.___lB__of _1.2 Project No. 1 1-4626

Neverthe less, the large llood leve l reduction at the 50-year disch;.u·ge rate in the WSP Sells model i~

due to a change in the now regime ( i.e. from free surface now to orifice now) thro ugh the I-95

cu lvert. Without the s luice gate, the di scharge rate is large eno ugh that it submerges the inlet of the 1-

95 culvert. As a result, a headwater bu ilds up on the upstream s ide of the cu lvert to provide the

necessary hydraulic head to pass the llow throu gh the culvert. Thi s headwater at the c.:ulven resu lts in

backwater effects upstream. With the insta llation o f the s luit:e gate, the peak discharge rate is

suffic ientl y less such that the discharge rate can rl ow through the culvert wi thout submerging the

inlet. Therefore. the now passes th ro ugh the cui vc rr as a free su rface flow and does nol create

backwater effects upstream. In comparison. in the R IZZO model. both cases (i.e. w ith and without the

s luice gate) arc orifice flows and consequentl y do not lead to a significant decrease in water level (See

Figure 3).

This phenomenon is not apparent in the 25-year f'lood levels o r the I 00-year tlood leve ls because in

both cases. the reduction in the peak discharge rate atlribut ab le to the s luice gate does not cause a

transition in the flow regime. For the 25-year lloocl. the discharge llow wi th and w itho ut the s luice

gale does not submerge the 1-95 culvert. Therefore. the now passes through the cu lvert as a free

surface flow. The flow trans ition occurs at a higher fl ow rate, o n the on.Jcr of lhe pred icted 50-year

flood. For the 100-year flood, the predicted bcncf'it o f the s luice gate is s igni llcantl y less. The

reduction in the nood leve ls for the I 00-year flood due to the s luice gutc is approximate ly 1 ft. W ith

o r wi thout the sluice gate . the fl ood is la rge enough that the 1-95 culvert is submerged, and as a result

c reates backwater effects (i.e., flooding) upstream.

..,.

~ Paul C. Rizzo A ssociates. Inc. ~ <__ CONSULTANTS 0 By AE Date 09/1 3/1 2 Checked by GMS Date 09/20/1 2

Subject Bowman A venue Dam Sheet No._ l_9 _ of J2 H yd ro logic and H vdraulic Studv fo r Rcs izin2 Project No. 11 -4626 the U ppcr Po nd Rescrvoi r

Figure 3: Representation of hydraulic conditions at the 1-95 Culvert for the 50-year flood

(\'!' :.=

,:.

M!' i ' i

APPENDIX A

SITE INSPECTION PHOTOGRAPHS

APPENDI X A SITE INSPECTIO:--.l PHOTOG RAPHS

PHOTOGRAPH NO. 1: BOWMAN AVENUE DAM- FEBRUARY 13, 2012

'So' , . ... ~ ~ ~ / ~.... - ..! • _ ....

PHOTOGRAPH N0.2: BO\VMAN A VENUE DAM- OUTLET OPENING WITH T IJ.\IIDE R LOGS- FEBR ARY 13, 2012

PI 11 -111~6/ 1 2 A- I

APPENDIX A SITE INSPECTION PHOTOGRAPHS

PHOTOGRAPH NO.3: UPPER POND RESERVOIR-MAY 1, 2012

- -PHOTOGRAPH NO.4: RIVERVIEW AT PURCHASE CULVERT-MAY 1, 2012

Pl 11-162N12 A-2

APPENDIX A SITE INSPECTION PHOTOGRAPHS

-PHOTOGRAPH NO.5: CROSS WESTCHESTER EXPRESSWAY (1-287) CULVERT

MAY 1, 20 12

,...

""' •J:-..~ ...... :::siliCJ

PHOTOGRAPH NO. 6: BLIND BROOK DIRECTLY DOWNSTREAM OF PURCHASE STREET CULVERT- MAY 1, 2012

""'

PI 11 -16 2611 2 A-3 ~

APPENDIX A SITE INSPECTION PHOTOGRAPHS

PHOTOGRAPH NO.7: DAMAGED HOUSE ON MOHAWK STREET (INDIAN VILLAGE)MA Y l , 2012

PHOTOGI~APH NO.8: DAMAGED HOUSE ON MENDOTA AVENUE (INDIAN VILLAGE)

MAY 1, 2012

Plll --16~6112 A -4

APPENDIX A SITE I NSPECTION PHOTOGRAPHS

PHOTOGRAPH NO.9: BLI ND BROOK DRIRECTLY DOWSNTREAM OF THE HIGHLAND ROAD BRIDGE-MAY 1, 2012

PHOTOGRAPH NO. 10: NEW ENGLAND THRUWAY CULVERT (195) - NlA Y I, 2012

PI l l-l626/12 A-5

APPENDIXB

APPROXIMATE GEOGRAPHIC BOUNDARIES FOR NRCS (SCS) RAINFALL

·• DISTRffiUTIONS (FROM REFERENCE 9)

-,.

r '

APPENDIX B

a oo

III

l~ainfa l l • 11 Di<> t rib u t Jo

D Typ e I

D T ype JA

D T ype ll

D Typ e III

ffliJt I

r

APPENDIXC

BLIND BROOK WATERSHED- PHYSICAL PARAMETERS .

>­>- al roa a w w > y 0 L>a: w 0.. I 0.. (.) <(

Saran Wood)

County Pol~

LEGEND

0 Bowman Dam

CJ Subwatersheds

World Street Map

Wulthe$ter councry Club

0.5 0.5 0.25 0

~~-ril.-~--~~~~---1

Miles

DATUM: NAD 83

FIGURE C-1

Site Location and Subwatershed Delineation

PREPARED FOR PROJECTION: State Plane New York East· Feet

REFERENCE(S): ESRI World Street Map WSP Sells

Briarcli ff Manor, NY

~ Paul C. Rino Engin.:.:ring - :'\cw York. PLLC ~ -'-._ ~ ~- 1' G I ;-.; E E R S I C 0 :0.: S L" I. T A 7' T S I C M

wcr -'W U:m (/) ::; -::l C> Z

z

~[Xi 0

LEGEND 0.5 0.25 0 0.5

CJ Subwatersheds - Grassland ~--1Miles FIGURE C-2

- Deciduous Forest - MLXed Forest DATUM: NAD 83

Land Use and Land Cover Types - Developed, High Intensity - Open Water PROJECTION: Slate Plane New York East· Foet

r-1 Developed. Low Intensity r-1 Pasture l.__j L-.1 REFERENCE(S) : Unned States Geological SUJvey,

Developed. Medium Intensity - Shrub 2011 , "LBCD 2006 Land Cover", 1st ed., http://www.mrlc.gov/nlcd2006.php CJ Developed, Open Space - Woody Wetlands

- Evergreen Forest

PREPARED FOR

WSP Sells

Briarcliff Manor, NY

~ Paul C. R.izzo Engineering - :--.cw York. PLLC 1- '---. ~ E t'o: <.: t :-.; E E H S I <.: n J' S l! I. rANT S I C M

UJC:: -'UJ U: CD en=< - => <.? Z

>­>- CD me 0 UJ

\!:! 6 <.> c:: UJ a. :r: a. <.> <(

LEGEND

c::J Subwatersheds

CJ Soii TypeB

- SoiiType C

DATUM: NAD 83 PROJECTION: State Plane New York East· Feet

0.5 0.5 0.25 0

~~~-~~~-~-ril.~~~~liiiiiliiiiiiiiiil' Miles

REFERENCE(S): Natural Resources Conservation Serv1ce.2006. "Digital General Soil Map of U.S.". NY and CT, US Department of Agriculture. http://soildatamart.nrcs.usda.gov

FIGURE C-3

STATSGO Soils (Hydro Group ID)

PREPARED FOR

WSP Sells

Briarcliff Manor, NY

~ P~d C. Rizzll En~ll.:.:ring - :-.:~.:w York. PLLC ~ -~ ~ki'G I 1\:EEHS I CO~S l i i. T A:-:T S I CM

Table C-1

Composite Curve Number Result Summary

Subwatenhed Land Use Soil CN Area (sq It) I Area (sq mil I" In Basin iTotal Area (sq mil I Composite CN Bowman Dam_ISWll ·---

)Deciduous Forest -L ·--- --l-l B SS 143,6S6 0.00521

C ___ 70 ~.SIS,___ 0:~

8 81 119,51S 0.0043

_,c __ j 8.sj _ 1,!4_8.90Sj~ o.oml --- --- ·Developed, Hish Intensity

B _l_6Sj __3!5.,116 ___ 0.0113 c 77. ___ 7,323,19_2~- 0.2627 B ___ 70. -~884~--- 0.0060' ----

-·---· --!Developed, Lo~·lntensity - ----, ·---- -----

1-287(SW4)

---;Developed, Medium Intensity C 80 4,043,798 0.14Sl

--~,8-~, 61•1,--- 771.463;- ----0.0277 __ _ ·Developed,OpenSpace - --· --~-- --· -

-~,-------- --- ~ ~:. - .. lS,l~~:!:i - - :::~_2!1 -~ Evers:reen Forest ,

·'--~·- 70. ___ 3,380,8~-' -- 0~ Mixed Forest

Open Water i Pasture

-!shrub

---.Deciduous Fore-st

c 70 319.806 0.0115 ·c 100 ~2s7 --- oooro--

jc I_74J _E!-2171 _ O.OllS, _ jc I 6sl 106,5621 o.oo381

-~1 5s1-- 133.8771- - oOO.Isl --·c ·~--7o· ~.467. --- 00678

---- Developed, High Intensity B 81-~ 401,384,_ 0.0144

-t~ f_ ···- !~~- - s!~:~~i_i -___ ~:::'----!----

Developed, Low Intensity .c __ ' _77, 10,068,4SO. --- 0.36.,_1:::2,_ __

----- ~Developed, Medium Intensity 8 70 642.086 0.0230 c ----sO· - 4,237,936:-=- 0~

--- -~·Developed, Open Space

Evergreen Forest

B 61 2S4,64lj 0.00911 C 74 ~~3,413] ___ O.Sl74 --C SS 324,841 0.0-11-7-. --

--- -~nd --- C 74 ISS.ooO-- 0.0056 • ---·Open Water 8 100 96,558 0.00=35:----[c ___ 100i ---19,691) ____ 0.0007,

Purchase St (SWS! Ia ssl ~mj_ o.Ol49~ Deciduous Forest --- --- -·Oe've~ghlntensity B 81 ___ l_,S74,872;___ 00~

---- ·Developed, low Intensity 8 6S s.02S.071 0.1802 ,c ---77· 91,6S3 00033

___ ~ped~Med1um Intensity

1_____ _ -J~roped, Open Space

'Evergreen Forest

l i 701 S,6S9,17ll ~ 0.2030 l 80 717,263 0~ 1-61 --- S,39S,997r- 0.1936

i_e ____ ss: --w6.s62 --- o.oo38

I-9S(SW6) Deciduous Forest B SS S99,4Sl ;--

-- -~J)ed,l1!8-hlntensity iii---, -81, ---m..ml ----o.imsj: __ _ 0.0063 0.08951 [De~d.Lowlntensity -ra--j 6s[ 2,49S,ssi: _

----====~-lDeveloped, Mtdium Intensity 'B 70 l,02l,S64 __ 0.0366 Developed, Open Space B 61 ___ 7_.230,S4I~--Evergreen Forest

Unc:oln Ave (SW.=,21.__ __ _

Deciduous Fore="----,---­Develaped, Hig~_lntensity___ Developed, Low Intensity

; Developed, Mtdi""' lntensoty j Developed, Open Space

- =vergreen Fores_i __ _ Grassland ·--- --- ··-- ---·

Mi•ed Forest

.B ssi 674,4831

~~--,1~ j j ·'--- 70 ·. 23,S37,217 -=== c 8S 1.194,454, c 77 ~96,4Sl:=--

80, 3,43S,645

j't=t 741 41,403,8SO.:-_ c 70 ~02,9211----c 74 1,038,098 ·c- - 101 - · 3,290,49s;_

,C

Open Water C 100 12S,937 Pasture ---- C ---74· -----xK;,021i

_W_o_o_d_y Wetia~ds -re----i SOl 222,812~1---

0.2S~

0.0242:

0.844~-004~1--0.41U 0.1232 1.4852

0.1~

0~ 0.1180 0.004S 00110j __ _

o.OOSOI Blind Brook CC (SW1) _L_____l I :

Deciduous Forest -[C ; 70[. _ 14,739.677----=:._ .. O.S287

__ ---~~loped, High lntens_ity__ c 8S 4,433,6().1~- O.IS50 Developed, Low Intensity C 77, 8,S72,354, 0.307SL--

------j'Developed, Medium Intensity :,---~ -8oj ~.3691 ·--- 0.324S~ ·s T"6li --·· · io.664 -- o.0004 Oevelaped, Open Space ·,-~- 74• 16.476,863 --· o~

____ --~ergreen Fore51_ 'c ---70. -699.179•---- 002Sl' Grassland 'c ---74. ------s33,845-- 0.0191

jMixed Forest k --~-. -7ol' . 2,S99 .• 2.s7' ---- 0.0932

-~ ----- _)C L_!4 - ~~S,93j~ 0.004S jshrub :C I 6S 319,687 0.011S Woody Wetlands 'C

1 90 1,007,498 0.0361

0.3S% IS.61% 0.29% 4.ii6%i--· 0.78_%_1 ---

18~ C.41% 9.96% 1.90%,

37.77%1- -0.20% ·----8.32% --·---0.79% 0.48% 0.79%i __ ,

0.~ j __

0.40%

S.68% 1.21% l.SS%, 0 29%;---------

3027% 193%

12 74% 077%·

- ·---43.37%

0.98% 047% 029% 00~

2.19%1 8.29%

26.47% 0.48%

29.810j6~ 3.78%1

28.42%1 O.S6%

4.91% 1.44%:

20.46% 8.38%

59.28% S.S3%1

I 25.7~

1.31% 12.57%

3.76% 4S.l7%,

s.91%[ --

~~ 3.60% 0.14% 0.33% -----0.24%

2S.l7% 7.S7')(,

14.64%;

IS.4S%1-0.02%

2~ 1.!9% 0.91% 4.44%, ·----0.22%1 O.SS%[ 1.72%1

J __

+-=_

----1.457-1~i ---

_, __

----1.1930:-----

__ I

·---~-

0.6810

-L o.un;---

I-t

) __ _ 3.28051

; ___ _

2.1007

-

----

--

--

-

74.28

-

-

·-

--

-

--

-

-

--67.03

-

·-

-

--

-

-

-

-

··--

---

-

75.19

APPENDIXD

RESIZED UPPER POND ALTERNATIVES

r

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CD I

ill N ill ..r I

w -"" -w "-m o::. <(:::J oz

wm <C3:

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oD wW :,:> oO w"' Ill. o!;,:

792000.

791900

791300

791200

791100

791000

790900

790700

::: ::: ::: '" '" '" 0 "' "' 0 0 0 0 0 0 0 0

\ \

::: ::: '" '" ... '" 0 0 0 0

\

::: '" 0> 0 0

::: ~ 0 0

::: ~ 0 0

::: "' ~ 0

::: "' ;!> 0

.I

ELEVATION[ AREA RELATIONSHIP

ELEVATIONS AREA (ft) (ACRES)

41 5.59

42 7.47

43 9.77

44 10.74

45 11.16 46 11.50

47 11.87 48 12.22 49 12.50 50 12.76 51 13.01 52 13.27 53 13.51 54 13.77 55 14.04 56 14.33 57 14.69 58 15.21 59 15.82 60 16.50 61 17.71 62 18.56

NOTE:

1. Projection is NAD83 New York State Plane, East Zone, US foot.

S CAL E ------150 0 150 FEET

FIGURE D-1

NORMAL RESIZED POOL SCENARIO BOWMAN AVENUE DAM SITE

UPPER POND RESERVOIR RESIZING PROJECT

PREPARED FOR

WSP SELLS MANOR, NEW YORK

~ Paul C. Rizzo Associates, Inc. ~ ~ENGINEERS/CONSULTANTS/CM

]

]

]

]

J J ]

J J J J J J J J J J J ,J

N m I

(!) N (!)

"'" I

z ;;::,_ 02(!) 0

792000

791300 .•

791200

791100

791000

790800

790700

::; ::; " ::; ::; ::; " ::; ::; ::; ~ "' "' "' "' "' "' "l "' "' "' "' "' "' "' "' "' ,. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

.-_/-

,,,, ' i-:

,.-, ,{

" "' "' 0 0

ELEVATION(,_ AREA RELATIONSHIP

39 5.50

40 7.67

41 8.57

42 9.60

43 10.25

44 10.78

45 11.22

46 11.55

47 11.93

48 12.27

49 12.56

50 12.84

51 13.10

52 13.35

53 13.60

54 13.85

55 14.12 56 14.41

57 14.75

58 15.22

59 15.82

60 16.51 61 17.87 62 18.64

NOTE:

1. Projection is NAD83 New York State Plane, East Zone, US foot.

S C A L E ------150 0 150 FEET

FIGURE D-2

MAXIMUM POOL ELEVATION AREAS BOWMAN AVENUE DAM SITE

UPPER POND RESERVOIR RESIZING PROJECT

PREPARED FOR

WSP SELLS MANOR, NEW YORK

~ Paul C. Rizzo Associates, Inc. ~ <_ENGINEERS I CONSULTANTS I CM

APPENDIXE

PLAN VIEW OF BOTH THE 2006 FEMA HEC­. RAS MODEL AND RIZZO HEC-RAS MODEL

WITH ORTHOIMAGERY

. . ~ ·.• ·~ .,

. -· lf.iif.il U.S. Arm~ Corps of En~:ineers ~ .\'cw York Dist rict

FIGURE E·l Plan View of2006 ·fEMA HEC·RAS Mod el

~ .. ' .. · Labeled Cross Section Locutions

(2006 FEMA Study)

Legend

--- Cross S.:ctions

r=J Subbasins Modeled

Ulind13 nx>k ~111~

OS u 1S U HS

Doh· Figure l'o.

~lar 2UU<) 4

LEGEND

-- Stream Centerl ine

-- Bridges

- lnlineStructures

-- XS Cutlines

Blocked Obstructions

.. Ineffective Flow Areas

0. 10.05 0 0. 1 0.2 ~P"'!§ii-~-5i-~~5iiiiiiiiiiiiil' l'.lfes

DATUM: NAD 83 PROJECTION: UTM Zone 18N

REFERENCE(S): ESRI World Imagery

FIGURE E-2

Plan View of RIZZO HEC-RAS Model with Orthoimagery

PREPARED FOR

WSP Sells Briarcliff Manor, NY

APPENDIXF

GIS DATA

r @

If" m t

r [

r r r

APPENDIXG

RIZZO HEC-HMS MODEL

r t

r {

i

r

APPENDIX H.

RIZZO HEC-RAS MODEL