HomeMy WebLinkAboutConsultant Review - 12 MASSACHUSETTS AVENUE 9/19/1996 (3) Mobil Gas Station
Storm Drainage Calculations
PREPARED FOR
MOBIL OIL CORPORATION
3225 GALLOWS ROAD
FAIRFAX, VA 22037
12 Massachusetts Avenue
North Andover, Massachusetts
Prepared by:
Tyree Consulting Co.
9 Otis Street
Westborough, Massachusetts 01581
July, 1996
01A OF Af,
STEPHEN
P. �e
DeCOURSEY
CIVIL
No. 3642-
MA
TABLE OF CONTENTS
Page
Drainage Report:
1. Introduction............................................................................................................................1
2. Methodology..........................................................................................................................1
3. Existing Conditions................................................................................................................1
4. Proposed Conditions..............................................................................................................3
5. Conclusions............................................................................................................................4
Supplements:
A. Storm Runoff Calculation Worksheets and Drainage Area Maps
DRAINAGE REPORT
INTRODUCTION
This report provides an analysis of the existing and proposed site drainage
associated with the re-development of a Mobil Oil gas station and
convenience store. The study establishes and compares pre- and post-
development peak rates of storm runoff for the 10, 25 and 100-year design
storms.
Drainage impacts of the proposed development and measures to mitigate any
adverse environmental affects are addressed in this report.
2. METHODOLOGY
This report examines the site under existing and proposed conditions for the
10, 25 and 100-year storm events. TR-55, Urban Hydrology for Small
Watersheds (Massachusetts Department of Public Works Highway Design
Manual/USDA-Soil Conservation Service) was used to estimate peak rates of
runoff. See Supplement A for runoff calculation worksheets. The rainfall
intensities were determined from the USDA-Soil Conservation Service
rainfall distribution tables.
3. EXISTING CONDITIONS
The site is located on Massachusetts Avenue in Andover, Massachusetts. The
property is triangular in shape and is bound on its three sides by
Massachusetts Avenue, the Shawsheen River, and the Lawrence Savings
Bank.
The site is currently developed with a 1500 square foot Mobil service station,
a gasoline pump island with two multi-hosed dispensers, a canopy over the
pump island, parking, and other facilities relating to the gas station. The site
is surrounded by a six foot high wooden fence along the river and savings
bank sides. The area around the service station is paved with bituminous
concrete. The area beyond the wooden fence along the Shawsheen River is
undeveloped.
The area of the site from the building forward drains into Massachusetts
Avenue and enters the storm drain system through an existing inlet. The
remainder of the site drains into the Shawsheen River. These are referred to
as Drainage Areas 2 and 1, respectively. See the attached Drainage Plan.
Runoff Quantities
A stormwater analysis was performed to calculate pre-development runoff
rates for the 10, 25 and 100-year storm events using the USDA-SCS TR-55
Method. This methodology is recommended in the Massachusetts DPW
Highway Design Manual previously referenced. The pre-development peak
rates of runoff are presented in Table 1. (Refer to Supplement A for
calculations.)
Table 1 PRE-DEVELOPMENT STORMWATER RUNOFF RATES
Runoff rates by Storm Event(cfs).t
10-Year 25-Year 100-Year
Drainage Area 1 1.60 1.89 2.35
Drainage Area 2 0.62 0.71 0.87
Total 2.22 2.60 3.22
* cfs=cubic feet per second
2
4. PROPOSED CONDITIONS
Under proposed conditions, the existing building will be demolished and a
new 1200 square foot building constructed further back on the site. -An
additional pump island and canopy will be installed adjacent to the existing
pump island. The existing pavement will be patched as required. Where
possible, existing pavement will be removed and replaced with landscaping.
There will be no work beyond the existing limits of development. The
drainage pattern for the site will remain essentially unchanged from the
existing to the developed condition.
Runoff Quantities
The stormwater analysis for proposed conditions was performed for the 10,
25 and 100-year storm events using the USDA-SCS TR-55 method. The
post-development runoff rates are listed in Table 2.
Table 2 POST-DEVELOPMENT STORMWATER RUNOFF RATES
Runoff rates by Storm EventLc—fs)—*
10-Year 25-Ye 100-Year
Drainage Area 1 1.51 1.85 2.27
Drainage Area 2 0.31 0.36 0.43
TOTAL 1.82 2.21 2.70
cfs=cubic feet per second
3
5. CONCLUSIONS
The proposed development will result in a slight decrease of the peak rate of
runoff from the pre-development condition for the 10, 25 and 100-year storm,
events under the post-development condition. A comparison of pre-
development and post-development conditions are presented in Table 3.
Table 3 STORMWATER RUNOFF RATE SUMMARY
Development
Condition Runoff rates by Storm Event(cfsZ*
10-Year 25-Year 100-Year
Pre-development 2.22 2.60 3.22
Post-development 1.82 2.21 2.70
Difference -0.40 -0.39 -0.52
The overall decrease in peak runoff rates is due to the additional landscaped
areas proposed for the site. Additionally,these landscaped areas will improve
the quality of stormwater runoff from the site.
4
Supplement A
Storm Runoff Calculation Worksheets and Drainage Area Maps
Worksheet 2: Runoff curve number and runoff
Project r4,0 L' *5A 01- 361 By. SS(L Date
Location POILI J MA Checked Date
Circle one: Present Developed 19AAtaA6r-- AkX A
1. Runoff curve number (CN)
Soil name Cover description 1/ Area Product
and CN — of
hydrologic (cover type, treatment, and CN x area
group hydrologic condition; C"4 `I i m acres
percent impervious; m N `V ❑mi2
unconnected/connected impervious p oa ❑
(appendix A) area ratio) F, -H w
U r. /NtP,4:-A--L,,l b V S ,V SPAA d
C, 1'9440P� Akr,A
lv-b"
LW
G �v000 p A"A 9�
NfbkA WAA
1/ Use only one CN source per line. Totals = 0. 3-7 3y 3 O
CN (weighted) = total product - ?7 = 9a�7 Use CN = `J3
total area 6?,-b7 ;
2. Runoff
Storm #1 Storm #2 Storm #3
Frequency yr /b /01)
Rainfall, P (24-hour) .. . .. .. . .. . ... . . . . in G,
Runoff, Q .... .. .. . ... . . .. in 318 S�
(Use P and CN with table 2-1, fig. 2-1,
or eqs. 2-3 and 2-4.)
ll-2 (210-VI TR-55, Second Ed., June 1986)
Worksheet 3: Time of concentration (Tc) or travel time (Tt)
Project WJjL -K A.p'� 7J5
By SS(L Date ? 6 b
Location PPAA MA Checked Date
CLCCIe one: Present Developed 'PAAINA6g A�� i
Circle one: Tc T through subarea
NOTES: Space for as many as two segments per flow type can be used for each
worksheet.
Include a map, schematic, or description of flow segments.
Sheet flow (Applicable to Tc only) Segment ID AQ bG
$hwD7/.1 WovnS
1. Surface description (table 3-1) v
2. Manning's roughness coeff., n (table 3-1) .. a' 0/I U
3. Flow length, L (total L < 300 ft) ......... .
ft
4. Two-yr 24-hr rainfall, P2 .................. in 7jrU 3�a
5. Land slope, s ............ ................. . ft/ft 603
6. T = 0.007 (nL)0.8 Compute T ..... hr '0� + F b�
t P 0.5 s0.4 t .
2
Shallow concentrated flow Segment ID
7.. Surface description (paved or unpaved)
8. Flow length, L ....... .... ..... ............. ft
9. Watercourse slope, s ....................... ft/ft
10. Average velocity, V (figure 3-1) ft/s L
=
L hr +
_
11. Tt 3600 V Compute Tt ......
Channel flow Segment ID
12. Cross sectional flow area, a ......... .... .. ft 2
13. Wetted perimeter, p w . ....... ............... ft
14. Hydraulic radius, r = a Compute r .. ... .. ft
Pa
15. Channel slope, s ..... ....... ..... .... ... . .. ft/ft
16. Manning's roughness coeff., n ....... . ... . ..
1.49 r2/3 s1/2
11. V = Compute V ..... . . ft/s
n
18. Flow length, L ....... ... .. .. .... . .... . .. . . . ft
L + _
19. T = Compute Tt hr
t 3600 V O, 07
20. Watershed or subarea T or T (add T in steps 6, 11, and 19) .. ..... 11r
LjSC 0.1 Ar• M)f-))W(Y\
"ti X72-55
Cnrruvi Rd .Tnno 1AR(:)
Worksheet 4: Graphical Peak Discharge method
Project q) 3�' 9 By S 2 Date
Location Nbl�-yl� gNooyt�(L� mA Checked Date
Circle one: Gs; Developed nAA1/)A6 AA-,C-4 I
1. Data.
Drainage area
Am --
o. OpO mil (acres/640)
Runoff curve number .... CN = l 3 (From worksheet 2)
Time of concentration .. Tc = Oa / hr (From worksheet 3)
Rainfall distribution type = (I, IA, II, III)
Pond and swamp areas spread
throughout watershed = D percent of A 2
P m (__ acres or. mi- covered)
Storm Il Storm #2 Storm /i3
2. Frequency . . . . . ... ... ... .. . . .. . . . . . . . . . .. yr /P Z 5 /PO
3. Rainfall, P (24-hour) ... . . . .. . . . . . .. . . .. in yi� S 3 �,
'�. Initial abstraction, I . . .
a in b./���_ 0,151
(Us.e CN _wi th* table 4-1.
5. Compute Ia/P G �'�� 0, Oa6
6. Unit peak discharge, q csm/in 7Dd 7bD 7dj�
(Use T and Ia/P with exhibit 4- )
..Runoff, Q .. .. in 3. 8
'-('From worksheet.2). •. • ••.. • . •. . .. .. . . . • ..
8. Pond and swamp adjustment factor, F . ... /
(Use percent pond and swamp area p
with table 4-2. Factor is 1.0 for
zero percent pond and swamp area.)
9. Peak discharge, q cfs
(Where qp = quAmQF )
P
D-4 (210-VI-TR-55, Second EA., June 198(1)
Worksheet 2: Runoff curve number and runoff
Project a1-38 By. 559 Date 7 �6
Location QVArN At-16Ov�VL/ MA Checked Date
Circle one: Present Developed -p1VAltdA6r-- / "A
1. Runoff curve number (CN)
Soil name Cover description Area Product
and CN 1/ of
hydrologic (cover type, treatment, and M CN x area
group _ hydrologic condition; cu i acres
percent impervious; W N ❑mi2
unconnected/connected impervious p �O oO ❑7
(appendix A) area ratio) H w w
PA&114 tJG— a
v�
(LAIMJ �vbvoo Aroma - 66no Gvao�rnnl 70 0,07
(1)i6AA(.ait�l� 8 d.l /3.7Z
G w�Z 9
(v�sun L a�d� OPT SPA 1-�—
`- G 6 bvU Gp�JOl7`tirJ
1/ Use only one CN source per line. Totals =
CN (weighted) = total product -317,247. = 9p. 9 Use CN = / '
total area p,y�
2. Runoff
Storm 111 Storm ,12 Storm #3
Frequency .. .... . . . . . . . .. . . . .. . . .. ... ... yr o
Rainfall, P (24-hour) . . . . . . .. . . . . . . . .. . in y S 3
Runoff, Q .. ..... .. .... ... . ... .. ..... ... in 3, � y 5,`I
(Use P and CN with table 2-1, fig. 2-1,
or eqs. 2-3 and 2-4.)
D-2 (210-V1-`I'R-55, Second Ed., June 1986)
Worksheet 3: Time of concentration (Td or travel time (Tt)
Project L 65,�( OI��JS J By SS2 Date
Location NPti'N Aa0uVr,-(L 1 h'lA Checked Date
Circle one: Present eveloped -P)F_A NAd j!� /4A-EA )X
Circle one: T T through subarea
NOTES: Space for as many as two segments per flow type can be used for each
worksheet.
Include a map, schematic, or description of flow segments.
Sheet flow (Applicable to T only) Segment ID A9
Sht.OD't
1. Surface description (table 3-1)
2. Manning's roughness coeff., n (table 3-1)
3. Flow length, L (total L < 300 ft) ......... . ft �0
4. Two-yr 24-hr rainfall, P2 in 3.0
5. Land slope, s ......................... .... . ft/ft
6. T = 0.007 (nL)0.8 +
Compute Tt hr
t P 0.5 s0.4
2
Shallow concentrated flow Segment ID C� GL?
� - 7. Surface description (paved or unpaved) .... .
&44S!5 -W P0105
8. Flow length, L ft 661 3,L
9. Watercourse slope, s .............. .... .....- ft/ft 0,01 0-7,5
10. Average velocity, V (figure 3-1) ft/s /40
11. Tt 3600 V Compute Tt ...... hr "� +
Channel flow Segment ID
12. Cross sectional flow area, a ............. .. ft2
13. Wetted perimeter, p w ........ .... ...... ..... ft
14. Hydraulic radius, r = a Compute r .. ... .. ft
p
w
15. Channel slope, s ..... .. .. ... . ... . . ... . .. . . . ft/ft
16. Manning's roughness coeff., n . .. ... . . . .. . ..
1.49 r2/3 sl/2
17. V = n Compute V .. .. . . . ft/s
18. Flow length, L ... .... .... ... . ... . . . .. . ... . . ft
19. Tr 3600 V Compute Tt hr +
20. Watershed or subarea T or T (add T in steps 6, 11, and 19) ....... hr
Vsg b, l hf-. MIN1nWM
(?.1(1•Vl-TR•f,:� CP/`f,Tlfl T"d ,Tenn 19R(i1 I) ;
Worksheet 4: Graphical Peak Discharge method
Project r'bV64- a
\ � 3�9 By Date
Location tJ0arN Aaoov /t M/� Checked
Date
Circle one: Present Developed D/U41NAGf-- AI(,C,� itf I
1. Data:
Drainage area .. . . . . .. . . A = 0, 9000 2
' m mi (acres/640)
Runoff curve number .... CN = 91
_________ (From worksheet 2)
Time of concentration .. T = hr (From worksheet 3)
Rainfall distribution type -
'J�-� (I, IA, II, III)
Pond and swamp areas spread
throughout watershed = percent of A
P m ( acres or mil covered)
Storm 1 Storm #2 Storm #3
2. Frequency A
3. Rainfall, P (24-hour) ... .. .. .. . . . .. . . . . . in
Initial abstraction I
�. . ., . _ a . . . . .. .. . .. . . . .. .in O. /9g 0'/98
(USe CN .with' table 4-1.)
5. Compute I /P
6. Unit peak discharge, q 7b
csm/in ?DD �aU
(Use T and I a/P with exhibit.. ... ..... .. . . . ..
Runoff, Q .. . . . . .. .. . . .... . . .. .. . . . . . . . ..
in
-'(From worksheet 2)
8. Pond and swamp adjustment factor, F
(Use percent pond and swamp area P ! r
with table 4-2. Factor is 1.0 for
zero percent pond and swamp area.)
9. Peak discharge, q cfs
P .. . . .. . . . . . . . . . . . . . ... .
(Where qP = quAmQF )
P
D-4 (210-VI-11R-55, Second E'd., June
I
Worksheet 2: Runoff curve number and runoff
Project Ma��l 55 O)-3 bq By.�� Date G6 d
Location Nvfi-A A/JDOOe4IN1A Checked Date
Circle one: Present Developed PkAI NA
1. Runoff curve number (CN)
Soil name Cover description 1/ Area Product
and CN — of
hydrologic (cover type, treatment, and cv CN x area
group hydrologic condition; N `i' i ®acres
percent impervious; a) `4 `V ❑mi2
unconnected/connected impervious .4n oO 0O ❑%
(appendix A) area ratio) `� -H If
H W 44
(urbort4,14) � nv ,osP,V Air qP o, i2
4A 7� o,Ob 3 o a�;z
6 bP o �or�A� pnl
s�a`sDS
1/ Use only one CN source per line. Totals =
CN (weighted) = total product - /� 9g _ 97� fb Use CN = 6 �I
total area
2. Runoff
Storm #1 Storm #2 Storm #3
Frequency .. .. .. .. .. . . . .. . .. .. . ... .. . . .. yr /D ZS /DD
Rainfall, P (24-hour) .. . . . . . . .. . . . . . . . . in y t�L
Runoff, Q .... . ........ . . . .... ..... . .. .. in �' 7 5
(Use P and CN with table 2-1, fig. 2-1,
or eqs. 2-3 and 2-4.)
D-2 (210-VI-,rR-55, Second Ed., June 198(1)
Worksheet 3: Time of concentration (Tc) or travel time 7t)
Project (9D(�)L SSA` Ol- $g By Sj Date )h 1
Location
I)Dh7AAN.00vL,!?.-/ IVIA Checked Date
Circle one: EE Developed D4,A1PA b QA-6A * 2
Circle one: Tc T t through subarea
NOTES: Space for as many as two segments per flow type can be used for each
worksheet.
Include a map, schematic, or description of flow segments.
Sheet flow (Applicable to T only) Segment ID 6-
srLov-fN -
1. Surface description (table 3-1) ............ QAv y
2. Manning's roughness coeff., n (table 3-1) .. 0,0//
3. Flow length, L (total L < 300 ft) .......... ft
p
4. Two-yr 24-hr rainfall, P2 ............ ...... in
5. Land slope, s ....................... ....... ft/ft 'd 2
Z
6. Tt = 0.0075(nL0)4 0.8 Compute Tt ,,,,,, hr +
� D
• P 0
2 s
Shallow concentrated flow Segment ID
7. Surface description (paved or unpaved) ..... --
8. Flow length, L ............................. ft
9. Watercourse slope, s ....................... ft/ft
10. Average velocity, V (figure 3-1) ... .. ... ... ft/s
11. Tt = 3600 V Compute Tr ...... hr + -
Channel flow Segment ID
12. Cross sectional flow area, a ft
13. Wetted perimeter, p ............... . ... .... ft
14. Hydraulic radius, r = a Compute r ....... ft
p
w
15. Channel slope, s .... . ... ..... .... .. . . .. . ... ft/ft
16. Manning's roughness coeff., n ... ... . . .. . . ..
1.49 r2/3 sl/2
17. V = Compute V .. . .. . . ft/s
n
18. Flow length, L ... .... ........ .... .. . .. .. . .. ft
19. Tt 3600 V Compute Tt hr +
20. Watershed or subarea Tc or Tt (add Tt in steps 6, 11, and 19) .... .. . 11
Vle ail kr, MJN11YVJM
ion. -C2-55
('?1O•VL•TR•S:: Cn(-nnrl rd Jiit)o 19R(;1 �) '�
Worksheet 4: Graphical Peak Discharge method
Project73� By 5�5fZ Date 6
Location 0Dl1 4 A,JOPyr-_a ,MA Checked Date
Circle one: resent Developed t21LA 0,64 q/1.6A
1. Data: r
Drainage area . ... . . . . . . Am = b•OD O 2 mil (acres/640)
Runoff curve number . ... CN = 71 (From worksheet 2)
Time of concentration .. T = �� � hr (From worksheet 3)
Rainfall distribution type = (I, IA, II, III)
Pond and swamp areas spread
throughout watershed = D percent of m ( acres or mil covered)
Storm I1 Storm #2 Storm #3
2. Frequency .. . . . . ... .. . .. .. .. .... . . . . .. . .. yr
3. Rainfall, P (24-hour) ... ... .. . . . . . . . . .. . in y
Initial abstraction, I in 2,06,2 0.062 O, Ob2
._.. a
(U�e CN .with' table 4-1.)
5. Compute I /P . .. .. .. ... . .. .. . . . . .. . . . . . .. O,dl'� O.b/2 0,01
6. Unit peak discharge, q u csm/in 7 Ob JO D 7o p
(Use T and Ia/P with exhibit 4- )
:.Runoff, Q .. . . . . . . .. . . . . .. . . .. .. . .. . .. .. . in
"('From worksheet 2).
8. Pond and swamp adjustment factor, F
(Use percent pond and swamp area p
with table 4-2. Factor is 1.0 for
zero percent pond and swamp area.)
9. Peak discharge, q P cfs
(Where qP = quAmQF )
P
DA (210-VI-TR-55, Second I-A., Junco 1418(1)
Worksheet 2: Runoff curve number and runoff
Project /fit P3 1L- 5.5>)*0)—'3 By• 55[1— Date -71m
9�
Location 0017"14 AooPu&/L! Checked Date
Circle one: Present Developed PITAtQAbe A1,;aA �2
1: Runoff curve number (CN)
Soil name Cover description 1� Area Product
and CN— of
hydrologic (cover type, treatment, and N CN x area
group hydrologic condition;
C'1 `i �I (�acres
percent impervious; o N N ❑mi2
unconnected/connected impervious p ❑
(appendix A) area ratio) F, w w
- �� �MP�rwtvvs A spN�t,�
(V,64n Lan d
PA",GI NCs- AAA qg a,�9 7y
(V�L44 L-and,) PA 7y APIP �.o?9b
C., Gsno C-9 t-0) PSI l
1� Use only one CN source per line. Totals = ooB g`D
CN (weighted) = total product - 8,,036 = q/ Use CN =
total area 0, 003
2. Runoff
Storm 111 Storm #2 Storm #3
�b lop
Frequency . . . ... .. .. . . . .. . .. .. .. .. .. .. . . yr 95-
Rainfall, P (24—hour) .. . .... . . . .. .. .. . . in 416-
Runoff, Q ..... ... .... .. .. .. ........ .. .. in
(Use P and CN with table 2-1, fig. 2-1,
or eqs. 2-3 and 2-4.)
D-2 (210-VI-TR-55, Second U., June 1086)
Worksheet 3: Time of concentration (Tc) or travel time (Tt)
Project 9 By Date
Location A,"40\1 41 MA Checked Date
Circle one: Present Developed Vg AIr)A 6 ri Akk1A
Circle one: Tc Tt through subarea
NOTES: Space for as many as two segments per flow type can be used for each
worksheet.
Include a map, schematic, or description of flow segments.
Sheet. flow (Applicable to Tc only) Segment ID li D
5r-owll
1. Surface description (table 3-1) AvEM G
2. Manning's roughness coeff., n (table 3-1)
3. Flow length, L (total L < 300 ft) .......... ft 6
4. Two-yr 24-hr rainfall, P2 .................. in
5. Land slope, s ........... ................... ft/ft 02
0.007 (nL)0.8 ,tj2 +
6. Tt = 0.5 0.4 Compute Tt ,...., hr
P2 s
Shallow concentrated flow Segment ID
7.. Surface description (paved or unpaved) ... .. -
8. Flow length, L .......... ................... ft
9. Watercourse slope, s .... ................... ft/ft
10. Average velocity, V (figure 3-1) ft/s
11. Tt 3600 V Compute Tt_ ...... hr +
Channel flow Segment ID
12. Cross sectional flow area, a ft
13. Wetted perimeter, p w ....................... ft
14. Hydraulic radius, r = a Compute r ... .. .. ft
p
w
15. Channel slope, s ... ..... . ... ....... .. .. . . .. ft/ft
16. Manning's roughness coeff., n . .. .... . .. . . ..
1 .49 r2/3 sl/2
11. V = n Compute V ... . . . . ft/s
18. Flow length, L ....... ... . . .. . . .. ... .. .. . . . . ft
19. Tt 3600 V Compute Tt hr +
20. Watershed or subarea Tc or Tt (add Tt in steps 6, 11, and 19) ...... . hr
\`-
0 e 0.1 {1 r. MINIMVM
C?10-V1-TR-.r)5 Cn.•nnd Fri .limn 1Qq(%) I)-3
Worksheet 4: Graphical Peak Discharge method
Project SS*D1- By 3Sf- Date
Location N�tiTN �4�pbV � Checked Date
Circle one: Present Developed V/lYikOA6P-- AAA ' 2
1. Data:
Drainage area .. . . .. .. .. Am = 0, 000/ m12 (acres/640)
Runoff curve number .... CN = 9'7 (From worksheet 2)
Time of concentration .. Tc = O, / hr (From worksheet 3)
Rainfall distribution type = (I, IA, II, III)
Pond and swamp areas spread
throughout watershed ..... . = percent of A
P m ( acres or mi2 covered)
Storm 11 Storm #2 S2. Frequency .. .. . ... ... . ... . . . .. .. . . .. .. . .. yr /d �5 3. Rainfall, P (24—hour) ... .. . .. . . . . . . . . . . . in y
Initial abstraction, I in E����O,ObZ a
(Luse dR'.with- table 4-1.)
5. Compute Ia/P
6. Unit peak discharge, qu csm/in 7DD _JDD -fab
(Use T and Ia/P with exhibit 4— )
. ', Runoff, Q . .. . . . .. . . . .. ... . . .. . . . . . . . . . .. in
--(From worksheet 2).
8. Pond and swamp adjustment factor, F
(Use percent pond and swamp area p
with table 4-2. Factor is 1.0 for
zero percent pond and swamp area.)
9. Peak discharge, q cfs
(Where qp = quAmQF )
P
D-4 (210-VI-TR-55, Second EA., JLine 1986)
p�a[ ���° .. � �r ° ip p � 'Q1� ' w�t [' [' @ !1= 1U 0. J+ �. ..1 o. d ►_
Ki
91
lit to��!�� pE t• � r 1 � it 11,1 1
`p't° ;
.a 1
pill
O ,
F ••�i�`��� � � • ,� i 11 t '
111
0
4
fill
1 PEW
r.
• .f
(000) i
W MST
cn
cn
sad
� Y