262, Construct a tennis court, Studies & Reports•
t201 S7L, 2556
FROM L. A. 772.1555
SOUTH BAY ENGINEERING CORPORATION
304 TEJON PLACE
PALOS VERDEB ESTATES. CALIFORNIA .00Y74
HYDROLOGIC
IMPACT REPORT
Proposed Residence
.for.
Mr.&Mrs.Gerald Katell.
at
#2.7 Crest .Road_
City *Of Rolling Hills
RAYMOND L.OUIOLI_Y
DONALD E. DAWSON
CONSULTING ENGINEERS
S.OUTH, SAY ENGINEERING L.ORPORATION
October 21, 1980
Hydrologic Impact Report
Introduction
This report presents the findings and conclusions of an engineering
investigation of the drainage conditions in an area north of Crest
Road and East of Johns Canyon Road. This investigation was undertaken
at the request of Linda Katell to determine the hydrologic impact that
the construction of "Proposed Residence of Mr. & Mrs. Gerald Katell"
at #27 Crest Road, City of Rolling Hills might have on the affected
drainage area.
Field Investigation
A visual inspection of the site, contiguous drainage areas, and the
off -site areas immediately downstream was made on August 25, 1980.
Topographic maps in the files of South Bay Engineering and the City
of Rolling Hills were used to aid this investigation.
Site Conditions
The 4.2 acre site at #27 Crest Road straddles an easterly to westerly
trending ridge running parallel with Crest Road. As such, the site
contributes to two drainage areas in this vicinity. The southerly
25% of the site presently drains to Crest Road. Here it combines
with off -site drainage and is conducted toward Alta Mira Canyon via
an 18" drop inlet and a 12" drop inlet located in Crest Road approximately
150 feet westerly of the site. The northerly 75% of the site, including
all existing structures, drains northerly combining with off -site drainage
to form the headwaters of the easterly branch of Agua Magna Canyon.
Site inspection reveals that this drainage pattern shows definition
beginning at approximately the northerly property line of the site.
This drainage flows on the surface, northerly through stretches of
-1-
UC1lH ZiINY-LINiGIN-Et RINo C:ORPORAT'$ON
' deep "erosion gullies" along the rear of #5 and #7 Johns Canyon Road
i
and becomes fully established as a canyon drainage channel northerly
of #7 Johns Canyon Road. See attached drainage map, figure 1.
Hydrology.
Estimated rainfall runoff was calculated using the "Rational Method"
for determining runoff. When applying the "Rational" formula, Q=CIA,
the coefficient of runoff, C, is a variable dependent on rainfall
intensity, soil condition, and cultural development. The Los Angeles
County Flood Control District (LACFCD) has graphed this coefficient
with respect to these dependent variables. The average rainfall
intensity, I, is dependent on a particular rainfall zone and storm
duration. The LACFCD has graphed this intensity for particular
hydrographic zones with respect to storm duration. Such intensities
are further characterized as that intensity which will have a statistical
probability of recurring once in a specific span of time. The total
tributary area, A, is of course dependent upon local topography and is
revealed from topographic maps and field investigation of a particular
area. The quantity of runoff, Q, is that portion of total precipitation
that appears as stream flow. For this analysis the following terms are
defined:
coefficient of runoff for single-family residential areas
Csf r=
Cimp= coefficient of runoff for effectively impervious areas
I = average rainfall intensity in inches per hour (in/hr)
I10 = average rainfall intensity (in/hr) for recurrence interval
of 10 years
A = tributary area in acres (Ac)
Aimp= tributary area for effectively impervious areas (Ac)
Asfr= tributary area for single family residential areas (Ac)
-2-
SOUTH. BAY ENGINEERING CORPORATION
t
t
i
t
Q = runoff flow in cubic feet per second (cfs)
Q10 = runoff flow in cfs for average rainfall intensity I10
Additional data was utilized from the Los Angeles County Flood Control
District Hydrology Manual.
Area A, 6.50 acres, (see Drainage Map, Figure 1) which includes 75% of
the subject site, comprises the initial drainage area for the easterly
branch of Agua Magna Canyon.
Area B, 8.34 acres, (see Drainage Map, Figure 1) which includes 25%
of the subject site may be considered as one of several initial drainage
areas of Alta Mira Canyon. It is assumed that all runoff upstream of
Area B, Area C, 6.4 acres, (see Drainage leap, Figure 1) is intercepted
by the existing 18" drop inlet located on the northerly side of Crest
Road approximately 1200 feet easterly of the site and directed to
Portuguese Canyon. Area B is intercepted by an 18" drop inlet located
on the northerly side and a 12" drop inlet located on the southerly
side of Crest Road approximately 150 feet westerly of the site and is
directed to Alta Mira Canyon.
For purposes of this analysis and comparison we have assumed a design
storm having an intensity such that the probability of recurrence is
once in ten years. For an initial time of concentration of 10 minutes,
this storm will have a probable intensity of 2.50 inches per hour. In
its present state of development, Area A is estimated to contribute
12.33 cfs of runoff from a design storm. The proposed construction on
the site would increase that portion of the site covered by impervious
materials from 0.39 acres to 0.89 acres. (See Drainage Map, Figure 2).
This construction will then increase the estimated runoff to 12.52 cfs.
�-3-
SOUTH BAY ENGINEERING CORPORATION
t
Increased runoff equals + 0.19 cfs or 1.5%.
In its present state of development,. Area B is estimated to contribute
15.65 cfs of runoff from a design storm.. The construction of the
proposed tennis court on site would increase that portion of the
site covered by impervious materials from 0.04 acres to 0.21 acres
(see Drainage Map, Figure 2). The construction will then increase
this estimated runoff to 15.72 cfs. Increased runoff equals 0.07 cfs
1 or + 0.5%.
The size and location of proposed impervious areas are shown per
Drainage Map, Figure 2.
The above quantities are summarized in Table 1 of the Appendix.
11
i
SOUTH 'BAY ENGINEERING CORPORATION
1
t
i
Conclusions and Recommendations
On -Site
Construction of the proposed improvements at #27 Crest Road will cause
relatively insignificant increases in the quantity of runoff from
either drainage area A or B. Those increases as noted are du-e to the
greater impervious area proposed to be constructed.
It is recommended that all grading and construction on site consider
the proper control and discharge of runoff. All runoff should be con-
ducted and conveyed in accordance with all applicable ordinances of
the City of Rolling Hills. All drainage should be designed to protect
slopes against saturation and erosion and not pose any potential hazard
to slope integrity. All roof drainage should be conveyed by means of
non -erodible devices to an acceptable point of discharge. The proposed
tennis court should be properly drained and the drainage conveyed by
means of non -erodible devices to a point of discharge in Crest Road.
Off -Site
Those stretches of extensive erosion, particularly along the rear
line of #5 Johns Canyon Road, would appear to be the natural result of
runoff flowing over steep terrain. While existing attempts at checking
this flow were in evidence,the practical impact of such attempts is
only very minor. Short of the installation of extensive drainage
improvements and facilities such as paved channels, closed conduits and
grading throughout the upper reaches of this drainage area, the natural
processes of erosion may be considered irreversible.
Reopening the N-S bridle trail along the rear line of #5 Johns Canyon
Road should be reviewed in consideration of the existing condition
i
-5-
SOUTH BAY ENGINEERING CORPORATION
of the trail. In our opinion, the existing steep terrain and advanced
erosion preclude a safe and serviceable bridle trail along the rear
line of #5 Johns Canyon Road.
The existing stable area at the rear of #7 Johns Canyon Road would
appear to be located within the natural drainage course. Though it is
located along much flatter reaches of the course, and no erosion was
evident in the immediate vicinity, previous flooding of this area was
apparent. To minimize the impact of flooding of the existing stable
area, consideration may be given to minor grading in the vicinity to
better define and redirect the drainage away from the stable area.
The existing E-W bridle trail along the rear of #27 Crest Road appears
reasonably unaffected by present drainage from upstream. However,
since proposed construction at #27 Crest Road may introduce new sources
of concentrated drainage, consideration should be given to discharging
such drainage downstream from the trail crossing.
t
i
APPENDIX
t
Agin /472 �a f
Canyon --
Agues MMgia Canyon
(Easterly Branch)
Arox.
Loppcofion
exisf. s/ob/e
\ \ aroma
Approx.
Loco'/icr
steep terrain
extensive
erosion ;
.
•
•
i•
••
:•
•
Exist Bridle
trail (closed)
• % -
\•
.,
•: ,Q •
•-
•ram" • • •V h�P' ,:cc;r4�f��
•
O�dt�,�
•,
•.,
eft
•
'I
1 i
•' •.••..•.w•
(a34
.•
•
•
1
••2
;d9e•.
...•-••••
•.•
••.
• •�-P6.) f 6 )
• *Pi r•40
�17
. (.p• `EQI'• ,
• (UP•
•
Apj
••
••.••' •/8"C.M.P
Ex/s/ing
impervious Areas
Drainage fo
Pcrfuguese Conyorn
FIGURE /
EX/STING CONDITIONS
DRAINAGE
MAP
SOUTH RAY
IINGINEZRINO
CORPORATION
304 TEJ01. PL_ACE
PALOS VERDES ESTATES
CALIFORNIA 90274
(213i 375-2556 711-1555
RA' MO'Q L. Qu'GtEY R.C.E. 7191
SCALE- /.,. 200' DRAWN v M.
DATE /0//3/60 CriECKED
JOB rvoJ .1215 -4A SHEET OF
4guo Magna N Canyon —S \ ,�
(
\sAgua Magna CanyonC(Easterly Branch)
Approx.
Location
exist. stable
ar o
Approx. '_„\
I
Location \'
h/ steep terrain
& extensive •
erosion
•
•
•
.
•
•
•.•.
•
•
•
•
•�
Ex,st Brid/e
trail (closed)
•
s.
•
stt
G '
\ 0 �1
....
� „03.' . 104 6
Q
. 10 OfO�t
P}
i
UP5{reAarr, of
—
' ,,o ROAD• .•/
.• •• •••
* � L
••� '• • � /8"C.M.P. .•.
•.••
Drainage to
Portuguese Canyon
Proposed Impervious Areas
FIGURE 2
PROPOSED CONDITIONS
DRAINAGE
MAP
of
SOUTH DAY,
ENG}INEZRINC
CORPORATION
304 TEJON PLACE
PALOS VERDES ESTATES
CALIFORNIA 90274
1213) 375-2556 772-1555
RAYMOND L. QUIGLEY R.C.E. 7191
SCALE: /„ = 200, DRAWN V
DATE ,,, / We„ By CHECKED A4. t. ,
JOB NO
J'1215-4A SHEET OF
an 111111 '.
Existing Proposed Existing Proposed Proposed Proposed
Drainage Tributary TributaryRunoff Runoff Delta Delta
Area Area(Ac) Area(Ac, (cfs) (cfs) Runoff(cfs) %
A zA As R Amp Q,o Q w
A(6.50Ac) 0.39 6.11 0.89 5.61
8(8.34Ac) 0.04 8.30 0.21 8.13
12.33 12.52
15.65 15.72
TABLE 1
+0.19
+0.07
:=r�v1f+'citrrr�a"C.'s7rrYt7'FiKreVi�i
t
t
I,.s S c'ts
/i z,a9eewB
- 180
168
- 10,000
- 8,000
156 , - 6,000
i - 5,000
• 144 ! - 4,000
- 132 3,000
>F
-120 0 -
- 2,000
-108 -' -
s•
- J
ot
-96 •-
- 84 it - 600
- 500
- 400
tIn.t - 300
s -
- 60 -t- 4.)- 200
=
-54 0 =
0- W -too
-
-48 ¢ -80'
-J -
0
0o -60
- 1,000
- 800
- 72
EXAMPLE
0.34'ech•s (3.0 too)
0.46ets
Nf• M11
0 Met)
11) 1.11 3.4 t- 4.
(2! 2.1 6.3
13) 2.2 4.6 L
f- 3-
.0 la fat
I C (1) Hoodoo
SIANUARV G la
2.3ciS
2"�'.r..veeAl ' )
-42 �N -50
c o - 40
36 - 30 H SCALE ENTRANC
W 0 TYPE
c -33•
cZte7 MAX =
(4pSTR /
Ao2.4A C
av
{21 Yit N t• calf eta
,• slops
- 27 - 10 (3) ►r•jectl•,
_-e
-24 -6
- 5 • ese scuts (2) or (3) project
- 21 - 4 s•r.lsstsllt to onto (1), tNe
/2,.5-c�s
Q,A/.Er, A141, = /SS'.t2, 3
Ale q 6
use str•igttt istli••t lies t•,s, h
0 •N 0 st•1•s, or r•ssra so
illy str•tid.
/.8
2.
oi-
-- f1.5
L _
Q� -1.5 -1.5
(1)
- 6.
(2)
- 5. - 6-
- 5.
(3)
- 6.
4. - 5.
- 3.
- 4.
- 3.
- 2. - 2.
z
0
z�
.7 -.7
-.7
�- .6
-.6
-.5
-.6
-.5
HEADWATER DEPTH FOR
C. M. PIPE CULVERTS
WITH INLET CCNTROL
SOUTH B A Y
ZNGINZZR ING
CORPORATION
304 TEJON PLACE
PALOS VERDES ESTATES
CALIFORNIA 90274
31Ia(213) 375-2556 772-1555
RAYMOND L. QUIGLEY R.C.E. 7191
2e�vicet:
ease.
estaly 4J?-.- • es:46 " •
!a•L' geo /C-.49.&). - - ;
eaeoe.emice;
•
,adv mie I J / 4,%4 i''d_f/_ /-/4-817 _ _
•y
JOB NO.:
JOB TITLE: /1/de'00,1 574a, . Zvi
- DATE:
/0-/2.80
(`ZT Cfeedr /GCJAv SCALE:
At.1Q j./441/.r,
cq
SHEET: 4OF
€�/•✓%// Z;s e •
•
&/Ced1.4640440,1)
-'-acv--4/a" 47" 7.->t1:1,-
./.(kAl?es.•\k-/..11/4/Aii.
BOVTH BAY
=NGZNXZRXNG
CORPORATION
304 TEJON PLACE
PALOS VERDES ESTATES
CALIFORNIA 90274
(213) 375-2556 772-1555
RAYMONO L. QUIGLEY R.C.E. 7191
JOB TITLE:
10 It 6:1/#11
. M�•rsi/ct .
•
,4mr = �• SAG.: .
. a39,de
4, /A4,0 401,1= • D • 99,4c •
:2 f476xAi"
r-s2V(g5)(6•//) A.620)(25)639) .= ig 3304
JOB NO.:_ ,,,,��
.r,2105 -211
DATE:
10—lL.-
SCALE:
SHEET:
2 OF 1
/"V/a Q.CF, 74 41; /AP
(zJ(;X") 7'(D.90)(248V _ /2, s2 0,6
QxE>r = 452 -/233 = a, /90
/23
/5%
SOUTH BAT
ENGINEERING
CORPORATION
304 TEJON PLACE
PALOS VERDES ESTATES
CALIFORNIA 90274
310 (2131 375-2556 772-1555
RAYMONO L. QUIGLEY R.C.E. 7191
.2JvA/aGE/v eo
Q.r_k74 •
JOB TITLE:
Ci drool
C,5•19c; =-�:
112r7. = g 3.Qc
•
p,, .•y�is'v ,rr, . � CA2l' .ac
Q• 17 C )(1.5) 01.-V .n.'.(°)(2°,5.)(C1.1)
i
Q4e ��n/i „".
- (y)(;5)q./41.---.� , ia)((.$)(2/�
•
. • . .
• • • - • •
d =' S7Z- /s6s I0,07
Q Q�r � 9rr�� /
-JOB-NO.:
f"/2/S'2A
•----- DATE:
•
I•I2- as
SCALE:
SHEET:
OF' 4
4 9� Q
•
•
sus
/f. C.5-2k
SOUTH RAT
ZNGINZZR ING
CORPORATION
304 TEJON PLACE
PALOS VERDES ESTATES
CALIFORNIA 90274
3110 12131 375-2556 772-1555
RAYMOND L. QUIGLEY R.C.E. 719)
JOB TITLE: : I
• 40,)4/4Q4 ye- /e.e-41
-&X :CIA.57-26-72A-7
- : -• • • • : - -
P47/4
"
/NM
ONO
si
• • - ./54e
- 25-
75.)(2.3-)(et
.0,6:9/0ZAJ&T riZoo 124
it4 / 2e25
Qi11‘41/4ile /2. 0 WS
• i
. . 4
- I
7;r-04
--•
Wenfizit.5.24
DA FE:
1012.-eo
SCALE:
SHE T:
OF'
--- /go cfs
.Ce6-3-7-- Red
See "Cf vs-e
See /4 Ze, vc%
4
Cp A 14i/sliak /0v)4,ec6lied