HomeMy WebLinkAboutCT 01-01; CALAVERA HILLS VILLAGE L2; HYDROLOGY STUDY; 2015-10-02HYDROLOGY STUDY
FOR
CALAVERA HILLS
VILLAGE L-2
7 s 2
Keith W. Hansen
RCE 60223 Exp. 6/30/04
Date
CTOl-Q]
This iiydrology study is a portion of the approved hydrology study for Carlsbad
Tract 00-02 that covers Village 'L-2'.
The proposed condition will be a si ngle-fam iiy residential sub-division with a single
street ending with a cul-de-sac. The existing tributary area to the west has been
reduced and will be all landscaped.
The following describes the proposed basin areas (see Exhibit "K" for areas):
Area L-2-1 discharges westerly while Area L-2-2 discharges northwesterly. Area L-2-
3 and L-2-4 discharges easterly towards the westerly portion of Cay Drive and
continue northerly along Cay Drive towards the adjacent sub-division, onto
Promontory Place or "E" Street as show on the Village 'Q' Hydrology Map (Exhibit
"J"), and ultimately into a storm conveyance system (Node 3 per Village 'Q'
Hydrology Map) at the end of the cul-de-sac. Area L-2-5 and L-2-6 dischiarges
easterly towards the westerly portion of Cay Drive and continue southerly along
Cay Drive, and ultimately into a storm drainage system (Node 37 per Village 'Q'
Hydrology Map) at the intersection of Cay Drive and Tamarack Avenue.
Calculations:
The hydrological analysis utilized to calculate the storm runoff for the 100-year
storm event was the Rational Method (Q = C * I * A).
Q = Runoff (cfs)
C = Runoff Coefficient
IA = Rainfall Intensity (inches/hour)
A = Area (acres)
Tc = Time of Concentration (Initial, overland, street gutter or pipe)
Determination of Runoff Coefficient
The runoff coefficient (C) is based on the soil group of the drainage basin.
Runoff coefficients are also dependent on the proposed land use of each basin.
Coefficients for this project were based from the County of San Diego Hydrology
Manual.
G:\sdsk\PROJ\981020\wp\L2SDRpt.doc
Determination of Intensity
Rainfall Intensity (1) is a function of the six-hour precipitation measure and the time
of concentration for the drainage basin, as defined by the County of San Diego
Hydrology Manual.
Determination of Areas
The area (A) of each drainage basin was determined from the drainage area map.
The drainage sub-basin has been based on the ultimate anticipated land use.
Analysis
The onsite 100-year peak flow rates were calculated as shown on the table below
(also see Exhibit "K"). A runoff coefficient of 0.55 was selected during preliminary
analysis. 0.55 was used throughout this analysis although Exhibit "A" shows a Type
'C soil classification, which would yield a runoff coefficient of 0.50. Using a 0.55 -
runoff coefficient will yield a higher peak runoff flow rate, which is a conservative
approach for the purpose of this analysis.
SUB-BASIN C AREA
(AC)
Tc
(MIN.)
1
(IN/HR)
Qioo
(CFS)
L-2-1 0.55 0.22 5.00 6.85 0.83
L-2-2 0.55 0.26 5.00 6.85 0.98
L-2-3 0.55 0.20 5.00 6.85 0.75
L-2-4 0.55 2.00 14.10 3.50 3.85
L-2-5 0.55 2.17 14.10 3.50 4.18
L-2-6 0.55 0.51 5.00 6.85 1.92
NOTE: L-2-5 INCLUDES L-2-6
The Time of Concentration values shown above were determined as shown below:
L-2-1 Tc, use minimum 5 min.
L-2-2 Tc, use minimum 5 min.
L-2-3 Tc, use minimum 5 min.
L-2-4 Tc, (Exhibit "F") urban area overland
(Lot 3, 130 ft @ 1.07o)
G:\sdsk\PROJ\981020\wp\L2SDRpt.doc
Tc = 12.5 min.
plus (Exhibit "G") gutter-velocity chart
4.5 ft/sec X 440 ft = 97.7/60 = 1.6 min.
Tc = 12.5 + 1.6 = 14.1 min.
L-2-5 Tc, (Exhibit "F") urban area overland
(Lot 1, 130 ft @ 1.07o)
Tc = 12.5 min.
plus (Exhibit "G") gutter-velocity chart
4.5 ft/sec X 440 ft = 97.7/60 = 1.6 min.
Tc = 12.5 + 1.6 = 14.1 min.
L-2-6 Tc, use minimum 5 min.
The total area entering Node 3 (see Exhibit "J") is approximately 5.30 acres, of
which 2.20 acres is a portion of Village 'L-2', and 3.10 (2.90-1-0.20 per Exhibit "J")
acres is the developed site adjacent to and downstream of Village 'L-2'. Using the
Time of Concentration (Tc) for L-2-3 of 14.1 minutes yields a rainfall intensity (1)
value of 3.50. Using the said Tc value yields a higher peak value since the actual
Tc value would be longer, thus resulting in a lower rainfall intensity value and
ultimately a lower peak flow value. Using a runoff coefficient value (C) of 0.55
yields a peak runoff value (Q) of 10.20 cubic feet per second (cfs). This 100 -year
peak flow value is less than the peak flow value of 14.4 cfs as shown on Node 3 of
the Village 'Q' Hydrology Map.
The total area entering Node 37 (see Exhibit "j") is approximately 4.78 acres, of
which 1.66 acres is a portion of Village 'L-2', 0.52 acres is area upstream of Village
'L-2', and 2.60 (1.60+ 1.0 per Exhibit "j") acres is the area downstream of Village 'L-
2'. Using the Time of Concentration (Tc) for L-2-4 of 14.1 minutes yields a rainfall
intensity (I) value of 3.50. Using a runoff coefficient value (C) of 0.55 yields a peak
runoff value (Q) of 9.20 cubic feet per second (cfs). This 100-year peak flow value
is less than the peak flow value of 9.70 cfs as shown on Node 37 of the Village 'Q'
Hydrology Map.
G:\sdsk\PRO.I\981020\wp\L2SDRpt.doc
TABLE 2
RUNOFF COEFFICIENTS (RATIONAL METHOD)
DEVELOPED AREAS (URBAN)
Land Use
Residential:
Si ngle FamiIy
Multi-Units
Hob iIe homes
Rural (lots greater than 1/2 acre)
Convnerci al (2)
80% Impervious
Industrial(2)
90% Impervious
Coefficient, C
Soi1 Group (1)
A B C 0
M .^5 .50 .55
A5 .50 .60 . 70 ,
M .50 .55 .65
.30 .35 .40 .45
.70 .75 .80 .85
.80 .85 .90 .95
MOTES
(1) Soil Group maps are available at the offices of the Department of Public Works.
(2)where actual conditions deviate significantly from the tabulated impervious-
ness values of 80% or 90%, the values given for coefficient C, may be revised
by multiplying 80% or 90% by the ratio of actual imperviousness to the
tabulated imperviousness. However, in no case shall the final coefficient
be less than 0.50. For example: Consider commercial property on D soil.group.
Actual imperviousness = 50%
Tabulated imperviousness = 80%
Revised C = 50 x O.85 = 0.53
80
IV-A-9
APPENDIX IX-B
Rev. 5/81
COU/fTY OF SAN DIEGO
DEPARTMENT OF SANITATION &
FLOOD CONTROL 100-YEAEi 6-!JOUl PflECIPITATIOiJ
^20^ ISOPLUVIALS
PnECIFlTATlOn \\\
OF lOO-YEAR 6-MOUR
lEuTiis or AH i;:ci!
33°
Prepn
U.S. DEPARTMEN
NATIONAL OCEANIC AND AT^J(I SPUE KIC ADMINISTRATION
SPECIAL STUOIES DRANCII, OFFICE OF II
30' J
I
Revised 1/85 APPENDIX XT-F.
COUNTY OF SAN DIEGO
DEPARTMENT OF SANITATION 5-
FLOOD CONTROL
'»5
33"
30'
15'
Hicp
U.S. DEPARTMLN
NATIONAL OCtAMC AND AT.,
SPECIAL STODIES BKANCII. OKI-ICE OF II'
30'
100-YEAIt 24-1101 R PRECIPITATION
-^20-^ISOPLUVIALS OF 100 -YEAR 24-IIOUR
PRECIPITATION IM ENTHS OF AN INCH
I I/i" 30' 117' 'i'i' in' IH' ir."
APPliNOIX XI-ll
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SAN DIEGO COUNTY URBAN AREAS OVERLAND TIME
DEPARTMENT OF SPECIAL DISTRICT SERVICES OF FLOW CURVES
DESIGN MANUAL DESIGN MANUAL
APPENDIX X-(
T \ (_ /> .1 fl
2%
5 6 7 8 9 10
DISCHARGE (C F S)
30 40 50
EXAMPLE:
Given: Q= 10 S= 2.5%
Chart gives: Depth = 0.4, Velocity = 4.4 f.ps.
SAN DIEGO COUNTY
DEPARTMENT OF SPECIAL OISTRICT SERVICES
OESIGN MANUAL
APPROVED /dt/^-/<h/jA*^^L4yhrT
GUTTEF; AND ROADWAY
DISCHARGE-VELOCITY CHART
APPENDIX X-D
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SAN DIEGO COUNTY
DEPARTMENT OF SPECIAL DISTRICT SERVICES
DESIGN MANUAL
APPROVED '^'/'^- .//4r/^-^^Ty^^^^J^^
NOMOGRAPH FOR DETERMINATFON
OF TIME OF CONCENTRATION (Tc)
FOR NATURAL WATERSHEDS
DATE APPENDIX X-A
lV-A-10 Rev. 5/81
INTENSITY-DUMTION DESIGN CHART
riTfiTrrrnin
Equation:
iTnntTtnmirs r~,—r
7,44 P,
rnirhn
Intensity (In./Hr.)
6 Hr. Precipitation (In.)
Duration (Min.)
Ili
15 20
Minutes
Directions for Application:
1) From precipitation naps detennine 6 hr. and
24 hr. amounts for the selected frequency.
These maps are printed In the County Hydrology
Manual (10, 50 nnd 100 yr. maps Included in the
Design and Procedure Manual).
2) Adjust 6 hr. precipitation (if necessary) so
that it is within the range of 45% to 65% of
the 24 hr. precipitation. (Mot nprlicable
to Desert)
3) Plot 6 hr. precipitation on the right side
of the chart.
4) Draw a line through the point parallel to the
plotted lines.
5) This line is the intensity-duration curve for
the location being analyzed.
Application Form:
0) Selected Frequency tOO yr.
1) Pfi - 1"'. P24" *h "
2) Adjusted *Pg-
3) t^-
4) I
24'
2*^ 24
in.
min.
6»Bf in/hr.
*Not Applicable to Deser
.AIXA L-Z •/
INTENSITY-DUMTION DESIGN CHART
I
3=
TJ -I n n
o a
zs n 3-n Ul
Directions for Application:
1} From precipitation naps determine 6 hr. and
24 hr. amounts for the selected frequency.
These maps are printed in the County Hydrolony
Manual (10, 50 and 100 yr. maps Included In the
Design and Procedure Manual).
2) Adjust 6 hr. precipitation (If necessary) so
that it is within the range of 45% to 65% of
the 24 hr. precipitation. (Not i\prlicable
to Desert)
3) Plot 6 hr. precipitation on the right side
of the chart.
4) Draw a line through the point parallel to the
plotted lines.
5) This line is the Intensity-duration curve for
the location being analyzed.
Application Form:
0) Selected Frequency yr.
1) Pfi " ll^ln., P24'' A'l? . *Pf. «^£%*
2) Adjusted *Pg»=
3) tg « ^ min.
4) I - 6*^$T in/hr.
24
in.
*Not Applicable to Deser 9
INTENSITV-DUMTION DESIGN CHART
Directions for Application:
1) From precipitation naps detennine 6 hr. and
24 hr. amounts for the selected frequency.
These maps are printed In the County Hydrology
Manual (10, 50 nnd 100 yr. maps Included in the
Design and Procedure Manual).
2) Adjust 6 hr. precipitation (if necessary) so
that it is within the range of 45% to 65% of
the 24 hr. precipitation. (Not applicable
to Desert)
3) Plot 6 hr. precipitation on the right side
of the chart.
4) Draw a line through the point parallel to the
plotted lines.
5) This line Is the intensity-duration curve for
the location being analyzed.
Application Form:
0) Selected Frequency lOO yr.
1)
2) Adjusted *Pg=
3) t. - S
4)
24
7.^ ^24
in.
%*
min.
I • i*B^ in/hr.
*Not Applicable to Deser
K4
5
f<5
AeCA- L-1' h
Minutes Hours
INTENSITY-DUMTION DESIGN CHART
Im.iii.ii.iiHmrr:;-! ; , i'i.i-j.i u i n I nifhr
Equation! I » 7.44 P, D
0
-.645
I Intensity (In./Hr.)
Pg = 6 Hr. Precipitation (In.)
D a Duration (Min.)
15 20
Minut.es
30 40 50 1 2 , 3
Hours
Directions for Application:
1) From precipitation naps detennine 6 hr. and
24 hr. amounts for the selected frequency.
These maps are printed in the County Hydrology
Manual (10, 50 nnd 100 yr. maps Included in the
Design and Procedure Manual).
2) Adjust 6 hr. precipitation (if necessary) so
that it is within the range of 45% to 65% of
the 24 hr. precipitation. (Not npplicable
to Desert)
3) Plot 6 hr. precipitation on the right side
of the chart.
4) Draw a line through the point parallel to the
plotted lines.
5) This line is the intensity-duration curve for
the location being analyzed.
Application Form:
0) Selected Frequency /^^ yr.
1) P^ ° in.. Po,= 4,? .*Pfi'^«^:
2) Adjusted *?f.' _
3) t. • /^t/ min.
4) I « .3^5^ in/hr.
*Not Applicable to Deser
24
in.
A«4 L'l -4-
-1
INTENSrTY-DU/V\TION DESIGN CHART
^iTriTIJIIilliI 11 i iiJmlin.iii.ii.niimm. ii" i'l.ia.i ii i Hinifhni
Equation: I » 7.44 P, D "'^^^
0
I » Intensity (In./Hr.)
Pg = 6 Hr. Precipitation (In.)
I
X o c
-t
T3 1 n> o
cu rt
O
3
n ro 1/1
15 20
Minutes
Directions for Application:
1) From precipitation naps determine 6 hr. and
24 hr. amounts for the selected frequency.
These maps are printed in the County Hydrology
Manual (10, 50 nnd 100 yr. maps included in the
Design and Procedure Manual).
2) Adjust 6 hr. precipitation (if necessary) so
that it is within the range of 45% to 65% of
the 24 hr. precipitation. (Not npplicable
to Desert)
3) Plot 6 hr. precipitation on the right side
of the chart.
4) Draw a line through the point parallel to the
plotted lines.
5) This line is the intensity-duration curve for
the location being analyzed.
Application Form:
0) Selected Frequency 1^ yr.
1) Pfi = 1n.. P24= 4i3 . *Pg = ^*^%*
2.^ 2) Adjusted *Pg=
min.
24
in.
3) tg-
4) I In/hr.
*Not Applicable to Deser
JNTENSITY-DUMTION DESIGN CHART
7T'~ 1 pTflTinfillii I H ' Nniliiiiiiiiiiiirnmtp::• i T r ll iriTrTi(hni
,1 Equation! I •••<- 7,44 D
I " Intensity (In./Hr.)
Pg = 6 Hr. Precipitation (In.)
15 20
Minutes
Directions for Application:
1) From precipitation naps determine 6 hr. and
24 hr. amounts for the selected frequency.
These maps are printed 1n the County Hydrolony
Manual (10, 50 nnd 100 yr. maps included in the
Design and Procedure Manual).
2) Adjust 6 hr. precipitation (if necessary) so
that it is within the range of 45% to 65% of
the 24 hr. precipitation. (Not applicable
to Desert)
3) Plot 6 hr. precipitation on the right side
of the chart.
4) Draw a line through the point parallel to the
plotted lines.
5) This line is the intensity-duration curve for
the location being analyzed.
Application Form:
0) Selected Frequency yr.
1) Pfi - 2iAp', P24= Ail-. *P6 %*
2) Adjusted *Pg=
3) t, = 5
7^6 24
in.
min.
4) I (i»B5^ in/hr.
*Not Applicable to Deser