HomeMy WebLinkAboutCDP 07-11; MORRISON RESIDENCE; PRELIMINARY HYDROLOGY STUDY; 2007-07-10SKYLINE
Engineering
Preliminary Hydrology Study
For
Whetsel Consultants
At
The Morrison Residence
Located At:
4338 Highland Drive
Carlsbad, California 92008
Date July 10, 2007
1220 South Ditmar St.
Oceanside, California
92054 .
760-721-3520
Job # 4-2007
· ,
SKYLINE
Engineering
Owner
Kevin Morrison
4336 Highland Dr.
Carlsbad, CaIif92008
Fax 1760-730-3 106 W 644-3025
K SMORRISON@SBCGLOBAL.l\TET
Site Address: 4338 Highland Dr.
Carlsbad, Calif 92008
Agent
Tim Whetsel
1352 Hodges Rd
Oceanside, CaIif92056
945-5249
1220 South Ditmar St.
Oceanside, California 92054
760-721-3520
7/6/2007 Job #4-2007
Hydrology Report Narrative
Introduction
Existing Conditions
The site is about .34 acres and is located off of Highland Drive, in Carlsbad. The
site is east of the 5 freeway and north of Agua Hedionda Lagoon. The site has both flat
and sloping areas. The site is accessed through a panhandle access. The west side of the
property is sloped to\vard a flatter eastern side.
Several easements exists on the pan handle access and other parts of the property.
The site is in a developed residential area. The existing house to the north of the pan
handle encroaches about 5' onto the panhandle access. A hydrology study of this area
was performed. Due to site topography, water from Highland Drive is not tributary to the
site. About .68 acres are tributary to the Morrison site. See the enclosed topographic
map. This area produces a 100 year storm flow, based on the San Diego County
Hydrology manual, of about 1.8 efs.
Currently rainfall that occurs on the site and the adjacent tributary area, will flow,
by sheet flO\v, south easterly to the south east comer of the property. The water flows on
to the existing adjacent residential properties. There is an existing earthen, natural drain
swale that flows ~O\"n toward park drive, whieh is located to the east.
Due to the hilly terrain, erosion is currently a problem for the site and adjacent
tributary off site areas. On site erosion is only a minor problem. The flatter eastern
portion of the site tends to slow do\\n the flows. Do\\nstream areas are steeper and flows
are allowed to speed up. The existing unlined natural channel, earthen \vith some stones,
appears to be performing well over the years. There is a high potential for erosion during
storms if the water is allowed continued to flow unchecked.
Proposed Conditions summary
The proposed drainage patterns of the site will remain substantially the same. The
stonn \vaters \\ill flow substantially southeasterly to the south east corner of the property.
The proposed improvements \\rill improve the water quality of the flows leaving the site
by reducing velocity which helps prevent erosion and attenuate the flow. The proposed
paving at the site \,rill reduce the amount of infiltration which increases volume~ yet the
proposed biosw~e will promote infiltration.
Tributary \vaters quickly flow, unchecked. down the existing slopes causing
erosion. The first critical change will be to construct ditches to collect the water. Yard
areas will also be landscaped. \Vater \\ill also be directed by sheet flow to shallow
sloping grassy bio-swale areas. These front and rear yard areas \\ill be used to treat the
\vater before in flows into the yard drain system. A network of pipes is proposed to
conduct the water \\ith out any on site erosion.
Ultimately most of the flows \\ill be directed to a pipe outfall at the south east
corner of the property. It is proposed that the drainage patterns for the site wHI remain
unchanged. A energy dissipater will be constructed that will substantially slow the water
down.
Hydrology Analysis
The area to the west of the property is sloped toward the Morrison property. See
the attached City, of Carlsbad topographic map. The drainage basin and :rvlorrison
property are Shm.Vl1 on the City of Carlsbad topographic map. The drainage basin-area
tributary to the site is approximately .68 acres. The rain fall intensity, soil type, time of
concentration and use of the property was determined, based on the San Diego County
hydrology manual, see page 1-6 of this report. A 100 year flow of about 1.8 cfs was
calculated. The pre & post development run-off volume is substantially the same.
Hydraulic Analysis
As discussed above there is a off site basin to the west that is tributary to the site.
As these water reach the site they \\ill encounter a brow ditch. The brow ditch 'will direct
the water into a number of catch basins. Standard 6" diameter pipes will be used to
relieve the yard. :tvlost of the \vater are tributary to a proposed 24" square concrete catch
basin. The size of the steeply sloping pipe, that relieves the basin are determined using
the attached alignment charts. The analysis used for this site design is based on the
County of San Diego Hydrology Manual. Pipes sizes were determined by the enclosed
alignment chart from the te:\.'t book "Hydraulic Engineering" by Robertson, Cassidy, and
Chaudhry 1988 Houghton Mifflin Company_
Conclusion
Pre & Post construction Hydrology Discussion
Flows volumes were determined based on the San Diego County hydrology
Manual. The manual provides techniques for estimating the flows. Based on the
tabulated values the proposed development may increase the flow by a negligible amount.
The proposed site is designed in such a way to mitigate any changes to the existing pre-
development flow regime. Several steps are bejng proposed that \\ill attenuate the flow.
reduce flow volumes and treat the water.
For example. The shallow sloped yard. During 10\..-flow storm events. its likely
that little or no water will leave the site. The yard allows for an increase in infiltration
due to the shallow ponds that \vill be created. This estimated increase, will have an
insignificant impact on the flood plain, flow characteristics and erosion characteristics
dovmstream. A energy dissipater will be added at the outfall. The proposed drainage
improvements will reduce the existing sediments that are leaving the site.
Please do not hesitate to call if you have questions or concerns regarding this project.
Sincerely
David Zernik, P.E
33'30'
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Datc: June 2003
Table 3-1
Section:
Page:
J',' --T_
RUNOFF COEFFICIENTS FOR URBAN AREAS
Land Use Runoff Coefficient "c"
Soil Tx.ee
NRCS Elements Coun Elements %IMPER. A B C
Undisturbed Natural Terrain (Natural) Permanent Open Space 0* 0.20 0.25 0.30
Low Density Residential (LDR) Residential, 1.0 DUI A or less 10 0.27 0.32 0.36
---f""Low Density Residential (LDR) Residential, 2.0 DUI A or less 20 0.34 fl .~ 0.38 t 0.42
Low Density Residential (LOR) Residential, 2.9 DU/A or less 25 0.38 0.41 0.45
Mcdium Density Residential (MDR) Residential, 4.3 DUiA or less 30 0.41 0.45 0.48
Medium Density Residential (MDR) Residential, 7.3 DUiA or less 40 0.48 0.51 0.54
Medium Density Residential (MDR) Residential, 10.9 nU/A or less 45 0.52 0.54 0.57
Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58 0.60
High Density Residential (HDR) Residential, 24.0 DUI A or less 65 0.66 0.67 0.69
High Density Residential (HDR) Residential, 43.0 DU/A or less 80 0,76 0.77 0.:f8
CommerciallIndustrial (N. Com) Neighborhood Commercial 80 0.76 0.77 0.78
CommerciaVlndustrial (G. Com) General Commercial 85 0.80 0.80 0.81
Commercialllndustrial (D.P. Com) Office ProfessionallCommercial 90 0.83 0.84 0.84
CommerciaVlndustrial (Limited I.) Limited Industrial 90 0.83 0.84 0.84 .
General Industrial 95 0.87 U.H7 0.87
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0.85
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is located in Cleveland National Forest).
DU/ A = dwelling units per acre
NRCS = National Resources Conservation Service
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DIrections for Applfcptlon:
(1) From precipitation maps determine 6 hr [111,1 2:1 hr amounts
for the selected frequency. These maps ;:;r-; Included In the
County Hydrology Manual (10. 50, and 100 yr maps tncluded
In the DesIgn and Procedure Manual).
(2) Adjust 6 hr precipitation (If neoessary) so that It is within
tho range of 45% to 65% of the 24 hr precipitation (not
appl/capJa to Dasert).
(3) Plot 6 hr preclpltnUon 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·duratlon curve for the loeaUon
being analyzed.
AppllcatJon Form:
(a) Selected frequency ~ year
-,:E':!"'" ~ ~ .• (b) P6 =1~ In., P24:= -~L 'P == ...... ,( %(2}
24
(0) Adjusted Pa(2) ::: ':!. --S in.
(d) tx ::: S--min .
(e) I::: .:l..-in./hr .
Note: This chart replaces the Intensify-Duration·Frequency
curves used sInce 1965.
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