HomeMy WebLinkAboutCDP 04-07; McGuire Residence; Drainage Study; 2005-01-11Drainage Study
for
McGuire Residence
"^"^ ^^^^
Prepared By:
LEPPERT ENGINEERING CORPORATION
5190 GOVERNOR DRIVE, SUITE 205
SANDIEGO, CA 92122
January 11,2005
eppert
xp.3-31-06
Table of Contents
Introduction 1
Method of Calculation 1
Hydrologic Criteria 1
Existing Condition 2
Proposed Development 4
Conclusion 5
Appendices
Appendix A Location Map
Appendix B Site Drainage Map of Existing / Proposed Condition
Appendix C Isopluvial Maps for Existing / Proposed Condition
Appendix D Excerpts from City of Carlsbad Subdivision Manual
McGuire Residence
Drainage Study
CAR 7.01-03.04
Jan 11,2005
introduction
The purpose of this drainage study is to estimate the quantity of storm water runoff from the proposed
development of a single family residence. The subject property is a trapezoid-shaped parcel of land with a
gross area of approximately 0.41 acres. The site is currently developed with a single family residence with
Tierra Del Oro Street along the frontage, and a steep hillside draining into the pacific ocean along the rear
of the property. The project site is located at 5035 Tierra Del Oro Street in the City of Carlsbad. A location
map of the project site is located in Appendix A. This study will analyze the existing runoff and compare
the runoff amount for the proposed development to determine the increase in runoff, if any.
IVIethod of Caicuiation
The total runoff from the site is calculated using the guidelines set forth in the City of Carlsbad,
Engineering Standards, Chapter 5, Drainage and Storm Drain Standards, and the County of San Diego
Hydrology Manual, dated June 2003. The specific method used is the Rational Method. Excerpts ofthe
City of Carlsbad Engineering Standards, Chapter 5, Drainage and Storm Drain Standards, are located in
Appendix F.
Hydrologic Criteria
The following criteria were used in computing runoff from the existing and proposed project.
• Hydrology Method: Rational Method (Q=CIA) per page 2 of the City of Carlsbad Engineering
Standards, Chapter 5, Drainage and Storm Drain Standards.
• Time of Concentration (T^): The time of concentration was computed per the San Diego County
Hydrology Manual.
• Runoff coefficient C: a runoff coefficient of C=0.9 for impervious surfaces and C=0.45 for pervious
surfaces was used per City of Carlsbad, Engineering Standards, Chapter 5, Drainage and Storm
Drain Standards.
• Intensity of Rainfall I: The rainfall intensity was calculated using the 6-hour storm precipitation
rates (100-year) and the Isopluvial Maps for a 6-hour precipitation from the City of Carlsbad
Design Standards. The 24-hour Isopluvial Map (100-year) was used from the County of San
Diego Design and Procedure Drainage Manual.
Existing Condition
McGuire Residence
Drainage Study
CAR 7.01-03.04
Jan 11,2005
The existing site is divided into two basins. Storm water runoff from Basin 1 is directed via sheet flow over
the steep hillside into the Pacific Ocean. Basin 1 has an area of approximately 0.13 acres. A runoff
coefficient factor of C= 0.81 was used for Basin 1 to account for the paved surface and the vegetated
surface in the existing back yard, based on its developed condition. Storm water runoff from Basin 2
surface drains to Tierra Del Oro Street. Basin 2 has an area of approximately 0.04 acres. A runoff factor
of C= 0.9 was used to account for the impervious surface. A site drainage map showing the existing
condition is located in Appendix B.
The 6 hour duration storm event was used to compute the runoff of the existing condition. The isopluvial
map for a 100 year storm is located in Appendix C. The rainfall intensity value for a 100-year frequency
storm was computed per the City of Carlsbad Engineering Standards, Chapter 5, Drainage and Storm
Drain Standards
I = 7.44 * Pfi * D
• Pg = adjusted 6-hour storm precipitation (if Pg is not within 45% and 65% of P24, increase or
decrease Pg as necessary to meet this criteria).
• D=Duration in minutes (use TJ
Basin 1:
A=0.13 acres
C=0.50 (concrete with lawn areas)
Time of concentration: T = (1.8 (1.1 -C) VD) / Vs
Length of watercourse in feet D = 104.0'
Upper elevation = 36.9'
Lower elevation = 30.0'
Slope s = (36.9-30.0)104.0 = 0.06635 - 6.64%
T = 5.86 min.
• for calculations of intensity for 100-year frequency see Appendix C.
Basin 1
Frequency Acreage Runoff Length of Upper Lower Aver. Tc(mln) Intensity Q (cfs)=
(Ac) Coeff. Watershed Elev. Elev. (ft) Slope (in/hr) CIA
(ft) (%)
McGuire Residence
Drainage Study
CAR 7.01-03.04
Jan 11,2005
100-year 0.13 0.50 104.0 36.9 30.0 6.64 5.86 9.51 0.37
Qioo,totai (flowing over steep hillside) = 0.37 cfs (166gpm)
Basin 2:
A=0.04 acres
C=0.6 (concrete with landscaped areas)
Time of concentration: T = (1.8 (1.1 -C) /D) / Vs
Length of watercourse in feet D = 32
Upper elevation = 36.9'
Lower elevation = 36.7'
Slope s = (36.9-36.7)/32.0 = 0.00625 - 0.6%
T = 6.0 min.
• for calculations of intensity for 100-year frequency see Appendix C.
Basin 2
Frequency Acreage Runoff Length of Upper Lower Aver. Tc (min) Intensity Q (cfs)=
(Ac) Coeff. Watershed Elev. Elev. (ft) Slope (in/hr) CIA
(ft) (%)
100-year 0.04 0.6 32.0 36.9 36.7 0.6 6.0 5.85 0.38
Qioo,totai (flowing into public storm drain) = 0.14 cfs (63 gpm)
McGuire Residence
Drainage Study
CAR 7.01-03.04
Jan 11,2005
Proposed Development
The proposed development consists of identical drainage basis. Basin 1 will be collected via onsite private
drains and deposited into a 4' x 4' x 4' nominal reservoir to be pumped using a triplex pumping system that
incorporates 1 larger pump working in tandem with 2 smaller pumps in order to accommodate both minor
runoff (irrigation) as well as a major storm runoff, through PVC pipe up to Tierra Del Oro and into the
public storm drain system. This will create minimal impact on the existing storm drain system as well as
preserve the existing steep slope located on the westerly half of the property. Basins 2 will remain
essentially unchanged and sheet drain towards Tierra del Oro. A runoff coefficient of C=0.7 will be used
to evaluate the runoff for the proposed development due to the proposal of more hard-scape areas. A site
drainage map showing the proposed condition is located in Appendix D.
Basin 1:
A=0.13 acres
C=0.70
Time of concentration: T = (1.8 (1.1-C) /D) / Vs
Length of watercourse in feet D = 104.0'
Upper elevation = 36.9'
Lower elevation = 30.0'
Slope s = (36.9-30.0)/104.0 = 0.06635 -> 6.64%
T = 3.91 min.
• for calculations of intensity for 100-year frequency see Appendix C.
Basin 1
Frequency Acreage
(Ac)
Runoff
Coeff.
Length of
Watershed
Upper
Elev. (ft)
Lower
Elev. (ft)
Aver.
Slope
(%)
Tc (min) Intensity
(in/hr)
Q (cfs)=
CIA
100-year 0.13 0.70 104.0 36.9 30.0 6.64 3.91 6.5 0.59
*100,total (collecting in sump to be pumped to street) = 0.59 cfs (265 gpm)
McGuire Residence
Drainage Study
CAR 7.01-03.04
Jan 11,2005
Basin 2:
A=0.04 acres
C=0.70
Time of concentration: T = (1.8 (1.1 -C) V"D) / Vs
Length of watercourse in feet D = 32.0'
Upper elevation = 36.9'
Lower elevation = 36.7'
Slope s = (36.9-36.7)/32.0 = 0.00625 - 0.63%
T = 4.75 min.
• for calculations of intensity for 100-year frequency see Appendix C.
Basin 2
Frequency Acreage Runoff Length of Upper Lower Aver. Tc (min) Intensity Q (cfs)=
(Ac) Coeff. Watershed Elev. (ft) Elev. (ft) Slope (in/hr) CIA
(%)
100-year 0.04 0.70 32.0 36.9 36.7 0.63 4.75 6.4 0.28
Qioo total (sheet flowing to Street) = 0.18 cfs (81 gpm)
*100,total = 0.18c.f.s. + 0.59c.f.s. = 0.77c.f.s,
Conclusion
Based on the above calculations, the proposed development will increase the amount of runoff that is
running into the public storm drain by approximately 0.67 cubic feet per second.
McGuire Residence
Drainage Study
CAR 7.01-03.04
Jan 11,2005
Appendix A
Location Map
PROJECT LOCATION MAP
SCALE: \ 1"=^ N.T.S.
McGUIRE RESIDENCE
McGuire Residence
Drainage Study
CAR 7.01-03.04
Jan 11, 2005
Appendix B
Site Drainage IVlap of Existing / Proposed Condition
(no change)
Appendix C
Isopluvial Maps for Existing / Proposed Condition
33.3(r—Orange.
-Countyj
32-45'
County of San Diego
Hydrology Manual
Rainfall Isopluvials
100 Year Raigfall Event - 24 Hours
• Isopluvial (inches)
^GIS SanGIS
•Htt»tB).MamNs.HirMcniMnmTD rw IM » Mutu/mt
. ' i - • j •, t l 'l jI •, -i : i : ! T i : : i • i ; —
iS'-t • I ' * i I i'i I ' ili- hi !i Sni • I , IT !
33W
: ! ii'^
1 fal i j i
: j T" M ; !
I I ; I
M e X' i' c p
8 32'3Cr
t rr!
County of San Diego
Hydrology Manual
Rainfall Isopluvials
100 Year Rainfall Event - 6 Houra
" Isopluvial (inches)
npw
MGIS SaiTGIS TiitUi-ir itriMTvrminfmr<rT-|VrifiniiinTnr tin'ifiji. rmynnirTi
. OM a^n. MCUXHM^ «JT MOT LMTEO TO TlIC imCU MAKHMTIU A CW'tffHUMHT'MUJTVAManTMWPUKkMNTKUAAIaMMMC.
3 0 3 Mllas
Appendix D
Excerpts from City of Carlsbad Hydrology Manual
CHAPTER 5- DRAINAGE AND STORM DRAIN STANDARDS
1. GENERAL
A All drainage design and requirements shall be in accordance with the latest City of
Carlsbad Standard Urban Storm Water Mitigation Plan (SUSMP), Jurisdictional
Urban Runoff Management Plan (JURMP), Master Drainage and Storm Water
Quality Management Pian and the requirements of the City Engineer and be based
on full development of upstream tributary basins.
B. Public drainage facilities shall be designed to carry the ten-year six-hour storm
underground and the 100-year six-hour storm between the top of curbs.
All culverts shall be designed to accommodate a 100-year six-hour storm with a one
foot freeboard at entry conditions such as inlets and head walls.
C. The use of underground storm drain systems, in addition to standard curb and
gutter shall be required:
1) When flooding or street overflow during 100-year six-hour storm cannot be
maintained between the top of curbs.
2) When 100-year six-hour storm flow from future upstream development (as
proposed in the existing General Plan) will cause damage to structures and
improvements.
3) When existing adequate drainage facilities are available for use (adjacent to
proposed development).
4) When more than one travel lane of arterial and collector streets would be
obstructed by 10-year 6-hour storm water flow. Special consideration will be
required for super-elevated streets.
D. The use of underground storm drain systems may be required:
1) When the water level in streets at the design storm is within 1" of top of curb.
2) When velocity of water in streets exceeds 11 FPS.
3) When the water travels on surface street improvements for more than 1,000'.
E. The type of drainage facility shall be selected on the basis of physical and cultural
adaptability to the proposed land use. Open channels may be considered in lieu of
underground systems when the peak flow exceeds the capacity of a 48" diameter
RCP. Fencing of open channels may be required as determined by the City
Engineer.
F. Permanent drainage facilities and right-of-way, including access, shall be provided
from development to point of approved disposal.
Page 1 of 5
G Storm Drains constructed at a depth of 15' or greater measured from finish grade to
the top of pipe or structure shall be considered deep storm drains and should be
avoided if at all possible. When required, special design consideration will be
required to the satisfaction of the City Engineer. Factors considered in the design
will include:
1) Oversized specially designed access holes/air shafts
2) Line encasements
3) Oversizing lines
4) Increased easement requirements for maintenance access
5) Water-tight joints
6) Additional thickness of storm drain
The project designer should meet with the planchecker prior to initiation of design to
review design parameters.
H. Concentrated drainage from lots or areas greater than 0.5 acres shall not be
discharged to City streets unless specifically approved by the City Engineer.
I. Diversion of drainage from natural or existing basins is discouraged.
J. Drainage design shall comply with the City's Jurisdictional Urban Runoff
Management Plan (JURMP) and requirements of the National Pollutant Discharge
Elimination System (NPDES) permit.
HYDROLOGY
A Off site, use a copy of the latest edition City 400-scale topographic mapping. Show
existing culverts, cross-gutters and drainage courses based on field review.
Indicate the direction of flow; clearly delineate each drainage basin showing the
area and discharge and the point of concentration.
B. On site, use the grading plan. If grading is not proposed, then use a 100-scale plan
or greater enlargement. Show all proposed and existing drainage facilities and
drainage courses. Indicate the direction of flow. Clearly delineate each drainage
basin showing the area and discharge and the point of concentration.
C. Use the charts in the San Diego County Hydrology Manual for finding the "Tc" and
"I". For small areas, a five minute "Tc" may be utilized with prior approval ofthe City
Engineer.
D. Use the existing or ultimate development, whichever gives the highest "C" factor.
E. Use the rational formula Q = CIA for watersheds less than 0.5 square mile unless
an alternate method is approved by the City Engineer. For watersheds in excess of
0.5 square mile, the method of analysis shall be approved by the City Engineer
prior to submitting calculations.
Page 2 of 5
HYDRAULICS
A Street - provide:
1) Depth of gutter flow calculation.
2) Inlet calculations.
3) Show gutter flow Q, inlet Q, and bypass Q on a plan of the street.
B. Storm Drain Pipes and Open Channels - provide:
1) Hydraulic loss calculations for: entrance, friction, junction, access holes,
bends, angles, reduction and enlargement.
2) Analyze existing conditions upstream and downstream from proposed
system, to be determined by the City Engineer on a case-by-case basis.
3) Calculate critical depth and normal depth for open channel flow conditions.
4) Design for non-silting velocity of 2 FPS in a two-year frequency storm unless
otherwise approved by the City Engineer.
5) All pipes and outlets shall show HGL, velocity and Q value(s) for design
storm.
6) Confluence angles shall be maintained between 45° and 90° from the main
upstream flow. Flows shall not oppose main line flows.
4. INLETS
A Curb inlets at a sump condition should be designated for two CFS per lineal foot of
opening when headwater may rise to the top of curb.
B. Curb inlets on a continuous grade should be designed based on the following
equation:
3/2 Q = 0.7 L (a + y)
Where: y = depth of flow in approach gutter in feet
a = depth of depression of flow line at inlet in feet
L = length of clear opening in feet (maximum 30 feet)
Q = flow in CFS, use 100-year design storm minimum
C. Grated inlets should be avoided. When necessary, the design should be based
on the Bureau of Public Roads Nomographs (now known as the Federal Highway
Administration). All grated inlets shall be bicycle proof.
D. All catch basins shall have an access hole in the top unless access through the
grate section satisfactory to the City Engineer is provided.
Page 3 of 5
E. Catch basins/curb inlets shall be located so as to eliminate, whenever possible,
cross gutters. Catch basins/curb inlets shall not be located within 5' of any curb
return or driveway.
F. Minimum connector pipe for public drainage systems shall be 18".
G Flow through inlets may be used when pipe size is 24" or less and open channel
flow characteristics exist.
STORM DRAINS
A Minimum pipe slope shall be .005 (.5%) unless otherwise approved by the City
Engineer.
B. Minimum storm drain, within public right-of-way, size shall be 18" diameter.
C. Provide cleanouts at 300' maximum spacing, at angle points and at breaks in
grade greater than 1%. For pipes 48" in diameter and larger, a maximum
spacing of 500' may be used.
When the storm drain clean-out Type A dimension of "V" less "Z" is greater than
18", a storm drain clean-out Type B shall be used.
D. The material for storm drains shall be reinforced concrete pipe designed in
conformance with San Diego County Flood Control District's design criteria, as
modified by Carlsbad Standard Specifications. Corrugated steel pipe shall not be
used.
Plastic/rubber collars shall be prohibited.
E. Horizontal curve design shall conform to manufacturer recommended
specifications. Vertical curves require prior approval from the City Engineer.
F. The pipe invert elevations, slope, pipe profile line and hydraulic grade line for
design flows shall be delineated on the mylar of the improvement plans. Any
utilities crossing the storm drain shall also be delineated.
The strength classification of any pipe shall be shown on the plans. Minimum
D-load for RCP shall be 1350 in all City streets or future rights-of-way. Minimum
D-load for depths less than 2', if allowed, shall be 2000 or greater.
G For all drainage designs not covered in these Standards, the current San Diego
County Hydrology and Design and Procedure Manuals shall be used.
H. For storm drain discharging into unprotected or natural channel, proper energy
dissipation measures shall be installed to prevent damage to the channel or
erosion. In cases of limited access or outlet velocities greater than 18 fps, a
concrete energy dissipater per SDRS D-41 will be required.
Page 4 of 5
I. The use of detention basins to even out storm peaks and reduce piping is
permitted with substantiating engineering calculation and proper maintenance
agreements. Detention basins shall be fenced.
J. Desiltation measures for silt caused by development shall be provided and
cleaned regularly during the rainy season (October 1 to April 30) and after major
rainfall as required by the City Engineer or his designated representative.
Adequate storage capacity as determined by the City Engineer shall be
maintained at all times.
K. Protection of downstream or adjacent properties from incremental flows (caused
by change from an undeveloped to a developed site) shall be provided. Such
flows shall not be concentrated and directed across unprotected adjacent
properties unless an easement and storm drains or channels to contain flows are
provided.
L. Unprotected downstream channels shall have erosion and grade control
structures installed to prevent degradation, erosion, alteration or downcutting of
the channel banks.
M. Storm drain pipes designed for flow meeting or exceeding 20 feet per second will
require additional cover over invert reinforcing steel as approved by the City
Engineer.
N. Storm drain pipe under pressure flow for the design storm, i.e., HGL above the
soffit of the pipe, shall meet the requirements of ASTM C76, C361, C443 for
water-tight joints in the sections of pipe calculated to be under pressure and an
additional safety length beyond the pressure flow point. Such safety length shalt
be determined to the satisfaction of the City Engineer taking into consideration
such factors as pipe diameter, Q, and velocity.
O. An all weather access road from a paved public right-of-way shall be constructed
to all drainage and utility improvements. The following design parameters are
required: Maximum grade 14%, 15 MPH speed, gated entry, minimum paved
width 12 feet, 38' minimum radius, paving shall be a minimum of 4" AC over 4"
Class 11 AB, turnaround required if over 300'. Work areas should be provided as
approved by the plan checker. Access roads should be shown on the tentative
project approval to ensure adequate environmental review.
P. Engineers are encouraged to gravity drain all lots to the street without use of a
yard drain system. On projects with new street improvements proposed, a curb
outlet per SDRSD D-27 shall be provided for single-family residential lots to allow
yard drains to connect to the streets gutter.
Page 5 of 5