HomeMy WebLinkAboutCDP 2019-0002; HILLSIDE RESIDENCE; PRELIMINARY HYDROLOGY STUDY; 2019-05-29PRELIMINARY HYDROLOGY STUDY
Smith Residence CDP 2019-0002
Benjamin R. Lund
For
Jessie Smith
44 7 Bougher Rd
San Marcos, CA 92068
Prepared By:
Ben Lund Engineering
Granite Ridge Rd
Escondido, CA 92026
Date: May 25, 2019
RCE68849 Date
TABLE OF CONTENTS
1.0 Project Description .............................................................................................................. 3
1.1 Existing Condition ................................................................................................... 3
1.2 Proposed Condition ................................................................................................. 3
1.3 Soil Characteristics .................................................................................................. 4
2.0 Rational Method Description ............................................................................................... 4
3.0 Hydrology Analysis ............................................................................................................. 5
4.0 Water Quality ...................................................................................................................... 5
Attachments:
1. Vicinity Map
2. Existing Condition Hydrology Calculations & Exhibit
3. Proposed Condition Hydrology Calculations & Exhibit
2
1.0 Project Description
The Smith Residence project is located on a 0.26 acre parcel in the City of Carlsbad fronting
Hillside Drive which is a public street. Proposed improvements consist of a single family
residence and driveway along with other associated improvements. The site is located on APN:
207-360-11, please see Attachment 1 for the Vicinity Map.
1.1 Existing Condition
The existing site is approximately 0.26 acres. A 20' wide utility easement is located along the
northeast property line and contains a 48" concrete storm drain pipe as well as a 1 O" sewer main
(DWG 196-lA). Stormwater runoff from the site drains overland to the south, exits the site, and
enters an existing 24" CMP riser (DWG 196-lA) which lugs into the 48" concrete pipe.
Off site storm water runoff runs onto the site from APN: 207-022-10 from the north via three area
drain systems that outfall close to the property line between APNs 207-022-10 and 207-022-11
but, also via small areas of overland flow.
One of the area drain system drains into an existing 18" pipe (DWG 411-8A) which conveys
emergency overflow water from a retention basin built for the James Canyon Estates (DWG 385-
7 A). Unless the retention basin fails, water normally flows into the same existing 48" concrete
pipe. This pipe outfalls near the property line between APN s 207-022-10 and 207-022-11. The
other two drain systems outfall near the 18" pipe outfall.
The existing impervious area of the project parcel is 100%.
1.2 Proposed Condition
The proposed condition will not alter the existing drainage patterns of the area. The proposed
condition will extend the 18" emergency overflow pipe underneath the proposed driveway. The
two offsite area drain outfalls will be replaced by inlets which will accept the small portion of
overland cross-lot drainage and will connect to the existing 18" overflow pipe. Another inlet will
be added and connect to the existing 18" pipe to make a total of three for redundancy and ease of
maintenance.
Stormwater generated by the site will be captured by area drains and conveyed, via storm drain
pipes, to the ravine. Runoff in the ravine flows overland to the south, exits the site, and enters an
existing 24" CMP riser (DWG 196-lA) which lugs into the existing 48" concrete pipe.
Detention of runoff from the property or off site flows is not proposed as this would cause the
developed condition peak to move closer to the upstream watershed peak which would increase
stormwater peak flows in downstream structures.
The finish floor elevation of the proposed residence will be a minimum of 2 feet above the
existing 24" CMP riser.
3
ervious area summa .
Drive 3,160 SF
Street 200 SF
Buildi 1,500 SF
Total 4,860 SF
1.3 Soil Characteristics
The following soil group definitions come from Technical Release 55 (TR-55) by the United
States Department of Agriculture:
Group A soils have low runoff potential and high infiltration rates even when thoroughly wetted.
They consist chiefly of deep, well to excessively drained sand or gravel and have a high rate of
water transmission (greater than 0.30 in/hr).
Group B soils have moderate infiltration rates when thoroughly wetted and consist chiefly of
moderately deep to deep, moderately well to well drained soils with moderately fine to
moderately course textures. These soils have a moderate rate of water transmission (0.15-0.30
in/hr).
Group C soils have low infiltration rates when thoroughly wetted and consist chiefly of soils
with a layer that impedes downward movement of water and soils with moderately fine to fine
texture. These soils have a low rate of water transmission (0.05-0.15 in/hr).
Group D soils have high runoff potential. They have very low infiltration rates when thoroughly
wetted and consist chiefly of clay soils with a high swelling potential, soils with a permanent
high water table, soils with a clay pan or clay layer at or near the surface, and shallow soils over
nearly impervious material. These soils have a very low rate of water transmission (0-0.05 in/hr).
Group D soils is conservatively assumed to size drainage structures.
2.0 Rational Method Description
The rational method, as described in the 2003 San Diego County Hydrology Manual, was used to
generate surface runoff flows, which were then used to size the drainage facilities.
The basic equation: Q = CiA
C = runoff coefficient (varies with surface)
i = Intensity (in/hr)
A= Area (acres)
The 6 hour and 24 hour rainfall isopluvial maps are found in the 2003 San Diego County
Hydrology Manual. Adjusted P6 calculations can be found on the spreadsheets in Attachments 2
and 3 along with the Rational Method routing calculations. Initial travel time calculations (Ti) are
based on the overland flow equation given in Figure 3-3 of the County's Hydrology Manual and
is limited to the maximum overland flow length in Table 3-2 of the County's Hydrology Manual.
Travel time calculations between nodes are calculated via manning's equation or by the Kirpich
equation as expressed in the County's Hydrology Manual. Travel time values are then entered
4
into the spreadsheet under Tt. Confluences are done by spreadsheet and are labeled by the node
number where the confluence occurs. Each outfall point is shown on the existing and proposed
condition hydrology exhibits with the flow rate (Q) at that particular location.
3.0 Hydrology Analysis
The table below summarizes the pre-and post-construction 100-year flows. The outfall points
are shown on the Existing and Proposed Drainage Exhibits included in this report.
Table 2 Summa osed stormwater runoff.
A Q
ac cfs
0.66 1.9
Pro osed 100-Yr Node #225 Outfall 0.66 1.9
The total pre-development 100 year flow is 1.9 cfs. The total post-development 100 year flow is
1.9 cfs.
4.0 Water Quality
The project is a 'Standard Project' and complies with 'Standard Project' stormwater
requirements.
5
References
1. City of Carlsbad Engineering Design Manual by the City of Carlsbad
2. San Diego County Drainage Design Manual by the County of San Diego, May 2005.
3. San Diego County Hydrology Manual by the County of San Diego, June 2003.
6
Attachment 1
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Attachment 2
100-yr Stenn
Pre-Development Condition 57.8% Adjusted P6 = 2.6 Calculated by BRL Date 5/25/19
Iner. Total Soil Land Used Iner. Total Ti Ti T1 Tt' Tc Tc i Q=CiA
Node Area Area Group Use C C C*A C*A Flow Slope min. min. min. (used) In/Hr. Q,cfs Hydraulics and Notes
Description ac. ac. Path, ft % min.
100-105 0.27 0.27 D R4.3 0.52 0.52 0.14 0.14 110 20.0% 4.0 4.0 5.0 6.85 1.0 Initial Area
105-110 0.13 0.40 D R4.3 0.52 0.52 0.07 0.21 0.2 5.2 5.2 6.68 1.4 Pipe
110-115 0.26 0.66 D u 0.35 0.35 0.09 0.30 0.5 5.7 5.7 6.30 1.9 Outfall
Smith-Hydro01.xlsx
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 30® by Autodesk, Inc.
NODE 105 -110
Circular
Diameter (ft)
Invert Elev (ft)
Slope(%)
N-Value
Calculations
Compute by:
Known Q (cfs)
Elev (ft)
0
= 1.50
= 96.00
= 3.00
= 0.024
Known Q
= 1.10
Friday, May 3 2019
Highlighted
Depth (ft) = 0.34
Q (cfs) = 1.100
Area (sqft) = 0.30
Velocity (ft/s) = 3.63
Wetted Perim (ft) = 1.49
Crit Depth, Ye (ft) = 0.39
Top Width (ft) = 1.26
EGL (ft) = 0.55
Section
2 3
Reach (ft)
Pre-development Klrplch Calculations
Node 110-115
Tt = (11.9*L3/~E)°"385
T1 = Time of concentration (hours)
L = Watercourse Distance (miles)
AE = Change in elevation along effective slope line
L (ft)= 65
AE = 5
T1 (min)= 0.5 ~---'
0 15' JO'
i 1 I
GRAPHIC SCALE
!" = 30'
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EXISTING CONDITION
HYDROLOGY
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Attachment 3
100-yr Stonn
Post-Development Condition 57.8% Adjusted P6 = 2.6 Calculated by BRL Date 5/25/2019
Iner. Total Soil Land Used Iner. Total Ti Ti T1 T' t Tc Tc i Q=CiA
Node Area Area Group Use C C C*A C*A Flow Slope min. min. min. (used) In/Hr. Q,cfs Hydraulics and Notes
Description ac. ac. Path, ft % min.
200-205 0.02 0.02 D R4.3 0.52 0.52 0.01 0.01 55 1.0% 7.7 7.7 7.7 5.19 0.05 Initial Area
205-225 0.05 0.07 D R43.0 0.79 0.79 0.04 0.05 0.9 8.6 8.6 4.83 0.2 Pipe
210-225 0.40 0.47 D R4.3 0.52 0.52 0.21 0.26 8.6 8.6 4.83 1.2 Add Area & Pipe
215-225 0.13 0.60 D R43.0 0.79 0.79 0.10 0.36 8.6 8.6 4.83 1.7 Pioe
220-225 0.06 0.66 D R4.3 0.52 0.52 0.03 0.39 8.6 8.6 4.83 1.9 Outfall
Smith-Hydro01.xlsx
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.
NODE 205-225
Circular
Diameter (ft)
Invert Elev (ft)
Slope(%)
N-Value
Calculations
Compute by:
Known Q (cfs)
Elev (ft)
108.00
107.50
107.25
0
= 0.50
= 107.00
= 1.00
= 0.013
Known Q
= 0.05
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ft/s)
Wetted Perim (ft)
Crit Depth, Ye (ft)
Top Width (ft)
EGL (ft)
1
Saturday, May 25 2019
= 0.11
= 0.050
= 0.03
= 1.55
= 0.49
= 0.11
= 0.42
= 0.15
Section
Reach (ft)
0 IS' JO'
! 1 I
GRAPHIC SCALE 1• = JO'
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PROPOSED CONDITION
HYDROLOGY
LEGEND
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