HomeMy WebLinkAboutSDP 00-10; Pavilion The Forum The; Site Development Plan (SDP) (11)I
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PLANNING
ENGINEERING
SURVEYING
IRVINE
RIVERSIDE
SAN DIEGO
HUNSAKER
&ASSOCIATES
5 A N D I E G 0, I N C.
HYDROLOGY STUDY
for
PAVILION PROPERTY
City of Carlsbad, California
Prepared for:
Thomas Enterprises, Inc.
2924 Emerson Street, Suite 206
San Diego, CA 92106
W.O. 2358-01
November 3, 2000
David A. Hammar, R.C.E.
DAvE HAMMAR PreSl·~~-:--..--r---;:::
JACK HILL Hunsaker & Assoc1a es an Diego, Inc.
LEX WILLIMAN
ALISA VIALPANDO
10179 Huennekens St.
San Di<;go, CA 92121
(858) 558-4500 PH
(858) 558-1414 F X
www.hunsaker.com
lnfo@HunsakerSD.com
RECEIVED
NOV 0 3 2000
CITY OF CARLSBAD
PLANNING DEPT
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Pavilion Property
Hydrology Study
Executive Summary
TABLE OF CONTENTS
Introduction
Summary of Results
References
Methodology & Model Development
City of Carlsbad Drainage Design Criteria
Rational Method Hydrologic Analysis
Rational Method Hydrology -Developed Conditions
Site Runoff to Existing Detention Basin
Developed Conditions Assume Full Commercial Development
Of the Pavilion Site
Developed Condition Hydrology Map
SECTION
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(pocket)
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Pavilion Property
Hydrology Study
Introduction
EXECUTIVE SUMMARY
The Pavilion project is a proposed commercial development located west of El
Camino Real and north of Leucadia Boulevard in the City of Carlsbad, California
(see Vicinity Map below). All runoff from the project site flows to an existing
detention basin located east of the site.
PACIFIC
OCEAN
VICINITY MAP
NO SCALE
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Per Grading Plans for Carlsbad Tract 92-08, prepared by P&D/CTE Engineers, Inc.
and obtained from the City of Carlsbad, runoff from the site as well as runoff from
the upstream Calle Barcelona storm drain system will empty into the existing
detention basin. According to these plans, the 1 00-year runoff in the existing storm
drain system is 82 cfs at the outfall to the detention basin. The 1 00-year outflow
from the existing Pavilion site desilting was listed as 25 cfs while the 1 00-year flow
in the upstream Calle Barcelona storm drain system upstream of the Pavilion
confluence was listed as 60 cfs. Of the 60 cfs, the Pavilion site contributed 25 cfs
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Pavilion Property
Hydrology Study
via a 24-inch stub-out at Sta. 23+00. Thus, the offsite runoff was assumed to be 35
cfs (60 -25).
In developed conditions, a portion of the site runoff will drain to the existing stub-out
to the existing Calle Barcelona storm drain system. This runoff will combine with
flow from the remainder of the Pavilion site (runoff to northeast corner of site) in the
existing Calle Barcelona system just upstream of the existing detention basin.
This study does not analyze the onsite storm drain system. The onsite storm drain
system, which will be analyzed in subsequent submittals to the City, will be sized so
that no onsite flooding will occur for the 1 00-year design storm. As noted in the plan
check comments, the final onsite developed condition peak flows may differ slightly
as a result of revised time of concentration values.
However, this analysis does assume a developed condition runoff coefficient of
0,85, which corresponds to commercial development. Thus, any future flow
differences will be small and not constitute large flow variances for downstream
facilities as compared to this analysis.
Summary of Results
Table 1 below summarizes developed condition drainage areas and 100-year peak
flows for the site. As stated earlier, the total offsite runoff in the Calle Barcelona
storm drain system was determined to be 35 cfs.
TABLE 1
Summary of Developed Condition Peak Flows
Location Drainage Area 1 00-Year Peak Flow
(acres) (cfs.)
Stub-Out to Existing Calle
Barcelone Storm Drain 5 21
System (Sta. 23+00)
Pavilion Site 14 40
Total Site Runoff to
Existing Calle Barcelona 19 55
Storm Drain System
As indicated earlier, the 24-inch stub-out at Sta. 23+00 was designed for a 100-year
flow of 25 cfs. This analysis predicts a developed conditions 1 00-year peak flow of
21 cfs at the same location. Calculations show the 100-year peak flow to the
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Pavilion Property
Hydrology Study
northeast corner of the site would be 40 cfs. This represents a 15 cfs increase as
compared to the existing study.
Thus, the total 1 00-year developed condition flow from the Calle Barcelona storm
drain system to the existing detention basin would be 90 cfs (35 cfs +55 cfs).
Though this represents an 8 cfs increase from the design flowrate (90 cfs-82 cfs).
Using the design flow of 82 cfs, the approved existing storm drain system was
already under pressure. The addition of 8 cfs will not cause flooding conditions in
the existing storm drain system.
References
Standards for Design and Construction of Public Works Improvements in the City of
Carlsbap, 1993
Drainage Design and Procedure Manual. County of San Diego: April 1993.
Master Drainage and Storm Water Quality Management Plan, City of Carlsbad:
March, 1994.
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Pavilion Property
Hydrology Study
Rainfall Intensity -Initial time of concentration values were determined using the
County of San Diego's overland flow nomograph for natural and urban areas. Per
County standards, a maximum 1 0-minute time increment is added to the initial
natural area subbasin. Downstream T c values are determined by adding the initial
subbasin time of concentration and the downstream routing time. Intensity values
were determined from the Intensity-Duration design chart from the County of San
Diego's Drainage Design Manual. Precipitation values correspond to the 1 00-year,
6-hour design storm.
Method of Analysis -The Rational Method is the most widely used hydrologic
model for estimating peak runoff rates. Applied to small urban and semi-urban
areas with drainage areas less than 0.5 square miles, the Rational Method relates
storm rainfall intensity, a runoff coefficient, and drainage area to peak runoff rate.
This relationship is expressed by the equation:
Q = CIA, where:
Q = The peak runoff rate in cubic feet per second at the point of analysis.
C = A runoff coefficient representing the area-averaged ratio of runoff to rainfall
intensity.
I = The time-averaged rainfall intensity in inches per hour corresponding to the
time of concentration.
A = The drainage basin area in acres.
To perform a node-link study, the total watershed area is divided into subareas
which discharge at designated nodes.
The procedure for the subarea summation model is as follows:
(1) Subdivide the watershed into an initial subarea (generally 1 lot) and
subsequent subareas, which are generally less than 10 acres in size. Assign
upstream and downstream node numbers to each subarea.
(2) Estimate an initial T c by using the appropriate nomograph or overland flow
velocity estimation.
(3) Using the initial Tc, determine the corresponding values of I. Then Q =CIA.
(4) Using Q, estimate the travel time between this node and the next by
Manning's equation as applied to the particular channel or conduit linking the
two nodes. Then, repeat the calculation for Q based on the revised intensity
(which is a function of the revised time of concentration)
The nodes are joined together by links, which may be street gutter flows, drainage
swales, drainage ditches, pipe flow, or various channel flows. The AES-99
computer subarea menu is as follows:
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Pavilion Property
Hydrology Study
SUBAREA HYDROLOGIC PROCESS
1. Confluence analysis at node.
2. Initial subarea analysis (including time of concentration calculation).
3. Pipeflow travel time (computer estimated).
4. Pipeflow travel time (user specified).
5. Trapezoidal channel travel time.
6. Street flow analysis through subarea.
7. User -specified information at node.
8. Addition of subarea runoff to main line.
9. V-gutter flow through area.
10. Copy main stream data to memory bank
11. Confluence main stream data with a memory bank
12. Clear a memory bank
At the confluence point of two or more basins, the following procedure is used to
combine peak flow rates to account for differences in the basin's times of
concentration. This adjustment is based on the assumption that each basin's
hydrographs are triangular in shape.
(1 ).
(2).
If the collection streams have the same times of concentration, then
the Q values are directly summed,
If the collection streams have different times of concentration, the
smaller of the tributary Q values may be adjusted as follows:
(i). The most frequent case is where the collection stream with the
longer time of concentration has the larger Q. The smaller Q
value is adjusted by the ratio of rainfall intensities.
(ii). In some cases, the collection stream with the shorter time of
concentration has the larger Q. Then the smaller Q is adjusted
by a ratio of the T values.
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****************************************************************************
RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE
Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT
1985,1981 HYDROLOGY MANUAL
(c) Copyright 1982-99 Advanced Engineering Software (aes)
Ver. 1.5A Release Date: 01/01/99 License ID 1239
Analysis prepared by:
Hunsaker & Associates San Diego, Inc.
10179 Huennekens Street
San Diego, California (619) 558-4500
Planning Engineering Surveying
************************** DESCRIPTION OF STUDY **************************
* PAVILION AT LA COSTA
* ON SITE 1,. * W.O. #2358-01
***********************************************************,***************
* * *
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FILE NAME: H:\AES99\2358\01\PAVIL10.RAT"
TIME/DATE OF STUDY: 7:58 7/ 5/2000 ----------------------------------------------------------------------------USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION:
1985 SAN DIEGO MANUAL CRITERIA
USER SPECIFIED STORM EVENT(YEAR) = 100.00
6-HOUR DURATION PRECIPITATION (INCHES) =
SPECIFIED MINIMUM PIPE SIZE(INCH) = 18.00
2.800
SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE =
SAN DIEGO HYDROLOGY MANUAL "C" -VALUES USED
NOTE: ONLY PEAK CONFLUENCE VALUES CONSIDERED
0.90
****************************************************************************
FLOW PROCESS FROM NODE 301.00 TO NODE 302.00 IS CODE = 21
>>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<<
========~===================================================================
*USER SPECIFIED(SUBAREA):
COMMERCIAL DEVELOPMENT RUNOFF COEFFICIENT = .8500
INITIAL SUBAREA FLOW-LENGTH = 160.00
UPSTREAM ELEVATION = 104.00
DOWNSTREAM ELEVATION= 102.00
ELEVATION DIFFERENCE = 2.00
URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) =
TIME OF CONCENTRATION ASSUMED AS 6-MINUTES
100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.559
SUBAREA RUNOFF(CFS) = 1.11
5.284
TOTAL AREA(ACRES) = 0.20 TOTAL RUNOFF(CFS) = 1.11
**************************************************************************** I FLOW PROCESS FROM NODE 302.00 TO NODE 3.00 IS CODE= 6 ----------------------------------------------------------------------------
>>>>>COMPUTE STREETFLOW TRAVELTIME THRU SUBAREA<<<<<
1 ============================================================================
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UPSTREAM ELEVATION = 102.00
STREET LENGTH(FEET} = 700.00
STREET HALFWIDTH(FEET) = 20.00
DOWNSTREAM ELEVATION =
CURB HEIGHT(INCHES) = 8.
DISTANCE FROM CROWN TO CROSSFALL GRADEBREAK =
INTERIOR STREET CROSSFALL(DECIMAL} = 0.020
OUTSIDE STREET CROSSFALL(DECIMAL) = 0.020
10.00
SPECIFIED NUMBER OF HALFSTREETS CARRYING RUNOFF = 2
**TRAVELTIME COMPUTED USING MEAN FLOW(CFS) =
STREETFLOW MODEL RESULTS:
STREET FLOWDEPTH(FEET) = 0.40
HALFSTREET FLOODWIDTH(FEET) = 11.84
AVERAGE FLOW VELOCITY(FEET/SEC.) =
PRODUCT OF DEPTH&VELOCITY = 1.36
3.45
STREETFLOW TRAVELTIME(MIN) = 3.38 TC(MIN} = 9.38
10.98
90.00
I 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.915
*USER SPECIFIED(SUBAREA):
, COMMERCIAL DEVELOPMENT RUNOFF COEFFICIENT = .8500
-SUBAREA AREA (ACRES) = 4 . 7 0 SUBAREA RUNOFF ( CFS) = I SUMMED AREA(ACRES) = 4.90 TOTAL RUNOFF(CFS) =
END OF SUBAREA STREETFLOW HYDRAULICS:
19. 64-
20.75
DEPTH(FEET) = 0.47 HALFSTREET FLOODWIDTH(FEET) = 15.78 I FLOW VELOCITY (FEET I SEC. } = 3 . 8 7 DEPTH*VELOCITY = 1 . 8 3
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FLOW PROCESS FROM NODE 3.00 TO NODE 2.00 IS CODE = 3
>>>>>COMPUTE PIPEFLOW TRAVELTIME THRU SUBAREA<<<<<
>>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<<
=====~======================================================================
DEPTH OF FLOW IN 24.0 INCH PIPE IS 15.5 INCHES
PIPEFLOW VELOCITY(FEET/SEC.) = 9.7
UPSTREAM NODE ELEVATION = 81.00
DOWNSTREAM NODE ELEVATION= 74.00
FLOWLENGTH(FEET} = 420.00 MANNING'S N = 0.013
ESTIMATED PIPE DIAMETER(INCH) = 24.00 NUMBER OF PIPES =
PIPEFLOW THRU SUBAREA(CFS) 20.75
TRAVEL TIME(MIN.) = 0.72 TC(MIN.) = 10.11
1
****************************************************************************
FLOW PROCESS FROM NODE 2.00 TO NODE 2.00 IS CODE = 1 -------------------------------------------------------------------------.---
>>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<<
=====~======================================================================
TOTAL NUMBER OF STREAMS = 2
CONFLUENCE VALUES USED FOR INDEPENDENT
TIME OF CONCENTRATION(MIN.) = 10.11
RAINFALL INTENSITY(INCH/HR) = 4.69
TOTAL STREAM AREA(ACRES) = 4.90
PEAK FLOW RATE(CFS) AT CONFLUENCE=
STREAM 1 ARE:
20.75
****************************************************************************
FLOW PROCESS FROM NODE 201.00 TO NODE 202.00 IS CODE = 21
----------------------------------------------------------------------------
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>>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<<
============================================================================
*USER SPECIFIED(SUBAREA):
COMMERCIAL DEVELOPMENT RUNOFF COEFFICIENT = .8500
INITIAL SUBAREA FLOW-LENGTH= 170.00
UPSTREAM ELEVATION = 106.00
DOWNSTREAM ELEVATION = 104.00
ELEVATION DIFFERENCE = 2.00
URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) =
TIME OF CONCENTRATION ASSUMED AS 6-MINUTES
100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.559
SUBAREA RUNOFF(CFS) = 2.23
5.558
TOTAL AREA(ACRES) = 0.40 TOTAL RUNOFF(CFS) = 2.23
****************************************************************************
FLOW PROCESS FROM NODE 202.00 TO NODE 2.00 IS CODE = 6
-----------------------------------------~----------------------------------
>>>>>COMPUTE STREETFLOW TRAVELTIME THRU SUBAREA<<<<<
============================================================================
UPSTREAM ELEVATION= 104.00 DOWNSTREAM ELEVATION =
CURB HEIGHT(INCHES) = 8.
88.00
-STREET LENGTH(FEET) = 2000.00
STREET HALFWIDTH(FEET) = 20.00
DISTANCE FROM CROWN TO CROSSFALL GRADEBREAK =
INTERIOR STREET CROSSFALL(DECIMAL) = 0.020
OUTSIDE STREET CROSSFALL(DECIMAL) = 0.020
10.00
SPECIFIED NUMBER OF HALFSTREETS CARRYING RUNOFF = 2
**TRAVELTIME COMPUTED USING MEAN FLOW(CFS) =
STREETFLOW MODEL RESULTS:
STREET FLOWDEPTH(FEET) = 0.54
HALFSTREET FLOODWIDTH(FEET) = 19.16
AVERAGE FLOW VELOCITY(FEET/SEC.) =
PRODUCT OF DEPTH&VELOCITY = 1.60
2.96
STREETFLOW TRAVELTIME(MIN) = 11.28 TC(MIN) =
100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 3.315
*USER $PECIFIED(SUBAREA):
17.28
COMMERCIAL DEVELOPMENT RUNOFF COEFFICIENT = .8500
SUBAREA AREA(ACRES) = 13.50 SUBAREA RUNOFF(CFS) =
SUMMED AREA(ACRES) = 13.90 TOTAL RUNOFF(CFS) =
END OF SUBAREA STREETFLOW HYDRAULICS:
22.81
38.04
40.27
DEPTH(FEET) = 0.63 HALFSTREET FLOODWIDTH(FEET) = 20.00
FLOW VELOCITY(FEET/SEC.) = 3.62 DEPTH*VELOCITY = 2.27
****************************************************************************
FLOW PROCESS FROM NODE 2.00 TO NODE 2.00 IS CODE = 1
----------------------------------------------------------------------------
>>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<<
>>>>>AND COMPUTE VARIOUS CONFLUENCED STREAM VALUES<<<<<
============================================================================
TOTAL NUMBER OF STREAMS = 2
CONFLUENCE VALUES USED FOR INDEPENDENT
TIME OF CONCENTRATION(MIN.) = 17.28
RAINFALL INTENSITY(INCH/HR) = 3.32
TOTAL STREAM AREA(ACRES) = 13.90
PEAK FLOW RATE(CFS) AT CONFLUENCE =
STREAM
40.27
2 ARE:
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** CONFLUENCE DATA **
STREAM RUNOFF
NUMBER (CFS)
1 20.75
2 40.27
Tc
(MIN.)
10.11
17.28
RAINFALL INTENSITY AND TIME
CONFLUENCE FORMULA USED FOR
** PEAK FLOW RATE TABLE **
STREAM RUNOFF Tc
NUMBER (CFS) (MIN.)
1 49.25 10.11
2 54.96 17.28
OF
2
INTENSITY
(INCH/HOUR)
4.685
3.315
CONCENTRATION
STREAMS.
INTENSITY
(INCH/HOUR)
4.685
3.315
COMPUTED CONFLUENCE ESTIMATES ARE AS FOLLOWS:
PEAK FLOW RATE(CFS) = 54.96 Tc(MIN.) =
TOTAL AREA(ACRES) = 18.80
AREA
(ACRE)
4.90
13.90
RATIO
17.28
****************************************************************************
FLOW PROCESS FROM NODE 2.00 TO NODE 1. 00 IS CODE = 3
>>>>>COMPUTE PIPEFLOW TRAVELTIME THRU SUBAREA<<<<<
>>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<<
============================================================================
DEPTH OF FLOW IN 33.0 INCH PIPE IS 22.6 INCHES
PIPEFLOW VELOCITY(FEET/SEC.) = 12.7
UPSTREAM NODE ELEVATION= 74.00
DOWNSTREAM NODE ELEVATION = 71.00
FLOWLENGTH(FEET) = 165.00 MANNING'S N = 0.013
ESTIMATED PIPE DIAMETER(INCH) = 33.00 NUMBER OF PIPES =
PIPEFLOW THRU SUBAREA(CFS) = 54.96
TRAVEL TIME(MIN.) = 0.22 TC(MIN.) = 17.50
1
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END OF STUDY SUMMARY:
PEAK FLOW RATE(CFS) =
TOTAL AREA(ACRES) =
54.96
18.80
Tc (MIN.) = 17.50
============================================================================
END OF RATIONAL METHOD ANALYSIS
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