HomeMy WebLinkAboutSDP 15-25; CARLSBAD OAKS LOTS 18 & 19; DRAINAGE STUDY FOR HIGH-TECH; 2016-06-03DRAINAGE STUDY
For
HIGH-TECH
CARLSBAD, CA
Prepared for:
Gregg Hamann
3575 Kenyon Street
San Diego Ca 92110
619-4407424
Prepared by
osuItanIs, Inc.
Bruce Robertson
REC Consultants, Inc
2442 Second Avenue
San Diego, CA 92101
Telephone: 619-232-9200
Report Prepared:
June 3, 2016
RECEIVED
JUN 032016
LAND DEVELOPMENT
ENGINEERING
High-Tech
Drainage Study
TABLE OF CONTENTS
SECTION
Chapter 1 - Executive Summary
1.1 Introduction
1.2 Summary of Existing Conditions
1.3 Summary of Developed Conditions
1.4 Summary of Results
1.5 References
Chapter 2 - Methodology II
2.1 County of San Diego Drainage Design Criteria
2.2 Design Rainfall Determination
2.2.1- 100-Year, 6-Hour Rainfall Isopluvial Map
2.2.2 -100-Year, 24-Hour Rainfall Isopluvial Map
2.3 Runoff Coefficient Determination
2.3 Rainfall Intensity Determination
2.4 Urban Watershed Overland Time of Flow Nomograph
2.5 County of San Diego Intensity-Duration Curves
2.6 Model Development Summary
(from County of San Diego Hydrology Manual)
Chapter 3— 100-Year Hydrologic Analysis for Existing Conditions
Chapter 4-100-Year Hydrologic Analysis for Developed Conditions IV
Chapter 5— Hydrology Maps V
High-Tech
Drainage Study
CHAPTER 1 - EXECUTIVE SUMMARY
1.1 -Introduction
The High-Tech Whiptail Loop project site is comprised of Lots18 and 19 of the
existing Carlsbad Oaks North development. The project is located north of the
Bobcat Ct. and Whiptail Loop E intersection.
Lots 18 and 19 are mass graded per the "As Built" plan for the Carlsbad Oaks North
Phase 2 C.T. 97-13 project.
Runoff from Lot 18 drains to one of two onsite basins. Discharge from the
easternmost basin is conveyed to an existing Modified Type 'F' catch basin and
Spillway via an existing 24-inch RCP stormdrain. Runoff from the westernmost basin
is also conveyed to this catch basin via an existing 24-inch RCP stormdrain. Runoff
from the catch basin is conveyed via a 24-inch RCP stormdrain to the existing
stormdrain line beneath Whiptail Loop E which ultimately outlets at the intersection
of Whiptail Loop E. and Faraday St.
Runoff from Lot 19 drains in a southeasterly direction toward an existing basin which
discharges to an existing 24-inch RCP stormdrain. The stormdrain line then
connects to an existing Type B curb inlet. Runoff from both the stormdrain and inlet
is then conveyed to an existing 24-inch RCP storm drain line beneath Whiptail Loop
W. which ultimately outlets at the intersection of Whiptail Loop W. and Faraday St.
The storm drain system within Whiptail Loop has been sized in anticipation of full
development of Lots 18 and 19. This study analyzes and verifies that the anticipated
100-year runoff from is equal to or less than the capacity of the existing system. For
hydromodiflcation analysis, two (2) points of comparison (POC) have been
designated downstream of the project site for hydrologic analysis purposes.
The project site lies outside any FEMA 100-year floodplain zones therefore no
Letters of Map Revision will be required.
Treatment of storm water runoff from the site has been addressed in a separate
report - the "Storm Water Mitigation Plan High-Tech" by REC. Hydromodification
(HMP) analysis has been presented within the "Technical Memorandum: SWMM
Modeling for High-Tech", dated February, 2016 by REC.
Per County of San Diego drainage criteria, the Modified Rational Method should be
used to determine peak design flowrateswhen the contributing drainage area is less
than 1.0 square mile. Since the total watershed area discharging from the site is
less than 1.0 square mile, the CIVIL-D computer software was used to model the pre
& post developed condition runoff response per the Modified Rational Method.
High-Tech
Drainage Study
Methodology used for the computation of design rainfall events, runoff coefficients,
and rainfall intensity values are consistent with criteria set forth in the "County of San
Diego Drainage Design Manual". A more detailed explanation of methodology used
for this analysis is listed in Chapter 2 of this report.
1.2— Summary of Existing Conditions
Currently, the High-Tech Whiptail Loop Lots 18 and 19 project site is composed of
two mass-graded lots. The lots have been graded, per City of Carlsbad project CT
97-13, in anticipation of full development of Lots 18 and 19.
Runoff from Lot 18 drains to one of two onsite sedimentation basins. Discharge from
the easternmost basin is conveyed to an existing Modified Type 'F' catch basin and
spillway via an existing 24-inch RCP stormdrain. Runoff from the westernmost basin
is also conveyed to this catch basin via an existing 24-inch RCP stormdrain. Runoff
from the catch basin is conveyed via a 24-inch RCP stormdrain to the existing
stormdrain line within Whiptail Loop (POC-1).
Runoff from Lot 19 drains in a southeasterly direction toward an existing basin which
discharges to an existing 24-inch RCP stormdrain. The stormdrain line then
connects to an existing Type B curb inlet. Runoff from both the stormdrain and inlet
is then conveyed to an existing 24-inch RCP storm drain line within Whiptail Loop
(POC-2).
Table I below summarizes the existing condition design 100-year peak flow from the
project site. The flow values provided are per C.T.97-13 Drawing No. 415-9J.
TABLE I - Summary of Existing Condition Flows*
Drainage Impervious 100-Year
Lot Discharge Location Area Percentage Peak Flow
(Ac) (cfs)
18 POC-1 5.10 0% 24.0
19 POC-2 4.20 0% 22.0
Flow values and drainage areas per City of Carlsbad Project NO. C.T. 97-13 Drawing No. 415-9J Sheet 17 and
18. (provided)
High-Tech
Drainage Study
1.3— Summary of Developed Conditions
The High-Tech Whiptail Loop Lots 18-19 project has a total area of 405,543.6 sf (9.3
ac). The proposed project will involve the construction of a 108,610sf office building
and 76,735sf of landscaping. The remaining 220,198sf will be composed of a
parking lot and sidewalks.
The project includes onsite storm drain improvements to convey flows to the two-
existing 24-inch RCP beneath Whiptail Loop as pre-development conditions. These
discharge locations are designated as POC-1 and POC-2. Refer to "Post-Developed
Condition" hydrology exhibit.
Per County of San Diego criteria, runoff coefficients of 0.35 and 0.90 were assumed
- - respectively for the open landscaped space and commercial developed areas. See
Chapter 2.3. Per County of San Diego rainfall isopluvial maps, the design 100-year
rainfall depth for the site area is 2.94 inches.
Table 2 below summarizes the developed condition design 100-year peak flow from
the project site.
TABLE 2— Summary of Developed Condition Flows
Drainage Impervious 100-Year
Discharge Location Area Percentage Peak Flow
(Ac) (cfs)
POC-1 5.72 66% 20.5
POC-2 3.56 74% 21.4
Prior to discharging from the project site, developed site runoff is intercepted by one
of six dual purpose onsite biofiltration best management practice (BMP) detention
facilities. Sizing for the proposed facilities is in accordance with standards set forth
by the Regional Water Quality Control Board and the County of San Diego's Storm
Water Standards (see "Storm Water Quality Management Plan (SWQMP) for High
Tech" by REC). These basins serve to meet water quality and hydromodification
requirements for the project site. Peak flow mitigation is not necessary as it is shown
in Table 3 of the following page that the existing stormdrain system has a capacity
larger than the unmitigated-developed 100-year design peak flow.
High-Tech
Drainage Study
1.4 - Summary of Results
- Table 3 summarizes developed and anticipated build out condition 100-year peak
flow rates at the discharge locations from the High Tech site. Per County of San
Diego rainfall isopluvial maps, the design 100-year rainfall depth for the site area is
2.96 inches.
TABLE 3 - SUMMARY OF PEAK FLOWS*
Discharge
Location Condition Drainage Area
(Ac)
100 Year Peak
Discharge (cfs)
POC I Existing 5.10 24.0
Developed 5.72 20.5
Difference -3.5
POC 2 Existing '- 4.20 22.0
Developed 3.56 21.4
Difference -0.6
Flow values and drainage areas per city ot carisDaci iroject NO. U. I. J(-1i iirawing NO. 41-J bneet it and
18. (provided)
As shown in the above table, the development of the proposed High Tech project
site will result in a net discharge that is lower than the design allowance capacity of
the existing infrastructure.
All developed runoff will receive water quality treatment in accordance with the site
specific SWMP. Additionally, the POCs are HMP compliant as analyzed in the
Hydromodification Technical Memo.
Final storm drain and inlet design details will be provided at the final engineering
phase of the development.
1.5 - References
- "County of San Diego Hydrology Manuaf', dated June 2003
"Storm Water Mitigation Plan for High Tech", dated February 2016 by REC
Consultants.
"Technical Memorandum: SWMM Modeling for High Tech", dated February 2016 by
REC Consultants
High-Tech
Drainage Study
CHAPTER 2
METHODOLOGY - RATIONAL METHOD PEAK
FLOWRATE DETERMINATION
2.1 - County of San Diego Design Criteria
San Diego County Hydrology Manual Section: 3
Date: June 2003 Page: 1 of 26
- SECTION 3
RATIONAL METHOD AND MODIFIED RATIONAL METHOD
3.1 THE RATIONAL METHOD
The Rational Method (RM) is a mathematical formula used to determine the maximum
runoff rate from a given rainfall. It has particular application in urban storm drainage, where
it is used to estimate peak runoff rates from small urban and rural watersheds for the design
of storm drains and small drainage structures. The RM is recommended for analyzing the
runoff response from drainage areas up to approximately 1 square mile in size. It should not
be used in instances where there is a junction of independent drainage systems or for
drainage areas greater than approximately 1 square mile in size. In these instances, the
Modified Rational Method (MRM) should be used for junctions of independent drainage
systems in watersheds up to approximately 1 square mile in size (see Section 3.4); or the
NRCS Hydrologic Method should be used for watersheds greater than approximately 1
square mile in size (see Section 4).
The RM can be applied using any design storm frequency (e.g., 100-year, 50-year, 10-year,
etc.). The local agency determines-the design storm frequency that must be used based on
the type of project and specific local requirements. A discussion of design storm frequency
is provided in Section 2.3 of this manual. A procedure has been developed that converts the
6-hour and 24-hour precipitation isopluvial map data to an Intensity-Duration curve that can
be used for the rainfall intensity in the RM formula as shown in Figure 3-1. The RM is
applicable to a 6-hour storm duration because the procedure uses Intensity-Duration Design
Charts that are based on a 6-hour storm duration.
3.1.1 Rational Method Formula
The RM formula estimates the peak rate of runoff at any location in a watershed as a function
of the drainage area (A), runoff coefficient (C), and rainfall intensity (I) for a duration equal
- to the time of concentration (Ta), which is the time required for water to
3-1
High-Tech
Drainage Study
CHAPTER 2
METHODOLOGY- RATIONAL METHOD PEAK
FLOWRATE DETERMINATION
2.2 - Design Rainfall Determination
ri
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Drainage Study
CHAPTER 2
METHODOLOGY - RATIONAL METHOD PEAK
FLOWRATE DETERMINATION
J
2.2 - 100-Year, 6-Hour Rainfall Isopluvial Map
High-Tech
Drainage Study
CHAPTER 2
METHODOLOGY - RATIONAL METHOD PEAK•
FLOWRATE DETERMINATION
2.2 - 100-Year, 24-Hour Rainfall Isopluvial Map
I
High-Tech
Drainage Study
CHAPTER 2
METHODOLOGY - RATIONAL METHOD. PEAK
FLOWRATE DETERMINATION
2.3 - Runoff Coefficient Determination
San Diego County Hydrology Manual Section: 3 Date: June 2003 Page: 4 of 26
The storm frequency of peak discharges is the same as that of! for the given T.
The fraction of rainfall that becomes runoff (or the runoff coefficient, C) is independent
of I or precipitation zone number (PZN) condition (PZN Condition is discussed in
Section 4.1.2.4).
The peak rate of runoff is the only information produced by using the RM.
3.1.2 Runoff Coefficient
Table 3-1 lists the estimated runoff coefficients for urban areas. The concepts related to the
runoff coefficient were evaluated in a report entitled Evaluation, Rational Method "C"
Values (Hill, 2002) that was reviewed by the Hydrology Manual Committee. The Report is
available at San Diego County Department of Public Works, Flood Control Section and on
the San Diego County Department of Public Works web page.
The runoff coefficients are based on land use and soil type. Soil type can be determined from
the soil type map provided in Appendix A. An appropriate runoff coefficient (C) for each
type of land use in the subarea should be selected from this table and multiplied by the
percentage of the total area (A) included in that class. The sum of the products for all land
uses is the weighted runoff coefficient (E[CA]). Good engineering judgment should be used
when applying the values presented in Table 3-1, as adjustments to these values may be
appropriate based on site-specific characteristics. In any event, the impervious percentage
(% Impervious) as given in the table, for any area, shall govern the selected value for C. The
runoff coefficient can also be calculated for an area based on soil type and impervious
percentage using the following formula:
San Diego County Hydrology Manual Section: 3
Date: June 2003 Page: 5 of 26
C=O.9Ox(% Impervious) +Cx(l-%Impervious)
Where: C, = Pervious Coefficient Runoff Value for the soil type (shown in
Table 3-1 as Undisturbed Natural Terrain/Permanent Open Space,
O% Impervious). Soil type can be determined from the soil type map
provided in Appendix A.
The values in Table 3-1 are typical for most urban areas. However,*if the basin contains rural
or agricultural land use, parks, golf courses, or other types of nonurban land use that are
expected to be permanent the appropriate value should be selected based upon the soil and
cover and approved by the local agency.
3-5
San Diego County Hydrology Manual Section: 3
Date: June 2003 Page: 6 of 26
Table 3-1
RUNOFF COEFFICIENTS FOR URBAN AREAS
Land Use Runoff Coefficient "C"
Soil Type
NRCS Elements County Elements % RAPER. B C D
Undisturbed Natural Terrain (Natural) Permanent Open Space 0*. 0.20 0.25 0.30 0.35
Low Density Residential (LDR) Residential, 1.0 DU/A or less 10 0.27 0.32 0.36 0.41
Low Density Residential (LDR) Residential, 2.0 DU/A or less 20 0.34 0.38 0.42 0.46
Low Density Residential (LDR) Residential, 2.9 DU/A or less 25 0.38 0.41 0.45 0.49
Medium Density Residential (MDR) Residential, 4.3 DU/A or less 30 0.41 0.45 0.48 0.52
Medium Density Residential (MDR) Residential, 7.3 DU/A or less 40 0.48 0.51 0.54 0.57
Medium Density Residential (MDR) Residential, 10.9 DU/A or less 45 0.52 0.54 0.57 0.60
Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58 0.60 0.63
High Density Residential (HDR) Residential, 24.0 DU/A or less 65 0.66 0.67 0.69 0.71
High Density Residential (HDR) Residential, 43.0 DU/A or less 80 0.76 0.77 0.78 0.79
Commercial/Industrial (N. Corn) Neighborhood Commercial 80 0.76 0.77 0.78 0.79
Commercial/Industrial (G. Corn) General Commercial 85 0.80 0.80 0.81 0.82
Commercial/Industrial (O.P. Corn) Office Professional/Commercial 90 0.83 0.84 0.84 0.85
Commercial/industrial (Limited I.) Limited Industrial . 90 0.83 0.84 0.84 0.85
Commercial/Industrial (General I.) General Industrial 95 0.87 0.87 0.87 0.87
*The values associated with 0% impervious may be used for direct calculation of the runoff coefficient as described in Section 3.1.2 (representing the pervious runoff
coefficient, Cp, for the soil type), or for areas that will remain undisturbed in perpetuity. Justification must be given that the area will remain natural forever (e.g., the area
is located in Cleveland National Forest).
DU/A = dwelling units per acre
NRCS = National Resources Conservation Service
3-6
POST DEVELOPED AREAS
I ImnDruintIc Tuna fl HR( I Pervious Tvoe D HSG
,., %irnpeiious . AreáT(a'c),. • :Cp
DMA 1 127465 2.93 0.90 0.73 46860 1.08 0.35 4.00
DMA 2 45781 1.05 0.90 0.87 6543 0.15 0.35 1.20 ... 0.83.
DMA 3 71929 1.65 0.90 0.80 18494 0.42 0.35 2.08 4
DMA 6818 0.16 0.90 0.53 6032 0.14 0.35 0.29 .
DMA 6044 0.14 0.90 0.50 6032 0.14 0.35 0.28 .063
DMA 24540 0.56 0.90 0.83 4950 0.11 0.35 0.68
8A51N4.2 19725 0.45 0.90 0.60 12949 0.30 0.35 0.75
6.49 2.04
Note: Formula used In Weighted C Is per San Diego County Hydrology Manual (2003): C = 0.90(%lmpervious) + Cp(1-%ImpervIous)
High-Tech
Drainage Study
CHAPTER 2
METHODOLOGY - RATIONAL METHOD PEAK
FLOWRATE DETERMINATION
2.4 - Urban Watershed Overland
Time of flow Nomograph
2.50% slope-4
2.0- -h
100 1.5- ______ 30
c" b .75 •
.50
-
I-
w
w LU- 0* ____J__ C, Z U. 0 20 I 02O I w
z
—J
LU co U.
D — — — — — -- — — . 10 z
0 C.) -I--
LU
LU
000
EXAMPLE:
Given: Watercourse Distance (D) = 70 Feet
Slope(s)=1.3% T =1.8(1.1) Runoff Coefficient (C) = 0.41
Overland Flow Time (T) = 9.5 Minutes
SOURCE: Airport Drainage, Federal Aviation Administration, 1965
FIGURE
Rational Formula - Overland Time of Flow Nomograph 3-3
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Drainage Study
CHAPTER 2
METHODOLOGY -RATIONAL METHOD PEAK
FLOWRATE DETERMINATION
2.5 - County of San Diego Intensity-
Duration Curve
High-Tech
Drainage Study
CHAPTER 2
METHODOLOGY - RATIONAL METHOD PEAK•
FLOWRATE DETERMINATION
2.6 - Model Development Summary
(from County of San Diego Hydrology Manual)
San Diego County Hydrology Manual
Date: June 2003
Section: 3 Page: 20 of 26
3.2 DEVELOPING INPuT DATA FOR THE RATIONAL METHOD
This section describes the development of the necessary data to perform RM calculations.
Section 3.3 describes the RM calculation process. Input data for calculating peak flows and
Tr.'s with the RM should be developed as follows:
On a topographic base map, outline the overall drainage area boundary, showing
adjacent drains, existing and proposed drains, and overland flow paths.
Verify the accuracy of the drainage map in the field.
Divide the drainage area into subareas by locating significant points of interest. These
divisions should be based on topography, soil type, and land use. Ensure that an
appropriate first subarea is delineated. For natural areas, the first subarea flow path
length should be less than or equal to 4,000 feet plus the overland flow length (Fable
3-2). For developed areas, the initial subarea flow path length should be consistent
with Table 3-2. The topography and slope within the initial subarea should be
generally uniform.
Working from upstream to downstream, assign a number representing each subarea in
the drainage system to each point of interest. Figure 3-8 provides guidelines for node
numbers for geographic information system (GIS)-based studies.
Measure each subarea in the drainage area to determine its size in acres (A).
Determine the length and effective slope of the flow path in each subarea.
Identify the soil type for each subarea.
3-20
StudyArea SC
LA
() Define Study Areas
(Two-Letter ID)
Define Major Fiowpatha
In Study Area
(i) Define Regions on
StudyAreá Basis
Node #
Map #
Region#
Stud yArea(ID)#
i I
L 01 01 03
1
03
Subarea ID R .
(LA0I0II2).
Number Noc.
Define Maps Define Model () Define Model Nodes
(or Subregions Subareas)on (Intersection of
on Region Basis) Map Basis Subarea Boundaries
With FioWpath Unes)'
GiSlHydroioglc Model I b U K
Data Base Linkage Setup:
Nodes, Subareas, Unks :34;
San Diego County Hydrology Manual
Date: June 2003
Section: 3
Page: 22 of 26
Determine the runoff coefficient (C) for each subarea based on Table 3-1. If the
subarea contains more than one type of development classification, use a proportionate
average for C. In determining C for the subarea, use future land use taken from the
applicable community plan, Multiple Species Conservation Plan, National Forest land
use plan, etc.
Calculate the CA value for the subarea.
Calculate the E(CA) value(s) for the subareas upstream of the point(s) of interest.
Determine P6 and P2A for the study using the isopluvial maps provided in Appendix B.
If necessary, adjust the value for P6 to be within 45% to 65% of the value for P.
See Section 3.3 for a description of the RM calculation process..
3.3 PERFORMING RATIONAL METHOD CALCULATIONS
This section describes the RM calculation process. Using the input data, calculation of peak
flows and Ta's should be performed as follows:
Determine Ti for the first subarea. Use Table 3-2 or Figure 3-3 as discussed in Section
3.1.4. If the watershed is natural, the travel time to the downstream end of the first
subarea can be added to ti to obtain the T. Refer to paragraph 3.1.4.2 (a).
Determine I for the subarea using Figure 3-1. If Ti was less than 5 minutes, use the 5
minute time to determine intensity for calculating the flow.
Calculate the peak discharge flow rate for the subarea, where Qp = E(CA) I.
In case that the downstream flow rate is less than the upstream flow rate, due to the
long travel time that is not offset by the additional subarea runoff use the upstream
peak flow for design purposes until downstream flows increase again.
3-22
San Diego County Hydrology Manual Section: 3
Date: June 2003 Page: 23 of 26
Estimate the Tt to the next point of interest.
Add the Tt to the previous T. to obtain a new T.
Continue with step 2, above, until the final point of interest is reached.
Note: The MRM should be used to calculate the peak discharge when there is a junction
from independent subareas into the drainage system.
3.4 MODuiiu, RATIONAL METHOD (FOR JUNCTION ANALYSIS)
The purpose of this section is to describe the steps necessary to develop a hydrology report
for a small watershed using the MRM. It is necessary to use the MRM if the watershed
contains junctions of independent drainage systems. The process is based on the design
manuals of the City/County of San Diego. The general process description for using this
method, including an example of the application of this method, is described below.
The engineer should only use the MRM for drainage areas up to approximately I square mile
in size. If the watershed will significantly exceed 1 square mile then the NRCS method
described in Section 4 should be used. The engineer may choose to use either the RM or the
MRM for calculations for up to an approximately 1-square-mile area and then transition the
study to the NRCS method for additional downstream areas that exceed approximately 1
square mile. The transition process is described in Section 4.
3.4.1 Modified Rational Method General Process Description
The general process for the MRM differs from the RM only when a junction of independent
drainage systems is reached. The peak Q, T, and I for each of the independent drainage
systems at the point of the junction are calculated by the RM. The independent drainage
systems are then combined using the MRM procedure described below. The peak Q, T, and
I for each of the independent drainage systems at the point of the junction must be calculated
prior to using the MRM procedure to combine the independent drainage systems, as these
3-23
San Diego County Hydrology Manual Section: 3
Date: June 2003 Page: 24 of 26
values will be used for the MRM calculations. After the independent drainage systems have
been combined, RM calculations are continued to the next point of interest.
3.4.2 Procedure for Combining Independent Drainage Systems at a Junction
Calculate the peak Q, T, and I for each of the independent drainage systems at the point of
the junction. These values will be used for the MRM calculations.
At the junction of two or more independent drainage systems, the respective peak flows are
combined to obtain the maximum flow out of the junction at T. Based on the approximation
that total runoff increases directly in proportion to time, a general equation may be written to
determine the maximum Q and its corresponding T using the peak Q, T, and I for each of
the independent drainage systems at the point immediately before the junction. The general
equation requires that contributing Q's be numbered in order of increasing T.
Let Qi, Ti, and 11 correspond to the tributary area with the shortest T. Likewise, let Q2, T2,
and 12 correspond to the tributary area with the next longer T; Q, T3, and 13 correspond to
the tributary area with the next longer T; and so on. When only two independent drainage
systems are combined, leave Q, T3, and 13 out of the equation. Combine the independent
drainage systems using the junction equation below:
Junction Equation: T1 <T2 < T3
QTL = TI Qt +
T2 T3
Q2 + Q3
Qn =Q2 +L
11 T3
QTI =Q3 4Q1+-Q2
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San Diego County Hydrology Manual Section: 3
Date: June 2003 Page: 25 of 26
Calculate Qri, Qr2, and Qr3. Select the largest Q and use the T associated with that Q for
furtheT calculations (see the three Notes for options). If the largest calculated Q's are equal
(e.g., Qii =Q,2> QF3), use the shorter of the T0's associated with that Q.
This equation may be expanded for a junction of more than three independent drainage
systems using the same concept. The concept is that when Q from a selected subarea (e.g.,
Q2) is combined with Q from another subarea with a shorter T (e.g., Qi), the Q from the
subarea with the shorter T is reduced by the ratio of the I's (Izfli); and when Q from a
selected subarea (e.g., Q2) is combined with Q from another subarea with a longer T (e.g.,
Q), the Q from the subarea with the longer T is reduced by the ratio of the Ta's (T2/T3).
Note #1: At a junction of two independent drainage systems that have the same T, the
tributary flows may be added to obtain the Q.
Q = Qi + Q2; when T1= T2; and T = Ti = T2
This can be verified by using the junction equation above. Let Q, T3, and 13 0. When T1
and T2 are the same, Ii and 12 are also the same, and Ti/T2 and WIi =1. TI/T2 and 1/11 are
cancelled from the equations. At this point Qri = Qr = Qi + Q2.
Note #2: In the upstream part of a watershed, a conservative computation is acceptable.
When the times of concentration M's) are relatively close in magnitude (within 100/6), use
the shorter T for the intensity and the equation Q = E(CA)I.
Note #3:. An optional method of determining the T is to use the equation
Tr = [( (CA)7.44 P6)/Q]'35
This equation is from Q = (CA)I = E(CA)(7.44 P6tr 5 ) and solving for T. The
advantage in this option is that the T is consistent with the peak flow Q, and avoids
inappropriate fluctuation in downstream flows in some cases.
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CHAPTER 3
00-Year Hydrologic Analysis
for
Existing Conditions
High-Tech
Drainage Study
CHAPTER 4
100-Year Hydrologic Analysis
for
Developed Conditions
San Diego County Rational Hydrology Program
CIVILCADD/CIVILDESIGN Engineering Software, (c)1991-2005 Version 7.5
Rational method hydrology program based on
San Diego County Flood Control Division 2003 hydrology manual
Rational Hydrology Study Date: 02/11/16 -----------------------------------------------------------------------
High-Tech Carlsbad
100 Year Storm
Developed Conditions
-----------------------------------------------------------------------
********* Hydrology Study Control Information **********
-----------------------------------------------------------------------
Program License Serial Number 4085
-----------------------------------------------------------------------
Rational hydrology study storm event year is 100.0
English (in-lb) input data Units used
Map data precipitation entered:
6 hour, precipitation(inches) = 2.940
24 hour precipitation(inches) = 4.960
P6/P24 = 59.3%
San Diego hydrology manual 'C' values used
+.++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 1.011 to Point/Station 1.012
INITIAL AREA EVALUATION
Decimal fraction soil group A = 1.000
Decimal fraction soil group B = 0.000
Decimal fraction soil group C = 0.000
Decimal fraction soil group D = 0.000
[COMMERCIAL area type
(Neighborhod Commercial
Impervious value, Ai = 0.800
Sub-Area C Value = 0.760
Initial subarea total flow distance = 110.000(Ft.)
Highest elevation = 495.000(Ft.)
Lowest elevation = 494.000(Ft.)
Elevation difference = 1.000(Ft.) Slope = 0.909 %
INITIAL AREA TIME OF CONCENTRATION CALCULATIONS:
The maximum overland flow distance is 60.00 (Ft)
for the top area slope value of 0.90 %, in a development type of
Neighborhod Commercial
In Accordance With Figure 3-3
Initial Area Time of Concentration = 4.91 minutes
PC = [1.8*(1.1_C)*distance(Ft.)A.5)/(% slopeA(1/3))
TC = [1.8*(1.1_0.7600)*( 60.000".5)/( 0.900A(1/3))= 4.91
Calculated TC of 4.910 minutes is less than 5 minutes,
resetting PC to 5.0 minutes for rainfall intensity calculations
Rainfall intensity (I) = 7.746(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for area (Q=KCIA) is C = 0.760
Subarea runoff = 0.706(CFS)
Total initial stream area = 0.120(Ac.)
Process from Point/Station 1.012 to Point/Station 1.013
**** STREET FLOW TRAVEL TIME + SUBAREA FLOW ADDITION
Top of street segment elevation = 494.000(Ft.)
End of street segment elevation = 480.740(Ft.)
Length of street segment = 845.000(Ft.)
Height of curb above gutter flowline = 8.0(m.)
Width of half street (curb to crown) = 24.000(Ft.)
Distance from crown to crossfall grade break = 22.500(Ft.)
Slope from gutter to grade break (v/hz) = 0.020
Slope from grade break to crown (v/hz) = 0.020
Street flow is on [1] side(s) of the street
Distance from curb to property line = 10.000(Ft.)
Slope from curb to property line (v/hz) = 0.025
Gutter width = 1.500(Ft.)
Gutter hike from flowline = 2.000(In.)
Manning's N in gutter = 0.0150
Manning's N from gutter to grade break = 0.0150
Manning's N from grade break to crown = 0.0150
Estimated mean flow rate at midpoint of street = 8.418(CFS)
Depth of flow = 0.438(Ft.), Average velocity = 3.548(Ft/s)
Streetflow hydraulics at midpoint of street travel:
Halfstreet flow width = 15.066(Ft.)
Flow velocity = 3.55 (Ft/s)
Travel time = 3.97 mm. TC = 8.88 mm.
Adding area flow to street
User specified 'C' value of 0.750 given for subarea
Rainfall intensity = 5.348(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for total area
(Q=KCIA) is C 0.750 CA = 3.000
Subarea runoff = 15.339(CFS) for 3.880(Ac.)
Total runoff = 16.045(CFS) Total area = 4.000(Ac.)
Street flow at end of street 16.045(CFS)
Half street flow at end of street = 16.045(CFS)
Depth of flow = 0.524 (Ft.), Average velocity = 4.156(Ft/s)
Flow width (from curb towards crown)= 19.387(Ft.)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 1.013 to Point/Station 1.013
**** CONFLUENCE OF MINOR STREAMS
Along Main Stream number: 1 in normal stream number 1
Stream flow area = 4.000(Ac.)
Runoff from this stream = 16.045(CFS)
Time of concentration = 8.88 mm.
Rainfall intensity = 5.348(In/Hr)
Process from Point/Station 6.011 to Point/Station 6.012
**** USER DEFINED FLOW INFORMATION AT A POINT
User specified 'C' value of 0.810 given for subarea
Rainfall intensity (I) = 7.746(In/Hr) for a 100.0 year storm
User specified values are as follows:
TC = 5.00 mm. Rain intensity = 7.75(In/Hr)
Total area = 0.680(Ac.) Total runoff = 4.270(CFS)
Process from Point/Station 6.012 to Point/Station 1.013
PIPEFLOW TRAVEL TIME (User specified size) ****
Upstream point/station elevation = 482.990(Ft.)
Downstream point/station elevation = 478.240(Ft.)
Pipe length = 92.00 (Ft.) Manning's N = 0.013
No. of pipes = 1 Required pipe flow = 4.270(CFS)
Given pipe size = 12.00 (In.)
Calculated individual pipe flow = 4.270(CFS)
• Normal flow depth in pipe = 6.19(In.)
Flow top width inside pipe 11.99(In.)
Critical Depth = 10.43(In.)
Pipe flow velocity = 10.45 (Ft/s)
Travel time through pipe = 0.15 mm.
Time of concentration (TC) = 5.15 mm.
+++++++++++++++++++-f++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 1.013 to Point/Station 1.013
**** CONFLUENCE OF MINOR STREAMS ****
Along Main Stream number: 1 in normal stream number 2
Stream flow area = 0.680 (Ac.)
Runoff from this stream = 4.270(CFS)
Time of concentration = 5.15 mm.
Rainfall intensity = 7.603(In/Hr)
Summary of stream data:
Stream Flow rate TC Rainfall Intensity
No. (CFS) (mm) (In/Hr)
1 16.045 8.88 5.348
2 4.270 5.15 7.603
Qmax(1) =
1.000 * 1.000 * 16.045) +
0.703 * 1.000 * 4.270) + = 19.049
Qmax(2) =
1.000 * 0.580 * 16.045) +
1.000 * 1.000 * 4.270) + = 13.571
Total of 2 streams to confluence:
Flow rates before confluence point:
16.045 4.270
Maximum flow rates at confluence using above data:
19.049 13.571
Area of streams before confluence:
4.000 0.680
Results of confluence:
Total flow rate = 19.049(CFS)
Time of concentration = 8.879 mm.
Effective stream area after confluence = 4.680(Ac.)
Process from Point/Station 1.013 to Point/Station 1.014
PIPEFLOW TRAVEL TIME (User specified size) ****
Upstream point/station elevation = 478.240(Ft.)
Downstream point/station elevation = 463.400 (Ft.)
Pipe length = 155.00(Ft.) Manning's N = 0.013
No. of pipes = 1 Required pipe flow = 19.049(CFS)
Given pipe size = 18.00(In.)
Calculated individual pipe flow = 19.049(CFS)
Normal flow depth in pipe = 9.90(In.)
Flow top width inside pipe = 17.91(In.)
Critical depth could not be calculated.
Pipe flow velocity = 19.12(Ft/s)
Travel time through pipe = 0.14 mm.
Time of concentration (TC) = 9.01 mm.
Process from Point/Station 1.014 to Point/Station 1.015
PIPEFLOW TRAVEL TIME (User specified size) ****
Upstream point/station elevation = 462.900(Ft.)
Downstream point/station elevation = 446.270 (Ft.)
Pipe length = 52.00(Ft.) Manning's N = 0.013
No. of pipes = 1 Required pipe flow = 19.049(CFS)
Given pipe size = 24.00(In.)
Calculated individual pipe flow = 19.049(CFS)
Normal flow depth in pipe = 6.26(In.)
Flow top width inside pipe = 21.07(In.)
Critical Depth = 18.84(In.)
Pipe flow velocity = 29.23 (Ft/s)
Travel time through pipe = 0.03 mm.
Time of concentration (TC) = 9.04 mm.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++.+++++++++++++
Process from Point/Station 1.016 to Point/Station 1.016
**** CONFLUENCE OF MINOR STREAMS
Along Main Stream number: 1 in normal stream number 1
Stream flow area = 4.680(Ac.)
Runoff from this stream = 19.049(CFS)
Time of concentration = 9.04 mm.
Rainfall intensity = 5.285(In/Hr)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++-f+-f++-f++++++++
Process from Point/Station 4.011 to Point/Station 4.012
INITIAL AREA EVALUATION
Decimal fraction soil group A = 0.000
Decimal fraction soil group B = 0.000
Decimal fraction soil group C = 0.000
Decimal fraction soil group D = 1.000
[MEDIUM DENSITY RESIDENTIAL
(14.5 DU/A or Less
Impervious value, Ai = 0.500
Sub-Area C Value = 0.630
Initial subarea total flow distance = 54.000(Ft.)
Highest elevation = 488.950(Ft.)
Lowest elevation = 487.000(Ft.)
Elevation difference = 1.950(Ft.) Slope = 3.611 %
Top of Initial Area Slope adjusted by User to 3.400 %
INITIAL AREA TIME OF CONCENTRATION CALCULATIONS:
The maximum overland flow distance is 90.00 (Ft)
for the top area slope value of 3.40 %, in a development type of
14.5 DU/A or -Less
In Accordance With Figure 3-3 -
Initial Area Time of Concentration = 5.34 minutes
TC = [1.8*(1.1_C)*distance(Ft.).5)/(% slope(1/3))
TC = [1.8*(1.1_0.6300)*( 90..000A.5)/( 3.400"(1/3)]= 5.34
Rainfall intensity (I) = 7.427(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for area (Q=KCIA) is C = 0.630
Subarea runoff = 0.187(CFS)
Total initial stream area = 0.040(Ac.)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 4.012 to Point/Station 4.013
**** STREET FLOW TRAVEL TIME + SUBAREA FLOW ADDITION
Top of street segment elevation = 487.000 (Ft.)
End of street segment elevation = 477.370 (Ft.)
Length of street segment = 95.000(Ft.)
Height of curb above gutter flowline = 6.0(In.)
Width of half street (curb to crown) = 24.000(Ft.)
Distance from crown to crossfall grade break = 22.500(Ft
Slope from gutter to grade break (v/hz) = 0.020
Slope from grade break to crown (v/hz) = 0.020
Street flow is on [1) side(s) of the street
Distance from curb to property line = 10.000(Ft.)
Slope from curb to property line (v/hz) = 0.025
Gutter width = 1.500(Ft.)
Gutter hike from flowline = 2.000(In.)
Manning's N in gutter = 0.0150
Manning's N from gutter to grade break 0.0150
Manning's N from grade break to crown = 0.0150
Estimated mean flow rate at midpoint of street =
Depth of flow = 0.176(Ft.), Average velocity =
Streetflow hydraulics at midpoint of street travel:
0. 725 (CFS)
5. 127 (Ft/s)
Halfstreet flow width = 1.972(Ft.)
Flow velocity = 5.13(Ft/s)
Travel time = 0.31 mm. TC = 5.65 mm.
Adding area flow to street
User specified 'C' value of 0.640 given for subarea
Rainfall intensity = 7.162(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for total area
(Q=KCIA) is C = 0.640 CA = 0.186
Subarea runoff = 1.142(CFS) for 0.250(Ac.)
Total runoff = 1.329(CFS) Total area = 0.290(Ac.)
Street flow at end of street = 1.329(CFS)
Half street flow at end of street = 1.329(CFS)
Depth of flow = 0.218(Ft.), Average velocity = 4.961(Ft/s)
Flow width (from curb towards crown)= 4.067(Ft.)
+++++++++++++++++-f++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 4.013 to Point/Station 1.015
PIPEFLOW TRAVEL TIME (User specified size) ****
Upstream point/station elevation = 477.370 (Ft.)
Downstream point/station elevation = 446.270(Ft.)
Pipe length = 319.00 (Ft.) Manning's N = 0.013
No. of pipes = 1 Required pipe flow = 1.329(CFS)
Given pipe size = 9.00(In.)
Calculated individual pipe flow = 1.329(CFS)
Normal flow depth in pipe = 3.11 (In.)
Flow top width inside pipe = 8.56(In.)
Critical Depth = 6.38(In.)
Pipe flow velocity = 9.80 (Ft/s)
Travel time through pipe = 0.54 mm.
Time of concentration (TO) = 6.19 mm.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 4.013 to Point/Station 1.015
**** CONFLUENCE OF MINOR STREAMS
Along Main Stream number: 1 in normal stream number 2
Stream flow area = 0.290(Ac.)
Runoff from this stream = 1.329(CFS)
Time of concentration = 6.19 mm.
Rainfall intensity = 6.750(In/Hr)
Summary of stream data:
Stream Flow rate TO Rainfall Intensity
No. (CFS) (mm) (In/Hr)
1 19.049 9.04 5.285
2 1.329 6.19 6.750
Qmax(1) =
1.000 * 1.000 * 19.049) +
0.783 * 1.000 * 1.329) + = 20.090
Qmax(2) =
1.000 * 0.684 * 19.049) +
1.000 * 1.000 * 1.329) + = 14.365
L
Total of 2 streams to confluence:
Flow rates before confluence point:
19.049 1.329
Maximum flow rates at confluence using above data:
20.090 14.365
Area of streams before confluence:
4.680 0.290
Results of confluence:
Total flow rate = 20.090(CFS)
Time of concentration = 9.044 mm.
Effective stream area after confluence = 4.970(Ac.)
Process from Point/Station 1.015 to Point/Station 1.016
PIPEFLOW TRAVEL TIME (User specified size) ****
Upstream point/station elevation = 446.270(Ft.)
Downstream point/station elevation = 441.600(Ft.')
Pipe length = 15.00(Ft.) Manning's N = 0.013
No. of pipes = 1 Required pipe flow = 20.090(CFS)
Given pipe size = 24.00(In.)
Calculated individual pipe flow = 20.090(CFS)
Normal flow depth in pipe = 6.47 (In.)
Flow top width inside pipe = 21.30(In.)
Critical Depth = 19.31(In.)
Pipe flow velocity = 29.40(Ft/s)
Travel time through pipe = 0.01 mm.
Time of concentration (TC) = 9.05 mm.
Process from Point/Station 4.200 to Point/Station 1.016
SUBAREA FLOW ADDITION
User specified 'C' value of 0.680 given for subarea
Time of concentration = 9.05 mm.
Rainfall intensity = 5.282(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for total area
(Q=KCIA) is C = 0.680 CA = 3.890
Subarea runoff = 0.456(CFS) for 0.750(Ac.)
Total runoff = 20.546(CFS) Total area = 5.720(Ac.)
Process from Point/Station 1.016 to Point/Station 1.016
**** CONFLUENCE OF MAIN STREAMS
The following data inside Main Stream is listed:
In Main Stream number: 1
Stream flow area = 5.720 (Ac.)
Runoff from this stream = 20.546(CFS)
Time of concentration = 9.05 mm.
Rainfall intensity = 5.282 (In/Br)
Summary of stream data:
Stream Flow rate
No. (CFS)
1 20.546
Qmax(1) =
1.000 *
TC Rainfall Intensity
(mm) (In/Hr)
9.05 5.282
1.000 * 20.546) + = 20.546
Total of 1 main streams to confluence:
Flow rates before confluence point:
20.546
Maximum flow rates at confluence using above data:
20.546
Area of streams before confluence:
5.720
Results of confluence:
Total flow rate = 20.546(CFS)
Time of concentration = 9.052 min.
Effective stream area after confluence = 5.720(Ac.)
Process from Point/Station 2.011 to Point/Station 2.012
INITIAL AREA EVALUATION
Decimal fraction soil group A = 1.000
Decimal fraction soil group B = 0.000
Decimal fraction soil group C = 0.000
Decimal fraction soil group D = 0.000
(COMMERCIAL area type
(Office Professional
Impervious value, Ai = 0.900
Sub-Area C Value = 0.830
Initial subarea total flow distance = 55.000(Ft.)
Highest elevation = 492.660(Ft.)
Lowest elevation = 492.260(Ft.)
Elevation difference = 0.400(Ft.) Slope = 0.727 %
INITIAL AREA TIME OF CONCENTRATION CALCULATIONS:
The maximum overland flow distance is 50.00 (Ft)
for the top area slope value of 0.73 %, in a development type of
Office Professional
In Accordance With Figure 3-3
Initial Area Time of Concentration = 3.82 minutes
TC = [1.8*(1.1_C)*distance(Ft.).5)/(% slope(1/3)]
TC = [1.8*(1.1_0.8300)*( 50.000A.5)/( 0.730A(1/3)]= 3.82
Calculated TC of 3.817 minutes is less than 5 minutes,
resetting TC to 5.0 minutes for rainfall intensity calculations
Rainfall intensity (I) = 7.746(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for area (Q=KCIA) is C = 0.830
Subarea runoff = 0.206(CFS)
Total initial stream area = 0.032(Ac.)
Process from Point/Station 2.021 to Point/Station 2.013
**** SUBAREA FLOW ADDITION
User specified 'C' value of 0.830 given for subarea
Time of concentration = 3.82 mm.
Rainfall intensity = 7.746(In/Hr) 'for a 100.0 year storm
Effective runoff coefficient used for total area
(Q=KCIA) is C = 0.830 CA = 0.998
Subarea runoff = 7.522(CFS) for 1.170(Ac.)
Total runoff = 7.728(CFS) Total area = 1.202(Ac.)
Process from Point/Station 2.013 to Point/Station 3.014
PIPEFLOW TRAVEL TIME (User specified size) ****
Upstream point/station elevation = 488.000(Ft.)
Downstream point/station elevation = 474.250 (Ft.)
Pipe length = 364.00(Ft.) Manning's N = 0.013
No. of pipes = 1 Required pipe flow = 7.728(CFS)
Given pipe size = 24.00 (In.)
Calculated individual pipe flow = 7.728(CFS)
Normal flow depth in pipe = 6.81 (In.)
Flow top width inside pipe = 21.64(In.)
Critical Depth = 11.87(In.)
Pipe flow velocity = 10.53(Ft/s)
Travel time through pipe = 0.58 mm.
Time of concentration (TC) = 4.39 mm.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-f+++++++++
Process from Point/Station 2.013 to Point/Station 3.014
**** CONFLUENCE OF MINOR STREAMS ****
Along Main Stream number: 1 in normal stream number 1
Stream flow area = 1.202 (Ac.)
Runoff from this stream = 7.728(CFS)
Time of concentration = 4.39 mm.
Rainfall intensity = 7.746(In/Hr)
Process from Point/Station ' 3.011 to Point/Station 3.012
**** INITIAL AREA EVALUATION
Decimal fraction soil group A = 0.000
Decimal fraction soil group B = 0.000
Decimal fraction soil group C = 0.000
Decimal fraction soil group D = 1.000
(COMMERCIAL area type
(Neighborhod Commercial
Impervious value, Ai = 0.800
Sub-Area C Value = 0.790
Initial subarea total flow distance = 79.000(Ft.)
Highest elevation = 496.000(Ft.)
Lowest elevation = 493.750(Ft.)
Elevation difference = 2.250(Ft.) Slope = 2.848 %
Top of Initial Area Slope adjusted by User to 4.590 %
INITIAL AREA TIME OF CONCENTRATION CALCULATIONS:
The maximum overland flow distance is 95.00 (Ft)
for the top area slope value of 4.59 %, in a development type of
Neighborhod Commercial
In Accordance With Figure 3-3
Initial Area Time of Concentration = 3.27 minutes
TC = [1.8*(1.1_C)*distance(Ft.)A.5)/(% slope A(1/3))
TC = [1.8*(1.1_0.7900)*( 95.000.5)/( 4.590A(1/3)1= 3.27
Calculated TC of 3.273 minutes is less than 5 minutes,
resetting PC to 5.0 minutes for rainfall intensity calculations
Rainfall intensity (I) = 7.746(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for area (Q=KCIA) is C = 0.790
Subarea runoff = 0.428(CFS)
Total initial stream area = 0.070(Ac.)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 3.012 to Point/Station 3.013
STREET FLOW TRAVEL TIME + SUBAREA FLOW ADDITION
Top of street segment elevation = 493.750(Ft.)
End of street segment elevation = 488.730(Ft.)
Length of street segment = 246.000(Ft.)
Height of curb above gutter flowline = 6.0(In.)
Width of half street (curb to crown) = 24.000(Ft.)
Distance from crown to crossfall grade break = 22.500(Ft.)
Slope from gutter to grade break (v/hz) = 0.020
Slope from grade break to crown (v/hz) = 0.020
Street flow is on [1] side(s) of the street
Distance from curb to property line = 10.000(Ft.)
Slope from curb to property line (v/hz) = 0.025
Gutter width = 1.500(Ft.)
Gutter hike from flowline = 2.000(In.)
Manning's N in gutter = 0.0150
Manning's N from gutter to grade break = 0.0150
Manning's N from grade break to crown = 0.0150
Estimated mean flow rate at midpoint of street = 6.534(CFS)
Depth of flow = 0.395(Ft.), Average velocity = 3.687(Ft/s)
Streetflow hydraulics at midpoint of street travel:
Halfstreet flow width = 12.922(Ft.)
Flow velocity = 3.69(Ft/s)
Travel time = 1.11 mm. TC = 4.38 mm.
Adding area flow to street
User specified 'C' value of 0.790 given for subarea
Rainfall intensity = 7.746(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for total area
(Q=KCIA) is C = 0.790 CA = 1.643
Subarea runoff = 12.300(CFS) for 2.010(Ac.)
Total runoff = 12.728(CFS) Total area = 2.080(Ac.)
Street flow at end of street = 12.728(CFS)
Half street flow at end of street = 12.728(CFS)
Depth of flow = 0.473(Ft.), Average velocity = 4.335(Ft/s)
Flow width (from curb towards crown)= 16.834(Ft.)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 3.013 to Point/Station 3.014
PIPEFLOW TRAVEL TIME (User specified size) ****
Upstream point/station elevation = 486.730(Ft.)
Downstream point/station elevation = 474.270(Ft.)
Pipe length = 65.00(Ft.) Manning's N = 0.013
No. of pipes = 1 Required pipe flow = 12.728(CFS)
Given pipe size = 18.00(m.)
Calculated individual pipe flow = 12.728(CFS)
Normal flow depth in pipe = 6.47 (In.)
Flow top width inside pipe = 17.28(In.)
Critical Depth = 16.10(In.)
Pipe flow velocity = 22.25(Ft/s)
Travel time through pipe = 0.05 mm.
Time of concentration (TC) = 4.43 mm.
Process from Point/Station 3.013 to Point/Station 3.014
**** CONFLUENCE OF MINOR STREAMS
Along Main Stream number: 1 in normal stream number 2
Stream flow area = 2.080(Ac.)
Runoff from this stream = 12.728(CFS)
Time of concentration = 4;43 mm.
Rainfall intensity = 7.746(In/Hr)
Summary of stream data:
Stream Flow rate TC Rainfall Intensity
No. (CFS) (mm) (In/Hr)
1 7.728 4.39 7.746
2 12.728 4.43 7.746
Qmax(1) =
1.000 * 1.000 * 7.728) +
1.000 * 0.991 * 12.728) + = 20.339
Qmax(2) =
1.000 * 1.000 * 7.728) +
1.000 * 1.000 * 12.728) + = 20.456
Total of 2 streams to confluence:
Flow rates before confluence point:
7.728 12.728
Maximum flow rates at confluence using above data:
20.339 20.456
Area of streams before confluence:
1.202 2.080
Results of confluence:
Total flow rate = 20.456(CFS)
Time of concentration = 4.433 min.
Effective stream area after confluence = 3.282(Ac.)
Process from Point/Station 3.014 to Point/Station 3.015
PIPEFLOW TRAVEL TIME (User specified size) ****
Upstream point/station elevation = 474.270(Ft.)
Downstream point/station elevation = 467.810(Ft.)
Pipe length = 38.00(Ft.) Manning's N = 0.013
No. of pipes = 1 Required pipe flow = 20.456(CFS)
Given pipe size = 24.00(In.)
Calculated individual pipe flow = 20.456(CFS)
Normal flow depth in pipe = 7.63(In.)
Flow top width inside pipe = 22.36(m.)
Critical Depth = 19.48(In.)
Pipe flow velocity = 23.79(Ft/s)
Travel time through pipe = 0.03 mm.
Time of concentration (TC) = 4.46 mm.
Process from Point/Station 3.014 to Point/Station 3.015
**** CONFLUENCE OF MINOR STREAMS
Along Main Stream number: 1 in normal stream number 1
Stream flow area = 3.282(Ac.)
Runoff from this stream = 20.456(CFS)
Time of concentration = 4.46 mm.
Rainfall intensity = 7.746(In/Hr)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 5.011 to Point/Station 5.012
INITIAL AREA EVALUATION ***
Decimal fraction soil group A = 0.000
Decimal fraction soil group B = 0.000
Decimal fraction soil group C = 0.000
Decimal fraction soil group D = 1.000
[MEDIUM DENSITY RESIDENTIAL
(14.5 DU/A or Less
Impervious value, Ai = 0.500
Sub-Area C Value = 0.630
Initial subarea total flow distance = 45.000(Ft.)
Highest elevation = 491.240(Ft.)
Lowest elevation = 489.660(Ft.)
Elevation difference = 1.580(Ft.) Slope = 3.511 %
Top of Initial Area Slope adjusted by User to 3.500 %
INITIAL AREA TIME OF CONCENTRATION CALCULATIONS:
The maximum overland flow distance is 90.00 (Ft)
for the top area slope value of 3.50 %, in a development type of
14.5 DU/A or Less
In Accordance With Figure 3-3
Initial Area Time of Concentration = 5.29 minutes
TC = (1.8*(1.1_C)*distance(Ft.)A.5)/(% slope '(1/3)]
TC = [1.8*(1.1_0.6300)*( 90.000".5)/( 3.500"(1/3)1= 5.29
Rainfall intensity (I) = 7.473(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for area (Q=KCIA) is C = 0.630
Subarea runoff = 0.141(CFS)
Total initial stream area = 0.030(Ac.)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 5.012 to Point/Station 5.013
**** STREET FLOW TRAVEL TIME + SUBAREA FLOW ADDITION
Top of street segment elevation = 490.730(Ft.)
End of street segment elevation = 480.300(Ft.)
Length of street segment = 112.000(Ft.)
Height of curb above gutter flowline = 6.0(In.)
Width of half street (curb to crown) = 24.000(Ft.)
Distance from crown to crossfall grade break = 22.500(Ft.)
Slope from gutter to grade break (v/hz) = 0.020
Slope from grade break to crown (v/hz) = 0.020
Street flow is on [1] side(s) of the street
Distance from curb to property line = 10.000(Ft.)
Slope from curb to property line (v/hz) = 0.025
Gutter width = 1.500(Ft.)
Gutter hike from flowline = 2.000(In.)
Manning's N in gutter = 0.0150
Manning's N from gutter to grade break = 0.0150
Manning's N from grade break to crown = 0.0150
Estimated mean flow rate at midpoint of street = 0.668(CFS)
Depth of flow = 0.166(Ft.), Average velocity = 5.353(Ft/s)
Streetfiow hydraulics at midpoint of street travel:
Halfstreet flow width = 1.500(Ft.)
Flow velocity = 5.35(Ft/s)
Travel time = 0.35 mm. TC = 5.63 mm.
Adding area flow to street
User specified 'C' value of 0.630 given for subarea
Rainfall intensity = 7.171(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for total area
(Q=KCIA) is C = 0.630 CA = 0.176
Subarea runoff = 1.124(CFS) for 0.250(Ac.)
Total runoff = 1.265(CFS) Total area = 0.280(Ac.)
Street flow at end of street = 1.265(CFS)
Half street flow at end of street = 1.265(CFS)
Depth of flow = 0.218(Ft.), Average velocity = 4.751(Ft/s)
Flow width (from curb towards crown)= 4.047 (Ft.)
Process from Point/Station 5.013 to Point/Station 3.015
PIPEFLOW TRAVEL TIME (User specified size) ****
Upstream point/station elevation = 478.830(Ft.)
Downstream point/station elevation = 467.810(Ft.)
Pipe length = 92.00(Ft.) Manning's N = 0.013
No. of pipes = 1 Required pipe flow = 1.265(CFS)
Given pipe size = 9.00(m.)
Calculated individual pipe flow = 1.265(CFS)
Normal flow depth in pipe = 2.88 (In.)
Flow top width inside pipe = 8.39(In.)
Critical Depth = 6.22(In.)
Pipe flow velocity = 10.41(Ft/s)
Travel time through pipe = 0.15 mm.
Time of concentration (TC) = 5.78 mm.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 3.015 to Point/Station 3.015
CONFLUENCE OF MINOR STREAMS ****
Along Main Stream number: 1 in normal stream number 2
Stream flow area = 0.280(Ac.)
Runoff from this stream = 1.265(CFS)
Time of concentration = 5.78 mm.
Rainfall intensity = 7.053(In/Hr)
Summary of stream data:
Stream Flow rate TC Rainfall Intensity
No. (CFS) (mm) (In/Br)
1 20.456 4.46 7.746
2 1.265 5.78 7.053
Qmax(1) =
1.000 * 1.000 * 20.456) +
1.000 * 0.771 * 1.265) + = 21.432
Qmax(2) =
0.911 * 1.000 * 20.456) +
1.000 * 1.000 * 1.265) + = 19.891
Total of 2 streams to confluence:
Flow rates before confluence point:
20.456 1.265
Maximum flow rates at confluence using above data:
21.432 19.891
Area of streams before confluence:
3.282 0.280
Results of confluence:
Total flow rate = 21.432(CFS)
Time of concentration = 4.460 mm.
Effective stream area after confluence = 3.562(Ac.)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 3.015 to Point/Station 3.016
PIPEFLOW TRAVEL TIME (User specified size) ****
Upstream point/station elevation = 467.810(Ft.)
Downstream point/station elevation = 464.030 (Ft.)
Pipe length = 22.00(Ft.) Manning's N = 0.013
No. of pipes = 1 Required pipe flow = 21.432(CFS)
Given pipe size = 24.00 (In.)
Calculated individual pipe flow = 21.432(CFS)
Normal flow depth in pipe = 7.80(In.)
Flow top width inside pipe = 22.49(In.)
Critical Depth = 19.88(m.)
Pipe flow velocity = 24.20 (Ft/s)
Travel time through pipe = 0.02 mm.
Time of concentration (TC) = 4.48 mm.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 3.016 to Point/Station 3.016
**** CONFLUENCE OF MAIN STREAMS ****
The following data inside Main Stream is listed:
In Main Stream number: 1
Stream flow area = 3.562(Ac.)
Runoff from this stream = 21.432(CFS)
Time of concentration = 4.48 mm.
Rainfall intensity = 7.746(In/Hr)
Summary of stream data:
Stream Flow rate TC
No. (CFS) (mm)
1 21.432 4.48
Qmax(1) =
1.000 * 1.000 *
Rainfall Intensity
(In/Hr)
7.746
21.432) + = 21.432
Total of 1 main streams to confluence:
Flow rates before confluence point:
21.432
Maximum flow rates at confluence using above data:
21.432
Area of streams before confluence:
3.562
Results of confluence:
Total flow rate = 21.432(CFS)
Time of concentration = 4.475 mm.
Effective stream area after confluence = 3.562 (Ac.)
End of computations, total study area = 9.282 (Ac.)
High-Tech
Drainage Study
CHAPTER 5
Hydrology Maps