HomeMy WebLinkAboutCT 81-10; KOLL BUSINESS PARK; DRAINAGE STUDY; 1981-04-13February 18, 1981
MEHORANDUM
TO: City Engineer
FROM: Director of Utilities & Maintenance
8-1-034
-ftE CEIVE r~,.
.FEBI81981
TV OF CARLSBAr'
'?,ineering pePFlr,1
SUBJECT~ Detention Basins, Koll Business Park
I have reviewed the draft drainage study for the Carlsbad Business Park
prepared by Boyle Engineering. '
I have no reservations concerning the effectiveness of the proposed
detention basins in minimizing siltation of the Agua Hedionda Lagoon. I
am concerned, however, with the problems relating to maintenance of these.
str~ctures so they will continue to function-as planned. I am unable to
determine from the data the amount of silt that would be accumulated in
an ~verage year, but whatever amount, it would most~likely require loadrng,
tran~porting and disposal of the silt each year. I ~m estimati~y_that
these costs will be in the neighborhood of $5.00 to $6.00 per y-ard and
could-be higher, depending on the transport distance for disposal. It
also-appears to me that disposal of this spoil will in and of itself
prese-nt future problems, as I know of no particular useful purpose for
which it can be used.
~~ ROG~~GREER Dir~~~ of Utilities & Maintenance
RWG:pab
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:(
DRAINAGE STUDY OF THE
CARLSBAD RESEARCH CENTER DEVELOPMENT
c-r SJ -'0
FOR
RICK ENGINEERING COMPANY
Prepared by
BOYLE ENGINEERING CORPORATION
Water Resources Division
April 1981
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TABLE OF CONTENTS
Summary, Conclusions and Recommendations
1.0 Introduction
2.0 Hydrologic Analysis
2.1 Basin Description ••••
2.2 Study Approach • • • • • • • •
2.3 Results •.••••••••• . . . . . . .
. . . . . . 3.0 Sedimentation Analysis
3.1 Study Approach .
3.2 Resul ts • •..• •
. . . .
4.0 Alternative Plans.
References • • •
Figure 1
Figure 2
Figure 3
FIGURES
Vicinity Map, Carlsbad Research Center.
Carlsbad Research Center Drainage Basins
for Existing Conditions ••••••••
Carlsbad Research Center Drainage Basins
for Developed Conditions ••••••••
Figure 4 Hydrologic Schematic for Carlsbad Research
Figure 5
Figure 6
Center Drainage Basins ••.••••••••••••••••
Carlsbad Research Center Drainage Basins
for Developed Conditions -Alternative I •
Carlsbad Research Center Drainage Basins
for Developed Conditions -Alternative II
Figure 7 Carlsbad Research Center Drainage Basins
for Developed Conditions -Alternative III •
Figure 8 Typical Riser and Dam Alignment
Figure 9 Inflow and Outflow Hydrographs from a 10-year,
24-hour Storm at Site III -Alternative III
Figure 10 Inflow and Outflow Hydrographs from a 100-year,
24-hour Storm at Site III -Alternative III
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1
5
8
8
8
12
16
16
18
20
37
6
10
11
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21
22
24
25
34
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Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
Table 7
Table 8
TABLES
Estimated la-year Peak Discharges for Existing
and Developed Conditions. • • • • • •••
Estimated lOa-year Peak Discharges for Existing
and Developed Conditions .......... .
Estimated Sediment Yield for Existing and Devel-
oped Conditions •..•••••••••••••
Dimensi~ns of Two-Way Covered Risers and Dams
Estimated la-year Peak Discharges for Existing
Conditions and Developed Conditions with Flood-
water Retarding Reservoirs (Alternative I) •••
Estimated lOa-year Peak Discharges for Existing
Conditions and Developed Conditions with Flood-
water Retarding Reservoirs (Alternative I) •••
Estimated la-year Peak Discharges for Existing
Conditions and Developed Conditions with Flood-
water Retarding Reservoirs (Alternative II)
Estimated lOa-year Peak Discharges for Existing
Conditions and Developed Conditions with Flood-
water Retarding Reservoirs (Alternative II)
Table 9 Estimated la-year Peak Discharges for Existing
Conditions and Developed Conditions with Flood-
water Retarding Reservoirs (Alternative III) ••
Table 10 Estimated lOa-year Peak Discharges for Existing
Conditions and Developed Conditions with Flood-
water Retarding Reservoirs (Alternative III) .•
ii
14
15
19
27
28
29
. . . . . . 30
31
32
33
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Summary
DRAINAGE STUDY FOR
CARLSBAD RESEARCH CENTER DEVELOPMENT
Summary, Conclusions and Recommendations
Industrial development of approximately 560 acres of land located just north
of Palomar Airport and east of Carlsbad is currently being considered by the
Koll Company. The Carlsbad Research Center development area is situated with-
in the Agua Hedionda Lagoon drainage basin. Increased sedimentation in the
lagoon due to upstream development is a significant concern.
More rapid runoff from developed areas can lead to increased erosion from
channels downstream, causing siltation wherever the sediment is deposited.
This study was prepared (1) to determine the impact that the proposed devel-
opment would have on storm and sediment runoff from the Agua Hedionda water-
shed, and (2) to develop control measures to reduce the increased runoff
rates due to the development.
Hydrologic analysis was made to estimate rainfall runoff under existing and
developed conditions through the use of a unit hydrograph approach. The
runoff resulting from 10-year and 100-year storms both for 6-hour and 24-hour
durations are presented in this report. The estimated sediment production
rates under existing and developed conditions are also presented.
Floodwater retarding reservoirs were considered as a possible means of miti-
gating the impact of increased runoff from the development. Three alternative
plans for floodwater retarding reservoir sites were described.
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Conclusions
1. Peak discharges and runoff volumes will increase as a result of the devel-
opment if proper control measures are not implemented. Present and future
values are presented below. These numbers result from the 6-hour and 24-
hour storm, whichever is greater.
D.A. % Area 10-Yr Flood (cfs) 100-Yr Flood (cfs)
Basin (sq.mi.) Developed Present Future Present Future
120 .30 78 50 150 230 340
130+140
+150 .96 63 150 290 470 780
(See Figures 2 and 3 for location of the basins)
2. As the development area reaches the ultimate development stage, the rate
of sediment production will be less than under existing conditions. How-
ever, the increased runoff rates could result in increased erosion of
stream channels downstream of the developed areas. Thus, proper measures
should be implemented to reduce the increased rate of runoff.
3. The increased rate of runoff can be reduced by floodwater retarding
reservoirs. There are several sites within the development area that
are suitable for reservoirs. Three alternatives are proposed.
Alternative I consists of two reservoirs. Runoff from Basin 120 would
be collected in a reservoir at site I, and runoff from Basins 131, 132,
and 140 would be collected in a reservoir at site II (see Figure 5 in
Section 4.0).
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Alternative II would also involve construction of two reservoirs. A reser-
voir at site I would collect runoff from Basin 120, as in Alternative I,
and a reservoir at site III would collect runoff from Basins 131 and 132
(see Figure 6 in Section 4.0). Although a reservoir at site III is being
planned for seasonal storage of reclaimed water, this reservoir could be
designed to be emptied during the rainy season and used for floodwater
retarding.
Alternative III would be to divert runoff from approximately 75 acres of
Basin 120 into a reservoir at site III. This would reduce runoff from
Basin 120 to flows equal to or below eXisting conditions without con-I 0
structing a reservoir at site ::t;:i (see Figure 7 in Section 4.0).
.4. The three alternatives can reduce peak runoff rates both for 10-year and
100-year conditions to existing orates or lower, as shown below.
Basin
Alternative I
120
130+140+150
Alternative II
120
130+140+150
Alternative III
120
130+140+150
D.A.
(sq.mi.)
.30
.96
.30
.96
.30
.96
% Area
Developed
78
63
78
63
78
63
Peak Discharge (cfs)
la-year lOO-year
40 (50) 140 (230)
140 ( 150) 410 (470)
40 (50) 140 (230)
120 ( 150) 280 (470)
60 (50) 180 (230)
160 ()60) 310 (470)
(The peak discharges under existing conditions are presented in parentheses
for comparison)
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Recommendations
1. That floodwater retarding reservoir(s} be constructed to control runoff
from the development area. If Alternative II or III is impl~mented, a
careful operational plan for Reservoir III should be established so that
it retards floodwaters without violating discharge water quality criteria.
2. That appropriate measures are taken to ensure the proper maintenance of
the proposed floodwater retarding reservoirs.
3. That appropriate erosion control measures be implemented in order to pre-
vent excess erosion during construction. Filter berms, jute matting,
diversion dikes, erosion checks or other methods should be employed, as
appropriate to specific conditions. In addition, the proposed flo~d
water retarding reservoirs should be constructed before grading the area
to serve as backup control.
• 4. Tha~ proper management practices be exercised in the development of the
area. Consideration should be given to use of pervious materials such
as gravel or crushed rocks for infrequently used roads, and gravel-
filled trenches located at the dripline of roofs or other elevated im-
permeable surfaces to increase infiltration and to prevent erosion of
the soil surfac~.
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1.0 INTRODUCTION
The Ko11 Company is considering the development of 560 acres east of Carlsbad
for a business park. The proposed Carlsbad Research Center development is
located just north of Palomar Airport and southwest of El Camino Real as shown
in Figure 1. It lies within Agua Hedionda Creek Watershed, a l3-mi1e long,
narrow drainage area with an average width of about 3 miles.
Agua Hedionda Creek originates in the San Marcos Mountains, a rather low range
of hills east of Vista. The creek flows generally westward from the mountains,
passes through Los Monos Canyon, and empties into Agua Hedionda Lagoon just
south of Carlsbad. Several tributaries feed into the creek along its length.
Increased siltation in the lagoon due to upstream development is a significant
concern. Erosion and sedimentation problems could arise both during construc-
tion and after complete development of projects in the watershed. Sedimenta-
tion problems during construction can be mitigated by implementing proper
construction management practices and/or constructing interim debris basins.
Once development is complete, sediment production will probably decrease. It
may even be less than sediment production under natural conditions because
areas previously subject to erosion will have been covered with impervious
materials and landscaping. However, problems can still occur in downstream
areas. Rates of storm runoff will probably rise due to decreased infiltration
in the developed areas and the reduced time of concentration. These increased
runoff rates can stimulate erosion of stream channels downstream of the devel-
oped area. Siltation in the lagoon could then increase as the additional sed-
iment is deposited downstream. Therefore, measures which effectively control
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/@--'
OCEANSIDE
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LA JOLLA[
PACIFIC BEAC~
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IMPERIAL BEACH
I VICINITY MAP
SAN DIEGO
COUNTY
CAJON
. UNIT~-______ --MEXICO
FIGURE'
I CARLSBAD RESEARCH CENTER
'-------:.-________ ~___iI
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increased runoff rates could become important, especially in this case~ where
sedimentation downstream of the developed area is of concern.
The development area was removed from the Coastal Commission permit area sub-
ject to several conditions. A drainage plan would have to be developed which
must be approved by the local government having jurisdiction over the area
after consultation with the Coastal Commission and the Department of Fish and
Game. The plan must assure that no detrimental increase occurs in runoff
from the area after development. In addition, the facilities necessary to
implement the plan must be installed as part of the development.
This study has been prepared in accordance with an agreement between Rick
Engineering Company and Boyle Engineering Corporation. The purposes are:
1) to determine the impact the proposed development would have on storm run-
off and sediment production from Agua Hedionda Watershed, and 2) to develop
control measures which will reduce increased runoff rates.
Technical information has been organized into three sections. Section 2.0
presents hydrologic analyses and computed peak discharges under present and
future conditions. Section 3.0 discusses sedimentation analyses and shows
total sediment yield calculated for the watershed under present and future
conditions. Section 4 describes the three alternatives proposed to control
increased runoff.
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2.0 HYDROLOGIC ANALYSIS
2.1 Basin Description
The Carlsbad Research Center development is located within the Agua Hedionda
Creek Watershed (Figure 1). The watershed has a total drainage area of ap-
proximately 30 square miles while the development area is approximately 0.9
square miles.
The drainage area encompassing the Carlsbad Research Center development area
can generally be divided into two parts: the northern part of the development
which drains northerly across El Camino Real Road into Agua Hedionda Creek;
and the southern part which drains westerly into Agua Hedionda lagoon through
an unnamed small creek.
Mean seasonal precipitation for the drainage area is about 10 inches. Most
precipitation occurs during the winter period from December to March. These
storms often last for several days and are accompanied by widespread rainfall.
Local thunderstorms can occur at any time of the year, but cover relatively
small areas and result in high intensity rainfall for durations of three hours
or less.
2.2 Study Approach
A hydrologic analysis was performed to estimate the impact that the development
will have on runoff from the affected drainage area. The analysis was carried
out by a unit hydrograph approach utilizing the Soil Conservation Service Com-
puter Program TR-20 (Reference 1). The hydrologic parame~ers for the model
were prepared in accordance with the procedures described in the San Diego
County hydrology manual (Reference 2) as outlined below.
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Drainage Area -San Diego County topographic survey maps of 1" = 200' were
used to define the drainage basin boundaries which encompass the proposed
development area. Considering the need for concentration points where dams
were proposed and where estimated peak discharges would be required, the total
drainage basin was divided into subdrainage areas. Figures 2 and 3 show
subdrainage boundaries for natural and developed conditions. The subdivision
map prepared by Rick Engineering was used to define basin boundaries for
developed conditions.
Precipitation Data -The precipitation intensity, duration, and frequency
relationships used in this study were obtained from the NOAA Atlas (Reference
3). The storm durations considered in the analyses were 6 hours and 24
'hours. The temporal distributions of these storms were taken to be those
suggested in the county manual.
Rainfall-Runoff Relationship -The amount of direct runoff from a specific
storm is dependent upon soil characteristics, land use, and antecedent mois-
ture condition (AMC) at the onset of the storm. The curve number (CN), which
represents infiltration potential for a specific soil group and land use type,
was developed from the available soil and land use information. The AMC was
selected to be 1.5 and 2.0 for 10-year and 100-year storm flows, respectively,
in accordance with the county manual.
Time of Concentration -Another parameter required in the hydrologic anal-
ysis is the time of concentration, Which represents the time it takes for
water to travel from the hydraulically most distant part of a watershed to
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LEGEND
---
..
PROPOSED DEVELOPMENT AREA
BASIN BOUNDARY
SUBBASIN BOUNDARY
~ "
~l---t-,· ~,
-" I .~~:. ~ ~~ ·-----L------( ::--~-=~-:~::
_.'
FLOW DIRECTION
CONCENTRATION POINT
---_-_-4000 I
CARLSBAD RESEARCH CENTER
DRAINAGE BASINS FOR DEVELOPED CONDITIONS
SCALE IN FEET
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the watershed outlet. This parameter was estimated for each subbasin using
the Corps of Engineers empirical equations as described in the county manual.
Figure 4 is a schematic presentation showing the summary of the input data as
developed above for use in the TR-20 model.
2.3 Results
The results of the analysis for existing and developed conditions are presented
in Tables 1 and 2. It should be noted that the peak discharges from the total
watershed area do not necessarily equal the sum of peak discharges from indi-
vidual drainage areas. This is because peak discharges occur at different
times depending on the time of concentration.
As shown in Tables 1 and 2, peak discharges would increase as a result of the
development, especially during more frequent and shorter duration storms.
These increased runoff rates could result in increased erosion of stream-.
'.\ o~,,'
channals downstream of the development. Such erosion is -of major concer~ ~"_
for this study. Therefore, alternative drainage plans were formulated to
reduce the peak discharges.
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-----------------.--
120 86 y
'. ' .. ' 120 94 ! .. Joe ... . 30 .21 . '. .31 .14 .
,
130 86 140 82 131· '95
.63 .63 .20 .23 .43 .32
LEGEND 0
V
v
BASIN CURVE 00 -132 95 0 NQ NQ' CO .18 .27 0') DRAINAGE TIME OF , 0
AREA CONCENTRATION 0
(SQ.M!.) (HRS.)
0')
150 85 140 86
.10 .16 :c .20 .16
t-O (.!) z 10 w_ . 0') -.It-:
LL.' 150 87 0 :c-
'¢ (.) .08 .08 « :0') W . 0 0:: 0 --
160 86 160 89
.12 .10 .12 .14
.,
EXISTING CONDITIONS 'DEVELOPED CONDFriONS
"TI HYDROLOGIC SCHEMATIC FOR I -~~ CARLSBAD RESEARCH CENTER
::0 DRAINAGE BASINS rn
-------------------
LOCATION
120
--'
..j::>
130
140
150
Subtotal
(130+140+150)
TABLE 1
ESTIMATED 10-YEAR PEAK DISCHARGES
For Existing and Developed Conditions
EXISTING CONDITIONS DEVELOPED CONDITIONS
..
D.A. STORM DISCHARGE {cfs} LOCATION D.A. STORM DISCHARGE ~cfs}
(sq.mi.) 6-HR 24-HR (sq"mi. ) 6-HR 24-HR
.30 50 50 120 . .31 150 100
131 .43 200 140
, 132 .18 90 60 .63 70 no 130 (131+132).61 270 190
.20 20 30 . 140 .20 40 ·40
.10 20 20 . 150 .Q8 20 20
.93 90 150 Subtotal .89 290 240
(130+140+150)
-------------------
LOCATION
120
.....
U1 130
140
150
Subtotal
(130+140+150)
TABLE 2
ESTIMATED 100-YEAR PEAK DISCHARGES'
For Existing And Developed Conditions
EXISTING CONDITIONS DEVELOPED CONDITIONS'
D.A. STORM DISCHARGE {cfs} LOCATION D.A. STORM DISCHARGE {cfs}
(sq.m;. ) 6-HR 24-HR (sq.mi. ) 6-HR -24-HR
.30 230 140 120 .31 340 180
131 .43 460 240
132 .18 200 100
.63 350 280 130 (131+132).61 630 . 340
.20 120 80 140 .20 160 90
.10 80 50 150 .08 60 40
.93 470 400 Subtota'
(130+140+150)
.89. 780 470
'-----
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3.0 SEDIMENTATION ANALYSIS
3.1 Study Approach
The sedimentation analysis was made to estimate the magnitude of the sediment
yield from the study area. Estimation was made both for existing and developed
conditions to determine the impact that the development would have on sedimen-
tation. This information would also be required to determine adequate sediment
storage capacity in the design of floodwater retarding reservoirs under consid-
eration.
The sediment yield was estimated using a modified version of the Universal Soil
Loss Equation--USLE (Reference 4). The USLE was developed originally to predict
the average annual soil losses at the point where soil is dislodged. It is an
erosion equation and is not designed to predict sediment yield. Eroded soil
materials often move only short distances before a decrease in runoff velocities
causes their deposition. They may remain in the fields where they originated
or may be deposited on more level slopes that are remote from the stream system.
A conventional method to determine sediment yields is to use the concept of
sediment delivery ratio. The sediment delivery ratio is the ratio of sediment
delivered at a given location to the gross erosion from the drainage area
above the location. A general equation for computing a watershed delivery
ratio is not yet available and its estimation often requires engineering
judgement. However, a modified version of the USLE, which was used in this
study, eliminates the need for a sediment delivery ratio by using a runoff
factor (runoff times peak rate) as the rainfall energy factor in the USLE.
This modification allows for prediction of sediment yield resulting from
individual storms as well as its long-term average volume.
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The modified USLE is:
Qsw =.a (Q qp)b K LS C P
where Qsw is the soil loss for wash load size in tons; Q is the volume of run-
off in acre-feet; qp is the peak runoff from the storm in cfs; K is the soil
erodibility factor; L is the slope-length factor; S is the slope-steepness
factor; C is the cover and management factor; P is the practice factor; and
a and b are constants. A detailed discussion of the universal soil loss _
. equation parameters, K, L, S, C, and P, is presented in the USDA Agricultural
Handbook No. 537 (Reference 5).
The soil erodibility factor, K, was obtained by identifying each different
soil group through the use of the information published in the USDA Soil
Survey Report for San Diego Area (Reference 6). The Soil Cons~rvation Service,
San Diego Area Office, was consulted for the determination of the K factor
for each different soil group.
The average slope length and gradient of each subbasin was measured from USGS
7.5 minute, topographic maps in accordance with the procedure described in
Williams and Berndt (Reference 7). The measured slope length and gradient were
then converted to the topographic factor, LS, as described in the USDA Agri-
cultural Handbook No. 537.
The cover and management factor C was determined based on Comprehensive Plan-
ning Organization (now renamed San Diego Association of Governments) land
use data for San Diego County, o~ field investigation$~ and on empirical
data presented in the previously mentioned handbook. The practice factor
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P was taken to be 1.0 throughout the basin because most of the basin area is
under natural conditions.
The coeffici~nts a and b in the modified USLE were taken to be 95 and 0.56,
respectively, as determined in the above referenced paper by Williams.
For the estimation of the average annual sediment yield, a weighted average
of sediment yields associated with different storm frequencies is computed
and multiplied by a factor of 2.6. This factor was determined by analyzing
streamflow records at adjacent basins (Reference 8).
3.2 Results
The estimated sediment yield under various conditions is pr~sented in Table 3.
The sediment yield under development conditions was estimated assuming that
no desilting or floodwater retarding reservoirs will be constructed. The
results are comparable with sediment estimations made for the other areas in
San Diego County (References 8 and 9).
As shown in Table 3, sediment yield for developed conditions would be less
than under existing conditions. This is due to increased impervious areas
and' landscaping which limits sediment supplies. However, as mentioned previ-
ously, the increased runoff rates could result in increased erosion of stream
channels downstream of the developed areas.
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\.0
TABLE 3
ESTIMATED SEDIMENT YIELD (TONS)
For Existing and Developed Conditions
EXISTING CONDITIONS DEVELOPED CONDITIONS
Sediment Yield (Tons) Sediment Yield (Tons)
D.A. 24-Hour Storm D .A. 24-Hour Storm
Basin (sq.mi.) Annual la-Year lOa-Year Basin (sq .mi. ) Annual la-Year lOO-Year
120 . .30 190 300 850 120 .31 140 180 370
130+140+150 .93 460 760 2200 130+140+150 .89 150 200 430
Total 1.23 650 1060 3050 Total 1.20 290 380 800
~----.--~---.---.~~-------------------~-~------~------.-~-----------~~--------~ '---
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4.0 ALTERNATIVE PLANS
Various alternatives to mitigat~ the impacts of increased runoff rates from
the proposed Carlsbad Research Center Development were studied. Floodwater
retarding reservoirs were considered to be the most effective measures to
reduce the increased runoff rates. The principle of a floodwater retarding
reservoir is to store storm runoff and to provide a principal spillway that
will release. water at a slow rate, thereby reducing the downstream impacts.
It would also be effective in reducing sediment runoff to a stream downstream.
Several floodwater retarding reservoir sites within and adjacent to the develop-
ment area were identified for potential use in controlling runoff. Three alter-
native plans were formulated from these various sites. Factors considered
include effectiveness of runoff control and ease of im~lementation.
Alternative I would involve construction of two reservoirs at sites I and II
as shown in Figure 5. The reservoir at site I is intended to control runoff
from the northern part of the development. The reservoir at site II is to
control runoff from most areas of the remaining development. This would
involve diversion of flows from Basins 131 and 132 into the reservoir.
Alternative II consists of two reservoirs at sites I and III (see Figure 6).
The reservoir at site I is the same as the one for Alternative I. The reser-
voir at site III will collect water from Basins 131 and 132. The reservoir
was originally planned for seasonal storage of reclaimed water for irrigation
purposes. However, the reservoir could be designed to be emptied during
the rainy season' and used for floodwater retarding purposes.
-20 -
r0
- -- - --
~' J '~\v.-~ "
" \" : : ) , -6l " . " 'W" ")' ll/. , , Lk;O'-t! " """"'. '_ " \,'", "~'\' '/ ~. .... .... ~. ' 7, \\j"/. {" I;"'~ • ' :\~\~ ~ \ f)'i', .,> ,.;.
''A , '>-/ ,p,O,!) ,'/ (
-11 .t'/ '~._ -: ,;' .. ';:-~ >oJ.'. f .." l'
'\.,<'" ~,I ,U '1
\; ,11'" \\ ~ 'I:::::~ ~\~. '~J • I,I "/ I'Q--'/ .1 "'''-.,---.. ~, (
~. ,
~ " ::: oS •
;: ~ I: ;::.' J ... 1
LEGEND
.
I
:1 ~ .. .:l :::
/
;' .
/
/
-"
."
... ---- ---
~1~1~~:~ PROPOSED DEVELOPMENT AREA
----
"'li
(j)
C
;0 rn
U1
•
J?Zl2)
BASIN BOUNDARY
SUBBASIN BOUNDARY
FLOW DIRECTION
CONCENTRATION POINT
FLOODWATER RETARDING BASIN
CARLSBAD RESEARCH CENTER
DRAINAGE BASINS FOR D~VELOPED CONDITIONS
ALTERNATIVE r
---- -
~---'
,J
-\
'1
4000
Pli!III
SCALE IN FEET
N
N
, - ---- --- -- ----- ----............. .--
~• 'A'"""" .--....--r-~-o--~.-.fJ!l--.---T-• ,V... -. II GI'-·','.N .' ,. II '; :,/: .' ., ~ " i,f / .. • • • , >f" , ,. h '>~J ' >J1\ii! t' :po CI , l"· /' .~{/." . ,~,,~ -..
\ ' ""'" -J \\ • ~' . , ~.:.'(', ~i \:'';' -~.,
",P' 0 • ~. b
\"./ 1\ \ ·h,-/ ~ .... A' ~tl' ~
'/:V-C '/ ,f' :/1 .' 61, .... , .... "",=/ 'II , \ ~. tF :' I " U /. .,
""/ , 'III : ~ .. '1 -.. ~ , ."""<~r, .. }1 . / -I' .1/, ••
. ---! I. / ' ,/
/ I I ,
/ ,
I
~~
"-\\ . _ 1. ..
• $. • '*' ~
LEGEND
t::C:~~:l;I PROPOSED DEVELOPMENT AREA
BASIN BOUNDARY
---SUBBASIN BOUNDARY
FLOW DIRECTION
• CONCENTRATION POINT \
~ FLOODWATER RETARDING BASIN
" G)
C
:::0
IT!
en
CARLSBAD 'RESEACH CENtER'
DRAINAGE BASINS FOR DEV.ELOPED CONDITIONS
ALTERNATIVE :rr
2000 4000
'?&M5J g" q ,,; J
SCALE IN FEET
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Alternative III is designed to utilize excess storage in the reservoir at
site III. Reduction of runoff from the northern part of the development
(Basin 120) w~ll be accomplished by diverting runoff from approximately 75
acres in Basin 120 into a reservoir at site III. This will reduce runoff
from Basin 120 to existing levels. The reservoir at site III has sufficient
capacity to control runoff from Basins 131 and 132 and diverted runoff from
Basin 120. Alternative III is illustrated in Figure 7.
A reservoir's effectiveness in controlling runoff depends on a number of
factors~ including reservoir storage; principal spillway dimensions; and
frequency~ duration~ and pattern of the storm under consideration.
For the preliminary hydraulic design purposes of this study~ an elevation-
storage relationship for each reservoir site was developed using available
topographic maps. The relationships may change as a result of more detailed
mapping or of changes associated with the final design of the reservoir. For
development of an elevation-outflow relationship~ a two-way covered riser in
combination with an overflow spillway of weir type was assumed. A typical
example is shown in Figure 8.
In determining proper capacity of a reservoir and alignment of a spillway,
considerations were given to the following:
1. A reservoir should meet the requirement that peak flow rates resulting
from lO-year storms both for 6-hour and lO-hour durations will be less
after development than under existing conditions. It should also be
effective in controlling runoff from less frequent storm events such as
-23 -
r'V r::,
1~
- -- -----
0----;-l;~""E' EI.r-;;-:~,~ ---fa---'(":'1?-/--~ ~ . ,;. : ; ," • ,I" U I' I _ -:;:: -: ~
j v'1_ ~ ~ r-" \\: : I') , • , 1,1 .. -)1. 1'1-;' - -'.
~:; • f..f ,\ r i .. ,' "); -:6 I '7"'~ ... ~~ ::: I/~/, 30
..... /~.r r"'\ I' 'F V /,., ,_ :9",
-/"0)\, I, } ".\;:1 ,,'-.: ~ 1\
)
.• /-/: 1\ :'n, "":' .-..... ~ "V::'" /1
t \ f"v j' :'1"' h""~1 IJ/ (; I
'\. II ,><'" ' ': i/ : ."'
LEGEND
"'I" ...:-'--',II ,
\ 11'-" ~\~\.=*~1
t"I~' /~
. ,'('
I ,
I
"' "1 ~ .=;
,
I
/
I
(\
l: "-. • ..1 ,(
:;', ,,:':, 'r"" -'..;,;·~;2 PROPOSED DEVELOPMENT AR~A
BASIN BOUNDARY
SUBBASIN BOUNDARY ---
FLOW DIRECTION
• CONCENTRATION POINT
f?Z) FLOODWATER RETARDING
-I \ \
It'
----- -
200
::!J
G')
C ::0 rn
-..J
CARLSBAD RESEARCH CENTER
DRAINAGE BASJN FOR DEVELOPED CONDITIONS
ALTERNATIVE 1Ir
, - - -
o 200
-
\.
r
(I
~It
-
f\'
/
'-!'(~.~
400 --~-~'\a: 4 .4 ea #Ai
SCALE IN FEET
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LOW-FLOW
INLET
t o
.................. :,,-
.I------l
,
.'
EMERGENCY SPILLWAY
PRINCIPAL SPILLWAY
r
m
'.
.'. ~ •••••• ~ ••••••• -~.-.:.~.~.~ •••• ...:...:..--j.: •• ~. ~---\
NOTE: SEE TABLE 4 FOR CORRESPONDING
DIMENSIONS
-25 -
. . ..
lL z
. .
I-z w :>-z (!) -.."J «
~
c:::(
·0
o z c:::(
0:::
W en
0:::
-1 « U -a.. >-I-
FIGURE
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2. A riser should be sized to pass the la-year storm peak flow rates without
overtopping the overflow spillway. The outlet for the riser should also
be located so that there is sufficient sediment storage.
3. Constructing a floodwater retarding reservoir on a tributary may result
in increased peak flows in the main streams below the tributary. This
should be avoided.
The capabilities of the three alternative plans of floodwater retarding
reservoirs were analyzed using the reservoir routing subroutine of the _
TR-20 computer program. Numerous computer runs were necessary ~o determine
proper reservoir capacity and spillway dimensions. Table 4 shows the design
features for the dams and spillways used for the final results.presented
below. It should be noted that a higher dam may be required to provide
sufficient emergency spillway capacity depending on the design criteria
determined during the final design.
Tables 5 and 6 show effects of the reservoir on peak runoff rates for Alter-
native I. Tables 7 and 8 show the same for Alternative II. Tables 9 and 10
show the reduction for Alternative III. As can be seen from the tables, all
three Alternatives will reduce the increased peak discharges to or below
existing rates on the tributaries. None of the-alternatives will cause
increased peak discharges in Agua Hedionda Creek. Figures 9 and 10 show
inflow and outflow hydrograpns resulting from storms of 24-hour duration at
site III (Alternative III).
-26 -
- - - - - - - - ---. - - - - - - - -
TABLE 4
Dimensions of 1
Two-Way Covered Risers and Dam5
Volume (Ac-Ft) at
D
Inches Description Feet
A B C E F G R I
Emergency Spillway Top 2
Crest of Dam
Alternative I .. Basin I 13 9 7.5 9 18 36 6 15 36 14.1 21.7
N "'-J Basin II 20 17 12.5 12 36 48 6 18 48 30.8 39.1
Alternative II
Basin I 13 9 7.5 9 18 36 6 15 36 14.1 21. 7
Basin III 18 16 10 9 24 36 12 18 36 46.0 55.7
Alternative III
. Bas tn .. J I 1. . 20 16 10 9 24 36 12 18 36 46.0 65.7
1 lSee Figure 5 for typical orientation
2A .higher dam 'may. be required to provide 'sufficient emergency spillway capacity •
• ,11 I I I, J,"I I, I . I
-------------------
TABLE 5
ESTIMATED 10-YEAR PEAK DISCHARGES
For Existing Conditions and Developed Conditions
With Floodwater Retarding Reservoirs (Alternative I)
EXISTING CONDITIONS DEVELOPED CONDITIONS WITH BASINS (ALT. I)
N co
LOCATION
120
130
140
150
.
Subtotal
(130+140+150)
D.A.
(sq;mi.)
.30
.63
.20
.10
.93
STORM DISCHARGE {cfs)
6-HR 24-HR
50 50
70 110
20 30
20 20
90 150
. *Include Diversion from Basin 130
"I I I. I ,
.
LOCATION D.A. STORM DISCHARGE (cfs)
(sq.m;. ) 6-HR 24-HR
120 .31 30 40
131 .43 -- --
132 .18 ----
130(131+132) .61 ----
140 .20 90* 130*
150 .Q8 20 20
Subtotal .89 90 140
(130+140+150)
\ ~~~
------------------.-
N
~
TABLE 6
ESTIMATED 100-YEAR PEAK DISCHARGES
For Existing Conditions and Developed Conditions
With Floodwater Retarding Reservoirs (Alternative I)
EXISTING CONDITIONS DEVELOPED CONDITIONS WITH BASINS (ALT.I)
LOCATION D.A. STORM DISCHARGE {cfs) LOCATION D.A. STORM DISCHARGE {cfs)
(sq.mi.) 6-HR 24-HR (sq.mi.) 6-HR 24-HR
120 .30 230 . 140 120 .31 120 140
131 .43 . ----132 .18 ----
130 .63 350 280 130 (131+132).61 ----
140 .20 120 80 140 .20 350* 390*
i 150 .10 80 50 150 .08 60 . 40
Subtotal .93 470 400 Subtotal .89 360 410 (130+140+150) (130+140+150)
-
*Include Diversion from Basin 130
•
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-------------------
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<:)
LOCATION
120
130
140
150 '
Subtota 1
(130+140+150)
TABLE 7
'ESTIMATED 10-YEAR PEAK DISCHARGES
For Existing Conditions and Developed Conditions
With Floodwater Retarding Reservoirs (Alternative II)
EXISTING CONDITIONS DEVELOPED CONDITIONS WITH BASINS (ALT. II)
D.A. -STORM DISCHARGE {cfs} LOCATION D.A. STORM DISCHARGE {cfs}
(sq.mi.) 6-HR 24-HR (sq.mi.) 6-HR 24-HR
.30 50 50 120 .31 30 40
131 .43 ----
132 .18 .63 70 110 130(131+132).61 50 100
.23 20 30 140 .20 . 40 -40
";'
.10 20 20 150 .08 20 20
.93 90 150 Subtotal .89 90 120
(130+140+150)
-----
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- - - - - - - - - ---.------ -
w ......
TABLE 8
ESTIMATED 100-YEAR PEAK DISCHARGES
For Exi~t1ng Conditions and Developed Conditions
With Floodwater Retarding Reservoirs (Alternative II)
----------------------------------------------------------~ .. ---------------------------------------------------EXISTING CONDITIONS DEVELOPED CONDITIONS WITH BASINS (ALT. II)
LOCATION D.A. STORM DISCHARGE {cfsl LOCATION D.A . STORM DISCHARGE {cfs}
. (sq.mi.) 6-HR 24-HR (sq.mi.) 6-HR -24-HR
120 .30 230 140 120 .31 12Q 14.0
131 .43
350 280 132 .18 130 .63 130(131+132) .61 120 130
140 .23 120 80 140 .20 160 .' 90
150 .10 80 50 150 .08 60 40
,; .
Subtotal .93 470 400 Subtotal .89 280 250 (130+ 140+ 150) (130+140+150)
•• I L , "
-------------------
W
N
Location
120
130
140
150
Subtotal
(130+140+150)
TABLE 9
ESTIMATED 10-YEAR PEAK DISCHARGES
For Existing Conditions and Developed Conditions
With Floodwater Retarding Reservoirs (Alternative III)
EXISTING CONDITIONS DEVELOPED CONDITIONS WITH BASINS (ALT. III)
Drainage Drainage
Area Storm Discharge (cfs) Area Storm Discharge (cfs)
(sq. mi.) 6-Rr. 2~-Rr. Location (sq. mi.) 6-Rr. 2~-Rr.
.30 50 50 120 .19 60 40
131 .43 ----
132 .32 ----
.63 70 110 1 30 (131 + 132) .75 70 120
.23 20 30 140 .20 40 40
.10 20 20 150 .08 20 20
.93 90 150 Subtotal 1.03 90 160
(130+140+150)
-----.---------
-------------------
w w
TABLE 10
ESTIMATED 100-YEAR PEAK DISCHARGES
For Existing Conditions and Developed Conditions
With Floodwater Retarding Reservoirs (Alternative III)
EXISTING CONDITIONS DEVELOPED CONDITIONS WITH BASINS (ALT. III)
Drainage Drainage
Area Storm Discharge (cfs) Area Storm Discharge (cfs)
Location (sq. mi.) 6-Hr. 24-Hr. Location (sq. mi.) 6-Hr. 24-Hr.
120 .30 230 140 120 .19 180 100
131 .43
132 .32
130 .63 350 280 130 (131+132) .75 160 250
140 .23 120 80 140 .20 160 90
150 .10 80 50 150 .08 60 40
Subtotal .93 470 400 Subtotal
( 130+ 140+ 150) . ( 130+140+150) 1.03 290 310
-_.-------
I I t.
~!
-------------------
-Cf)
IJ..
0 -LU
C!}
0: « :c 0
Cf)
'0
'oo'lr!.!'!'III!I!llllllllllllll!IIII!!!!I:I!!"::;I!r.Il' ..... , ..... "'''':1.: ... 1.
,..4i.: : Ii: i;: .. :··'··'
160
140
.: .:. .:"::: ~ §._ ':' ..... -!-'-'-l-H+ ~". . '1-....
• • • • • ~ ~. _ ; ••• ~........ EXISTING CUNDITIOfi •••••. . . j i' i! it ~ . DEVElDPED cooDrilDN VlnlOllT BASI" t--
---'-h-: ------:;.:, :I~
. ,i-'-+--H-I-H ~. ~
;:f"1'
.-!-
• : .::: ' • : •. : • : •.•• : •••• ~ . ._._._ •• DEVELOPED CONDITION vHH BASIN _. . ',::; ""., · 'i'~~ril:·~\ ,.e-d' "' •• ".. .,',~.' '~~'~~
.' . . . . +++1" ; -~ .... '" . .... ., ~ . :. ". .-H-' '.' ::-:.~~-.-. :: \~:".: .. :. :. ..: -'~i~~~~
80 . .;.... ....0' .. 'f-./-¢ 1 :. : :. ",.' ~ _,"--,_:'::'
. ,-r-, . ·r·~ \ ...•. , ,r.. • . :. 4-,' .. i'~.:j: '-~ . . \ . ." .. .' . -:::r:::::=;:J+
'+1. :" t::!§:J. -\ ': .:: .\--'-: . ... ': =-....w+J:
60 \. ..!., ..... :, ... :..... + ~.\-'--rt-.,-,-,-,-•• ~ ." . ...... ...:., :. . .. : . ".::;:;:g: .. ¢ ....... f-'.,;;: '.:II .-~ :~~........ ',': ~.-.. -.~ . .,.;:-:.-. .:..-.~._.~ .... _._.... . :: ... :. '.' ... -:.,::: i ;It
. ' t.!1 : -~ .~~ "·.i.., " I ., • • .J....!J .~-
-i---' ': :..:;::: .1J:.:':~j{-,'.:' '\~-:~ ", . '... ... ' .. -.... _._. __ .... : .... .... ...: ::,d:'n:
40· -'-'---" ' ~;Ji' .. .' .. ;. . ~ ~ ...l..: . , _'-+:-I~~.-._.,_ l~ J... ... , : .. ,. "~"I 1.1" _ _. .. .. -~.~. .... . _ ' . .. . : ]E. ,,: .. J • .... ••• ~;:-ttW;t", ---tt-:-;;-;-" .. ~I ....... .~-.J,...L...... ~/.:·r;~·w:. .. "~'-'-". .. ..... 11. '''::-!±I-T ............. :..... .. ~'. .t~~ ±:t::h: Z=:'~,~~'::::: ,,:: '~ -t-:+:-o -~ ~ :: •••• :.:;~~-:-· ... ·-~'r~· ~ .... ~.. ~ ~~~ '.'" . ' .... ,. .. .... . ~.u.
,.' -,~ ~i' '-~"~ ::: .... ~.!.;.; •. , ...... .-.-••.. ~:-ri. .. ..... ~ .' -I. .,.-L4-'-Lj:l -;,,:;.rt ':-:. . ' " , . -..-+1 . .~-. .l-H H . ~~;..;:;m .. ,: . . . ; ... '-i "', . . -W.fl:!:!:j:J
o .t=fE~:gE!E~~~~~i':: ... ·~·'·-:~ ., . \"''''~'~ ~ ... :"'.~.~
0.0 3.0 6.0 9.0 12.0 115.0 18.0 21.0 24.0 27.0 30.0
TIME. (HOURS)
."
lOG) C
_ .:::0 .-rn
INFLOW
FROM·
AND OUTFLOW HYDROGRAPHS
A 10 -YEAR', 24 -HOUR STORM
AT SITE lIT -ALTERNATlVE][
..
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'lJ· J 1· 'J ..' I '-~rl: .:. j1 Wf ~ .1111111]1 1 ' .. J1:-"I. llijjl. : I fJ . wl'1~1tm . .. .. f. d. i.i.j;r,!ril J mi~t 1. n· 1!isw, q ... .. ·l'~·ili .... .', f mr/i ~
........................ <..'.· ...... ·.··· ... · ... lW·
.... , '. '.': ..... :'.:. . . . :.:'. :. ..': IlX1 ' .. ~
...................................................... ?i .·..l ..
. . -. -i
8· ¢
(8.::10) 38HVH0810
-35 -
-en 0: ::::> o
J: -
FIGURE
10
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It should be mentioned that the master drainage plan for the city of Carlsbad
was recently prepared by the consulting firm of VTN (Reference 10). This plan
recommended storm drain facilities appropriate for the Carlsbad Research Center
development area. Also noted in the plan are two debris basins downstream of
the tributaries where the Carlsbad Research Center development area is located.
The debris basins are to protect the lagoon from siltation by new development.
However, these debris basins would have a minimal effect on reducing the in-
creased runoff rates which are of major concern for this study.
-36 -
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REFERENCES
1. u.S. Department of Agriculture. Soil Conservation Service, 1965.
Computer Program for Project Formulation -Hydrology. Technical Re-
lease No. 20.
2. County of San Diego, Department of Sanitation and Flood Control; 1973.
Hydrology Manual.
3. u.S. Department of Commerce, National Oceanic and Atmospheric Admin-
istration, 1973. Precipitation -Frequency Atlas of the Western United
States, Vol. XI -California.
4. Williams, J.R., 1975. Sediment-Yield Prediction with Universal Equation
Using Runoff Energy Factor, in Present and Prospective Technology for
Predicting Sediment Yields and Sources, Sediment Yield Workshop Proceed-
ings, ~SDA ARS-S-40.
5. U.S. Department of Agriculture, 1978. Predicting Rainfall Erosion Losses,
A Guide to Conservation Planning. Agriculture Handbook no. 537.
6. u.S. Department of Agriculture. Soil Conservation Service and Forest
Service, 1973. Soil Survey, San Diego area, California.
7. Williams, J.R. and H.D. Berndt, 1977. Determining the Universal Soil Loss
Equation's Length-Slope Factor for Watersheds, in Soil Erosion: Pre-
diction and Control, Special Publication No. 21-,-Soil Conservation
Society of America.
8. Boyle Engineering Corporation and the City of San Diego, 1980. Pre-
liminary Report, Flood and Sediment Control Study for the San Pasqua1
Vall ey.
9. California Department of Water Resources. Southern District, 1977.
Erosion and Sedimentation in San Diego County Watersheds.
I 10. VTN, 1980. Master Drainage Plan for the City of Carlsbad, California.
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I -37 -