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BUENt1 VISTA LAGOON AIVC� v�.%�1�_Ral-IEU
SEDIMENI C3�NTRC}L S i U[1`t'
FOR
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THE Cl�t_T�C���NI� C+JA ;TAL i f)P�'�EF:',��,PdCY
Ccasial C�ns�rvancy 2G5 t,:�' ,r:�r3t:
Buena Vi sta Lagaon Se�fi�rF�rit Marac�ernert P:���s� T I 53-�53-�i -48-C
�Y
JUNE APPLEGATE, P.E,
Sept�mber 3, 1985
����9 ��e��� ���e���i , �a��aL��s��, ��p�€���'.�3�s°� ��k�9'c,d�' �� ���� ���5�_�' �I�.��`�
PFtCJ�CT TEAM
<:CA�"_'�L �itiS�,�'�1CY
?e�-,.er Grc�x.ell, E�ecutive Officer
�1yse Jaco�son, �hanc��nent Program Manager
La.urie Marcus, Project Manager
JtJ'VE APPI�EGATE & ASSOCIATES
June Applegate, �rincipal
D?�IP i�7II�I,IAM� & ASSCCIA'I'F�S
Philip williams, Principal
Jane Kerlinger, Hydrolagist
TABLE C�F C�N'I'EN'I'S
SLMMARi'
I . INT�OI�UCTIC�I
II. ??'HE ��'ER.SI�D AND LAC�? SYST.E��'I
Historic Changes
Buena Vista Creek
The Lagoon
StBta�iazy
III. SIDIlKII�7T SOURCE Q�RACTE',RIZATIC)N
N
TV. P�LYSIS
The Watershed �dels
The Lagoon Model
V. CC3�tCLUSIC�VS
VI. RECO�IDATIODTS
VII. BIBLIOGRAPHY
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Subbasin Characteristic Calculations
Cost Effectiveness Ca.lculations
Upper Middle Reach Erosion Calculations
Lagc�n Sediznentation Calculations
LIST OF FIGL'RES AND TABLES
FIGURE 1 R�gional Locati�n
FIGURE 2 Watershed Subareas
rIGURE 3 Natural Conditions
FIGURE 4 Detention Basin Locations
FIGURE 5 Prc3posed Channel Cross Section
FIGURE 6 Hydrogra�hs
FIGURE 7 SchPmatic Diagram of Buena Vista Lagoon
TABI� 1 Erosion Control Alternatives
T�BLE 2 Sediment Size Distribution for
Different Hydrographs
TABLE 3 Sed�ment Source S�manazy
TABLE 4 S�u�anary of HEC-1 peak flaws and
ti.me to peak for future conditions
at the lagcon
TABLE 5 Projected Sed�ment Reductions
TABLE 6 Sediment Rating C�.lrve Relationships
LTsed in Analysis �
TABLE 7 Buena Vista Lagoon Co�uter Model �s
TABLE 8 Sw�mary of Inflaw Hyci�oyraphs
TABLE 9 Sumnary of Lagoon and Watershed Simulations
PAGE
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IP'
Ii�ITRODUCTION
Due to the rapid sedimentation of Buena Vista Lagoon, the Ca.lifornia State
_ Coastal Consexvancy funded this study of sediment control for the lagoon and
its watershed, A Phase �Yie study was perforn�d by Brown & Vogt of Vista.
Leedshill-Herkenhoff of San Francisco subconsulted and provided the hydrology
models of the watexshed. The findings of the Phase One Study indicated that
— several alternatives needed to be evaluated for sediment control.
The California State Water Resources Control Board and the Coastal Conservancy
then funded a Phase 'I� Study. June Applegate & Associates of Carlsbad was
hired to perfozm the watershed modelling, project coordination, and
alternatives evaluation. Phi].ip Williams & Assaciates of San Francisco
preFared the h_ydraulic analyses of the lagoon. The primary goal of this study
is to fornlulate a prioritized list of sediment management procedures for the
Buena Vista watershed and lagoon based on a cost-benefit comparison.
— Buena Vista Lagoon is the only freshwater lagoon in southern California. It is
situated between Carlsbad and Cceanside. Its 19 sc�uuare mi.le watershed includes
the ci�ies of Vista, Oceanside and Carlsbad (see Figure 1). The water level is
— maintained by a fixed v,�ir at the mouth of the lagoon. The fills of the
railroad, Hzll Street, Interstate 5 and Jefferson Street cross the lagoon.
Since the position and size of the mouth of fhe lagoon was made t�ermanent and
_ the flow restricted, there has been an increase in the sed�mentation rate of
the lagoon. Incxeased urbanization �n the watershed furfher accelerated the
sedi�ientation and necessitated the dredging of a portion of the lagoon.
If projected future sed�ment rates materialize, the lifet�me of Buena Vista
Lagoon could be less than 10 years,
THE LAGOON SYSTF�I
Buena Vista Lagoon was created by the rapid rise in sea level after the last
� ice age. Tn its natural state, it appears that the amaunt of sedim�..nt
deposited in the lagoon was balanced by the rate of sea level rise. Two
factors have upset this balance. One is the limi�ation of the lagoon's ability
to flush sediment t.o the ocean by the placement of a weir at the nx�uth and road
— fills that cross and restrict the lagoon. The other is the increase in
sed�ment delivezy to fihe lagoon from the watershed.. The cause for this
increase is two-fold. Urbanization has increased flaws to the lagoan.
— r�croachment upon the flood.plains that once accepted sed�ment from the creek
during large storm flaws has eliminated mast of this buffer and sediment naw
flows directly into tne lagoon.
Before the Yruman-caused disturbances to the watershed, creek, marsh, and lagoon
much of the sediment frcgn the watershed was deposit� before it reachecl the
lagcon. Sediment was deposited on the broad floodplain i.n the middle reach.
Then in the lower reach, a Iarge marsh area spread and filtered the stonn
water, trapping �re sediment before it entered the lagoon.
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The cnly renmant of this protection system is the area west of South Coast
Asphalt and east of the Haymar Street cul-de-sac. This reach of the creek is
currently absorbing very large quantities of sediment and is the last natural
buffer to prevent sane of the se�iment frcan enteri.ng the lagoon. The best
functioning portion of this reach is the thick riparian area just east of the
Haymar Street cul-�e-sac.
The other sed�ment buffer was the marsh abo��e the lagoon. This marsh has been
cc�letely filled. The cattails in the channel between the shopping center and
Highway 78 and on both sides of Nbnroe Street at Marron Rr�ad are all that are
left of this marsh. Before the filling of the marsh, the water slowed and
found its way through the tules to the lagoon dropping most of the finer
sediment that was left aftex the riparian area upstream.
After changes in the watershed, particularly urbanization in the I.ast two
decades, increased peak flcw have dramatically transfo� the natural
hydrological system. The increased flcx,�s not only discharge more sed�ment from
the watershed into the creek, but, more in�ortantly, have caused the creek bed
to start to erode (degrade) in portions of creek. The increase in stream flow
enerqy has caused this stream dc�mcutting. The process will continue until a
new and lawer equili.briLun can be reached ( see Figure 3).
A11 of these factors contributed to the rapid filling of the lagoon from 1978
to 1981, the years that marked the end of a 13-year dry period in this region.
In 1981 the eastern portion of the lagoon was dredged. The puz-pose of this
study is to explore alternatives to continued dredging of the lagoon.
THE STUDY
Hydrology models of the watershed and hydraulic �dels of the lagoon were
dev�loped. and evaluated. Maximizing the flushing action of the lagoon resulted
in a small reduction in the sediment ac�lation rate. Greater reduction in
the sediment delivezy rate can be produced by reducing the peaks of the storm
flows into the lagoon.
Reductions in the peak flows were modeled by opt�mizing feasible detention
basins in the upper reaches and by modeling channel enhancement that would
slow velocities in the middle reach.
Regional sediment transport ctiirves were integrated with the inflc7w hydrographs
in the hydraulic model of the lagoon. Because the quantity of sedimP�nt
txansported is an exponential function of the quantity of water, the peak flaws
are responsible for a large portion of the sed�ment transported to the lagoon.
Reducing these peak flaws resulted in much Iarger reductions in sediment flaws
into the lagoon.
The study reviewed nine alternativ��for controlling sedimentation of the
lagoon (see Table 1). These include: LZ) modify the lagoon flushing action by
increasing the weis size, the size of the Hill Street Bridge and clearing the
opening under I-5; L2) dredging a flaw�through channel through the lagoon from
Jefferson to the w�eir; W1) construction of stornnwater detention basi.ns in the
upper watershed.; WSy enhancen�nt of the main channel to lower mai.n channel
4
� phlll Willlams R AssoclatPs
Cc,nsuP�t.,nl5 m tiSc�;��l�,;ly
C � 0 S S
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Figure 3 Natural Conditions
,�;•s�r�ic'i^ S!reaT
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5
TABLE G'�]E
EROSION CON'I�ZOL ALTERNATIVES
ALTERI�TIVE ESTIl�TID ESTIMATID P�]T AI�TNUAL COST-
IN�ITIAL ANNUAL RIDUC- COST BIIJEFIT
COST O&Ni COST TION RIDUC'N 1 RATIO 2
PHASE II
LAGOC,Y�1 MODIFICATIQNS:
L1 WEIR+HILL ST+I-5 $570,000 $15,000 12$ $168,000 3.0
L2 CHANNEL $4,030,000 $2,010,000 14� $197,000 .1
PHASE I
WATERS�D MODIFICATICJ�7S:
W1 DEI' BA.SINS Const. $92,000 $139,000 20$ $281,000 2.0
I;and Acquisitions $750,000
WA'I`ERSF�D MODIFIC'ATICN WITH SIDIl�lIIVT SOURCE CONTROL:
W5 CREEK ENHANC $800,000 $160,000 32a $440,000 2.8
SIDIME� SOURCE G'aNTRUL:
Sl E.C.R. SIDE ARROYO $30,000 $6,000 1� $7,000 1.2
S2 GRADID AREAS $6,000 $6,000 30 $37,000 6.3
S3 AGRICUL'IURAL $6,000 $6,000 2� $33,000 5.6
S4 S.COAST SID BASIN $12,000 $12,000 lo $18,000 1.6
S5 JEFF. SID BASIN $5,400 $5,400 l� $12,000 2.2
NO MODIFICATION: $1,410,000 3 BASTS OF COMPARISCAv 1.0
1. Anrrual oost reduction is equal to the pexcent reduction times $1,410,000
{the estimated annual cost of dredging with no modifications to the lagoon
or watershed). Annual cost reduction is the annual benefit.
2. Estimated total annual cost divide by the annual benefit.
3. Z"his figure is the annual cost of removing 191,500 cubic yards of
estimated sed�ment delivered into the lagoon at $7.35 a cubic yard for
dredg�ng .
F�arther details on the derivation of these figures is included in Appendix 'I'wo.
0
0
velocities and help repaix esosion damage; S1) side channel arroyv repair;
S2? erosion control education for protection of graded lands; S3) erosion
— control education for protection of agricultural lands; S4) a sediment basin at
South Coast Asphalt; and S5) a sediment basin at Jefferson Street. The nine
alternatives c�re campared to no mcdifications and the consequential dred.ging
— of the lagoon at the anticzpated rate of sed�ment acc�zmulation in the future.
Er'FECTIVE SOLUTIGY�tS
Eight detention basins (WI) in the upper reaches will produce an anticipated 20
percent reduction in annual sediment acctmnxlation. A detantion basin consists
of a small check structure (i.e.: a 5' high dam or a road crossing) and a
restricted outlet like an 18" pipe. This allaws the water to pond during
storm� and to be released at a greatly reduced rate. There are eight detention
basins proposed in this alternative (see Figure 4 for detention basins in
Vista} ,
Creek enhancement (WS) proposes peak flow velocities to be less than six feet
� pex second, allc7wing rigarian grawth in the creek. This can be accc�pZished
with a 15 to 30 feet increase in creek width and drop stsuctures which reduce
the grade of the channel and thereby red.uce the velocity of the water (see
Figure 5). Creek enhancement was �delled wi.th the detention basi.ns in place.
— The combination of creek enhancement and the detention basins resulted in a 45
percent reduction in annual sed�ment accimrulation because of the resulting
reduction in storm flaws. Since the detention model alone yielded. a 2d percent
— reduction, it is assLuned that the reductian in storm flows due to the creek
enhancement alone can reduce sed�ment deliv�ry by a min�mimi of 25 percent.
Reducing the erosion of the main channel (which is the major sediment source in
_ the watershed) by this enhancement will further recluce the sediment
acc�mtulation by an additional 7 percent, for a estimated. total of 32 percent
reduction. Addi�ti.onally, the lawPx middle reach floodplain should be
presezved.
The combination of a movable and 80' wide w�ir, a 100' bridge opening at Hill
Street and dredging under I-5 (L1) produced an estimated annual sed,iment
— acc�umzlation reduction of 13 percent. However, this alternative has major
drawbacks that can not be measured by a dollars and cents camparison. La�eri.ng
the �ir will create other problems that are not related to sediment
_ accLmnilation. Among those concerns are water quality, and salt water
i.ntrusion. This alternative increases the probability of lawer water surface
levels in the lagoon. Shallaw water allaws sunlight to penetrate the water,
warniing it and increasing algae grawth. Iawering the weir also increases the
— probability of ocean waves overtopping the weir, introducing saZt water to the
lagoon. Another anticipated probleln with this solution is that it is likely
that the ch�nnel dredging under I-5 will ha�� to occur frequently.
Spencling a relatively sna11 annual sum of money on education for sediment
contxol on grading sites (S2) will produce an estimated twn thirds reduction of
_ this source. Reducing sedunent sources will change the sedi.ment rating curves,
thereby resulting in a reduction of sed.iment accim�lation in the lagoon. There
is no data on the relationship between sediment source reduction and the
reduction of sed�m�ent acc�mtulation in Buena Vista Lagoon. This study asstmies
7
that for evezy cubic yard of erosion controlled, there is one ha.lf of a cubic _
yard of reduction of sediment acctunulation in the lagoon. The anticipated two
thirds reduction in the grading site sed�ment source nnzltiplied by one
half indicates that this improvement �uld mean a three percent reduction in
annual sediment acc�nzlation rate in the lagoon. Ta.ble One indicates that this —
has the highest rate of return on dollar invested.
Similar results are anticipated for agricultural sites (S3). The budget for
this program should reduce as the land for agriculture diminishes. Currently a
reduction of 2 percent of the total sediment acc-�miulation in the lagoon per
year is anticipated. -
It is anticipated that 5,000 cubic yards of sediment per year could effectively
be removed fran a sediment basin located at the South Coast Asphalt property
(S4). It is estimated that this c�uld result in an annual reduction of 2,500
cubic yards of sediment per year, using the source and acc�aulation
relationship est�mate described above. This w�uld mean a one percent reduction
in the annual sed�ment acctiurnzlation rate in the lagoon. Removing sedimQ_nt at
this site wc�uld reduce the sediment acc�ulation rate of the lagoon.
Another 1,600 cubic yards of sed�ment per year could effectively be rem�ved at
the mr�uth of the creek, just east of Jefferson Street (S5). Since there is no
dan�pening effect expected at this close proximity to the lagoon, it is assumed
that this is a dixect reduction in the sed�ment acc.•umulation in the lagoon.
This could result in a reduction in annual sed.�ment acc�ttulation in the
lagoon of one percent.
I�. is also effective to rena;r side channel arroyos {S1) in the manner —
descri.bed for the main channel. The example given is the channel which is on
the west side of El Camino Real (E.C.R.) frcgn Hosp to Chestnut. Repairing this
arroyo also yields a one percent reduction and is cost-effective. —
The alternative that proved to be far too costly was to maintain a deep channel
in the lagoon from Jefferson Street to the weir (L2). It is anticipated that _
laxge amounts of material would have to be dredged fran this channel, because
the channel w�uld act as a sediment trap for the lagoon. The high sed�ment
rate of the lagoon means that the channel would fill in at a rapid rate. It
is est�snated to cost over twe mi.11ion dollars per year to maintain such a —
channel because of the large volLunes of material to be removed.
Refini.ng the estimates with data frc�n a watershed, creek, and lagoon nx�nitoring _
program, and with more precise cost estimates may or may not improve the
cost-effectiveness ratio for this alternative.
�� « ��
In the order of effectiveness the following solutions are reccam�ended: creek
enhanc�nt (including floodplain presezvation in the lower reach), detention
basins, sediment control education, sediment basins, and side channel arroyo
repair.
0
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LEGENQ
� � 1 PHASE 1 DETENTION BASIN FOR STORM ATTENUATION (4 LOC'NS)
� 2 PHASE 2 DETENTION BASIN FOR STORM ATTENUATION (2 LOC'fVS)
CHANNEL ENHANCEMENT DOWNSTREAM OF BRENGLE TERRACE PARK TO
COLLEGE AVENUE.
�(1 MODELED IN PHASE 1, BI.IT NOT PNASE 2
�( 2 MODELED TN P�IAS� 2, BUT PdOT EFFECTIUE
� Fi gure 4
STORM ATTEIVUATI0IV BASIN & CHANNEL ENHANCEMENT
MAP
9
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� Figure 5 Cross Section of Proposed _
Channel
10
The study four�d scme lagoon modifications to be cost-effective, however there
_ are major concerns for the ecology of the lagoon if these are i�lemented. 'The
cost-effective modifications included a mr�veable and widened weir, enlarging
the Hi11 Street Bridge to be 100' Iong, and keeping the opening under I-5
c�sedged .
��i�
I . IlVTRODUCTIC�I
This is a report of the Phase Zt,ao study of sed�ment control for Buena Vista
lagc�on and watershed for the California Coastal Conservaricy and the State Water
Resources Control Boa.rd. Findings of the Phase One Study indicated fihat
several alternatives needed to be evaluated for sediment control. June
Applegate and Associates, Civil IIzgineers of Carlsbad was selected by the
Coastal Conservancy to perforr�n this study. Philip Williams & Associates of San
Francisco was hired to subconsult and pravide the hydraulic analyses of the
lagc�on. The watershed modelling, project co-ordination, and alternative
evaluation were perforn�ed by June Applegate and Associates and are �rized
in this report. The Phase �o study relied upon the findings of the Phase One
study and has greatly expanded and revised their rec�ndaitons. This degree
of in-depth research into the Phase One rec�ndations has resulted in the
div�en�ent findi.ngs of the Phase Two report.
It is the primazy goal of this study to report a prioritized list of sediment
management procedures for the Buena Vista watershed and lagoon ba.sed on a --
cost-benefit comparison.
The Buena Vista uratershed is an ungauged watershed. Al1 of the predic�tions in
this study are based on synthetic hydrographs, synthetic mathematical models of
the lagoon, and sediment rating curves extracted from other similar small
coastal watersheds. Sediment monitoring using detailed bathcanetric surveys of
the lagoon after major storm events, stream flaw sediment monitoring, and rain
gauge information during sto�n events will yield more accurate predictions of
sediment acc�nulation, sediment flaws and sources. Due to limited budget,
almost no field data, and a range of uncertainties, the sed�ment predictions in
this report have a wide range of exror changing the true cost-effectiveness
analysis dramatically. �,
Consistent techniques �re applied unifoxmly for each category of modification.
The estimate of reduction of arinual sed�ment acc�urnzlation in the lagoon
pravided a relative ranking of the effectiveness of each alternative. The
categories of alternatives in which the relative cost-effectiveness ranking is
valid is; maximization of the flushing ability of the Iagoon wi.th lagoon
modifications (L1 and L2), mi.nimization of the sed�ment delivery to the lagoon
with watershed modifications (W1 and WS), and minimization of erosion in the
watershed (WS, arx� S1 through S5) .
II. THE h�,TERSI�D AND LAGOOIV SYSTII�I
Buena Vista Lagoon was forn�d during the rapid rise in sea Ievel at the end of
the last ice age, ten to fifteen thousand years age. During the last five to.
seven fihousand years sea level rise has been more gradual, apparently about
1/2 foot per centuzy. The slow rate of rise was sufficient to ccgnpensate for
natural sedamentation rates in the lagoon, allawing it �o survive for thousands
of years.
Wave action caused the littoral transport of sand along the coast, sealing off
the entrance to the lagoon with a barrier beach. Fxcept possibly during an
12
early stage in its evolution, L�he �cidal prism of the lagoon was insufficient
_ to scour a channel across the beach. Tidal action occurred for a short pericd
in the lagcon, and only w�en winter floods opened up a channel. Some sedu�uent
carried. into the lagc;on during floods discharged directly to the ocean through
the c�ening. Scm� sediment deposi�ed in the lagoon �uld later be resuspended
— by wave and tidal action, and would �e flushed out of the lagoon during ebb
tide.
— Because of the �arrier beach across its mouth, the character of the lagoon
varied greatly frcan season to season, and frcan year to year. In nornnal
winters, stonn xunoff filled the lagoon with freshwater until at some point it
_ overtopped the barrier beach. In the spring, after the beach was
reestablished, the lagoon Ievel dropped, fed only by springs and the base flow
of Buena Vista Creek. In s�r and fall the inflaw decreased further until
eva�oration exceeded inflow. Water sali.nities increased and large areas of n�ud
— flats or salt pans woL:?d be exposed.. During drought periods it is likely that
the lagoon a]most cx�mpletely dried out, and was fed mainly by salt water
seeping through the beach.
In its natural state the watershed of Buena Vista Lagoon was cavered with
native plant vegetation. The plants generally provided a higher resistance to
_ erosion than many of the introduced, n�w species. They not only protected
against direct erosion from rain drops but allawed the infiltration of storm
runoff into the soil, reducing peak runoff rates downstream and providing
greater base flaws in the creek later in the year.
'I'r!ese flaws supported dense riparian vegetation along the creek banks and on
its floodplain. In its lo�r section the creek would have disc,harged into a
— tule freshwater marsh at the upper end of the lagcon. The floodplain and marsh
vegetation acted as sediment traps during high flood flows, building up the
alluvial floodplain and reducing the amount of sed�ment discharging to the
_ Iagoon.
Historic Changes
In the two centuries since Europeans settled the area, man has made major
modificatians to the natural hydrologic system.
— The hyraulics of the lagoon have been ccm�letely altered since 1940, when
outlet culverts wpxe installed at the mouth to regulate maxinn�n water levels.
This eliminated tidal action until the big flood of 1969, when the culverts
` �re washed out, re-creating the natural entrance for a short while until the
existing fixec'. outlet w�is was installed in 1970. Since that time tidal flows
have been excluded and the lagoon has been converted to a freshwater lake.
— The canstruction, first of the Hill Street road embanlanent and then of the I-5
freeway emlx-�n�nent across the lagoon, has also affected the hydraulics by
segregating the Iagoon into three distinct basins. These changes have greatly
— limited the lagoon's ability to flush sediment out to the ocean.
Urbanized runoff pollutants discharged directly into the lagoon degraded water
quality. In adcti.tion, until the 1960s, sewage was discharged directly into the
13
lagoon.
The watershed has also changed dramatically, k�tensive grazing and, later,
farming, rempved soil cover, increasing erosion and sedime.ntation in the
lagcon. Urbanization, which has been particularly rapid since the 1970s,
increases flood peaks, causing gullying and creating arroyos. This process
greatly accelerates erosion and dawnstream sedimentation. In addition, t-he
floodplain of Buena Vista Creek has been filled in sev�exal locations, reducing
the filtering effect of the riparian v�getation.
The floodplain in the middle section cf Buena Vista Creek has evolved as a
result of sed�ment frcen the surrounding hillslopes being transported. as bedload
in the creek. During flood flaws, these fl�,vs would overtop the creek banks
and deposit sed�ment on the adjacent floodplain. The floodplain and the creek
buiZt up over time. Buena Vista Creek was aggrading in this m�ner throughout
the mi�dle and iower reaches �n ancient times (see Figure 3). Only a fraction
of the total sediment eroded �n the watershed actually reached the lagoon.
After changes in the watershed, particularly in the last two decades, the
increased peak flaws have dram�atically txansformed the natural hydrological
syst�n. The increased flows not only discharge more sediment frcan the
watershed into the creek, but, more iunportantly have caused the creek bed to
start to erode (degrade) in portions of the creek. The increases in stream
flaa energy hav� caused the stream to downcut. This process will continue
until a new and lawer equilibriLun can be reached.
At the same time one of the largest sed�ment buffers in the watershed has been
fillzd in. The marsh ak�ave the Iagoon was the spreading area for storm flaws.
Here the water slawed and found its way through the tules to the lagoon,
dropping mach of its sediment load. All that is left of that marsh area is a
small area where cattails graw in the channeZ between the shopping center and
Highway 78.
Buena Vista Creek
Water flowing into Buena Vista Lagoon comes pr�marily through Buen� Vista
Creek. The 19 square mile watershed that drains into the creek and lagoon
covers areas of Oceanside, Carlsbad and Vista. Vista is in the upper reach of
the watershed, covers over halt of the watershed and has the major impact on
the flow characteristics of the system and yet it does not border the lagoon.
The creek can be identified by reach. The upper reach is the reach above
Highway 78. The middle reach is from Highway 78 to E1 Camino Real. 'I'he lower
reach is fran E1 Camino Real to Jefferson Street (see Figure 2).
The upper reach is in its natural channel io Brengle Terrace Park. Abave
Wilchv�od Park the creek has been stabilized by check structures. They were
built in the 1930's and it appears that only one of th�n has failed. This
channel naa appears to have the potential to averflow and flood the surrounding
area, probably because of increases in runoff frc�n the urbanization of the
watershed. The creek has heen channeled into concrete structures through the
dawntcnm area of Vista to Melrose Drive. These structures were also designed
14
and built before the major urbanization of the area.
The middle reach was a wide aggrading floodplai.n. It has been divided inio
twn by the falls just downstream of College Avenue. The tU,n sections
fiinctioned very similiarly before the impact of urbanization occurred. Now
the falls mark the location of the hydraulic division of this reach.
7n the upp�x middle reach, frcan Highway 78 to College Avenue, the creek has
— dramatically changed fran trapping sediment in its broad floodplain {aggrading)
to a dawn-cutting creek. This difference is marked by the large gully which
has cut into the ancient floodplain deposits in the area of the old sewage
— treatlnent plant in Vista. Instead of absorbing much of the sediment it
receives as it had done in the past, this reach is naw sending that sedim�ent
plus the eroded material doumstream.
C`i.�rrer.tly the lower middle reach (College Avenue wt�sterly to El Camino Real) is
still aggrading. In fact, it is aggrading at an alarmting rate of up to four
feet per season. This indicates that the lower middle reach is absorbang much
— of t7:e sed�ment before it gets to the lagoon.
The cause of c3�m-cutting i.n the upper middle reach is the �ncrease in the
— scour action of the creek. I�aweririg the fla,a line of the channel at various
road crossings has contributed. to this degradation, but this is a long-term
phencsnenan. If the creek still had aggrading characteristics it would fiZl in
_ these crossi.ngs with sediment as the middle reach of Lama Alta Creek has.
�rpically during urbanization downstream channels start to erode. This is in
response to higher peak flows of water fran the deueloping area. The existing
— and future hydrographs modeled in the phase one study indicate that the peak
flows have the potential to double in this reach. This means that�the sediment
transport capacity of the creek more than doubles.
If the sediment transport capacity increases to the point that it is greater
than the sediment entering the reach, the creek then has enough energy to cut
_ into the bed material. When it had too n�uch sed�ment to transport it dropped
its load on the wide floodplain. Naa it is hungry for sedim�nt and erades into
these ancient fluvial deposits and carries them and its original load
downstream (see Figure 3).
The increase in peak flow explains the cause of the erosion in the upper middle
reach. It is also a warning. Channelizing the upper middle reach will cause
— the peaks in the lower middle reach to increase dramatically and could trigger
dawn-cutting in the lower middle reach. Since there is very Iittle buffer
between the lawer middle r�ach and the Iagoon, the Iagoon will experience an
_ even greater sedimentation acc�mnxlation rate than w� havc previously seen.
In the lower reach, above the lagoon there was a wide flat marsh. At the
location of El Cam.ino Real. the creek spread over the marshland. The flatness
— of the land and the thick grawth of the marsh plants greatly red.uced the
velocities o£ the water. Here the water slowed and found its way through the
tules to the lagoon, dropping much of its sed�ment load. The marsh acted as a
— filter for the water entering the lagoon.
15
The marsh has been filled. Presently the only evidence of that marsh area is a
small area where cattails graa in the ch�nnel between the shoppi.ng center and
Hic�way 78. This channel is naw the lower reach af Buena Vista Creek.
The Lagoon
Because of the changes in the lagoon hydraulics and the greatly increased rates
of sedamentation the lagoon is no longer in equilibriLmn with natrual hydrologic
processes and is rapidly silting in.
Most sediment deposited into the lagoon is discharged during the peak flows of
large storms, such as those in 1969, 1978 and 1980. Sediment discharge is
e.xponentially related to the flaw velocity by a paw�r of two to three.
Consequently, though peak flaws may last only a few hours, they can carry tens
of thousands of tons of sediment into the lagoon.
It appears that sedime.nt carried into the lagoon is predaninantly silt. The
typical size distribution of suspended sediment for different sotsms is shawn
in Table 2. The Table is based on sediment sampling on other San Diego County
coastal streams (see Appendix 4) and synthetic flood hydrographs generated for
the Buena Vista Creek watershed.
As the floodflow approaches the lagoon, ba.c.kwater reduces the velocity and
carryirig cagacity of the flaa. Much of the bed load, consisting of coarser
sands, appears io be deposited on the floodplain and in the channel between the
South Coast Asphalt quarry and Jefferson Street, while most of the suspended
sed�ment, consisting of sands, silts, and clays, are discharged into the
lagoon.
As the flood flows enter the lagoon, flaw velocities drop to a'�raction of a
foot pex second. These velocities are insufficient t� keep the sedlment in
suspension, and particles, start to settle aut. The settling ve7.oczty of sands
if vezy rapid, so they tend to settle out itrnn�diately. Silts settle o�zt more
gradually but rapidly enough for mr�st of them to be deposited upstream of I-5.
Clays settle out vezy slawly, but because velocities thxough the lagoon are so
laa, most are deposited in the lagoon and only a fraction are discharged to the
ocean. The roadfills of I-5 and Hill Street and the outlet weir have reduced
flaa velocities through the lagoon, increasing sed�mentation. Buena Vista
Lagoon naw acts as a very efficient sediment trap.
Based on the very limited boring inforntation availabl.e, it appears fihat, prior
to 1940, the lagoon bed consisted of fine sands at an elevation of aboixt -1.5
ft NGVD. By 196I approximately 2.5 ft of organic ri,ch mud had accamulated in
the lagoon in the vicinity of I-5, and by 1982 an additional 2.5 ft of organic
rich silty clay had acc�mttz].ated. In the last 42 years, presuming the same
siltation ra-te ovex the 200 acre lagoon, this amaunts to about one and a half
million cubic yards or tons (for these sedimP..nts, a cubic yard weighs roughly a
ton), or abo�zt 35,000 tons/year. For the 19 square mile watershed this amounts
to 1840 tons/square mile/year which is camparable to an earlier estimate of
1,000 to 2,000 tons/square mile/year (Inman 1976).
16
� After initial deposition during and after a flood, sed�ments can be resuspended
by wave action and redistxibuted in the Iagoon. Water depths are fazrly
constant, dee�n� ng to two to three feet in areas of high wave action. TYze
� thick grawth of tules under the I-5 bridge prevents all except the finest
sed�ments from circulating into the �,�estern sec�ents of the lagoon.
Consequently, sed.iments acciucAzlating in the eastern segmexit are mainly sands,
— silts and mzds, whereas to the west of I-5 sedim�ents are mainly organic muds.
In �he wind-protected area betw�_n the rai]xoad and the beach, sediments are
highly organ.ic and appear to contain s�aage sludge.
Water levels in the lagoon are maintained at a miniirn�n elevation of 5.8 ft NGVD
by the c7utlet �is crest or more cca��mr�nly between about 5.8 ft and 6.5 ft NG'VD
by the barrier beach forming across the outlet. Water depths in the eastern
sec�nent are typically 1.5 to 2 ft, and �n the western segments 2 to 2.5 ft.
��
Before the hiunan-caused disturbances to the watershed, creek, marsh, and
lagoon, much of the sed�ment frcm the watershed was deposited before it reached
— the lagoon. Secii.ment was deposited on the broad floodplain in the middle
reach. Then, in the lc�r reach, a large marsh area spread and filtered the
storm watex, trapping more sediment before it entered the lagoon.
The only remnant of tl�.is protection syst�n is the axea. w�st of South Coast
Asphalt and east of the Haymar Street cul-de-sac. This reach of the creek is
currently absorbing very laxge quantities of sediment and is the last natural
buffer to prevent some of the sed.iment fran entering the lagoon. The best
fluzctionirig portion of this reach is the thick riparian area east of the Haymar
Street cul-de-sac.
17
TABLE 'IWO. Sediment Size Distri.bution for
Different Hydrographs
Stozm
2-yr
5-yr
10-yr
25-yr
50-yr
100-yr
Sedin�nt
Peak Load at � by Particle Size at Peak Flow
Flaw Peak Q
(cfs) (tons/day) <.004 .004-.016 .016-.064 .064-.25 .25-1.O�un
5
1371 1.2x10 25 6 23 33 11
5
1979 3.2x10 23 5 26 38 9
5
2589 6.8x10 20 4 28 40 8
6
3659 1.7x10 18 3 31 44 6
6
5832 6.7x10 15 2 32 47 4
7
7200 1.6x10 13 2 33 48 4
m
III. SIDINI�.'TVT SOURCE �iARACI'ERIZATION
Channel Erosion
It appears that there is an estimated total of 173,000 cubic yards of erosion
— in the ma�n channel of the creek in the middle reach between Melrose Avenue
ar.d College Loulevard. 'This Was calculated by using a real topography flown in
the spririg of 1985. Based on newspaper clippings, most of this erosion has
— occurred si.nce 1978. 1978 marked the end of a a 13 year dry period in this
area. Larx3 use had changed frc�n primarily niral and agricultural to
urbanization in that t�me. The c�nbination of the increase oF rainfall and
_ urbanization created a dramatic increase in th� am�unt of runoff experienced.
what had been an aggrading section of creek where sedament was deposited upon a
broad floodplain became a degrading section. The dawn-cutting is evident in a
gully that i.s in excess of 15 feet deep in stxne places in this reach.
C�Zrrently Graded Area.s
Presently there is approx�mately 600 acres of graded area in the watershed.
Vista, Carlsbad and Oceanside adopted sedime.nt control ordinances as part of
_ their grading orclinances. Sediment control plans must be filed �n September
and approved by October. The sediment control is supposed to be in place in
November, and rP�tiain effective until March.
Generally, on-site sed�ment control is still not effective. There appears to
be a lack of understanding as to what it takes to keep sediment from leaving
the site. Much of the w�rk done in the creek in Vista duri.ng the winter of
1984 had no protection what so ever. Much of the sedime.nt control as installed
�n the other cities was not effective.
_ Sometimes sediment is directed into the stozm drain system in the form of nuzddy
water. Another ccannon practice is to use sand bags that were not sealed, but
just folded aver. Same of these bags do not make it through the winter season
before spilling their contents and adding ta the sediment leaving fran the
— site.
Education of the oontractors, inspectors and design professionals who s-�zkx�iit
— and those w�w review the plans is desperately needed. The ordinances are good,
but they are not yet being fully i�lemented.
The local citizens are concerned and would be excellent watchdogs, if educated.
The Buena Vista Lagoon Foundatiori has a hotline that is available for the
reporting of sed�ment probl�ns. The local citizens are dedirated to the
saving of fhe lagoon, but do not yet recognize some of these problems.
Sediment yields frcan these graded areas can vary frcan one cubic yard per acre
per year to 30 cubic yards per acre per year, This is why good sed�ment
— control is so in�ortant. Sediment yields are still high frcxn this source, so
using an estimate of 25 cubic yards per acre per year over the 600 acres
currently being graded gives a sediment est3mate of 15,000 cubic yards of
_ sed�ment �r year.
�y
Aqriculture �
The follawing is a stu�nary of interviews with Haward Nh.ieller, who is currently
a consultant arxi has worked for fihe Soil Conservation Service. While wr�rking
for the Soil Conservation Service, he c�piled the "Important Farmland Map" for
the Buena Vista Watershed.
The a�unt of farmland in the Buena Vista Watershed has been a constant of
approxim-�tely 5 percent (approximately 600 acres) avocado groves and 5 percent
truck crops . Hawever, with the various ecancani.c and social pressures on the
farmers these lands will decrease ar�ci beccxne an insignificant sediment source
within 5 to 10 years and will become completely urbanized within 20 years.
Avocado groves of three years old or younger (of which there is 10 to 15
percent of all qraves) produce 15 to 20 tons of sed�ment per acre per year.
The r�naining 85 to 90 percent of the groves have sufficient canopy and leaf
litter to reduce the sed�ment yield to one to two tons of sedim�_nt per acre per
year.
Well managed tsuck crops also have a sediment yield of one to two tons of
sediment per acre per year. Hawever, poorly managed txuck crops produce as
much as 20 to 30 tons of sedi.ment per acre per year. Historically, the poorly
manaqed truck crop land constitutes about 1 percent of the watershed, and the
well managed. truck crop land constitutes the r�naining 4 percent. Presently,
the well managed farms only constitute one and a half percent of the 5 percent
total.
Historically, the agricultural land produced an estimated 5800 tons of sed�ment
per year in the Buena Vista watershed. Presently they are producing an
estimated 13,000 tons of sediment per year and within the next five to 10 yeaz'�
this source of sediment will be negligible.
By co�arison, the natural areas, which had periodically k7urned, yielded one to
t� tons of sedime.nt per acre per year, average.
Ftiiture Land Uses
The follawing estimates for future land uses wexe made by each of the three
cities in the watershed {in acres):
Carlsbad
�- - .._. -
.- .- - ..-.
Vacant land :
Area with approved plans :
Area without approved plans:
Area currently being graded:
1700
300
250
250
190
�
Vista
5760
1500
2750
765
325
Oceanside
3000
5 00
134
2000
85
The underdeveloped land is part of the total of the developed area, how�ver it
is likeiy to �e redevelope�3 '-� a higher use.
Natural Ercdible Areas
-- These rnmibers indicate that thexe is approximately 6,000 acres of natural
erodible area. Using an average of two tons of sed:iment per acre per year
indicates an estimate of 12,G00 tons of sediment from this source per year.
South Coast Asphalt
South Coast Asphalt has a rock quarry just west of College Avenue. The
- excavatior�s extend approximately 50 feet below the streambed. They have
maintained the falls by keeping the banks and adding levees. In the flatter
portion of the creek, there is nuioff fran the plant site and there is
- potential for erosion. Since the quarry area is granitic rock, the exposed
faces do not have much erosion potential. The erosion potential on the site is
in the reach with loose dirt banks. The plant has supplied detailed areal
_ photography of the land for this study.
E�isting channel velocities in alZ but the snallest flaws are in excess of 6
feet per second. These are erosive velocities, however since the creek has
� been carrying so much sediment in recent years. This section of the creek
continues to aggrade. Higner peak flaws could reverse this and this reach
could start to degrade.
In the first large flaw in 1979 a portian of a southerly stockpiZe uras eroded.
To prevent this loss of material, South Coast Asphalt naa protects the
_ tockpiles with riprap at the toe. Hawever t.his site has the potential for
erosion becau� of abc�v� mentioned velocities, Iittle bank protection, and
fill-dirt stream banks that are wlnerable to erosion.
- The rock quarry is estimated to close in 1990. Plans for the development of
the property are naw �eing prepared. and revi�wed. The awners plan to de�elop
the creek portion betw�_n 1990 and 1995. Ultimately the awners wnuld Iike to
- have a natural. looking channel, use the creek as a visual amenity to the
project and maintain the falls.
_ During the time between naw and the ultimate develo�zt, the potential for
erosion in this reach can be reduced. by widen.ing and adding revetrt�ent to the
channel. Adding 30 feet to the width of the dirt channel will reduce the
velocities by appro�mately 20 percent.
This will be beneficial in three ways. Lawering the velocities will decrease
the sediment transport capabilities of the stream and thereby decrease the
- potential for creek erosion. It will also make a small contribution to
reducing the peak flaws at the lagoon. Revetment of the creek banks will
reduce the potential for erosion.
21
TABLE THR�
SEDIl�r SOURCE S[JN�RY
Approximate annual average erosion rates frcxn each source in cubic yards per
year:
Main channel erosion: 25,000
Graded areas: 15,000
Agricultural: 13,000 (currently)
Natural erodible areas: 12,000
Side channel erosion: 11,000
ti
22
IV, ANALYSIS
— The ��aters�}ed analysis was
at reducir�g the peak flaws
reduction was evaluated.
two-folcl. h�drologic watershed modifications aimed
frcan stonn runoff were ar.alyzed. Sediment source
Reducing peak flows will reduce the sediment caz'nling caPacity of the stream.
There is an e�onential relationship between the stx'eam's sediment carrying
capacity and the �rater flow. Cons�quently a reduction in the storm peaks
results in a much higher reduction in tY'�e sed�ment delivery to the lagoon.
g�u��q peak flows also has the side benefit of reducing flooding. Specific
areas identified as areas of concern that will be benefited are in the law
lyinq areas around the lagoon and areas in Vista.
Sed�ment source reduction will reduce the sed�ment rating ct�rves of a
watershed. The sediment rating curves are a plot of the relationship of the
�,rater flow to sediment tr'ansport• 'I'he estimates of sed�ment acc�rnzlation
reduction for sediment control could be an order of magnitude off. Hawever,
tre cost for greatly improvir:g the source control is relatively'low, return on
the dollar spent is very high-
� r• �- i�� •�� �+
g1��aged b�, the peak flaw reductions mcdeled in the Phase One stu�, �of��
frcm those original watershed models v„�re re-entered into the Ar�nY zP
Engineers Hydraulic Ehgineex'ing Center's H.E.0 - 1 hydrology model and rerun on
a mainframe canputer in order to print hydrographs for the spectrum of six
storms. These �re the 2-year, the 5-year, the 10-year, the 25-year, the
50-year and the 100-yea�' storms. 'I'!-iose six stozms were nan for the Phase One's
"E�cisting��Ce:,.�ition", "Future Condition" and "Existing Condition with
Detention . Very late in the Phase Ztao analysis s�ne proble�ns in same of the
asstim�ptions for these models were noted and the watershed had to be remodeled.
The Phase One input data was used as a skeleton and a new watershed model was
created for the Ftizture Condition. Since this is an ungauged watershed, the
model could not be calibrated.. Appendix One describes the calculations for the
Ftiiture Conditions. These include a�Y of � S°il typeS� ��'e
develoFxnent types, Soil Conservation Service Lag, and SCS curve nLm�Y�er for e�ch
of the Phase One subbasins. The 2-year and the 100-year hyPothetical stozms
�,,�re run on this mr�del. (Note: The future condition watershed models for
Future Condition, Fi.iture Condition with Detenhted acd198t5.�eFuna glwas�not
Detention anc� Channel EizhancemP.nt are copyr q
allocated for this re-modelling�. ) �
The main channel beginning belaw Brengle Terrace Park to College Avenue (a
portion of the upper arx� the entire upper mi.ddle reach) is modeled as a
trapezoidal channel hav�ng a bottcgn width of 20 feet, side slopes of 1.5 to 1
and a Manning coefficient of 0.02. This is typical of the Tri-lock channel
that zs �eing placed at Breeze Hill.
23
Detention �iasin model (Wl)
Because the future condition would have the major long range in�act on the
lagoon, the future condition was then modeled with eight detention basins.
The basin locatians had all been modeled in the Phase One study. � of thenn
w�re re-sized based upon more detailed topographic inforntiation. The two
re-sized laasins �ere at Brengle Terrace Park and at Monte Vista School.
Detention Basin Locations
The detention basins in Vista (shown in Figure 4) are located at:
1.
2.
3.
4.
5.
6.
Creek crossing Wa�nlands Avenue,
Drive
Creek Crossing Warnnlands Avenue,
Sueqnark Terrace
Creek Crossing Wannlands Avenue,
Simoloa
Creek CYossing Stephanie Lane on
Brengle Terrace Park
Nlonte Vista School
agprox�mately 200 feet Northerly of Elm
approx�mately 200 feet Northerly of
approximately 100 feet Northerly of Ca.11e
the north side of Vale Terrace Drive
The other Phase One detention basins are located at:
7. The canyon north of Mira Costa College in Oceanside
8. The canyon to the east of the extension of Elm Avenue
-- � - - ..-
To model the effects of an enhanced channel, with vegetation, the detention
basins were kept in place and the above mentioned channel was widened. 'The
channel in this third model had a bottan width of 15' above Santa Fe Drive and
a bottan width of 40 feet wide belaw Santa Fe Drive with side slopes of 2 to 1
� a Manning ooefficient of 0.04. The energy slope is about one quarter of a
percent. This was the most effective improve�nent to the model. Table 4
gives the s�nnazy of the results of these new models.
The 6 feet per second maxiirnIIn allawable velocity is attainable with 0.25 to
0.35 percent slope, a M��uing coefficient of 0.040, 2:1 side slopes and a 40
foot bottan in the upper mi.ddle reach reducing in width up the creek until it
is alaout 15 feet wide.
Table 4 lists the s�nary of the peak flaws and lag t�mes at the lagoon for
each m�del. Figure 6 shaws graphs for the 2 and 100-year storms in the
future conditian, future condition with detention basins, and future condition
with creek enhancement for a location in the dawntown area of Vista, in the
middle reach, and at the lagoon. Comparison hydrographs are shawn in Figure 6
for a point at the lagoon and a point at Breeze Hill.
24
TABLE FC}UR
S�r�nary of H.E.C.- 1�ak flows and time t.o peak for future conditions at the
lagcon.
- 100 year:
Ftiiture cnndition With detention With enhancement
- 13,734 cfs 11,431 cfs 9,231 cfs
2.94 hours 2.95 hours 3.28 hours
2 year:
Future condition With detention With enhanceme,nt
3,213 cts 2,590 cfs 2,130 cfs
- 3.27 hours 3.28 hours 3.82 hours
TABLE FZVE
- PRCk7EC1'ID SIDIME;NT REDUCTIONS
ALT PIATT�R.SHID LAGOON ANN[JAL
_ C.`OND COND SID�]'I'
iZEDL1CT .
NO FCT1'URE EXI5TING BASIS
- L1 FL3T[1RE COMB l2�
FLTI't7RE COMB+�N 2 6 0
L2 FL]TURE CHAN CCR�]TRIBUTIUN 14�
-- Wl F W/DEI' �STIlVG 20$
DET+Ei�ki EXIT 52� **
ws ENi-iANC EXIST 32�
* TR�UTARY RIDUCTI�] OF THIS ALTERNATIVE
� ** 45 o D+k-iIC�i IS DUE 'PO
S'IiORM F`L�OW ATTENUATICN I1LUS 6. 5% RIDUCTION IN ANNUAL SIDIl�NT P�;CUMUI�ATION DUE
TO TI� REDL�TICIV OF THIS SIDIl��T SOURCE
25
CFS
15,000
10,000
5,000
�
CFS
10,000
5,000
0
i ❑r,nnN
CFS
3,000
2,000
1,000
0
2
EEZE f�ILL
CFS
3,000
2,000
1,000
0
HOUP.S
100—YEAR STORM
ABBREVIATIC��
FC FUl'URE CHARPJELIZED CONDITIOt�
FD FUTURE DETE"!TIOfd �'ODEL
FE FUTURE idITH DETEI7TICN At�D ENI�ANCEiJED CHANPlEL hiODEL
Figure 6 Hydrographs
110URS
2—YEAR STORM
26
3 4 5
HOURS
100—YEAR STORM
3 4 5
IiOURS
2—YEAR STORM
Sedimen� Source Control
� Main Ch�nnel (WS ) :
The average of 25,000 cubic yards of sed�.nt per year eroded frcan the main
channel primarily occl�rred during the 5 years fr�n 1978 to 1983. Al.t.hough this
— source will not be ccgnpletely elimu�ated with the channel mcclifications, the
reach of the rec�mended enhancement is at least three times the lenc�th of the
badly degraded section frcan where the Z5,000 cubic yards cair�. Protecting the
— Main Channel will reduce the sedime,nt source to the lagoon by 25,000 cubic
yards per year. For the com�arative analysis half af this quantity was added
to the reduction in sedament delivery for the "Channel E�hancement"
_ alternative, because it is assumed that for every cubic yard sed�ment source
reduction there is a correspanding reduction of a halt of a cubic yard of
reduction in the sediment accti�nulation in the lagoon.
Graded Areas (S2):
The adopted sediment control orclinances for graded areas are good and m�ney is
being expended by the developers and the cities for the design construction and
review of sediment control plans. However, there is still an estimated 15,OD0
cubic yards of sediment escaping frcan fresn these sites. Misplaced or broken
sand and gravel bags are allawing sediment flow into the storm drains and
channels. Saretimes the projects are caught wi.fh their gravel bags dc�m by a
surprise rainstorm.
Educa�tion of the engineers, inspectors and contrac�Eors involved will probably
reduce this source to one third of the vol�ne it is today.
Agricultural (S3) :
— A similar education program for agriculture could be as effective as education
for grading. This c�ould red.uce the sed�ment sourc� by an additional 5 percent.
Naturai erodible areas:
This source has such a low cnncentration very little improvement can be made.
Side Channel Erosion (S1):.
— Three side channels that need recons�tnlction and enhancement have been
identified. They are just west of Pamelo Drive, on the westerly side of El
Camino Rea1 between E]m and Chestnut and next to NYanroe, south of Marron.
Accorcling to the Vista City staff and the Carlsbad City Staff the side channel
arrayos at Pamelo and Monroe are in areas that are approved for develo�anent.
` 'Ifie requ.irements for the develognents include repairing and preventing these
arroyos.
The side channel arrayo on the westerly side of El Camino Real between Elm and
— Chestnut locations could effectively be repa.ired using drop sinictures in the
same manner as the recan�nended mai.n channel repair in the upper middle reach.
This will reduce the total watershed sediment source by an estimated one
— percent.
27
� IAGOON NYJDEL,
To determine the most effective means to reduce sediment acc�nulation in the
lagoon, its sedi�nt budget must be est�mated under different conditions. A
sediment budget is si�ly an accounting of the inflow, outflow and stroage of
sed�ment in the lagoon for a particular time period.
Sediment infZow is detexmined by �irical relationships between the variation
of sediment dischaxge and flaw rate during flood events. The sequence of flaw
rates, l�awn as a hydrograph, are can�uted for particular storn�s using a
standan� co�uter model simulation referred to as I�C-1.
When the sediment enters the lagoon, some settles out, same is discharged to
th�e ocean, and sare re�nains in suspension for a particular time period. The
am�unt settling ozzt is calcalated using settling velocity relationships for
each pa.rticle size. The amount remaining is suspension is deterniined by the
difference in sediment inflow and the a�unt settling out in a particular time
period. The amount discharged to the ocean is the sedim�_nt cancentration
rem�i.ning in suspension at the outlet, multiplied by the discharge vol�ne.
Mo�t sedi.ment is carried into the lagoon by a few large, infrequent floods.
Consequently, the sediment budgets must be averaged statistically aver a long
period of t�me to estimate an average annual sediment budget. The average
annual sediment budget can be calculated for different inflaw and lagoon
conditions to provide a comparison of the average annual sed�ment accturnzlation
in the lagoon under different conditions.
Because of the enornwus rnunber of calculations requixed to estimate average
annual sed�ment acc�urnzlation, it is best done using a computer model tnat
simulates the move�nent of both water and sediment through the lagoon system.
Such a�uter model was developed specifically for this study and is
described in succeeding sections.
It should be noted that there are a great many uncertainties in most of the
calculations involved in dete��n��; a sed5ment budget. Consequently sediment
budgets of this type should be used for cc�q�arative purposes only.
Sed�ment Inflow
The best method for detezmining sedirc�nt discharge to the lagoon is to develop
a sedimexit rating curve for Buena Vista Creek. A sediment rating ci.�rve plots
suspended sediment against flaw discharge measured at a particular point on the
stream. Unfortunately, neither suspended sediment nor discharge data exists
for Buena Vista Creek. Therefore, a sediment rating curve was constructed,
based on samiple data fresn other streams.
Stream gauge data frcan Il gauging stations on coastal streams south of Dana
Point were examined (see Appendix 4). The results shawed that streams with
watersheds greater than 100 square miles had different sediment rating curves
than those with smaller watersheds. Consequently only data frcan the five
smaller watersheds �re used.
:
TABLE SIX. SIDIl�I'r RATING CZJRVE
RELATIONSHIPS USID IN ANALYSIS
Sediment Pasticle Size qs tons day} Fal Velccity (ft sec
-4 2.4 -5
Clay <,004 mm 9 x 10 Q 1.31 x 10
Silts
.004 - ,016 mm
-3
4 x 10 Q
-5
1 x 10 Q
2
-4
1.15 x 1Q
-3
2.3 x 10
Sands
.016 - .064 �n
.064 - .25 mm
.25 - Z.10 mm
3
-5 3 -2
1.6 x 10 Q 3.28 x 10
-3 2.1 -1
3.7 x 10 Q 2.3 x 10
� The suspended sediment data was broken down into five different size fractions
representing muds, fine silt, coarse silt, fine sand and coarse sand. The
plots are shown in Appenclix 4. 'I'�.ere is a large amount of scatter in the
— data. Up to an order of ma.gnitude of scatter is typical of sedin�ent rating
curves. Hawever, the rating curves for each size fraction can be simplified
as the straight Line relationships shows in Table 6. These are used in
_ calculatizlg sediment inf�ow to the lagoon.
A portion of the ooarser sediment discharge, oft�n estimated t� be an
additional 20�, is carried along the channel bed as "bedload". This was not
� included in the sediment inflow because most of the coarser material ar�pears to
be deposited in the Buena Vista Channel upstream of the lagoon, and because it
represents only a snall portion of the total sed�ment Ioad discharged to the
— lagoon.
The sediment inflow for a particular storm is calculated by integrat�ng the
sediment rating curv� with the inflaw hydrograph for successive tim�
increments.
Lagoon I-iydraulics
In order to calculate the sedim�nt accululation in the lagoon for a particular
flood, a flood routing calculation must be carried out to detezmi.ne the water
— surface elevations, voltunes and flow velocities at different times, as the
flood flows enter the lagoon.
__ For Buena Vista Lagoon this is ccstiplicated, because hydraulically the lagoon
acts as three distinct cells. The eastern ce11 includes the area ir�n the
inflaw point at Jefferson to the I-5 embanl�nent. The �nban}anent constricts
outflow to the cen'-,..ral cell that exiends frcgn I-5 to Hi11 Street. Sediment
29
acctuttulation further constricts outflaws Lmder the I-5 bridge to approxamately —
the existing lagoon lev�el. The central cell discharges to the w�estern cell
through a �onstricted culvert imder Hill Street, or over the top of the
roadway, if the water Ievel rises high enough. The western cell discharges to _
the ocean aver the exist�ng sharp crested weir. The railway bridge crossing
does not significantly constrict flood flaws in the western cell. A sketch of
the lagoon is shown in Figure 7.
A flood routing is a sequential calculation that calculates outFla�, water
surfaoe elevation, change in storage and average flaw v�elocity for a given
inflaw and initial lagoon conditions. Unfortunately, no detailed suzvey of the
}aathymetzy of Buena Vista Lagoon exists. Therefore, the water
elevation/storage relationship for each of the cells is est�mated based on few
point soundings ar�cl available topoghraphic surv�ey. These are shown in Appendix
4. Outflaw frcan each cell is detezmined by standard c�ir flow or culvert flaw
fonnulae. Average velocities are simply calculated as the outflow divided by
the average cross-sectioned area for a given instant in t�me.
Sed�ment Acc�unulation
Sedime.nt inflow to the ],agoon is asstmzed to be uniformly vextically mixed in
the flaa. When it reaches the lagoon, flt7w velocities drop considerably and
sediment garticles settle aut. The rate at which they settle out is detezmined
by the particle settli.ng velocity. For the median diameter of each of the five
size fractions, this value is shawn in Table 'Itao. It can be seen that there is
roughly an order of magnitude difference between the settling rates of each
size fraction. Dividing the sediment inflaa into five discrete size fractions
ca� therefore introduce another source of error in the sediment budget.
Sedime.nt acc�nilation is detezmined by the fraction of sediment that settles
out while the sed.u-nent-laden flaw travels fran the inflaw to the outflaw end of
each cell. It is assumed that flow travelling through the I-5 bridge and the
Hill Street culvert ccx�letely mixes the sed�ment, so that sediment discharged
to the next oell is uniformly mixed.
The model for sediment deposition described above is strictly valid only for
quiescent unifonn flcnvs in stilling basins. In Buena Vista Lagoon tlood flaws
entering the lagoon will be highly turbulent, which tends to hinder settling of
sediment particles until the turbulence dies out. Unfortunately there is no
feasi.ble way to model this process, and calculating deposition based strictly
on time of travel may overest�mate sediment acc�unulation ��+;cularly for the
finer sediment fractions.
The velocity of the flaw in the lagoon itself can generate turbulence that can
keep particles suspe.nded. There is this lawer l�mi.t of sedin�nt concentration
in the lagoon for a garticular average lagoon v�locity. There are many
alternative methods of calculating this lc�r limit; an,d as is ccannon in the
field of sedimEnt hydraulics, there are significant differences in different
estimates. For these calculations the relationship developed by Bagnold was
used (Yalin 1971).
30
TABLE 7. BUENA VISTA LAGOON COMPUTER MODEL RUNS •
RUN
yu. INFLOW HYDRuCRAPH UGOpN CONDITIUNS SEUIMENT ACCUMUI.ATION RESULTS
- ln![tel Dis-
Hilt �rater Inflov Deposl[ed charged
I-5 St. Outlet Weir surfaee tone ons Z
Frequency WaCershed Weir Width inverC len�[h elev HGVU
- Con.11tions Elev ft culvert ft ft ft
f[ elev ft
Cosnencc
' 1 2-yr Exiscing 5.8 15 2.0 BU S.0 5.8 1U.915 1U,095 92 B Existing vatershrd 6 La¢�on
condltions;ouclec velr�Nu'
* 2 S-yr Existing 5.8 15 2.0 8U 5.8 5.8 26,SFSU 24,125 91 9 Existinq waCershed 6 laguon
condiciona; outlet veir-tlu'
* 3 25-yr EzSecinR 5.8 15 2.0 80 5.8 5.8 142,7T0 126,SI0 89 11 Exieting vaterched 6 lagoon
condicion¢; outle[ vetr on'
*� 100-yr ExistSnR S.8 15 2.0 8U 5.8 5.8 872,440 7b7,SU5 88 12 Exiscing va[ershed 6 laqo�n
condf [Sons; ou[le[ vef r�lt��'
5 1-yr Future 5.8 15 2.0 SU 5.8 5.8 2U,U50 18,310 92 8 Existing lagoon b fut.�ater-
- shed cond.; ou[let veir80'
6 5-yr Fucure 5.8 15 2.0 SU 5.8 5.8 51,635 �6,6lS 90 !0 ExlscLng lagoon 6 fut.vater
shed cond.; outlet �eir-B��'
i 25-yr Future 5.8 15 2.0 BU 5.6 S.8 235,SeU 2U8�725 By 11 Exieting lagoon i fut.watcr
� ahed coad.; ou[le[ �efr�b�r'
B l0U-yr Fucure 5.8 15 2.0 80 5.8 S.tl 1,147,6Z0 t,O11,465 BB 12 Exiecing laQoo� b fuc. vec�••
shed cond.;ouclet velz�ki�'
- 9 2-yr Fucure 1.5 IS 2.0 80 5.8 5.8 20,I85 l8,510 9'L tl 1-5 velr lorered; no otl�r�
laboon chanqes
10 5-yr Future I.S 15 2.0 8U S,y 5.8 51,92U 46 985 90 10 I-S veir lovered• no o[hei
1! 25-yr Fu[ure
12 100-yt Future
1J 2-yr Future
14 5-yr Fucure
1S ZS�yr Future
_ 16 lU0-yr Fu[ure
17 2ryr Pu[ure
18 5-yr Future
19 25-yr Fucure
2U IW-yr Future
21 2-yr Future
24 I00-yr Fu[ure
� 29 2-yr Fucure
� 30 100ryr Fu[ure
l.5 15 2.0 Su
1.5 15 2.0
S.8 !UO 2.0
5.8 100 2.0
5.8 lUU 2.0
s.a ioo z.o
5.8 IS 2.0
5.8 15 2.0
S.8 15 2.0
5.8 15 2.0
L.5 l0U 2.0
1.5 l0U 2.0
5.8 !S 2.0
S.8 l5 2.0
80
50
50
50
SU
80
80
SU
80
BU
tlU
SD
SO
S.tl 5.1i 235,56U 208,595
S.tl 5.8' 1,195,U70 1,012,OU0
5.6 S.B 2U,u15 l9,240
5.8 5.8 51,165 �6,510
5.8 5.8 - --
5.8 5.8 I,I43,265 1,012,3I5
1.8 5.8 20,06U 17.545
1.8 5.8 51,64U 44,945
1.8 S.B 235,965 204,525
1.8 5.8 1,t45,875 9Y4,9y5
l.b 5.lS 2U,UbU 15,605
l.b 5.8 I,147,tl)U Y63,440
5.8 5.8 YU,U)5 18,215
S.tl 5.8 1,149,200 1,U21,SU5
31
lagoon changes �
89 L1 1-S veir luwered; no othc•r
ligoon changes
85 15 I-5 veir lovered, no other
lagoon ci�aaRee
86 14 Hi12 St. opened; ou[let
reir at 50'
9l 9 Hill St. opened; ou[let
veir •t SU'
- - -- Ilill St. opened; outlet
�etr ae SU'
88 12 Nfll St, opened; ou[le[
veir a[ SO'
87 13 lhiclet veir lwered to
I.8' NGVD
97 13 Outlet veir lovered to
l.tl' XGYD
87 13 Outlet velr lovered to
l.8' NGVD .
8J 13 Outlet veir lwered to
l.tl' MGVU
78 22 Co�bSnacion run: I-5,
Hill St. s 1-5 opened up
tf4 16 Cosbina[!on run: 1-5,
kill St., 6 I-S opened u�
9U !0 Wtlet veir at orlglna]
lenRth:Existing lagoon coi�4.
89 11 Uuclet veir at oriRlnal
lenght:Existfnq lagoon c��id.
TABLE 7 , page 2
xcrN � -
M0. INFLOY HYDROGRAPH (aG00N CONDITIONS SP.DIMEHT ACCUMULAT[ON RESUL7S
Inittal Dis-
HS11 veter lnflor Deposlted ch�rRed Corents
I_5 S[. Outlet We1r surf�ee tons ous -�- -
rreQu��c> Yacer�hed 4eir Vidth lnvert lengeh elev HGVD
Condltlons E1�� !t eulv�tt Et f[ f[
tt ele� t[
J1 100-�r Future 1.5 l00 2.0 K�� 1.8 1•8 - •- -- - r,o�bination run: lnictal
VS�L-l.N': FASAL ERRUR
->I�K of neR. no.
+ 3Z 100-qr Future I.S lU0 1.8 80 t.tf 1.8 L,14y,31U 974,64u 85 15 Lo�ered H(ll St. ruivrrt
- invert [o avold above crn
]3 l2-yr Fucuce l.5 lUU 1.8 8U 1.8 1.8 - - - - No flov out oE Bacin 2 �r 3
No[e, pcogras did run
• l� 2-7rr Fucu n l.5 IOU 1.7 BU 1.8 1.H 2O,U�U 16,UIU 8U 20 Lovercd Hlll St. [o I.7' �e
•vert above probleu
35 100-7r[ Exls[. v/det. I.S 200 1.7 80 1.8 1.8 316,l35 282,Y25 82 t8 CF Ru� !32 6 30 (for
e:isting lsgoon condltion••/ _
36 100-yr Future 1.5 100 1.) t!0 . 1.8 1.8 1,143,670 965,935 84 16 �hannel sl�ulatlon: vidtl,,[
eren�l/10 orlgin�l conlf�•��r.•
[lun wlUx
•37 100-7r Exi�t.v/det. 5.8 15 2.0 50 5.8 5.8 367,i65 JU:i,�10 ' 87 13 Exloting legoon condittonr
38 706-rr Future 1.5 100 1.8 80 ].8 1.8 I,149�31U 9�8,SSU 83 17 Sare as f3e but depth
tncreesed 6y 5 [[
39 100-�r Future l.5 100 1.8 80 !.tl l.8 1,14),i7U 904,160 BU 20 10' ehannel, SU'vlde, nrP.�
eceled dovn by ratlo ot
vidthe (�ee SEU.DAS filrl
* �0 l00-7r Fucure -8.'S 100 -8.0 EO 1.8 l.8 1,14t,985 892,94U 78 22 !0' deep ch�nnel, 50'vfAr; _
� th1■ !e b�at u�e ■c�nn�l�
• �! 2-7r /ut�re -8.5 !00 8.0 tlU I.N 1.R 2t1,q35 �4,2t5 7t 29 Ill' deep ch���el, SO' �I�1.
[hIs la best case scennri��
• 42 100-yr C�cl�t v/ d�t. �E.a lbl) -S.0 8U l.e 1.8 7�tl,�7U 26),l�S 76 2� Yutur� 1�6�* vith ah�nnvi ^
• �i 2-�r E:1�t v/ det. -8.S 100 -8.0 BO 1.8 1.8 9,7W 6,360 6B J2 Fukure 1nRoo� v/ channel
• 41 2-7r Exl�c r/det. 5.8 IS 2.0 SO S.B S.if 9,125 8,650 93 1 Exlsting la600n conditiun•
•�5 2-�r Future S.S 15 2.0 50 5.8 S.B 61,676 56,592 90 !0 Revi�ed h�drolosy
•�6 100-�r Fucure S.S 1S 2.0 SO 5.8 S.tl 2,514,779 2,2'15,23U 88 t2 Reviaed h�drology
• l7 2-�r Fut.v/det. 5.9 1S 2.0 50 S.8 S.tl •8,565 6�,Y81 91 9 Revi�ed hrdcoloqy -
•�8 100-yr Fut.v/det. 5.8 !S 1.0 50 S.8 S.B 1,90l,Ou2 1,672.57U D8 12 Aevl�ed hydrologr
•�9 2-�r Fut.v/det. S.a 15 2.0 SU 5.8 S.tl 3),92U 31,'ltlU Y2 e Ilevi�ed h7rdrology
enh. eMnn�l _
• SU l00-�r Fu[.v/det. 5.9 IS 1.D SU 5.8 5.8 1,36y,914 1,I90,359 87 13 Nevised hydroloRY
� enh. channel
_ 32 _ __. - -- - -
q = pV* Um(0.17 + .Ol Um/w
s
where e Um/v* = 2.5/n(3.32 V*h/y}
where:
qs is sedirnent discharge
p is the fluid density
V* is the shear velocity
L�n is the mean velocity
w is �he garticle fall velocity
h is the depth
)) is the kinematic viscosity
Thzs lcwer limit is �xzrticularly ii�ortant �n estimating net acctiunulation of
the finer sed.iment fractions.
The total s�ediment acctunulation for a particular flood hydrograph for each cell
can be est:�mated by stmIIning the accturnzlation in each time period.
The Computer Model
A computer model was developed to simulate sedim�nt acc�nrnzlation in the three
ce11s of Buena Vista Lagoon for a given inflow flood hydrograph. This model,
identified as NIPOND c PV� 1985, was an adaption of an earlier lagoon flood
routing model with the addition of sed�ment routing subroutines•.
TY��e input data requi ed is the inflow flood hydrograph, sediment rating curves
for each sediment size selected, lagoon geometry, and �„�eir and culvext
characteristics.
The otitput is a cxmrputation for each hour of the sediment inf law, sed�ment
accLnmzlation, and sediment dischaxge, for each fraction for each basin in the
— lagoon. The ccn�uter model also calculates inflow, outflcw, water surface
elevation and velocities of each basin for each hour. Over the entire
hydrograph geriod the model calculates the total sed�ment acc�miulation and
— discharge for each basin.
Results
A total of 50 ccxnputer nuis were carried out to examine the combinations of
different scenarios of watershed conditions and lagoon hydraulics. A c�nplete
s�y of these runs is shavn in Table Seven. Forty-four of the runs were
carried out based on HEC-1 inflaa hydrographs representing three different
watershed oonditions that were developed in the Phase One siudy. These w�re:
33
1. E�isting �r.ditions
2. �ture conditions with no action
3. E�isting canc'.itions with detention basins.
For each condition the 2-year and 100-year flood hydrograph was analyzed, and
in 9a�e instances the 5- and 25-year hydrograhs as w�Il. Late in the study,
errors were found in these F�C-1 inflcw hydrographs. Accordingly they w�ere
recalculated and six additional ccs�uter runs based on three new sets of
hydrographs were carried aut:
4. Recalculated future conditions with no action
5. Recalculated future oonditions with detention basins
6. Recalculated future aonditions with detention basins and preserving the
floodplain upstseam.
A stu��azy of the inflcw hydrographs used is given in Table Eight.
Although the earlier I�C-I hydrographs were not accurate, the cc�uter
mcdelling results can sti.11 be used as a basis for contparing the effectiveness
of different modifications to the hydraulics of the lagoon. Five diffesent
lagoon hydraulics canditions �re examined, either individually or in
ccmbination:
1. E�cisting conditions
2. Remaving the sed�ment acccmnilated tmder the I-5 bridge
3. Enlarging the Hill Street culvert
4. Increasing the capacity of the outlet weir by widening and lawering its
crest
5. F�cavating a deep channel through the lagoon fran Jefferson Street to the
outlet weir.
The average annual sed�ment acc►Jmulation for selected scenarios is shawn in
Table Nine. Thes� values are detezmined by plotting a sediment acci.�nulation
probability curve using the 2-year and 100-yeax �uter run results for total
sediment acc�n�lation and then calculating the avpxage annual. sed�me.nt
accumulation by the method desc.ribed in the ASCE Sedim�ntation Engineer�ng
Handboc�k Table 4.18.
Table Nine shows that average annual sediment acctunulation in about 33,000
tons/year under existing conditions (scenario I). Tha.s airounts to about
20 acre feet per year which, averaged over the whole lagoon, is about 0.1
ft/year. At this rate the lagoon �uld fill in ccxnpletely in twenty to thi.rty
years. Sediment acce�nulation of 33,000 tons/year, assisning a trap efficiency
c3'�
TABLE EIGHT. SU�RY QF INP�AW HYDROGRAPHS
Flood Flood
Watershed Return Peak Flaw Vol�e
- Source Condition Frequency cfs acre ft.
- Phase I study E�isting 2 1371 429
Phase I study E�isting 5 1979 608
^ Phase I study E�isting 25 3659 1067
Phase I study E�cisting 100 7200 1942
Phase I study Future 2 1712 539
- Phase I study Future 5 2485 741
Phase I study �zture 25 4412 1245
� Phase I study Futux'e 100 8000 2145
Phase 1 study Existing w/det 2 1227 414
Phase I study Existing w/det 100 5044 1553
- Phase II study �z-Eure 2 3213 428
Phase II study �zture 100 13734 1583
� Phase II study Future w/det 2 2590 -�-
Phase II study Future w/det �00 11431 1483
Phase II study Future w/det & fp 2 2130 314
- Phase II study Future w/det & fp 100 9231 1351
35
TABLE NINE. SUN7NIARY OF LAGOON AND L�,TERSI�D SIMULATIONS
Avg. Annua.l
Simulation Watershed Hydrograph Lagoon Computer Sed. Accu. �
No. Coriditions Source Cond. Runs (tons) reduct.
1 E�isting Phase I Ex.isting 1,2,3,4 32,970 N/A
2 �ture Phase I �isting 29,30 73,550 0
3 �iture Phase I Ftiiture _
Camb. 32,34 64,230 13
4 Future Phase I Elzture
Ccxnb. �
w/channel 40,41 56,280 23
5 Existing —
w/det Phase I �xisting 37,44 25,490 &5
6. E�isting _
w/det Phase I F�.iture
Catnb .
w/channel 42,43 19,840 73
7 �zture Phase II r'�isting 45,46 191,500 0
8 F�tux'e
w.det Phase II Existing 4i,48 153,600 20
9 Ftiiture
w det of
floodplain Phase II �.i.sting 49,50 105,100 45
36
of about 90�, corr�sponds to a watershed sediment yield of 1500
tons/squaremiZe/year, a value fairly typical of this area. It also corresponds
c closely to �.he obsezved historic rate of acclurn�lation of approximately 35,000
tons/year. Hawever, such a corre�or.dence should �e regarded as fortuitous
'pecause of the Iarge poter_tial er�-ors u�herent in analyses of this type.
� Sedim�nt acctmlulation under future watershed conditions with increased
uxbanization and no s�_nt con�rol is projected. to increase by a�ltiple of
s� to abaut 20Q,000 tons/year (scenario 7). This is due to the increase
— inpeak flaws fran stonn drains, li.ned channels and paved surfaces, and the
exponential relationship bet�,een sediment delivery and flaw rate. The
resulting predicted watershed sedi.ment yield of 7,500 tons/square mile/year is
_ not uncca�a�n in urbanizing watersheds of this type. A sediment acc�nulation of
200,000 tons/year if distributed e�ually in the lagoon, cnuld fill it in four
to five years.
V. Ct'h�TC'LUSIC�IS
The F�zture of the Lagoon
If no action is taken and the e.x.�.sting sed.imentation rates continue, nx�st of
the lagoon will probably fill with sed�ment within the next 20 to 40 years.
_ However, because of additional urbanization in the watershed (undezway or
planned), and the filling of the Buena Vista Creek floodplain, most of the
lagoon might fill in an �h.e ne.:�t 10 to 20 years. This sed.imentation cx�uld not
occur gradually but more likely as a result of 2 or 3 major flooc7.s.
— Consequently, the rate of filling will depend on the sequence of wet and dxy
years.
— There are two strategies for reducing sedimentatian in the lagoon: either
. reduce sediment inflaw or improve the flushing abiliiy of the lagoon. Table
One shaws t�:e relative successes of these twr� strategies. The m�st effective
_ alternativ-e for mitigating increased sedjment flows fio the lagoon is channel
• enhancement (Alternative WS). Channel enhancement was modeled fran dawnstream
of Brengle Terrace Park to South Coast Asphalt. Various channel configurations
will accomplish this goal but a max.urnun velocity of 6 feet per second must be
�" maintained. The key io keeping the velocities at this level will be to install
check structures along the creek and recontour the channel as necessary. This
velocity wi11 all�,v for the grawth of riparian vegetatian; however, in many
— areas the existing "natural" crlannel will hav� to be redesigned, drop
structures installed, and creek banks revegetated to meet this velocity goal.
Fortunately we have a model to follow. Gul1y restoration was accc�rcplished in
_ the Tahce Basin using check structures. These have bee.n in place for several
years. Not only c�es channel enhanceme�lt decrease peak flood flows to the
lagcon more effectively it also decreases the erosion hazard for the major
source of sediment to the lagoon.
Alrrost as effective in decreasing peak flood flows is the design, installation
and m�aintena.-�ce of eight stonn attenuation basins (Alterna�ive WI) . The
— location of these and the channel enhanceme.nt are shawn on Figure 4. All of
the attenuation locations �re modeled in the Phase One study. Twa were
r�eled, based on r�ore detailed topoyr�phy.
37
s
�
�
�� 11 st�
��
� c
�� s
� a.
�
�
�
�
.�
�
�
�
C
J.
N
C'1'
�
r
a
c:�
O
O
�
\
38
�'
I-S
It is evident tl^�at theze is a�otential for decreasing lagoon sedimentation by
a�out 45� by reducing flood peaks under future conditions by constnzcting
_ detention ix-�sins and presezving and enhancing the floodplain upstream
(Alternatives Tr7 and Ti�rS) . _
The third m�st effective m�tnod of reducing sediment to the lagoon is stopping
� the soil Ioss frcgn grading and agricultural operatians. The grading ardinances
for the three cities adequately require sediment control for gracling
operations. An education process stil.l r�eeds to occur for the methods that
— are effective to comply with the ordinances. Agriculture is still a major
source of sediment and there appears to be no ordinances for this source.
Agrictzlture will probably dwindle to be very small within 2D years, as the
watershed is urbanized.
This study envisions a program of education for the City personnel wha check
gradir�g plans and the operators and building inspectors who are responsible for
— trie outc�me of these plans. The �ducation program would give a review of the
requir�ments of the erosion control orclinance and specific recc�ndations for
cost-effective design and i�lementation of th� ordinance.
Similiarly the agricultural education program would focus on agricultural
opexators and the Soil Conservation Service and emphasize cas�-effective
i�Ie�-r�ntation of best management practices in the watershed.
Sina1l amounts of the total sediment can be removed in two sediment basins
lccated at South Coast Asphalt and the mouth of the lagoon (Alternatives S4 and
J S5). The one at South Coast Asphalt will require less costly maintenance, as
the material could probably be used on the site. The advantage to these
sed�merit basins is that it is Iess costly to remove the material at these
— locations than after it reaches the lagoon. The natu�.e of the material ren�oved
will be sandier than the total sediment acc�uni�lating in the Zagoon, therefore a
moze usable material,
The sedime.nt frc�n side channel arroyos can be effectively controlled by
repairing the arroyo and preventing further erosion {Alternatives S1). These
w�ould be repaired in the same fashion as the ma.in creek channel.
Sediment inflaw can be further red.uced by control of sedim�nt sources in the
watershed. The releative success of these sediment control measures is not
— easily quantifiable. Hawever, it is not unreasonable to suggest that vigorous
application of such measures could reduce the sed�ment Zoad by about 50�.
This, ccqnbined wit'� reduction of the flood peaks, would mean that the sediment
_ inflaw would be reduced to about 30� of its expected future value.
In contrast, modifyi.ng the lagoon hydraulics is not nearly as effective in
rec?ucing sediment acc�snulation. With a11 the reasonably feasible nx�d.ificaitons
� -- clearing the I-5 bridge, widening the Hi11 Street culvert and lowoering and
widening the outlet c�ir, the sedimes�t acclmiulation reduces or.ly by 13$. E�en
with these modifications, maintai.ning a deep channel through the entire lagoon
-- reduces sediment acceuzrulation by 23� {Alternative L2) . A deep channel weuld
require constant maintenance as it wnuld tend to fill with sediment resuspended
by wave action in the �r, and is not a v�ry practical aption.
39
The effectiveness of �ndividual mo3ifications in the lagoon is negligible.
They only achieve the 13$ reduction when im�lemented together. This can be —
seen by c�anparing runs 9 and 12, 13 and 16, 17 and 20, with 29 and 30, and with
32 and 34, as shc�um in Table Seven.
In its present state, managed as a fresh water lake, Buena Vista Lagoon is a
vexy efficient sediment trap. It traps about 90$ of all sed�ment which enters
it. The only hydraulically feasible way of greatly �ncreasing the flushing of
sediment frcm the lagoon is to restore it to tidal action. Havever, because
the sed�ment discharge to the lagoon is naw so large, even with tidal action
the lagoon would probably silt up to a fraction of its original size. Eben
with the best possible scenario of watershed improv�ments, considerable aQnounts
of sediment will have to be r�noved �n order to maintain the lagoon in its
existing state.
To predict the aQnount of dredging required, flow mesurements and sediment
samples will have to be taken on Buena Vista Creek and at the outflaw weir in
order to calculate a more accurate sedimP�nt k�.idget. In addition, periodic
bathymetric suiveys will need to be made of the lagoon to measure actual
sediment acc�mtulation. Based on the exi.sting analysis using data frcm other
watersheds, the average dredging requirement probably will be in the range of
10,000 to 100,000 tons/year, ass�ning the watershed modifications are
impl��n�ed. Probably between five and twenty percent of this sed�ment will be
of suitable size far beach replenishment.
VI. RECONA�IDATIONS
1. The Lagoon's Ftiiture
In its existing state Buena Vista Lagoon acts as a v�ry effective sediment
trap. Under exi.sting watershed condition� it appears that the entire
lagoon will silt in aver the next twenty or thirty years, with nx�st of
the siltation occurring during a few large stonns. Under future watershed
conditions the rate of siltation will increase substantially, red.ucing the
expected lifetime of the lagoon to less than ten years. The mr�st
effective means of reducing sed�me.nt accumulation in the lagoon is to
reduce sediment inflaw frcgn the watershed. SedimP_nt acc�urnllation in the
lagoon can be reduced by about 50g by reducing flood peaks in the
wate7-shed and enhancing the creek, thereby reducing sedime.nt inflaw.
2 . Cre�k �hanceqne.nt (WS )
To reduce sedime,nt entering the lagoon �am creekbed erosion, a maxisrnam
channel velocity criteria of six feet per secorxl is required. This is
effective and was modelled as the maxim�IIn velocity that vegetation
coul.d conceivably wi.thstand. Lawer velocities are recca�mended and will be
more effective.
All initial creek design should check flood control requirements, and
utilize the maxitrnun velocities using Manning roughness coefficients of
0.030 to 0.050, which is the range of the vegetation gravth roughness in
the channel. So the velocity of the 100 year stonn should not exceed six
40
~ feet Fer second using a A'�nning roughness coefficient of 0.030 ar� the
finishe�d floor°elevations should be one foot higher than tne anticipated
water surface elevation using a Manni-ng coefficient of 0.050 for 100-year
— stornns . � �
A lcw flow channel should be des�gned to acconmodate the 2-Year storm
flaws. This law flaw channel should �acedf �the channellt hlow�rherever
possible. Drop structUres should be p
velocities and banks revegetated to prevent erosion. A typical stream
cross section is shaHm in Fiqu�'e 5.
The lo�r middle reach is absorbing large quantities of s�ediment and is
presently offeri.ng a significant buffer for the lagoon by accomadating
qreat quantities of sediment being tz'ansPorte� in the creek. This section
of the floodplain rcwst be Presezved i�n its present state.
3, D�tention Basins (V�71)
The eight detention basins outlined on Figure 4 should be built and
maintained. Maximtmn Peak attenuation for the 2 to 100-year storms should
be the design criteria for these basins.
4. La oon Nt�lifications (Ll)
The mast effective method of decreasing the sediment accturnilation in the
lagoon wi.th lagoon enhancement is a ccanbination � aat�H 11 Street to 100
�aeir with a uridth to 80 feet, enlarging the °Pen g
feet wide, excavating the material under' the freeway, and breachi.ng the
barrier beach durinq storms. This scenario of i�rovements reduces
sediment acclmnulation by only 13� and r.as many environmP_ntal drawbacks.
5, Continuin Erosion Control Fr zcation (S2 and S3)
The first erosion control �rkshap was well attended. 'I"here seems to be a
�¢rnu�it�, con�unit�nent to erosion control. Efficient erosion control
both for grading and agriculture will pay off well in tern�s of reducing
sediment acctim�nzlation in the lagoon be beneficial.
6, Sediment Basins (S4 and S5)
The two feasible locations for sediment basins are at South Coast Asphalt
and just upstream of Jefferson Street.
7. Dradging '� .
Even with a11 of the effective methods outlined herein, the lagoon will
have to continue to be dredged Periodically. The alternatives were all
con�ared to this inevitable and ongoing solution.
41
8. Monitoring
The fact that this is a c�mpletely ungauged watershed gives the finclings
of this study an amount of uncertainty. There is a need for monitoring so
more accurate estirnates of flood flows, sediment transport and sediment
acc�nulation rates can be obser�red. The models used in this study then
can be calibrated and the accuracy i�roved greatly.
Rain gauge and stream flaw nbnitoring are needed to calibrate watershed
models. These will also help to ans�r many of the local questions
regarding storm flav values. Present estimates of these stornt flaw values
vary vrildly.
Sediment �lang in the creek will provide rrore definite correlation
between the sediment flaws and the flood flows. This wi.11 help develop a
sediment rating ctuve for the Buena Vista watershed.
Bathymetric suxveys of the lagoon need to be taken, especially before and
after major stornn events in order to monitor the sediment accumulation .
42
V±I. BIBLIOGRAPHY
ASCE Manuals and Reports on �gineering Fractice, No. 54, 1975. Sedimentation
i and E.�gineerir.g, V. Vanon.i., ed.
Hoffman, J. S., et al. 1983. Projecting Future Sea1 Leve1 Rise, Nlethodology,
� Est:mates to �he Year 2100, and Research Needs. A Report ot the
U.S. Enviroxunental Protection Agency.
SimQns, Li & Associates, Fort Collins, C0. 1984. Effect of the Santa Margarita
Project on Beach Sarid Replenishment. Prepared under contract with the Bureau
of Reclamation.
U.S. Arniy Corps of Ehgineers, 1973. Flood Plain Information, Buena Vista
Creek, Pacific Ocean to Vista, San Diego County, CA. Prepared for San Diego
Coturty .
Yalin, M. S., 1972. N�chanics of Sedsment Transport. Perganinon Press, Oxford.
— United States Geological Survey Water Resources Data for California, 1975-82.
United States Geological Siirvey, Menlo Park, CA.
�
43
APPENDIX ONE
SUBBASINS
FUTURE
HYDROLOGICAL CONDITIONS
CALCULATIONS
IJATERSHED SUBBASIN FUTURE CHARATERISTICS 0.38
LAG = 24n(L X Lc/SQRT s)
- SUB- LU SOIL 7 SCS CN ELEU LENGTH PC-CPJT SASIN SLOPE
BASTN CPl X� DIF L(FT) Lc (FT) n(FT/�iI)
- 1 COMi�I D 40% 92 36.8 220 3500 1800 0.05 332
HDR 0.0
h1DR D 20% 88 17.6
LDR 0.0 COMPOSIT
FP�IST D 40% 86 34.4 CN LAG (HR)
� 0.0 89 0.2263
2 COP�M D 407 92 36.8 150 3500 1400 0.045 226
HDR D 40% 90 36.0
- MDR D 20% 88 77.6
LDR 0.0 COMPOSIT
FMST 0.0 CN LAG (HR)
_ 0.0 90 0.1991
3 COf�lh1 0.0 700 4000 2200 0.05 924
- HDR 0.0
I�IDR 0.0
LDR 0.0 COMPOSIT
- FMST D 100% 86 86.0 CN LAG (HR) '
0.0 86 0.2115
4 COMM D 30% 92 27.6 340 4700 2200 0,045 382
HDR D 307 90 27.0
MDR D 20% 88 17.6
- LDR O.Q COMPOSIT
FP�IST D 20� 86 17. 2 CN LAG ( H R)
0.0 89 0.2394
5 COMh1 D 50% 92 46.0 50 3000 1500 0.03 88
HDR D 507 90 45.0
MDR 0. 0
LDR 0.0 COMPOSIT
FMST 0.0 CN LAG (HR)
- 0.0 91 0.1537
_- 6 COMM D 50% 92 46.0 150 250Q 1000 0.03 317
HDR D 30% 90 27.0
MDR D 20% 88 17.6
LDR 0.0 CO�IPOSIT
FMST 0.0 CN LAG (NR)
0.0 91 0.0964
A-1
r
7 COP�h1 0. 0 650 6000 3500 0, 05 572
HDR 0.0
� MDR 0.0 _
LDR 0.0 COMPOSIT
FMST D �00% 86 86.0 CN LAG (NR)
0.0 86 0.3224
8 COMM . 0.0 900 4000 2500 0.05 1�88
HDR 0. 0 -
MDR 0.0
LDR 0.0 COMPOSIT
FMST D 100% 86 86.0 CN LAG (HR) _
0.0 86 0.2117
9 COMM 0.0 450 4000 2000 0.05 594 --
HDR 0.0
MDR 0.0
LL1R 0.0 COMPOSIT -
FMST D 1009 86 86.0 CN LAG (HR)
0.0 86 0.2218
10 COMM 0.0 650 6000 2500 0.05 572
HDR 0.0
MDR 0. 0 -
�DR C 507 84 42.0 COMPOSIT
FMST C 50% 82 41.0 CN LAG (HR)
, 0.0 83 0.2837 -
11 COMM 0.0 650 5000 2500 0.05 686 _
HDR 0.0
MDR 0.0
LDR 0.0 COMPOSIT
FMST D 100� 86 86.0 CN LAG (HR) -
0.0 86 0.2557
12 COMM 0.0 150 5000 250Q 0.035 158
. . HDR 0.0 �
MDR C 40% 86 34.4
LDR C 40% 84 33.6 COMPOSIT
FP�ST C 20% 82 16.4 CN LAG (HR)
0.0 84 0.2365
13 COMM 0.0 200 3000 1500 0.035 352
HDR 0.0 --
MDR 0.0
LDR D 30% 87 26.1 COMPOSIT
FMST 0.0 CPl LAG (HR)
PARK D 70% 82 57.4 84 0.1378 �
A-2
� a� cor1r� o. 0 600 � o000 4000 0. os 3> >
- HDR 0.0
MDR 0.0
LDR C 30% 84 25.2 COMPOSIT
- FMST C 70� 82 57.4 CN LAG (HR)
0,0 83 0.4609
15 COyIPf 0.0 250 3000 1500 0.035 440
. HDR 0.0
MDR 0.0
- LDR C 40% 84 33.6 CO��IPOSIT
F��ST 0.0 CN LAG (HR)
PARK C 60% 77 46.2 80 0.1354
16 COMhI B 40% 90 36,0 250 3200 1500 0.03 413
HDR B 40% 82 32.8
P�iDR 0.0
LDP, B 20% 78 15.6 COMPOSIT
' FMST 0.0 CN LAG (HR)
- 0,0 $4 0.7175
- 17 COP1t�1 B b0% 90 54.0 250 3000 1000 0.03 440
HDR 0.0
P�DR B 40% 80 32.0
LDR 0.0 COMPOSIT
FMST 0.0 CN LAG (NR)
0.0 86 0.0970
18 COMf� C 40% 91 36.4 250 9000 5000 0.028 147
HDR C 20% 88 17.6
- MDR C 207 86 17.2
LDR C 20% 84 16.8 COMPOSIT
FMST 0.0 CN LAG (HR)
_ 0. 0 88 0. 3124
19 C01�11�1 0.0 500 6000 3000 0.05 440
- HDR 0.0
MDR 0.�
LDR C 30% 84 25.2 COMPOSIT
- FMST C 70% 82 57.4 CN LAG (HR)
0.0 83 0.3196
20 COMt�1 C 30% 91 27.3 250 9500 5000 0.035 139
HDR 0.0
MDR C 30% 86 25.8
- LDR C 30% 84 25.2 COMPOSIT
FMST C 10� 82 8.2 CN LAG (HR)
0.0 $7 0.4027
A-3
21 COMM D
HDR D
MDR D
LDR D
FMST
22 COM� i C
HDR B
MDR
LDR
FP�9ST
23 COMM D
HDR D
MDR D
LDR D
FMST
24 COMM C
HDR C
MDR C
LDR
Ft�1ST
25 CQIhM C
HDR C
MDR C
LDR C
FMST
26 COMM
HDR
MDR D
LDR
FMST
30� 92 27.6 100 10000 6000 0,03 53
309 90 27.0
307 88 26.4
10% 87 8.7 COMPOSIT
0.0 CN
0. 0 90
LAG (HR)
0.4534
50� 91 45.5 80 2000 1000 0.028 211
50% 82 41.0
0. 0
0.0 COMPOSIT
0. 0 C!V
0.0 87
LAG (HR)
0. 0893
407 92 36.8 220 9000 4000 0.028 129
207 90 18. 0
30% 88 26,4
1Q% 87 8.7 COMPOSIT
0.0 CN LAG (HR)
0.0 90 0.2941
60% 91 54.6 85 4000 2000 0.028
30� 88 26.4
10% 86 8.6
0.0 COMPOSIT
0. 0 CN
0. 0 90
LAG (HR)
0.1705
407 91 36.4 180 5000 2500 0.03
207 88 17. 6
30% 86 25.8
10% 84 8.4 COMPOSIT
0. 0 CN
0. 0 88
LAG (HR)
0.1958
112
190
0.0 170 5000 2500 0.035 180
0. 0
100� 88 $8.0
Q.0 COMPCISIT
' 0.0 CN
0. 0 88
LAG (HR)
0.2310
Z7 COMP�i C 20% 9i 18.2 200 6000 3000 0.035
HDR C 20% 88 17.6
��DR C 60% 86 51.6
LDR 0.0 COMPOSIT
FMST 0.0 CPd LAG (HR)
0.0 87 0.2663
A-4
176
28 COMM C 20% 91 78.2 1$0 4500 2500 0.035 211
� HDR D 40% 90 36.0
NIDR D 40% 88 35.2
LDR 0,0 COMPOSIT
- FMST 0.0 CN LAG (HR)
0. 0 89 0. 2151
29 COMM 0.0 120 4000 1800 0.035 158
NDR 0.0
MDR D 100% 88 88.0
- LDR 0.0 COMPOSiT
FMST 0.0 CN LAG (NR)
0. 0 88 0.1918
30 COMr�� D 2a� 92 18.4 150 5000 2500 0.035 158
_ HDR D 30� 90 27.0
MDR D 50� 88 44.0
LDR 0.0 COMPOSIT
FMST 0.0 CN LAG (NR)
- 0.0 89 0.2365
-- 31 COMM C 20% 91 18.2 220 3400 1500 Q.035 342
HDR D 50% 90 45.0
hIDR D 30% 88 26.4
LDR 0.0 COMPOSIT
� FMST 0.0 CN LAG (HR)
0.0 90 0.1454
32 COMM D 40% 92 36.8 260 7000 3500 0.035 196
HDR D 30% 90 27.0
- MDR D 30% 88 26.4
LDR 0.0 COMPOSIT
FMST 0.0 CN LAG (HR)
_ 0.0 90 0.2933
33 COMM 0.0 180 4000 2200 0.035 238
- HDR 0.0
MDR D 1007 88 88.0
LDR 0.0 COMPOSIT
- FMST 0.0 CN LAG (HR)
0,0 88 0.1916
� 34 COM��1 D 50% 92 46.0 180 4700 2500 0.035 202
HDR D 30% 90 27.0
MDR D 20� 88 17.6
� LDR 0.0 COMPOSIT
FMST 0.0 CN LAG (HR)
0, 0 91 0. 2205
A-5
35 COMM D �0� 92 9.2 200 5000 2000 0.035 211
HDR D 20% 90 18.0
MDR D 70% 88 b1.6
LDR 0.0 COMPOSIT
FMST 0.0 CN LAG (HR) __
0.0 89 0.2057
36 COMM C 107, 91 9.1 200 4000 2000 0.035 264
HDR D 20% 90 18.0 -
MDR D 70% 88 61.6
LDR 0.0 COMPQSIT
FMST 0.0 CN LAG (HR) _
0.0 89 0.1811
37 COMM 0.0 370 4500 2200 0.035 434 -
HDR 0. p
MDR D 100� 88 88.0
LDR 0.0 COMPOSIT -
FMST 0.0 CN l.AG (HR)
0.0 88 0.1787
38 COP�1h1 0.0 340 5500 2500 0.035 326
HDR C 40� 88 35.2
MDR D 60% 88 52.8 -
LDR 0.0 COMPOSIT
FMST 0.0 CN LAG (HR)
0. 0 88 0. 2138 -
39 0.0 340 4000 2000 ' 0.035 449�
MDR A 10% 73 7.3
MDR C 20% 86 17.2
MDR D 707 88 61.6 COMPOSIT
0.0 CPJ LAG (HR) �
0.0 86 0,1638
40 0.0 320 3500 1500 0.035 483
MDR C 30% 86 25.8
MDR D 70% 88 61.6
0.0 COMPOSIT
0.0 CN LAG (HR)
� 0.0 87 0.1376
41 0.0 280 6000 3500 0.035 246
MDR C 60� 86 51.6 _
MDR D 40% 88 35.2
0.0 COMPOSIT
0.0 CN LAG (HR)
0.0 87 0.2649
A-6
42 0.0 240 3000 1500 0.035 422
MDR C 64% 86 51.6
� MDR D 40% 88 35.2
0. 0 COP�POS I T
0.0 CN LAG (NR)
0.0 87 0.1331
43 Q.0 220 2500 1200 0.035 465
- P4DR C 50� 86 43.0
MDR Q 50� 88 44.0
0,0 C0�1POSIT
� 0.0 CN LAG (HR)
0.0 87 0.1121
� 44 0.0 240 4500 Z000 0.035 282
MDR C 40% 86 34.4
MDR D 607 88 52.8
-- 0.0 COMPOSIT
0,0 CN LAG (HR)
0.0 87 0.1871
45 COMM 0.0 2$0 4000 1500 0.035 370
NDR 0. 0
� MDR C 307 77 23.1
LDR 0.0 COMPOSIT .
FP,1ST 0.0 CN LAG (HR)
- PARK C 707 86 60.2 83 0.1523
_ 46 COMf� C 10� 91 9.1 240 4500 2000 0.035 282
NDR 0.0
MDR C 80� 8$ 70.4
LDR 0.0 COMPOSIT
� FMST 0.0 CN LAG (HR)
OPEN C 10% 77 7.1 87 0.1871
47 0.0 260 3700 1500 0.035 371
r�1DR C 30% 86 25.8
_. MDR C 70� 88 61.6
0.0 COMPOSTT
0.0 CN LAG (HR)
0.0 87 0.1478
48 COMP�i D 40% 92 36.8 220 4500 3000 0.035 258
- COi�1M C 40% 91 36.4
HDR D 107 90 9.0
MDR D 10% 88 8.8 COh1POSIT
_ F�Y1ST 0.0 CN LAG (HR)
0.0 91 0.2220
A-7
49 COMh9 C 407 91 36.4 280 6500 2200 0.035 227
HDR D 20% 90 18.0
MDR D 407 88 35.2
LDR 0.0 COMPOSIT
FMST 0.0 CN LAG (HR)
0.0 90 0.2324
50 COMM 0.0 330 7000 3000 0.035 249
HDR 0.0
��iDR A 100% 73 73.0
LDR 0.0 COh1POSIT
FMST 0.0 CN LAG (HR)
0.0 73 0.2644
��
APPEiVDIX TWO
COST-EFFECTIVENESS
ANALYSIS
O
ANPdUAL COSTS
DREDGIPIG:
LAGOOPJ IP! EXISTIPdG COPJDITIOP!
!�lATERSHED IN FUTURE COP,IDITIOf�
191.500 CY SEDIMENT DELIVERY X
�7.35 /CY =$1,407.525
LAGOON MODIFICATIO�lS:
LAGOON I�IITH 80' LOIA�ERIPJG U1EIR, 100' HILL ST. BRIDGE & DREDGING AT I-5
WATERSHED T�J FUTURE CONDITIOP�
4JEIR: $400.000 INITIAL COSTS LIFE: 20 YEARS = �20.000
OPERATION AND t�-1AThJTAPJE�dCE: $20.000
HILL ST: $740,000 iNITIAL COSTS LIFE: 50 YEARS = $2.800
I-5 $30,000 INITIAL COSTS LIFE: 2 YEARS = $15.000
TOTAL ANNUAL COSTS: $57,800
LAGOOfV CHANNEL DREDGED 10' DEEP 100' WIDE '
WATERSHED IN FUTURE CObJDITIOPJ
268.500 CY X $15 PER CY =
$4,�27�500 IPJITIAL COSTS LIFE: 2 YEARS = $2,013.750
� DETE1VTi0�� BASIPJS
LAGOON :[N EXISTTNG COfJDITION
4JATERSHED IN FUTURE COPIDITION 4JITH 8 DETENTION BASINS
LAP,ID: 19 ACRES X $130.000 PER ACRE _$2.470.00Q
LIFE: 50 YEARS =
CC���1ST' N: $11, 500 EACH X 8= $92. 000
LIFE: 10 YEARS =
h1AINT:
TOTAL ANNUAL COSTS:
CREEK ENHANCEMEtJT
LAGOON !PJ EXISTiNG CONDITIO�J
WATERSHED IN FUTURE CONDITION WITH 8 DETENTION BASINS
LAP1D: 1.050.000 SQ FT X $4 PER SQ FT =$4.200.000
LIFE: 50 YEARS =
DROP STR �5,000 EACH X 160 = $800,000
LIFE: 5 YEARS =
TOTAL ANNUAL COSTS:
SIDE'CHAPlNEL REPAIR
DROP STR $3,000 EACH X
10 = $30.000
LIFE: 5 YEARS =
TOTAL ANNUAL CQSTS:
�49. 400
$9. 200
$130,000
$188,600
$84,000
$160.000
$244, 000
$6. 000
$6,000
A—g
SOUTN COAST SEDIi�iEf�dT BASIf!
5, 000 CY SEDIf�IENT DELIUERY X $2.35 �/CY = $11, 750 Af�!f�dU.aL CJSTS
JEFFERSO��! SEDI�r1EI�JT BASI^J
1, 600 CY SEDIi�E�iT DELIVERY X $3. 35 ��/CY = $5, 360 AN��IUAL COSTS
� If•lCLUDES P.EDUCTIOP! If: PP.ICE OF $4/CY FOR THE VkLUE OF THE P�IATEP.I ^,L
A-10
PRU7ECTED SEDINIF�IT REDUCTIONS
ln�Z�tSHID LAGOCAQ � RIDiTGT ANNiTAL ANNUAL
CC3ND COND SIDIl�]T SEDIl�IT
ACCUM RIDUCT.
FUTURE EXISTING BASIS 191,500 —
F'CPI'[JRE C� 12� 168,520 22,980
FUiiiRE ��&CHANN 26� 141, 710 49, 790
F'U'I'[7RE CHAI�II�i EE'F�7C,T 26, 810 MIlVIl�JM
F W/DET E�STING 20� 153,600 37,900
DET&F�i EXIT 45� 105,100 86,400
ET�NC F�ST 48, 500 MIlVIl�'IIJM
ALTERNATIVE ANNiJAL ANNfJAL RIDUCTION COST—
COST SIDIl�iVT X BENEFIT
RIDUGTION $7.35 RATIO
NO MLIDIFTCATIdN $1,407,525 — — 1.00
WEIR+HII,L ST+I-5 $57,800 22,980 $168,903 3.0
C�IANI�L, $2, 013, 750 26, 810 $197, 054 .1
DET BASINS $139,200 37,900 $278,565 2.0
CRF�R IIVHANC $160,000 61,000 $448,350 2.8
E.C.R SIDE ARROYO $6,000 1,000 $7,350 1.2
GRADID ARF�18 $6,000 5,000 $36,750 6.3
AGRICtJI,TLTRAL $6, 000 4, 500 $33, 075 5. 6
S.COAST SID BASIN $11,750 2,50Q $18,375 1.6
JEE'F. SID SASIN $5,360 1,600 $11,76Q 2.2
A-11
' APPENDIX THREE
MIDDLE REACH EROSION
CALCULATIONS
0
.
DISTANCE VOLUME
SECTION CROSS BETWEEN (CY)
. NUMBER SECTION SECiIONS
AREA (FEET)
(SF)
100 655
840 13� 963
101 243
510 3.612
102 139
440 5. 361
103 514
1,460 28.242
104 526
980 21,252
105 645
275 5. 930
106 520
780 15,893
107 581
640 11,435
108 384
59Q 24, 900
109 1895
Z00 8. 94i
110 519
' 710 12.238
111 412
420 3. 864
112 85
110 284
li3 54
460 3,869
114 400
640 9.170
115 374
300 2,590
116 92.5
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