HomeMy WebLinkAbout1986-05-20; City Council; Resolution 8569* I
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RESOLUTION NO. 8569
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A RESOLUTION OF THE CITY COUNCIL OF THE CITY
OF CARLSBAD, CALIFORNIA, ADOPTING THE BUENA
VISTA LAGOON WATERSHED SEDIMENT CONTROL PLAN.
The City Council of the City of Carlsbad, resolves as follows:
1. The Buena Vista Lagoon Watershed Sediment Control Plan prepared by
lune Applegate and Associates September 3, 1985 indicated as Exhibit 3,
ittached hereto and incorporated herein, is adopted as the instrument to guide
.he control of sedimentation entering the Buena Vista Lagoon.
2. The Mayor is authorized to request funding from the State Coastal
:onservancy to provide funding for construct ion of the recommendat ions
:ontained in the report.
3. The Mayor is authorized to urge the members of the Buena Vista Joint
'owers Committee to approve an equitable arrangement of costs for an operation
md maintenance program prior to implementing recommendations of the report.
PASSED, APPROVED AND ADOPTED at a regular meeting of the Carlsbad City
:ouncil held on the 20th day of May , 1986 by the following vote, to
tit:
-
AYES: Council Members Casler, Lewis, Kulchin and Pettine
NOES: None
ABSENT: Council Member Chick c
MARY H. JCASLER, Mayor \TTEST:
(SEAL )
BUENA VISTA LAGQBN
WATERSHED SEDIMENT
CONTROL PLAN
Prepared by
June Applegate & Associates
Philip Williams & Associates
BUENA VISTA LAGOON AND WATERSHED
SEDIMENT CONTROL STUDY
FOR
THE CALIFORNIA COASTAL CONSERVANCY
Coastal Conservancy 205 (J) grant
Buena Vista Lagoon Sediment Management Phase I I 83-058-81 -48-C
BY
JUNE APPLEGATE, P.E.
September 3, 1985
2531 STATE STREET, CARLSBAD, CALIFORNIA 92008 (619) 729-7109 r
Peter Grenell, Executim Officer
Alp Jacobson, Bihancemnt Program mger
Laurie Marcus, hroject Manager
JUNE APpLEzAm & ASSOCIATES
June -legate, Principal
Philip williams, Principal
Jane KerLinger, Hydrologist
I, 11 .
111. Iv.
V.
VI.
VII.
"M CNE suhbasin characteristic Calculations
APPENDIX m Cost Effectiveness Calculations
24PPENDIX lnREE
APPENDIX FOUR fagoon mtation Calculations
upper Middle Reach Erosion Calculations
FIGURF: 2 subareas FIGUKE 3 Nawal conditions FIGURE 4 Detention Basin Iocations
FIGUKE 5
FIGURE 6 Hydrographs FIGURE 7
TAELFll Erosion control Alternatives
TABLe2 Sediment Size Distribution for
TABLE 3 sediment source slmmccy
hrdposed Channel Cross Section
-tic Diagram of Bum Vista Lagoon
Different Hydrographs
tinva to peak for future conditions at the lagoon
Used in Analysis
TABLE 4 surmrary of NEC-1 peak flows and
TABLE 5 Projected Sediment Reductions TABLE6 sediment Rating a;lrve Relationships
T- 7 Buena Vista Lagoon Cmputer Model Runs
PACZ
i
12
12 13 14
16
17 19
23
23
28 37 39
43
-
2
3
5 9 10
26 38
6
18
22
25
25
29 31 35 TA8IrE 8
TABIIF: 9 Sumrrary of IagOOn and "shed Shmlations 36
SUmMlry of Inflaw y.drographs
3
Due to the rapid -tation of Buena Vista Iagmn, the California State
Coastal Conservancy funded this study of sedht control for the lagoon and
its watershed.
Leedshill-Herkenhoff of San Francisco subconsulted and provided the hydrology models of the watershed, several alternatives needed to ke evaluated for sedimnt control.
A Phase One study was performed by 3m & Vcqt of Vista.
The findings of the Phase One Study indicated that
The California State Water Resources Control Board and the Coastal Conservancy
then funded a Phase Ttm Study. hired to perform the watershed delling, project coordination, and alternatives evaluation.
prepared the hydxaulic analyses of the lagcun.
is to formulate a prioritized list of sediment magemat procedures for the Buena Vista watershed and lagcon based on a cost-benefit comparison.
June @iega&! & Associates of Carisbad was
Philip Williams & Associates of San Francisco The primary goal of this study
Buena vista Lagoon is the only freshwater lagoon in southern California.
situated between Carlsbad and Oceanside.
the cities of Vista, Oceanside and Carlsbad (see Figure I),
maintained by a fixed weir at the muth of the lagoon.
railroad, Hill Street, Interstate 5 and Jefferson Street cross the lagoon, Since the psition and size of the muth of the lagoon was made permanent and
the flcw restricted, there has been an increase in the s-tation rate of
the lagcon, Increased, urbanization b~ the watershed further accelerated the sedimntation and necessitated the dredging of a portion of the lagoon,
It is
Its 19 square mile watershed includes
The water level is
The fills of the
If projected future sedimnt rates materialize, the lifetime of mens Vista
Lap could be less than 10 years.
T€rE L%Cm SySTEM
Bum Vista Lagoon was created by the rapid rise in sea level after the last
ice age. In its natural state, it appears that the munt of sedi.”t deposited in the lagcon was balanced by the rate of sea level rise. factors have upset this balance, One is the limitation of the lagoon’s ability
to flush sediment to the ocean by the placement of a wir at the muth and road fills that cross and restrict the lagoon, The other is the increase in sediment delivery to the lagoon frm the watershed. The cause for this increase is two-fold.
Encroachment upon the floodplains that once accepted sedimnt frm the creek
during large stonn flacrs has eliminated mst of this buffer and sediment now flms directly into the lagoon,
Before the human-caused disturbances to the watershed, creek, marsh, and lagoon
much of the sedimnt fran the watershed was deposited before it reached the lagoon. Then in the 1- reach, a large marsh area spread and filtered the stonn water, trapping mre sediment before it entered the lagoon.
Tfm
Urbanization has increased flws to the lagoon.
sediment was deposited on the broad floodplain in the middle reach,
I- w w LL
8 3m
The only remnant 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 cnmently absorbing very large quantities of sedinmt and is the last natural buffer to prevent saw of tke s&hent frcm entering the lagcon.
functioning prtion of this reach is the thick riparian area just east of the
Haymar Street cul4e-sac.
The best
The other sediment buffer was the marsh above the lagoon.
campletely filled. Highwzy 78 aril an bo+& si&s of b%nrce SLreet st
left of this marsh. found its way through the tules to the lagmn dropping mst of the finer
sediment that was left after the riparian area upstream.
This marsh has been
The cattails in the channel betwen the shopping center and
lbad are dl that are Before the filling of the msh, the water sl0tRd and
After changes in the watershed, particularly urbanization in the last two decades, increased peak flm have dramatically transformed the natural hydrological system. the watershed into the creek, but, mre importantly, have caused the creek bed
to start to erode (degrade) in portions of creek. The bcrease in stream flow energy has caused this stream dawncutting. new and lower equilibrium can be reached (see Figure 3).
The increased flaws not only discharge mre sedinent frcan
The process will continue until a
All 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 dq period in this region. In 1981 the eastern portion of the lagoon was dredged.
study is to explore alternatives to continued dredging of the lagoon. The purpose of this
THE STUDY
Hydrolcgy ncdels of the watershed and hydraulic mdels of the lagoon wxe developed and evaluated.
in a -11 reduction in the sediment accumulation rate. Greater reduction in
the sedht delivery rate can he produced by reducing the peaks of the storm
flaws into the lagoon.
Reductions in the peak flms *re deled by optimizing feasible detention
basins in the upper reaches and by mde1ix-q channel enhancamnt that muld slaw veiocities in the milic;iie reach.
Maxuru * 'zing the flushing action of the lagcon resulted
Regional sediment transport curves =re integrated with the inflm hydrographs in the hydraulic del of the lagoon.
transported is an exponential function of the quantity of water, the peak flows
are responsible for a laxge portion of the sedinu3nt transported to the lagoon. Reducing these peak flw resulted in much larger reductions in sediment flaws into the lagan.
The study reviewed nine alternative for controlling sedimentation of the
lagmn (see Table I). These include: L1) dify the lagoon flushing action by increasing the weir size, the size of the Kill Street Bridge and clearing the opening under 1-5; L2) dredging a flow-through channel through the lagoon from
Jefferson to the weir; Wl) construction of stomter detention basins in the upper watershed;
Because the quantity of sediment
WS) enhancerent of the main channel to lmr main channel
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ESTIMATED ESTIMATES) PERCE3ST lwNLTAL COST- INITIAL ANNUAL muc- COST l?mEFIT
CCST O&MCCST TION REDX’N 1 RATIO 2
PHASE I1 IAGCCN MIDIFIcpiTIoNS:
$15,000 12% $168,000 3.0 ~1 WEIRi-HILL ST+I-5 $570,000 .I L2 CHANNEL $4,030,000 $2,010,000 14% $197,000
PHASE I
Wl DGT BASINS Const. $92,000 $139,000
ws CREzKENEmIc $800,000 $160,000 32% $440,000 2.8
WATERSHED mIF1CATIONS:
20% $281,000 2.0 Land Acquisitions $750,000
mIF1CATIoN WITH s” so- a”L:
SEDIMENT SOURCE cxxcF.oL:
S1 E.C.R. SIDE -YO $30,000 $6,000 1% $7,000 1.2 s2 GRADEDAREAS $6,000 $6,000 3% $37,000 6.3 s3 AGRICULTURAL $6,000 $6,000 2% $33,000 5.6 s4 S.” SED BASIN $12,000 $12,000 1% $18,000 1.6 s5 JEFF. SED” $5,400 $5,400 1% $12,000 2.2
No MODIFICATION: $1,410,000 3 BASIS OF CCME“m 1.0
I. Annual cost reduction is equal to the percent reduction ~~TES $1,410,000
(the estimated annual cost of dredging with no modifications to the lagoon or watershed). Annual. cost reduction is the annual benefit. Estimated total annual cost divide by the annual. benefit. This figure is the annual cost of remving 191,500 cubic yards of
estimated sediment delivered into the lagoon at $7.35 a cubic yard for
2.
3.
Further details on the derivation of these figures is included in Appendix Two.
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ss s E c 'r IO N
Figure 3 Natural Conditions
........
: .;I
.C
......... \.. ..... ......... .... r) 1 1 u v i 11 m ,:.:.:.:.I:: .................... .... .... .>P ..................................
............... ......... -_ --L-.---
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that for every cubic yard of erosion controlled, there is one half of a cubic
yard of reduction of sediment accumulation in the lagoon.
thirds rduction in the grading site sediment source multiplied by one half indicates that this improveZnent wxld mean a three percent reduction in annual sediment accumulation rate in the lagmn.
has the highest rate of return on dollar invested.
Similar results are anticipated for agricultural sites (S3) . this program should reduce as the land for agriculture diminishes. reduction of 2 percent of the total sediment accurmlation in the lam per
year is anticipated.
It is anticipated that 5,000 cubic yards of sedirclent per year dd effectively
be remved fran a sediment basin lccated at the South Coast Asphalt property
(S4). cubic yards of sedirrent per year, using the source and accumulation relationship esthte described above. in the anrmal sediment accumulation rate in the lagoon. this site wuld reduce the sediment accumulation rate of the lagoon.
The anticipated two
Table One indicates that this
The budget for Currently a
It is estimted that this muld result in an annual reduction of 2,500
mving sediment at
This dd rean a one percent reduction
Another 1,600 cubic yards of sediment per year could effectively be renvwed at
the mth of the creek, just east of Jefferson Street (S5) . Since there is no
dampening effect expected at this close proximity to the lagoon, it is assumd
that this is a direct reduction in the sdimmt acdation in the lagoon,
This could result in a reduction in annual sedimnt accumulation in the lagoon of one percent.
It is also effective to repair side channel arroyos (Sl) in the manna
described for the main channel. !The example given is the channel which is on the west side of El Camino &al (E.C.R.) fKm Hosp to Chestnut. Repairing this
arroyo also yields a one percent reduction ad is cost-effective.
The alternative that proved to be far too costly was to maintain a deep channel in the lagoon frcsn Jefferson Street to the weir (L2) . It is anticipated that larye amounts of material Fxluld have to be dredged frcan this channel, because the channel wuld act as a sedimnt trap for the lagoon. The high sediment rate of the lagoon nvaans that the channel dd fill in at a rapid rate. It
is estimated to cost over two million dollars per year to fiaintain such a
channel kcause of the large volumes of material to be rseroved.
Refining the estimates with data fran a watershed, creek, and lagoon mnitoring program, and with mre precise cost estimates may or may not improve the cost-effectiveness ratio for this alternative.
coNQ;us1ms
~n the order of effectiveness the follawing solutions are reccmekW: creek
t=nha,nmt {including floodplain preservation in the laer reach) , detention basins, sediment control education, sediment basins, and side channel arroyo
repair.
8 I4
velccities and help repair erosion damage;
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. alternatives were catpared to no moaifications and the consequential dredging
of the lagoon at the anticipated rate of sediment accumulation in the future,
SI) side channel arroyo repair;
The nine
Eight detention basins (Wl) in the upper reaches will produce an anticipated 20 percent reduction in annual sediment: accumulation.
of a snall check structure (i.e.: a 5' high dam or a road crossing) and a restricted outlet like an 18" pipe. This allm the water to poM Zing stom and to be released at a greatly reduced rate,
basins proposed h this alternative (see Figure 4 for detention basins in
Vista).
A detention bash consists
There are eight detention
Creek enhanmt (FJS) proposes peak flm velocities to be less than six feet per second, allcwing riparian grmth in the creek, with a 15 to 30 feet increase in creek width and drop structures which reduce the grade of the channel and thereby reduce the velocity of the water (see
Figure 5). Creek enhancerent was delled With the detention basins in place.
The &ination of creek enhancement and the detention basins resulted in a 45 percent reduction in annual sediment accurclulation because of the resulting reduction in storm flows. reduction, it is asd that the reduction in storm flaws due to the creek
enhancement alone can reduce sediment delivery by a mini" of 25 percent. Reducing the erosion of the main channel (which is the major sediment source in the watershed) by this enhancement will further reduce the sediment accumulation by an additional 7 percent, for a estimated total of 32 percent
reduction. preserved ,
'This can be accanplished
Since the detention del alone yielded a 20 percent
Additionally, the 1- middle reach floodplain should be
The ambination of a nrrmble and 80' wide weir, a 100' bridge aPening at Hill
Street and dredging under 1-5 (Ll) produced an estimated mud. sedirru3nt accmulation reduction of 13 percent.
drawbacks that can not he measured by a dollars and cents canprison.
the mir will create other problems that are not related to sediment accumulation. Mong those concerns are water quality, and salt water intrusion. levels in the lagoon.
warning it and increasing algae grd.
probability of ocean waves overtopping the weir, intrcducing salt water to the lagoon.
that the channel dredging under 1-5 will have to occur frequently.
Hmever, this alternative has major
Lawring
This alternative increases the probability of lower water surface
Imering the weir also increases the Shallow water allows sunlight to penetrate the water,
Another anticipated problem With this solution is that it is likely
Sp&g a relatively mall annual sum of mney on education for sediment
control on grading sites (S2) will produce an estimated tw thirds reduction of this source, Reaucinq sediment sources will change the sedimnt rating curves, thereby resulting in a reduction of sediment accumulation in the lagoon. There is no data on the relationship betseen sediment source reduction and the reduction of sediment accumulation in Buena Vista Lagoon, This study assums
7
.. rl) . ... _. .. . . . . .. -. . .
NORTH
i
*...-. : .'
b I
j
' CHANNEL
LOW FLOW i
>- ! -'
\ 100-YEAR, 6 FEET PER SECOND CHANNEL *.-- ___ ____ ___ -__-_ -_ r
I
Figure 5 Cross Section of Proposed Channel
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LEGEND
e1 PHASE 1 DETENTION BASIN FOR STORM ATTENUATION (4 LOC'NS)
PHASE 2 DETENTION BASIN FOR STORM ATTENUATION (2 LOC'NS)
CHANNEL ENHANCEMENT DOWNSTREAM OF BRENGLE TERRACE PARK TO
MODELED IN PHASE 1, BUT NOT PHASE 2 MODELED IN PHASE 2, BUT NOT EFFECTIVE
e2
COLLEGE AVENUE.
' Figure 4
STORM ATTENUATION BASIN & CHANNEL ENHANCEMENT
MAP -
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The study found sans lagmn mdifications to be cost-effective, however there
are major concerns for the ecology of the lagoon if these are implax?nted. The
the Hill Street Bridge to be 100' long, and keeping the opening under 1-5
cost-effective dfications included a "able and widmed weir, enlarging
dredged.
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This is a report of the Phase l3m study of sediment control for 3uena Vista
lagoon and watershed for the California Coastdl Conservancy and the State Water Resources Control €!card. several alternatives needed to ke evaluated for sedht control,
Applegate and Associates, Civil Ehgineers of Carlsbad was selected by the Coastal Conservancy to perform this study,
Francisco was hired to sulxonsult and provide the hydraulic analyses of the
lagoon. evaluation rere perfod by June Applegate and Associates an6 are sm".rizd
in this reprt,
study and has greatly expand& and revised their reccarmendaitons, of in-depth research into the Phase One recohrmendations has resulted in the
divergent findings of the Phase Tbm report.
Findings of the Phase One Study indicated that
June
Philip Williams & Associates of San
The watershed modelling, project co-ordination, and alternative
The Phase M study relied upon the findings of the Phase One
This degree
It is the primary god of this study to reprt a prioritized list of sedimsnt managerent prccedures for the kena Vista watershed and lagoon based on a cost-benefit camparison.
The mens Vista watershed is an ungauged watershed. tkis study are based on synthetic hydrcgraphs, synthetic mathemtical models of
"he lagoon, and sedimnt rating curves extracted frm other similar small
coastal watersheds, sediment mnitoring using detailed bathmetric surveys of
the lagoon after major storm events, stream flcw sediment monitoring, and rain gauge informatian during storm events will yield mre accurate predictions of sediment axumulation, sediment flms and sources, Due to limited budget, ahst no field data, and a range of uncertainties, the sdimnt predictions in
this report have a wide range of error changing the true cost-effectiveness analysis dramatically.
Consistent techniques were applied uniformly for each categoxy of dification.
The estimate of reduction of mu& sediment accumulation in the lagoon provided a relative rankinq of the effectiveness of each alternative. categories of alternatives in which the relative cost-effectiveness ranking is
valid is: maximization of the flushing ability of the lagoon with lagoon
mcdifications (Ll and L2), minimization of the sediment delivery to the lagoon
with mtershed rrcdifications (Wl and WS)
Watersm
All of the predictions in
The
and minimization of erosion in the (ws, and s1 through S5).
Buena Vista Tagcon was fo& during the rapid rise in sea level at the end of
the last ice age, ten to fifteen thousand years age.
seven thousand years sea level rise has been mre gradual, apparently abut
1/2 foot per century. natural sedimentation rates in the lagoon, alluwing it to survive for thousands of years.
During the last five to
The slow rate of rise was sufficient to capensate for
Wave action caused the Littoral transport of sand along the coast, sealing off
the entrance to the lagoon with a hrrier beach. Esccept possibly during an
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lagoon.
The Watershed has also changed dramatically, farming, removed soil cover, increasing erosion and -tation in the
lagoon. increases flood peaks, causing gullying and creating arroyos. greatly accelerates erosion and dcrwnstream sedimentation.
floodplain of ~~ena Vista Creek has been filled in several locations, reducing the filtering effect of the riparian vegetation.
The floodplain in the middle section of Buena Vista Creek has evolved as a result of sediment kan the surrounding hillslops being transported as bedload in the creek. and deposit sediment on the adjacent flccdplain.
built up over time.
the middle and bwer reaches in ancient tks (see Figure 3).
of the total sediment eroded in the watershed actually reached the lagoon.
Extensive grazing and, later,
Urbanization, which has been particularly rapid since the 1970~~ This process In addition, the
During flood flows, these flows Fxnitd overtop the creek banks The floodplain and the creek
Buena Vista creek PELS aggrading in this manner throughout only a fraction
After changes in the watershed, particularly in the last tsm decades, the
increased peak flows have dramtically transformed the natural hydrological system. The increased flows not only discharye more sediment fran the watershed him the creek, but, mre @ortantly have caused the creek bed to start to de (degrade) in portions of the creek. The increases in stream
flm energy have caused the stream to downcut. until a new and lower equilibrium can be reached, This process will continue
At the same th one of the largest sediment buffers in the watershed has been
filled in. The marsh above the lagoon was the spreading area for storm flaws.
Here the water sld and found its way through the tules to the lagon, dropping mch of its sedinaent load. All that is left of that marsh area is a small area where cattails ~rcrw in the channel be- the shopping center and
Highway 78.
Buena Vista Creek
Water flowing into Buena Vista Lagoon comes primarily through mens Vista
Creek.
covers areas of Oceanside, Carlsbad and Vista.
the watershed, covers over half of the watershed and has the major impact on the flow characteristics of the system and yet it does not border the lagoon.
The 19 square mile watershed that drains into the creek and lagam Vista is in the upper reach of
The creek can be identified by reach. The upper reach is the reach abve
Highway 78. reach is frm El Camino Real to Jefferson Street (see Figure 2) .
The uppr reach is in its natural channel to Brengle Terrace Park. Above
WilM Park the creek has been stabilized by check structures, They were built in the 1930’s and it appears that only one of them has failed,
channel 11clw appears to have the potential to overflow and flood the “ding
The middle reach is from Highway 78 to El Camino Real. The lower
This
area, probabli-bause of watershed. The me& bas dawntown area of Vista to
increases in runoff fran the urbanization of the been channeled into concrete structures through the Melrose Drive. These structures were also designed
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early stage in its evolution, the tidal prism of the lagcon was insufficient
to scour a channel across the beach. Tidal action occurred for a short period
in the lagcon, and only hen winter flocds opened up a channel, Sarne s.edimnt
carried into the lagoon during floods discharged directly to the ocean thmuqh
the apening. %me sediment deposited in the lagoon muld later be resuspended
by wave and tidal action, and muld be flushed out of the lagoon during ebb
tide.
Because of the
varied greatly
winters, storm overtopped the
reestsblishzd,
of Euena Vista
barrier beach across its muth, the character of the lagcon
fran season to season, and fran year to year. runoff filled the lagoon with freshwater until at same point it
barrier beach. In the spring, after the beach was
the kgwn level dropx6, fed snly by spricqs and the base flow
Creek. In s"er and fall the inflcw decreased further until
In normal
evaporation exceeded inflow. flats or salt pans mdd be -sed.
the lagcon bst cmpletely dried out, and was fed mainly by salt water
seeping through the beach,
Water salinities increased and large areas of md
During drought periods it is likely that
In its natural state the watershed of Buena Vista faqmn was covered with
native plant vegetation. erosion than many of the introduced, new species. against direct erosion from rain drops but allowed the infiltration of storm moff into the soil, reducing peak runoff rates duwnstream and providing
greater base flm in the creek later in the year.
These flows supported dense riparian vegetation along the creek banks and on its floodplain. In its lower section the creek muld have discharged into a
tule freshwater marsh at the upper end of the lagoon, vegetation acted as sediment traps during high flood flows, building up the alluvial floodplain and reducing the amDunt of sediment discharging to the lagoon.
The plants generally provided a higher resistance to They not only protected
The floodplain and marsh
Historic Changes
In the two centuries since Eurcpans settled the area, man has made major modifications to the natural hydrolqic system.
The hyraulics of the lagmn have been ccanpletely altered since 1940, when
outlet culverts were installed at the muth to regulate maximum water levels,
This eliminated uciai action until the big €id of 1963, kkar th ciilvsrts
were washed aut, re-creating the natural entrance for a short -&ile mtil the existing fixed outlet weir was installed in 1970. have been excluded and the lagoon has been converted to a freshwater lake, Since that tjm! tidal flows
The construction, first of the Hill Street road &ankn?ent and then of the 1-5
freeway e"t across the laqmn, has also affected the hydraulics by segregating the lagoon 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
qyality. In addition, until the 1960s, sewage was discharged directly into the
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The marsh has been filled. Presently the only evidence of that -&.area is a small area where cattails grow in the channel betwen the shopping center and Highway 78, This channel is nuw the lower reach of Buena Vista Creek.
The Iagoon
Because of the changes in the lagoon hydraulics and the greatly increased rates of sedimentation the lagoon is no longer in equilibrium with natrual hydrologic processes and is rapidly silting in,
Most sediment deposited into the lagoon is discharged during the peak flows of large stom, such as those in 1969, 1978 and 1980, Sediment discharge is exponentially related to the flow velocity by a y of tm to three.
Consequently, though peak flows may last only a few hours, they can carry tens of thousands of tons of sediment into the lagccm.
It appears that sediment carried into the lagoon is prebmnan ’ tly silt. The typical size distribution of suspended sediment for different .so- is shcwn in Table 2, The Table is based on sediment sampling on other San Diego County
coastal streams (see Appenaix 4) and synthetic flood hydrographs generated for the Buena Vista Creek watershed.
As the flocdflm approaches the lagoon, backwater reduces the velocity and
carrying capacity of the flw.
sands, appears to be depsited on the floodplain and in the chamel betvieen the South Coast Asphalt quarry and Jefferson Street, while most of the suspended sedimnt, consisting of sands, silts, and clays, are discharged into the ligoon.
As tfie flood flows enter the lagoon, flow velocities drop to a fraction of a foot per second. suspension, and particles start to settle out. The settling velocity of sands
if very rapid, so they tend to settle out i.xm&iately.
gradually ht rapidly enough for most of thm to be deposited upstream of 1-5.
Clays settle out very slowly, but because velocities through the lagoon are so
low, mst are depsited in the lagmn and only a fraction are discharged to the ocean. The roadfills of 1-5 and Hill Street and the outlet weir have reduced
flow velocities through the lagoon, increasing sedimentation, Lagoon now acts as a very efficient sediment trap.
Much of the bed load, consisting of ccarser
These velocities are insufficient to keep the sediment in
Silts settle cut more
mena Vista
&sed on the very limited boring information available, it appears that, prior
to 1940, the lagoon bed consisted of fine sands at an elemtion of about -1.5 ft NGVD. the lagoon in the vicinity of 1-5, and by 1982 an additional 2.5 ft of organic rich silty clay had accxlrraxlated. In the last 42 years, presuming the same
siltation rate over the 200 acre lagoon, this amunts to about one and a half million cubic yards or tons (for these sediments, a cubic yard eighs roughly a
ton), or about 35,000 tons/year. For the 19 square mile watershed this amounts to 1840 tondsquare mile/year which is canparable to an earlier estimate of 1,000 to 2,000 tons/square mile/year (Irnnan 1976).
By 1961 approximately 2.5 ft of organic rich rnud had accumulated in ..
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& built before the major urbanization of the area.
The middle reach was a Wide aggrading flocdplain. two by the falls just downstream of College Avenue. functioned very similiarly before the impact of urbanization occurred.
the falls mark the location of the hyciraulic division of this reach.
It has been divided into
Now
The tm sections
In the upper middle reach, fran Highway 78 to College Avenue, the creek has dramatically changed frcxn trapping sediment in its broad floodplain (aggrading)
to a dam-cutting creek. has cut into the ancient flooc3plain deposits in the area of the old sewage treatment plant in Vista.
plus the eroded mterial dawnstream.
This difference is marked by the large gully which
Instead of absorbing much of the sediment it receives as it had done in the past, this reach is nm sending that sediment
Currently the lcrwer middle reach (College Avenue esterly to El Camino Real) is still aggrading. feet per season.
of the sediment before it gets to the lagcon.
In fact, it is aggrading at an alarming rate of up to four
This indicates that the later middle reach is absorbing mch
The cause of Chm-cutting in the upper middle reach is the increase in the
scour action of the creek. road crossings has contributed to this degradation, but this is a long-term
phenmon,
these crossings with sediment as the middle reach of Ima Alta Creek has.
llxeriq the flcw line of the channel at various
If the creek still had aggrading characteristics it wuld fill in
Typically during urbanization downstream channels start to de. response to higher peak flows of water frcan the developing area.
and future hydrographs modeled in the phase one study indicate that the peak
transport capacity of the creek mre than doubles.
This is in
The existing
flows have the potential to double in this reach. This mans that the sediment
If the sediment transport capacity increases to the pint 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 mch sediment to transport it dropped its load on the wide floodplain. these ancient fluvial depsits and carries them and its original load downstream (see Figure 3).
Nm it is hungry for sediment and erdes into
The increase in pak flow -lains the cause of the erosion in the upper middle reach. the peaks in the lower ~ddle reach to increase dramatically and could trigger dam-cutting in the 1- middle reach. Since there is very little buffer
between the her middle reach and the lagoon, the lagoon will expzrience an
even greater sedimentation accumulation rate than we have previously seen.
It is also a warning. Channelizing the upper middle reach will cause
In the lower reach, above the lagwn there was a wide flat marsh.
location of El Camino &a,l the creek spread over the marshland. of the land and the thick grcwth of the marsh plants greatly reduced the
velocities of the water.
tules to the lagoon, dropping much of its sedimnt load.
filter for the water entering the lagoon.
At the
The flatness
Here the water slowed and found its way though the The marsh acted as a
15
._ . .I ...
storm -
2-yr
5-yr
10-yr
25-~
5 0-yr
100-yr
TABLE "I. sediment Size Distribution for Different yrdrogr aphs
sedim3t peak madat % by Particle Size at Peak Flow
Flow Peak Q (cfs) (tons/day) F (-004 .004-.016 .016-.064 .064--25 .25-1.0Qnn
11
9
8
J 1371 1.2~10 25 6 23 33
5
5
1979 3.2~10 23 5 26 38
2589 6.8~10 20 4 28 40
6 3659 1.7~10 18 3
6 5832 6.7~10 15 2
31 44 6
32 47 4
7 I 13 2 33 48 4 7200 1.6~10
18
. .. . .. .. .. .. . r . . . :
After initial deposition during and after a flood, sediments can be resuspended
by wave action and redistributed in the lagoon,
constant, deepening to tw to three feet in areas of hi& wave action.
thick growth of tules under the 1-5 bridge prevents all except the finest
sediments frm circulating into the vestern segnents of the lagoon. Consequently, sediments acdating in the eastern segment are mainly sands, silts and rmds, wfiereas to the west of 1-5 sediments are minly organic mds. In the wind-protected area between the railroad and the beach, sediments are
highly organic and appar to Contain sewage sludge.
Water depths are fairly
The
Water levels in the lagoon are maintained at a mini" elevation of 5.8 ft NGW)
by the outlet eir crest or mre cmmonly b-en about 5.8 ft and 6.5 ft NGVD
by the barrier beach forming across the ouflet, segment are typically 1.5 to 2 ft, and in the =stern segments 2 to 2.5 ft,
S-
??at= dep*&i i? the astern
Before the human-caused disturbances to the watershed, creek, rnarsh, and
lagoon, much of the s-t fran the watershed was deposited before it reached
the lagoon. reach. storm water, trapping mre sediment before it entered the lagoon,
sediment was deposited on the broad floodplain in the middle
Then, in the 1- reach, a larqe marsh area spread and filtered the
The only remnant 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 same of the sediment frm entering the lagoon.
functioning portion of this reach is the thick riparian area east of the Haymar Street cul-de-sac,
The best
17
Agriculture
The following is a sumnary of interviews with Howard Mueller, who is currently
a consultant and has worked for the Soil Conservation Service. for the Soil Conservation Service, he "piled the "Impartant Fannland Map" for While mrking
The a"t of fafinland in the mena Vista watershed has been a constant of
approximately 5 percent (app"ate1y 600 acres) avocado groves and 5 percent
truck crops. farmrs these lands will decrease and becane an insignificant sediment source
within 5 to 10 years and will beccane completely urbanized within 20 years.
Howlever, with the Various econcdnic and social pressures on the
Avocado groves of three years old or younger (of which there is 10 to 15 percent of all groves) produce 15 to 20 tons of sedimnt per acre per year.
The rmabhg 85 to 90 percent of the groves have sufficient canopy and leaf litter to reduce the sediment yield to one to two tons of sediment per acre per
year-
Well managed truck crops also have a sediment yield of one to two tons of sediment per acre per year. Hawser, poorly managed truck crops produce as much as 20 to 30 tons of sedinwt per acre per year. Historically, the poorly
managed truck crop land constitutes about 1 percent of the watershed, and the
well "ged truck crop land constitutes the remining 4 percent. Presently, the ell managed farms only constitue one and a half percent of the 5 percent total.
Historidly, the agricultural land produced an estimated 5800 tans of sediment per year in the Buena Vista watershed. esthated 13,000 tans of sediment per year and within the next five to 10 years Presently they are producing an
this source Of sedjmnt will be negligible.
By canpadson, the natural areas, ach had periodically burned, yielded. one to tvm tons of sediment per acre per year, average.
Future Lad Uses
The following estimates for future land uses viere made by each of the three cities in the watershed (in acres):
Carlsbad Vista Oceanside
Deve~~ area: Underdeveloped: 1700 5760 3000
300 1500 500
Vacarrt land: Area with approved plans: 2 50 2750 134
=ea currently being graded: 190 3 25 85
=ea without approved plans: 250 765 2000
20
channel Erosion
It appears that there is an estimated totdl of 173,000 cubic yards of erosion in the min channel of the creek in the
and College Boulevard. the spring of 1985. Based on newspaper clippings, most of this erosion has
occurred since 1978. 1978 marked the end of a a 13 year dry period in this
area. urbanization in that time. The ccmbination of the increase of rainfall and urbanization created a dramatic increase in the munt of runoff ex_periend.
What had keen an aggrading section of creek where sediment was deposited upon a
broad floodplain becarre a degrading section, gully that is in excess of 15 feet deep in some places in this reach,
currentlv Gra6ed Areas
middle reach between Mehose Avenue
This was calculated by using a real toFography flm in
Lard use had changed frm primarily rural and agricultural to
The down-cuttinq is evident in a
Presently there is approximately 600 acres of graded area in the watershed.
Vista, Carlsbad and Cceanside adopted sediment control ordinances as part of their grading ordinances. sediment control plans mst b filed in September
and approved by October. The s-t control is supposed to be in place in
Novenhr, and remain effective until March,
Generally, on-site sedimznt control is still not effective.
be a lack of understanding as to what it takes to keep sediment fm leaving
the site,
1984 had no protection what so ever.
in the other cities was not effective.
There appears to
Much of the mrk done in the creek in Vista during the winter of Much of the sedkm-k control as installed
Sorretimes sediment is directed into the stom drain system in the form of muddy
water.
just folded aver. before spilling their contents and adding to the sediment leaving frcm the
site.
Another mn practice is to use sand bags that were not sealed, but
Some of these bags do not make it through the Winter season
Education of the omtractors, inspectors and design professionals who suhnit
and those wfio revim the plans is desperately needed. The ordinances are good,
'=It .bo.Iy zre Pit ;et *L?g $21177 1 iEp1me?.?+A.
The local citizens are concerned and wuld be excellent watchdcgs, if educated,
The Buena Vista Lagcon Foundation has a hotline that is available for the
rep0rtb-g of sediment problans. The local citizens are dedicated to the
saving of the lagoon, but do not yet recognize some of these problems,
Sedimnt yields fran these graded areas can vary fran one cubic yard per acre
control is so important. Sediment yields are still high frm this source, so
using an estimate of 25 cubic yards per acre per year over the 600 acres
currently be+ graded gives a sedkt estimate of 15,000 cubic yards of sediment per year.
per year to 30 cubic yards per acre per year. This is why good sediment
1Y
. The underdevelopd land is part of the total of the developd area, hmwer it is likely to be redevelo@ to a higher use.
Natural Erdible Areas
These &rs indicate that there is approximately 6,000 acres of natural
erodible area. Using an average of tm tons of sediment per acre per year indicates an estimate of 12,000 tons of sediment fram this source per year.
south coast Asphalt
South Coast Asphalt has a rock quarry just west of College Avenue. excavatioIls extend approxifiately 50 feet below the streanbed.
maintained the falls by keeping the banks and adding levees.
portion of the creek, there is runoff fran the plant site and there is potential for erosion. faces do not have mch erosion potential. in ~e reach with loose dirt banks. photography of the lard for this study.
Existing channel velocities in all but the mallest flows are in excess of 6 feet per second.
been carrying so mch sediment in recent years.
continues to aggrade. could start to degrade.
In the first large flow in 1979 a portion of a southerly stockpile was ercded.
!b prevent this loss of material, South Coast Asphalt nuw protects the tockpiles with riprap at the toe. However this site has the potential for erosion because of above mentioned velocities, little bank protection, and fill-dirt stream banks that are vulnerable to erosion.
The
In the flatter They have
Since the quarry area is granitic rock, the exposed The erosion potential on the site is
The plant has sup@ied detailed areal
These are erosive velocities, however since the creek has This section of the creek Higher peak flaws could reverse this and this reach
The rock quarry is estiroated to close in 1990.
the property are now being prepared and reviewed. the creek portion between 1990 and 1995. have a natural looking channel, use the creek as a visual. amenity to the project and maintain the falls.
During the time between now and the ultimate developcent, the potential for
erosion in this reach can be reduced by widening and adding revetment to the
channel. velocities by approximately 20 percent.
This will be beneficial in three ways.
the sediment transport capabilities of the stream and thereby decrease the potential for creek erosion. reduciq the peak flaws at the lagoon. reduce the potential for erosion.
Plans for the developn=nt of
The mers plan to develop
Ultimately the owners would like to
Adding 30 feet to the width of the dirt channel will reduce the
bering the velocities will decrease
Revetmnt of the creek banks will
It will also make a dl contribution to
21
TABLE THREE
S" sOuRa3 SUMMARY
Wproximate annual average erosion rates frcm each source in cubic yards per
year:
Main channel erosion: 25 , 000
Grad& areas: 15,000
Agricultural: 13,000 (~UTel'ldy) Natural erodible areas:: 12 , 000 Side chameel erosion: 11,000
22
Detention basin del (Wl.)
&cause the future condition wuld have the major long range impact on the
lagoon, the future condition was then modeled with eight detention basins.
The basin locations had dl been died in the Phase One study. Ttm of than were re-sized based upn mre detailed topgraphic infonnation. The two re-sized basins *re at 13rengle Terrace Park and at Monte Vista School.
Detention Basin Locations
The detention basins in Vista (shuwn in Figure 4) are located at:
1.
2.
3.
4.
5. Brengle Terrace Park
6. mnte Vista Sc-1
The other Phase (be detention basins are located at:
7.
8.
Creek crossing Warmlands Avenue, apprcoCirnately 200 feet Northerly of Elm Drive
.Creek Crossing Wannlands Averme, appradmately 200 feet Northerly of
Suemark Terrace Creek Crossing Wannlands Avenue, appraxvM '
Sinaoloa Creek Crossing Ste1;We Lane on the north side of Vale Terrace Drive
tely 100 feetwrtherly of Calle
The canyon north of Mira Costa College in Oceanside
The canyon to the east of the extension of Elm Avenue
Creek Enhancement -1 (ws)
To del the effects of an enhanced channel, with vegetation, the detention
basins wre kept in place and the above mentioned channel was widened, The
channel in this third mdel had a bottom width.of 15' above Santa Fe Drive and a bottan wid* of 40 feet wide below Santa Fe Drive with side slopes of 2 to 1
and a Manning aoefficielnt of 0.04. The energy slope is abaut one quarter of a percent. This was the ~mst effective i.mprovem=nt to the del. Table 4 gives the sunanary of *t results of these new dels.
The 6 feet per second m axi." allowable velocity is attainable with 0.25 to
0.35 percent slope, a M-g coefficient of 0.040, 2:l side slopes and a 40 foot bottan in the upper middle reach reducing in width up the creek until it is about 15 feet wide.
Table 4 lists the summary of the peak flows and lag tims at the lagoon for
each del.
future condition, future condition with detention basins, and future condition with creek enhan-t for a location in the dmtm area of Vista, in the middle reach, and at the lagoon. CcknparisOn hydrographs are shown in Fiwe 6 for a point at the lagcan and a pint at Breeze Hill.
Figure 6 shaws graphs for the 2 and 100-year stonns in the
24
The watershed analysis was *fold. at reducixq the peak flows fran stom runoff were analyzed.
reduction ms evaluated.
Hydrologic watershed dfications aimed Sediment source
Reducing peak flows Will reduce the sedinment carrying capacity of the stream.
There is an expnential. relationship between the stream's sediment carrying capcity and the water flow. results in a MU& higher reduction in the sediment delivery to the lagoon.
Reducing peak flows alm has the side benefit of reducing flooding,
areas identified as areas of concern that will be benefited are in the iow
lying areas around the lagoon and areas in Vista.
Consequently a reduction in the storm peaks
Specific
Sediment source reduction will reduce the sediment rating curves of a
watershed. water flm to sediment transport. reduction for sediment control could be an order of xragnitude off.
the cost for greatly innproving the source control is relatively low, retum on
the dollar spent is very high.
The sedimerit rating cwves are a plot of the relationship of the
Hawever, The estimates of sediment accumulation
Encouraged by the peak flow reductions deled in the Phase One study, the data fran those original watershed mdels were reentered into the Army Corps of
Engineers Hydraulic Enqheerhq Center's H.E.C - I hydrology del and rerun on a mainfrarre ccB[Iputer in order to print hydrcqraphs for the spectrum of six storms. SO-year d the 100-year storms. Those six storms rere run for the Phase One's
"ESristhg Condition", '"Future Condition" and "Existing Condition with Detention", Very late in the Phase l'" analysis sam problems in scare of the
assumptions for these ircdels were noted and the watershed had to be rdeled.
The Phase One input data was used as a skeleton and a new watershed del was created for the Future condition. Since this is an ungauged watershed, the
model could not be calibrated. Appendix One describes the calculations for the
Future Conditions. developmnt types, Soil Conservation Service Lag, and SCS curve number for eqch
af the Phase One shhshs,
mre run on this del,
Future Condition, Future Condition with Detention and Future Condition with Detention and Channel Enhancement are copyrighted c 1985. Funding was not
allocated for this re-mdelling.)
These rere the 2-year, the 5-year, the 10-year, the 2!5-year, the
Tkese include a suna~lry of the soil types, future
The 2-year and the 100-y~~ hypthetical storm (Note: The future condition watershed models for
The
portion of the upper and the entire upper middle reach) is deled as a
trapezoidal channel having a bttan width of 20 feet, side slopes of 1.5 to 1
and a Pw coefficient of 0.02. that is king placed at Breeze Hill.
channel beginning below Brengle Terrace Park to College Avenue (a
This is typical of the Tri-lock,chamel
23
sm of H.E.c.- 1 pak flows and time to peak for future conditions at the
lagoon.
100 year:
Future oonditim
13,734 cfs 2.94 hours
With detmtion 11,431 cfs
2.95 hours
With enhancenent
9,231 cfs 3.28 hours
2 year:
Future condition
3,213 cfs 3.27 hours
with detention 2,590 cfs
3.. 28 hours
With enhancmt 2,130 cfs
3.82 hours
NO E’UTURE EXISTING BASIS
L1 ?.?“a CDMB 12%
ET“E cm” 26% ~2 EVNRE CHAN ~IBVTION 14% W1 F W/DE;T EXISTING 20% DET+ENH EXIT 52% ** ws E”c MIST 3 2%
** 45% FMIcfi Is DUE To
STORM EWW ATTENUATICH PLUS 6.5% REDUCTICIN IN ANNUAL SEDIMENT mTIcR3 DUE
To THE ”Im QF THIS SED= ExxEm
25
15,000
cFs I LAGOON
CFS
3,000
2 3 4 5 HOURS
10,000
5,000
0
2 3 4 5 HOURS
100-YEAR STORM
2,000
1,000
0
CFS
\ BREEZE HILL
HOURS
2-YEAR STORFi
c
5 4 ‘3
IiOURS
100-YEAR STORM 2-YEAR STORK
ABBKEVIATICN
FC FUTURE CHANNELIZED CONDITIW FD FUTURE DETEI!TIOII KOOEL FE FUTURE WITH DETENTIGN AIJD ENliAI,ICEIiED CHAKFIEL EODEL
Fi ljure 6 Hydrographs
26
To detedne the mst effective means to reduce sediment accumulation in the lagoon, its sedhznt budget rnust be estimated under different conditions. A sedimtnt budget is simply an accounting of th inflaw, outflow and stroage of sedimnt in the lagoon for a particular tim period.
Sediment inflow is determined by empirical relationships betwsn the variation
of sedhent discharye and flow rate during flood events. The sequence of flow rates, &wn as a hydrograph, are ocanputed for particular stoms using a
standard cqmtw del simlati. referred ~ as HtE-I,
When the sediment enters the lagoon, som settles aut, some is discharged to
the ocean, d scm ramins in suspension for a particular tinre period. The anrmnt settling aut is calculated using settling velocity relationships for each particle size. The imrsunt remaining is suspension is detemined by the difference in sdimmt inflw and the a"t settling aut in a particular the
period. The munt discharged to the ocean is the sediment concentration remahing in suspension at the outlet, dtiplied by the discharge volume.
Yist se is carried into the lagcon by a few large, infrequent floods, Consequently, the sediment budgets mt be averaged statistically over a long
pericd of time to estimate an average annual edkmt budget,
annual. sedhent budget can be calculated for different inflcrw and lagoon conditions to provide a ccgnparison of the average annual sedimnt accumulation in the lagoon under different conditions.
The average
Because of the eno~us ntrmber of calculations required to estimate average d sedinaent accumulation, it is best done using a ccrmputer del that simulates the "ent of both water and sediment through the lagoon system.
Such a ccanputer del was developed specifically for this study and is described in succeediq sections.
It should be noted that there are a great many uncertainties in mst of the calculations involved in detemimhg a sedimnt budget. budgets of this type auld be used for amparatin purposes only. Consequmtly sedirrrt3nt
sediment Inflow
The best Illethod for de- sediment discharge to the lagoon is to develop
a sedimnt rating curve for Buena Vista Creek. A sediment rating curve plots
suspended sediment against flm discharge measured at a particular point on the
stream, for mens Vista Creek.
based on sample data froan other streams.
Unfortunately, neither suspended sediment nor discharge data exists
Therefore, a sediment rating curve was constructed,
watersheds greater than
than those with dler dler watersheds =re
Strean gauge data fran 11 gauging stations on coastal streams south of Dana Point bere exarmned ' (see Appendix 4). The results shawed that streams with 100 square miles had different sediment rating curves watersheds. consequently only data frcm the five
used.
28
Sediment Source Control
M? Channel (W):
The average of 25,000 cubic yards of sediment
channel primarily occurred duriq the 5 years
source will not k “pletelv eliminated with
per year ercded frm the min
frm 1978 to 1983,
the channel rtdifications, the
Althouqh this
reach of the recc”d&i &cerrcent is at least three times the length of the
kadly degraded section frm where the 25,000 cubic yards cam. Protecting the
Main channel will reduce the sedinaent source to the lagoon by 25,000 cubic
yards per year, to the reduction in sedinaent delivery for the “Channel Enhancement”
alternative, because it is assumed that for every cubic yard sediment sou~ce
reduction there is a eorpespoilding rductio~ of a hzlf of a cubic yard of reduction in the sediment accumulation in the lagoon,
For the camparative analysis half of this quantity was added
Graded Areas (S2):
The adopted sediment control ordinances for graded areas are good and mney 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 15,000
cubic yards of sediment escaping frm fran these sites.
sand and gravel kgs are allowing sedimxk fluw into the storm drains and channels, surprise rainstorm,
Misplaced or broken
Smtimes the projects are caught with their gravel bags down by a
Education of the engineers, inspectors and contractors involved will probably
reduce this source to one third of the volute it is today,
Agricultural (S3):
A similar &cation program for agriculture could be as effective as education for grading. This would reduce the sediment source by an additional 5 percent,
Natural. erodible areas: This surce has such a lm concentration very little improvement can be mde.
Side Channel Erosion (Sl):
Three side channels that need reconstruction and enhancement have been
identified. Camino Real between Elm and Chestnut and next to &”e, south of Mamon, They are just west of Pamelo Drive, on the westerly side of El
According to the Vista City staff and the Carlsbad City Staff the side channel
arroyos at Pamelo and Monroe are in areas that are apprcvd f~r dei,*&qnezt,
The requirements for the developznts include repairing and premtincj these
arroyos.
The side channel arroyo on the vesterly side of El Camino Real beheen Eh and
Chestnut locations muld effectively be repaired using drup structures in the same mer as the recamended min channel repair in the upper middle reach.
This will reduce the total watershed s&imnt source by an estimated one percent.
27
accumulation further constricts outflows under the 1-5 bridge to approximately
tke existing lagoon level. The central cell discharges to the western cell
through a constricted culvert under Hill Street, or over the top of the roadway, if the water level rises high enough. The *stern cell discharges to
the ocean over the existing sharp crested weir. The railway bridge crossing does not significantly constrict flood fluws the. bestern cell, A sketch of the lagcon is Shawn h Figure 7.
A flood muting is a sequential calculation that CdLCulates outflow, water surface elevation, change in storage and average flow velocity for a given inflow and initial lag- oonditions. bathymetxy of Buem Vista Lagoon exists. elevation/storage relationship for each of the cells is estimated based on few pint soundlll * gs and available topogfrraphic survey.
4. Outflow frm each cell is desed by standard wir flcw or culvert flow formulae. the average cross-sectioned area for a given instant in time.
Unfortunately, no detailed survey of the
These are shown in Pspenaix
Therefore, the water
Averaqe velocities are simply calculated as the outflm divided by
Sediment inflm to the lagoon is asd to be unifody vertically mixed in
the Elm. When it reaches the lagoon, flow velocities drop considerably and
sedbwnt particles settle out. The rate at which they settle aut is &teed
by the particle settling velocity. For the median dianeter of each of the five size fractions, this value is ShaJn in Table W. It can be seen that there is
roughly an order of magnitude difference betseen the settling rates of each size fraction.
can therefore intrcduce another source of error in the sediment budget.
Dividing the sediment inflow into five discrete size fractions
sediment accumulation is detexrtined by the fraction of sediment that settles out while the sedimnt-laden flaw travels fran the influw to the outflck~ each cell,
Hill Street culvert ccanpletely mixes the sediment, so that sediment discharged
The -el for sediment depsition descrikd above is strictly valid only for quiescent unifonn flows in stilling basins. entering the lagoon will be highly turbulent, which tends to hinder settling of
sedimrtnt particles until the turbulence dies out. Unfortunately there is no feasible way to model this process, and calculating deposition based strictly on tjm of travel. may overestimate sediment accumulation particularly for the finer sediment fkactions.
of
It is assumed that flow travelling through the 1-5 bridge and the
to the nexk cell is uniformly mixed.
lh Bue~ Vista Lagcon flocd flows
The velocity of the flow in the lagoon itself can generate turbulence that can keep particles suspended, There is this 1- limit of sediment concentration in the lagoon for a particular average lagoon velocity, alternative methods of calculating this lower limit; and as is cc" 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),
There are ~~ny
30
TABLE SIX. SEDIMENT RATING CURVE
mTIcNms USED IN ANALYSIS
Sediment Particle Size gs (tons/day) Fa1 Velocity (ft/sec)
-5 -4 2.4
Clay (-004 mm 9x10 Q 1.31 x 10
-4
-3
-3 2
-5 3 Silts .004 - .016" 4x10 Q 1.15 x 10
.016 - ,064 1x10 Q 2.3 x 10
-2
-1
-5 3
-3 2.1 1.6 x 10 Q 3.28 x 10 Sar!!S .064 - .25 IIP~
.25 - 1.10 IIP~ 3.7 x 10 Q 2.3 x 10
The suspended sedkt data was broken down into five different size fractions
representing nuds, fine silt, coarse silt, fine sand and coarse sand.
plots are sham in Appendix 4.
data.
curves. as the straight line relationships shows in Table 6. calculating sediment inflow to the lagoon.
The
There is a large of scatter in the
Vp to an order of magnitude of scatter is typical of sediment rating However, the rating curves for each size fraction can be simplified These are used in
A portion of the coarser sediment discharge, often estimated to be an additional 20%, is carried along the channel bed as "bedload". This was not
included in the sediment inflcw because mst of the coarser material appears to be deposited in the Euena Vista Channel upstream of the lagoon, and because it represents only a snall portion of the total sediment load discharged to the lagoon.
The sediment inflow for a particular storm is calculated by integrating the
sediment rating curve with the inflow hydrcgraph for successive time increnents .
Lagoon qdriulics
In order to calculate the sediment accululation in the lagoon for a particular flood, a flood routing calculation must be carried out to determine the water surface elevations, volumes and flow velocities at different times, as the
flocd flows enter the lagoon.
For Euena Vista Lagoon this is ccanplicated, because hydraulically the lagoon
acts as three distinct cells.
inflow pint at Jefferson to the 1-5 embankment. outflm to the central cell that extends frm 1-5 to Hill Street,
The eastern cell includes the area fran the The ak"ent constricts Sediment
29
-_
TABLE7 . BUENA VISTA LAGOON COMPUTER MODEL RUNS
MIN
NO. INFLOY HYDRUCRAPH UCOON CONDITIONS SEIJlMENT ACCUIIUWTLON RESULTS -
In1 ti a1 Di 6- Hi 11 vacer Inflow Deposited charged Corcnts
1-5 Sc. Outlet Weir surface cons Lon6 x.7 r -- -
Frequency Watershed Yelr Width invert length clev XCVU
Conditions Elev fr culvert ft ft ft
90 IO hrrler weir at original
Iengrh:hfrting lagoon ~014.
1enghC:ExiStfng Inyoon evld.
89 11 (rutlet weir ae ociiinil
* I 2-yr Existing
2 5-yr Existing
3 257r Existing
4 1007r ~~i~ting
5 Z7r Future
6 5-yr Future
i 25yr Future
. 8 10lhyr Future
9 .27r Future
10 S-yr Future
11 2s-yr Future
I2 1-r Future
13 27r Future
14 5-yr Future
15 25-yr Future
16 lOO-yr Future
17 27r Future
18 3-yr Future
19 257r Future
20 1-r Future
21 Z7r Future
24 100-yr Future
29 27r Future
10071 Future
ft elev ft
5.8 15 2.0
5.8 1s 2.0
S.8 15 2.0
5.8 15 2.0
5.8 15 2.0
5.R IS 2.0
5.8 IS 2.0
5.8 15 2.0
1.5 1s 2.0
1.5 15 2.0
1.5 15 2.0
1.5 1s 2.0
5.8 loo 2.0
5.8 100 2.0
5.0 100 2.0
5.11 100 2.0
9.8 15 2.0
5.8 13 2.0
S.8 15 2.0
5.8 1s 2.0
1.5 100 2.0
1.5 100 2.u
5.8 15 2.0
5.8 I5 2.0
80 5.u 5.8
8u 5.8 5.8
80 5.8 3.8
80 3.8 S.8
80 5.8 5.8
ao 5.8 5.8
80 5.8 5.8
80 3.8 5.8
80 5.8 5.8
80 5.8 5.8
80 5.8 5.8
80 5.8 5.8
50 5.8 5.8
M 5.8 5.6
SO 5.8 5.8
50 5.8 5.8
a0 1.8 5.8
80 1.8 5.8
80 1.8 5.8
80 1.8 5.8
80 1.u 5.11
8U 1.8 5.8
50 5.8 5.8
50 5.8 5.8
10.915
26.5110
112.770
872.b40
20,050
51.b35
235,560
I, 147.620
20.185
S1.YZO
235 .%0
1.195.070
2U.OIS
51.165 -
1.143.265
20,060
51 ,6&0
235,965
1,145,875
20 ,060
1.1C7.030
20,075
1.1L9,200
31
10,095
Z4,IZS
1261510
767 .SO5
18.370
46.635
2oa,ns
I .011.46S
18,510
4b.985
208,595
I ,012.wo
19.240
46.510 -
I.Ol2.31S
17.545
44.945
204.525
994 * 9Y 5
IS ,6bS
Y63.440
18,275
1,021.505
89 11 bfrttng wtershed b lagoon conbittons; outlet ueir 80'
88 12 &xisting watershed 6 lagonn conditions; outlet weir-W'
92 8 Cxistlng lagoon b fut.vrter- shed cond.; outlet weir-80'
90 10 Exlrtlng lagoon b fut.Water shed cond.: ourlet weir-Uc,'
YZ 8 1-5 mi? lorered; no otki
lagoon changes
90 10 1-5 ueir lovered; no ocher
lagoon changes
89 11 1-2 weir lowered; no ocher lagoon changer
85 If 1-5 wlr lowered, no other lag- changes
66 14 Hill St. opened: outlet weir at SO*
91 9 Hill St. opened: outlet ueir at 50'
Mll St. opened; outlet
weir at 50'
---
88 12 Hill SC. opened; outlet
uelr ac SO'
87 13 Outlet weir lowered to
1.8' NCVD
87 13 O~tlet uelr lacred CO
1.8' WGVD
87 13 Outlet vcir lowered to 1.8' NCVO
U7 13 Outlet weir lwered to
1.8' NGVU
711 22 Combination run: 1-5,
Hill St. L 1-5 opened up
L(1 16 Coibtnatiat run: 1-5,
Hill SI., b 1-5 opened up
TABLE 7,
Run
NO. IN- MOROCMPN UCOOM CoMOlTlONS SIDIMEHT ACCUWLATIOW RESULTS
Inltlal 01.-
C-ntt n111 uater lnflou Dapsi ttd chbrgtd
St. Outlet Ycir aurEace tons toils rt 1-5 -- -
frrgu*ncy UatorDhd Mlr Width lnwrt hnsth .lev WVD condiclona clev fc eulmrt tc tt ft
tt el.. IC
31 1007r future 1.5
32 IW7r Fucurr I .5 -.
33 12-yr Future I .5
34 27r futum 1.5
3) 100-yr Exlsc. r/dcr. 1.5
36 100-7r Future 1.5
a37 lW7r ExIst.u/det. 5.8
38 LOO-yr Future I .5
39 1007r Tuture 1.5
0 LO 100-w Future -0 -3
100
100
lVU
I ou
200
IO0
15
100
IO0
LOO
-8.3
-8.5
5.8
5.8
5.8
5-8
5.8
5.8
5.8
100
100
IS
13
15
15
la
15
13
2.1)
I .8
I .a
1.7
1.7
1.7
2 .o
1 .8
I .a
-8.0
8.0
-8.0
-8.0
2 -0
2.0
2.0
2.0
2 .o
2.0
2.0
nil
no
8ci
80
80
80
50
80
80
80
uu
IU
80
50
M
50
50
M
53
w
1.8 1.8
1.8 1.8
1.8 1.8
1.8 1.8
1.8 1.8
1.8 1.8
1.8 5.8
1.8 1.8
1.8 1.8
1.8 1.8
1.8 l.n
L.6 1.0
1.8 1.8
5.8 5.U
5.8 5.8
s.u 5.1)
5.11 5.0
9.8 3-8
5.3 5.8
5.8 s.8
I, ICY ,310
-
20 .Ob0
34b,135
1,143,470
347,265
1,149,310
I, 143 ,b70
1.141.985
20.1115
>41),2W
Y ,JW
9,325
61.636
2.51b,77Y
48.565
..
1.901.OU2
33.92U
1.369 .Y IC 1.1 90,359
971 ,bkO
-
16.U10
282,YZS
965.935
3UJ.?IO
9b8.550
909.160
892.940
Ib.215
tbJ.545
6.360
8,6M
56,592
Z.ZZ5.230
43,YLIl
1.672.570
31,ZW
- - - Comblnation run: lntrlat
USEL- 1. n * : FATAL ERROR
->)OK of ne*. no.
ti5 15 Lontred HI11 St. rutvrri
--
80 20
82 18
86 16
87 13
83 17
80 20
18 22
71 29
7b 21
68 32
93 7
90 10
us 12
91 9
88 I2
YZ a
87 13
Invert to avoid above crr.
NO flar out of Basin z or 3
Note, program dld run
Loucrad Htll St. to 1.7. 18
avert above problem
CP Run t32 b 30 (for
ex1 sclng lagoon condl t l on4
Channel birulation: uidtii B
rrer-l/IO original con1 tptvh.
tlun v-IUX
Exircing lagoon condl t1on.:
Sar as t3e but depth lncrtsaod by 5 ft
IO' channel. SU'uldc, nrc.1
ecalcd dwn by racio ot
uidthD (gee SLU.DIT file!
lo' deep channel. 50'ulAc: thl8 in kat cane acetimi i.
IO' deep channel. IO' ulh
this 1. best cmae scrnari
vucutv Iaswn rith ohrnnrl
Future lrRoM u/ channel
Existing lagoon COndfLiUl1.
Lcvimed hydrology
Rev1 ~cd hydrology
Ltvtwd hydrolosf
Rcvf md hydrology
Ilrvl8ed hydrology
Revtsed hydrolony
qs is sediment discharye
p is the fluid density
V* is the shear velocity
IBn is the man velocity
w is the particle fall velocity
h is the depth
yf$ is *e kinemtic viscosity
This lower limit is particularly important in estimating net accundation of
the finer sediment fractions.
The total sediment accurrrulation for a particular flood hydrograph for each cell can ke estimated by surrsning the accumulation in each time period.
The (2on-p uter plbdel
A ccanputer del was developed to simulate sediment acwation in the three
cells of Buena Vista Lagcon for a given inflaw flood hydrograph. This model, identified as MPOND c FWA 1985, was an adaption of an earlier lagoon flood rout- model with the additim of sediment routhg subroutines.
The input data required is the inflow flood hydrograph, sedhent rating cu~ves for each sediment size selected, lagcon geometry, and weir and culvert-. characteristics.
accumulation, and sedimnt discharge, for each fraction for each basin in the lagoon. The ccanputer mdel also calculates inflow, outflaw, wter surface elevation ad velocities of each basin for each hour.
hydrograph pericd the -1 calculates the total sediment accumulation and discharge for each basin.
The output is a amputation for each hour of the sediment inflaw, sfament
Over the entire
A total. of 50 ccmputer runs were ded aut to examine the dinations of different scenarios of watershed conditions and lagoon hydraulics.
sx"ry of these ~uns is shown in Table Seven. Forty-four of the runs ere carried out based on FEZ-1 inflow hydrographs representing three different watershed conditions that were develop& in the Phase One study.
A cqletz
These wsre:
33
Y3
1, misting conditions
2. Future conditions with no action
3. misting conditions with detention basins.
For each condition the 2-year and 100-year flood hydrograph was analyzd, and in sane instances the 5- and 25-year hydrograhs as tell,
errors tere found in these HEC-1 hflm hydrographs.
recalculated and six additional computer runs based on three new sets of hydmqraphs were carried out:
Late in the study, Accordhgly they w=re
4. Recalculated future conditions with no action
5. Recalculated future Conditions with detention basins
6. Recalculated future conditions With detention basins and preserving the
floodplain upstream,
A surc~nary of the influw hydrographs used is qiven in Table Eight.
Although the earlier HEC-1 hydrographs wxe not accurate, the ccmputer modelling results can still be used as a basis for comparing the effectiveness of different dfiations to the hydraulics of the lagoon, lagoon hydraulics conditions were examined, either individually or in
dination:
Five different
1. Ekisting conditions
2. Remmhg the sediment accumulated under the 1-5 bridge
3. Enlaxying the Kill Street culvert
4. increasing the capacity of the outlet wir by widening and lowering its
crest
5. Esrcavating a deep channel through the lagoon frm Jefferson Street to the outlet weir.
The average annual sediment accunilation for selected scenarios is shown in
Table Nine.
probability curve usbq the 2-year and IOO-year amputer run results for total sediment accumulation and then calculating the average annual sedinvtnt adation by the mthcd described in the ASCE Sedimentation Engineering
Handkook Table 4.18.
These values are detennined by plotthj a sediment accumulation
Table Nine shows that average annual sediment accumulation in about 33,000
tons/year under existing conditions (scenario I).
20 acre feet per year which, averaged over the whole lagan, is abaut 0-1
ft/year. At this rate the lagoan wuld fill h ccmpletely in twenty tu thb2y years.
This am~unts to about
sediment accumulation of 33,000 tons/year, assuming a trap efficiency
34
--
Source
Fld Flood
Watershed condition
~ -~ Return Peak Flow vo3.um cfs acre ft. Frequency
Phase I study
Phase I study
Phase I study
Phase I study
phase I study
Phase I study
Phase I study
Phase I study
Phase 1 study
Phase I study
Phase I1 study
Phase I1 study
Phase I1 study
Phase I1 study
phase I1 study
Phase I1 study
Existing
Existing
Existing
Existing
Future
Future
Future
Future
Existing w/det
Existing w/det
Future
Future
Future w/det
Future w/det
Future w/det & fp
Future w/det & fp
2
5
25
100
2
5
25
100
2
100
2
100
2
100
2
100
1371
1979
3659
7200
1712
2485
4412
8000
1227
5044
3213
13734
2590
11431
2130
9231
429
608
1067
1942
539
741
1245
2145
414
1553
428
1583 -
1483
314
1351
35
TABLE "E, LbGcoN AND mmm s="s
Avg. Annual
Simulation Watershed Hydrograph Iagmn ccarrputer Sed, Accu. 8 source cod. Runs (tons) reduct. No. Coditions
32,970 N/A 1 Existing Phase I Existing 1,2,3,4
2 Future Phase I Existing 29,30 73,550 0
3 Phase I Future 13 Future CQnb, 32,34 64,230
4 mture Phase I Future
Ccanb, w/channel 40,41 56,280 23
5 65 Existing wldet Phase I misting 37,44 25,490
6, Existing wldet Phase I Future
Ccsnb, w/channel 42,43 19 , 840 73
Phase I1 Existing 45,46 191,500 0 7 Future
8 20 mture w.det Phase I1 Existing 47,48 153,600
w det of fldplain Phase I1 Existing 49,50 105,100 45
36
U
I- D a- 0 0 3
of about 903, corresponds to a watershed sedhxmt yield of 1500
tons/squaremile/year, a value fairly typical of this area,
closely to the observed historic rate of accumulation of approximately 35,000
tons/year. Haever, such a correspnclence should be regarded as fortuitous because of the large potential errors inherent in analyses of this type.
It also corresponds
Sedimmt accumulation under future watershed conditions with increased urbanization and no sediment control is projected to increase by a mltiple of
six to about 200,000 tons/year (scenario 7).
inpeak flaJs frcan storm drains, lined channels and paved surfaces, and the
expnential relationship betrzjeen s-t delivery and flcw rate. The resulting predicted watershed sedhent yield of 7,500 tons/square mile/ye.a- is
not unmn in urbanizing watersheds of this type.
200,000 tons/year if distributed equally in the lagoon, could fiii it ip1 €ow to five years.
This is due to the increase
A sediment accumulation of
The hture of the Lagmn
If no action is taken and the existing sedimentation rates continue, most of
the lag-oon will probably fill with s-t within the next 20 to 40 yeass. Hwver, because of additional urbanization in the watershed (underway or
planned), and the filling of the Buena Vista Creek floodplain, mst of the lagoon might fill in in the next 10 to 20 years. ccm gradually butmre likely as a result of 2 or 3 major floods.
Consequently, the rate of filling will depend on the sequence of wet and dry
years.
Tkis sedimntation wuld not
There are two strategies for ducing sedimentation in the lagoon:
reduce s-t inflow or inprove the flushing ability of the lawn, Table
One shows the relative successes of these tsm strategies. alternative for mitigating increased sedimnt flows to the lagoon is channel
enhancement (Alternative W. Channel enhancement was rdeled frm downstream of Brengle Terrace Park to South Coast Asphalt, Vaxious channel configurations
will accxxnplish this goal but a maxi" velocity of 6 feet per second xlust be
maintained,
check structures along the cr& and recontour the channel as necessary, This velocity will dlcw for the growth of riparian vegetation; haever, in many areas the existing "natural" channel will have to be redesigned, drop
structures installed, and creek banks revegetated to meet this velocity goal.
Fortunately ve have a mdel to follow. Gully restoration was acccmplished in
the Tahoe Basin using check structures, These have been in place for several
years. Not only does channel enhancement decrease peak flood flaws to the lagoon mre effectively it also decreases the erosion hazard for the major
source of sediment to the lagoon,
either
The mst effective
The key to keep- the velocities at this level will be to install
Mmst as effective in decreasing peak flocd flows is the design, installation
and maintenance of eight storm attenuation basins (Alternative WI). The location of these and the channel enhancement are shown on Figure 4. the attenuation locations were mdeled in the Phase One study. Tt;o ere
rdeled, based on mre Zetailed toposraphy.
.sP1 of
37
The effectiveness
They only achieve
seen by ccmparing
of individual. mdifications in the lagam is negligible,
the 13% reduction when implmted together,
runs 9 and 12, 13 and 16, 17 and 20, with 29 and 30, and with This can be
32 and 34, as shown in Table Seven,
In its present state, lMnaged as a fresh water lake, %em Vista Lagoon is a
very efficient sediment trap,
it, sedinrent fran the lagoon is to restore it to tidal action. However, because the sediment dischaye to the lagoon is now so large, even with tidal action the lagoon dd probably silt up to a fraction of its original size, with the best pssible scenario of watershed impruveinents, considerable amounts of SediImk will have to be renrrwed in order to maintain the lagoon in its existing state,
To pdct the amount of dredging required, flaw msurenmts and at
samples will have to ke taken on mens vista Creek and at the outflow weir in
order to calculate a mre accurate sedi"t fiudget. bathymetric surveys will need to be made of the lagoon to msure actual sediment accumulation,
watersheds, the average dredging requirement probably will be in the range of 10,000 to 100,000 trms/year, assuming the watershed dfications are implemxked, of suitable size for beach replenisfrment,
It traps about 90% of all sediment which enters
The only hydraulically feasible way of greatly increasing the flushing of
Even
In addition, periodic
Based on the existing analysis using data frm other
probably betseen five and twenty percent of this sediment will be
VI,
1, -
2,
The Taqoon's mture
In its existing state Buena Vista Lagcon acts as a very effective sedimnt
trap. lagoon will silt in over the next benty or thirty PmSr with mst of
the siltation occurrkg during a few large storms. Under future watershed conditions the rate of siltation will increase substantially, reducing the
expected lifetime of the lagoon to less than ten years,
effective means of reducing sediment accumulation in the lag- is to
reduoe sediment inflaw fran the watershed.
laqoon can be reduced by about 50% by reducing flood peaks in the
Under existing watershed conditions it appears that the entire
The most
sedinaent acnmdation in the
watershed and enhancing the creek, thereby reducing SediREnt inflow,
To reduce sediment entering the lagoon fran creekbed erosion, a "m channel velocity criteria of six feet per second is required, effective and was modelled as the maximum velocity that vegetation could conceivably withstand, more effective,
This is
her velocities are recQmranded and will be
All initial creek design should check flood control requirements, and utilize the "I velocities using Manning roughness coefficients of
0.030 to 0.050, which is the range of the vegetation growth roughness in the channel, So the velocity of the 100 year storm should not exceed six
40
It is evident that there is a ptential for decreasing lagoon sedimentation by
about 453 by reducing flccd peaks under future conditions by constructing detention basins and preserving and enhancing the floodplain upstream (Alternatives W and WS) (.
The third most effective mthod of reducing sediment to the lagmn is stopping
the soil loss frcm grading and agricultural operations, for the three cities adequately require sedinent control for grading operations.
are effective to amply with the ordinances. Agriculture is still a major
soure of sdmnt and there appears to be no ordinances for this source.
Agriculture will probably dwindle to be very snall within 20 years, as the watershed is urbanized.
The grading ordinances
An education process still needs to occur for the methcds that
This study envisions a program of education for the City personnel who check
grading plans and the operators and building inspectors who are responsible for
Lhe outcam of these plans.
requirements of the erosion control ordinance and specific recomnendations for
cost-effective design and implemntation of the ordinance.
me education prcgram muld give a review of the
Similiarly the agricultural education program Fxnild focus on agricultural
operators and the Soil Conservation Service and emphasize cost-effective implemntation of best management practices in the watershed.
Small mmts of the total sedimentcanberemovedinm sediment basins lccated at South Coast Asphalt ard the muth of the lagcon (Alternatives S4 and
S5). the material could probably be used on the site. sediment basins is that it is less costly to remve the material at these locations than after it reaches the lawn. The nature of the material remJved
will be sandier than the total sedim;nt acdating in the lagoon, therefore a mm usable mterial,
The one at South Coast Asphalt will require less costly mintenance, as
The advantage to these
The sdimmt frm side channel arroyos can be effectively controlled by
repairing the arroyo and preventing further erosion (Alternatims Sl). These would be repired in the same fashion as the main creek channel.
Sediment inflaw can ke further reduced by control of sediment sources in the watershed, easily quantifiable. Hcwever, it is not unreasonable to suqgest that vigorous application of such "r es CMitd reduce the sediment load by about 50%-
This, cmbined with reduction of the El& peaks, muld mean that the sediment inflm wuld be reduced to about 30% of its expected future value.
The releative success of these sediment control masures is not
In contrast, ncdifying the lagcon hydraulics is not nearly as effective in
rducinq sediment accumulation. - clear- the 1-5 bridge, wid- the Hill Street culvert and lmerinq and
widening the outlet eir, the sedimnt accurrrulation reduces only by 13%. Even with these modifications, maintaining a deep channel througfi the entire lagoon
reduces sediment accumulation by 23% (Alternative L2).
require constant maintenance as it Would tend to fill with sedimnt resuspended by mve action in the summer, and is not a very practical option.
With all the reasonably feasible dficaitons
A deep channel would
39
.
The fact that this is a ccqletely ungauged watershed gives the findings of this study an mt of uncertainty. mre accurate estimates of flood flaws, sediment transport and sediment accumulation rates can be observed. The mdels used in this study then
can be calibrated and the accuracy inprd greatly.
Rain gauge and stream flcrw mnitoring are needed to calibrate watershed Wls.
regarding stonn flow values.
There is a need for dtoring so
These will also help to answex many of the local questions Present estimates of these stom flow values
vary wildly.
Sediment sampling in the creek Will provide more definite correlation be- the sediment flaws and the flood flows. This will help develop a
sedimnt rating curve for the Buena Vista watershed.
Bathymetric surveys of the lagoon need to be taken, especially before and after major stom events in order to monitor the sediment accumulation .
42
3.
4.
5.
6.
7.
feet per second using a Manning roughness coefficient of 0.030 and the
finished floor elevations should be one foot higher than the anticipated water surface elevation using a "ning coefficient of 0.050 for 100-year
storms.
A low flow channel should be designed to accorrmodate the 2-year stom
flaws, possible. velocities and banks revegetated to prevent erosion. cross section is shown in Figure 5.
This lm flaw channel should be configured to be in shade wherever
Drop structures should be placed in the channel to lower
A typical stream
The lower middle reach is absorbing large quantities of sediment and is
presently offering a significant buffer for the lagoon by acccxMdating
great quantities of sediment being transporteti in the creek, of the fldplain must ke preserved in its present state.
This section
Detention Basins (Wl)
The eight detention basins outlined on Fipe 4 should be built and maintained.
be the design criteria for these basins.
Maximum peak attenuation for the 2 to 100-year stonns should
Lagcon Mfications (L1)
The mst effective mthcd of decreasing the sediment accumulation in the
lagoon with lagoon enhancement is a ccanbination of a mwhle crest teFr with a width to 80 feet, enlarging the opening at Hill Street to 100 feet wide, excavating the material under the freeway, and breaching the
barrier beach during storms.
sediment accunrulation by only 13% and has many enviromtal drawbacks.
This scenario of improvements reduces
Continuing Erosion Control Elfucation (S2 and S3)
The fixst erosion control wrkshop was ell attended. ccaranunity aCanmitnEnt to erosion control. both for grading and agriculture will pay off well in terms of reducfns
sediment accumulation in the lagoon be beneficial.
There seems to be a
Efficient erosion control
sediment Basins (S4 and S5)
The txm feasible locations for sedimnt basins are at South Coast Asphalt
and just upstream of Jefferson Street.
Drdgbg
Even with all of
have to continue compared to this
the effective mthcds outlined herein, the lagoon will to be dredged periodically. The alternatives were all
inevitable and ongoing solution.
41
..
ASCE "ais and Re” on Ehgineerhg Practice, No. 54, 1975. sedimentation
Hofhan, J. S., et d. 1983. Projecting Future Seal. &vel Rise, Wthdoloqr,
Estirrates to the Year 2100, and Research Needs. A Report of the
U.S. Eh~omental Protection Zgency.
Sinr>ns, Li & Associates, Fort Collins, 00. 1984.
Project on Beach Sand Replenishrent.
of Fedamtion.
U.S. Army Corps of Engineers, 1973.
Creek, Pacific Ocean to Vista, San Diego county, CA.
county.
Yalh, M. S., 1972. Wchan~ ‘cs of Sedkmt Transport.
United States Geological Survey Water Resources Data for California, 1975-82.
United States Geological my, Wo Park, CA.
and Engineering, v. Van&, ed.
Effect of the Santa Margarita
Prepared under contract with the Bureau
Flood Plain Infoxnation, Buena Vista Prepared for San Diego
Pergmn Press, Oxford.
..
43
APPENDIX ONE
SUBBAS INS
FUTURE
HYDROLOGICAL CONDITIONS
CALCULATIONS
.
7 com 0.0 650 6000 3500 0.05 572
0.0 HDR
MDR 0.0
LDR 0.0 COMPOSIT FMST D 100% 86 86.0 CN LAG (HR)
..
0.0 86 0.3224
8 COMM 0.0 900 4000 2500 0.05 1188
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 LDR 0.0 COMPOSIT FMST D 100% 86 86.0 CN LAG (HR) 0.0 86 0.221 8
10 COMM 0.0 650 6000 2500 0.05 572
HDR 0.0 MDR 0. 0 LDR C 50% 84 42.0 COMPOSIT FMST C 50% 82 41.0 Cl% LAG (HR)
. 3.0 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 2500 0.035 158
HDR 0.0 MDR C 40% 86 34.4 LDR C 40% 84 33.6 COMPOSIT FMST 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 30X 87 26.1 COMPOSIT FMST 0.0 CN LAG (HR) PARK D 70% 82 57.4 84 0.1378
A-2
b!ATi!?SHED SUBBASIN FUTURE CHARATERISTICS 0.38 LAG = 24n( L X Lc/SQRT s)
SUB- LU SOIL % BASIN
1 COMi.1 HDR F.1 D R
LOR FMST
2 COMM D HDR D
MDR D
LDR
FMST
3 COMM HDR MDR LDR FMST D
4 COMM D HDR D MDR D
LDR
FMST D
5 COMM D HDR D MDR LDR
FMST
6 COMM D HDR D MOR D
LDR
FMST
D 40%
D 20%
D 40%
40%
40% 20%
100%
30% 30% 20%
20%
50%
50%
50% 30% 20%
scs
C N
92
88
86
92
90
88
86
92
90 88
86
92 90
92 90 88
CN ELEV LENGTH PC-CNT BASIN SLOPE
X 7, DIF L (FT) Lc (FT) n (FT/bSI)
36.8 220 3500 1800 0.05
0.0 17.6 0.0 COMPOSIT
34.4 CN LAG (HR)
0.0 89 0.2263
H- I
36.8 150 3500 1400 0.045
36.0
17.6 0.0 COMPOSIT
0.0 CN LAG (HR) 0.0 90 0.1991
0.0 700 4000 2200 0.05
0.0
0.0 0.0 COMPOSIT
86.0 CN LAG (HR)
0.0 86 0.2115
27.6 340 4700 2200 0.045
27.0 17.6 0.0 COMPOSIT
17.2 CN LAG (HR) 0.0 89 0.2394
46.0 50 3000 1500 0.03 45.0
0.0 0.0 COMPOSIT
0.0 C N 0.0 91 LAG (HR) 0.1537
46.0 150 2500 1000 0.03 27.0 17.6
0.0 COMPOSIT
0.0 CN LAG (HR)
0.0 91 0.0964
332
22 6
924
382
88
31 7
n4
.
21 COMM D 30% 92 27.6 100 10000 6000 0.03 53 HDR D 30% 90 27.0 MDR D 30% 88 26.4 LDR D 10% 87 8.7 COMPOSIT
FMST 0.0 CN LAG (HR)
0.0 90 0.4534
22 COMPI C 50% 91 45.5 80 2000 1000 0.028 211 HDR B 50% 82 41.0 MDR LDR FMST
0.0 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 87 0.0893
23 COMM D 40% 92 36.8 220 9000 4000 0.028 129 HDR D 20% 90 18.0 MDR D 30% 88 26.4 LDR D 10% 87 8.7 COMPOSIT
FMST 0.0 CN LAG (HR) 0.0 90 0.2941
24 COMM C 60% 91 54.6 85 4000 2000 0.028 112 HDR C 30% 88 26.4 MDR C 10% 86 8.6 LDR 0.0 COMPOSIT
FMST 0.0 CN LAG (HR) 0.0 90 0.1705
25 COMM C 40% 91 36.4 180 5000 2500 0.03 190 HDR C 20% 88 17.6 MDR C 30% 86 25.8 LDR C 10% 84 8.4 COMPOSIT
FMST 0.0 CN LAG (HR) 0.0 88 0.1 958
26 COMM 0.0 170 .5000 .2500 0.035 180 HDR 0.0 MDR D 100% 88 88.0 LDR 0.0 COMPOSIT FMST 0.0 CN *LAG (HR) 0.0 88 0.231 0
27 COMM C 20% 91 18.2 200 6000 3000 0.035 176 HDR C 20% 88 17.6 MDR C 60% 86 51.6
LDR 0.0 COMPOSIT
FMST 0.0 CN LAG (HR) 0.0 87 0.2663
A-4
14 COFlM 0.0 600 10000 4000 0.05
HDR 0.0
MDR 0.0 LDR C 30% 84 25.2 COMPOSIT FMST C 70% 82 57.4 C N LAG (HR) 0.0 83 0.4609
15 COHM 0.0 250 3000 1600 0.035
HDR 0.0
LDR C 40% 84 33.6 COMPOSIT YDR 0. e
FtvlST 0.0 CN LAG (HR)
PARK C 60% 77 46.2 80 0.1354
16 COMM B 40% 90 36.0 250 3200 1500 0.03 HDR B 40% 82 32.8
MDR 0.0
LDR B 20% 78 15.6 COMPOSIT
FMST 0.0 CN LAG (HR)
0.0 84 0.1175
17 COMM B 60% 90 54.0 250 3000 1000 0.03
HDR 0.0 U MDR B 40% 80 32.0
LDR 0.0 COMPOSIT
0.0 CN LAG (HR) 0.0 86 0.0970 FMST
18 COMM C 40% 91 36.4 250 9000 5000 0.028
HDR C 20% 88 17.6 MDR C 20% 86 17.2 LOR C 20% 84 16.8 COMPOSIT
FMST 0.0 CN LAG (HR) 0.0 88 0.31 24
19 COMM 0.0 500 6000 3000 0.05
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 0.31 96
20 COMtil C 30% 91 27.3 250 9500 5000 0.035
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)
31 7
440
41 3
440
c
147
440
139
0.0 87 0.4027
A-3
35 COMM D HDR 0 MDR D LDR FMST
36 COMM C HDR D MOR D LDR FMST
37 COMM HDR MDR D LDR FMST
38 COMM HDR C MDR D LDR FMST
39 MDR A MDR C MDR D
40 MOR C MDR D
0
41 MDR C MDR D
1 0%
20% 70%
1 0%
20% 70%
100%
40% 60%
10% 20% 70%
30% 70%
60% 40%
92 9.2 200 5000 2000 0.035
90 18.0 88 61.6 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 89 0.2057
91 9.1 200 4000 2000 0.035
90 18.0 88 61.6 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 89 0.181 1
0.0 370 4500 2200 0.035
0. 0 88 88.0 0.0 COMPOSIT 0.0 CN LAG (HR)
0. 0 0.1787 88
0.0 340 5500 2500 0.035
88 35.2 88 52.8 0.0 COMPOSIT 0. 0 CN LAG (HR) 0. 0 88 0.21 38
0.0 340 4000 2000 0.035 73 7.3
86 17.2 88 61.6 COMPOSIT 0.0 C N LAG (HR) 0.0 86 0.1638
0.0 320 3500 1500 0.035
0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 87 0.1376
86 25.8 88 61.6
0.0 280 6000 3500 0.035 86 51.6 88 35.2 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 87 0.2649
A-6
21 1
264
434
326
449
483
246
28 COMM C HDR D MDR D LDR
FMST
29 corm HDR MOR D LDR
FMST
30 COMM D HDR D MDF? D LDR FMST
31 COMM C HDR D MDR D LDR FMST
32 COMM D HDR D MDR D LDR FMST
20%
40%
4 0%
100%
20% 30% 50%
20% 50% 30%
40%
30%
30%
91 18.2 780 4500 2500 0.035 90 36.0 88 35.2
0.0 COMPOSIT 0.0 0.0 CN 89 LAG (HR) 0.21 51
0.0 120 4000 1800 0.035 0- 0 88 88I0
0.0 COMPOSIT
0.0 CN 0.0 88 LAG (HR) 0.1918
92 18.4 150 5000 25.00 0.035 90 27.0 88 44.0
0.0 COMPOS1 T
0.0 CN LAG (HR) 0.0 89 0.2365
91 18.2 220 3400 1500 0.035
90 45.0
88 26.4
0.0 COMPOSIT
0.0 CN
0.0 90 LAG (HR) 0.1454
92 36.8 260 7000 3500 0.035 90 27-0 88 2614
0.0 COMPOSIT
0.0 CN 0.0 90 LAG (HR) 0.2933
33 COMM HDR
MOR D 100% LDR
FMST
34 COMFl D 50% HDR D 30%
1 DR FMST
MDR D 20%
0.0 180 4000 . 2200 0.035
0.0 88 88.0
0.0 COMPOSIT
0.0 CN LAG (HR) 0.0 88 0.1916
92 46.0 180 4700 2500 0.035 90 27.0
88 17.6
0.0 COMPOSIT 0.0 0.0 CN 91 LAG (HR) 0.2205
21 1
158
158
342
196
238
202
A-5
0
49 COFlM C 40%
HDR D 20%
MDR 0 40% LDR
FMST
50 COMM HDR
MDR A 100%
LDR FMST
91 36.4 280 6500 2200 0.035 227
90 18.0 88 35.2 0.0 COMPOSIT
0.0 CN LAG (HR) 0.0 90 0,2324
0.0 330 7000 3000 0.035 249
0.0 73 73.0
0.0 COMPOSIT
0.0 CN LAG (HR) 0.0 73 0.2644
A-8
L.
42
MDR C MDR D
43 MDR C MDR D
44 MDR C MDR D
45 COMM HDR MDR C
LDR FMST PPRK C
46 COMM C
HDR MDR C
LDR
FMST OPEN C
47 MDR C MOR C
48 COMM D COi4M C HDR D MDR D FCiST
60% a6 40% 88
50% 86 50% 88
409, 86 60% 88
30% 77
70% 86
10% 91
80% a8
10% 71
30% 86 702 88
40% 92
40% 91
10% 90
10% 88
0.0 240 3000 1500 0.035 422
51.6 35.2 0.0 COMPOS IT
0.0 CN LAG (HR) 0.0 a7 0.1331
0.0 220 2500 1200 0.035 465
43.0
44.0 0.0 COMPOSIT
0.0 CN LAG (HR) 0.0 87 0.1121
0.0 240 4500 2000 0.035 282 34.4
52. a 0.0 COMPOSIT
0.0 CN LAG (HR) 0.0 87 0.1871
0.0 280 4000 1500 0.035 370 0.0 23.1 0.0 COMPOSIT
0.0 CN LAG (HR) 60.2 83 0.1523
9.1 240 4500 2000 0.035 282
0.0 70.4 0.0 COMPOSIT
0.0 CN LAG (HR) 7.1 87 0.1871,
260 3900 1500 0.035 371 f. Tr V. v
25.8
61.6 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 87 0.1478
36.8 220 4500 3000 0.035 258 36.4
9.0 8.8 COMPOSIT 0.0 CN LAG (HR) 0.0 91 0.2220
A-7
ANMUAL COSTS
DREDGING:
LAGOOM IM EXISTING COF.IDITIOFI
WATER SHED IN FUTURE COI\JDITION 191 , 500 CY SEDIMENT DELIVERY X $7.35 /CY =$1,407,525
LAGOON MODIFICATIONS:
LAGOON UITH 80' LOMERIIJG WEIR, 100' HILL ST. BRIDGE & DREDGING AT 1-5
WATERSHED IN FUTURE CONDITION WEIR: OPERAT ION AND MA1 NTANENCE : HILL ST: $140,000 INITIAL COSTS LIFE: 50 YEARS =
1-5
$400,000 INITIAL COSTS LIFE: 20 YEARS = $20,000 $20,000 $2 , 800 LIFE: 2 YEARS = $1 5,000 $57,800 $30,000 INITIAL COSTS TOTAL ANNUAL COSTS:
LAGOON CHANNEL DREDGED 10' DEEP 100' WIDE *
WATERSHED IN FUTURE CONDITION 268,500 CY X -$15 PER CY =
$4,027,500 INITIAL COSTS LIFE: 2 YEARS = $2,013,750
DETENT ION BAS INS
LAGOON- IN EXISTING CONDITION UATERSHED IN FUTURE CONDITION NITH 8 DETENTION BASINS LAND: 19 ACRES X $130,000 PER ACRE = $2,470,000 LIFE: 50 YEARS =
CONST'N: $1 1 , 500 EACH X
MAINT:
- 83 $92,000
LIFE: 10 YEARS =
TOTAL ANNUAL COSTS:
$49,400
$9,200 $1 30,000
$1 88,600
CREEK ENHANCEMENT
LAGOON IN EXISTING CONDITION
WATERSHED IN FUTURE CONDITION WITH 8 DETENTION BASINS LAND: 1,050,000 SQ FT X $4 PER SQ FT =$4,200,000
DROP STR $5,000 EACH X 160 = $800,000
LIFE: 50 YEARS = $84,000
LIFE: 5 YEARS = $1 60,000
TOTAL ANNUAL COSTS: $244,000
SIDE' CHANNEL REPAIR DROP STR $3,000 EACH X 10 = $30,000 LIFE: 5 YEARS = $6,000
TOTAL ANNUAL COSTS: $6,000
APPENDIX TWO
COST-EFFECTIVENESS
ANALYSIS
63
E7"MISTING BASIS 191,500 -
F+"oQMB 12% 168,520 22,980 FVNRE (2a"N 26% 141,710 49,790 nrmRE CHANNEFEECT 26,810 MINIMUM
F W/Dm EXISTING 20% 153,600 37,900
DGT&ENEi EXIT 45% 105,100 86,400 E"c EXIST 48,500 MINIMUM
NO MlDIFICATIoN
WEIR-tHILL ST+I-5
CHANNEL DGT BASINS
CREm E"C E.C.R SME ARROYO
GRADED AREAS
AGRICUL~ S.=T SED BASIN m. SEDBASIN
$1,407,525
$57,800 $2,013,750 $139,200 $160,000
$6,000 $6,000 $6,000 $11,750 $5,360
- -
22,980 $168,903
26,810 $197,054 37,900 $278,565 61,000 $448,350 1,000 $7,350
5,000 $36,750 4,500 $33,075 2,500 $18,375 1,600 $11,760
A-11
CCST-
B.E"
RATIO
1.00
3.0 .1
2.0
2.8
1.2 6.3
5.6 1.6 2.2
SOL'TH COAST SEDIl4EKT BASI!.!
5,000 CY SEDIMEIJT DELIVERY X $2.35 "/CY = $11,750 A!Ji.!!JAL COSTS
JEFFERSO!! SEDIIXIJT BASIN
1,600 CY SEDIMENT DELIVERY X $3.35 */CY = $5,360 ANNUAL COSTS
*xIrlCLl!DES REDUCTIOFI I:! PRICE OF $4/CY FOR THE VALUE OF THE MATERIAL
A-1 0
... . --a
DISTANCE SECTION CROSS BETWEEN NUMBER SECTION SECTIONS AREA (SF) 100 655
101 243
102 139
103 51 9
104 526
105 645
106 520
107 581
108 384
109 1895
110 51 9
111 41 2
112 85
113 54
114 400
115 374
116 92.5
(FEET)
840 13,963
510 3,612
440 5,361
1,460 28,242
980 21,252
275 5,930
780 15,893
640 11,435
590 24,900
200 8,941
710 12,238
420 3,864
110 284,
460 3,869
640 9,170
300 2,590
171,542 TOTAL EROSION IN THE UPPER MIDDLE REACH
-.
.. .
APPENDIX THREE
MIDDLE REACH EROSION
CALCULATIONS
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A-14
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A-15
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