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HomeMy WebLinkAbout; Buena Vista Lagoon Watershed; Sediment Control Plan; 1985-09-03BUENA VISTA LAGOON WATERSHED SEDIMENT CONTROL PLAN CALIFORNIA STATE COASTAL CONSERVANCY Prepared by June Applegate %t Associates Philip Williams & Aasociatss =- JUNf APPLEGATE & ASSOC. CIVIL ENGINEERS BUENA VISTA LAGOON AND WATERSHED SEDIMENT CONTROL STUDY FOR THE CALIFORNIA COASTAL CONSERVANCY Coastal Conservancy 205 (J) grant Buena Vista Lagoon Sediment Management Phase I1 83-058-81-48-C BY JUNE APPLEGATE, P.E. September 3, 1985 2531 STATE STREET, CARLSBAD, CALIFORNIA 92008 (619) 729-7109 PmJEmTEpM coAsTAt 03blsERvANCy ?eter &enell, Zxtecutive Officer Alyse Jambson, Fhhar.cemnt Prcyram Manager Laurie Marcus, Project mger Pm h philip Williams, Principal Jane Kerlinger, Hydrologist I. TT ir. 111. Iv. V. Kt. VI1 . 12 12 13 14 16 17 19 23 23 28 37 39 43 FIGURE 2 FIGVRE 3 Natural conditions FIGURE 4 Detention Basin I.mations FIGURE 5 Proposes Channel apss Section FIGURE 6 Hydrosraphs FIGURE 7 SChaMtic Diagram of Buena Vista Lagcon TABLE 1 TABLF2 TABLE 3 TABLE 4 TABLE 5 TABLE 6 TABLE 7 TABLE 8 T- 9 mion control Alternatives sediment Size Distribution for sedimnt source SUmnaKy Different HydrograFhs SLmmary of HEC-1 peak flm ard Projected S€&im%t &ductions sediment Rating cuve %lationship 6uena Vista Iagtxm ccnplter -1 Funs SLmmary of Mlw yldrographs sunmq of hqam and matershed Sinulations tim to peak for future aditions at the lagam Used in. Analysis 9 5 10 26 38 6 18 22 25 25 29 31 35 36 Due to the rapid seoimentation of wlena Vista Lagoon, the California state Ccastal Conservancy Wed this study of sediment control for the lagoon and Leedshill-Herkenhoff of San Francism submnsulted and provided the hydrolcgy its watershed. A phase Cne stw3y was, psrfonned by Brown h Vcqt of Vista. mcdels of the watershed. 'Ihe findings of the Fkse One Study indicated that several alternatives needed to be evaluated for s-t control. The California State Water &sources control Board and the Coastal Conservancy then funded a Phase 'Itro Study. June Applegate h Associates of Carlsbad kas hired to perform the watershed trcdelling, project amrdination, and prepred the iqdraulic analyses of the lagoon. The primary goal of this study alternatives evaluation. Philip Williams & Associates of San Francisco is to fomlate a prioritized list of sediment BU- vista waterW and lagoon based on a wit-benefit anpzuison. managfatent procedures for the Buena Vista bgcm is the only freshw~ter laqccn in scuthern California. It is situated between Carlsbad and Oceanside. Its 19 square mile watershed includes mintained by a fixed weix at the muth of the lagcon. 'Ihe fills of the the cities of Vista, Cceanside am3 Carlsbad (see Figure 1). 'Ibe water level is railroad, Hill Street, Interstate 5 and Jeffersm Street cross the lagoon. Since the psition and size of the muth of the lagmn v.as mde permanent and the flcw restricted, there has been an increase in the sedimntation rate of the lawn. Increased urbanization in the watershed further accelerated the sedirrentation and necessitated the dredging of a portion of the lagoon. If projected future Lagoon auld be less than 10 years. sediment rates materialize, the Lifetime of Bum Vista THE maxm SYSTEM Buena Vista Lagoan created by the rapid rise in sea level after the last deposited in the lagam mas balanced by the rate of sea level rise. W ice age. In its natural state, it appears that the amunt of sediment factors have upset this balance. h? is the limitation of the lagam's ability to flush sediment to tk ocean by the pzaCanent of a & at the rrnuth and road fills that cross ard restrict the lagoon. The other is the -se in sediment deli- to the lagum fran the watershed. ?he cause for this increase is -fold. Urbanizatim has increased flm to the lagoon. haoadment upon the flccdplains that ace accepted sediment fran the creek durirq large stonn flaws has eliminated mst of this buffer and sediment now flaws directly into the lagoan. Before the hnnan-caused disturbances to the vatershed, creek, marsh, and lagoon much of the sediment fran the mtershed vms deposit& before it reached the Then in the lower reach, a large marsh area spread and filtered the stonn lagoon. Sedimnt uas deposited on the koad flccdplain in the middle reach. water, trapping mre sediment before it entered the lapn. . Figure 1 Regional Location - ! 1 r ! ; ! 1 I I I ! i ! ! I j 'I I ! ! ! I i [ i ! 1 ! i The only rennant of this pmtection system is the area test of south Coast Asphalt and east of the liav Street cul-de-sac. ?his reach of the creek is buffer to prevent sene of tk Sedirrent fran entering the lagwn. The best currently absorbing very We quantities of sedinwt and is the last natural functioning won of this reach is the thick riparian area just east of the Hayrar Street cul-de-sac. The other sediment buffer was the marsh above the lagcon. This msh has ken carrpletely filled. The cattails in the channel be- the shopping center and Highway 78 and on both sides of brume Street at Marmn Road are all that are left of this marsh. Before the fi1lb-q of the mrsh, the water slowed and found its way through the tules to the lagoon dropping mst of the finer sedimnt that wa5 left after tk riparian area upstream. After changes in the watershed, particularly urbanization in the last two decades, increased peak flow have dramtically transfozmd the natural hydrological system. “Ye increased flows not cdy discharge mre sedimnt fran tbe watershed into the creek, but, mre importantly, have caused the creek bed energy has caused this stream hcutting. The process will continue until a to start to ercde (degrade) in portions of creek. The increase in strem flcw new and lower equilibrium can be reached (see Figure 3). All of these factors contributed to the rapid filling of the lagam fmn 1978 to 1981, the years that marked the end of a 13” dry pericd in this region. In 1981 the eastern portion of the lagcon was dredged. The purpose of this stdy is to explore alternatives to continued dredging of the laqmn. THE SWY Hydrology -1s of the watershed ami hydraulic ncdels of the lagan vere developed and evaluated. Maximizirq tk flushing action of the lagoon resulted the in a dl reduction in the sediment acclmzlation rate. Greater reduction in se3mnt delivery rate can be prcdud by reducing the peaks of the stonn flows into the lagcon. Reductions in the peak flom ere Med by optimizing feasible detention basins in the upper reaches ard by eliq channel enhanmt that wxild slow velocities in the middle reach. Regional. sediwnt transpozt curves wre integrated with the inflow hydrographs in the hydraulic model of the laqcm. Because the quantity of sediment transported is an exponential function of the quantity of water, the peak flows are respndble for a laqe portian of tbe SedimMt transported to the lagoon. Reduciln3 tkse peak flam resulted in rmch larger reductions in seainrent flows into the lagcon. The study reviewed nine al-tive for control^ sedhentation of the lagaon (see Table 1). These inclwk: L1) moaify the lagam flushing action by increasing the teir size, the size of the Hill Street Bridge and clearing the opening under 1-5; L2) dredging a flw-tlucugh chnnel through the lagum fm Jefferson to the mir; Wl) canstrudion of stoxnuater detention basins in the upper watershed; IS) enhancenent of the main channel to lawer rnain channel 4 Fi7ut-e 3 Natural Conditions 5 .=-NE pspm EslmATm PEFawr ANNtIAL m- INITIAL ANNuAt m- COST BENEFIT COST OWCOST TICN FEDCC'N 1 RATIO 2 PHASE I1 L1 N€IR+HILT., sI+I-5 $570,000 $15,000 -12% $168,000 3.0 KDIFICATIb.IS: L2 CHANNEL $4,030,000 $2,010,000 14% $197,000 .1 trl DFT BASINS Const. $92,000 $139,000 20% $281,000 2.0 WATERSHED rnIFICA!rIcN m SEDIMEm souTa=E cix?lmL: ws CREEKEMIANC $800,000 $160,000 32% $440,000 2.8 smm SOURCE ccNmJL: S1 E.C.R. SIDE my0 $30,000 $6,000 1% $7,000 1.2 s2 GPAnIEL)maas $6,000 $6,000 3% $37,000 6.3 s3 PGRICUL'NRAZ, $6,000 $6,000 2% $33,000 5.6 s4 s.copsp SED BASIN $12,000 $12,000 1% $18,000 1.6 SS JEFF. SED BASE4 $5,400 $5,400 1% $12,000 2.2 No MODrFIWIoN: $1,410,000 3 BRSIS OF CCMPARISCN 1.0 Land Acquisiticns $750,000 1. ANolal cost reduction is equal to the percent reduction tinres $1,410,000 (the estimated annual cost of dredgirg with no rrodifications to the lagoon 2. Estimated total annual cost divide by the annual benefit. or vatershed) . Annual ast redudion is the annual benefit. 3. This figure is the annual cost of raroving 191,500 cubic yank of estimated sediment delivered into the lagoan at $7.35 a cubic yard for -ins. Fuzther details on the derivation of these figures is included in Appdix M. 6 velocities and help =pair erosion -; S1) side channel ~oyo repair; S2) erosim control education for protectian of wad& lands; 53) erosion control education for protection of agricultural lands; S4) a et basin at %uCh Coast Asphalt; ard S5) a Sedh2nt basin at Jefferson Street. The nine alte--natives -re cmpred to no ndifications and the consequential dr&ging sf +& lagoon at the anticipated rate of sediment accmulation in the future. EFFEmIvE SOUTPICNS Eight detention basins (Wl) in the upper reaches will prcduce an anticipated 20 prcent reduction in annual sediment acnnrPilation. A detention basin consists of a 61 &e& structure (i.e.: a 5' high dam or a road crossing) and a restricted outlet like an 18" pipe. This allow the water to pond during storms 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 enhancanmt (E) propses peak flow wlccities to be less than six feet with a 15 to 30 feet increase in creek width and drop structures which reduce per wnd, a~c~ing riparian gmwth in tk creek. his can be accapli~hed "k the gra& of the channel and thereby reduce the velocity of the water (see Figure 5). Creek enhancetent was elled with the detention basins in place. The carbination of creek enhancenent ard the detention basins resulted in a 45 percent reduction in annual sediment accmulation because of the resulting reiuction, it is assun& that the reduction in stonn flaws due to the a& reduction in storm flows. Since the detention mdel alone yielded a 20 went enhanmt alone can reduce delivery by a minimnn of 25 percent. &ducing the erosion of the main channel (wfrich is the mjor seainwt xxrrce in the watershed) by this enhanceuent will further reduce the sedimmt accumlation by an additional 7 percent, for a estimated totdl of 32 percent reduction. Fdditionally, the lower middle reach floodplain should be presswed. The &ination of a nuvable and 80' wide weir, a 100' bridge opening at Hill Street and dredging under 1-5 (L1) prcduced an estimated annual sediment drawbadcs that can not be measured by a dollars and cents anparison. Imering acclmnilation reduction of 13 percent. ?kxever, this alternative has m]or acmndation. AmDng those concerns are water quality, and salt water the weir will create other problems that are mt related to sediment intrusion. This alternative increases the probability of lower water surface levels in the lagwn. Shallw water allow sunlisht to penetrate the water, wanning it ani incmasing algae grawth. -ring the weir also increases the probability of ocean waves overtopping the wir, introducing salt water to the lagoan. Anather anticipated problem with this solution is that it is likely that the channel dredqirq Ll&x 1-5 will ham to a3w frequently. Spenains a relatively dl annual arm of mrmey on education for sediment control on gradirq sites (S2) will prcduce an estimated tw thirds reduction of thereby resulting in a reduction of sediment accmulation in the lagcon. There is no data on the relationship bebeen sediment sou~ce reduction and the reduction of sedimmt accumlation in Buena Vista Lagaon. This study assLrmes 7 this source. Reaucing sediment sources will change the sedjnent rating cwves, that for eveq cubic yard of erosion conttolled, there is one half of a cubic yad of reducticm of sedimnt thirds miuction in the grading site sediment sou~ce rmltiplied by one accrmulation in tt~ lagoon. % anticipated two half irdicates that this inprovment wxld man a three percent reduction LT axuml seaiment accmdation rate in the laqam. Table One indicates that this has +A hiqhest rate of return on dollar invested. this program should reduce as the land for agriculture diminishes. Currently a Similar results are anticipated for agricultural sites (S3. The Nget for reduction of 2 percent of the total sediment accrmnrlation in the iagcxm per yea is anticipated. It is anticipated that 5,000 cubic yards of bemmvdfrana sedimnt basin located at ttk? South -st Asphalt property sediment per year could effectively (54) . It is estimated that this would result in an annual reduction of 2,500 cubic prds of sedimnt per year, using the source and accumlation relationship estimate described above. ‘RLis wwld m3an a one percent reduction in the annual sedimnt acmlatim rate in the lagwn. binq sedimnt at this site would reduce the sediment ammulation rate of the lagcon. Another 1,600 cubic yards of sedimnt per year could effectively be remved at the mxlth of the creek, just east of Jefferson Street (SS). Since there is M that this is a direct reduction in the sediment acmmlation in the lawn. daqairq effect at this close proximity to the lagcon, it is assuued This could result in a reduction in annual sedimnt amsrmlation in the lagcon of cme percent. described for the main channel. The exanple qiven is the channel which is on It is also effective to rem side channel arroyos (S1) in the xmnner the *st side of El Cadno &al (E.C.R.) - Fiosp to Chestnut. *wing this mop a.lm yields a one percent reduction and is cost-effective. The alternative that pmved to be far too costly vas to maintain a deep channel in the lagoon - Jefferson stre& to the weir (~2). It is antici-ted that large amounts of material dd have to te dredged €ran this channel, because the channel muld act as a sedimmt trap far the lagoon. The high sedh?nt rate of the lagoon rreans that the -1 dd fill in at a rapid rate. It channel tecause of the large mimes of xmterial to be raroved. is estimated to cost over tvm million dollars per year to maintain such a Refining the estimates with data fran a watershe& creek, ard lagam rmnitorinq prqratn, an3 with mm precise cost estimates may ar may rot inprove the cost-effectivealess ratio for this alternative. ccN(=IlTSIcNS enhancanent (including floodplain preservatian in the 1- reach) , detention In the order of effectiveness the following solutims are M: creek basins, sediment osntrol education, sedjmnt basins, and side channel arroyo repair. 9 NORTH LOW FLOW ~ 7 CHANNEL 100-YEAR, 6 FEET PER SECOND CHANNEL " . . " "_ " .. - .. ... -~ - . "" " c 10 The study found sare lagm ndifications to be cost-effective, howver there are major amms for tk ecology of the hgcm if these are implmted. 'Ihe cost-effective npdifications included a mxeable and widend *i~, enlarqinq the Hill Street Bridge to be 100' long, ard keep* the opening mder 1-5 C?zrqed. 11 I. ImmxrrICN This is a report of the phase lb stucty of sediment control for kens vista lagoon d watershed for the California Coastal Consenmncy and the state water Resources control Board. Findings of the phase che Study indicated 'chat several alternatives needed to ke evaluated for sedinrent control. Jure Applegate and Associates, Civil Ehqineers of Carlsbad was selected by the Coastal Conservancy to perform this study. Philip Williams 6 Associates of Sari Francism was hired to subconsult and provide the hydraulic analyses of the evaluation viere perfon& by June Applegate and Associates and are slmmarized lagoon. The watershed modelling, project ceordimtion, and alternative in this report. The Phase "w study relie3 upn the findinqs of the Phase One of in-depth research into the Phase one remnrrendations has resulted in the stdy and has greatly expanded and revised their recarmndaitons. lhis deg-ree divergent findings of the phase 'Itm report. It is the primary goal of this study to report a prioritized list of sediment mnagemnt procedures for the Euena Vista watershed and lagam based on a cost-benefit ccmparison. The Euena Vista watershed is an ungauged watershed. All of the predictions in this study are based on synthetic hydrographs, synthetic mathematical models of the lagcon, and sediment rating a.uves extracted fran other similar -11 coastal watersheds. sedimznt monitor- us- detailed bathcrnetric surveys of the lagcon after mjor storm events, stream flm sedimnt mnitoring, and rain gauge infomation dur- storm events will yield mre accurate predictions of sediment acdation, sediment flaws and sou~ces. Cue to limited budget, almost M field data, and a range of uncertainties, the sdimnt predictions in analysis dramtically. this mrt have a wide range of error chanqing the true cost-effectiveness Consistent techniques viere applied uniformly for each category of mdification. The estimate of reduction of annudl sediTnent accrmPllation in the lawn provided a relative ranking of the effectiveness of each alternative. The valid is: maximization of the flushing ability of the lagcon with laqoon categories of alternatives in which the relative cost-effectiveness rankinq is nodifications (L1 and U), minimization of the sediment delivery to the lagcon with watershed dfications (Kt and , and minimization of erosion in the watershed (ws, ad s1 t3lrcu* SS). Buena Vista Tagcon was fo& during the rapid rise in sea level at the end of thehsti&age,tentofifteenthausandyearsage. ~ingthehSt:Fiveto seven thousard years sea level rise has heen mre gradual, apparently abut 1/2 foot per century. The slcw rate of rise was sufficient to -sate for natural sedimentation rates in the lagam, allowing it to SUNive for thousands of years. Wave action caused the Littorat transport of sand along the coast, sea- off tbe entrance to the lagoon with a barrier beach. Ekcept possibly during an 12 early stage in its evolution, the tidal prism of the lagoon was insufficient to Scmx a channel across the beach. Tidal action occurred for a short period. Carried i7t0 the lagoon during floods discharged directly to the ccean through Ln the laqmn, and only hen winter floods opened up a channel. i%xt~ sedinwt %he opninq. Scm ky wave am? tidal action, and muld be flushed out of the lagoon durinq ebb et deplsited in the lagoon wuld later lx resuspsn6e5 tide. %cause of *e Sarrier kach across its mth, the cha.racter of 'the iagcon mid greatly frm Season to season, and frm year to year. In nom1 winters, storm runof f filled the lagoon with freshater until at some pint it overtopped tk barrier beach. In the spring, after the beach was reestablished, the lagcxm level dropped, fed only by spr-s and the base flow of Bue~ Vista Creek. In simmer and fall the inflaw decreased fuzther until evaporation exceded inflcu. Water salinities increased and larqe areas of nud flats or salt pans muld be expsed. During drought pericds it is likely that the laqoon almst mnpletely dried cut, and was. fed my by salt water seep- throuqb the teach. In its natural state the watershed of 6uena Vista Lagcon was covered with native plant veqetation. The plants generally prwide3 a higher resistance to erosion than my of the intrabced, new species. They not only protected against direct erosion fran rain drops but allawed the infiltration of storm runoff imo the soil, reducing peak runoff rates downstream and providing greater base flaw in the creek later in the year. These flaws supported dense riparian vegetation along the creek banks and on its floodplain. In its 1- section the creek wuld have dischay& into a vegetation acted as sediment traps king high flood flaw, building up the tule freshwater marsh at the upper end of the lagmn. The floodplain and msh alluvial floodplain and reducing the mmnt of wt discharging to the lagmn. Bistoric Chqes In the tw centuries since Europeans settled the area, IM~ has made mjor rrpdifications to the natural hydrologic system. The hyraulics of the lagam have been Ecnpletely altered since 1940, when This eliminated tidal action until the big flood of 1969, when the culverts outlet culverts were installed at the mth to regulate maxinnn water levels. me washed aut, re-creating the ~tUral entrance for a short while until the evisting fixed cutlet six was installed in 1970. Since that tine tidal flaws havebeenexcludedandthelidgarm~beencormertedtoafreslwaterlake. The construction, first of the Hill street road -t and then of the 1-5 freeway anban)rment aaoss the lagcon, has also affected the hydraulics by limited the lagxnn's ability to flush segregating the lagcon into three distinct basins. lhese charaps have greatly sediment cut to the ocean. Urbanized nmoff pollutants discharged directly intn the lagcon degraded water quality. In addition, until the 1960s, saage m discharged directly into the 13 lagoon. The watershed has also changed dramatically. Extensive grazing and, later, fanning, removed soil cuver, increasing erosion and sedirnentaton in the lagoon. Urbanization, which has teen particularly rapid since the 1970s, increases fld peaks, causing gullying and creatirq arroyos. This process greatly accelerates erosion and bm&ream sdmzntation. In adfition, the fldplain of &em Vista Creek has been filled in several locations, reducinq the filtering effect of the riprian vegetation. The floodplain in the middle section of Buena Vista Creek has evr.11~2 as a result of sedinwt fran the sunmdmg and deposit sedinwt on the adjacent flccdplain. The floodplain and the creek built up over time. BueM Vista creek was aqqradiq in this mer througficut the middle and Icwer reaches in ancient times (see Figure 3). only a fraction of the total sedimnt era in the watershed actually reached the lagoon. After cbanges in the vatershed, particularly in the last two decades, the increased peak flms have dramatically transformed the ~t~ral hydrological watershed into the creek, kt, mre importantly have causd tbe creek bed to systan. The increased flows not dy discharge mre sediment fran the start to erode (degrade) in portions of the creek. ‘he increases in stream flaw energy have caused the stream to damcut. This process will continue until a new and lmer quilibrim can be reached. At the same time one of the largest sediment filled in. The mrsh above the lagccm vas the spreading area for stom flows. buffers in the mtershed has been Here the water slawed and fourd its way tl”Uqh the tules to the lagam, dmpping rmch of its sediment laad. All that is left of that marsh area is a sn&.l.l area where cattails grw in the channel between the sln~~~irq center and Highway 78. Buem Vista Creek Water flminy into &ena Vista lagmn cares prjmarily throu#~ Buena Vista Creek. The 19 square mile =term that drains into the creek and lagoon covers areas of Oceanside, Carlsbad ad Vista. Vista is in the upper reach of the watershed, covers over half of the mtershed and has the major inpact on the flow characteristics of the system and yet it does not brder the lagcon. he creek can be identified ty reach. ~k UFper reach is the reach ahme Highway 78. ‘&e middle rea& is frcm Hi-y 78 to El Camino Peal. Ihe her reach is fmm El Camim bal to Jeffersnn Street (see Figure 2). TheupperreachisinitsrnturalchanneltoBrengle~park. Above wildwwd park the creek has hen stabilized ty check structures. were ’ built in the 1930‘s ard it qpars that only ane of thgn has failed. This Channel XnrJ appears to have the potential to overflow and fld the sxmwdbg watershed. The creek has been channeled into amaete structures through the area, probably because of increases in runoff fran the urbanizaticm of the downtown area of Vista to Melrose Drive. ’Ihese stmctwes wxe also desi@ 14 in the creek. Dur* flood flows, these flw *rould Overtop the creek banks . hillslopes him3 transported as bedload ani hiTt tefore t!e mjcr urbanization of the area. P.e mise reach was a wide aggrading flocdplain. It has been di~zed into +xu by the falls just chnstream of College Avenue. ?he tK, sections functioned veri similiarly Sefore the inpact of urbmization occurred. ljow tle falls .rark t!e location of the hydraulic division of this reach. In tke upper mic?dle reach, fran Highway 78 to College Avenue, the creek has drmtically changed fran trapping seclinmt in its broad floodplain (aggradinql to a dmn-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 treabwnt plant in Vista. Instead of absorbing mch of the sedimnt it plus the eroded material downstream. receives as it had &ne in the past, this reach is ncw sending that sediment Currently the her middle reach (College Avenue esterly to El Cmim -1) is still aggrading. In fact, it is aggrading at an asarmirq rate of up to faur of the sedimnt before it sets to the lagam. feet per season. mis iralicates that the middle reach is absorbing nuch The cause of dcwn-cutting in the uppr middle reach is the increase in the SCOUT action of the creek. =irq the flm line of the channel at various phen-n. If the creek still had aggradirg characteristics it WOUM. fill in road crossings has contributed to this &gradation, but this is a long-term these crossirqs with sediment as the middle reach of Lcma Alta Creek has. ?&pically during urbanization downstream channels start to ercde. This is in response to higher pak flows of water €ran the developing area. 'Ihe existing ard future hydrosrapls deled in the phase one study i?dicdte that the peak flaw have the ptential to double in this reach. mis means that the sedhmt transport capacity of the creek mre than doubles. thanthe If the sediment transport capacity increases to the pint that it is grater into the bed mterial. when it had toa nu& sediment to transport it dropped sedimnten~thereach,thecreekthenhasmghenergytocut its load on the wide floodplain. Naw it is huqq for sediuent an3 endes into these ancient fluvial deposits and carries them and its original load dawnstream (see Figure 3) . The increase in peak flaw explains the cause of the etosion in the upper middle reach. It is also a waxniq. Channelizirq the per middle reach will cause thepeaksintk~middlereachto~~~ti~lyand~dtrigger dcwm-cuttirq in the lower middle reach. since there is very little buffer even greater sdnentaticm ac-tion rate than ve hare previously seen. In the her reach, aknre the lagam there UQS a wide flat marsh. At the of the lard an3 the thick grmth of the mSh plants greatly reduced the location of El Camin0 Real the creek spred aver the marshland. Ihe flatness velocities of the wate. Here the water slared and found its way thmugh the tules to the lagoon, dropping much of its sediuent W. The marsh acted as a filter for the water entering the lagccm. between the -2 luiddle reach and tbe lagccm, the lagcon will experience an 15 The marsh ins been filled. Presently the ~nly evidence of that rrarsh area is a dl area. where cattails grow in the channel between the shoFpisq center d FLighway 78. RLis channel is ncw the laser reach of Buena Vista Creek. Because of the ctarqes in the lagcon hydraulics and the greatly increase3 rates of s&h=ntation the lagoon is no longer in quilibrim with natrual hydrologic processes d is rapidly silting in. mst sediuent deposited into the lagm is discfiarged during the peak flays of 1- storms, such as those in 1969, 1978 and 1980. sediment discharge is exponentially related to the flow velocity by a power of tm to three. Consequently, mgh peak flws may last only a few hours, they can any tens of thousands of tons of sediuent into the lagoon. It appears that sedimnt carried into the lagum is preaaniMntly silt. Ihe typical size distribution of suspended sediment for different sotrms is sham in Table 2. The Table is based on sedhent coastal streams (see Apperdix 4) and synthetic flccd hydrographs generated for sanpling on other San Diego County the BueM Vista Creek watershed. AS the flocdflow approaches the lagcon, bckwater reduces the elocity and carry- capacity of the flw. Much of the bed load, consisting of coarser south coast Asphalt quamy and Jefferson Street, while mst of the suspended sands, appears to be deposited on the fl-lain and in the channel between the sediment, consisting of sands, silts, and clays, are discharged into the 1-n. As the flocd flows enter the lagcon, flaw velocities amp to a -action of a foot per second. These velocities are insufficient to keep the -et in suspension, and particles start to settle aut. Ihe settling velocity of sands gradually but rapidly enough for mst of tkn to be depsited ups- of 1-5. if very rapid, 90 they tend to settle out hediately. Silts settle aut mre Clays settle out very slowly, but because velocities thrcugh the lagccm are so ocean. m roadfills of 1-5 anl Kill street ard the outlet weir have reduced low, mst are deposited in the lagoon and cnly a fraction are dischaxqd to the flow elmities through the lagam, inneasbq sedimentation. Buena Vista Lagcon now acts as a very efficient sedimnt trap. %sed on the -.cry Limited boring infonoatim available, it appears that, prior to 1940, ths Lsgcm bed consisted of fhe sands at an elevation of abcut -1.5 ft NGM. By 1961 a-tely 2.5 ft of organic rich md had ,acmddted in the lagcon in the vicinity of 1-5, and by 1982 an additional 2.5 ft of organic rich silty clay had acamulated. In the last 42 years, preslrming the same siltation rate over the 200 acre lagcon, this zm~unts to abaut one ard a half million cubic yards or tons (for these sediments, a cubic yanl weighs roughly a ton), 01 about 35,000 tonsfyear. For the 19 sqw.x-e mile watershed this anrrunts to 1840 tonsfsquare defyear dch is ccnparable to an earlier estimate of 1,000 to 2,000 tansfsquare milefyear (Inman 1976). 16 After initial depitim &ring and after a flood, sediments can te resuspended by wa~ action and redistributed in the lagcan. Water depths are fairly constant, aeepening to two to three feet in areas of hiqh wave action. me thick growth of tules under the 1-5 bridge prewnts all except the finest sedimnts h circulating into the western sezpnents of the laqwn. Consequently, silts ad nuds, whereas tc the kest of 1-5 sdircents are minly organic mds. sedimznts acdtirq in the eastern segment are mjnly sands, ~1: the wind-protected area beheen the railroad ard the beach, sedirrents are highly organic and appar to contain sewage sludge. water levels in the lagoon are maintained at a mininun elevatiun of 5.8 ft NGVD by the outlet weir crest or mre CcnmDnly betwefin about 5.8 ft and 6.5 ft NGVD by the barrier beach forming across the outlet. Water depths in the eastern seqznt a.re typically 1.5 to 2 ft, and in the =stern segmnts 2 to 2.5 ft. s- Before the innnan-caused disturbances to the "shed, creek, nnrsh, and lagcon, m& of the sedimnt €ran the watershd was deposited before it reached the lagcon. sediment was deposited on the broad flccdplain in the middle reach. Then, in the 1me.r reach, a 1- marsh area spread ard filtered the storm water, trapping mre sediment before it entered the laqmn. Asphalt and east of the Hayrw Street cul-de-sac. lhis reach of the creek is ,-,? The only renmant of this pmtectim systen is the area west of south Coast F currently absorbimg very hrge quantities of sedirrent ami is the last natural ' buffer to prevent m of the sediment fran enterins the lagoon. ?he best Street cul-de-sac. functioning porticn of this reach is the thiok riparian area east of the Haymar 17 TABLE ?wD. Sedhnt Size Distribution for Different ?Wxqa@s sedimnt peak Load at % by Particle Size at Peak Flow Flaw Peak Q Stom (cfs) (tms/day) <.004 .004-.016 .016-.064 .064-.25 .25-1.0(mn - 5 5 5 2-F 1371 1.2x10 25 6 23 33 5-F 1979 3.2~10 23 5 26 10-vr 2589 6.8~10 20 4 28 40 8 11 38 9 - 6 6 2 5-p 3659 1.7x10 18 3 31 44 6 - SO-p 5832 6.7~10 15 2 32 47 4 7 100-p 7200 1.6~10 13 2 33 48 4 18 It appars that there is an estimated total of 173,000 cubic yards of erosion ard College Boulevard. mis was calculated by usinq a real toposraphy flown iz L. the main channel of the creek in the middle reach bebeen Melrose Avenue the sprinq of 1985. 5asec.m newspaper clippings, mst of this erosion has occurred since 1978. 1978 marked the end of a a 13 year dry pricd in this urbanization in that time. lke ccrrbination of the increase of rainfall and area. Lard use had changed €ran primrily mal and agricultural to hhat had keen an aggrading section of creek here sediment was deposited upn a urbanization create3 a dxmtic increase in the amxlnt of runoff experienced. broad floodplain bscam a degrading section. The h-cuttiq is evident in a gully that is in excess of 15 feet deep in scme places in this reach. currently Graded A!zem Presently there is approximately 600 acres of graded area in the watershed. Vista, Carlsbad and Cceanside adopted smt control ordinances as part of their grading ordinances. and approved by October, 'Be sediment control is sup~osed to be in place in sediment control plans nust ke filed in Septmbr Novenber, and remain effective until "i. werally, on-site sedhent control is still not effective. There appears to be a lack of understarding as to what it takes to keep sedimnt fran leaving the site. ttuch of the wrk done in the creek in Vista duriq the winter of 1984 had M protection what so ever. bbch of the sediment Contrcl as installed in the other cities was not effective. water. Another ammn practice is to use sand bags that wre not sealed, but scrmettnes sediment is direaed into the storm drain systan in the form of rmddy before spilling their CCntMts ard adding to the sediment just folded over. ktre of these bags a mt mke it through the winter season 1- fran the site. Education of the amtractors, hspeckus and &sign professids who sutmit and those win revim the plans is desperately needed. ordinances are good, but they are mt yet being fully inpl-ted. The lccal citizens are concerned ad wnild be excellent watchdogs, if educated. The mens Vista Lagam Fbmdatim has a btline that is available for the rep- of sedimwt problems. The local citizens are dedicated to the saving of the lagoon, but do mt yet recOgnize sum of these @la. peryearto3Ocubicyrdsperacreperye~. Thisiswhygood Sedimnt yields fran these graded amas can vaxy frcm one cubic yard pr acre sediment control is so important. Sedhsnt yields are still high fran this SOUTC~, SO using an estimate of 25 cubic yards per acre per year over the 600 acres currently be% graded gives a sediment estimate of 15,000 cubic ~d-5 of sediment per year. 1Y Agriculture The follawing is a sum~~y of interviews with W beller, who is currently a consultant ard has wrked for the Soil Conservation Senrice. while wrkxq. for the Soil conservation service, he canpiled the "Important Fannland Map" for the Bue~ Vista Watershed. The anrnmt of fannland in the Buena Vista Watershed has keen a constant of approximately 5 percent (approximately 600 acres) groves and S percent truck crops. Howwer, with the various eaniunic and social pressures on the within 5 to 10 years ard will become mnpletely urbanized within 20 years. fms these lands will decrease am3 berrme an insignificant sediment source Avocacb groves of three years old or ywriqer (of which there is 10 to 15 percent of all groves) prcduce 15 to 20 tons of sediment per acre per year. The remaining 85 to 90 percent of the groves have sufficient campy ard leaf litter to reduce the sedimnt yield to one to two tons of sedinent pr acre per year - well managed truck crops also have a sediment yield of one to two tons of sdinent per acre per year. Hawever, poorly ~"ged truck crops proauCe as mch as 20 to 30 tans of sediment per acre per year. Historically, the prly managed truck crop land constitutes abcut 1 percent of the watershed, ard the xranage3 truck crop land constitutes the mining 4 percent. Presently, ';be wll managed farms only constitute one an3 a half percent of the 5 percent total. Historically, the agricultural land phoauced an estirrated 5800 tans of sedinwt per year in the Buena Vista watershed. Presently they are prcducinq an estimated 13,000 tons of sediment per year and within the next five to 10 years this source of sedirrpnt will be negligible. By ccmparison, the ~tural areas, which had pericdically turned, yielded one to tw tons of sediment per acre per year, average. Future Lard Uses The folla estimates for future land uses were made by each of the three cities in tb watershed (in acres) : Develope3 area: Ilnderdeveloped: Vacant land: Area with appmved plans: Area withcut appmvsd plans: Are3 Qltrently be* graded: Carlsbad Vista oceanside 1700 5760 3000 300 1500 500 250 2750 250 134 765 2000 190 325 85 20 %ese drs indicate that there is aprcxinately 6,000 acres of natural ercdhie mea. Using an average of tm tons of s-t per acre per year LAicates an estimate of 12,000 tons of sediment frm this source per year. southCoastAsphalt South Coast Asphalt has a rock guarry just best of College Avenue. ?he excaMtions extend approximately 50 feet helm the stre-. They have maintained the falls by keeping the banks and adding levees. In the flatter portion of the creek, there is nmoff fran tk plant site ard there is potential for erasion. Since the quarq area is granitic rock, the -sed faces do not have nnrch erosion potential. The erosion potential an the site is photography of the land for this study. in the reach with loose dirt banks. The plant has suplied detailed areal Dcisting channel velccities in all tut the dlest flows are in excess of 6 been carrying go nuch feet per seaxd. Tkse are erosive velocities, tmever since the creek has continues to aggrad&. Higher peak flaw could reverse this ard this reach sediment in recent years. ?his section of the creek could start to degrade. In the first large flow in 1979 a portion of a sxtherly stmile was emded. To prevent this loss of material, south Coast Asphalt nar protects the takpiles with riprap at the toe. Ihwer this site has the potential for erosion because of above mtioned velocities, little bank protection, and fill- stream banks that are vulnerable to erosion. The rock guarry is estimated to close in 1990. Plans for the developnent of the are NW kirq prepand and revid. The owners plan to develop have a ~tural looking channel, use the creek as a visual mznity to the the creek portion be- 1990 and 1995. Ultimately the owners wuld like to project and maintain the falls. Wing the time kern m and the ultimate &velopnent, the ptential for erosioninthisreachcanbcreducedbywideningaJd~~tothe velocities W-tely 20 percent. 'Ihis will be beneficial in three wys. Lavering the velocities will decrease the sedimnt transport capabilities of the stream ard thereby decrease the potential for creek erwion. It will also make a snall contribution to reducirg the peak flows at the lagoon. Rwetmmt of the creek banks will reduce the potential for erosion. chanrd. M&rg 30 feet to the width of the dirt &ultn?l will reduce the . 21 SFm" SOUIICE m TABLE 'IWREE .3pproximate anmial average erosion rates firm each souzce in cubic yards per F: -in channel erosion: 25,000 Graded areas: 15,000 Agricultural: 13,000 (currently) Natural erodible areas: 12,000 side channel erosion: 11,000 22 N. ANALYSIS ,The watershed analysis was *fold. Hydrologic watershed dfiations aimed at reduckq the peak flcm fran stom moff were analyzed. -t source reduction was evaluated. There is an exponential relationship tern the stream's sedtnent carrying Recjlcing pak flow will reduce the sec?iment carrying capacity of the stream. capacity and the water flow. Consequently a reduction in the storm peaks results in a mch Ggher reduction in the sedinwt delivery to the lawn. Rececaing @ flow also has the side benefit of reducing flcding. Specific anas ickntified as areas of concern that will be benefited are in the law lying areas amund the lagcun and areas in Vista. sedimnt Source reduction win reduce tbe watershed. The sediment ratirog cu~es are a plot of the relatimship of the sedimnt rating curves of a water flw to sediment transport. The estirmtes of sediment acnnRztation reduction for sediment control could ke an order of mgnitude off. Hcwever, the cost for greatly improvirq the source control is relatively low, return on the dollar spent is ve~y high. m mERsHED mm hmuraged by the peak flw reductions modeled in the phase One study, the data fran those original watershed mcdels were reentered into the Amy Corps of hgineers Hydraulic mineering Center's H.E.C - 1 hydrology mdel and rerun on a mainfrane -ter in order to print hydrogram for the spectnmn of six storm. These ere the 2-year, the 5-year, the 10-year, the ZS-year, the 50-year and the 1OO-yeax storms. lkose six storms were run for the Phase One's 'kisting Cordition", "Future Camlition" and "-sting Conditicm with Detention". Very late in tb Phase "m analysis xm problans in sare of the asqtions for these mdels were noted and the watershed had to be -led. The Phase &e irrplt data was used as a skeletm and a new watershed del was del amld nut te calibrated. pppenaix one describes the calculations for the created for h ma cordition. since this is an ungauged mtershed, the Future Corditions. "ese include a sumnary of the soil types, future developrent types, Soil Consenmtion Service Lag, and SCS curve nmber for each were run cn this -1. (Note: The future amditicm watershed models for of the phase me subbasins. The 2-year and the 100-year hypothetical stow Future conaition, ma coniiticol with Detention and fiture condition with Detention and Channel hhancanent a.re copyrighted c 1985. Funding was not allocated ~r this rwmdelliq.) The min channel keginning belaw Brenglc Terrace Park to College Avenue (a portion of the upper ani the entise upper middle reach) is &led as a trapezoidal cfiannel having a bttun width of 20 feet, si& slops of 1.5 to 1 and a coefficient of 0.02. This is typical of the hi-lodc channel that is being placed at Breeze Hill. - 23 Because the kture andition dd have the mjor long range impact on the lagocn, the future condition was then modeled with eight detention basins. The basin locations had all been -led in the Phase me study. ’hm of them wze re-sized based upon mre detailed toposraphic infoxmation. “e tvo re-sized basins sere at Brengle Terrace Park and at Monte Vista school. Detention Basin locations The detention basins in Vista (shewn in Figure 4) are lccated at: 1. Creek crossisg Wamdmis Avenue, appmxhately 200 feet Northerly of Elm 2. Creek Crossing wannlands Avenue, approximtely 200 feet Northerly of 3. Creek Crossing wannlands Avenue, apprwirnately 100 feet Mrtherly of Calk 4. Creek Crossing Stephanie Iane on the mrth side of Vale Terrace Drive 5. Brengle Terrace Park 6. Monte Vista school The other phase me detention basins are located at: 7. ?he CKlyOn north of Mira Costa College in Cceanside 8. The carryon to the east of the extension of Elm Avenue Drive SUaMIjc ”errace Simoloa TO del the effects of an enhanced channel, with vegetation, the detention basins kere kept in place and the abwe mentioned channel was widened. ?he channel in this third -1 had a bottan width of 15’ above Santa Fe Drive and a bottan width of 40 feet wide belcw Wta Fe Drive with side slopes of 2 to 1 and a “q cwfficient of 0.04. !I& enerqy slope is about me guarter of a percent. mis was the mst effective inprowsent to the ucdel. Table 4 gives the sunnary of the results of these I~RJ mxkLs. ?he 6 feet per second maxinun allowable velocity is attainable with 0.25 to 0.35 percent sw, a Mmaing mefficient of 0.040, 2:l side slapes and a 40 fwtbottcmintheuppermiddle~~reducinginwidthupthecreek~tilit is about 15 feet wide. Table 4 lists the smmary of the peak flows and lag times at the lagcon for each nodel. Figure 6 shows gram for the 2 and 10- stom6 in the future oonditim, future condition with Qtenticn basins, and future condition withcreekenhancementfara~tioninthe~~areaofVista,in~ middle reach, and at the lagcon. canparison -s are shown in Fiqure 6 for a point at the lagaa! and a point at Breeze Kill. 24 TABLE ECUR Smam of 3.E.C.- 1 weak flms and the to peak for future mn6itions at the - lagcon. 1CO year: Ftture andition 13,734 cfs 2.94 blxs 2 year: Fume condition 3,213 cfs 3.27 hours MISTING With detention 11,431 cfs 2.95 hours With detention 3.28 hours 2,590 cfs TABLE FIVE PFmB2XED SEDIMEEfiIIEwcmcNs AN@nmL mIMENT REnXT. BASIS a?m 12% aB5m 264 CHAN aNTFUBUTIm 14% WSTING EXIT 20% 52% ** EXIST 32% With enhancawnt 9,231 cfs 3.28 hours With edmcment 2,130 cfs 3.92 hours 25 CFS 10.000 . LdGCON CFS I 3,300 2.000 1,000 0 2 3 4 3 IHOURS 100-YEP! STORM 2-YEAR STORK BREEZE HILL CFS I 3,000 . 2 3 4 HOURS 100-YEAR STORM FC FUTURE CHPNNELIZEO COHOITIOtd FO FUTURE flETE!!TIOtl t1)OEL FE FUTURE WITH OETENTICN AliD ENHANCEIIEO CHANNEL MOOEL IiOURS 2-YEAR STORF: Figure 5 Hydrographs 26 SeCirnent Source Control &in Cbmnnel (W) : me average of 25,000 cubic yards of sediment per year era2& €ran the min ckmel prirwily occurred durirq the 5 years fran 1978 to 1983. Altlxmgh this reach of ti-e reccnmended enhancmt is at least three tims the l@ of the scurce will not ke ccmpletely eliminate3 with the channel mdifications, the badly waded section fran where the 25,000 cubic yar& cam. Pr0teei.q the Main -el will reduce the sediment source to "e laqcon by 25,000 cubic yards per year. For the ccnparative analysis half of this quantity was added to tl-e redudion in sedifient delivery for the "channel Enhancerent" alternative, because it is asslnned that for every dic yard -t sou~ce reduction there is a corresponding reduction of a half of a cubic yard of reduction in the edirrent ammulation in the lagoon. Graded Areas (S2) : The adopt& sediment control ordinancss for graded areas are cpd and mney is be- expetxied by the developers and the cities for th design construction and review of sediment control plans. €%%ever, there is still an estimated 15,000 cubic yards of sediment escaping fmn fran these sites. Misplaced or broken sand and gravel bags are al1cwi.q Sedimnt flow into the storm drains and channels. sanetines the projects are caught with the& gravel bags Qwn by a surprise rainstorm. Education of the engineers, inspectors and contractors imrolved will probably reduce this source to one thixd of the volm it is today. Agricultural (S31: A similar &cation program for agriculture could be as effective as education for grading. This would reduce the sediirwt source by an additional 5 percent. Natural erodible areas: This snuce has such a law ConcMtratiOn very little inprovetent can ke mde. Side Channel Fxosion (Sl) : l?hree side channels that need recoIlstruction and enhanenent have teen identified. They are just west of Palo Drive, on the westerly side of El camino Real between Elm and olestnut and next to Mnrce, mth of "on. According to the Vista City staff and the Carlsbad City Staff the side channel The requimmnts far the developnents include repairing and preventing these icf~oyos at Pamelo and mnroe are in areas that are appmvad for developent. arroyos * The side channel armyo on the msterly si& of El camina Real between Elm and Qzestnut locations could effectively be repaired using drop structures in the samemnneras~recarmended~~repairintheupprmiddlereach. This will redua the total watershed sedimnt source by an estimated one percent. 27 TIIE"R TO &termine the mst effective mans to reduce sediment acclmpllation in the lagoon, its sediment budget must be estimated under different coilditions. A Wt Wget is siuply an accounting of the inflow, outflcw and strcage of sedirrent in the lagcon for a particular time period. sediment inflow is de- by wpirical relationship tetween the variation of sedimerrt discharge ard flcw rate during flood events. The sequence of flow rates, IolcxJn as a hydrqraph, are mted for particular stonns usbg a standard ccmpter rmdel sirrnrlaticn referred to as HEC-1. when the sdimnt enters the lagam, scme settles cut, some is discharged to the ccean, at-d s~ne ranains in suspension for a particular time perid. The amxlnt settlinq at is calculated wing settling velocity relationships for each particle size. The mt reMining is suspension is determined by the difference in sediment inflow and the ammt settling at in a particular time period. "e anwnt discharged raniring in suspension at the cutlet, nultiplied by the discharge volm. to tbe ocean is the sediment concentration mst sedimnt is carried into the lagoan by a few.laqe, infrvt floods. perid of time to estimate an average annual sedimnt consequently, the sediment kudqets rmst be averaged statistically over a lmq inxiget. "e average armal sediment hdget can be calculated for different inflw and lag- conditions to provide a ccmparism of tbe average annual sediment acdation in the lagcon under different mnditions. Because of the ~M~II(YIUS n& of calculations requked to estimate average annual sdimnt acamdaticm, it is best &ne using a carplter nodel that sirrmlates the lmveuem of bath water an3 SedLnent aqtl the lasocn system. descrihd in succeedirg secticns. calculations inwlved in detemmq a sedtnem buaget. Ccmecpntly seainwt Such a qter xrcdel was &vel@ specifically for this stuay and is It should be noted that there are a great many uncertainties in nost of the . buigets of this type should be used for ccmparative pvposes dy. *. ~testlrettrodfordetermininJsedjmentdisd.rargetothelagoonistDdevelop asdmnt suspended sedimmt against flow discharqe nmsured at a particular point cn the ratkg curve for BueM Vista Creek. A sediment rating cure plots stream. Unfortunately, neither suspendea sediment nor discharge data exists for mena Vista Creek. Iherefore, a sedimnt rating culve was -, based QI SaUQle data €ran other streaw. stream gauge data €ran 11 gauging stdticms on coastal streamrs south of Dana Point were ewmined (see Appenaix 4). The results shwd that streanrs with watersheds greater than 100 square miles had different sediment rating culves than those with dler watersheds. consequently only data fran the five dler watersheds ere used. 28 SeaxElt Particle Size qs (tons/dav) Fa1 Velocitv (ft/sec) Clay <.004 m 9x10 Q -4 2.4 1.31 x 10 -5 Silts -3 2 -5 3 .004 - .016 mn 4x10 Q .016 - .064 mn 1x10 Q 1.15 x 10 2.3 x 10 -4 -3 sands .064 - -25 ~TII 1.6 x 10 Q 3.28 x 10 .25 - 1.10 mn 3.7 x 10 Q 2.3 x 10 -5 3 -2 -3 2.1 -1 lh suspended sedimnt data was broken down into five different size fractions plots are shown in Appndix 4. There is a large ammt of scatter in the representing rruds, fine silt, mse silt, fine sand and mse sand. me data. Lip to an odr of magnitude of scatter is typical of sediment rating as the straight Line relationships shows in Table 6. These are used in cuzws. However, the rating cuzves for each size fraction can be simplified calculatirg seoiment inflow to the lagcon. A portion of the mser sediment discharge, often estimated to be an additional 20%, is carried slow the channel bed as "bedload". This was not included in the sedimnt inflow because mst of the coarser material appears to be deposited in the Buena Vista Channel upstream of tb lagoon, ard because it represents dy a dl portion of the total sediment load discharged to the lagcon. The sediment inflow for a particular storm is &dated by integrating the sedhznt rating cure with the inflow hyYzrqa* for successive time in-ts . Lagoon HydrauUcs ~n order to calculate the sedimnt acalulation in the lagcon for a partinrlar flood, a flocd mting calculatim must be carried out to determine the water surface elwaticols, volums and flow velocities at different times, the flocd flcnJs enter * Lagcon. For Euena Vista Lagoon this is canplicated, because hydraulically the hqWn acts as three distinct cells. Tfe eash=rn ell includes the area fran the 0utf10w to the central cell th& extends fran 1-5 to Hill Street. inflow pint at Jefferson to the 1-5 enbnbent. ?he anban)anent constricts sediment 29 acdation further constricts oufflcrws wder the 1-5 bridge to apprcprimately through a constricted culvert under Hill Street, or over the tap of the rcadway, if tk water level rises high enough. 'rhz western cell discharges to dces not significantly mnstrict flooj. flows in the western cell. A sketch of the ocean wer the existing sharp crested weir. me railmy bridge crossing the lagcon is sbm in Figure 7. A fld muting is a sequential calculation that calculates mfflaw, mtex surfae elevation, chanqe in storage ard a-ge flcw velocity for a given inflow and initial lagcon aditions. Vnfortuna-ly, no detailed sunrey of the bathptry of wlena Vista Iagcm exists. Therefore, the water elevation/storage relationship for each of the cells is estimated bad on few 4. cktflaw kxn each cell is determined by StardKd mir flaw or culvert flow fonrmlae. Averaqe velocities are simply calculatd as the mtflcw divided by the average cross-sectioned area for a given instant in time. the existing lisgoan level. The central cell discharges to the *sdlerrl cell point soumlln ' gs ard available tqxqhraphic survey. These are shown in pppendix sediment &dation sediment inflow to the lagoon is assumd to be uniformly vertically lrcixed in the flw. rvhen it reaches the lagom, flcw velocities drq, miderably and by the particle settliq velocity. For the median diareter of each of the five sediment particles settle out. 'Ihe rate at which they settle cut is detennjned size fractions, this value is shown in Table lb. It can be seen that there is roughly an order of magnitude differen- ketwzen the settling rates of each size fraction. Dividing the mt inflw into five discrete size fractions can therefor& intrcduce another source of error in the sediment budget. sediment acdation is cletemined by the fraction of sediment that settles out while the sedimnt-laden flcw travels fran the inflow &a the cufflcu erd of each cell. It is assumed that flow travel- through the 1-5 bridge and the Hill Street culvert canpletely mixes the sediment, so that sediment discfiarged to the m cell is rnrifolmly mixed. quiescent unifonn flaws in stilling basins. In Buena vista L%gcon flood flows The del for -t &position described above is strictly valid cnly for entering the lagcon will be highly turfxllent, which tends to M s&tling of sediment particles until the turbulence dies out. Unfortunately there is no feasible way to del this praxss, and calculating aepoSiticm based strictly on time of travel may owestirrate accMulation particularly for the finer sediment fractions. The velocity of the flaw in the lagocpl itself can mte men- that can keep particles suspended. There is this 1- Ut of sediment mncantration alternative nrethcds of calculating this luer limit; and as is anum in the in the lagcon fior a particular average lagccm velacity. There are uany field of sedknent hydradics, there are significant differences in different estimates. For these calculations the relationshiq develcpea by Bagnold was used (Yalin 1971). 30 TABLE 7 . BUENA VISTA LAGOON COMPIJTER MODEL RUNS TABLE 7, page 2 IW 100 I5 15 15 I5 I5 I5 I5 4.0 4.0 1.0 1.0 a.0 2.0 2.0 1.0 1.0 q = pvt Un(0.17 + .01 Un/w where e b/v* = 2.5/n(3.32 v*h/y) +.*ere : qs is sediment discharge p is the fluid density V* is the shear velocity Urn is the man velocity w is the particle fall velocity h is the depth )) is the kinerratic viscosity S This lower limit is particularly inportant in estimating net accurrpllation of the finer sediment fracticms. The total SedinWt acomilation for a particular flod hydrograph for each cell can te estimated by the accwpilation in each tbm period. A mnputer nrdel was dwelOpea to sindate sediment accumulation in the three cells of Buena Vista Lagoan for a given inflow flad hydrograph. This nodel, identified as MRNY c 1985, was an adaption of an earlier lagcon flad routing del with the addition of sedimerrt rmtktg subroutines. The input data requized is the inflow flood hyamsraph, sedim=nt raw ms for each sediment size selected, lagan getmetry; and we& anl culvert characteristics. The output is a ccmputation for each bur of the sediment inflow, sediment accmulation, and et discharge, for each fraction for each basin in the elevatim an3 velocities of each basin for each hnu. &ez the entire lagoon. The unputer -1 also calculates inflow, outflow, water surface hydrcgraph perioa the -1 calculates the totdl sediment acamlation and disc- far each basin. Results A total of 50 ccnplter runs bere carried out to examine the mrbiMtiW of different scenarios of hetershed mnditions ard lagom maulics. A anplete sumnary of these runs is shown in Table Seven. Ebrty-four of the runs were carried out based rn m-1 inflaw hydzographs representing three different watershed conditions that were developed in the phase me study. 'Ihese were: 33 1. E?fistiligamditions 2. fiture mnditians with no action 3. Existing mditions with detention basins. For each condition the 2-year and 100-year flood hydrcqa@ %as analyzed, and in scme instances the 5- and 25" hydrosrahs as well. Ute in the study, errors wa'e feud in these HEC-1 inflcw hydrcqqhs. Pccordingly they were recalculated anl six additional ccnputer runs based on three new sets of hydrosraphs wzre carried cut: 4. &calculated future conditions with no action 5. Recaldated future wnditions with detention basins 6. Recalculated future conditions with detention basins and preserving the floodplain upstreall. A sum~zy of the inflow hydrographs used is given in Table Eight. Although the earlier HEC-1 hydrographs wxe not ackurate, the crmplter mdelling remrlts can still be used as a basis for axpu" the effectiveness of different modifications to the hydraulics of the lagcon. Five different lagoon hydraulics conditions wx-e exmnined, either individually or in cabination: 1. rxisting conditions 2. Fmwving the sediment acarmlated under the 1-5 bridge 3. Enlarging the Hill st?2eet culvert 4. Increasjng the capacity of the atlet weir by widening and lcwering its crest 5. Ekavating a deep channel thrmgh the lagm frcm Jeff@rson Street to the outlet weir. The average annual sedinent accrmilaticm for selected scenarios is sham in Table Nine. These values are determined by plotting a sedinmt accunuhtion pmbability amre using the 2-year and 100year eorprter run results for total accumulatim by the method described in the ASCE Sedimentation -i.q Handbodr. Table 4.18. Table Nine shnvs that average annual sedimnt accznnrlation in about 33,000 tcmsjyear under exi- ccnditians (sa=nario I). This amxmts to about 20 acre feet per year which, averaged over the &le la-, is about 0.1 ft/year. At this rate tk lagccrt would fill in conpletely in twenty to thirty years. Sediment accwoilaticm of 33,000 tasjyear, asnrming a trap efficiency SdiIIent acarmlation and then calculating the swage allnual sedknent 34 Flood Flocd Watershed Return Peak Flow Source Cordition Frequency cfs VOl~ acre ft. Phase I study Phase I study Phase I study Pbse 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 isristing Existing misting misting Future Future F'uture F'uture ExistiIq wldet ncisting W1ae.t F'uture Future Future Wfdet Future Wldet mture Wldet & fp fiture wldet & 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 1 -sting Phase I 2 mtlue Phase I 3 Future Phase I 4 Future phase1 5 Dtisting wf det Phase1 6. widet Existirq Phase I Existing 1,2,3,4 32,970 NIA Existinq 29,30 73,550 0 Future curb. 32,34 64,230 13 Ccnb. wlcbannel 40,41 56,280 23 Existing 37,44 25,490 65 Future Ccmb. wfchannel 42.43 19,840 13 7 Future Phase I1 Existing 45,46 191,500 0 8 Future W.det phase I1 Existing 47,48 153,600 20 9 w det of mture fkdplain Phase 11 DListing 49,50 105,100 45 36 of abut go%, corresponds to a watershed sediment yield of 1500 tcns/squanmile/year, a value fairly typical of this area. It also co-spm~s closely to the &served historic rate of accumulation of apprcocimately 35,000 tcns/yeaz. H-r, such a correspndence sW6 ke regarded as fortuitous kecause of tie larqe ptential mrs inherent in analyses of this p. urSanization and 110 SedLmqt accumulation under future watershed conditions with increased saiiment control is projectea to increase by a mltiple of six to abxt 200,000 tms/year (scenario 7) . This is &e to the increase iqeak flcws *an storm drains, Lined channels and paved surfaces, and the expnential relationship ktween sedimnt delivery and flow rate. The resulting predicted katershed sediment yield of 7,500 tadsquare mile/- is not unmn in urbanizing watersheds of this type. A sediment accumulation of 200,000 tons/year if distributed equally in the lagwn, could fill it in four to five years. The E'uture of the Lagwn If 110 action is taken and the existing the lagwn will probably fill with sediment within the next 20 to 40 years. sedimentaton rates continue, mst of ~wwer, because of additid urbanization in the wtershed (underway or planned), ard the filliq of the Bue~ Vista Creek floodplain, mst of the cccut gradually but mre likely as a result of 2 or 3 mjor flocds. lagwn might fill in in the next 10 to 20 years. zhis sedimentation would not Conseguently, the rate of filling will on the sequence of wt and WS. There are tm strategies for reducing sedimentation in the lagwn: either reduce sedim=nt inflow or inprove the flus- ability of the lagoon. Table One slww-s the relative successes of these twD strategies. 'Ihe mst effective alternative for mitigatiq increased sediment flcws to the lagwn is channel enhanmt (Uternative E). Channel enhancanent vas nodeled fmn damstream of Brengle "race Pa& to south Coast Asphalt. Various channel mnfiqurations will accomplish this cpl but a maximm velocity of 6 feet per second mt be maintained. W key to bepirg the velocities at this level will be to install velocity will allow far the growth of riparian vegetation; haever, in many chedc structures along the creek and recontollT the channel as necessary. zhis areas the existing "natural" channel will have to be redesigned, drop Fortunately have a Ilodel to follow. Gully restoration was acmnplished in structures installed, and creek banks revegetated to meet this velocity goal. the Tahoe Basin us- check structures. These have been in place for several years. Not cnly does channel erhmaent decrease peak flood flows to the lagoon mre effectively it also decreases the erosion hazard for the major source of sediwnt to the lagam. Mmst as effective in aecreaSing peak flood flows is the design, installation anl mainteMnce of eight storm attenuation basins (Alternative WI1. The location of these and the channel enhanmt are shm on Figure 4. All of tihe attenuation locations were modelei in the Phase Gne study. lk =e rarodeled, based on mre detailed topgra@y, 37 It is evident that there is a ptential for &creasinq laycon -tation by &tention basins and preserJing and enhancing the flodplain upstream (Alternatives W and Tis). The t5ird mt effective method of ecing sediment to the lagam is stopeinq the soil loss fran gracting ard agricultural operations. Ihe grading ordinances for the three cities isdequately require sedimnt wntrol for grading operations. An education p?rocess still needs to occuf for the nethods that are effective to mly with the ordinances. Agriculture is still a mjor source of +iculture will pmbably &idle to be very dl within 20 years, as the sediment and there appars to be m ordinances for this source. watershed is urbanized. This study envisions a program of education for the City pervsnnel who check qradirq plans and the operators and buildirq inspectors who are responsible for the outaane of these plans. The education propan muld give a review of the requirerents of the erosion contzol ordinance an3 specific recanrendations for cost-effective &sign and implmtation of the ordinance. Similiarly the aq-ricultural education pmgrm muld focus on agricultural opators and the Soil Consexvation swice and e@asize cost-effective implmtation of best managanent practices in the mtershed. small amDunts of the total sedinwt can be LemcNed in sedimnt basins located at South Coast Asphalt and the mxlM of the lagcon (Alternatives S4 and 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 Sedinwt basins is that it is less costly to remve the material at these locations than after it reaches the lagcon. The nature of the material rennved will be sardier than the total sedment accumlating in the lagcon, therefore a mre usable raterial. The sediment *an side channel arroyos can be effectively antrolled by repair- the axrop and preventing further erosion (Alternati- Sl). These r*ouldterep&xedinthesamefashionastherraincreekchnnel. dmut 45% by reducing flocd peaks w future conditions by cQnstmlcting sediroent inflaw CM LT2 further reducel by antrol of sediment sources in the watershed. 'Ihe releative success of these sediment amtrol ueasures is not easily quantifiable. Haever, it is not unreasonable to suggest that vigorous application of such measures could reduce the sediment 14 by about 50%. inflaw wuld be reduced to about 30% of its expcted future value. This, canbined with reauction of the flood peaks, klould mean that the sediment ~n contrast, nuiifying the lagom hydraulics is not nearly as effective in reducing sediment accrmulation. with all the reasonably feasible Eadificaitons - cleariq the 1-5 bridge, widenjq the Hill Street culverk and I.0wd-q and widening the aatlet wix, the sediwnt accxmulation reduces only by 13%. Even with these modifications, maintainirg a deep channel through the entire lagoon reduces sediment acamulation by 23% (Alternative L2). A deep channel wuld requize constant mintenance as it wndd tend to fill with sediment resusp~ded by wave action in the smuer, and is mt a very practical won. 39 .. The effectiveness of individual uaiificatims in the lagocpl is negligible. Tlq only achim the 13% re&ct.ion when hpleaented together. This can be seen by canparing rum 9 and 12, 13 ard 16, 17 and 20, with 29 and 30, and with 32 and 34, as shm in Table Seven. ~n its present state, managed as a fresh water lake , Euena Vista Lagoon is a very efficient sedinwt trap. It traps abut 90% of all sediment which enters it. 'Ihe cmly hydraulically feasible way of greatly in-sing the flushing of sediment fran the lagoon is to restore it to tiddl action. Haever, because the -t discharge to the lagoon is MW 90 laxye, even with tidal action the 1- vnuld probably silt up to a fractim of its original size. Even with the best pssible scenario of watershed improvements, considerable mounts of sedinwt will have to ke remved in order to maintain the lagam in its existing state. To predict the aanxrnt of dredging requird, flaw n'esuranents and sedinwt samples will have to be taken on Buena Vista Qe& ard at the cutflow wir in order to calculate a mre accurate sedinrent hdget. In addition, periodic bathymetric surveys will need to be made of the lagocm to measure actual sediment acdation. Based on the existing analysis using data fran other watersheds, the average dredgirq requhmmt probably will be in the range of inplmentd. Probably between five ard twenty percent of this sediment will be 10,000 to 100,000 tcpls/year, asmning the watershed xdifications are of suitable size for beach replenishmnt. VI. 1. - 2. -1ais The Lagoon's mture In its existing state Ellena Vista Lagocn acts as a very effective sediment trap. under existing watershed mnditions it appezm? that the entire the siltation 0caurir-q during a few h.rqe stow. under future watershed lagcon will silt in over the next twenty or thirty years, with mst of conlitions the rate of siltation will increase substantially, reducing the expect& lifetime of the lagam to less than ten years. 'Lhe nwt effective m=ans of reducing reduce sediment infh frcm the watershed. Sdimmt accumlation in the sediment ammulation in the lagum is to watershed and enhancirg the creek, thereby reaucilq sediment inflm. lagoon can be reduced by about 50% by reducing flmd peaks in the To reziuce sediment entering the lagum &an creewmd erosion, a maximm effective rad vas -led as the m&mm wlocity that vegetation muld amceiviibly withstand. her velocities are & and will be mre effective. All initial creek design should check flood control requirements, and utilize the maxknm velocities using "q mugtnress coefficients of tbe channel. So the velocity of the 100 year stom shauld not exceed six 0.030 to 0.050, which is the range of the vegetation grawth muqhmss in charnrdl~tycriteriaofaixfeetper~isrequired. Thisis 40 feet per second U3i.q a Ydming roughness coefficient of 0.030 ard the finished flm elevations skdd be one fcut higher than the anticipated water surface elevation using a Manning coefficient of 0.050 for 1OO-year storms. A low flow channel should be designed to accnmodate the 2-year storm possible. Drop structures should ke placed in the channel to 1- flows. This lcw flaw channel should be configured to ke in shade wherever velocities and banks revqetated to prevent erosion. A typical stream cross section is &.awn in Figure 5. Tb lower middle reach is absorbing large quantities of sedim=nt and is presently offering a significant tuffer for the lagcan by acmdating great quantities of sediment be- tranqorted in the creek. This section of the flocdplain rmst be preserved in its present state. 3. Detention Basins rn) The eight detenticm basins outliwd on Figure 4 sbdd be built and be the &sign criteria for these basins. maintained. &dmn peak attenuation for the 2 to 1OO-year storm should The mst effective method of decreasing the sedknent accunulation in the lagoon with lagoon enhancemnt is a &ination of a rrnvable crest wsir with a width to 80 feet, enlaqinq the apening at Hill Street to 100 feet wide, excavating the material under the freeway, and breaching the barrier beach during storms. This scenario of inprovenmts reduces sediment acdtion by only 13% ard has mny emrirornnental drawbacks. 5. Continuinq Ehsior. Control Education (S2 and S31 The first erosion control workshap was well attended. There seems to be a comuniq carmitroent to erosion control. Efficient erosion control bth for grading anl agriculture will pay off well in terns of reducing sediment acamulation in the lagoon be beneficial. "e two feasible locations for sdimnt basins are at Smth coast Asphalt ard just upskeam of Jefferscm Street. 7. Dredg* Even with all of the effective mthcds outlined herein, the hgm will have to continue to be dredged pericdically. The alternatives wre all ccnpared to this inevitable and ongoing solutim. 41 8. bl-dto3zLrq The fact that this is a mnpletely mgauged meshed gives the findings mre accurate estirrates of fld flaws, of this shyty an anwnt of uncertainty. There is a need for mcplitoring so sediment t?zinsp?=t and seokrwt accundation rates can be observed. The mcdels used in this study then can h calibrated and the accuracy inprwed greatly. -in gauge anl stream flaw mnitoring an? needed to calibrate watershed mcdels. nese will also help to anser rrwy of the local questicns regazdirg storm flaw values. Present estimates of these storm flow =lues Mlry wildly. sediment sampling in the creek will pwide mre definite correlation between the sedimnt flaws and the flccd flcws. This will help develop a sedimnt rat- curve for the Buena Vista watershed. Bathptric surveys of the lagum need to be taken, especially before and after major stom events in order to monitor the s=diment ammulation . 42 .wals and Reprts on Engineering Practice, No. 54, 1975. Sedimentation ard Enqined.n~, v. Vanoni, ed. %of*, J. S., et al. 1983. Projecting ature Seal Level Rise, !-kth&logy, %timates to the Year 2100, ar$. Research Needs. A Report of the Z.S. Olviromtal Protection -cy. Project an Beach Sand Replenishtent. prepared under contract with the Bureau Sinuns, Li 6 Associates, Fort Collins, CO. 1984. Effect of the Sane Nuqarita of &clanation. U.S. Amy Corps of Engineers, 1973. Flood Plain Information, Euma Vista creek, Pacific Ocean to Vista, San Diego county, CA. Preparea for San Diego County. Yalin, M. S., 1972. Elechar!ics of Sdim=nt Transport. Peqanmn Press, Oxford. United States Geological Survey Water Resources Data for California, 1975-82. United States Geological Survey, &nlo Park, CA. 43 APPENDIX ONE SUBBASINS FUTURE HYDROLOGICAL CONDITIONS CALCULATIONS NATEgSHED SUBBASIII FUTURE CHARATERISTICS 0.32 LAG = 24n(L X Lc/SQRT s) sua- LU SOIL R 5AS!1! 1 coi*1:1 HOR NOR LDR FMST 2 COMM 0 HOR 0 MOR 0 LOR FMST 3 corn HOR MOR LOR FMST 0 4 COMM 0 HOR 0 MOR 0 LOR FMST 0 5 CMl D HDR 0 MOR LDR FMST 6 COMM 0 HOR 0 MOR 0 LOR FMST 0 404 0 20R 0 40% 40% 402 20% 100% 30% 30% 20% 20% 50% 50% 50% 30% 20% scs cr! 92 aa a6 92 90 88 86 92 88 90 86 92 90 92 88 90 X 2 OiF L (FT) LC (FT) n (Fi/i.;! ) C:4 ELEV LENGTH PC-C!IT BASIN SL3PE 36.8 220 3500 1800 0.05 332 0.0 17.6 0.0 COMPOSIT 34.4 CN LAG (HR) 0.0 89 0.2263 ". 36.8 150 3500 1400 0.045 226 36.0 17.6 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 90 0.1991 0.0 700 4000 2200 0.05 924 0.0 0.0 0;O COMPOSIT 0.0 86 0.2115 86.0 CN LAG (HR) ' 0.0 COMPOSIT 17.2 CN LAG (HR) 0.0 89 0.2394 46.0 50 3000 1500 0.03 88 45.0 0.0 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 91 0.1537 46.0 150 2500 1000 0.03 317 27.0 17.6 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 91 0.0964 A-1 7 CO” HOR MOR FMST 0 LOR 8 COMV HOR MOR LOR FMST 0 9 COMM MOR HOR FMST D LOR 10 COMM HOR MOR LOR C FMST C 11 CO” HOR MDR LOR FMST 12 co” HRR MDR C LDR C FMST C 13 COMM MOR HOR LOR 0 FMST PARK D 100% 100% 100% 50% 50: 0 100% 40% 40% 20% 30% 7 0% 0.0 650 6000 3500 0.05 572 0.0 0.0 COMPOSIT 0.0 0.0 86 0.3224 86 86.0 CN LAG (HR) 0.0 900 4000 2500 0.05 1188 0.0 0.0 0.0 COMPOSIT 0.0 86 0.2117 86 86.0 CN LAG (HR) 0.0 450 4000 2000 0.05 594 0.0 0.0 0.0 COMPOSIT 0.0 86 0.221 8 86 86.0 CN LAG (HR) 0.0 650 6000 2500 0.05 572 0.0 0.0 84 42.0 COMPOSIT 82 41.0 CN LAG (HR) 0.0 83 0.2837 0.0 650 5000 2500 0.05 686 0.0 0.0 0.0 COMPOSIT 0.0 86 0.2557 86 86.0 CN LAG (HR) 0.0 150 5000 2500 0.035 158 0.0 86 .34.4 84 33.6 COMPOSIT 82 16.4 CN LAG (HR) ” ~ 0.0 84 0.2365 0.0 200 3000 1500 0.035 352 0.0 0.0 0.0 CN LAG (HR) 87 26.1 COMPOSIT 82 57.4 84 0.1378 A-2 14 COFV HOR MOR 0.0 600 10000 4000 O.CE 317 0.0 84 25.2 COMPOSIT e. 0 30Z 702 FMST C LDR C 82 57;4 CPI LAG (HR) e. 0 83 0.4609 15 coMr4 MOR HDR LOR C 0.0 250 3000 1500 0.035 440 0.0 84 33.6 COMPOSIT 0.0 0.0 CN 77 46.2 80 LAG (HR) 0.1354 4 02 60% FYST PARK C 40% 40% 20% 1 6 COMI.! B HOR B MOR LOR B FMST 90 36.0 250 3200 1500 0.03 413 82 32.8 78 15.6 COMPOSIT 0.0 0.0 CN LAG (HR) 0.0 84 0.1175 60% 40Z 17 COMM B HDR MOR B L3R 90 54.3 250 3000 1000 0.03 440 0.0 80 32.0 0.0 COMPOSIT FMST 0.0 CN LAG (HR) 0.0 86 0.0970 18 COMM C HDR C 40% 91 36.4 250 9000 5000 0.028 147 88 17.6 MOR C LDR C FMST 86 17I2 84 16.8 COMPOSIT 0.0 CN LAG (HR) 0.0 88 0.3124 . 19 co" HDR MOR LOR C FMST C 0.0 500 6000 3000 0.05 440 0.0 0.0 84 25.2 COMPOSIT 82 57.4 CN LAG (HR) 0.0 83 0.31 96 30% 70% 20 COMM c HDR MOR C LOR C FMST C 30% 30% 91 27.3 250 9500 5000 0.035 139 0.0 86 25.8 30% 10% 84 25;Z COMPOSIT 82 8.2 . CN LAG (HR) 0.0 87 0.4027 A-3 21 COMM 0 HDR 0 30% 92 MOR 0 30X 90 LOR 0 30% 88 10% 87 FMST 22 COMM C HOR B 50% 91 50% 82 MOR LOR FMST 23 COMM D 40% 92 HOR 0 202 90 MOR D 30% 88 LDR D 10% 87 FMST 24 COMM c 60% 91 HOR C MDR C 30% 88 10% 86 LOR FMST 25 COMM C 40% 91 ~~ HDR C 20% 88 MDR C 30% 86 LDR C 10% 84 FMST 26 COm HDR MDR D 100% 88 LDR FMST 27 COMM C 20% 91 MOR C HDR C 20% 88 60.2 86 27.6 100 10000 6000 0.03 53 27.0 26.4 8.7 COMPOSIT 0.0 CN LAG (HR) 0.0 90 0.4534 45.5 80 2000 1000 0.028 211 41.0 0.0 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 87 0.0893 36.8 220 9000 4000 0.028 129 18.0 26.4 8.7 COMPOSIT 0.0 CN LAG (HR) 0.0 90 0.2941 54.6 85 4000 2000 0.028 11 2 26.4 8.6 0.0 COMPOSIT 0.0 CN LAG (HR) or 0 90 0.1705 ' 36.4 180 5000 2500 0.03 190 17.6 25.8 8.4 COMPOSIT 0.0 CN LAG (HR) 0.0 88 0.1958 0.0 170 5000 2500 0.035 180 a. 0 88.0 " - 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 88 0.2310 18.2 200 6000 3000 0.035 176 17.6 51.6 0.0 COMPOSIT FMST LDR 0.0 CN LAG (HR) 0.0 87 0.2663 ._ ~ ~~~ ~ A-4 28 COMM C HDR 0 MOR 0 FMST L3R 29 COMI-I HOR MOR 0 LOR FMST 30 COMM D HDR 0 MO2 D LDR FMST 31 COMM C HDR 0 MDR D LDR FMST 32 COMM D HDR D MOR D LDR FMST 20% 91 18.2 180 4500 2500 0.035 21 1 40% 90 36.0 40% 88 35.2 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 89 0.21 51 0.0 120 4000 1800 0.035 158 0.0 100% 88 88.0 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 88 0.1918 20% 92 18.4 150 5000 2500 0.035 158 30% 90 27.0 50% 88 44.0 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 89 0.2365 20% 91 18.2 220 3400 1500 0.035 342 504 90 45.0 304 88 26.4 ~. 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 90 0.1454 40% 92 36.8 260 7000 3500 0.035 196 304 90 27.0 304 88 26.4 0.0 COMPOSIT 0; 0 CN LAG (HR) 0.0 90 0.2933 33 cm HOR MDR D 1@0% LOR FMST 34 COMM 0 50% MOR D HOR D 304 20% LDR FMST 0.0 180 4000 2200 0.035 238 0.0 88 8816 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 88 0.1916 92 46.0 180 4700 2500 0.035 202 88 17.6 90 27.0 0.0 COMPOSIT 0.0’ CN LAG (HR) 0.0 91 0.2205 A-5 35 COMM D HDR 0 MDR 0 FMST LOR 36 COMM C HOR 0 MDR 0 LOR FMST 37 COMM HDR MDR D LDR FMST 38 COMM HOR C MOR 0 LDR FMST 39 MDR A MOR C MOR D 40 MOR C MOR 0 41 MDR C MOR D 1 0% 2 0% 70% 10% 20% 70% 100% 60% 40% 10% 20% 7 0% 30% 70% 60% 40% 92 90 aa 91 90 a8 88 88 88 73 88 86 86 88 86 88 9.2 200 5000 2000 0.035 18.0 61.6 0.0 COMPOSIT 0.0 C N 0.0 89 LAG (HR) 0.2057 9.1 200 4000 2000 0.035 61.6 18.0 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 a9 0.181 1 0.0 370 4500 2200 0.035 0.0 88.0 ~- ~ 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 88 0.1787 0.0 340 5500 2500 0.035 35.2 52.8 ~~ 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 88 0.21 38 0.0 340 4000 2000 0.035 7.3 " 17.2 61.6 COMPOSIT 0.0 CN LAG (HR) 0.0 86 0.1638 0.0 320 3500 1500 0.035 61.6 25.8 . 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 87 0.1376 0.0 280 6000 3500 0.035 51.6 35.2 0.0 COMPOSIT 0.0 CN LAG (HR) 21 1 264 434 326 449 483 246 0: 0 a7 0.2649 . 4-6 42 MOR C MOR D 43 EKIR C MOR D 44 KOR C MOR 0 45 cow4 HOR MOR C LOR FMST PARK C 46 COMM C MOR C HDR LOR FMST OPEN C 47 MDR C MOR C 48 COMM D COMM C MOR 0 HDR 0 FXST 60% 402 50% 50% 40% 6 0% 30% 70% 10% aox 10% 30% 70% 40% 40% 10% 10% 86 0.0 51.6 240 3000 1500 0.035 88 35.2 ~ .~ 0.0 COMPOSIT 0.0 C ?! 0.0 a7 LAG (HR) 0.1331 422 0.0 220 2500 1200 0.035 465 86 43.0 88 44.0 0.0 COMPOSIT 0.0 c N LAG (RR) 0.0 87 0.1121 a6 34.4 0.0 240 4500 2000 0.035 282 88 52.8 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 a7 0.1871 0.0 280 4000 1500 0.035 370 0.0 77 23.1 0.0 COMPOSIT 0.0 CN 86 60.2 a3 LAG (HR) 0.1523 91 9.1 240 4500 2000 0.035 282 88 70.4 0.0 0.0 COMPOSIT 0.0 CN LAG (HR) 71 7.1 a7 0.1871 0.0 260 3700 1500 0.035 371 a6 25.8 88 61.6 0.0 COMPOSIT 0.0 CN LAG (HR) 0.0 87 0.1478 92 36.8 220 4500 3000 0.035 258 91 36.4 88 8.8 COMPOSIT 90 9.0 0.0 CN 0.0 LAG (HR) 91 0.2220 A- 7 49 CO" c 40% 91 36.4 280 6500 2200 0.035 227 HDR D MDR 0 20: 90 18.0 LDR 40% aa 35.2 0.0 COFIPOSIT 0.0 90 0.2324 FMST 0.0 c N LAG (HR) 50 COMM 0.0 330 7000 3000 0.035 249 HnR 0.0 ". 14DR A 100% 73 73.0 LDR 0.0 COMPOSIT FMST 0.0 CN LAG (HR) 0.0 73 0.2644 A-a APPENDIX TWO COST-EFFECTIVENESS ANALYS!S ANNUAL COSTS DREDGING: NATERSHED IN FUTVRE COFIDITIOk 191.500 CY SEDIME?JT DELIVERY X $7.35 /CY =fl, 407.525 LAGOON IN EXISTING COIIDITIOfI LAGOON MODIFICATIOM: WATERSHED IN FUTURE CONDITION LAGOON !:IITH 80' LOI4ERIiIG !$EIR, 100' HILL ST. BRIDGE & DREDGING AT 1-5 WEIR: $400.000 INITIAL COSTS LIFE: 20 YEARS = OPERATION AND I.IAINTANEIICE: 520.r300 HILL ST: $140.000 INITIAL COSTS LIFE: 50 YEARS = s20.000 $30.000 INITIAL COSTS $2.800 1-5 TOTAL ANNUAL COSTS: LIFE: 2 YEARS = $1 5.000 $57.800 LAGOOM CHANNEL DREDGED 10' OEEP 100' WIDE WATERSHED IN FUTURE -CONOITIO~ 268.500 CY X $4.027.500 INITIAL COSTS LIFE: 2 YEARS = $2,013,750 615 PER CY DETENTION BASINS WATERSHED IN FUTURE CONDITION WITH 8 DETENTION BASINS LAGOON IN EXISTING CONDITION LAIXI: 19 ACRES X $1 30,000 PER ACRE = $2,470,000 LIFE: 50 YEARS = COIIST'N: $11.500 EACH X $49.400 8- $92.000 LIFE: 10 YEARS = $9.200 MAINT: $1 30.000 TOTAL ANNUAL COSTS: $188.600 CREEK ENHANCEMENT WATERSHED IN FUTURE CONDITION WITH 8 DETENTION BASINS LAGOON IN EXISTING CONDITION LAND: 1,050,000 SQ FT X $4 PER SQ FT =$4.200.000 LIFE: 50 YEARS = DROP STR $5.000 EACH X $84,000 160 - $800.000 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 A-9 A-10 Pm-lEmmsD~mxKTI~ wA!lmsHEDL?EKN %mxKT ANNUAL - CmD a3-m smm sEDIMR?r Acxm Fnxrl!. FVNRE WSTW BASIS FwlURE~ 191,500 - 12% 168,520 22,980 ETmJKE aIm€icn?Qa 26% 141,710 49,790 Ewmm ~~ 26,810 F WDET WSTlX 20% 153,600 37,900 DGT&EMI EXIT 45% 105,100 86,400 EMIANC wsp 48,500 MINI" $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 4,500 $33,075 5,000 $36,750 2,500 $18,375 1,600 $11,760 - 1.00 3.0 2.0 .1 2.8 1.2 6.3 5.6 1.6 2.2 .. APPENDIX THREE MIDDLE REACH EROSION CALCULATIONS DISTANCE VOLUME SECTION CROSS BETWEEN (CY) NUMBER SECTION SECTIONS AREA (FEET) 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 (SF) 655 243 139 51 9 526 645 520 581 384 1895 51 9 41 2 85 54 400 374 92.5 840 51 0 440 1.460 980 275 7 80 640 590 200 710 420 110 460 640 300 13.963 3,612 5.361 28,242 21,252 5.930 15,893 11,435 24.900 8.941 12.238 3,864 284 3,869 9.170 2,590 171,542 TOTAL EROSION IN THE UPPER MIDDLE REACH A-13 . " . . . D& a@, '. . 'e - 0; QU .. ....... o'c 0' 0' .. 9" -. ..... .. .. ...... , . .... - "A__. - : , I , -I ! '7 .--- - '' ?" ... - . a. - 0- 8 ... ..... - r- '9 .. .... Q + 0 .. ... . -. . i .. .. -- a I . L .) ,I .. I * i .......... "" ... ...... .... 623 ..... , .. . .- " ..... .. .. ,' .. I. .:._.I I. .. ,'I .. , i. ,,. I. * . -. "- -1 "I ......-. .~- ..- ........ .. ,, ! ,, c '5 I , ' I" ' '' ' ! 1 : . ::.. . . . ., , I A-19 A-20 STATE OF CALIF~NIA4ES0UllCES AGENCV GEORGE DEUKMUIAN Germor CALIFORNIA STATE COASTAL CONSERVANCY 1330 MIOADWAV. SUITE 1100 OAKLAND. CA 94612 ATSS 561.1070 TELEPHONE 415/464-1015 .*I October 1, 1985 Dear Friend of Buena Vista Lagoon: We are pleased to send you a copy of the final Buena Vista Lagoon Watershed Sediment Control Plan and Implementation Plan. A great deal of research & effort has gone into this plan and we feel its findings represent the best combination of solutions to controlling sediment entering Buena Vista alternative and represents a combination of State and local funding. Lagoon. The implementation plan outlines a funding strategy for each will last no more than 20 years if no sedimentation controls are instituted Perhaps the most ominous conclusion of the study is that Buena Vista Lagoon or the lagoon is not dredged continuously. Such a finding should serve as a warning to State & local government officials,local citizens and lagoon supporters that the time for acting to preserve the lagoon is now, or we may not have a lagoon to preserve. The Conservancy expects to continue working to implement this plan and we hope to count on your continued support. We would appreciate recieving any comments on the plans at the address above. &&w Sincerely, Laurie Marcus Project Manager LM/mc STATE G+ CALIFORNIA~ESOUICES AGENC( GEOFGE MUUMUIAN. br-r CALIFORNIA STATE COASTAL CONSERVANCY 1330 WOADWAY. SUITE 1100 OAKLAND. CA 94612 ATSS 56-1070 TELEPHONE 1I5/W1015 ~VIm" -cN PLAN M?mGEmm SNDY Ihe State Coastal Conservancy proposes to inplment the reammdations of the &era Vista Lagoon Watershed sediment control Study according to the following plan. This plan is only a pmposal and will require the apprwal of the Comerwaxy Board and mopration of the identified agencies before any funding will be ma& available. Ccmm~11t.5 cn the inplmtatim plan shnzld be at any 03nsWancy Board meeting at which fradLg fcu this plan is amsidered. sent to the Consemmcy at the address belaw. , mlic cnnnent my also be mde Please amtact the Conservancy for the date and lccatim of these Board meetings. Table che mtlines the reonmdaticms of the study and their apprcocimate benefits and costs. It is proposed to inplemtt these Wtiom in two phases. "e first dd involve alternatives Wl, VS, S1, S2, S3, 54 arrd SS, (all the mterskd dfiatims). phase tm whi& includes lagum dficatims &I) has a nrmber of envimnn?nhl inpacts associated with it. These include potential loss of fish fran a ld weir, possible salt water cowtruction. RLis alteznatitre should be vid as a last mrt in intrusion into the lrmer lagoon and disruptim of the lagwn ~JX- omtrow sdhentatim and all imprwements in the watershed should be canpleted first. Alternative L2 is not recanoended for implem~taticn due to its law benefit cost ratio. detention basins and to pmvide Icng" operatitn and main- of the carplete, WB and the cohservan~y will discuss the allocaticm of responsibility for aoquisitim -. -cy staff has proposed this scenario to the must also apwe fundirq prior to any propeay plrchase. staffof~andtheywillbecansideringitinthewttrronth. "heirboard The engineering design and conskudim costs for this alternative are estimated at SU2,OOO - $122,000. The Conwrvancy has applied for $112,000 fran the hvirommental License Plate Fund for fiscal year 1986 - 87. 'Ihe F!em Agency, Iegislature and Governar rmst am this request ad appropriation. Consezvancy grants urder its Wscmrce Rhncenmt proSram auttnrity, dd be proposed for the cities to armstruct the basins within their jurisdiction. zhe Cohserrmncy Board rmst appmrre any experditure of operation and maintename responsibilities. Envircummal License Plate funds or sqpletent with QnservaMy bmd or other fmdsasneeded. basinsifthestatepnchasestheneededlands. mcetheappraisalsare fmdsarr3.eachcitycouncilrmst~andacceptthegrantandlongtenn . upcnthe actual msts an3 timing of the ocnstruction, the Qnservancy may apply for additional Sediment Source Control This alternative includes five separate kctiw. %st of these actions are Iaxgely of lcw initial cost and require yearly operation and maintenance. The repair of the side array0 at El cwiro M is estimated to cost $30,000 and will be accomplished through the use of dmp structures and revegetation. This arroyo lies within the City of Carlsbad. The Qmsemmcy dd consider funding a portim of the cast for this repair if the City of carlsbad is unable to frod this repais thnxqh aeVelopnent conliticns or other Snares. Ihe hu &.vation programs, S2 and S3, dd best be irrplanentea by the Joint Pwxs ccmaittee in the sate manner as the previous erwion mt~~l wrkstqs. These programs are envisioned as a hads-on style wrkshop with the primary benefits aimad at City review am3 enf-t staff and camunity contractors and farmers. Ihe Qnsenrancy Rccmaends that the cities each donate finds to the Joint FTJWXS ccmaitte to proceai with organization and annual to bi- basis. %e Crnservancy is not specifically fqxmerd to administration of these worlrshops. lhese worlcshops sharld be repeate3 0x1 an fipd ducaticmal psograus. Alternatives s4 and ss irmolve parly main- of sediuent basins at two locations - Scuth Best As@mlt ard the Jefferacn Street overcr~ssing. 'Ihe basin lies on the border of the cities of Oceanside am3 Carl&&. Wle the S&h Coast Asphalt hasin is within the City of Qrlshd. The Jefferson Street Co~Qn"~0ffacilitiesthe~doesnotfund cpraticn and makrtenance annual nE&l-, the Bnswancy . As the prjmary benefit of these basins is their is mt able to furd these two alternatives. Staff therefore mcxmmas the cities of Carl- d oceanside irmestigete the possibilities of requiring crnstnrticn and m&&naxe of the basin at Smth Bast Aeplalt as a cerditim of develcpaent or fom an assessment district to furd~mainteMnceof~hubaat'ls. m u . e 0 rc *o . rn Y -c >rn mw .: