CHAPTER 37 GENERAL ASPECTS OF A STUDY ON THE REGIMEN OF LAKE MARACAIBO

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CHAPTER 37 GENERAL ASPECTS OF A STUDY ON THE REGIMEN OF LAKE MARACAIBO G. A. McCmmon Creole Petroleum Corportion Crcs, Venezuel Mrcibo Bsin in Western Venezuel, Figure 1, hs n re of 90,000 squre kilometers.

1 CHAPTER 37 GENERAL ASPECTS OF A STUDY ON THE REGIMEN OF LAKE MARACAIBO G. A. McCmmon Creole Petroleum Corportion Crcs, Venezuel Mrcibo Bsin in Western Venezuel, Figure 1, hs n re of 90,000 squre kilometers. It is isolted from the rest of Venezuel on the Est nd South, nd from Columbi on the West, by mountin rnges which rech height of 5,000 meters t the southern boundry of the Bsin. Lke Mrcibo nd its mrginl swmps cover 17,700 squre kilometers of the Bsin. The Lke proper, pproximtely 150 kilometers long by 110 kilometers wide, is connected to the Gulf of Venezuel by the Strits of Mrcibo nd brod shllow Tblzo By. It is bout 50 kilometers from the lke proper to the gulf. Tblzo By is seprted from the Gulf of Venezuel by series of shifting snd islnds nd brs. The Lke Mrcibo Bsin contins one of the world's lrge oil fields. Creole Petroleum Corportion s the lrgest producer of oil from this re, hs deep interest in ll the fctors which ffect the region. From time to time wi hve investigted the phenomenon of nture. The principl chrcteristics of the region which hve been studied so fr re: the climte, rin fll, lke currents, lke slinity, tides, nd the ction of the chnnels nd brs between the lke nd the Gulf of Venezuel. Since the entrnce conditions to the lke vitlly ffected the trnsport of oil from the fields to the world's mrkets they were the first to be studied by the oil compnies. When oil strted moving out of Lke Mrcibo the drft of the vessels ws limited to nine feet by n outer nd inner br, Figure 2. The chnnel cross the outer br ws not fixed becuse of the shifting snd, generllj the chnnel moved from est to west until it reched n extreme position nd reopened new chnnel to the est. The inner br covers the whole of Tblzo By nd it is pproximtely 21 kilometers cross. Wether on the outer br is generlly rough s wves re built up by the north-esterly wind cross the Gulf of Venezuel. On the inner br it is comprtively clm since it is protected by the chin of islnds which form the outer br. The first step in the study of the Br ws to form permnent survey body jhich ws orgnized by the joint ction of the oil compnies in Surveys nde by this prty determined tht the nturl chnnel migrted westwrd nd ccelerted its movements during certin periods to s much s three feet per ly. In 1935, the chnnel hd reched the extreme western position of its cycle >f migrtion nd hd deteriorted to the extent tht the opertions of the shllow drft tnkers were seriously hndicpped. Records showed tht new :hnnel would brek through the br somewhere to the est of the deteriorting :hnnel. This cycle of migrtion consumed period of bout 20 yers. As oil production incresed,the limittion of the br becme more serious, 'he oil compnies found tht they must open deeper chnnel. A model ws preprec y the Wterwys Experiment Sttion t Vicksburg, Mississippi, to determine the lost prcticl route for dredged chnnel. The tnker Invercibo ws converted o segoing hopper dredge nd commenced opertions in Up to 1947, she ompleted nd mintined 20 foot high wter chnnel. At the sme time, strtng in 1940, pipe line dredge deepened the 21 kilometer long chnnel cross the nner br. 625

COASTAL ENGINEERING Additionl.topper dredges ssisted the Invercibo from 1947 to 1949 but it ws evident tht this chnnel did not fulfill the needs of nvigtion into Lke Mrcibo.

2 COASTAL ENGINEERING Additionl.topper dredges ssisted the Invercibo from 1947 to 1949 but it ws evident tht this chnnel did not fulfill the needs of nvigtion into Lke Mrcibo. Severl studies of deep drft chnnel indicted th it ws possible but the studies differed in their recommendtions nd in the estimted cost of the project. In April 1953, the Venezuel Government initited project to provide 35 foot chnnel through which ocen going vessels could enter nd leve the lke unhmpered by the former restricted drft. The southern section of the project is chnnel 600 feet wide from deep wter of the lke to the northe limit of the inner br, length of 22.5 kilometers. In the northern section the chnnel widens to 1000 feet for 12 kilometers cross the outer br. The southern end of the outer chnnel is protected by rock brekwter 3.2 kilometers long constructed pproximtely 1 kilometer est of the chnnel. This chnnel hs now been in opertion for pproximtely yer. The chnnel cross the inner br hs been stble nd requires only minor dredgi by pipe line suction dredge to mintin it. The mintennce dredge strtc widening nd deepening the chnnel t the southern end this yer s the nei step in providing n outlet from Mrcibo for the still lrger tnkers ente ing the world pet-roleum trde. As ws expected, the outer chnnel requires constnt dredging to mintin its position nd depth. The rock brekwter protects the inner prt of the chnnel from the westwrd drifting snd but there is constnt snd encrochment from the est for some three kilometers north of the outer nd of the brekwter. The Venezueln Governmn.- expect to mintin this chnnel nd grdully deepens it by n ocen going hopper dredge which is now under design. The brs hve protected Lke Mrcibo from the encrochment of slt wter. The opening of deep chnnel from the Gulf of Venezuel into the 1 nturlly rised questions s to its ffect upon the slinity nd other chrcteristics of the lke. Creole is interested in ny chnge in slinit Although our oil field orgniztions use well wter for drinking they depen -pon lke wter for irrigtion, snittion nd industril uses. The lke furnishes fish nd shrimp for food* Any chnge of slinity would directly ffect the niml life nd would chnge the incidence of ttck from mrine borers. One of our mjor oil field problems is corrosion nd it would be ggrvted by n increse in the slt content. In order to be prepred for future chnges in the nturd. conditions, Creole undertook study of the lke to determine the fctors which ffectc its slinity, currents, wve ction nd ny other fctor which might be dis covered during the work. We requested the Woodshole Ocenogrphic Institul to mke the first studies, set up progrm of dt gthering, interpret tl dt which they obtined nd help us form n orgniztion to crry on the work. The study strted in April 1953, under the direction of Dr. Alfred ( Rdfield. It ws thought desirble not only to secure description of the distribution of slt in the lke s it existed in 1953, but to ttempt to dr consistent picture of the processes, motions nd influences which determ this distribution s it exists nd s it my vry from time to time. Dr. Redfield'o group set up progrm to mesure wter temperture, oxygen, 626

3 GENERAL ASPECTS OF A STUDY ON THE REGIMEN OF LAKE MARACAIBO u u PQ o oi o U esi H m -I 627

4 COASTAL ENGINEERING DW IfCX* «0tf 7 *30" SURFACE CURRENTS (FT/SEC) 71*00 MARCH 1954 Pig. 3. Surfce currents - ft. per sec. (Mrch 1954). SURFACE CHLORIDE MARCH I9S4 Surfce chloride (Mrch 1954) STATION NE sw - I /» / eo oo^ J eo ^/ 100 ^V* ^fck _ CHLORIDE - ppm STATION NW SE \ 60 \ j ' _ ^5 0^ CHLORIDE - ppm Fig. 5. Chloride concentrtion with depth 72*00 BOTTOM CHLORIDE 71*00 MARCH 1964 Fig. 6. Bottom chloride (Mrch 1954). 628

GENERAL ASPECTS OF A STUDY ON THE REGIMEN OF LAKE MARACAIBO, hosphorue nd chlorides. They lso estblished sttions in the Strit of Mr to observe tide cycle nd the currents.

5 GENERAL ASPECTS OF A STUDY ON THE REGIMEN OF LAKE MARACAIBO, hosphorue nd chlorides. They lso estblished sttions in the Strit of Mr to observe tide cycle nd the currents. They exmined the vilble dt of the slt content of the lke t previous times, pertinent informtion on tides, se level, rin fll nd winds. From this informtion they set up progrm of observtions to be mde t intervls to provide criticl informtion on the se sonl nd long term chnge in lke wter. After the Spring observtions by the representtives of the Woodshole Ocenogrphic Institution Creole personnel con dt gthering until Mrch 1954 when the representtives of wooushole returned for dditionl observtions. Since tht time Creole stff hs continued to gt dt to follow the chnges in the lke s they occur. As might be expected, the study brought forth fcts which were surprise us. It ws commonly thought tht the chlorides vried from mximum t the nori of the lke ner the entrnce to minimum t the south. Field observtions di< not be<?r this out. The surfce chlorides were found to be uniform round the edge of the lke nd to increse towrds the center. The cuse of this distribution ws the counter-clock wise circulting current in the lke. This current is probbly cused by the wind. The velocity of the current diminishes from the surfce towrd the bottom nd hs men vlue t the surfce of th order of 0.7 foot per second. At this velocity prticl of wter mid-wy between the center of the lke nd the shore would require bout 10 dys to complete the circuit of the lke. The current ppers to fluctute slightly s the result of semidiurnl tidl components. The velocity decline s the seson dvnces nd my become immesurble in mid-summer. Figure 3 ehc> the surfce currents, in feet per second, which were mesured in Mrch The lk3 contins two distinct clsses of wter which cn be distinguished by th chloride content: A. The Epilimnion, or upper lyer, in which the chlorides vry only slightly from plce to plce, nd with depth. 3. Th Hypolimnion,- or deep lyer, in which the concentrtion of chloride is distinctly higher nd increse with depth. The Epilimnion contins the lrge mjority of the lke's wter. In 1954, it constituted of the volume. Its uniform chloride content indictes tht th circultion nd the turbulence due to wind-wves re very effective in mixing th<2 fresh nd slt wter. Chemicl nlyses of the chloride nd other slts of the lke wter show tht the slinity is derived from the wters of the Cribben Se. In 1953/54 the verge chloride of the epilimnion ws 660 PPM. The mixed wter of the epilimnion consequently ws mixture of bout one prt Cribben se-wter nd 30 prts fresh wter. The concentrtion of chloride in the surfce wter of the lke, s observed in Mrch 1954, * s shown in Figure 4. The chloride is highest t th center of the lke nd lowest in bnd extending long the shore from the southwest side of the lke to, the northest. Over greter portion of the lke's surfce the chlorides rnge from 700 to 750 PPM in 1954, vrition of 7%. This generl distribution of surfce chlorides grees with dt collected by erly observers nd by the Woodshole Survey of During recent yers chlorides in the, 7>iliivtnion hve rnged from 400 to 1400 PPM. 629

6 COASTAL ENGINEERING The more sline wter of the hypolimnion occupies cone with its pex t the center of the lke. The chloride concentrtion over the bottom of the lke in 1954 is shown in Figure 6 nd should be compred with the surfce chlorids in Figure 4. The slt of the hypolimnion origintes from se wter which finds it wy periodiclly into the lke from the Gulf of Venezuel. The mixture of se wter nd lke wter which is produced by tidl mixing long the pproches to the lk hs greter density thn the lke wter. On entering the lke this wter sinks the deeper prts to form the hypolimnion. The concentrtion of chloride with depth is shown in Figure 5 representing two sections, mde in Mrch 1954, which crossed the lke obliquely t n ngle of 60 from one nother. Above the 800 PPM isochlor, the chloride concentrtion vries very little with depth. Below the point of 800 PPM the chloride increses grdully but t ccelerting rte until it exceeds 2000 PPM t the bottom ner the center of the lke. Dr. Redfield suggests the rotry circultion of the lke cuses the dense wter of the hypolimnion to be spun up into cone with its pex t the vortex of the eddy. As result the hypolimnion is withdrwn from the bottom round the mrgines nd the epilimnion occupies the entire wter column even to depth of 100 feet. The epilimnion nd hypolimnion mix most intensely in the vortex nc consequently this re is the pricipl source of the slt in the epilimnion nd the chlorides in the lke surfce re highest in the center. He concludes tht the velocity of the lke's circultion is dequte to cuse the observed ccumultion of denser wter of the hypolimnion t the center of the'lke. Between 1954 nd 1957 the hypolimnion disppered completely from Lke Mrcibo. This unexpected phenomenon ocurred during the time tht the outer nd inner brs were being dredged. Sometime erly in 1957, the hypolimnion strted to reform s wter of higher slt content entered the lke. The concentrtion of slt depends upon blnce between the inflow of fresh wter from the run off of rin fll, losses to evportion, nd the introduction of slt wter from the Gulf of Venezuel by tidl exchnge. The slt concentrtion vries with the sesonl vrition in these fctors. The stbility of the system depends upon the reltion between the volume of the lke nd the rte of exchnge of its wter. A study of the wter blnce of the Lke Mrcibo Bsin by Mr, Dougls B. Crter indictes tht the men run off from the lnd re of the bsin nerly equls the evportion from the lke, pproximtely 32 x 10^ cubic meters per yer. The precipittion on the lke proper pproximte 22 x 10^ cubic meters per yer nd is of the sme order of mgnitude s the net volume of fresh wter supplied to the lke. The men monthly vlues of the fresh wter dded to the lke is shown in Figure 7. The men monthly vlues of the evportion from the lke surfce re reltively constnt throughout the yer, but precipittion nd run-off vry in such wy tht during Februry, Mrch nd April less wter is gined thn is lost by evportion. Chnges in tide levels ffect the inflow n <i outflow from the lke but in generl terms we cn expect tht during nine months of the yer there will be net outflow from the lke wheres for three months there will be 630

7 GENERAL ASPECTS OF A STUDY ON THE REGIMEN 6r- OF LAKE MARACAIBO J FMAMJJASONO Fig. 7. Outflow nd inflow of the Mrcibo bsin. & 1500 " k 1 K s,.. \ 1 X ft i< <* S3 Is z«oj» 500 s * IS t ' i %» t \ < HLORIOES W PPM TEREDO RA 'V'sTD PAN L #*""""" " *.«**»» «.. ST* = 3» SB* RAINFALL LA SAL1NA M^BBHL ^_ Fig. 8. Reltionship between rinfll, slt content nd Teredo infesttion in Lke Mrcibo. 631

8 COASTAL ENGINEERING net inflow. Our studies hve not covered enough yers to determine if this cycle is n verge or how much it vries from the men during yers of high rin fll nd yers of low rin fll. Crter estimtes tht the exchnged volumes of wter re s follows: Net Accession fresh wter 21,34 10^ cubic meters per yer Inflow se wter ' cubic meters per yer Outflow lke wter ^ cubic meters per yer With the knowledge of the mechnics of Lke Mrcibo gined from this excellent study by Dr. Redfield nd his ssocites, we hve prepred Figure 8 which shows the reltionship between the rin fll, the slt content of the lke, nd the ttck of teredo Nvlis, the mrine borer which hs cused so much destruction mong our mrine instlltions. We re now ble to explin some of the nomlies of observed mrine borer ttck nd cn understnd why mterils tested t different time." in the lke show vrying resistnce to mrl borers. It is too erly to determine if the dredging of the deep chnnel through the Mrcibo br will influence the inflow of the hevier slt wter. Any effect of the chnnel which my hve been produced to-dte hs been msked by series of riny yers with high run-off. We expect to continue observtions to see if long time trend cn be determined. 632

Applications of Bernoulli s theorem. Lecture - 7

Applications of Bernoulli s theorem. Lecture - 7 Applictions of Bernoulli s theorem Lecture - 7 Prcticl Applictions of Bernoulli s Theorem The Bernoulli eqution cn be pplied to gret mny situtions not just the pipe flow we hve been considering up to now.