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CENTRE

Th e Lake M aracaibo R em ediatio n Study is a maj o r mu lti- disc iplinary study for t h e Pecroleos de Ven ezu ela SA (PDVSA) carri ed out by an in te rnational co n s o rtiu m h ea d e d b y B ec ht e l Inte rnational Systems and includin g the Ce ntre for W ate r R esearch . Lake Maracaibo is o ne of Ve n ezu ela's m ost important water resources, providing fresh water for ag ri c ultu re and supporting a local fi she ry, and is also the lo ca tio n o f a m aj o r pe tro leum industry. H owever, over the past fe w decades the water quality in the lake has dete rio rated , due pri ma rily to inc reas ing sa lini ty and eu crophication caused by the d redgi ng of naviga tion chann els and th e increas ing indu stria lisatio n and urbanisation o f th e shores o f the Lak e. Th e o bjectives o f this study are to co mpl e te a co mpreh ensive analysis of the e nviron menta l condition of th e Lake, collect additio nal e nviro nmental data , and develo p analytica l m o delin g cools that al.low th e evaluatio n of alternati ve re m ediatio n strategi es. A basic question posed repeatedly o ve r the years is wh et her re du cin g th e sa lini ty would help re duce nutrie nt levels, increase di ssol ved oxygen con cen tratio ns in th e Lake, and improve the o ve rall e nviro nm ental quality of th e Lake . C WR has had a maj o r ro le in several o f important aspects of th is project, in clu din g th e planning and participati o n

FOR

WATER

RESEARCH

in th e m ajor fi e ld prog ram to co ll ec t hydrod ynamic and water quality data and the modelling of the Lake usin g the o ned i m e n si o n al h y drod yn a mi c m o d e l DYRESM . T he Ce ntre also provides o ngoin g a d v ice on asp ec ts o f th e consortium's remediation proposals. O cher m embe rs o f th e proj ect team are : Mo fa tc and Nic hols (U SA), the Danish H ydraulic In sti tute (D e nmark), lncoscas (Venezuela) and C CR lnge nie ria (Ven ezuela).

The Lake Maracaibo system La ke M aracaibo, loca ted in wes te rn Ve nezu ela, is the larges t lake in So uth Ame ri ca and a water body o f g reat economic and ecological importance. The Lake M araca ibo area is the largest oil productio n center in Venezuela. T he Lake is about 160 km lon g in the no rth-so uth directi o n and 110 km w ide in th e eastwest direction , and has an area o f about 12,000 km 2 , a maximum depth of30 111 , and a volume o f 300 J 09 111 3 . lt is conn ected w ith the G ul f of Ve n ezue la thro ugh the Strait of Maracaibo and T ablazo Ba y. Several rivers flow into th e Lake drai n ing a watershed of app rox im atel y 89 ,000 km 2, th e largest o f whic h is the R..io Catatu mbo (w hose m o uth and plume is shown above) accounting for close to 60 perce nt of all fresh w ater fl o w into the Lake. Th e m ean fresh water flo w from all rivers drain in g in th e Lake is abou t 40 10 9 111 3 p er yea r or abou t on e

e igh th of the Lake vo lum e. Ri ver flo ws vary also seasonall y be ing at a m ax imum in M ay, and in O ctobe r- Novembe r, and at a mi nimum du ring the J anuary- M arch d ry season. Flo ws also vary fro m year to year. During a 19-year pe ri o d (19761990) fo r w hic h there are system ati c estimates o f th e total river flow into th e Lake, th e monthl y fl o ws vari ed between 0 .3 and 2. 7 tim es the m ea n fl o w fo r tha t pe riod (CGR, 1993). Fresh wate r coming into th e Lake from th e ri vers m ixes with its su rface wa te rs and an eq ual volum e o f wate r leaves the Lake th rough the Strait. Ti dal action in combinatio n w ith seve ral o th e r fac to rs brings saline water from the G ulf o f Ve ne zu ela into Tablazo Bay and th e Strait of M ara caibo. T he ex tent o f th e salt wedge intrusion entering the system depe nds o n th e combi nation of several facto rs, w hich, besides the tides, in clude the race of fres h wa ter fl o w into th e La ke, w ind di rection and speed , and atm osph eri c pressure dist ribution. In dry years under low river flo w conditio ns, c om b in e d w ith fa vo rable w ind a nd barocropic condition s at the entran ce co the syste111 , the salt wedge can advance to the south end of the Strait o f M aracai bo , and from the re to the botto m o f the Lake. This process raises th e salinity of the Lake, es pecial ly in the h yp o limni o n , and co ntri butes to its den sity stra ti fi cati on. Th e e nvironme ntal co nditio n o f the Lake is a fun ctio n o f the combinati o n o f WATER MARCH 2001

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Profile for australianwater

Water Journal March 2001  

Water Journal March 2001