• 5. WATER RESOURCES IN SURINAME
5.1 Surface water (a) River Basins. Seven first-oeder rivers drain the area of Suriname towards the Atlantic Ocean. Three main groups are distinguishable when ~omparing the extent and shape of the drainage areas (FIG.5.l-1). A fTf-st group is repfeaentedby the larger Marowijne and Corantijn Rivers, with drainage areas of 68 700 and 67 600 km 2, respectively,which form the eastern and western boundaries of Suriname. Together they drain 58~ of the country. A second group is represented by the Coppename River (21 700 km 2) and the Suriname River (16 000 km 2 j, which drain approximately 24% of the country. The basins are elongated in a NE - 'SW direction located in the north-central area. They are seperated by the Saramacca basin , except in the extreme headwater area, where they have a common divide. A third group is represented by the Nickerie River (10 100 km2 ), the Saramacca Hiver (9 000 km 2 ), and the Commewijne Hiver (6 600 km 2). Together they drain about 16% of the country. The centrally located
Saramacca basin is elongated in a NE ~W direction. The Nickerie ba sin in the west is less elongated, and the Commewijne basin in the east is sub triangular. ihe drainage towards the coast is such that 38~ of the area drains to the extreme west \Corantijn and Nickerie Hivers) and 27% to the ex treme west \Marowijne «iverj.The remaining 35% drains to the east cen tral area discharging at the Coppename-Saramacca rivermouth and the Suriname-Commewijne rivermouth. The rivers are tidal generally up to the most seaward rapids about 90 to 120 km inland. (b) River Flows. The most important river-gaugung stations are loca ted in the basement area upstream from the tidal influence. The loca tions and the corresponding drainage basin areas are shown in FIG.5.1-l. The flows are listed in Tables5.1-1 and 5.1-2 (UNDP, 1972). They compare in magnitude with the three groups of drainage basins outlined. Flows vary seasonally, comparing with the seasonal rainfall dis tribution. This is illustrated by the hydrographs of the Marowijne and Corantijn Rivers (FIG.5.1-2). The highest flows are in May, June, and July, with a peak generally in Mayor early June, corresponding With the long wet season. The lowest flows are in November at the end of the long dry season. The short wet and short dry season are not as well defined, and at times they cannot be distinguished. 121
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, , ..! " , , "" , , " t...... ••,••• .~.-cf\D'. , , , ••".t U."• .,. _.,. "', u.!.!..!.!.. .~••• to. • tor ID ·t. ~.r I "'.~ o. " "'1. (IJ] I •••., ' ~ ~~.It., n .. •.... OJ] I.•• r •••" -_.-...... _ 11 , ..,. ".,1 tf __" .....1...... t,...... •. .. , " , ••,. , 11 \Brazll '. • 1"1G.5.1-1 Drainage ballns af Surinam lFrom: UNDP, 1972)
1-22
.!t .;g. -----
TABLE 5.1-1 (From: UNDP, 1972) ! RUN-OFF AND RAINFALL CHARACTERISTICS OF THE SURINAME AND MAROWIJNE RIVERS AND THEIR BASINS, 1952-1960 , , Year. ! , River, Station, and Drainage Area 1952 1953 1954 1955 1956 1957 1958 1959 1960 , + Suriname River 197 378 295 269 293 220 139 155 234 at Pokigron 25.4 48.7 38.1 34.7 . 37.8 28.4 17.9 20.0 . -30. J 2 2.624 2.563 2.383 2.076 1.848 2.212 7,750 km 2.177 2.381 1.974
MarOl~ijne River 1.529 2.088 1.717 1.955 1.943 1.776 .1.50J i . at Langeta~betje 24.0 32.8 26.9 30.7 30.5 27.9 . 22.,~ 2 2,569 2.510 2.249 2.194 1,745 2.095 2.5U J 63.700 1an -- + 197 Mean annual discharge in m3/s 25.4 Average annual unit discharge in I/s/km2 2.177 Annual rainfall total in mm E Estimated
f-' IU ,.oJ };'
.i; TABLE ;.1-2 (From: UNDP, 1972)
RUN-OFF AND RAINFALL CHARACTERISTICS OF THE SURINAM RIVERS· AND THEIR BASINS, 1961~1970
River, Station, and Year Drainage Area 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970(1) + E E E Corantijn River 811 1,388 1,647· 1,434 1,464 . at Mataway 15.7 26.9 31.9 27.8 28.~ 2 2,138 2,354 2,534. 1,893 2,436 51;600 1an E E E E . Kabalebo River 53 71 166 252 154 155 at Avanavero 5.9 7.9 18.4 27.9 17.1 17 .2 2 1;463 2,025 2.171 2,705 . 2,134 2,464 9,020 lan . - Nickerie River 33 at Blanche Marie 26.2 2 2,446 1,260 lan E Nickerie River 141 18 38 43 86 . 116 83 113 at Stondansie 27.3 3.5 7.4 8.3 16.7 22.5 16.1 21.9 2 2,714 . 1.700 1,947 1,965 2,408 2·,594 2,083 2,766 5,160 km + 811 Mean annual discharge in m3/s 15.7 Average annual unit discharge in l/s/km2 2,138 Annual rainfall total in rom E Estimated
I-'
,'"~ TABLE 5.1-2 (cant.)
T ,)! (From: UNDP, 19'(2) RUN-OFF AND RAINFALL CHARACTERISTICS OF THE SURINAM RIVERS AND THEIR BASINS, 1961-1970
River, Station, and Year , Drainage Area 1961 1962 1963 1964 196.5 1966 1967 1968 1969 1970 + ·E Coppenmne River 189 211 267 382 334 at Maksita Kreek 15.4 17 .2 21.7 31.1 27.1 2 2,115 2,511 2,866 2,307 12,300 1an I 2,175
- K. Sarmnacca River 14.4 26.4 6.7 12.6 9.7 at Anoema£oetoe 10.8 19.7 5.0 9.4 7.2 . 2 1,913 2,287 1,966 2,016 2,150 1,340 1an
! Sarmnacca River 52 82 135 32 64 ,j 64 90 119 128 96 at Dramhosso 14.8 23.3 38.4 9.11 18.2; 18.2 25.6 33.8 36.4 27.3 2 1,968 2,053 .2,799 1,765 2,115 2,202 2,228 2,817 3,520 1an 2,391 2,605 I
Suriname· River 145 181 290 86 142 142 201 293 257 199 at Pokigron 18.7 23.4 37.4 11.1 18.3 18.3 25.9 37.• 8 33.1 25.7 2 2,175 2,153 2,734 1,772 2,225 2,468 2,539 3,180 . 2,291 2,604 7,750 1an E E E Marowijne River 1,049 2,261 992 960 1,715 1,784 1,642 at Langetabbetje 16.5 35.5 15.6 15.1 26.9 28.1 2'li .~ 2 1,907 1,891 2,843 1,842 2,059 2,434 2,481 2,979 1,955 2,'6ll1 63,700 km
+ 189 Mean annual discharge in m3/s 15.4 Average annual unit discharge in 1/s/kJn2 2,11.5 Annual rainfall total in mm
~ J. E Estimated n w ":':.'.C" 6000 u 1 .. ~ 1\ s ,. >S ~. (J '000 M VII , ,~ \~ 20"" ltv. 1\ 1Il A ~\ V '~ f\A \ l\ ~ v' IV\. I ~A I.. ~ '. , ~ ./ '\I 1.1\ ...... ~,~ ,~ \c; 19 63 II ~Lf \J' ....,.J 19 64 ~~,- ~~ J .19 6S ~ °JAN FEB MAR ....R MAY JUN JUL AU& SEP OCT NaY DEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT INDY DEC JAN FEB MAR APR MloY JUN JUL AUG SEP OCT NaY DEC --- Marowijne Riyer at Langatabbetj. ---- Coranlijn Riyor at Malaway .. I 6000 I '. i , \ \ I , I , \ '\ I'llOIl 110 P , ru ,\/ I . .. I ,." . i .. , I , ... I ~ J' I, I ,,' \~ I "S ~ I I c , I I ' I ., I I .= "I WI I \ tI, I ' J d" , (J , ! III In )'! I~ :IlIOO I ' • I • I I I 1'j.J ~. I II~\ I I 'oJ' I V W, I Lll ; \ I , I •.A , \J ~ V M:: , ~ , I I!~~ ... N I J , I It F\ , I .. - ~ "\J I N', IV\.~ ~. \ , V, I " .' \ .\ II ~ IJ\ ,,j ", I I\lr;. I 1" ~ v ...... , I 19 66 " .....l 19 67 ~~J 19 68 N ~ ' .. -~ I.!-' '- v r--'" " AN FEB ""MAR APR MAY JUN JUL AU& SEP OCT NaY DIC JAN FEB MloR APR MAY JUN JUL AUG SEP OCT NDY- DEC JAN FEB MAR APR HAY. JUN JUL AUG SEP OCT .!£ ..... :FIG.5.1-2 Hydrographs of the Marowijne and Corantijn Rivers "-' 0\ (Fro:ll: l1NDP, 19'12) , , __ _---- (c) Unit Discharge. A wide variation of annual unit discharge is evident from the values .listed in Tabloo 5.1-1 and 5.1-2. The parameter represents swerage conditions within a basin. It tends to decrease with increasing area, but in Suriname this is not necessarily the case. The values plotted against basin areas (FIG.5.1-3) show a slight decrease with increasing basin areas for most years, but this cannot be considered significant because of the variations in annual rainfall. The frequency of average annual unit discharges for the years 1952-1970 inclusive is illustrated in FIG.5.1-4, with the basins di vided into two groups. The first group represents high runoff basins for which the median unit discharge is 25 1/s/km2, and the second group represents relatively low runoff basins for which the median unit discharge is 15 1/s/km2• A relationship is evident between the low and high runoff groups of basins in the form of a linear correlation between the two, which differ quatitatively (FIG.5.1-5). In the low runoff group the values of runoff are only 39 to 69% of those originating from the same rainfall depth in the high runoff group. Altnough several factors such as the amount of intensity of rainfall, geology, topography, vegetation, and evaporation contribute to the fu~ount of runoff and consequently the unit discharge, it is apparent that the geology in particular ardthe rainfall contribute most to the differences bebJeen basins. (d) Hydrologically distinct areas. Differences in runoff as illustrated by unit discharge are evident within the drainage basins in the basement area as mapped (Fotogeologische Kaart van Suriname). Notably, the Kabalebo, Kleine Sararnacca, and Nickerie (. itondansie) basins are charac terized by low runoff. In addi tion to this, a common feature is their location along· the northern fringe of the basement area on which at least a discontinuous veneer of basin sedi.ments extellds beyond the limi t of the coastal basin, as shown by the Savannah area. The Nickerie and Kabalebo b,asins actually include part of the Savannah upstream from the gauging station. The"unit discharges represent average conditions tnroughout a basin, which may vary considerably. This is illustrated by differences in unit alscnarge for the Nickerie basin in 1967 (Table ,.1-2 and FIG.5.1-6) at Blanche Marie (26.2 1/s/km2 ) and at Stondansie (16.72 1/s/km2 ). Unfortu 127 ,.."',...... ~"'~'~"'.__ ,'""'••~.., If'i( ..·iiI "-l' I , ..II,. 0: ... OX .. ' ' 0" ...... II .~ - ...... ,. u 0 ... ' .. ... > II ... .. ,_ 0 > u >0 .. a > ·-0 ...... > .• a: III 0: > - ...... !:'~ 0: ... " .. •• III 0: .. III .0:- '" ~>o. .c E~ 0: .. 0 0:'" ,. a"g II" a II~ 0" a &. "Cl .. Ci E:::: '" ;l: Ci E ~¢0" ._• uc: t:e 0'" ,~ a :;~ III .. ..c a" E:i ",oX .- 0 ,- 0 .~ .. a e' 00 ~ .. c '- ,, f'IG.5.1-3 Average annual unit discharges and basin areas ..... N co (From: UNDP, 19'(2) . ,I ~ ~,;.., .. _-" 2 I.' 39l/s/km ~._. ~" 27l/s/km2 f ~- '---i- --- ~- f--";;':'--- I ~ 7" .. ------7 90 " 9 .I ".../' 80 / / 8 >. 1/ u VCumulative c: /J 70 frequency / 7 .;:,• VI ~ c: 1/' Gl ...CD 60 / 6 .- .- I a { -~ Med~n CD 1.5YS~~ __ J..5J.1s/ k!!.? ~- '-----. '--- - I- S ...CD a > - - - III > ...... - /~._l .c ... a 40 1/ 4 . 0 ....CD -;:, 1/ c: I 0 . E 1/ j - ;:, 30 3 c: ~.' ... a u ill Ii .lil 20 / 2 ,e ...e I) i· 10 I ,,- / 1 2 ",:;:;. ~l 1Y/S/k 2 Sl/s/km j I Ol~' 0 8 12 16 20 24 28 32 36 40 44 48 4 8 12 16 20 24 211 Average an nua! unit discharge • ! /s/km2 Corantijn River - Mataway Kaba! ebo River - Avanavero Nickerie River - Bl.Marie Nickerie River - Stondansie Saramacca River - Dramhos so K!.Saramacca R. - Anoemafoetoe Suriname River - Pokigrom MarQwijne River - Langatabbetje l FIG.5.1-4 • Distr bution of average annual unit discharge for the >-' N ~ years 19152 -1970 inclusive (Fr0m: U'N!DiP, 1972) .' I . I I • I corantijJRiver ~a bale bo River at Nataway Q;t Avanavero <> Nickerie River Hiekerie River at Blanche Marie at Stondansie + Saram a cca Riv·er at Dramhosso + Kleine Saramacca River at Anoemafoetoe o Surina me Rive.r ! at Pokigron I I , ,< ~N -f---r----'i--l--l-l---I---+--f----i---1rl--l--,II I MarowPjne Ri~erl ! f, oXE . • ! r .... at Langatabbetje { .V1 l .... ! i , I j 1 I I c!!!. GI. ' Ann u a I r a infall --l--'------.---+--i----+--+-+-----,j; ~ ----:.3L_ r/I-,:r- - 2400 2700 I 3000mm I a 1 fO 0 i ~ 7 I ,J i ..- b t , . ; ,~ I~ 'C ! ' i I' ii i ~:; -rlf-rlH-P'¥-'F,'y'rlrlf--+----4rlHH-+~--+--__t_-+-_+___t___t___1 - L-:, I ! I , II ' ::;, 0'('1/,.'0+ I I I '27 B 2700mm -,,~ ,-,_.- -, ~ 25 c::<; - 2l100 22711 I 2500 mm I /1'" i -.0 I' I I; d , 20 ; L! I I I , ,., i I GI 01 i J.. I/Q-/(' i I ! liT' I I ...a GI I (.~t) I \ 'I ~_ ..t.·i/_I~II-_7-2~2::...:,70mm > < , i I I I -u_, -1--1- - 1700 1880 2100 mm II 10 /0; Ii 1+ i 'i / c , //I! Ilt '// I I -~Fi~;li- I-~!!'O mm o III i lill 000 ! 000 MOlD ! MOlD . ..I...... -..t ID t-o- r-., """ GD 47 Control pain ts 19 Control points I 'I Annual rainfall in millimeters 1000 2000 300014000 I I I I 11000 I 2000 3000 FIG.5.1-S Relationship between annual rai'nfa:tl and average annual unit dischQr~e (From: UNDF, 1972) '1. I Kilometers ,, Basement ," Savannah _.~ Watershed -- f'ossibl it fault lineat ions .\ 1967 • Area km 2 Discharge Unit Discharge m 3 /s . I/s/km2 Stondansie 5160 86 16.7 Blanche Marie 1260 IU.,"I.I . 33 26. Bt. Mar ie to Stondanie 3900175.6"101 53 . 13.£ Savannah 980119 °1.1 FIG. ~.1-6 The Nicker/it River basin (From: UNDP. 19'72 J nately, discharge measurements at Blanche Marie are available only for the one year, and, whereas it serves to illustrate the difference, its quatitative significance is questionable. ~he basin received above average rainfall in 1967, which could give an above-average runoff in the upper basin, but it followed three years of below-aver~ge rainfall and therefore runoff in the lower basin might have,been lower than ex pected 'b'ecauseof-de-pleted floil mois'ture; The part playe-d by the Savannah, remnants of older basin sediments, and possibly deeper weathering with less erosion in areas of low relief would be to retain water that would normally runoff a bare rock surface. ~ome of this may enter the zone of saturation, percolate locally to streams, 'and reappear as an effluent flow, while much of it would evapotranspire. Differences in the amount of runoff probably occur in the Kabalebo basin as in the Nickerie basin with high runoff in the upstream areas; indeed, the diffe~ence likely exists in all the basins with a belt of low runoff extending along the entire northern fringe of the basement area. The possible BOUthem limit of this low runoff belt is shown in FIG.5.1-1. The Suriname basin upstream from POkigron falls south of it and hence high runoff is measured. The southward bulge coinciding with the Kleine Saramacca basin may represent the influence of low rainfall, in addition. Unfortunately, there are no flow data available for the coastal area, and the runoff characteristics can be considered onIY indirectly. Infil tration and effluent ground water flow to streams is a feature of the Savannah area and most of the Old Coastal Plain, while natural discharge in the Young Coastal Plain is incipient and swamps abound. (e) Hydrologically distinct seasons. Long wet Seaoson. The influence of the long wet season on runoff is best illustrated by runoff data from the Suriname and ~laro\'lijne Rivers, for which the longest records are available (19 years). The volume of discharge of the Suriname River at Fokigron in the four months of the long wet season, April-July inclusive, varies between 50 and 70% (average 62~) of the annual discharge volume. The weight of the long wet season in contrilJuting to the annual runoff of the Marowijne River basin is lower than for the Suriname River aasin. It amounts to between 45 and 64%, for an average of 56%. ·, Long Dry Season. The discharge of the Suriname River at Pokigron during the four-month long dry season (August-November, inclusive) for the 19 year observation period varies between 10 and 28~, for an average of 17% of the total disch"rge. Thus, the average volume of the long wet season . , runoff is 3.65 times larger than that of the long dry season. A parallel situation occurs in the Marowijne Hiver basin, with the seasonalfltlws' varying' between 10 and 32 .. for. an average of 171 of the annual flow. 5.2 Ground water (al precambrian basement as an aquifer. The rOlilks of tLe basement are for the most part granites, gneiss and similar rock-types, known as crystalline rocks which generally are impervious. They are deeply weath ered, :iu t the process involves the decompo,si tion of feldspars and ferro magnesian minerals into cl£y minerals; although the weathered rocks may become more porous, the hydraulic conductivity would be too low to con sider tnem as aquifer material. Clayey and micaceous sands were inter sected locally above the hard basement by tests drilled in the Savannah area. Widespread faulting of the base~ent is part of the tectonic history of the region, the illOS t notably of which being the Bakhuis faul t zone. However, a series of evidences indicate that it seems unlikely that significant quantities of water flow through fractures in the basement at the present time. (b) Cretaceous aquifers. The Nickerie formation of Cretaceous age is ; confined deep in the coastal area (FIG.5.2-1). There is a dominance of sand and gravel, but water is brackish. Because of its water quality and depth, the formation is not considered further. (c) Onverdacht aqUifers. The Onverdacht aquifers include the sand members of the Cnverdacht formation. It has not been as Widely explored for ground vlater as the overlying formations. Onverdacht formations occur as an alillost continuous downfaulted coastel unit, confined beneath younger Tertiary sediments; it ends against the rising basemen t illlmediately north of the Bauxite Bel t. In the Paramaribo area the top is at depths of 120 to 450 m. The sand horizons are 30 to 50 m thick, and the aqUifers constitute between 30 and 50% of 133 ._--~; J lAS' WEST t~1 U.-2 '1-2 JMS·' .m ,.. ...,-, TN-' $"5.. 1 cc·' ,"-, ell••tlr_ t'...... •,_...._,.1",••• "" '.t.•••...~.;'C'.·'.'I·',...,.. ~ • , ...... 1. :~I ::::: t: ._, ..::.:, z . ..".. o.. • • _._'rIoi' • .". -~.:: o • "".~' nO.I"-..... III -~ :'1-··.. . -...... NO . ....,---_. " ,",,, ..-: ", • '. • OS •.• • -' _ - ~-..:.------•• ' •. '. I "'"'n.: "...'" -'01 .~:!\ - ,." ---...... r :'.' ,.. ' . . . . .' ...... ;..... 'I ' ::::1-: ...... ~ .• ' Z····· .' .::: -'.: ", •..• 0 • -.' ..'I': :.••••••••••.. ~:: •• ' .•••V c :,:. -". - III i 'M ~ :. i::::-:-:: <::.:~-<:::''!'''.",-:' ..-- .-:-::' ,..../ -:.1 -... .' .' ...-~--...-.... ._,".-;;:.;---I:-=-=.:.:. ... c:") . - . . -' -- .... ,,,._,., ., = ~-... 211· . : :.:.:.:.:.::L~~...... , .. ".-..• ' ..",. c ...... • '. "". p;:t ....••• Oil., ,.;.•ue I.' ..., ';'>." ... _! 0 .' . ., . ' . I. .," 0 [ '.: ... '''--~- --, 0, '.-., ... - '~:=. It. f ...-, ... o 0 ,J" ·.. o- -;----- ! ,.:" .... . ,..... \ : .••••• '.,> .. • , 0 ,n ...... / ...... I ••' ~ -., .., _. ',.7 a• [ew>" . . j ., · . . ' ...../ I •.• ... % LEGEND .' ../ ~ z ,' ' "ft••••• , '::t .. ( •••• "."'~ ... '" CI •• C ,C , "" , •• = l.l_f...... -.c' ..,..... Ir_ A ,•• 1010 "1 If;'; I ...... -..,....., ,.,. - t.l."....._C"O., ,...... , , '."'" '.C.D ;••11•• , ..'. .... (.F:G ' ...... I " .....,' .t••••.••••, •• ~ ,,'0_"" "" _. ..._.-·...·1 .t •••• n,..... 'IO•••c, . ~ M·'" I lo'"'''' -. __ t , ,. '" ., C."...... E:L.. ------ O:""--j .. .. '''' •• " " t c _ .-f1 , ...... ~•••IIt •••t" """. .. • ••••• uu , .'1_1111 11"" H' • 'it ",!, .~ t-' Section Nlckerie' to Alliance showing lithology and groundwaler salinity of r.rtler,y .·nd VJ , . FI G. 5.2-1 .<>. Quaternary sediments as deduced 'rom well logs (From: UNDP, 197;:1) .. ' . "The formation in most areas (FIG.5.2-1). A more or less discontinuous unit is present at higher levels in the Bauxite Belt. The only aquifer test under leaky artesian condi tions rendered a ;; transmissivi ty of 75 m2/day and corresponding hydraulic condue tivity 4 ~f 8 m/day, and storativity in the order of 10-3 to 10- • At other places, incomplete tests indicated hydraulic conductivity values from 5 to 40m/day. It is assumed that non-l"eaky confined"conditionsp-revail throughout the coastal area. The chemical quality is variable according to the occurrence. At Onverdacht (Bauxite Belt) wells yield water low in dissolved solid: dry residue of 75 ppm and chloride of 19 ppm. Close to the north".brackish water is reported (chloride content 4065 and 3672 ppm). In the coastal area east and northeast of Paramaribo the water is mainly brackish (chlorides generally in excess of 1500 ppm). At Meerzorg, the chlorides in the interval 16'1 to 188 m increase wi th depth from 32'3 to 590 ppm. At Livorno, chloride content is III ppm. A similar condition with A-Sand aquifer containing fresh water overlying directly the Onverdacht formation appears to exist north of Jarikaba. Historical water levels in the coastal area indicated the highest level in the test well at Nieuw Amsterdam (3.9 m ACL or about 5 m NSP). The level is lower farther inland at Jagtlust (0.97 m ACL or about 3 m NSP), Meerzorg (0.75 mACL or about 2.7 m NSP), and at Tamanredjo (0.2 m BeL or about 2.0 m NSP). This an evidence of an apparent inland flow of ground water. Since in the coastal areas the On verdacht 8quifers are everywhere confined to the inland slope of the piezometric surface, and water levels are higher than in the overlying aquifers, such conditions rule out the possibility of modern recharge. In the Bauxite Belt, the possibility of local recharge is present. (d) A-Sand aqUifer. The unit corlesponds with the A-Sand formation, probably of Oligocene age, consisting of coa,se- and fine-9rained angul ar sand and in places of coarse anbular s~ld and fine-rounded bravel. The aqUifer is present in the coastal plain north of the 3auxite Belt. It thins inland ending against the rising b",s€rr;ent or intervening eocene sediments. It is confineu beneath Coesewijne olays E~d above the Onver dacht formation. Locally it is in contact with the lo~est Coesewijne aqUifer, which is also confined, and with sands of the Onverdacht forma 135 ·tion below. The roof is relatively uniform, sloping gently with a gra dient of about 0.003 m/m to the north, but the floor is irregular, con forming with the topography of the post-Eocene surface (FIG.5.2-2). AlonG the coastal area an eastern and a western unit are eVident, seperated by 'an area coinciding wi th the Bakhuis zone, where the floor is higher and the aquifer is thinner or missing. The·-eastern un-i·t extends inland. south .of Paramaribo to the.northern edge of the Bauxite Belt. It does not continue east beyond the Suriname Hiver in areas south and east of Meerzorg. The aqUifer is at a depth of 120 m in the south and 160 m near the coast, with corresponding thick nesses of a few meter to 60 m, respectively. A relatively thick section of aquifer extends inland following the SE Bakhuis fault, likely as an infilled burried valley. The western unit is not exploited for water supplies, but it is knolOn 'from oil tests. It extends inland from 30 to 50 km. In the Nickerie area the top is at a depth of 350m and the aquifer is up to 80 m thick. The eastern and western unit connect in the coastal strip by the Saramacca River near Calcutta and Tambaredjo. How far offshore the aqui fer continues is unknown, but almost 100 km offshore sediments of the same age consists of sand and limestone, at depths of 1400 to 1450 m; thus, the aquifer as it is known onshore is not in open contact with the ocean. The aqUifer is everywhere confined. Flowing artesian conditions existed in Paramaribo before withdrawals and probably exist in the west ern unit at the present time. Storage coefficients in the range of 10-4 to 10-5 have been deter mined from pumping tests in Paramaribo, rounding Paramaribo where, before witndrawals, the pie~ometric surface W"IJ lo·,.er than in the underlying Onverdacht aqUifers, but higher than in the overlying a~uifers (FIG.5.2-3). 136 / A T, L A / N T c, o c E A N / l£GENO: " ---10m} liliOIlClcll tlu, ---l m -,_. Coniour. 01'1 109 of .. 50"d ...... r..achlor" part. pt, ""1110" CI~.'b.for. \ ~ wllhdrawals) ~ QQOl; Aoc.. boundary \ ~ CO"locl with On...rdacht a parllol bo',"dar, \ \ ~, • WO ••,} \ T.st. and ••11. \ _.\.-._. e 011 1. .-" I ~'-I-'- @ EstlmOI.1I hydraulic COt'lductl"Il,. Illlda, r I . 1 11 ....,1 Corr.el.e1 Car bot! all. Clq. at ...... _._,_ ----I-- '-",J::------J:=.-. __ "groundwal., '1'1 .,.an 8~ /.,.." I 1 '_'_', ._._.,.__. ~I ~I ,// "'-1~·L-'r -;1 ,.0/ ;' .,...' I / 1 -1-1-_,_,-I -I.._ ,/' ,/ ..;-'-/- : I . /' ' ../ ...... -II.· a. : .....g.;. lEg.., ./ ,0./ .~: ._._. .i-. ft :..~ ._ .-' .....\-..... ,,'1. u • .../" I': ."'" 1C ••It. • . ../ I /./' ...... Q./ /~ ~ --- ;/ {,(' .. / // /f! /. -"" ./" .,...,/,/,..G./' / / 1'//'/Jor'''abt /,~~./I ~/ / ._....-.'7 I. : - I ~ ~/. o 5 10 [ , I(ItOl'l'l.lt,. 0' +G'O.' .~..,,\ ,,,,,.' o,ct , fl.... (.'f:' H~ron ....0..• " Sal'll FlC,~.2-2 f-' Hydroll"ologlcal Ie.alure.s 01 the A Sana Aquil"r Vl -.)' (From: UNDP. 19'1'2) , , ,:.,.,.;_.:;.;:,;<;'.i,~,.il-.'~;~~ c~.~ -.. -...... "" • Co I ··C';: • >.' ;.I(!~"'';;~.i,-J:]f.,;;i.-u .."tk~~~~,~, j' $l?j,j$lre ~.,-( 2 :.... --~., - 5 N -12 SQvannah Old C•••t.1 PI.I. 12 Yewn.' C•••tal Phi" • ,'a • :E 10 ~• B '\ <> ..o ': m .. II: "... • ~: ~ ~: . ... ~, u ~z 0 ... • Ul .. • ,g:. ::E- :E :> ~:. ~. 4, • ~u ~ IE e- ...... :.'" .... •• . -e • .. II: K ~. z ~" z• N 5, l B :=. ., ~.. E.. - •• := I \ \ ! S 2". .. . ~ flO; ~. Ii. .. .. _ \ \ ~ e;::;: •.•••••• :: ~ ~:~ ~ , ., . ~ i! ;: E : :: 4 ~ ,.... . ------.""..,;. . ,2 •• z a a-.;.__~ a NSP TI~d un•• : \ • I \ ; -2 I \ •I -I LEGENO: \ I• \ I \ • Zanderij aquifer I i I Zor, In tiD., w.n field a Upp.r C•••ewij"e aquifers , I- interhr.rici J I , -4. -4 i" •• Lower COI.lwijnl alluihr i, I','" I \ I ", • A Sand a~uiftr \ I Republi.lI· Win I, I , I , I _& fi.ld inhrflrenn -~ \ I Horizontal Scale: 1:200000 ~oli' s~.-u-:-t:-h-.-r-.~,:-:i-m-:i71-.-:' 1 5 , " A Sand aquifer i Kilometer f-' bas~n ~,J FIG.5.2-3 Wain I.nls of aquifns in Ih. coaslal from lh. Savannah ar.a n.Q'r la,"~.f'ii 10 I·h·. (J) Young C,o&sla·( Plain n.ar Para'marlbo I (p·rom: or·inP, 19'1'2) , The water contains mainly sodium chloride in solution, with , dissolved solid concentrations ranging from 340 to 2100 ppm. The dissolved solid content increases north~ard towards the coast. This is illustrated by the isochlorides in FIG.5.2-2. In ~estern Suriname relatively fresh water is indicated, as deduced from the logs of tests drilled for oil. An exception may the area at the mouth of the :3aramacca River (well SMS-l,-FIG.5.2-1). There is no evidence of modern recharge to the aquifer, at least in the eastern basin. (e) Coesewijne aquifer. The unit is composed largely of clay and sandy clay with interbedded sand aqUifers, which appear to be hydraulically interconnected. The zone is up to 100 m ttick in the Saramacca and Suriname Hivers area and up to 120 m in the Nickerie area, where the top is' about 230 m below ground surface. The zone is covered by the Zanderij aqUifer. There are no KnOWn outcrops of the formation. The aquifers generally make up from 30 to 50% of the entire zone and in the east appear most frequently in the upper section. individual a:.;.uifers are normally up to lu m thick, but locelly they form complexes of two or more sana bodies seperated by only thin partings. The NNW dip of the zone is greater than that of the Zanderij aqui fer, and thus there is con tac t bet~een tilem in the Bauxi te Belt and im mediately to the north where water in the Zanderij a~uifer contains brackish water and subsurface outcrops of the Coesewijne aquifers along the sides of the burried valley are in contact with it. The lowest aqui fer is in contact with the A-Sand al1uifer at places in the coastal area. The zone is everywhere confined. Local exceptions may exist in the extreme south of the basin, where there is contact with the Zanderij aqUi fer at locations where it is unconfined. The confined condition of the aquifers is reflected by the storage coefficient (S=10-4 to 10-5). Hy draulic conductivities estimated fall within the range of 10 to 130 m/day. The highest value was estimated for the supply well of the DWV Kwatta water supply plant. Aver-ages of all hydraulic conductivi ties estimated are 43 m/day for the lower aqUifers ~nd 70 m/day for the upper aqUifers. In general, v~lues decrease west of the Saramacca River. In western Suriname, hydraUlic conductivities of 10 and 42 m/day have been esti~ated. Effec tive porosi ties of the Coese\oOijne aqui fer vary from 8 to 13%( overall value = 10%). 139 • " Ground water in the Coesewijne aquifer is relatively low in dis~ solved solids throughout the coastal area except at locations near the coastline in the eastern part of the country. The dissolved solids are generally less than 800 ppm. The lowest values was determined for a well at Rijsdijkweg (164 ppm) and the highest value for the aquifer at Nieuw Amsterdam (907 ppm). The salinity increases northward towards the coast in the Saramacca - Suriname, Rivers area., The piezometric surface in the coastal area near Paramaribo is 1.0 to 2.0 m NSP or close to ground level. This condition continues inland for about 24 km to the Vicinity of Uitkijk and Koewarasan (FIG.5.2-3). Immediately to the south the level is lower. The lowest levels were measured at Helena Christinaweg (less than 0.5 m NSP). Farther to the , south, the ~~uifers are in contact with the overlying zanderij aquifer. ..~ 1 There are no known outcrops of the zone, and therefor recharge by the direct infiltration of rainfall may be discounted. Since the rivers and streams are effluent under natural conditions, recharge as an in fluent flow from surface water is also doubtful. (f) zanderij aquifer. The Zanderij aqUifer is eqUivalent to the s~ndy facies of the Zanderij form&tion. It crops out, forming the Savannah Belt, and continues northward, dipping gently in that direction con fined beneath the Coropina clays and above the Coesewijne formation. It is not knmm hO~i far the coarse sand al1uifer extends offshore. At about 100 km offshore its equivalent is silty and sandy clay ",nd clE-Y. In the Savannah Belt the distribution of aquifers is very irregular. In places there are no clean sands. Where presen t the sands are normally highly kaolini tic. Conditions improve northward, and in the Bauxite Bel t the a"ui fer appears to be pI'esent everywhere except locally, where buried bauxite hills rise to higher elevations. the base is irregular, corresponding to the post-middle ~iocene erosion surface \FIG.5.2-4). The upper limit of the aquifer is taken as the top of the main sandbody, bu t in places this is aifficul t to define due to overlying Quaternary sunds. Thicknesses vary up to 20 m in the Savannah Belt ana are generally between 10 and 20m in the Bauxite Belt. In the coast8l area of eastern Suriname the aqUifer begins at a depth of about 30 to 40 m and the thick~ ness attains 40 to 50 m in the burried valleys. At Nickerie in western Surinw~e, it begins at about 50 m and the thickness is appoximately 169 ro, but this illay include some overlying Coropina sands. 140 T L T ~: _~, -..__...... ~...... f C:JL e-.,..I_., c...... --~~_ .., .. ''''-iI -..ot.. tiydroi••lDliciI\ teaturtl ud UllflltJ .htrlbuUon In tht Z....d.'lj .'Iul", In the 'flcin't, of Param-arlbo ond landerlj (From, UNDf. 1972) In the coastal area the aquifer is confined beneath Coropina and Demerara clays, whereas southward the overlying Coropina sediments locally become more arenaceous and leaky artesian and unconfined con di tions exist. The hydraulic conductivi ty is low in the Savannah Belt and adja cent areas to the north, limited mainly by the presence of kaolin. At 2 RepUbliek, tralisJilHfiH vitiesoetweeh24 and "126 m /day have beert ca1"" culatedfor an average of 82 m2/day. The equivalent hydraulic conduc~· tivity probably is in the order of 15 to 20 m/day. At Rijsdijk an average transmissivity of 880 m2/day was calculated, which, with an aquifer thickness of 20 m, gives an average hydraulic conductivity of 44 m/day. A specific yield of 1310 was estimated for the aquifer at Republiek. The ground water is fresh in the Savannah and Bauxite Belt, but , ' the salinity increases northward towards the coast. In the Savannah area the water is very low in dissolved material. Dissolved solids of 46 to 86 ppm have been determined for samples taken in the Zanderij Matta area. The northern limit of fresh ground water varies consider ably (FIG.5.2-4) and the change to brackish water may be qUite sharp. Fresh ground water near the northern limit for fresh water contains 1 dissolved solids between 50 and 250 ppm. The salinity is highest in ] the thickest parts of the aquifer, where the dissolved solids are be j tween 2000 and 5000 ppm. In the southern coastal area the thickest parts of the aquifer aproximate the locations of the present Suriname and Saramacca ~ivers, suggesting deposition in the form of deltas. I'later levels are highest in the Savannah area (10m NSF). At Republiek, the water level fluctuates between 0 and 2.5 m NSF (average 1.25 m NSF). The level declines northward to the area of Helena Chris tinaweg (about sealevel), then it increases again (FIG.5.2-3). The Zanderij aquifer is probably the only aquifer in the basin that receives recharge directly by infiltration of rainfall., This takes place mainly in the Savannah area and immedi&tely to tne north. (g) Coropina and Demerara aguifers. The Demerara and Coropina are essen tially clay fo rma tions confining the Zanderi j aquifer below. Interbedded sand aqUifers occur locally mainly in the form of lenses (FIG.5.2-5). In the coastal area the Coropina aquifers are difficult to distinguish from the Zanderij aqUifer below. They probably are all interconnec ted. 142 R . . o " " o• . I," I " • N• "a lO; z .. ~ ~ 0 (\I -... r ..... , .! '" , . .Cl ~ • P< .. Q a" z :::> c; 2 .. e -.. 0 oil I-. ~ ~ • m . • • 1 ; =· • N i : • ; i r. ·· . • ~ . (;l i H ·.. . ~ s ·••• =. .g ·• • ~. : 'i t ~, ~ w I ~ · "1 g" ·... .:: .. ! • • • • = ! :.• · . . o • " w :. : t:> ..: , o : v / .. ,••.., .•• ' ...... ··'1 _~='=='="""...... !!!!iI!!!!!!!!!!!!!!!!!!!!_14(. In the Bauxite Belt, the Coropina sands are connected hydraulic ally with the underlying Zanderij aquifer at least locallY(FIG.5.2-6). In this area the sand formations are exploi ted for small individual water supplies by means of dug wells. On a regional scale, the forma tion may be regarded as an aquitard above the Zanderij aquifer. At Wageningen in the west, a relatively thin sand layer extends fhro-iighout- an area of several- kilometers in the depth in terval fr~m 23 to 40 m. The only aquifer parameters known are from a test in Wageningen 4 (K = 75 to 50 m/day and S = 1.4xI0- ). The salini ty distribution appears to follow the same pattern as in the Zanderij aqUifer below, with mainly brackish water in the coastal area and fresh water in the Bauxite Belt and river valley areas to the south. Water levels are known only locally and therefore it is not pos sible to construct a regional flow pattern. it appears that the levels '.-' I are similar thrcughout the coastal basin and that very little flow , ., can be expected. -I The seasonal fluctu~tions in the Zanderij aquifer at Rijsdijk must be a result of recharge entering the Lelydorp (Upper Coropina) 1 aquifer above. 144 S'R--,""