The contemporary geomorphology of the Letaba Ri ver in the Kr uger 
National Pa rk 

B.P. MOON a nd G. L. H E RITAGE 

Moon. B.P. and G.L. Heritage. 200 1. The contemporary geomorphology of the Le taba 
Ri ver in the Kruger National Park . Koedoe 44( 1): 45-55. Pretoria. lSSN 0075-6458. 

The Letaba Rive r drains part of Nonhem Provi nce in nonh-east South Africa. Its catch-
ment has been mod ified significantl y by hu man activ ity which has affec ted the flow 
regime: it experiences only ephemera l flows through the Kruger National Park to its 
confl uence wi th the Oli fants River. Although the Lelaba is similar to the other rivers in 
the Kruger National Park in thaI it displays some bedrock-infl uenced channel features, 
increased sediment delivery from the degraded catchment upstream has resulted in 
extensive atl uviation within the channel. Sections of channel flowing over bedrock with 
no sediment covering are rare, and the river com prises a series of channel types: mixed 
anastomosi ng, all uvial braided, mixed pool-rapid and al luvial single thread. Eac h is 
characterised by a differe nt combi nation of morphological units which relate to the 
degree of all uviation in the channel. These channel types are described in detai l and 
infere nces are made concern in g the ir fonna tion and maintenance from fie ld observat ion 
and measu rement. 

Key words: channel type, channe l change, geomorphology, Lelaba River, mot'phologi-
cal units. 

B.P. Moon. Centre/or Water in the Environment. Universityo/ the Witwatersrand. I Jon 
Smuts Avenue. Johannesburg. Republic 0/ Soulh A/rica (I32abm@atlas.wits.ac.tJl); 
G.L Heritage, Department 0/ Geography, Peel Building, Unil'ersity 0/ Salford, Man-
chester M54WT, United Kingdom (GL Heritage@saljorri.ac.uk). 

Int rod uct io n 

Duri ng the las t ce ntury the Leta ba Ri ver in 
the Kru ger National Park has changed fro m a 
perenn ial to a n ep heme ral ri ver (Steffen 
Robe rtso n & Ki rste n I 990a). In c reased 
abstraction of water fo r development. and the 
construc ti on of da ms, have led to a modi fica-
tion of the flow regime and a s hift in the ba l-
ance of catc hme nt c ont rol va ria bles 
(Heritage et a l. 1997). Th e consequ e nt 
marked geomorph olog ica l c hanges have 
bee n doc umen te d ( Vog t 1992), and a 
recen tly-comp leted fi ve-year proj ect o n the 
ri vers of th e Kruge r Nat io na l Park has 
focused o n an unde rsta nd ing of th ose 
changes (He ri tage et aJ. 1997). Increas ing 
water abstrac tion and an expansion of agri-
cu ltural practices are like ly to result in fur-
ther flow reduc tio n and increased sedime nt 

ISSN 0075-6458 " 

inputs to the ri ver ( Birkhead et al. 1995) 
leading to furth er mo rph olog ica l c han ge . 

Recently the re has bee n a marked growth in 
research into th e natu re and d ynamics of 
South Afri can ri ver systems (fo r exam ple, 
the work of Ro wntree & Wadeson 1996; 
Wadeson & Rowntree 1996; Heritage et al. 
in press; Ro untree et al. in press). 

In th is paper, fo llowi ng an ove rvi ew of the 
Letaba catc hme nt. the contemporary geo-
morphology of the Le taba Ri ver is descri bed 
within the framework of its compone nt c han-
nel types. Four di ffere nt c hanne l types have 
been recogni sed : mi xed anas to mos ing, all u-
vial braided. mi xed pool-rapid and all uv ia l 
s ingle thread, each re flec ting a different com-
bi nation of mo rphological units. The nature 
of change in the differe nt cha nne l types is 
discussed in re lat ion to reduced flo ws and 
in creased a lluvi ation ove r time. 

Kued(N 4411 (200t) 



Fig. I. The Letaba. River catchment. Nonhern Province. South 
Africa. (a) location. (b) precipitation (mmla) and evaporation 
(mmla). (c) sed iment prod uction (tkm"a). (after StelTen 
Robertson & Kirsten I99Ob). 

KodOf' 4411 (200 1) 46 

The Le ta ba catchment 

The Letaba catc hmenl covers an area 
of 13400 km1 in the Northern 
Prov in ce of South Afri ca. In the 
Lowveld region its major tri butaries 
are the Molotsi and Kl ei n-Letaba 
rive rs, and the Let aba join s the 
Olifan ts near the Mozambique border 
(Fi g. la). The catchment is class ified 
as se mi-arid. receivin g be tween 500 
and 1800 mm of ra infa ll in the moun · 
tai nous western parts of the catch-
ment , fa llin g to between 450 mm and 
700 mm in the east (Fi g. Ib). Evapo-
ration is hi gh, rangi ng from 1400 mm 
in the west to 1900 mm in the east 
(Fig. Ib). Precipitation is concentrat· 
ed in the summer month s whereas 
evaporat ion potent ial is more even ly 
di stri buted (S teffen Robert son & 
Ki rs ten I 99Oa). Runoff is now sea· 
sonal and became ephemera l during 
the drought of the 1990s when sur· 
face flow in the lower reac hes 
occurred onl y in response to severe 
stonn eve nts in the catchment . Virg in 
mean an nua l run off has been est imat-
ed at 556 milli on cubic metres per 
annu m (M ml/a) (S teffe n Robenson 
& Kirsten 1990a) compared with the 
present MAR of 323 Mml/a. 

In the upper catchment . outsi de the 
park, ex tensive areas of land are used 
for fo restry and commerc ial agri cul -
ture. Intense subsistence fann ing and 
irrigation also occ urs along th e ri ver 
where access to water is good (S tef-
fen Robe rtso n & Ki rste n I 99Oa). 
Forested areas (47600 ha in 1985) 
require a water vol um e of 64 Mm'/a 
(S teffe n Robenson & Ki rsten 1990a). 
Irrigati on of fru it, vegetables and 
grai n cash crops req ui res 220 Mm'/a. 
and domesti c and indu stri al water use 
amoun ts to approx imatel y 17 Mml/a. 
A furthe r approximately 7 Mm1/a is 
exported to urban areas ou tside the 
ca tchment. Potenti al in crease in 
demand as a result of increasing agri-
cu llu ral. industrial and rural water 

tSSN 0075-6458 



• ---""""'-
• 

+ 

.........'-'*"~ D _SIIBrIM . 
MiQd_~ CJ 

............ _~1:!i:!I 
CIIanneI typ. btuk --.... -

1
51101 CO 

- W- % 
189 1011 1213 

, b _SllBrI"". 
Ubed ""SIOr'nOSing t2'2I ------

+ 
',---,'~ 

it 

: c 

+ 
• 
" 

......... SIIEId .... _ 

MIled~ ~ 
Mixed pooLIrapid CJ 

""""" "'" ---- -

iii: I: ;: ... iii 
0123 . S 8 r'il01112131. ' 516171aI9 

. , ~ 

Fig. 2: The sequence of c hannel types along the Letaba River in the Kroger National Park (seq uence a-d: 
upstream 10 downstream, weSI to east through the reserve 10 the conllLlence with the OlifanlS Ri ver). 

usage is like ly to o utstrip water availability 
within the catchme nt , and conseq ue ntly land 
degradation and sedime nt produc tion will 
increase (S teffen, Robertson & Kirsten 
1990b; Birkhead et ai. 1995). It is therefore 
likely that the already degrad ed Letaba Rive r 
will ex peri e nce furt he r reductions in water 
vol ume and an in crease in sed ime nt input. 
Geomorpholog ica l and ecological c hanges 
will occur as a resu lt . and it is for Ih is rea-
son that the nature of geo morphologica l 
chan ge needs to be understood. 

Sediment produ ction in the Letaba catc h-
ment has been estimated from land use, so il 
type. geomorpho logy, vegetation an d rainfall 
variab les (S te ffe n Ro bertso n & Kirsten 
1990b). Yi e lds ra nge fro m 150 tkm2/a to in 
excess of 400 tkm1/a (Fig. I c) with the hi gh-
est yields occuning in the de nse ly populated 
rura l areas in the west of the catc hment . Thi s 

ISSN 0015-6458 47 

material will eve ntu all y be tran sferred from 
th e drainage bas in into the ri ver (Knigh ton 
1991). affecting a ll reaches of the Letaba 
River to vary ing degrees. Increas ing pres-
s ures on the catchme nt as a result o f greate r 
water abstracti o n and an ex pa nsio n of agri-
c ultural practices are like ly to result in fu r-
the r now reduction and inc reased sediment 
inputs to the ri ver (Birkhead et of. 1995 ). 

Geomorp hol ogy 

The Letaba Ri ve r in the Lowveld cons ists of 
a mac ro-channel th at is inc ised into the sur-
rounding landscape by so me 5- 10 m o n 
average and ove r 30 m in the gorge close to 
th e conflu e nce wi th the O li fa nt s Ri ve r 
( Heritage el 01. 1997). With in the mac ro-
c hannel there are o ne or more sub-channel s 
that are ac tivated as discharge ri ses follo w-

K~d~441 t (2001) 



Table I 
Description of the morphological units found on the utaN River in the Kurger National Park 

Morphological 
unit 

Rapid 

Rime 

Pool 

Braid bar 

Lateral bar 

Point bar 

Bedrock 
core bar 

L<ebM 

Bedrock 
backwater 

Alluvial 
backwater 

River cliff 

Apical poo l 

Rip channel 

Boulder bed 

Armoured 
=, 
Alluvial 
distributary 

Bedrock 
distributary 

Terrace 

Descri pt ion 

Steep bedrock sections, hi gh veloc ity concentrated fl ow. 

Accumulation of coarser sediment as a topographic high point as part of a pool rime 
seque nce. 

Topographic low point characterised by finer sediments, as part of a pool-ri m e sequence. 

Accumu lation of sediment in mid-channe l causing the flow to diverge over a scale \hat 
approx imates to the channel width. 

Acc um ulation of sedi ment attached to the side of the channel. may occur sequentially down· 
stream as altern ate bars. 

Accumulation of sediment on the inside of a meander bend. 

Accumulatio n o f finer sediment on top of bedrock in bedrock anastomosing areas. 

Accumulation o f sediment in the lee of flow obstructions. 

Stationary or near stationary bodies o f water in bedroc k, adjace nt to the active c hannel. 

Stationary o r near stationary bodies of water in alluvium, adjacent to the active channel. 

Vertical or near vertical alluvial erosion face . 

Deep section of channel located on the outer bend of a meander, associa ted wi th point bars. 

Hi gh discharge distributary channel on the inside of poi nt and lateral bars. 

Accumulation of locally derived material exceeding 0.25 m. 

Accumulation of coarser sedi ments due to winnowing of finer material. 

Individua l active channel in an alluvial braided or anastomosi ng system. 

Individual active channe l in a bedrock anastomos in g system. 

Relic fl oodplain or valley floor deposits above the present river level. 

in g rainfall eve nts. Th e macro-c hanne l 
ex tends across th e width of the incised valley 
and is characterised by discrete sedimentary 
depos its forming all uvial morphological 
units many of which are colonised by ripari -
an vegetation. 

that on the Sabie River (Heritage & Moon 
2(00). Sedi ment from the degraded catch-
ment has accu mulated within th e macro-
channel creatin g a preponderance of allu vial 
reac hes. These, often ex tensive, allu vial areas 
are characterised by sparsel y vegetated sand 
sheets and associated lateral terrace-like 
depos its of cohesive all uvium. Wet season 
floods inundate the sand sheets whereas the 
terrace features are overtopped only by less 
frequent flows of greater mag nitude . 

Although the river has incised several metre s 
in to bedrock and allu vial material to fo nnthe 
macro-c hannel, the influ ence of bedrock on 
th e channe l floor is considerabl y less than 

Koedoe 4411 (200 1) 48 tSSN 0075-6458 



Table 2 
DistributiQ1I of tht morphological u1IilS fou1Id 011 tht utaba Ril,tr;1I tht Knlgtr National Park 

-- --
Morphological Unit Mixed 

Anastomosing 
- - - --

Rapid ./ 

Rime 

Pool Rime 

Apical 

Rapid 

Braid bar 

Lateral bar 

Point bar 

Bedrock core bar ./ 

'" "" ./ 
Backwater Bedroc k ./ 

Allu vial 

Mixed 

River cliff 

Apical pool 

Rip channe l 

Bou lder bed 

"""""" ~ ./ 
Distributary Bedrock ./ 

Alluvial ./ 

Mixed ./ 

T,~ 

Bedroc k· influenced reaches are limited in 
exten t and ex hibit considerable alluv ial 
COVe r in the fonn of un co nsolidaled sands 
and fine gravel s. In such reaches the channel 
divides 10 fonn a multipl e di stributary net· 
work flowin g around bedrock o ut crops 
exposed in th e bed of the channel. 

Aerial photographs taken in 1989 together 
with field observations were used to cate-
gorise the Letaba Ri ver in a hi erarchi ca l 
framewor k. The basic components of the 
framework are morpholog ica l units. eac h 
with a di stinctive character and micro- habi· 

ISSN 0075-6458 

- - - -- -- -- --
Alluvial Mixed pool. Alluvial single. 
Braided rapid thread 

---- ---------

49 

./ 

./ ./ 

./ ./ 

./ ./ 

./ 

./ = 

./ ./ 

./ ./ 

= 
./ 

./ 

./ 

./ 

./ 

./ 

./ ./ 

./ 

./ 

./ ./ 

tat (Van Niekerk & Heritage 1993). Morpho--
logical un its are seen to associate together to 
fonn different channel types (Heritage et al. 
in press). There is a functi onal re lati onship 
belween differem chann el lypeS wh ich may 
be grouped int o reac hes. where one channel 
type may be influ encing directl y the nature 
of the channel type upstream or downstream . 
The interaction of a range of flows on 
bedrock and all uv ium has ge neraled a varied 
assemblage of morpho logical un its 
(Tab le I). 

KfH dfH 4411 (200 1) 



Fig. 3: A mixed anastomosing channel type on the: 
Letaba River in ihe Kruge r National Park . 

Visual in terpre tation of aerial photogra ph s 
( I: 10 000 sca le), ae ri al video footage take n 
during winter low flow co ndition s and 
extensive fieldwork prov ided the basis for 
identify in g characteristic mo rphological 
asse mblage s or channe l types. Four common 
chan nel types (mi xed anastomos ing, mixed 
pool-rap id, alluv ial single thread and allu vial 
braided) are found along the Letaba Ri ve r 
(Fig. 2). Gradations betwee n the four prima-
ry channel types indicate that individua l 
channe l types are pan of a spat ial and tem-
pora l continuum of cha nne l fonn. The chan-
nel types ex hibit ed by th e Letaba are 
described below. 

Mixed anastomosillg 

Some sect ions of the river di sp lay a wider 
macro-c hannel than the average (Fig. 3). 
Bot h sedimentary and bedrock features 
(Table 2) are found in the channel which is 
characterised by a tonuous distri butary net-

Koedoe4411 (200 1) 

work that follows weakn esses in th e bedrock 
and covers the ent ire width of the macro-
channel . 

Waler leve ls within the various di stributary 
chann els are oft en al different elevations as a 
result of flow being conce ntrated along lines 
of weakness as defined by the bedroc k tem-
plate. Loca ll y bedroc k out crops within the 
channe ls act to obstruct the flow effectively 
acting as local hydrauli c co ntrol s. This 
results in a di scontinuou s phreati c surface 
with no sub-s urface water fl ow linkage. The 
all uvia l deposits covering muc h of the 
bedrock exist as a thin (less than 1.5 m) 
ve neer on the interfl uves be twee n the dis-
lributary chan nels. The material is generally 
unconso lidated or only se mi -consol idated 
bei ng composed of sa nds and fi ne gravel s 
with little clay or silt and Ih ere are few large 
bedrock core bar deposits . Occasional 
deposi ts of coarse r grave ls and cobb les exist 
as armoured areas an d lag deposits in the 
sect ions of the channel dominated by 
bedrock. Distri bu tary channels tend to be 
lined with reed and sc rub vegetation. Aerial 
photographic analy sis of the effects of high 
flow s (w hich inundate the entire macro-
chan nel ) on mix ed anastomos ing channels 
has revea led that thei r planfonn is stable in 
that fl ow returns 10 pre-existing channels as 
the flood stage d imi ni shes. 

Alii/vial braided 

Short sec ti ons of river are characleri sed by 
ex tensive san d sheets (Table 2) dissected by 
a multi -c hannel network of alluvial di stribu-
taries that flow over the sandy surface . The 
low- fl ow d istributary channels split and 
rejo in arou nd unco nsol idated mid-channel 
deposil s over di slances that approximate the 
distri bulary width (Fig. 4). Flow leve ls in 
these chan nels are similar, ind icati ng a well-
connecled phreatic surface across the macro-
channe l. Pl anfor m change is rapid and 
observat ion of the river afler a flood reveals 
that thi s is often associated with new channel 
cutti ng on the falling lim b of the flood 
hydrograph , except where reed growth has 
paniall y Slabil ised and restricted the lateral 

ISSN 0075-6458 



Fig. 4: }\ bmidcd ch;lII lleltypc on the Letaha River 
in the Kn' gcr National P;lr k. 

migrat io n of di Slribu taries. EXlens ive sa nd 
sheel s dom ina te the macro-c han nel: sta lled 
s and dunes and sca~()nal d istribu lary chan-
nel s formed d uring the prev io us flood event 
complicate Iheir morpho logy. Fi ne ma leria l 
doc s not accumu late on the s urface of the 
s:.I11 d shee ts (Fig. 4 ). It is suggested that this 
is due to the li ne ma te rial. carr ied by flood 
flow s. re mains in s uspe ns ion because of 
hig h e ne rgy level s :l nd contin ue dOW I1 -
stream. Lower e nergy levels arc expe rienced 
close to the mac ro-channel margi ns whe re 
li nes arc de l)Qs iled c re at in g s ub- linear ter-
race- li ke featu re s composed of clays. s ilts 
a nd sand y depo s it s. Occ as ion:t1 allu vial 

ISSN 0075-6-t58 " 

Fig . 5: ;\ mixed IXKJI-rdpid dwnncltypc un lhe LC1~ ­
ha Ri .'cr in the Kn' ger National P;,rk. 

backwat ers develop (Fig. 4) fo llowing now 
recessio n and I)QO I iso lation. Fin er material 
characterises the bed o f these areas. 

MiXl'{/l'orJ/ -mpid 

Bedrock eX I)Qsures o n th e macro-c hannel 
floor influence Ihe course and st nl ct ure of 
Ihe low- fl ow channe l and ge nera le a se ries 
o f bedrock ra pid s and assoc iated upstrea m 
pool s (Fig. 5). O flelll he now netwoi-k for ms 
a number of sub -pa rallel pools separat ed by 
bedrock rap ids ( Fig. 5). Evide nce from s im -
ilar fealures on the Sabi e River (C hes hire 
1994) ind ica te Ihall ocal geology. wi th alter-
nating weake !" (pools) and more res isl:11l1 
litho log ies (rapi ds). influence s the nature of 
these morpho logical u nils (Tab le 2). Mixed 
poo l-rapid c hannel s arc common in th e high-
e r ene rgy zones along Ihe ri"c r. p:lniclilarly 

Ko.·,/"" -1 -1 / 1 ( 2001) 



Fig . 6: ,\ 11 ~lIu\'i,ll s ingte thread I:hannc t !ype on Ih e 
LC!:Iba River in Ihe Kru ger Nali()n~1 Park (W,l\'C 
trai ns ca n be M:c n in !he lOp ri ght uf Ihe ,a nd ~hcc!). 

whe re sedimc nt suppl y is locall y redu ced. 
for examp lc dow nstrea m of s mall dams. 
Cohes ive sed imen ta ry de pos it s ar..: res tric ted 
to occ as ion al dissec ted re mn a nt s o f more 
ex te ns ive tc rrace fe Mures o ft e n fo rmin g 
ex posed 'ri ve r c li ffs' nca r the s ides of the 
mac ro-c hannel. Allu viati Oll across mu ch o f 
th e mac ro-c hannel f0 1"ms cx te nsive but thin 
sand sheets infillin g lowe r areas of ex pose d 
bedroc k pa ve mc nt. Coarser arm o ured area s 
occ asionally fo rm rime -lik e fe atures of la g 
mat e rial in th e ac ti ve c hannel (Fi g. 7a). 

AIlIl 1"ia/ .~il1gll! Ihread 

Therc is ev id e nce o f swi tching bet wee n 
bra ided. mi xed an asto mosing a nd s ingle 
thread sys t e l1l ~ in allu vial sec tions of the 
rive r. In s ingle th read reaches low n ows are 

conveyed along a s ingle a ll uv ial channel 
across an exten sive sand s hee t whe re no 
bedrock feature s arc ev ident (Table 2). Oft e n 
suc h channel s arc close 10 the s ide of the 
mac ro-chan nel. :md alternate fro m s ide to 
side bearing no rei;ltion to the m:!c ro·c hannel 
planfonn (Fi g . 6). llle re arc s igns of in cipi -
ent braidin g with the comm o n devel o pm e nt 
of shallow lo w now rime s composed of s and 
and fin e gra vel s and m id -c hann e l bars 
(Fig.7b). T he e xten s ive c hann el-s ide rced 
growth. howeve r. restricts lat e ral e rosio n :lnd 
stabili ses the planfo rm . Th e restric tion o n 
lateral movement is often compe nsated for 
by venical eros ioll. and as a res ult the low-
n o w channe l appears ove r-deep in re lati o n to 
its width. An exte nsive network of seasonal 
c hannel s exist s on the surf,lce of th e sand 
sheet . s imilar to that found in bra id ed sec-
tio ns. Their dcvelopmcn t is esse nt ia ll y the 
same in both c hannel types (Fi g. 7b ). T he 
pres enc e of e xte ns ive coh es ive alluv ial 
deposi ts as lateral mac ro-c hannel te rra cc-
like feature s is also related 10 s i milar features 
co mpo sed of fine r mate ri .. 1 in braided sec-
ti o ns. and .. gg rad e follo wing majo r n ood 
e ve nts. 

52 

C h a nnel c han ge 0 11 t he Lel a ba Rive r 

Chan ges 10 th e Let ab:. River h:! \'e bee n 
an alysed us in g ae rial pholOgraph s of the 
ri ver in the Kru ge r National Park fro m the 
1960s 10 the 1980s (Vogt 1992). Th ese 
includ e pos iti o nal c han ges in sin gle thre ad 
c hannels. occas io nal ne w c h;mnels be in g CUI 
throu g h ex isting sedim entary de pos it s. and 
occasio na l ne w in -channel late ral fea ture s 
whi ch wc re depos ited in th e 1960s and 
1980s. Limit ed di sscc ti o n o f large po int bars 
occ urred in 1974 . In multi -thread reac hes. 
the abando nment of di stributary c hannel s as 
a res ult of bar coalesce nce occ urred in the 
1960s and 1980 ), co ntc mpo raneo us ly w ith 
th e depositi o n of in -c hann el lat e ral feature s. 
New channel s were clltthro ugh ex istin g sed-
im e nt s in th e 1970s. Th e ev ide ncc sugge sts 
pe riods of de pos it io n in the 1960s and 198 0s 
se parated by an e ros io nal phase in th e 1970s 
(Vog t 1992). 

tSSN 0075·6-' 51; 



.. 
. ' 

. , 
~ 

•• . -
' .. 

Fig. 7: (a) ,\rmourcu :orca in a mixed pool-r..pitl channel. nOl\ i~ right 10 lefl :UlU Ihe ch:umd "idlh is approx-
imately 40m. (b) ~i ng lc thread channel hightigluing :111 cX!.::Il,j,·c \;IJ\U ,heet. f\. ... -d ·cu\crcd mid-channel b;,r 
~nd ct)hc~i\'c Iuw ICTr.I!.-C deposits <II the m:trt;in\ of the m:,cro.-challncl. til\' ;Icli\'c ('halilid is appm.xirn:ucly 
10m Ilidc. 

Ev id e nce of short -term c han ge has bee n 
ob tained from a fe-survey of twenly c ro:.s-
sections c~tablishcd on the Lelah:! I~ivcr in 
1993 (Heri tage l 'l al. 1997). Th e Oood of 
February 1995. whic h geller.lled it I>cak now 
gauge reading of 655 1111/s OIl Enge lha rd 
O;Ull. close to Lelab:! rest camp in the Kruger 
National Park, resulted in rcrna rbbly litt le 
cha nnel change. Low-flow channel:-

ISSN 0()75 · (>-I5!! 

rema in ed slab lc. In so me sec tions there was 
dissection of sa nd ~ho.!ets a~ a res ult of cha n-
nel dev el oplllo.!l1\ during the waning-flow of a 
flood. The sig nili cant c han ges we re in b ulk 
sediment mass. "tor:.Jge o n the sand sheets 
with deposi ti o n and erosion occurring a lo ng 
the river. The p.l\lCrn of c hange was not 
related 10 th e c hann eltypc distribution ( Her-
itage ;'/ 01. 1997). This may reflecl Ihe 



1ll0\'e rn e llt of sedime nt s lu gs as d une field 
wavc trains al o ng th e system ( Fi g. 6 ). Con -
s id er.lble depos its of fi ne se dime nt we re left 
o n teIT:ICC fe'ltures o n the s ides o f the n1ac ro-
channel . 

Th e available evide nce s uggests, wi th the 
cxcept ion o f loc .. li \Cd e rosio n and some 
minor c hannel c hange resulling from infre-
(Iuent hi g h. n ow cvenl ~, that the Le t:tba 
Ri\'e r is gener-Ill y becoming more allu viated 
( Bi rkhe:ld e l al. 19(5). With decreasi ng now 
volumes and inc re:ls ing sediment inputs the 
prog ress io n of e h.mge in the different c han -
nel types is li kel y to be from mi xed 1>001-
mpid or mi xed :lnasto mos ing 10 allu vi al s in· 
glc thread or .. l1ll vial bmidcd ( Herit .. gc ('/ 
lIl. 19(9 ). 

C onclu s ioll 

Despitc th e Lc taba Ri vcr ha vin g incised into 
bed roc k in the pa sl. allu vial c hannel t)' pe s 
domina lc Ihe rive r. Th e in n uc ncc o f the 
underlyi ng bedrock has bee n l o~ t du e to the 
depos it ion o f un co nsolid:ned and con so lidat-
ed all uv ial mat e rial. Bed roc k- innu e nced 
ch .. nncl types arc resuic led to shon le ng ths 
of c ha nnel .. nd arc oft e n as~oc i a t ed wi th ani -
fieia l stmclures that alter the sedim e nt ba l-
:mce loca ll y. 

La nd deg radat io n within the catchmc nt alld 
assoc i:ltcd red uc lio ns in now reach ing the 
do wnstream c nd of Ihe rive r. ha ve undoubt-
ed ly hel ped 10 mai nt a in the ri ver in its pre-
sent stat e ( Birkhe.1l1 ('I (II. 1(95). Rat es of 
ch:tnnel c h.rn ge arc slo wer .md th e l1Ia£ ni-
tud e of geo mo rpholog ical adj us tm e nt is 
mino r in compa ri~on wi lh syste ms such as 
the Sabie Ri ve r (Va n Nie kerk & I-I e riw ge 
199 3: I·lcrita ge ('/ (II. 1997: Heritage & Moon 
2000). The relati ve slabi lil)' of the Le taba is 
probabl y rcl ;lI ed to the declin e in o ve mll 
n o w e ne rgy con sc(lil e nt upon th e mu ch 
reduced now freque ncy .md Ill :lgnitude as a 
result of int e ns ive wal c r abstmction wi lhi n 
the catc hme nt (Ste ffen Ro bert s & Kirste n 
I 99();I) 

It is anti cipated that c han ge wilhin Ihe sys-
te m will now occ ur o nl y in re latio n to s ig-

nific:l nl e \'c nts th at n ood Ih e mac ro-ch.mn e!. 
The in fe rred con se(llle nCe of s uch nood s will 
be the de posi lion of fine se dime nt at the base 
o f the macro·c hann e l bank and the rewo rk -
ing o f un conso lidated s.mds and fine growe l 
ove r th e surf;lce o f e xt e ns ive sand shee ts. 
S tabil isati o n o f some :Ireas. p.1nic ularly the 
ba nk s o f Ih e lo w- now di stribut a ry c ha nnel s 
llI ay funh er inhib it chan nel c h:mge, and the 
inferred con seque nce is the de vel o pme nt o f 
stable. o\'e r-dl..-cp ch .. nnel ne two rks in la rge-
scale deposi ts o f unconso lid ated allu vium . 

Obse rvation of the tre nd s on th e Lelab:l 
Ri ve r suggesl that de ve lopmc nt of th e te r-
race- like cohes ive de posi ls <II the s ides of the 
macro·chann el is li kel y to co ntinu e b), ven i-
cal acc re tion provi ded nond fl ows o f suffi -
ci e nt ma gni tude COlllinu c to reac h the Knl ger 
Nati o na l Park . Similar nuws :Ire rCtlu ire<l 10 
maintain the sand shee ts, it is infe rred tha t 
the se remai n free o f fine sedime nt as a re sult 
o f prolon ged nood recess io ll . !\ rl..'<iuc tio n in 
the dura ti o n of inte rmediate wanin g nows 
may lead to th e de pos itio n of fine suspe nded 
mate ria l across the surface of Ihc sand s hee ts 
in stea d o f this mate ri:.l con tinuin g to be 
transpon cd do wn strea m. T he lack of pm-
lorl£ed flo ws cap .. ble of re lilo bili sing fine 
mat erial. du e 10 inc reas in g wat er usage with-
in the catc hment . will further e xacerb:ne the 
poss ibilit y of cohes i\'e st.-d iment build· up. 

Ack nowled ge mell ts 

The a uthor.. gr.lldulJ)' aei",o\'. led gc lhe fun d ing pro-
I'idcd fo r Ih i~ projcci by Ihc Walcr Re~arch Corn· 
rni ... ~ion o f Soul h A rric a. Logi'lic;,1 -'111111011 \'.·a~ pro-
vided by Ihe N:u iOll al I' arks Board of Soulh Africa. 
P<lrt ic Il1 ~r Ih~,,' ks 111 U,1 be cXIClldcd III M r BCl1)., us 
Erl~Jill :1nd /I.'tr Mitt iun Xho~~, for Ihei r hc tp in Ihc 
fic ld. 1\·l r G. 1)Obn), nski is Ih ;111kcd for h i~ C~," (J· 
gr.'phic ~k i ll s. AnOrly 11111 11 ~ rerCI'Ces ~ ,re Ilmn kcd fo r 
thc ma ny enn ~I IlJC li \'e comme nt , in Ihei r I'Cl'iews. 

RcfercnCl..'S 

1~IR KHt:AD. 1\ .1.. & G.Lll o m i\CL 1995. T<."Chniquc .. 
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(fllft's of Iht' M,·" " ,/r Smllil ,V,;("/I<I NlI/;mllll 

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Ko .. ,11Jl' +111 (200!)