A Survey Near Tambara Along the Lower Zambezi River

environments Article A Survey near Tambara along the Lower Zambezi River Francesco Pasanisi 1,*, Carlo Tebano 1 and Francesco Zarlenga 2 1 ENEA, Italian National Agency for New Technologies, Energy and Sustainable Economic Development, Sustainable Territorial and Production Systems Department, Models and Technologies for Mitigation of Human Impacts and Natural Hazards Division, Seismic Engineering and Prevention of Natural Hazards Laboratory; Portici Research Centre, Piazzale Enrico Fermi 1, Portici (NA) 80055, Italy; [email protected] 2 ENEA, Italian National Agency for New Technologies, Energy and Sustainable Economic Development, Energy Technologies Department, Technical-Strategical Support Unit; Casaccia Research Centre, Via Anguillarese 301, Santa Maria di Galeria (Roma) 00123, Italy; [email protected] * Correspondence: [email protected]; Tel.: +39-081-7723306; Fax: +39-081-7723344 Academic Editor: Yu-Pin Lin Received: 27 October 2015; Accepted: 16 February 2016; Published: 25 February 2016 Abstract: The paper reports a field investigation on a reach of the lower Zambezi River about 230–240 km downstream of the Cahora Bassa dam in the Republic of Mozambique. In the framework of a wider research program, bathymetric measures of the riverbed were performed on a 10 km stretch of the river using an echo sounder, a GPS receiver, and an integrated navigation-acquisition system. Field observations and measures revealed a general agreement with macro-features of river morphology reported in early literature, dealing with the morphological response of the river to the construction of large dams, in the second half of the 20th century. Results hereby reported are some of the few examples of direct field measures in the lower Zambezi reported in literature, and could be used by researchers and practitioners either as a knowledge base for further surveys or as input data for validation and calibration of mathematical models and remote sensing observations. Keywords: field survey; bathymetry; morphology; Zambezi; Mozambique 1. Introduction The Zambezi River is one of the main rivers in southern Africa and the longest African river flowing into the Indian Ocean. The river basin, lying between latitudes 9–20˝ South and longitudes 18–36˝ East, covers an area about 1.4 million km2 wide, and is the fourth-largest catchment area in Africa after the Congo, Nile, and Niger watersheds. It is shared by eight countries (Angola, Botswana, Malawi, Mozambique, Namibia, Tanzania, Zambia, and Zimbabwe), and has an estimated population of 30 million people. Figure1 illustrates the major African river basins and the Zambezi river basin, divided into its main sub-basins, representative of major tributaries and drainage areas [1]. A large body of literature exists on the Zambezi River system, dealing with its geological, hydrological, morphological, ecological, and socio-economic aspects [2–8]. The main stem of the river has an estimated length of 2524 km [2], subdivided into three major segments (upper, middle and lower Zambezi), each having distinct geomorphological and hydrological features. The upper Zambezi, about 1078 km long [2], flows from the river source near Kalene Hill (in Zambia, at an altitude of 1450 m) to Victoria Falls. In this reach, the river flows across a vast plateau with low gradients and is, to a large extent, confined in a well-defined channel; exceptions are the Barotse and Chobe swamps, two extended flood plains in which the river cross-section locally widens up to Environments 2016, 3, 6; doi:10.3390/environments3010006 www.mdpi.com/journal/environments Environments 2016, 3, 6 2 of 14 Environments 2016, 3, 6 2 of 14 tens(Mosi-oa-Tunia, of kilometres. “the The smoke upper Zambezithat thunders” abruptly in the ends local at theidiom), well-known with a drop Victoria of 108 Falls m and (Mosi-oa-Tunia, a width of “the1700 smoke m. that thunders” in the local idiom), with a drop of 108 m and a width of 1700 m. FigureFigure 1. 1.(a )(a Map) Map of of the the African African major major riverriver basins.basins. (b) Overview of of Zambezi Zambezi catchment catchment area. area. Maps Maps werewere adapted adapted from from Grid-Arendal Grid-Arendal website website [1[1].]. The middle Zambezi is comprised of the stretch between Victoria Falls and the Cahora Bassa Lake,The with middle an approximate Zambezi is comprised length of 853 of the km stretch [2]. Th betweenis is the Victoriareach with Falls the and steepest the Cahora gradient Bassa of the Lake, withentire an approximatecourse of the lengthZambezi, of 853characterized km [2]. This by narrow is the reach gorges with and the rapids. steepest Along gradient this reach of the in entirethe coursesecond of half the Zambezi,of the last characterizedcentury, the Kariba by narrow and the gorges Cahora and Bassa rapids. dams Along were thisbuilt reach for hydroelectric in the second halfenergy of the production. last century, The the Kariba Kariba dam, and thealong Cahora the border Bassa damsbetween were Zambia built for and hydroelectric Zimbabwe, energywas production.completed Thein 1959 Kariba and dam, created along an artificial the border lake between with a storage Zambia capacity and Zimbabwe, of 180.6 billion was completed m3 and a in 1959surface and createdarea of 5364 an artificial km2 [9]. lakeThe Cahora with a storageBassa dam, capacity in Mozambique, of 180.6 billion was completed m3 and a surfaceat the end area of of 53641974; km it2 [gives9]. The rise Cahora to an artificial Bassa dam, lake inthat, Mozambique, according to wasdata completed provided by at the electrical end of 1974; company it gives riseHidroeléctrica to an artificial de Cahora lake that, Bassa according [10], has ato useful data capacity provided of by52 thebillion electrical m3, a length company of 270Hidroeléctrica km, a width de Cahoraof 30 Bassakm, and[10 ],a hassurface a useful area of capacity 2900 km of2 at 52 maximum billion m 3water, a length level. of Other 270 km,minor a width dams are of 30 present km, and in a surfacethe basin area of of the 2900 middle km2 Zambezi;at maximum among water them, level. the most Other important minor dams are the are Kafue present Gorge in the dam basin and ofthe the middleItezhi-Tezhi Zambezi; dam, among on the them, Kafue the ri mostver, which important flows are into the the Kafue main Gorge stem of dam the andZambezi, the Itezhi-Tezhi about 80 km dam, ondownstream the Kafue river, of the which Kariba flows dam. into the main stem of the Zambezi, about 80 km downstream of the The lower Zambezi, about 593 km long [2], is the segment of the river downstream of the Cahora Kariba dam. Bassa dam, descending from the Central African Plateau to the Mozambique coastal plain and the The lower Zambezi, about 593 km long [2], is the segment of the river downstream of the Cahora Indian Ocean. The first reach, upstream of Tete, is characterized by boulder and bedrock outcrops Bassa dam, descending from the Central African Plateau to the Mozambique coastal plain and the with gorges and rapids [9]. The alluvial plain begins downstream of Tete, where the river flows on Indian Ocean. The first reach, upstream of Tete, is characterized by boulder and bedrock outcrops with Karoo sediments and is interrupted at Lupata gorge, near Mount Nhamalongo, where the river cuts gorgesvolcanic and rock rapids outcrops [9]. The (basalt alluvial and plainrhyolite) begins [11–1 downstream3] and the cross-section of Tete, where narrows the river to a flowsfew hundred on Karoo sedimentsmeters. Downstream and is interrupted of the Lupata at Lupata gorge, gorge, a large near low-gradient Mount Nhamalongo, alluvial plain where characterizes the river cutsthe course volcanic rockof the outcrops river with (basalt multiple and rhyolite) channels [and11– 13islands] and covered the cross-section by vegetation. narrows The mouth to a few of hundredthe Zambezi meters. is Downstreama wide delta of with the very Lupata low gorge, gradients a large and low-gradient altitudes, frequently alluvial subjected plain characterizes to flooding,the depending courseof on the riverriver with flow multiple and tide, channels which can and extend islands up covered to 40–50 by km vegetation. inland [7]. TheThe mouthdelta is ofcharacterized the Zambezi by is a arich wide deltaalluvial with soil very with low flooded gradients grasslands and altitudes, near the frequently banks and subjected mangroves to flooding,in the coastal depending zone. on river flow and tide,The which banks can and extend riverbed up toof 40–50the lower km inlandcourse [of7]. the The Zambezi delta is are characterized incised on the by aCretaceous rich alluvial and soil withTertiary flooded sedimentary grasslands cover near of the the banks alluvial and plain, mangroves and are in mostly the coastal composed zone. of unconsolidated gravel andThe sand banks [7,9]. and Unpublished riverbed of previous the lower results course of grain of the size Zambezi analyses are on incised sediment on thesamples Cretaceous taken on and TertiaryZambezi sedimentary river banks cover near Tete of the confirm alluvial the plain, predominance and are mostly of coarse composed sand, with of unconsolidatedan average of 76% gravel of andsediment sand [7 in,9]. the Unpublished range 0.5–1.0 previous mm. results of grain size analyses on sediment samples taken on ZambeziFigure river 2a banks reports near a Tetemap confirm of the thelower predominance Zambezi region, of coarse created sand, using with QGIS an average software of 76%and of sedimentOpenLayers in the plugin range 0.5–1.0with MapQuest-Open mm. Aerial and OpenStreetMap data. In Figure 2b, a longitudinalFigure2a reportsprofile of a the map main of stem the of lower the river Zambezi is plotted, region, derived created from usingRonco QGISet al. data software [14]. and OpenLayers plugin with MapQuest-Open Aerial and OpenStreetMap data.

Load more