The aim of this paper is to assess the hydrological system of the Okavango headwater tributaries, namely the Cuito and Cubango subcatchments, and the flow characteristics of the Okavango after their confluence at Mukwe. This assessment was applied at several gauging stations in the Cubango River reaching from the station Chinhama in Angola down to the station Rundu in Namibia and for two gauging stations (Cuito Cuanavale and Dirico) in the Cuito River system. Identifying hydrological flow characteristics by analysing time series discharge data in terms of frequency, low and peak flow events, and upstream downstream linkages in the mentioned tributaries was supported by the analysis of spatially distributed climate time series and basin characteristics. The analysis of the existing datasets in this data scarce region revealed that the headwater catchments are different in runoff generation, river bed morphology, and storage capacities. The amount of delivered discharge from the Cubango is more varied in amplitude and frequency compared to the more base flow dominated Cuito discharge. Analysing spatial datasets indicated significant differences in natural landscape system features leading to different runoff generation, from fast discharge hydrographs (Cubango) to base flow driven flow dynamics (Cuito). Compiled data as well as assessed hydrological dynamics will allow for the follow-up application of process based J2000 and J2000-g hydrological models for water balance assessment and river basin rainfall-runoff modelling.Keywords: Cubango River; Cuito River; flow duration curves; hydrological assessment; Okavango catchment; upstream-downstream analysis.A avaliação da dinâmica hidrológica no alto da bacia do rio Okavango Resumo: O objetivo deste trabalho é avaliar o sistema hidrológico dos afluentes da cabeceira do Okavango, ou seja, as subbacias Cuito e Cubango, e as características do fluxo do Okavango após sua confluência no Mukwe. Essa avaliação foi aplicada em várias estações de medição no rio Cubango, atingindo desde a estação Chinhama em Angola, descendo até a estação Rundu na Namíbia e duas estações de medição no sistema do rio Cuito (Cuito Cuanavale e Dirico). A identificação das características do fluxo hidrológico por meio da análise de dados de descarga de séries temporais, em termos de frequência, eventos de fluxos baixos e de picos, e as ligações a jusante e a montante nos afluentes mencionados, foi apoiada pela análise das séries temporais climáticas espacialmente distribuídas e das caracteristicas da bacia. A análise dos conjuntos de dados existentes, nessa região escassa de dados, revelou que as cabeceiras das bacias são diferentes na geração de escoamento, na morfologia do leito do rio e na capacidade de armazenamento. A quantidade de descarga distribuida pela Cubango é mais variada em amplitude e freqüência em comparação com a descarga de maior fluxo de base dominada de Cuito. A análise do conjunto de dados espaciais indicou diferenças significativas nas características do sistema de p...

Abstract. The neighbouring river systems Cubango and Cuito drain the southeastern part of the Angolan Highlands and form the Okavango River after their confluence, thus providing 95% of the Okavango River discharge. Although they are characterised by similar environmental conditions, runoff records indicate remarkable differences regarding the hydrological dynamics. The Cubango River is known for rapid discharges with high peaks and low baseflow whereas the Cuito runoff appears more balanced. These differences are mainly caused by heterogeneous geological conditions or terrain features. The Cubango headwaters are dominated by crystalline bedrock and steeper, v-shaped valleys while the Cuito system is characterised by wide, swampy valleys and thick sand layers, thus attenuating runoff. This study presents model exercises which have been performed to assess and quantify these effects by applying the distributive model J2000g for each sub-basin. The models provide reasonable results representing the spatio-temporal runoff pattern, although some peaks are over- or underestimated, particularly in the Cuito catchment. This is explained by the scarce information on extent and structure of storages, such as aquifers or swamps, in the Cuito system. However, the model results aid understanding of the differences of both tributaries in runoff generation and underpin the importance of floodplains regarding the control of runoff peaks and low flows in the Cuito system. Model exercises reveal that basin heterogeneity needs to be taken into account and must be parameterised appropriately for reliable modelling and assessment of the entire Okavango River basin for managing the water resources of the transboundary Okavango River in a harmonious way.

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