An algorithm is described that was initially developed as a simple method for patching and extending observed time series of daily streamflow. It is based on the use of 1-day flow duration curves for each month of the year and on the assumption that flows occurring simultaneously at sites in reasonably close proximity to each other correspond to similar percentage points on their respective duration curves. The algorithm has been incorporated into a model that allows flows at a destination site to be estimated from flows occurring at several source sites. The model has been applied to six groups of catchments within southern Africa and the resulting streamflow simulations compare favourably with those obtained using a semi-distributed, physically-based, daily time step rainfall-runoff model. The current limitations of the approach and its future potential value are discussed.

A method is described that allows long-term 1-day annual and seasonal flow duration curves at any ungauged location in one of the drainage regions of South Africa to be established. The method is based on normalization of observed flow duration curves by a long-term mean daily flow and subsequent averaging of normalized ordinates of the curves. The estimate of mean daily discharge for an ungauged site is obtained using the information from the existing national data base of flow characteristics. The established set of flow duration curves at a site is further translated into actual daily streamflow time series using a simple nonlinear spatial interpolation technique. Régionalisation des caractéristiques des débits journaliers dans une région du Cap Oriental (Afrique du Sud)Résumé La méthode décrite permet d'établir pour n'importe quel site non jaugé de l'une des régions de drainage d'Afrique du Sud, les courbes des débits journaliers classés annuelles et saisonnières. La méthode est basée sur la normalisation, par le débit journalier moyen, des courbes de débits journaliers classés observées, dont on moyenne ensuite les ordonnées. L'estimation du débit journalier moyen pour un site non jaugé est obtenue à partir de l'information contenue dans la base de données nationale des caractéristiques d'écoulement. Les courbes des débits classés ainsi calculées sont converties en séries temporelles d'écoulement journalier, en utilisant une simple technique d'interpolation spatiale non linéaire.

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Abstract:The paper describes a parsimonious approach for generating continuous daily stream-¯ow time-series from observed daily rainfall data in a catchment. The key characteristic in the method is a duration curve. It is used to convert the daily rainfall information from source rain gauges into a continuous daily hydrograph at the destination river site. For each source rain gauge a time-series of rainfall related`current precipitation index' is generated and its duration curve is established. The current precipitation index re¯ects the current catchment wetness and is de®ned as a continuous function of precipitation, which accumulates on rainy days and exponentially decays during the periods of no rainfall. The process of rainfall-to-runo conversion is based on the assumption that daily current precipitation index values at rainfall site(s) in a catchment and the destination site's daily¯ows correspond to similar probabilities on their respective duration curves. The method is tested in several small catchments in South Africa. The method is designed primarily for application at ungauged sites in data-poor regions where the use of more complex and information consuming techniques of data generation may not be justi®ed.

The paper describes a parsimonious approach for generating continuous daily stream-¯ow time-series from observed daily rainfall data in a catchment. The key characteristic in the method is a duration curve. It is used to convert the daily rainfall information from source rain gauges into a continuous daily hydrograph at the destination river site. For each source rain gauge a time-series of rainfall related`current precipitation index' is generated and its duration curve is established. The current precipitation index re¯ects the current catchment wetness and is de®ned as a continuous function of precipitation, which accumulates on rainy days and exponentially decays during the periods of no rainfall. The process of rainfall-to-runo conversion is based on the assumption that daily current precipitation index values at rainfall site(s) in a catchment and the destination site's daily¯ows correspond to similar probabilities on their respective duration curves. The method is tested in several small catchments in South Africa. The method is designed primarily for application at ungauged sites in data-poor regions where the use of more complex and information consuming techniques of data generation may not be justi®ed.