Modeling for transboundary water resources planning and allocation: the case of Southern Africa

Abstract

Abstract. International water resources agreements for transboundary rivers in southern Africa are generally founded in system analysis models for water planning and allocation. The Water Resources Yield Model (WRYM) developed in South Africa has so far been the only model applied in official joint water resources studies aimed to form watersharing agreements. The continuous discussion around the model performance and growing distress over it being South African, where it was originally developed, while South Africa is one of the interested parties in the process, results in an increased controversy over the system analysis results that are often only meant to guide in selecting the options for water resources management in a given set of scenarios. The objective of this study was therefore to assess the model performance of two other models; WAFLEX and WEAP21 in the Umbeluzi River Basin system where the WRYM was previously applied as part of a Joint River Basin Study. A set of basin development scenarios was equally tested in the three models and the results compared. The results show that the three models all are possible tools for system analysis of river basins in southern Africa, although the structure and complexity of the models are different. The obtained level of satisfaction for specific water users could, however, vary depending on which model was used, which causes uncertainties. The reason for the diverse results is the structurally different ways of describing allocation and prioritization of water in the three models. However, the large degrees of freedom in all system models cause even larger uncertainty in the results since the model developer can, intentionally or unintentionally, direct the results to favor certain water user. The conclusion of this study is therefore that the choice of model does not per se affect the decision of best water allocation and infrastructure layout of a shared river basin. The chosen Correspondence to: D. Juízo (juizo@hotmail.com) allocation and prioritization principles for the specific river basin and the model developer's experience and integrity are more important factors to find the optimal and equitable allocation.

Determination of cost coefficients of a priority-based water allocation linear programming model – a network flow approach

“…For models that allocate water across multiple time steps, links connect reservoir nodes in different time periods to represent carryover storage. These models have been applied in reservoir sizing (Kuczera, 1989;Khaliquzzaman and Chander, 1997), capacity expansion (Martin, 1987;Gondolfi et al, 1997), the derivation of reservoir operating rules (Lund and Ferreira, 1996;Bessler et al, 2003), water transfer during droughts (Cheng et al, 2009), and the optimal real-time flood control operation of reservoirs (Braga and Barbosa, 2001). Single time step models allocate water only within an operational unit period, but the allocation is sequentially solved in every step during the simulation time horizon.…”

“…The lack of a systematic and precise way to establish and interpret the objective function may prevent the model from being entrusted or accepted by all involved stakeholders. For example, Juízo and Lidén (2010) reported the experiences of implementing an optimization-based model on transboundary water allocation in South Africa. They found that "the results from the system analysis tool are not easily understood by the stakeholders, and government representatives of different countries bear some suspicion about the results".…”

Optimal water resource allocation modelling in the Lowveld of Zimbabwe

“…These infrastructures, coupled with the need for improved operational skills of watershed-scale reservoirs and water distribution networks necessitates the development and application of water allocation models (Namchaiswadwong, 2004;Sert et al, 2007;Juízo and Lidén, 2010). Simulation-based allocation models are used to meet this need and they simulate water allocation with pre-determined water use priorities and reservoir operation rules.…”

“…Simulation-based allocation models are used to meet this need and they simulate water allocation with pre-determined water use priorities and reservoir operation rules. These models have poor flexibility if anthropogenic and hydro-climatic factors are taken into consideration as they operate in a "what-if-then" scenario (Jha and Gupta, 2003). Therefore considering these limitations, integrated optimal water resources allocation modelling should consider all the water users and equitably allocate water amongst users, whilst taking into consideration hydro-climatic variability.…”

A simulation tool for managing environmental flows in regulated rivers

“…Scenario-based tools developed to support water management decisions, including HEC-5 (USACE, 1998), MIKE SHE (Graham and Butts, 2005), WEAP21 (Juizo and Liden, 2010) and WRAP (Wurbs, 2005), often have fixed demands, modelling environmental flows with flows for human needs, ignoring important differences between the two. Software for modelling river systems (e.g.…”