Gerd Lahmeyer Segelmachermeister

A modelling study is performed to evaluate interannual and decadal-scale streamflow variability into the Grand Ethiopian Renaissance Dam (GERD) reservoir and comparison of various filling strategies for hydropower and downstream releases to Sudan and Egypt from this dam. To capture these aspects, simulations of probabilistic streamflow via wavelet analysis are produced to define the propensity towards wetter or drier conditions for absolute, threshold and percentage-based filling strategies. Absolute filling strategies have lower uncertainty than percentage-based strategies, benefiting upstream planning; however, downstream releases may be near zero on occasion. Consensus among the riparian countries prior to initiation of filling is strongly encouraged. Jeuland et al., 2014 ; Tilmant and Kinzelbach , 2012; Teasley and McKinney, 2011; Whittington et al., 2005 ).

Cooperative game theory concepts that address relative power of the riparian states in capturing incremental benefits from cooperation, such as the Core, the Shapley Value, and the Nash-Harsanyi (N-H) solution are compared under several scenarios, namely with and without water trade, and with and without existence of unidirectional externalities in the form of soil erosion and siltation impact. We find that the stability of Shapley and N-H benefits allocations are sensitive to the initial water rights allocation, which may explain the present caution of the basin states to be engaged in cooperation arrangements. We also find that when a Core exists it is very small, which indicates also a fragile basis for cooperation. This study examines management approaches for hydropower generation and irrigation and domestic water supply for the Tekeze-Atbara, a transboundary river between Ethiopia, Eritrea and Sudan, in above- and below-normal hydrologic conditions, considering current and future water demand scenarios.

The case study is the addition of the Grand Ethiopian Renaissance Dam (GERD) and considers how its operation may be coordinated with adaptations to the operations of Egypt’s High Aswan Dam. The results demonstrate that a lack of coordination is likely to be harmful to downstream riparians and suggest that adaptations to infrastructure in Sudan and Egypt can reduce risks to water supplies and energy generation. Although risks can be substantially reduced by agreed releases from the GERD and basic adaptations to the High Aswan Dam, these measures are still insufficient to assure that no additional risk is assumed by Egypt. The method then demonstrates how improvements to water security for both downstream riparians can be achieved through dynamic adaptation of the operation of the GERD during drought conditions. Finally, the paper demonstrates how the robustness of potential management arrangements can be evaluated considering potential effects of climate change, including increased interannual variability and highly uncertain changes such as increases in the future persistence of droughts.

Sudan’s large irrigation potential, hydroelectric dams, and prime location within the basin mean that Sudan’s water management decisions will have great social, economic and political implications for the region. At the same time, Sudan’s water use options are constrained by tradeoffs between upstream irrigation developments and downstream hydropower facilities as well as by the country’s commitments under existing or future transboundary water sharing agreements. Here, we present a model that can be applied to evaluate optimal allocation of surface water resources to irrigation and hydropower in the Sudanese portion of the Blue Nile.

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gerd lahmeyer

For example, some of the planned irrigation schemes in upstream countries are not economically sound if the power stations that are in an advanced planning phase are implemented. This study also reveals that the economic value of the three largest storage infrastructure (Kariba, Itezhitezhi, Cahora Bassa) is around US$443 million/year.

Full supply level may be reached after four years or not at all, depending on filling policies and assumptions of seepage rates. Under recent hydro-climatic conditions, the dam may produce 13 TWh −a , which is below the envisaged target of 15.7 TWh −a. The ensemble mean suggests slightly increasing hydropower production in the future.

This is compared with fullscale system-wide optimization through an Stochastic Dual Dynamic Programming algorithm to represent fully coordinated reservoir operation (upper bound). For our case study, results indicate that better coordination reduced spills and improved releases timing according to reservoirs characteristics and location, allowing overall gains between 3% and 8% in energy and 7.9% in revenues, with revenues mostly improved by coordination in dry years. Larger reservoirs presented the highest gains in absolute terms, while the smaller ones presented the highest relative increases. By indicating individual gains at each reservoir, valuable information is produced to support future negotiations and benefit sharing among different agents, being water agencies or power companies.

Stochastic dual dynamic programming (SDDP) is one of the few algorithmic solutions available to optimize large-scale water resources systems while explicitly considering uncertainty. This paper explores the consequences of, and proposes a solution to, the existence of multiple near-optimal solutions (MNOS) when using SDDP for mid- or long-term river basin management. These issues arise when the optimization problem cannot be properly parametrized due to poorly defined and/or unavailable data sets. This work shows that when MNOS exists, 1) SDDP explores more than one solution trajectory in the same run, suggesting different decisions in distinct simulation years even for the same point in the state-space, and 2) SDDP is shown to be very sensitive to even minimal variations of the problem setting, e.g. initial conditions — we call this “algorithmic chaos”.

gerd lahmeyer

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