Hydropower configuration scenarios for Zambia

Assessment of sustainable hydropower development scenarios in Zambia

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We worked with WWF-Zambia to develop an assessment for future hydropower configuration scenarios at the national scale for Zambia. Our comprehensive, system-scale approach to hydropower pathway development aims to maximize climate-resilient energy provision while maintaining healthy and productive river systems. The results of this assessment include a roadmap and decision support tools to help inform ongoing strategic renewable energy planning efforts.

Our ‘system-scale planning’ (SSP) approach is a large-scale perspective which considers the complex interactions and cumulative effects of different dam combinations. This large-scale approach is intended to complement traditional, local methods of planning such as Environmental Impact Assessments. Rather than determining the impacts of each dam project individually, this approach considers the regional and downstream effects of the entire hydropower scenario. Additionally, this is a comprehensive process which integrates economic, environmental, and social priorities from the earliest planning stages. Our assessment included engagements with stakeholders to embed multiple objectives into the planning process.

Methodology

The modeling framework used for this project combines spatial hydrologic modeling with a multi-objective trade-off analysis to compare different hydropower development scenarios in Zambia. The hydrologic modeling is performed including all rivers within, as well as upstream and downstream of Zambia. The hydrological model component uses HydroSHEDS (Lehner et al. 2008) together with a river routing model termed HydroROUT (Lehner and Grill 2013) and incorporates discharge information from the large-scale hydrological model WaterGAP (Döll et al. 2003). This modeling framework allows for a multi-scale trade-off analysis to assess the hydro environmental performance and impacts of different hydropower configuration scenarios.

Our hydrological model uses the Connectivity Status Index (CSI) to analyze human pressures on river connectivity and assess hydro-environmental impacts. The CSI is a novel metric that was developed by Grill et al. (2019) in their study to map the global extent of ‘free-flowing rivers’. The CSI quantifies the degree to which an individual river reach (i.e. the short river segment between two tributaries) remains connected to its neighboring reaches within the larger river network. River connectivity is defined to extend in four dimensions: longitudinal (connectivity between up- and downstream river reaches), latitudinal (connectivity to floodplains and riparian areas), vertical (connectivity to groundwater and atmosphere), and temporal (connectivity based on seasonality of flows).

In order to develop hydropower scenarios, we combined our hydrological modelling framework with a multi-objective optimization module to produce a range of optimized portfolios which have the lowest environmental impacts relative to additional hydropower capacity. We applied this software to identify examples of scenarios which were optimized for multiple objectives, including hydropower generation, stakeholder needs, and environmental impacts.

Map of an example hydropower configuration scenario and resultant hydro-environmental impacts

Workshops and outcomes

We conducted two half-day workshops with participants including representatives from WWF-Zambia, the Ministry of Energy, ZESCO, the National Heritage Conservation Commission, the Kafue Gorge Regional Training Centre, the Zambezi River Authority, the Ministry of Water, Rural Electrification Authority, and others.

The focus of the first workshop was to provide background on the assessment, discuss a range of plausible hydropower development options, and hold a discussion session to develop customized scenarios to inform the next steps of the assessment. We used the input of this workshop to develop customized hydropower scenarios to directly fit stakeholder proposals, as well as to create metrics for use in our multi-objective scenario development.

The second workshop built on the content of the first workshop and included the presentation of model outcomes for customized and optimized scenarios, as well as a discussion of trade-offs between scenarios.

As a part of this assessment, we developed and shared the following tools with WWF-Zambia to support continued hydropower planning efforts:

a) a system-scale planning (SSP) model which can generate dam portfolios and evaluate their environmental impact;

b) a Portfolio Analysis Tool (PAT) which allows users to easily compare the outcomes of the dam portfolios that were generated by the SSP model; and

c) a GIS environment in which selected dam portfolios and their impacts can be visualized as a map.

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