The value of streamflow forecasts to inform water infrastructure operations has been extensively studied. Yet, their value in informing infrastructure design is still unexplored. In this work, we investigate how dam design is shaped by information feedbacks. We demonstrate how flexible operating policies informed by streamflow forecasts enable the design of less costly reservoir relative to alternatives that do not rely on forecast information. Our approach initially establishes information bounds by selecting the most informative lead times of perfect streamflow forecasts to be included in the infrastructure design. We then analyze the design and operational sensitivities relative to realistic imperfect streamflow forecasts synthetically modeled to explicitly represent different biases. We demonstrate our approach through an ex-post analysis of the Kariba dam in the Zambezi river basin.
Results show that informing dam design with perfect forecasts enable attaining the same hydropower production of the existing dam, while reducing infrastructure size and associated capital costs by 20%. The use of forecasts with lower skill reduces this gain to approximately 15%. Finally, the adoption of forecast information in the operation of the existing system facilitate an annual average increase of 60 GWh in hydropower production. This finding, extrapolated to the new planned dams in the basin, suggests that consideration of forecast informed policies could yield power production benefits equal to 75% of the current annual electricity consumption of the Zambian agricultural sector. Forecast information feedbacks have a strong potential to become a valuable asset for the ongoing hydropower expansion in the basin.