The world is increasingly shifting toward low-head hydropower as a sustainable form of renewable energy in response to the negative socioeconomic impacts of large hydroelectric plants. In this context, the article presents a novel design involving retrofitting the gates of existing dam structures with Dethridge waterwheel technology. This innovative solution installs the wheel under the gate to harvest the untapped potential energy resulting from the head difference at these already-existing facilities while simultaneously reducing the need for costly civil work and preventing new installations in freshwater systems. The El-Reah El-Tawfiqy barrage in Egypt served as the model case study for evaluating the implementation of the proposed design. According to the results, the plant’s levelized cost is 29 USD/MWh, less expensive than traditional hydropower projects and achieves grid parity. With an estimated 140 MWh of electricity produced annually, the project is expected to cut around 1460 tons of CO2 equivalent over its 25-year lifespan. This study includes several novelties, including modifying hydraulic structure gates for pico power generation. Additionally, a thorough numerical analysis was performed to estimate the output power instead of relying on theoretical approaches for the economic viability study. These results can guide policymakers and stakeholders in implementing affordable and sustainable renewable energy solutions.