Water diversions from rivers and torrents for anthropic uses of the resource alter the natural flow regime. As a measure, environmental flows have been prescribed and often are enforced by law to follow policies (e.g., minimal flow, proportional redistribution, etc.) that may vary from geographical location, environmental constraints and country-dependent environmental protection laws. There is not yet general consensus about the optimal release policy to be adopted, although scientific research generally agrees that flow variability for environmental flows should be a hydrological attribute fundamental for maintaining riverine biodiversity. Along with the previous assumption, non-proportional flow release strategies both for small hydropower and for traditional hydropower were proposed to generate optimal solution (sensu Pareto) for energy production and riverine ecology. Although non-proportional flow redistribution can easily be achieved by regulating flow devices (e.g., hydraulic gates), there is an interest to avoid the use of blocking structure for both safety control and energy consumption reasons. In this work, we study the redistribution capacity and flow hydrodynamics of asymmetric plate geometries that we propose as a technical and zero-operational-costs solution for generating the desired nonproportional repartition rule. Such plates can be easily mounted to partially cover the metallic rack installed at water intakes and used to intercept the stream while guaranteeing technical and environmental constraints (e.g., minimal and maximal turbined flow, minimal flow release and fish passage scales, transport capacity during high flow, etc.). We perform our study analytically and compare some performances also numerically. In summary, we demonstrate via the proposed analytical framework that different plate geometries correspond to different non-proportional fraction of water left to the environment for varying incoming flow. This work sets the premises for further studies where our approach could be adopted also for design purposes.