Concept Note: Distributed Transition Management for Legacy Water Infrastructure

This preprint presents a distributed, passive framework for managing unavoidable transitions in legacy water and drainage infrastructure, such as vertical drops, pressure-reducing valves, outfalls, and inlet structures. These transitions already function as unacknowledged weirs or dams, where energy is dissipated chaotically, accelerating asset wear and transporting pollutants downstream. The work formalises a retrofit-friendly approach using decreasing hopper modules arranged in series to progressively intercept coarse debris, grit, floatables, and fine material while maintaining uninterrupted flow through normally-open bypass paths. The framework does not introduce new head, impoundment, or energy demand. Instead, it recovers structure, separation, and diagnostic visibility from gradients that already exist, converting uncontrolled energy loss into ordered, serviceable, and observable behaviour. The contribution is architectural rather than theoretical, offering a practical lens for civilising existing drops in built and natural water systems without system redesign or active control. This work forms a constrained, self-contained concept note intended to support further application, adaptation, and integration into stormwater management, building services, and distributed environmental protection systems. Keywords distributed infrastructure; stormwater management; passive water systems; energy dissipation; weirs and dams; sediment separation; floatables capture; grit removal; retrofit design; drainage infrastructure; pressure-reducing valves; outfalls; environmental protection; modular systems