Conveyance systems are the interconnected natural and engineered pathways within a drainage or stormwater system that are specifically designed to transport water from one location to another. Their primary function is to move runoff efficiently from points of collection, such as inlets or overland flow areas, to points of discharge, storage, or treatment, such as channels, basins, or receiving waters.
In stormwater management, conveyance systems include a wide range of components, both open and closed. Open conveyance elements include swales, ditches, streams, and engineered channels, which carry water along the land surface. Closed conveyance elements include storm drains, pipes, culverts, and tunnels, which transport water underground or through enclosed structures. These components are hydraulically connected, forming a continuous network that routes water through the system.
The performance of a conveyance system is governed by hydraulic principles, including flow capacity, velocity, slope, and resistance (or roughness). Proper design ensures that the system can handle anticipated runoff volumes without overtopping, surcharging, or causing excessive erosion. Flow velocities must be carefully balanced, as velocities that are too low can lead to sediment deposition and clogging, while velocities that are too high can cause channel erosion and downstream instability.
Conveyance systems serve a critical role in managing both the quantity and timing of stormwater flows. By directing water away from developed areas, they reduce the risk of localized flooding and infrastructure damage. At the same time, modern stormwater design often integrates conveyance with treatment and storage practices to avoid simply transferring problems downstream. For example, vegetated swales and natural channels can slow flows, promote infiltration, and provide some level of pollutant removal while still functioning as conveyance features.
In addition to engineered infrastructure, natural watercourses such as streams and rivers are integral parts of conveyance systems at the watershed scale. These natural features not only transport water but also provide ecological functions, including habitat support and nutrient cycling.
Conveyance systems are the transport backbone of drainage and stormwater networks, responsible for moving water through the landscape in a controlled manner while balancing hydraulic efficiency, infrastructure protection, and environmental considerations.