Closed Drainage Systems

Abstract

A closed drainage system is one of the urban drainage systems, which receives the runoff and/or wastewater from inlets and conveys it/them by a closed conduit to terminal points, where water is treated and/or discharged into a channel, pool, lake, ocean, etc. It is expensive to build and requires more sophisticated engineering techniques to design, construct, and maintain. To design the closed storm drainage system, the rational method is applied to estimate the peak flow resulting from rainfall events for the hydraulic structures, e.g., inlets, underground storm sewers, open outfall discharge points. The conveyance conduit pipes can be determined using Manning’s equation. In addition, the effects of increased stormwater quantity and mitigation of the negative impacts need to be assessed. To solve potential sediment deposition in the closed drainage pipe system, design guidance has been developed based on the physical laws, which govern the motion of water and sediment. Therefore, determination of the sediment grain size distribution and specific weight in the drain system is the first step; the sediment incipient motion and sediment transport rates are estimated according to the hydraulic performance of pipe flow characteristics, pipe wall characteristics, and the sediment characteristics; finally, the pipe size/flow rate needs to be corrected consistently with the design criteria. To promote urban water harvesting and conservation, best management practices (BMPs) including a variety of structural and nonstructural practices, as well as low-impact development (LID), are crucial. Consideration of a BMP system depends on the physical site characteristics, the design and maintenance requirement, effectiveness, and cost. The integrated urban water management modeling, e.g., SWMM, City Drain, becomes a great approach to simulate the water quantity and quality for the closed urban drainage systems. The chapter has summarized the design procedure of the closed storm drainage system, the design guidance to consider sedimentation in the closed drainage system, the modern best management practices (BMPs) for controlling urban runoff quantity and quality and their effectiveness, and the current integrated urban water management modeling for the closed drainage system.