Guicheng Xiaxi River | From Sewage-Filled Creek to Clear Water
This creek in Guicheng Xiaxi suffered the classic problems of an urban combined sewer: in dry weather sewage seeped from the outfall and the channel turned black and odorous; in wet weather river water flowed backwards, drainage was blocked and flooding regularly returned. The root cause was a small component - an ageing gravity flap gate, deformed and no longer sealing, which neither stopped sewage escaping nor prevented river backflow. It also diluted influent concentration at the treatment plant and obstructed storm drainage.
The Retrofit
The upgrade followed six tightly linked stages: removing the old flap gate, installing the device base, fitting the mechanical and electrical control units, running power and cabling, system commissioning, and training with handover. Crews worked in the water to dismantle the corroded, deformed gate section by section, while new green mechanical and control cabinets were installed beside the bridge railing. To minimise disruption to residents and river levels, some operations were deliberately scheduled at night.
The Solution: "Three Preventions, Two Foundations"
The Smart Outfall System Device (commonly called the smart flap gate) combines mechatronics, information and intelligent control. The three preventions are preventing sewage overflow, preventing urban flooding and preventing river backflow - protecting the water environment, water safety and influent concentration. The two foundations are an intelligent control and analysis platform and a digital O&M system, moving management from experience-based to data-driven. Using level and rainfall data as control signals, the gate closes in dry weather to send sewage to the treatment plant, and opens intelligently according to rainfall intensity to discharge stormwater while still preventing backflow.
Results
Dry-weather interception and wet-weather drainage are now achieved. Sewage discharge, black-odorous water and local flooding have been substantially reduced and water quality has improved markedly. The supporting O&M platform runs as a mobile mini-program with four modules - data monitoring, O&M parameters, device control and event list - allowing multiple sites to be viewed by level, ponding depth and gate status on a single phone. The project is effective, economical, energy-saving and environmentally sound.
From an ageing flap gate to a system that can "think", outfall management is evolving from a simple mechanical device to intelligent control - offering a replicable path for combined-sewer areas to achieve both interception and drainage.
