To prevent debris from blocking the debris screen and ensure the normal long-distance operation of the unit, the power station-ship employs methods such as guiding the debris, discharging the waste, and cleaning the debris. Due to the varying importance of each power station, the nature and quantity of the debris, the measures taken differ accordingly.

One: Lead Pollution Control

Pollution guidance is set up several dozen meters away from the intake weir of the power station. A floating barrier net is installed to block pollutants in front of it, and guide them towards the spillway in front, ultimately releasing them downstream. To facilitate the smooth discharge of pollutants under the influence of water power, the floating net should be set at an angle relative to the water flow direction, generally no more than 30°. Operational practice shows that the floating net can only block surface pollutants.

Wastewater Discharge

(1) Waste discharge involves implementing certain measures in the arrangement of hydropower structures, such as installing dedicated discharge channels or holes in the overflow dam to allow floating pollutants to be flushed downstream with the water flow, thereby reducing the chance of pollutant accumulation at the intake. Regulatory gates are set up on the discharge channels.

(2) Allow non-destructive waste to be discharged by the crew. For certain equipment, waste can be categorized into destructive and non-destructive types. If the crew is permitted to dispose of non-destructive waste while the debris screen only retains destructive waste, the cleaning frequency of the debris screen will significantly decrease. To achieve this, it is necessary to appropriately increase the spacing between the bars of the screen. For instance: At the Yan Guo Xia Hydropower Station, most of the waste is non-destructive, consisting of flexible herbaceous plants. After increasing the spacing between the bars of the incoming debris screen from 100mm to 250mm, the volume of harmless waste such as aquatic plants was increased. Concurrently, with the completion of the Liujiaxia Hydropower Station upstream, the cleaning of the debris screen has decreased by approximately 80% in recent years.

Sanitation Services

1. Manual Cleaning

Typically, for small hydropower stations with shallow water levels in front of the screen and low flow velocities through the screen, workers directly scoop debris off the screen using rakes or clean the area with bamboo rafts or wooden boats in front of the screen. However, in some large and medium-sized hydropower stations, due to the lack of effective cleaning equipment, manual cleaning is also employed. When the water depth exceeds 5 meters and there is a significant amount of debris, surface cleaning becomes challenging. Some stations send divers to clean debris in front of the screen. Manual cleaning is labor-intensive, with poor working conditions, especially when underwater, where the situation is complex. The amount of cleaned debris is limited. Moreover, manual cleaning often requires shutdown operations, which is economically inefficient.

2. Two debris racks are being cleaned.

Since the 1960s, many power stations in China with high levels of debris have installed two vertical debris barriers at the intake. One is the primary barrier, which is in constant use, and the other is the secondary barrier, usually located on the platform. When the primary barrier needs to be removed for cleaning, the secondary barrier takes over, and the primary barrier is lifted to the platform, where debris is manually removed before being put back into the water. Then, the secondary barrier is lifted to the platform for cleaning, completing the cleaning process. To prevent debris from falling off when the barrier leaves the water surface, there are one to several debris collection hooks, each extending 200 to 400mm along the height of the barrier. Since the barrier moves with the water's small rise and fall, it can be equipped with either cantilevered or simply supported main wheels. Practice has shown that the two barriers can clean debris without shutting down the station, with good cleaning results. However, there are also drawbacks; when a large amount of debris arrives, cleaning becomes frequent, and the workload on workers increases significantly.

3. Mechanical Cleaning

Mechanical cleaning involves using machinery to remove debris from a grate surface. It is suitable for various types of power stations and different kinds of dirt, offering high efficiency. It saves a significant amount of labor and reduces the physical strain on workers, improving working conditions. Particularly, it can operate in flowing water, which is unmatched by manual cleaning methods.