What Is a Grit Chamber?

When taking water on a sandy river, although sand prevention measures were taken at the water intake, the sand content and particle size of the water could not fully meet the requirements for water use. Therefore, a grit chamber can be set downstream of the water inlet. By expanding the cross section of the water and reducing the flow velocity, sediment that does not meet the requirements of water use can be settled. When irrigation water is used, sediment with a particle size greater than 0.03 to 0.05 mm should be deposited. For power generation and diversion, sediment with a particle size greater than 0.25 mm is sufficient. The sedimentation rate of the sedimentation tank is generally 80% to 90%. ^[1]

China's DL / T 5107-1999 "Code for design of sedimentation tanks of hydropower and water conservancy projects" (hereinafter referred to as "

The "Specifications" stipulates the basic principles for the location and type selection of sedimentation rooms, as follows:

(1) The settling chamber should be located near the water intake of the first water intake hub. When restricted by topographic conditions or the flushing head cannot meet the requirements, it can be moved down the diversion channel to an appropriate location or it can be arranged underground. The layout of the grit chamber should reasonably use the topographical and geological conditions to avoid bad areas, otherwise, corresponding engineering measures should be taken.

(2) The hydraulic flushing grit chamber should have sufficient flushing head and flow. If the terrain is open, periodic flushing grit chambers should be selected for the grit chambers of hydropower stations and hydraulic projects; if the terrain is narrow, continuous grit chambers should be selected for the grit chambers of hydropower stations.

(3) In the mountainous and hilly areas, there are sufficient sand flushing chambers for water conservancy projects. Under the condition that there is no adverse impact on the environment, a multi-room periodic flushing chamber is recommended. Canal sedimentation room should be used.

(4) When the flushing head is insufficient, a mechanical dredging settling chamber can be used. There should be enough sand storage sites in the grit chamber where mechanical dredging is used, and it will not adversely affect the environment and engineering in the area.

The grit chamber can be divided into box grit chamber, curved grit chamber, and channel grit chamber according to the plane shape of the tank compartment.

According to the dredging method, the grit chamber can be divided into hydraulic flushing grit chamber, mechanical dredging grit chamber and non-flushing grit chamber. Among them, the hydraulic flushing can be divided into regular flushing grit chamber due to different flushing methods There are two types of chambers and continuous flushing grit chambers. These types are briefly introduced below.

The sedimentation room of the hydropower station is mainly designed to reduce the wear of the pumps and turbines, and to ensure the normal operation of the hydropower station without being affected by sediment. Most of the water and irrigation grit chambers are used in diversion canals or diversion channels to reduce the sedimentation of water conveyance systems such as canals, sedimentary sediments and partially suspended sediments; in addition, micro-irrigation projects using surface water are cited. In general, a settling chamber is generally set up between the water conveyance system and the irrigation system, that is, the sprayed micro-irrigation settling chamber. The suspended sediment mainly contained in the water transport system exceeds the index of the sprayed micro-irrigation system. Treatment to reduce the sediment content entering the spray micro irrigation system, prevent the spray micro irrigation system from being blocked, and reduce the burden of subsequent sediment processing equipment (such as filters). Industrial grit chambers are mainly used in urban water supply and drainage and industrial water supply and drainage. With the development of the country and the progress of society, the sedimentation chamber has gradually been applied and developed in the aspects of river regulation, pre-cultivation and solidification of embankments, water and sand resource management, silt formation and water environment regulation. ^[2]