Weirs can be classified based on the shape of their opening as follows:
Rectangular weirs: These weirs have a rectangular opening and are the most common type of weir. They are used in a wide range of applications and are easy to construct.
Triangular weirs: These weirs have a triangular opening and are commonly used in irrigation systems. They are also used in water treatment plants and in other applications where a moderate flow rate is required.
Trapezoidal weirs: These weirs have a trapezoidal opening and are commonly used in large-scale irrigation systems. They are also used in industrial applications where a high flow rate is required.
Cipoletti weirs: These weirs have a curved opening and are used in applications where a high flow rate is required. They are commonly used in large-scale irrigation systems and in hydroelectric power plants.