It is a tradition among the Arab designers not to consider the effect of sediments in their design of drainage systems which would give a wrong design, especially according to the lack of maintenance of drainage systems. Ignoring the effect of sediments leads to ignoring a major factor affecting the hydraulic roughness of the flow, where sediments increase the hydraulic roughness and also decrease the cross section of the sewers. The aim of this paper is to introduce a new approach to handle the design of storm sewers and also to include all hydraulic factors which affect the flow, these factors are:
1. Properties of sediments (diameter, shape and density).
2. Water properties (density, viscosity and temperature).
3. Flow characteristics (velocity, sediment concentration, sediment depth, gravitational force and depth of sediments) In order to achieve this model, laboratory tests (carried out by the author on a prototype at Salford Hydraulic Laboratory in Manchester).

It is a tradition among the Arab designers not to consider the effect of sediments in their design of drainage systems which would give a wrong design, especially according to the lack of maintenance of drainage systems. Ignoring the effect of sediments leads to ignoring a major factor affecting the hydraulic roughness of the flow, where sediments increase the hydraulic roughness and also decrease the cross section of the sewers. The aim of this paper is to introduce a new approach to handle the design of storm sewers and also to include all hydraulic factors which affect the flow, these factors are:
1. Properties of sediments (diameter, shape and density).
2. Water properties (density, viscosity and temperature).
3. Flow characteristics (velocity, sediment concentration, sediment depth, gravitational force and depth of sediments) In order to achieve this model, laboratory tests (carried out by the author on a prototype at Salford Hydraulic Laboratory in Manchester).