Analytical Techniques for Engineers
The channel is designed to transport the waste water from a lagoon. It implies that the flow will be almost regular and steady. Since depth remains constant and discharge does not change with time, thus, we can assume the flow to be uniform steady flow. In this flow, the cross section does not change (prismatic channel). Design of this channel solely depends on the following aspects either by combining or using them singly:
- The best hydraulic section procedure
- Find the limit velocity procedure
- Normal depth procedure
- Depth-limited procedure.
In this case, we use the best hydraulic procedure to design this channel. The best hydraulic channel refers to the area which simultaneous minimizes cross sectional area and the wetted perimeter. As a result, the quantity of excavation is reduced to the minimal but the most optimal. Also, the minimization of the wetted perimeter minimizes the quantity of lining. Since this channel is a trapezoidal in design, the best hydraulic section will represent half of a regular hexagon.
Using the below procedure, the width and the depth of the best hydraulic section can be computed as the finished lining will represent a float finished concrete.
- First, the lining is determined and its manning’s roughness coefficient determined. From the table below, we can establish n to be 0.015 since the finished lining will represent a float finished concrete.
- Secondly, the side slope that is suitable for the type of soil and the lining is determined. In this case, the side slope will be equal to the base.