Drain Channel Design Program

The drain channel is a concrete channel built to handle the flow of unsafe water to waste. The channel is positioned along the inlet channel side of the plant.

The purpose of this program is to design the dimensions of the drain channel based on the height of the water in the plant, length of the plant, and assumptions regarding desired drainage time and basic tank geometry. The Drain Channel is constructed as a separate channel built along the side of the flocculator and the sedimentation tank on the inlet channel side. The channel will have its highest elevation near the bottom of the sedimentation tank extending in the ground. Drain valves will open the flow of water into the channel from the flocculation and sedimentation tanks.

The Drain Channel must be built to accommodate the maximum flow through all the drain valves of the flocculation tank and sedimentation tank. This is calculated as:

Design Assumptions

Geometric constraints used in the design come from some basic assumptions. The depth of the drain channel at the beginning of the flocculator is equal to one half the head loss at the opposite end of the drain channel.

Another assumption is that the slope of the drain channel is equal to this head loss at the sedimentation tank end per unit length of the inlet channel side of the plant.

In order to calculate the cross sectional area and depth of the drain channel, other assumptions have also been made.

1. The channel can be treated as uniform open channel flow over a long distance

2. We will over-design the channel by calculating the height and width of the cross-section as if it were a rectangle.

This allows us to use standard fluids functions in our calculations where we will determine a desired ratio of width/height and use an iterative function to determine the headloss for the channel. From this, all other dimensions can be determined.