Final answer:
To increase the drainage coefficient, devices such as the one shown in Figure 12.28 can be used to increase the flow rate. To decrease drain spacing, drains can be placed closer together.
Step-by-step explanation:
The coefficient of drainage (q) and drain spacing are related to the flow rate in drains. The coefficient of drainage refers to the efficiency of the drain in removing water. To increase the drainage coefficient, you can use devices like the one shown in Figure 12.28, which increase the flow rate.
On the other hand, to decrease drain spacing, you can place the drains closer together. This allows for a greater number of drains in a given area, improving the overall drainage efficiency.