Chapter 4
Q. 4.5
A very small village has an average day design demand of 190 m³/d and a maximum day design demand of 380 m³/d. They will have a distribution system. Compare the number of wells and the capacity of each well for a system that includes the wells and one elevated storage tank and a system that does not have an elevated storage tank.
Step-by-Step
Verified Solution
To meet regulatory redundancy requirements there must be a minimum of two wells. Each well must be capable of meeting the maximum day design demand with one pump out of service.
Some alternative selections are:
Two wells, each well rated at 380 m³/d. For the average day, one well would pump for 12 hours, that is
\left(\frac{12 h}{24 h} \right) (380 m³/d) = 190 m³/d
Two wells, each well capable of providing the average day demand in two hours to take advantage of a higher efficiency pump. For the maximum day, the pump would operate for four hours. Each well would have a rated capacity of
\left(\frac{24 h}{12 h} \right) (380 m³/d) = 4, 560 m³/d
Thus, the provision of an elevated storage system gives a range of pumping capacity from 190 m³/d to 4,560 m³/d. Without the storage tank, the pump capacity is restricted to 190 m³/d.