In the mass curve method for estimating the balancing storage of a distribution reservoir, the required storage is determined by
- AThe difference between the maximum cumulative demand and the minimum cumulative supply
- BThe sum of all hourly demands
- CThe maximum positive and negative deviations between cumulative supply and cumulative demandCorrect
- DThe area under the demand curve divided by 24 hours
Solution
Concept
Mass curve method for reservoir storage
Formula
Balancing Storage = Max Cumulative Deficit + Max Cumulative Surplus
Step-by-step solution
1. Rippl's mass curve plots cumulative supply and cumulative demand over 24 hours. 2. Demand exceeding supply causes reservoir depletion (deficit). 3. Supply exceeding demand refills reservoir capacity (surplus). 4. Required balancing storage equals the sum of maximum positive and negative departures between cumulative curves. Answer: C
Explanation
In the mass curve (Rippl's) method, cumulative supply and cumulative demand curves are plotted against time. The required balancing storage capacity is determined as the sum of the maximum positive departure (maximum surplus) and maximum negative departure (maximum deficit) between the cumulative supply and demand curves.
Why the other options are wrong
A) Balancing storage depends on cumulative departure between supply and demand, not absolute extremes. B) Sum of hourly demands is total daily water volume consumed. D) Area under the demand curve divided by 24 gives average hourly flow rate.
Shortcut
Mass curve storage = Sum of max positive and negative departures between cumulative supply and demand.
Common mistake
Confusing balancing storage with total daily demand or average hourly demand.
Correct answer: C) The maximum positive and negative deviations between cumulative supply and cumulative demand