- 2075 Asoj · 8 marks
Balancing reservoir: 500 population, spring 0.28 lps
Short answer
Daily demand is 22.5 m³ and spring yield is 24.19 m³/day, but peak demand rates exceed the inflow, so a balancing reservoir is necessary. Mass-curve gives maximum deficit 6.44 m³ and surplus 1.69 m³; capacity ≈ 8.14 m³, adopt about 9–10 m³.
A village has design year population of 500 nos and water demand of 45 lpcd. The demand is met by a continuous system of supply from a spring source with safe yield of 0.28 lps. The consumption pattern is as follows:
| Time (Hours) | 05 - 07 | 07 - 12 | 12 - 17 | 17 - 19 | 19 - 05 |
|---|---|---|---|---|---|
| Consumption (%) | 15 | 45 | 10 | 20 | 10 |
Is balancing reservoir necessary? Calculate its capacity if necessary and justify your answer.
Given data
- Population 500 × 45 lpcd = 22,500 L/day = 22.5 m³/day
- Spring yield = 0.28 lps = 24,192 L/day = 24.19 m³/day = 1.008 m³/h
- Demand: 5–7 h 15%, 7–12 h 45%, 12–17 h 10%, 17–19 h 20%, 19–5 h 10%
Check of source and need of storage
The yield (24.19 m³/day) is more than the demand (22.5 m³/day), so the source is adequate. The demand rate in 7–12 h is 0.45 × 22.5/5 = 2.03 m³/h, and in 5–7 h it is 1.69 m³/h, both more than the inflow rate of 1.008 m³/h. So a balancing reservoir is necessary.
Mass-curve table (analytical method)
Inflow: 1.008 m³/h (spring yield). Time is counted from the start of the first demand period; a positive cumulative value means surplus in the tank.
| Time | Demand (m³) | Inflow (m³) | Inflow − demand | Cumulative |
|---|---|---|---|---|
| 05:00–07:00 | 3.38 | 2.02 | -1.36 | -1.36 |
| 07:00–12:00 | 10.12 | 5.04 | -5.08 | -6.44 |
| 12:00–17:00 | 2.25 | 5.04 | +2.79 | -3.65 |
| 17:00–19:00 | 4.50 | 2.02 | -2.48 | -6.14 |
| 19:00–05:00 | 2.25 | 10.08 | +7.83 | +1.69 |
Total demand = 22.50 m³; total inflow = 24.19 m³.
Capacity
- Maximum cumulative surplus = 1.69 m³
- Maximum cumulative deficit = 6.44 m³
- Balancing capacity = max. surplus + max. deficit = 1.69 + 6.44 = 8.14 m³
- Because the inflow in a day (24.19 m³) is more than the demand, the extra water simply overflows once the tank is full. The minimum storage that still meets every demand is the largest draw-down, 6.44 m³. The textbook value 8.14 m³ is on the safe side.
Answer: Balancing reservoir is necessary; capacity ≈ 8.1 m³ (adopt 9 m³ or 10 m³). It is needed because the peak demand in the morning is about twice the continuous spring flow.
✓ Answer checked by Claude Opus 5.5 (high effort)
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