- 2070 Asar · 8 marks
Balancing reservoir: village 600 population, 65 lpcd
Short answer
Daily demand is 39 m³ and spring yield is 43.2 m³/day, but peak demand rates exceed inflow, so a balancing reservoir is necessary. Mass-curve gives maximum deficit 11.85 m³ and surplus 4.20 m³; capacity ≈ 16.05 m³, adopt 16–17 m³.
A small village has design year population of 600 with 65 lpcd per capita demand. The demand is to be fulfilled by spring sources with safe yield 0.5 l/s. The consumption pattern in % of a day is as below.
| Time | 05-07 | 07-12 | 12-17 | 17-19 | 19-05 |
|---|---|---|---|---|---|
| Water consumption (%) | 30 | 30 | 15 | 20 | 5 |
Is balancing reservoir necessary? Calculate capacity of balancing reservoir if needed.
Given data
- Population 600 × 65 lpcd = 39,000 L/day = 39 m³/day
- Spring yield = 0.5 lps = 43,200 L/day = 43.2 m³/day = 1.8 m³/h
- Demand: 5–7 h 30%, 7–12 h 30%, 12–17 h 15%, 17–19 h 20%, 19–5 h 5%
Check of source and need of storage
The yield (43.2 m³/day) exceeds the demand (39 m³/day). But the demand in 5–7 h is 0.30 × 39/2 = 5.85 m³/h and in 7–12 h it is 2.34 m³/h, both more than the inflow of 1.8 m³/h. So the balancing reservoir is necessary.
Mass-curve table (analytical method)
Inflow: 1.8 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 | 11.70 | 3.60 | -8.10 | -8.10 |
| 07:00–12:00 | 11.70 | 9.00 | -2.70 | -10.80 |
| 12:00–17:00 | 5.85 | 9.00 | +3.15 | -7.65 |
| 17:00–19:00 | 7.80 | 3.60 | -4.20 | -11.85 |
| 19:00–05:00 | 1.95 | 18.00 | +16.05 | +4.20 |
Total demand = 39.00 m³; total inflow = 43.20 m³.
Capacity
- Maximum cumulative surplus = 4.20 m³
- Maximum cumulative deficit = 11.85 m³
- Balancing capacity = max. surplus + max. deficit = 4.20 + 11.85 = 16.05 m³
- Because the inflow in a day (43.20 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, 11.85 m³. The textbook value 16.05 m³ is on the safe side.
Answer: Balancing reservoir is necessary; capacity ≈ 16.1 m³ (adopt 16–17 m³).
✓ Answer checked by Claude Opus 5.5 (high effort)
Related questions
- Balancing reservoir: 500 population, spring 0.28 lps · Water Supply Engineering, chapter 7
- Balancing tank: village 80000 L/day, spring 0.8 lps · Water Supply Engineering, chapter 7
- Is reservoir necessary: village of 800, spring 0.5 L/s · Water Supply Engineering, chapter 7
- Is balancing tank necessary: 20000 L/day spring · Water Supply Engineering, chapter 7
- Population from spring yield of 5 L/s · Water Supply Engineering, chapter 3
- Population 2088 by three methods, design year demand · Water Supply Engineering, chapter 3
- Peak demand of load center from load pattern · Transmission and Distribution System Design, chapter 6 · asked 2×
- World energy resources and consumption pattern · Energy Resources, chapter 8