🎓 Lesson 19
D5
Scenario Planning for Drought and Flood Resilience
Scenario planning for drought and flood resilience means preparing water distribution systems in advance for both extreme dry periods and sudden heavy rains so they keep delivering safe water reliably.
🎯 Learning Objectives
- ✓ Analyze historical precipitation and streamflow data to identify drought/flood frequency thresholds
- ✓ Design storage and pressure management strategies using scenario-based demand-supply balancing
- ✓ Apply reliability metrics (e.g., continuity of supply index) to evaluate network performance across drought and flood scenarios
- ✓ Explain trade-offs between capital investment in redundancy and operational flexibility in real-time control
📖 Why This Matters
Mining operations depend entirely on stable water supply—for dust suppression, ore processing, tailings management, and worker safety. A single month of drought can halt production; a flash flood can breach containment structures or contaminate intakes. In 2022, the Pilbara region experienced simultaneous multi-week drought followed by a Category 3 tropical cyclone—causing $47M in unplanned water infrastructure downtime. Scenario planning isn’t about predicting the weather—it’s about engineering systems that *respond effectively* no matter what climate extremes deliver.
📘 Core Principles
Resilience in water distribution begins with recognizing non-stationarity: historical rainfall statistics no longer reliably predict future extremes. Scenario planning replaces single-design-storm approaches with three-tiered futures: (1) Baseline (current climate norms), (2) Drought-Intensified (e.g., 1-in-20-year deficit amplified by 30% per IPCC AR6 RCP 4.5), and (3) Flood-Intensified (e.g., 1-in-10-year peak flow increased by 40% due to convective intensification). Each scenario drives distinct stress tests: drought stresses source yield, storage depletion, and pump energy; flood stresses intake submersion, sediment loading, and hydraulic transients. Crucially, scenarios must be *actionable*: they feed directly into control logic (e.g., SCADA setpoint adjustments), maintenance triggers (e.g., pre-storm valve inspections), and capital prioritization (e.g., elevated raw water intakes).
📐 Continuity of Supply Index (CSI)
The Continuity of Supply Index quantifies the percentage of time a node in the distribution network maintains pressure ≥ 20 m (200 kPa)—a minimum required for fire protection and process reliability—across a defined scenario period. It is calculated from hydraulic model outputs (e.g., EPANET simulations run under each scenario) and serves as a pass/fail metric for resilience targets.
Continuity of Supply Index (CSI)
CSI = (T_{≥20m} / T_{total}) × 100Measures percentage of time during a scenario period that minimum required pressure (20 m head) is maintained at a critical node.
Variables:
| Symbol | Name | Unit | Description |
|---|---|---|---|
| T_{≥20m} | Time with pressure ≥ 20 m | days or hours | Cumulative duration when hydraulic pressure at node meets or exceeds 20 m head |
| T_{total} | Total scenario duration | days or hours | Length of the simulated drought or flood period |
Typical Ranges:
Critical mining process node: 95–100%
Non-critical service area: 85–92%
💡 Worked Example
Problem: A mine’s water network was simulated over a 365-day drought scenario. Hydraulic model output shows pressure ≥ 20 m at the critical processing plant node for 312 days. Total simulation period = 365 days.
1.
Step 1: Extract number of hours/days where pressure ≥ 20 m from simulation results (here: 312 days).
2.
Step 2: Divide by total scenario duration (312 ÷ 365).
3.
Step 3: Multiply by 100 to express as percentage.
Answer:
The CSI is 85.5%, which falls below the industry target of ≥95% for critical mining infrastructure per ICMM Water Management Guidelines.
🏗️ Real-World Application
At Newmont’s Boddington Gold Mine (Western Australia), scenario planning led to a dual-reservoir strategy: a primary dam optimized for average inflows, plus a smaller, elevated emergency reservoir fed by pumped groundwater. During the 2019–2020 drought (lowest 5% inflow on record), the primary reservoir fell to 18% capacity—but the emergency reservoir sustained full processing for 47 days via automated SCADA-triggered transfer. When Cyclone Veronica hit in March 2019, intake turbidity spiked to >4,000 NTU; pre-planned diversion to pre-sedimentation basins and activated carbon dosing prevented treatment plant failure—maintaining CSI >98% throughout the event.
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