🎓 Lesson 5
D3
Building Your First EPANET Model
EPANET is a free computer program that lets engineers simulate how water flows and pressure changes in pipes, tanks, and pumps of a drinking water system.
🎯 Learning Objectives
- ✓ Construct a basic EPANET model from field data including pipe lengths, diameters, and node elevations
- ✓ Analyze hydraulic performance by interpreting pressure head and flow results at critical nodes
- ✓ Apply demand allocation methods to assign residential water consumption to junctions
- ✓ Validate model accuracy by comparing simulated pressures against measured field data
📖 Why This Matters
Every day, millions rely on safe, reliable drinking water — but leaks, low pressure, or contamination can go unnoticed until it’s too late. EPANET allows engineers to virtually 'test' design changes, emergency responses, or infrastructure upgrades before spending a dollar on construction. In mining, it’s essential for camp water systems, dewatering networks, and tailings facility supply lines — where failure risks safety, compliance, and production.
📘 Core Principles
An EPANET model rests on three foundational layers: (1) Topology — the physical layout of pipes, nodes, and components; (2) Hydraulics — governed by the continuity equation (mass balance) and energy equation (head loss via Hazen-Williams or Darcy-Weisbach); and (3) Time-based simulation — enabling analysis of diurnal demand patterns or pump scheduling. Nodes represent points of demand, supply, or elevation change; links represent flow paths with resistance properties. Model calibration ensures simulated outputs match real-world measurements — the cornerstone of credible analysis.
📐 Hazen-Williams Head Loss
The Hazen-Williams equation estimates frictional head loss in water distribution pipes under turbulent flow — the default method in EPANET for municipal and mining camp systems due to its empirical fit for common pipe materials and flow velocities.
Hazen-Williams Head Loss
h_f = 10.67 × L × Q^1.852 / (C^1.852 × D^4.871)Calculates frictional head loss (m) in full-flow circular pipes under turbulent conditions.
Variables:
| Symbol | Name | Unit | Description |
|---|---|---|---|
| h_f | Friction head loss | m | Energy loss due to pipe wall friction |
| L | Pipe length | m | Centerline distance between nodes |
| Q | Volumetric flow rate | m³/s | Flow through the pipe |
| C | Hazen-Williams roughness coefficient | unitless | Empirical measure of pipe interior smoothness |
| D | Internal pipe diameter | m | Hydraulic diameter for circular pipes |
Typical Ranges:
New HDPE pipe: 140 – 150
Aged cast iron: 80 – 100
Mining camp PVC distribution: 130 – 150
💡 Worked Example
Problem: A 300-mm HDPE pipe (C = 150) carries 45 L/s over 650 m. Ground elevation drops 12 m from start to end. Calculate head loss and residual pressure at downstream node if upstream pressure is 52 m head.
1.
Step 1: Convert flow Q = 45 L/s = 0.045 m³/s; diameter D = 0.3 m; L = 650 m; C = 150
2.
Step 2: Apply Hazen-Williams: h_f = 10.67 × L × Q^1.852 / (C^1.852 × D^4.871) = 10.67 × 650 × (0.045)^1.852 / (150^1.852 × 0.3^4.871)
3.
Step 3: Compute: h_f ≈ 8.3 m. Elevation drop = 12 m → downstream elevation = upstream − 12. Residual head = 52 − 8.3 = 43.7 m. Residual pressure = 43.7 − (downstream elevation) — verify against minimum required (e.g., 20 m for mining camps per WHO/MSA guidelines).
Answer:
The head loss is 8.3 m, yielding a residual pressure head of ~43.7 m — well above the 20–30 m minimum recommended for remote mining operations.
🏗️ Real-World Application
At the Telfer Gold Mine (Western Australia), engineers used EPANET to redesign the camp water network after population doubled. They modeled 12 km of PVC piping, 3 elevated tanks, and 5 booster pumps. By simulating peak morning demand (2.8 L/s per person), they identified two low-pressure zones (<15 m head) near dormitory blocks. Adding a small booster station and adjusting tank setpoints increased minimum pressure to 28 m head — verified via 17 field pressure loggers — avoiding costly pipe replacement.
✏️ Model-Building Exercise
Using the provided sketch (4 junctions, 5 pipes, 1 reservoir, 1 tank), assign: pipe lengths (120–450 m), diameters (150–300 mm), Hazen-Williams C values (140 for aged steel, 150 for new HDPE), and nodal demands (35–120 L/s). Build the model in EPANET v2.2, run a 24-hr extended period simulation with diurnal pattern (pattern factor peaks at 7–9 AM and 6–8 PM), and report: (a) minimum pressure head at Junction J3, (b) maximum velocity in Pipe P2, and (c) tank level fluctuation range. Submit .inp file and summary table.
🔧 Interactive Calculator
🔧 Open Water Distribution Network Analysis Calculator📋 Case Connection
📋 Calibration of Lagos Metropolitan Water Network
Persistent model–field mismatch (>25% pressure error) due to undocumented pipe replacements and unaccounted demand growt...
📋 Water Quality Model Validation for Singapore’s Deep Tunnel Sewerage System (DTSS) Supply Branch
Disinfectant residual dropping below 0.2 mg/L at farthest nodes despite design dosing; suspected wall reaction dominance