EPANET Total Head Explorer
A Hands-On Interactive Companion to EPANET's Hydraulic Head Calculations
The EPANET Total Head Explorer is an interactive, browser-based educational tool designed to demystify how EPANET (the industry-standard water distribution modeling software from the U.S. EPA) calculates total head at every node in a water network. Built with live sliders, real-time visualizations, and step-by-step solver demonstrations, this application serves as an invaluable learning companion for water resources engineers, students, and professionals.
What Is the EPANET Total Head Explorer?
The EPANET Total Head Explorer is a single-page interactive web application that breaks down EPANET's total head calculations into four intuitive, interactive sections. It is explicitly designed as a companion tool to EPANET 2.2, not a replacement for the full solver. Users can manipulate parameters in real-time and immediately see how changes affect hydraulic head, pressure, and flow distribution throughout a water network.
Total Head Basics
Elevation + Pressure = Total Head with live HGL visualization
Series Network (HGL)
Reservoir-to-junction chain with Hazen-Williams headloss
How EPANET Solves It
Global Gradient Algorithm with step-by-step iteration
Formula Reference
Headloss equations and engineering constants
Section 1: Total Head Basics
Elevation + Pressure = Total Head
This foundational section introduces the core concept that EPANET reports at every node: hydraulic head, which represents the water's total mechanical energy expressed as a height. The total head always splits into two distinct components that are set separately in any EPANET model:
- Elevation (E) -- The physical height of the node above a reference datum (e.g., 700 ft)
- Pressure Head (P) -- The height water would rise in a piezometric tube above the node (e.g., 130 ft)
The app displays the formula in real-time: Total Head, H = E + P, yielding 830.0 ft in the default example. It also converts pressure head to PSI using the standard conversion: Pressure (psi) = P / 2.31 = 56.3 psi.
Interactive Features:
- Live sliders for both Elevation (E) and Pressure Head (P) -- drag to adjust values
- Real-time calculation of Total Head and Pressure in PSI
- Visual Hydraulic Grade Line (HGL) -- a dashed teal line showing how high water would rise in a thin open tube (piezometer) stuck into the pipe
- Immediate visual feedback as the HGL moves with slider adjustments
Key Learning Point: The Hydraulic Grade Line's height above the node represents pressure head; its height above the datum represents total head. This is one of the most important visual concepts in hydraulic engineering.
Section 2: Series Network (HGL)
Reservoir -> J1 -> J2: Headloss Down the Line
This section extends the concept to a real network topology: a reservoir feeding two junctions connected in series. Users learn that head is lost to friction as water moves through each pipe, and EPANET walks the energy equation h_i - h_j = headloss across every link in turn.
Adjustable Network Parameters:
| Component | Parameters | Default Value |
|---|---|---|
| Reservoir | Head (H_R) | 700 ft |
| Pipe 1 | Length, Diameter, C-factor | 3000 ft, 12 in, 100 |
| Junction 1 | Elevation, Demand | 710 ft, 150 gpm |
| Pipe 2 | Length, Diameter, C-factor | 5000 ft, 8 in, 100 |
| Junction 2 | Elevation, Demand | 700 ft, 150 gpm |
Calculated Node-by-Node Results:
The application computes and displays a complete results table in real-time:
- Flow in Pipe 1 (carrying J1 + J2 demand): 300 gpm
- Headloss in Pipe 1 (Hazen-Williams): 1.33 ft
- Head at J1: 698.67 ft
- Pressure at J1: -11.33 ft (-4.9 psi)
- Flow in Pipe 2 (J2 demand only): 150 gpm
- Headloss in Pipe 2: 4.42 ft
- Head at J2: 694.25 ft
- Pressure at J2: -5.75 ft (-2.5 psi)
Warning System: The app includes a smart alert system -- when junction pressures turn negative (as in the default example), a prominent warning banner appears: "Negative pressure at J1 and J2 -- EPANET would flag this. Lower demand/elevation, raise reservoir head, or upsize a pipe." This teaches users to recognize and diagnose real modeling problems.
Section 3: How EPANET Solves It
Why Looped Networks Need Iteration
This is the most advanced section, demonstrating why looped networks require iterative solving. A straight chain (like Section 2) solves node-by-node. But the moment a junction is reachable via two different paths -- like the parallel pipes shown above -- the flow split becomes unknown until heads and flows are solved together.
This section implements EPANET's Global Gradient Algorithm (GGA), originally developed by Todini & Pilati (1988), which follows this iterative process:
- Guess initial flows through each pipe
- Linearize the headloss-vs-flow relationship
- Solve for nodal head at the junction
- Correct the flows based on the new head
- Repeat until the imbalance is negligible
Interactive Solver Controls:
Step One Iteration
Manually advance the GGA by one iteration step
Run to Convergence
Automatically iterate until solution converges
Reset
Clear the iteration log and start over
Iteration Log (Convergence Example):
| Iter | h_J (ft) | q_A (gpm) | q_B (gpm) | Δflow/flow |
|---|---|---|---|---|
| 1 | 697.22 | 287 | 113 | 21.473% |
| 2 | 697.09 | 291 | 109 | 2.216% |
| 3 | 697.09 | 291 | 109 | 0.024% ✓ |
Balance Check at Convergence:
Once converged, the app displays a comprehensive balance verification:
- Flow balance: q_A + q_B = 400 gpm (matches demand D = 400 gpm)
- Headloss Pipe A: H_R - h_J = 2.914 ft (matches computed headloss)
- Headloss Pipe B: H_R - h_J = 2.914 ft (matches computed headloss)
- Pressure at J: -2.91 ft (-1.3 psi)
Network Parameters (Adjustable via Sliders):
- Reservoir Head (H_R): 700 ft
- Demand at Junction (J): 400 gpm
- Elevation at Junction (J): 700 ft
- Pipe A: Length 4000 ft, Diameter 10 in, C-factor 120
- Pipe B: Length 6000 ft, Diameter 8 in, C-factor 100
Section 4: Formula Reference
Headloss Formulas EPANET Can Use
All three headloss formulas reduce to the common form: h_L = A * q^B where headloss is in feet and flow is in cfs. EPANET calculates the resistance coefficient A from each pipe's physical properties and re-derives it whenever those properties change.
| Formula | Resistance Coeff. A | Exponent B | Roughness Input |
|---|---|---|---|
| Hazen-Williams | 4.727 * C^-1.852 * d^-4.871 * L | 1.852 | C-factor |
| Darcy-Weisbach | 0.0252 * f(ε,d,q) * d^-5 * L | 2 | ε, roughness (ft) |
| Chezy-Manning | 4.66 * n^2 * d^-5.33 * L | 2 | Manning's n |
Handy Engineering Constants:
| Constant | Value |
|---|---|
| Pressure to Head (water, SG = 1) | 1 psi ≈ 2.31 ft |
| Reynolds Regimes (Darcy-Weisbach) | laminar < 2,000 | turbulent > 4,000 |
| Default GGA Convergence | Σ|Δq| / Σ|q| < 0.001 |
References: Todini & Pilati (1988); EPANET 2.2 User Manual, US EPA (2020).
Getting Started: Interactive Walkthrough
The application includes a built-in guided tutorial accessible via the "How to use" button in the top-right corner. The walkthrough covers all four sections:
Tutorial Steps:
- Welcome: "A small companion to what we just worked through: how EPANET arrives at the total head it reports at every node. Four stops, all with live sliders."
- Total Head Basics: "Total head is elevation plus pressure head, full stop. Drag the sliders and watch the hydraulic grade line move."
- Series Network: "Chain a reservoir and two junctions and total head becomes a walk down the line -- each pipe eats head to friction, computed with real Hazen-Williams math."
- How EPANET Solves It: "Give a junction two paths in and the split is no longer obvious. Click 'Step one iteration' and watch the Global Gradient Algorithm converge by hand."
- Formula Reference: "Tab 4 holds the headloss formulas EPANET supports. Tap ? in the corner any time to see this again."
A floating "?" button in the bottom-right corner allows users to replay the tutorial at any time, making the tool self-documenting and beginner-friendly.
Key Features Summary
⚡ Real-Time Interactivity
Every slider adjustment instantly updates calculations, visualizations, and result tables -- no page refresh needed.
🌎 Browser-Based
No installation required -- runs entirely in any modern web browser, accessible from desktop or mobile devices.
🎯 Guided Tutorial
Built-in 5-step walkthrough with a replayable help system ensures users never feel lost.
⚙ Real EPANET Math
Uses actual Hazen-Williams headloss equations and the authentic Global Gradient Algorithm from EPANET 2.2.
💡 Error Detection
Smart warnings flag negative pressures and suggest corrective actions, teaching diagnostic skills.
📚 Formula Reference
Complete reference for all three headloss formulas plus handy engineering constants always at hand.
Who Is This Tool For?
- Water Resources Engineering Students -- Visualize abstract hydraulic concepts that textbooks describe only with equations
- Professional Engineers -- Quickly sanity-check EPANET results and understand the solver's internal mechanics
- EPANET Users -- Learn how the software arrives at the head values reported in output files
- Educators & Instructors -- Use as a classroom demonstration tool for teaching hydraulic network analysis
- Researchers -- Validate understanding of the Global Gradient Algorithm and headloss formulations
Try the EPANET Total Head Explorer
Experience the interactive tool firsthand. Manipulate live sliders, watch the solver converge step-by-step, and master the fundamentals of hydraulic head calculations.
A hands-on companion to EPANET's total-head math · not a substitute for the EPANET 2.2 solver
This page summarizes the EPANET Total Head Explorer interactive educational tool. All screenshots and diagrams are representative of the application's functionality. References: Todini & Pilati (1988); EPANET 2.2 User Manual, US EPA (2020).
