EPANET Total Head Explorer
A Detailed Summary of the Interactive Educational Tool
https://epanet-total-head-explorer.netlify.app/
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.
The tool is explicitly designed as a companion 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.
Figure 1: EPANET Total Head Explorer – Interactive Water Network Visualization
What Is the EPANET Total Head Explorer?
The application breaks down EPANET’s total head calculations into four intuitive, interactive sections, each with live sliders and real-time feedback:
| 1 Total Head Basics Elevation + Pressure = Total Head with live HGL visualization | 2 Series Network (HGL) Reservoir-to-junction chain with Hazen-Williams headloss | 3 How EPANET Solves It Global Gradient Algorithm with step-by-step iteration | 4 Formula Reference Headloss equations and engineering constants |
Section 1: Total Head Basics
Figure 2: Total Head Basics – Elevation, Pressure Head, and Hydraulic Grade Line
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:
• 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: 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)
Figure 3: Series Network – Reservoir connected to two junctions with Hydraulic Grade Line
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: 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
Figure 4: Parallel Network – Global Gradient Algorithm iteration process
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) | Delta flow/flow |
| 1 | 697.22 | 287 | 113 | 21.473% |
| 2 | 697.09 | 291 | 109 | 2.216% |
| 3 | 697.09 | 291 | 109 | 0.024% (converged) |
Balance Check at Convergence
• 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)
Section 4: Formula Reference
Figure 5: Formula Reference – Headloss equations and engineering constants
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(e,d,q)*d^-5*L | 2 | Epsilon, 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 4,000 |
| Default GGA Convergence | Sum|Delta q| / Sum|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:
- 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 at: epanet-total-head-explorer.netlify.app |
A hands-on companion to EPANET’s total-head math. Not a substitute for the EPANET 2.2 solver.