New Tool Release: Multi-Reservoir Pipe Network Calculator

New Tool Release: Multi-Reservoir Pipe Network Calculator

In real-world water distribution, systems are rarely as simple as a single pipe connecting point A to point B. Municipal networks often rely on multiple storage tanks, reservoirs, and water towers interacting simultaneously to meet demand and maintain system pressure.

To help engineers untangle these complex, multi-source hydraulic systems, I am thrilled to release the Water Distribution Network: Multi-Reservoir Model! 🚰🌐

This dynamic web-based workstation automates the rigorous application of the Hazen-Williams friction equation and the Principle of Continuity. Utilizing a high-speed numerical bisection algorithm, it instantly determines the unique piezometric head at your central junction, dictates flow directions, and calculates the exact flow rates for up to 6 interconnected reservoirs.

civilsheets.blogspot.com/p/water-distribution-network-multi.html
Water Distribution Network: Multi-Reservoir
Hydraulic Junction Solver
Metric (L/s)
Imperial (GPM)
Export Network Data
1. Reservoir A REMOVE
Water Surface Elev.
120.0 m
Pipe Length (L)
1000 m
Diameter (D)
300 mm
2. Reservoir B REMOVE
Water Surface Elev.
100.0 m
Pipe Length (L)
2000 m
+ ADD RESERVOIR
SOLUTION
Junction Head Hj
92.68 m
Converged in 24 iterations
Continuity (ΣQ)
0.00 L/s
Error margin (must be ~ 0)
Res A
FLOW Q₁
185.4 L/s
Supply to Junction ↓
Res B
FLOW Q₂
22.1 L/s
Supply to Junction ↓
Res C
FLOW Q₃
207.5 L/s
Receive from Junction ↑
Hydraulic Profile Schematic Dashes indicate flow direction
120.0 100.0 92.7 80.0 Hj = 92.7 Res A Res B Res C

The Engineering Problem

Imagine a typical water supply network: a high-elevation mountain reservoir feeds gravity pressure into a distribution grid, but the city also relies on a local municipal water tower and an intermediate ground storage tank. If all three sources converge at a central junction, which way is the water flowing?

Is the mountain reservoir filling the city tower, or is the city tower draining into the network alongside it? What is the exact pressure at the junction?

Solving this mathematically relies on two fundamental principles:

  • The Hazen-Williams Equation: The flow ($Q$) through any individual pipe is directly proportional to the difference between its source elevation ($Z_i$) and the piezometric head at the junction ($H_j$).
  • The Principle of Continuity ($\sum Q = 0$): Mass cannot be created or destroyed. At the central junction, the sum of all incoming flows must perfectly equal the sum of all outgoing flows.

Because the friction formulas are non-linear, you cannot isolate and solve for $H_j$ algebraically. Historically, engineers had to guess a junction head, manually balance the flows, and iteratively refine their guess. This tool utilizes a high-speed Numerical Bisection Algorithm to find absolute convergence instantly.


How to Use the Workstation

This solver eliminates the spreadsheet trial-and-error. Here is the 4-step workflow to analyze your multi-source network:

1

Define the Topography

Enter the Water Surface Elevation ($Z$) for your initial reservoirs. The elevation determines the potential energy available to drive water toward the junction.

1. Reservoir A (Pipe 1)
Water Surface Elev. (Z_A)
120.0 m
2

Configure the Piping

For each connected branch, enter the Length ($L$), Diameter ($D$), and the Hazen-Williams Roughness Coefficient ($C$). Use the handy dropdown menu to quickly select standard C-factors for PVC, Ductile Iron, Steel, or Cast Iron.

Pipe Length (L)
1000 m
Diameter (D)
300 mm
Hazen-Williams (C)
120
3

Expand the Network (Up to 6 Nodes!)

Not limited to a simple 3-tank problem! Click the Add Reservoir button in the left panel to dynamically insert up to 6 unique sources or storage tanks into the system. The schematic and math engine will automatically adapt to handle complex junctions.

4. Reservoir D (Pipe 4) REMOVE
Water Surface Elev.
93.0 m
+ ADD RESERVOIR
4

Analyze the Solution

The moment parameters change, the tool balances the network. It outputs the stabilized Junction Head ($H_j$). Check the color-coded flow cards: Green flow rates indicate water leaving the tank (supplying), and Orange flow rates indicate water entering the tank (receiving).

Res A
FLOW Q₁
201.8 L/s
Supply to Junction ↓
Res B
FLOW Q₂
38.7 L/s
Supply to Junction ↓
Res C
FLOW Q₃
247.0 L/s
Receive from Junction ↑
Res D
FLOW Q₄
6.5 L/s
Supply to Junction ↓

Smart Checks & Warnings

Invalid Geometry Failsafes

Mathematical algorithms fail catastrophically if divided by zero. If you accidentally input a pipe length or diameter of 0 (or a negative number), the solver instantly pauses and throws a bright red warning banner, preventing nonsense outputs or NaN errors until the geometry is corrected.

The Continuity Check

Next to your solution head is a large Continuity Check (ΣQ) box. Because this relies on a numerical bisection method (closing in on the answer fraction by fraction), this box acts as your verification. The net flow should always read exactly 0.00 L/s (or extremely close to zero, like $10^{-6}$), proving the system is perfectly balanced.

Export and Report

Once you are satisfied with your pipe sizing and flow distribution, scroll down to the Detailed Hydraulics Table. You can review the exact pipeline velocity, head loss, and friction slope (m/km) for every single branch. Click the Export Network Data button to download a clean, formatted CSV report of your entire hydraulic model.

Head over to the tool page and try modeling a 4 or 5 tank system! If you find this helpful, or if you want to see extended capabilities (like adding minor losses or nodal demands) added to CivilSheets, let me know in the comments.

Happy Designing!
- CivilSheets

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