Example Data Table
| Station |
Datum m |
Pressure kPa |
Velocity m/s |
Loss m |
Pipe Length m |
Friction Slope |
| A |
100.00 |
120 |
1.50 |
0.20 |
80 |
0.004 |
| B |
98.50 |
135 |
1.80 |
0.35 |
120 |
0.003 |
| C |
97.20 |
110 |
2.10 |
0.40 |
150 |
0.0025 |
Formula Used
The basic hydraulic grade line elevation is:
HGL = z + p / γ
Here, z is datum elevation. The term p is pressure. The term γ is specific weight. Since γ equals fluid density multiplied by gravity, pressure head is p divided by ρg.
When a known reference grade is used, the adjusted relation is:
HGL at station = Reference HGL - Total head loss
The energy grade line is also shown:
EGL = HGL + v² / 2g
Velocity head is not part of HGL. It is added only for energy grade comparison.
How To Use This Calculator
Enter the station name first. Choose the calculation mode that matches your data. Use pressure mode when local pressure is known. Use reference mode when upstream HGL and losses are known. Use energy mode when EGL is already available.
Enter datum elevation, pressure, velocity, and loss values. Add pipe length and friction slope if you want route loss included. If flow rate and diameter are entered, the tool calculates velocity from them. Press the calculate button. Review the HGL elevation above the form.
Use the CSV and PDF buttons after a result appears. These exports help save station checks and share review records.
Hydraulic Grade Line Elevation Guide
Overview
A hydraulic grade line shows usable water head along a pipe, channel, or pressure system. It combines elevation head and pressure head. Designers use it to see whether flow has enough energy at each station. It also helps locate low pressure, high pressure, and possible surcharge points.
Purpose
This calculator focuses on elevation based HGL review. You can enter local pressure, a datum elevation, velocity, diameter, flow, and loss values. The tool converts common pressure and length units. It then reports pressure head, velocity head, adjusted HGL, and energy grade elevation. These outputs support quick checks before detailed hydraulic modeling.
Design Value
The HGL is especially useful for pipes under pressure. If the line falls below a pipe crown, flow may not remain full. If the line rises too high, fittings, joints, or covers may need review. For gravity systems, the line can show expected water surface levels. For pumped systems, it can show whether losses are reasonable.
Loss Review
Head loss matters because energy drops along the route. Friction, bends, valves, entrances, exits, and fittings can reduce head. A small loss can be entered directly. A longer route can use pipe length and friction slope. The calculator adds those terms into the station summary.
Velocity Head
Velocity head is shown beside HGL. It does not belong inside the hydraulic grade elevation. It is added to HGL to estimate the energy grade line. This comparison helps separate pressure effects from motion effects.
Example Records
The example table gives sample station inputs. Use it to understand the required data style. You may also paste batch rows in the advanced box. Each row can describe one station. The export buttons create records for notes, reports, or review files.
Practical Notes
This tool is not a substitute for a complete design. It is a checking aid. Always verify units, boundary conditions, pipe data, and standards before final use.
Good results depend on clear assumptions. Choose one unit family for each project. Keep station names consistent. Note whether the datum is pipe centerline, invert, or ground. Record any correction loss separately. When values look unusual, check pressure units first. Many errors come from mixing psi, kilopascals, feet, and meters.
Confirm flow direction before using upstream loss based mode. Negative head loss can hide setup mistakes.
FAQs
What is hydraulic grade line elevation?
It is the elevation of the pressure head plus datum head. It shows the level water would rise to in a piezometer connected at that point.
Does velocity head belong in HGL?
No. Velocity head belongs to the energy grade line. HGL uses elevation head and pressure head only.
What does pressure head mean?
Pressure head is pressure converted into an equivalent water height. It equals pressure divided by fluid density and gravity.
Can I use feet and meters together?
Yes. The calculator converts entered units internally. Still, consistent project units reduce mistakes and make reports easier to review.
When should I use reference HGL mode?
Use it when you know an upstream or starting HGL. The tool subtracts total head loss to estimate the station HGL.
What is friction slope?
Friction slope is head loss per unit length. Multiplying it by pipe length gives estimated friction head loss.
Why is my pressure head negative?
A negative value means HGL is below the datum. Check units, flow direction, loss entries, and whether vacuum conditions are possible.
Can this replace hydraulic design software?
No. It is a checking tool for quick station calculations. Final designs need verified models, standards, and engineering review.