The civil works of a micro-hydro plant are five structures, in the order the water meets them: an intake with a trash rack, a settling basin, a penstock pipe, a powerhouse, and a tailrace. Build from the intake downstream and test each before adding the next, and expect the penstock alone to cost 30 to 50% of a small installation.
Part of Micro-Hydro Turbine
Civil works are everything built of earth, stone, concrete, timber or pipe to bring water to the turbine and take it away again; the turbine and generator are the small part.
The Water Meets Five Structures In A Fixed Order
| Order | Structure | Its job | Read next |
|---|---|---|---|
| 1 | Intake and trash rack | divert part of the stream and keep sticks and leaves out | Intake & Trash Rack |
| 2 | Settling basin | slow the water so sand drops out | same article |
| 3 | Penstock | carry water down to the turbine under pressure | Penstock Design & Materials |
| 4 | Powerhouse | shelter turbine, generator and controls | Powerhouse Location |
| 5 | Tailrace | return the used water to the stream | Tailrace & Environmental Flow |
The weir that raises the stream level for the intake is a small diversion dam; Diversion Dams describes one that lifts a stream by 30 centimeters to 2 meters. A bypass gate beside the intake lets you send the whole flow past the turbine for maintenance, as the carrier requires.
Build In Order From The Intake Down
The Installation page lays out the sequence for hydropower: survey the head and the minimum seasonal flow, build the weir, intake and settling tank, excavate and lay the penstock, then set the powerhouse, turbine, generator and electrical panel. Testing each stage before the next means a leaking joint is found while it is still easy to reach. Installation also gives three design numbers for the civil works:
- A settling tank sized for 2 to 3 minutes of retention at design flow.
- A penstock buried with 0.5 to 1 meter of cover to protect it from frost and damage.
- A powerhouse floor at least 0.5 meter above the highest flood level you can identify.
Where The Money And Risk Sit
The Penstock Design page states that the penstock often represents 30 to 50% of the total cost of a small hydro installation, and is the component most often undersized by first-time builders. The riskiest period is the first flood after construction, when the weir, intake and powerhouse floor are tested by water they were not designed around.
Measure first. The head and the dry-season flow decide what size every one of these structures must be (Head Measurement, Seasonal Variation).
Common Mistakes
- Building the powerhouse first — it ends up below a flood level or far from where the pipe actually comes down.
- Skipping the settling basin — sand wears a runner or nozzle in a few seasons.
- Taking the whole stream — leave water in the channel (Tailrace & Environmental Flow).
Safety
Trenches and floods
A deep penstock trench with unsupported walls can collapse on a person without warning, and a stream can rise within minutes after rain upstream. Shore trench walls over knee depth, never work alone in a trench, and stop work and move to high ground when the water level or color changes.
What’s Next
- Learn next: Intake & Trash Rack for the first structure the water meets
- Combine with: Turbine Types to choose the machine the works must serve