---
title: "General river intake and site selection"
subject: "Water Supply Engineering"
chapter: 5
key: "semester_5/water_supply_engineering:general-river-intake"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/general-river-intake
site: BCT Engineering
---

# General river intake and site selection

Water Supply Engineering · Chapter 5: Intakes

- Asked in: 2076 Asoj, 8 marks; 2073 Shrawan, 8 marks; 2079 Baisakh, 8 marks (asked 3 times)
- Video: [Types of Intake Structure - Water Supply and Distribution of Water - Environmental Engineering 1](https://www.youtube.com/watch?v=RrtbXAqmyIo) — Ekeeda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/general-river-intake
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-5

## Question

Sketch and explain the general river intake arrangement. What are the points to be considered for the selection of site for an intake?

## Short answer

A river intake tower has multiple ports with screens at different levels to draw clearest water; gates regulate flow; low entrance velocity (0.15-0.3 m/s) reduces silt. Site selection considers water quantity/quality, stable bank, depth at low water, flood level, foundation, navigation, proximity to plant, accessibility, and sedimentation.

## Answer

#### General river intake
A river intake is a tower or well built in (or at the edge of) the river with openings at different levels. Water enters the openings through screens, passes into the well and then flows by gravity (or is pumped) through the intake pipe to the treatment plant.

```text
   Foot bridge
  =========|===========
           |   Intake tower
 HFL ~~~~~ |  [ ]  gate/valve
           | __|__ upper port
 NWL ~~~~~ |/  |  \  <-- screens
           |   |__ middle port
 LWL ~~~~~ |   |
           |___|__ lower port
  River bed ///|\\\
              \|/ intake pipe to
                   pump well/treatment
```

**Working**
- Ports at two or three levels let the operator draw the clearest water at any river stage: the upper ports when the river is high (the surface water carries less silt), and the lower ports when the river is low.
- Coarse and fine screens at the ports stop floating matter, leaves, fish and debris.
- Gates or valves on each port regulate flow and isolate a port for repair.
- The water travels from the intake well through the intake pipe to the pump well or the plant.
- The entrance velocity is kept low (0.15 to 0.3 m/s) so that little silt and debris are drawn in. A foot bridge gives access for operation and cleaning.

#### Points to consider in site selection
1. **Water quantity**: the source must give the design flow even in the driest season; the minimum flow must exceed the demand.
2. **Water quality**: the site should be upstream of towns, sewage and industrial discharges, and away from tributaries that bring silt or pollution.
3. **Stable bank and bed**: choose a stable, non-eroding reach, preferably on the concave (outer) side of a bend where the water is deep and the current scours silt away.
4. **Depth of water**: enough depth at all stages so the intake port stays submerged at low water.
5. **Flood level**: the structure must stand above the highest flood level (HFL) or be safe against it, and the site should be free from flood and drift damage.
6. **Foundation**: sound strata for the foundation of the intake tower and pipes.
7. **Navigation**: the site must not obstruct navigation and should not be in a navigation channel.
8. **Distance and elevation**: close to the treatment plant and consumers (shorter pipeline, lower cost); for gravity schemes, enough head.
9. **Accessibility**: access for construction, inspection and maintenance in all seasons, and nearness to power for pumping.
10. **Future expansion** and **ownership of land/legal rights** at the site.
11. **Ice and silt**: the site should not be affected by ice formation or heavy sedimentation.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why are ports provided at several levels?
   A. To increase flood level
   B. To draw the clearest water at any river stage
   C. To reduce pipe size
   D. To avoid screens
   Answer: B. The operator picks the port with the best water as river level and silt change. (Key point: Ports at levels)

2. Why is entrance velocity kept low (0.15 to 0.3 m/s)?
   A. To freeze water
   B. So little silt and debris is drawn in
   C. To prevent navigation
   D. To increase pump head
   Answer: B. Low velocity reduces entry of silt and floating matter. (Key point: Entrance velocity)

3. Where in a bend is the intake preferably placed?
   A. Convex (inner) side
   B. Downstream of town
   C. At a tributary mouth
   D. Concave (outer) side where water is deep and silt is scoured
   Answer: D. The outer side has depth and a scouring current, so less silt deposits. (Key point: Bend location)

4. Why site the intake upstream of towns?
   A. To avoid sewage and industrial discharges
   B. To get higher floods
   C. To lengthen the pipeline
   D. To use navigation
   Answer: A. Upstream water is not yet polluted by town discharges. (Key point: Pollution)

## Related in Water Supply Engineering

- [Reservoir intake and site selection factors](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Areservoir-intake-site-factors) — Water Supply Engineering, chapter 5, asked 2×
- [Intake definition, components, river intake](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aintake-components-river) — Water Supply Engineering, chapter 5, asked 2×
- [Intake site factors; spring intake](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aspring-intake-site-factors) — Water Supply Engineering, chapter 5
- [Intake, its functions and site factors](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aintake-functions-site-factors) — Water Supply Engineering, chapter 5
- [Intake components and site factors](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aintake-components-site-factors) — Water Supply Engineering, chapter 5
- [Dry river intake with sketch](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Adry-river-intake) — Water Supply Engineering, chapter 5, asked 2×

## Related in other subjects

- [Intake site selection for RoR plant](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aintake-site-selection-ror) — Hydro Power, chapter 5
- [Powerhouse general arrangement and dimensions](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apowerhouse-arrangement-and-dimensions) — Hydropower Engineering, chapter 8, asked 3×
- [Site preparation components and facility arrangement](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Asite-preparation-facilities-urban) — Construction Management, chapter 6
- [Common RoR intakes in Nepal; site selection](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-common-intakes-nepal-location) — Hydropower Engineering, chapter 5, asked 2×