---
title: "Wet (typical) reservoir intake"
subject: "Water Supply Engineering"
chapter: 5
key: "semester_5/water_supply_engineering:wet-reservoir-intake"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/wet-reservoir-intake
site: BCT Engineering
---

# Wet (typical) reservoir intake

Water Supply Engineering · Chapter 5: Intakes

- Asked in: 2081 Baisakh, 4 marks; 2068 Chaitra, 8 marks (asked 2 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/wet-reservoir-intake
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-5

## Question

When is a reservoir intake constructed? Describe a typical (wet) reservoir intake with a neat sketch.

## Short answer

A reservoir intake is built when water is stored behind a dam and quality varies with depth. A wet intake tower in the reservoir has multiple screened ports at different depths; water enters at reservoir level, passes through gates into the well, then via conduit to plant. Gates are operated from the top platform; bottom port is above silt level.

## Answer

#### When a reservoir intake is constructed
A reservoir intake is built when the supply comes from an impounding (storage) reservoir or lake, for example when the river flow in the dry season is less than the demand, so water is stored behind a dam and drawn through a tower. It is used when the quality changes with depth and season, and when the supply must be taken at a controlled level.

#### Typical wet reservoir intake
A **reservoir intake** draws water from an impounding reservoir (a natural lake or an artificial lake formed by a dam). A **wet intake tower** is a vertical tower, usually of masonry or concrete, set in the reservoir near the dam, with ports at different depths. The water level inside the tower is the same as in the reservoir.

```text
  Foot bridge ==============+
                            | operating
  HFL ~~~~~~~~~~~~~~~~~~    | stem
  NWL ~~~~~~~[ ]~~~~~~~~~~~ |
       top port + screen    |
  MDDL ~~~~~[ ]~~~~~~~~~~~~ |
       middle port + screen |
       ~~~~~[ ]~~~~~~~~~~~~ |
       bottom port          |
  bed //////|  intake well  |////
            +--------pipe/conduit--> outlet to plant
```

**Characteristics and working**
- The tower has ports (usually 3) at different levels. Water is taken from the level of best quality: top water in summer when the deeper water is cold and poor (low oxygen, high iron and manganese), and deeper water in winter when the surface is cold or frozen.
- Water entering the port passes through coarse and fine screens, then the sluice gate or valve, into the well, and from the well by the intake pipe or conduit to the plant.
- Gates are operated from the top by stems and handwheels on the service platform; access is through a foot bridge.
- Low entrance velocity avoids drawing silt and floating matter. The bottom port is placed above the sludge/silt level.

## Check yourself

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

1. When is a reservoir intake built?
   A. When groundwater is used
   B. When river flow always exceeds demand
   C. When supply comes from an impounding reservoir or lake, e.g. dry-season flow is below demand
   D. When water comes from a spring
   Answer: C. Storage behind a dam is used when river flow cannot meet demand. (Key point: When constructed)

2. What is the water level inside a wet intake tower?
   A. Lower than reservoir
   B. Always full to the top
   C. Dry
   D. Same as the reservoir
   Answer: D. The wet tower is open to the reservoir through its ports. (Key point: Water level)

3. Which water is taken in summer?
   A. Silt layer
   B. Bottom water
   C. Mixed from all ports
   D. Top water, since deeper water is cold and poor (low oxygen, iron and manganese)
   Answer: D. In summer deeper water is poor quality, so top ports are used. (Key point: Port selection)

4. Where is the bottom port placed?
   A. Above HFL
   B. Beyond the dam
   C. At the very bed
   D. Above the sludge/silt level
   Answer: D. This avoids drawing silt. (Key point: Bottom port)

## Related in Water Supply Engineering

- [Reservoir intake for an earth dam](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Areservoir-intake-earth-dam) — Water Supply Engineering, chapter 5, asked 2×
- [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×
- [Wet and dry river intake](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Awet-dry-river-intake) — Water Supply Engineering, chapter 5

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- [Installed capacity, energy and daily peaking reservoir (2079)](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-capacity-plant-factor-18cumec-peaking-79) — Hydropower Engineering, chapter 3, asked 2×
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