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

# Reservoir intake and site selection factors

Water Supply Engineering · Chapter 5: Intakes

- Asked in: 2080 Baisakh, 4+4 marks; 2070 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/reservoir-intake-site-factors
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-5

## Question

What are the factors that should be considered during selection of an intake site? Describe the characteristics of a wet reservoir intake with a neat sketch.

## Short answer

Factors include adequate water quantity and quality, stable river reach with sufficient depth, safe flood level, sound foundation, accessibility, and proximity to treatment plant. A wet reservoir intake is a vertical tower in the reservoir with multiple ports at different depths, each with screens and gates operated from a top platform via a footbridge, allowing selection of best quality water.

## Answer

#### Factors for selecting an intake site
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.

#### Characteristics of a 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. What must the source provide?
   A. Design flow even in the driest season
   B. Half the demand
   C. Average flow only
   D. Flood flow
   Answer: A. Minimum flow must exceed the demand. (Key point: Water quantity)

2. Which location is preferred?
   A. Eroding bank
   B. Stable reach, outer side of a bend with depth
   C. Inner bend
   D. Shallow bar
   Answer: B. The outer bend has depth and scour, reducing silt. (Key point: Bank and bend)

3. Why enough depth at all stages?
   A. To create waves
   B. To reduce HFL
   C. To enable navigation
   D. Port stays submerged at low water
   Answer: D. Ports must never be exposed. (Key point: Port depth)

4. What is the water level in a wet intake tower?
   A. Zero
   B. Same as reservoir
   C. Dry
   D. Above HFL
   Answer: B. Water enters the ports so the levels match. (Key point: Wet tower)

## Related in Water Supply Engineering

- [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
- [Wet (typical) reservoir intake](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Awet-reservoir-intake) — Water Supply Engineering, chapter 5, asked 2×
- [General river intake and site selection](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ageneral-river-intake) — Water Supply Engineering, chapter 5, asked 3×
- [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
- [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×

## Related in other subjects

- [Hydropower site selection factors](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Asite-selection-discharge-factors) — Power Plant Design, chapter 3
- [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
- [Foundation selection factors, excavation in wet areas](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aexcavation-selection-wet-080c) — Building Technology, chapter 2
- [Geology in reservoir site selection](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Areservoir-site-selection) — Engineering Geology II, chapter 4