--- title: "Factors in constructing a spring intake" subject: "Water Supply Engineering" chapter: 5 key: "semester_5/water_supply_engineering:spring-intake-factors-constructing" source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/spring-intake-factors-constructing site: BCT Engineering --- # Factors in constructing a spring intake Water Supply Engineering · Chapter 5: Intakes - Asked in: 2072 Chaitra, 8 marks - Video: [Intake Structure /Gravity flow water supply system/ water supply](https://www.youtube.com/watch?v=1H2R1JtNZSY) — Er Rajesh Chhatkuli - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/spring-intake-factors-constructing - Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-5 ## Question With neat sketches describe the factors that should be considered while constructing a spring intake. ## Short answer Construction must collect the whole spring yield without damming the eye, sit on firm impervious ground, and use watertight 1:3 mortar. Protect against pollution with a clay cap, fence, and diversion drain; keep the outlet above the floor, provide overflow, washout, vent, manhole, and gravel filter. ## Answer A spring intake must collect the whole spring yield without disturbing the natural flow or letting pollution in. Its parts and layout are shown first, followed by the factors to be considered while constructing it. A **spring intake** (spring box or spring capture) is a small chamber built at the spring eye to collect all the flow from the spring, protect it from pollution, and send it to the pipeline by gravity. It is the most common intake for rural hilly areas of Nepal because springs give clean water at a high level. **Parts of a spring intake** - **Collection chamber** (spring box) of stone masonry or concrete, with a pre-cast cover and manhole. - **Gravel filter / perforated pipes** at the back wall to collect water uniformly from the spring eye. - **Outlet pipe** with a gate valve (and a strainer) to the pipeline. - **Overflow pipe** to take excess water; **washout (drain) pipe** with a valve for cleaning; **vent pipe** with a screen. - **Protection works**: clay/impervious cap over the spring, a **diversion drain** (catch drain) uphill to divert surface water, a **fence**, and a vegetation or plantation cover. **Plan** ```text Diversion drain (uphill) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | fence | | +---------------------+ | | | gravel filter :::: | | | | (spring eye) |-->| overflow | | collection chamber | | | | [manhole] outlet |==>| pipe to tank | +----------+----------+ | | washout pipe | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ``` **Section / elevation** ```text Vent Manhole cover | ____|_____ ground | | | clay cap (0.5 m) =======+--+ +============= | | air | Spring->|::| water lvl|--> overflow gravel |::|~~~~~~~~~~| filter |::| |==> outlet+valve |__|__________| washout pipe ``` #### Factors to be considered 1. **Spring yield**: measure the minimum (dry-season) yield to check that it meets the demand, and size the chamber and pipes for the maximum flow; the overflow takes the surplus. 2. **Location of the spring eye**: all eyes must be captured inside one chamber; the box must sit on the eye itself and must not dam the water back (the water level in the box must stay below the eye, or the spring may find another path and be lost); excavate carefully. 3. **Foundation**: put the box on firm impervious rock or hard clay and keep the back wall open to the spring (through the gravel filter), while the other walls are water-tight. 4. **Protection against pollution**: cover with an impervious clay cap, fence off, keep animals and latrines away, and construct a diversion drain uphill. 5. **Water tightness**: use rich cement mortar (1:3) for walls and plaster the inside. 6. **Gravel filter**: graded stone or gravel at the face to hold the soil back and spread the flow. 7. **Overflow and washout pipes**: place the outlet pipe a little above the floor so that sediment settles below it and is flushed out through the washout. 8. **Ventilation and access**: a screened vent pipe and a lockable manhole. 9. **Local materials and cost**, since these schemes are community-managed. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In a spring box, which wall is left open to the spring through a gravel filter? A. The back wall facing the spring eye, with the other walls water-tight B. All four walls C. The floor only D. The front wall with the outlet Answer: A. The back wall stays open with gravel so water enters uniformly; the other walls are water-tight to keep out pollution. (Key point: Foundation and walls) 2. How is the spring intake sized with respect to yield? A. Designed for minimum yield only, with no overflow B. Yield is ignored for small springs C. Minimum yield is measured, the outlet is designed for maximum flow and the overflow takes surplus D. Designed for average yield and the overflow is blocked Answer: C. Dry-season minimum is checked for adequacy, while outlet is designed for maximum flow and overflow takes the surplus. (Key point: Spring yield design) 3. Why must the box be built exactly on the spring eye without damming it? A. To raise the water level above the spring B. So all eyes are captured and flow is not diverted into another path and lost C. To make the box look neat D. To reduce masonry cost Answer: B. Damming or disturbing the eye can push water to other outlets, reducing the collected yield. (Key point: Location of spring eye) 4. Why is the outlet pipe placed a little above the floor of the box? A. To make cleaning impossible B. To increase the pressure in the pipe C. To allow air to enter D. So that sediments settle on the floor and do not enter the pipeline Answer: D. A raised outlet leaves a sediment space below, and the washout pipe is used to clean it. 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