--- title: "Wet and dry river intake" subject: "Water Supply Engineering" chapter: 5 key: "semester_5/water_supply_engineering:wet-dry-river-intake" source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/wet-dry-river-intake site: BCT Engineering --- # Wet and dry river intake Water Supply Engineering · Chapter 5: Intakes - Asked in: 2075 Asoj, 4 marks - 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-dry-river-intake - Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-5 ## Question Define wet and dry river intake with neat sketch and briefly describe their operation and maintenance, showing all major components in the sketch. ## Short answer A wet river intake is a tower in the river with interior flooded to river level; water enters through screened ports and exits via a bottom pipe, gates operated from a top bridge. A dry river intake is on the bank with a dry interior; water enters ports, passes through valves in the dry chamber to a sump, allowing easy maintenance. Wet intakes are cheaper but harder to maintain; dry intakes cost more but offer easy access. ## Answer #### Wet river intake A **wet intake** is a tower (or well) built in the river, with its interior filled with water up to river level. Ports at different levels admit water, and the intake pipe leaves from the bottom of the well. The valves are operated from the top, since they are underwater. ```text Foot bridge =====#===== Stem (control rod) | HFL ~~~~~~~~~~~~~~~~~~~~ | NWL ~~~~~~[port + screen]| <- water inside LWL ~~~~~~[port + screen]| well = river level bed ///////[port]--------| | intake pipe +---------------> to pump well / plant ``` **Operation and maintenance**: The tower is filled with water and the pipe is always flooded. Gates at each port are operated from the bridge by a stem. Screens must be raked and cleaned from above, and divers or stop-logs are used when the tower has to be examined. It is cheaper than a dry intake, but harder to maintain. #### Dry river intake A **dry intake** is a tower built on the river bank (or just inside it) whose interior is kept dry. Water enters through ports in the wall, flows into a **separate sump** by a connecting pipe, and only the valves and pipes are in the dry chamber. The operator can work inside it at any time. ```text Foot bridge ===+ | operating floor HFL ~~~~~~~~~ || gate valves ||[=]---+ NWL ~~~~~~~~ ||[=]---+--> pipe to ||[=]---+ sump/pump well LWL ~~~~~~~ || dry chamber ///////// ||____________ screens at ports river bed | (water-tight walls) ``` **Operation** - Water flows from the river through the screened ports, then through the valves in the dry chamber, to the sump or directly to the pump. - The operator selects the port at the best level and closes the others. - Valves and screens can be inspected, cleaned or repaired from inside, in dry conditions. **Merits and demerits**: Operation and maintenance are easy, but it needs stronger water-tight walls and a heavier, deeper foundation (to resist floatation when it is empty), so it costs more than a wet intake. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is a wet intake? A. Canal head B. Tower filled with water to river level; valves operated from top C. Dry tower with a sump D. Spring box Answer: B. Valves underwater are operated by stems from the bridge. (Key point: Wet intake) 2. How are screens cleaned in a wet intake? A. Raked from above; divers or stop-logs for examination B. From a dry chamber C. Never D. By the sump Answer: A. It is harder to maintain. (Key point: Maintenance) 3. Which statement is right? A. Both identical B. Dry is cheaper C. Wet is cheaper but harder to maintain; dry is costlier but easier D. Wet is costlier Answer: C. Dry needs watertight walls and deeper foundations. (Key point: Comparison) ## Related in Water Supply Engineering - [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× - [Dry and wet river intakes; unstable bank](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Awet-dry-intake-unstable-bank) — Water Supply Engineering, chapter 5 - [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× - [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× - [Short note: River intake](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ariver-intake-note) — Water Supply Engineering, chapter 5 ## Related in other subjects - [Peaking RoR: max power and wet/dry energy ratio](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apeaking-ror-reservoir-250m-q25) — Hydropower Engineering, chapter 3 - [Canal discharge for dry and wet crops](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Akor-discharge-dry-wet-20000-30000) — Irrigation and Drainage Engineering, chapter 2, asked 2× - [Canal discharge for dry and wet crops (30000/40000 ha)](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Akor-discharge-dry-wet-30000-40000) — Irrigation and Drainage Engineering, chapter 2, asked 2× - [When wet process is better than dry](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Awet-process-better-than-dry) — Civil Engineering Materials, chapter 5