---
title: "Street inlets and their types"
subject: "Sanitary Engineering"
chapter: 4
key: "semester_6/sanitary_engineering:street-inlets-types"
source: https://www.bctengineer.com/q/semester_6/sanitary_engineering/street-inlets-types
site: BCT Engineering
---

# Street inlets and their types

Sanitary Engineering · Chapter 4: Sewer Appurtenances

- Asked in: 2077 Chaitra, 1+3 marks; 2076 Baisakh, 1+3 marks (asked 2 times)
- Video: [Sewer Inlets | street inlets | Curb inlets | Gutter inlets with diagram |  IN HINDI by EASY CIVIL](https://www.youtube.com/watch?v=KQPGvbz4KE4) — EASY CIVIL
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/sanitary_engineering/street-inlets-types
- Whole chapter: https://www.bctengineer.com/md/semester_6/sanitary_engineering/chapter-4

## Question

What are street inlets? With neat sketches describe different types of street inlets.

## Short answer

Street inlets admit surface storm water from roads into drains. Curb inlets have a vertical opening in the kerb face, suitable for flat areas with debris. Gutter inlets have a horizontal grating in the gutter, efficient on slopes. Combined inlets use both for high capacity.

## Answer

**Street inlets** (storm water inlets) are openings, with a grating or a slot, built at the edge of a road or in the gutter to admit surface storm water into the storm drain or combined sewer.

#### Types of street inlets
Street inlets are of three main types: curb inlet, gutter inlet and combined inlet.

#### 1. Curb inlet
A vertical opening in the curb (kerb) face through which water enters the chamber. It is most effective on flat roads, at sag (low) points and where leaves and debris are heavy, because the vertical opening is not blocked easily (but silt can still collect). On steep roads much of the fast gutter flow runs past it.

```text
  Road   Gutter  Curb
  ______         |
        \_______ |  <- opening (10-15 cm high)
                 |_____ Inlet chamber
         ---------> to sewer
```

#### 2. Gutter inlet
A horizontal opening in the gutter covered by a cast iron grating (cast iron bars parallel to the flow). Water falls through the grating into the chamber. It is more efficient than a curb inlet on continuous (moderate to steep) grades and can handle a large flow, although some fast flow may skip over the grating. It may be blocked by leaves, paper and debris, and it is a risk to cyclists.

```text
   Curb |  Gutter
        |__[#######]__    <- grating
        |  |       |
        |  | chamber|----> to sewer
        |  |________|
```

#### 3. Combined inlet
A curb inlet and a gutter inlet are provided together, so that water enters through both. If the grating is blocked, the curb opening continues to work. It has high capacity and is widely used on busy city roads.

#### Other points
- The inlet is connected to the sewer by a 150-300 mm pipe, and a catch basin (silt pit with 0.6-0.9 m deep sump) or a trapped inlet is often provided to stop grit and smell.
- Inlets are spaced at 30-60 m on a road, depending on road slope, width and rainfall, and they are placed at street corners, low points and before pedestrian crossings.

## Check yourself

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

1. What is the function of a street inlet?
   A. Release sewer gases
   B. Flush the sewer
   C. Allow workers to enter the sewer
   D. Admit surface storm water from the road into the storm drain or combined sewer
   Answer: D. Inlets admit road surface water to the drain. (Key point: Definition)

2. Which are the three main types of street inlets?
   A. Curb, gutter and combined inlets
   B. Drop, ramp and cascade inlets
   C. Sand, grease and oil inlets
   D. Circular, square and oval inlets
   Answer: A. The types are curb, gutter and combined. (Key point: Types)

3. Why is a combined inlet advantageous?
   A. It needs no chamber
   B. If the grating is blocked, the curb opening keeps working
   C. It never needs cleaning
   D. It can be used only on flat roads
   Answer: B. Both openings together give high capacity and a backup. (Key point: Combined inlet)

4. What is the usual spacing of street inlets on a road?
   A. 3-6 m
   B. 300-600 m
   C. 30-60 m
   D. 1-2 km
   Answer: C. Inlets are spaced about 30-60 m, depending on slope, width and rainfall. (Key point: Spacing)

## Related in Sanitary Engineering

- [Street inlets and catch basins](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Astreet-inlets-catch-basins) — Sanitary Engineering, chapter 4
- [Street inlets: curb vs gutter inlet](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Astreet-inlets-curb-gutter) — Sanitary Engineering, chapter 4

## Related in other subjects

- [On-street vs off-street parking; kerb parking geometry](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aparking-onstreet-offstreet-comparison-geometry) — Transportation Engineering II, chapter 1