Code of practice for construction and maintenance of road gullies

IS 7740: Scope Summary

• Purpose: IS 7740 specifies requirements for the design, testing, and quality of structural elements/materials covered under the standard.
• Definitions: Clause 2.0 provides essential definitions for terms used throughout the standard.
• Rounding Off: As per IS 2-1960, all test or calculation results must be rounded off to the same number of significant figures as specified values in IS 7740.

Key Points:

No direct formulas or tables are specified under "Scope" in IS 7740; it mainly defines the applicability and rounding conventions.

flowchart TD
    A[Start: Test/Analysis Result] --> B{Round off?}
    B -- Yes --> C[Apply IS 2-1960 rounding]
    B -- No --> D[Use original value]
    C --> E[Retain same significant figures as specified]
    D --> E
    E --> F[Final value for compliance check]

IS 7740 - Definitions & Key Specifications Summary

• Clause 2.0: Defines terms used in the standard for clarity and uniformity.

• Rounding Off (Clause 0.3):

  • Final test or calculation results must be rounded per IS 2:1960 rules.
  • Retain the same number of significant figures as the specified values in IS 7740.

• Provision Highlights:

  • Allows curb inlet without gully chamber.
  • Includes figures for combination inlet gully design.

Important Notes:

• Always refer to IS 2:1960 for rounding off values (e.g., 0.345 rounded to 2 decimals = 0.35).
• Definitions ensure consistent interpretation of terms like curb inlet, gully chamber, etc.

If you need formulas or tables related to specific components (e.g., hydraulic capacity, dimensions), please specify!

Classification of Storm Water Inlets (IS 7740: Clause 3.1)

Storm water inlets are classified into three major groups:

1. Curb Inlets (3.1.1)

   • Opening in curb piece allowing gutter flow.
   • Minimal traffic obstruction, less clogging.
   • Types:
     • 3.1.1.1 Curb Inlets with Gully Chambers: Flow enters gully chamber then pipe to sewer (Fig. 1).
   • Typical pipe: 250 mm ID RCC pipe with slope ≥ 1:30.
   • Grating angle: 45° to 90°.
   • Construction layers include cement plaster, brick masonry, and concrete.

2. Gutter Inlets (3.1.2)

   • Horizontal openings in gutter covered by grates.
   • Grates with slots parallel to curb reduce clogging but admit more debris.
   • Preferred grates have openings perpendicular to flow, spacing 25 mm.
   • Cast iron gratings per IS: 5961-1970.
   • Single or double gully covers depending on flow (Fig. 4 & 5).
   • Top level of gully grating should be ~25 mm below channel level.

3. Combination Inlets

   • Incorporate vertical and horizontal gratings (Fig. 3).
   • Provide mosquito-proof covers (Fig. 6).
   • Water seal provision where necessary.

Key Specifications Summary

Typical Cross-Section Diagram (Simplified)

flowchart LR
    A[Gutter Flow] --> B[Curb Inlet Opening]
    B --> C[Gully Chamber]
    C --> D[Pipe (250 mm RCC, slope ≥ 1:30)]
    D --> E[Main Storm Sewer]

IS 7740: Location of Road Gullies - Key Points

1. Location Guidelines

• For road width ≥ 6 m, gullies are placed at the edge of the ultimate road width near curbs.
• For road width ≥ 3.65 m, gullies are located similarly but adjusted for narrower cross-section.
• Roads are designed with a cross slope towards curbs to facilitate drainage.
• Gullies align with curb and channel for efficient surface water disposal.

2. Typical Dimensions (from Fig. 7)

3. Design Notes

• Gullies should be located at the edge of ultimate road width even if initial road width is less.
• This avoids relocation during future widening.
• Road cross-section slopes towards the curb to direct water into gullies.

flowchart LR
    Road[Road Cross Section]
    Road -->|Slope towards| Curb[Curb & Channel]
    Curb -->|Water flows to| Gully[Road Gully]
    Gully -->|Drains to| SWP[Storm Water Pipe]

Summary: Position gullies at curb edges aligned with ultimate road width, ensuring road slopes direct water efficiently to storm water pipes.

IS 7740: Construction of Road Gullies – Key Points

Though IS 7740 lacks detailed formulas, the code provides essential guidelines for road gully construction:

Location & Layout (Clause 4.2)

• Gullies are placed at road curbs on one or both sides depending on road width.
• Road cross-section slopes towards curbs for surface water drainage.
• For staged road widening, locate gullies at the ultimate curb line to avoid relocation.

Construction Specifications (General)

• Gullies must be water-tight and robust to withstand traffic loads.
• Use concrete or precast units with proper reinforcement.
• Provide suitable inlet gratings to prevent debris entry.
• Ensure easy access for cleaning and maintenance.

Typical Dimensions (from common practice)

Drainage Slope

• Road cross slope typically 1.5% to 2% towards the curb to facilitate flow into gullies.

flowchart LR
    RoadSurface -->|Slope 1.5-2%| Curb
    Curb -->|Gully Inlet| RoadGully
    RoadGully -->|Drainage Pipe| SewerSystem

For detailed reinforcement, materials, and maintenance, refer to IS 7740 full text and related drainage codes like IS 456.

Key Specifications & Details for Road Gully Grating (IS 7740)

1. Material & Standards

• Cast iron gratings must conform to IS: 5961-1970.
• Alternative: Gratings made of 16 mm dia mild steel bars welded to 40x6 mm mild steel flats/angles.
• RCC gully gratings are also permissible.

2. Grating Types

• Vertical Grating
• Horizontal Gully Grating (preferred slot orientation is perpendicular to flow for less clogging and better public convenience).
• Slot opening between bars: 25 mm.

3. Structural Dimensions & Components

• Pipe diameter: Usually 150 mm or 250 mm RCC pipes.
• Top grating level: About 25 mm below the channel level of curb and channel drain.
• Concrete layers:
  • Cement concrete (1:3:6 or 1:5:10) for base and bedding.
  • 12 mm thick cement plaster finish.
  • Lime concrete with 30 mm gauge brick ballast or lean cement concrete.

4. Gully Chamber Types

• Single Gully Chamber (Fig. 4)
• Double Gully Chamber (Fig. 5) — used for main roads with metalled width ≥ 9 m.

5. Maintenance Notes

• Inlets prone to clogging by sand, grit, organic matter, leaves, and roots.
• Hinged cast iron frames for easy removal/replacement.
• Provision for mosquito-proof covers (Fig. 6).
• RCC pipes laid with slope not less than 1:30.

Summary Table: Typical Dimensions & Materials

Maintenance of Road Gullies (IS 7740)

While IS 7740 provides guidance on construction and maintenance, specific formulas or tables for maintenance are not explicitly detailed. Key points from the code and engineering practice include:

Key Specifications:

• Gratings: Cast iron gratings as per IS 5961-1970 or mild steel bars (16 mm dia) welded to 40x6 mm flats/angles.
• Alternate Gratings: RCC gully gratings are permissible (see Fig. 8 in the code).

Maintenance Guidelines:

• Regular Cleaning: Remove silt, debris, and blockages to maintain free flow.
• Inspection Frequency: Monthly or post-heavy rainfall to prevent clogging.
• Structural Checks: Inspect gratings and frames for corrosion, damage, or displacement.
• Repairs: Replace damaged gratings or frames promptly to avoid hazards.

Recommended Maintenance Formula (for sediment removal rate):

[ Q = A \times v ]

Where:

• (Q) = discharge capacity (m³/s)
• (A) = cross-sectional area of gully opening (m²)
• (v) = velocity of flow (m/s)

Maintaining (Q) ensures gullies function effectively.

flowchart TD
    A[Surface Water] --> B[Road Gully]
    B --> C{Grating}
    C -->|Clean| D[Free Flow]
    C -->|Blocked| E[Maintenance Required]
    E --> F[Cleaning & Repair]
    F --> D

Summary: Regular inspection, cleaning, and timely repair of gratings and frames ensure efficient gully maintenance per IS 7740.

IS 7740 - Materials and Specifications: Key Points

• Clear Cover to Reinforcement: Minimum 20 mm to protect steel from corrosion and ensure bond.

• Bearing Course Thickness: Use a 12.5 mm thick cement mortar bearing course (1:2 mix) under RCC elements for proper load transfer.

• Bed Block: In-situ bed blocks should be made of Cement Concrete (1:2:4 mix) for stable support.

• RCC Mix for Slab Covers: Use 1:1:2 (cement:sand:coarse aggregate) mix for casting slab covers.

• Dimensioning: All dimensions are in millimeters.

• Rounding Off: Test or calculated values must be rounded off as per IS 2-1960, retaining the same significant figures as specified.

Typical RCC Gully Grating Design (Fig. 8 reference)

• Reinforcement cover: 20 mm

• Bed block: C.C. 1:2:4

• Bearing course: 12.5 mm cement mortar 1:2

Summary Table

flowchart TD
    A[Slab Cover (RCC 1:1:2)] --> B[Bearing Course (12.5 mm Cement Mortar 1:2)]
    B --> C[Bed Block (C.C. 1:2:4)]
    C --> D[Foundation/Base]
    style A fill:#f9f,stroke:#333,stroke-width:2px
    style B fill:#bbf,stroke:#333,stroke-width:2px
    style C fill:#bfb,stroke:#333,stroke-width:2px

For detailed design, always refer to IS 7740:1985 and IS 2-1960 for rounding rules.

IS 7740: Design Details and Dimensions - Key Specifications

1. Bearing Course

• Thickness: 12.5 mm thick bearing course in cement mortar (1:2 mix).
• Bed Block: In-situ bed block in cement concrete (1:2:4).

2. Reinforcement Cover

• Clear cover under reinforcement: 20 mm.

3. Slab and Grating Details

• Slab covers cast in RCC (1:1:2 mix).
• Typical RCC gully grating dimensions:
  • Width: 150 mm
  • Length: 100 mm
  • Thickness: 50 mm

4. Materials

• Mild steel plate: 1.5 mm thick.
• Washers: 12 mm thick, welded with plate.
• Cement plaster finished with neat cement.
• Cement concrete: 1:5:10 mix for bedding.

5. Typical Gully Chamber Construction

• Brick masonry: One brick thick.
• Cement concrete layer: 40 mm thick.
• Lime concrete: 150 mm thick with 30 mm gauge brick ballast.
• RCC pipes: 150 mm and 250 mm diameter as per design.
• Top level of gully grating: ~25 mm below channel level of curb and channel drain.

6. Drainage Gratings

• Cast iron gratings for drainage.
• Vertical and horizontal grating types specified.
• Mosquito proof gully gratings with mild steel plate and welded washers.

Summary Table: Typical Dimensions

IS 7740: Connection to Storm Water Drain — Key Specifications & Details

1. Minimum Length of Pipe Between Gully Chamber & Manhole

• No explicit formula in IS 7740.
• General practice: Provide sufficient length to ensure smooth flow and avoid clogging, typically ≥ 1 meter.
• Use 150 mm or 250 mm RCC pipes as per gully size.

2. Materials & Components

3. Construction Details

• Top level of gully grating: About 25 mm below channel level of curb and channel drain to prevent overflow.
• Section Layers (from top to bottom):
  • Grating (vertical/horizontal)
  • Cement plaster finish
  • Cement concrete layer (40 mm thick)
  • Brick masonry (one brick thick)
  • Lime concrete or lean cement concrete base

4. Common Dimensions

5. Additional Notes

• Inlets and drains must be designed to minimize clogging from sand, grit, leaves, and roots.
• Use combination inlet type road gully with both vertical and horizontal gratings for better debris control.

Mermaid Diagram: Storm Water Drain Connection Layers

graph TD
    A[Gully Grating (CI)] --> B[Cement Plaster (12 mm)]
    B --> C[Cement Concrete (40 mm)]
    C --> D[Brick Masonry (One brick

IS 7740: Mosquito Proofing & Anti-Corrosion Key Points

Mosquito Proofing (Clause 7.3)

• Mosquito proof flaps must be lowered during cleaning to allow water flow but prevent mosquito entry.
• Gully gratings must have intact bars to block large debris.
• After rains, paint gully gratings and bottom flap with anti-corrosive paint.
• Bottom flap should be closed after paint dries to ensure mosquito proofing.
• Regular maintenance:
  • Clean covers before rainy season.
  • Flush gratings with water from hydrants.
  • Monthly cleaning during rains.
  • Post-rain cleaning and inspection.

Material Specifications

• Mild steel plate thickness: 1.5 mm (Clause 1.5).
• Washer thickness: 12 mm, welded with plate.
• Typical gully grating design uses cast iron for durability.

Anti-Corrosion

• Apply anti-corrosive paint on gratings and flaps after cleaning.
• Paint should be dried before closing bottom flap to maintain protection.

Summary Table: Mosquito Proofing and Anti-Corrosion Measures

flowchart TD
    A[Start of Rainy Season] --> B[Open Covers & Clean]
    B --> C[Lower Mosquito Proof Flap]
    C --> D[Flush Gully Gratings]
    D --> E[Check & Repair Broken Bars]
    E --> F[During Rain: Monthly Cleaning]
    F --> G[After Rain: Clean & Paint with Anti-corrosive Paint]
    G --> H[Close Bottom Flap to Prevent Mosquito Entry]

This ensures effective mosquito proofing and corrosion resistance as per IS 7740.

IS 7740 - Inspection & Preventive Maintenance of Road Gullies

Key Specifications (Clause 7.1 & 7.3)

• Objective: Keep the gully system clean and unobstructed, especially before and during the rainy season.
• Frequency:
  • Pre-monsoon: Open covers, clean manually, check mosquito-proof flaps, and repair/replace broken gratings.
  • During monsoon: Inspect monthly; clear any clogging immediately.
  • Post-monsoon: Clean deposits, paint gratings and flaps with anti-corrosive paint, close flaps after drying to prevent mosquitoes.
• Checks:
  • Ensure gratings bars intact and sized to prevent entry of large debris.
  • Flush gratings with water if possible before rains.

Maintenance Table Summary (Clause 7.3)

Maintenance Flowchart

flowchart TD
    A[Pre-monsoon Inspection] --> B{Clean Inlets?}
    B -- Yes --> C[Check & Repair Gratings]
    C --> D[Lower Mosquito Flaps]
    D --> E[Flush Gratings]
    E --> F[Ready for Rainy Season]
    F --> G[Monthly Inspection During Rains]
    G --> H{Clogging Found?}
    H -- Yes --> I[Clear Deposits Immediately]
    H -- No --> G
    G --> J[Post-monsoon Cleaning]
    J --> K[Paint Gratings & Flaps]
    K --> L[Close Mosquito Flaps]

Summary:
Regular, systematic inspection and cleaning—especially before, during, and after the rainy season—are critical for effective road gully maintenance per IS