IRC SP 50 (First Revision, 2013) provides comprehensive guidelines for urban drainage design, construction, and maintenance tailored for Indian urban environments. It addresses surface and subsurface drainage systems, stormwater management, infiltration techniques, and water quality protection measures, including riparian buffers and detention ponds. This standard is essential for engineers, planners, and authorities involved in urban infrastructure to effectively manage stormwater runoff, prevent flooding, and promote groundwater recharge in rapidly urbanizing areas.
10Sections
298Clauses Indexed
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2013Edition
Roads and Bridges IRC- Indian road congress Category
IRC SP 50 (First Revision, 2013) provides comprehensive guidelines for urban drainage design, construction, and maintenance tailored for Indian urban environments. It addresses surface and subsurface drainage systems, stormwater management, infiltration techniques, and water quality protection measures, including riparian buffers and detention ponds. This standard is essential for engineers, planners, and authorities involved in urban infrastructure to effectively manage stormwater runoff, prevent flooding, and promote groundwater recharge in rapidly urbanizing areas.
Audience
Who Uses This Standard
Urban Infrastructure Engineers
Municipal Drainage Planners
Civil and Environmental Engineers
Highway and Road Design Engineers
Water Resource Managers
Urban Planners
Public Works Department Officials
Contents
Key Topics Covered
✓Design of surface and subsurface drainage systems
✓Stormwater runoff estimation and time of concentration
✓Riparian buffer zones and vegetated filters
✓Infiltration and groundwater recharge techniques
✓Drainage at intersections, flyovers, and rotaries
✓Use of gravel filters and silt traps
✓Drainage system maintenance and cleaning protocols
✓Design of manholes and drainage appurtenances
✓Detention and retention ponds for stormwater control
✓Retrofit options for existing urban roads
✓Drainage of pavements and shoulders
✓Water quality management in urban drainage
✓Subsoil water drainage and permeability considerations
Structure
Table of Contents
1Scope▼
IRC SP 50 - Scope Summary & Key Specifications
Scope (Clause 5)
Covers design, construction, and maintenance of storm water drainage systems for highways.
Includes surface drainage, subsurface drainage, storm water management, and special location drainage.
Addresses runoff estimation, filter materials, drainage design, and maintenance.
Key Formulas & Tables
1. Rational Formula for Peak Runoff (Clause 6.1)
[
Q = C \times I \times A
]
Q = Peak runoff rate (m³/s)
C = Coefficient of runoff (from Table 6.1)
I = Rainfall intensity (mm/hr)
A = Catchment area (ha)
2. Coefficient of Runoff (Table 6.1)
Surface Description
Coefficient (C)
Watertight pavement (concrete/bitumen)
0.90
Green area (Loamy soil)
0.30
Green area (Sandy soil)
0.20
Unpaved area along roads
0.30
Lawns and parks
0.15
Flat built-up area (~60% impervious)
0.55
Moderately steep built-up (~70% impervious)
0.80
3. Grading Requirements for Filter Materials (Table 7.1)
Sieve Size (mm)
Class I % Passing
Class II % Passing
Class III % Passing
53
-
-
100
45
-
-
97-100
26.5
-
100
-
22.4
-
95-100
58-100
11.2
100
48-100
20-60
5.6
92-100
28-54
4-32
3Drainage of Pavements and Shoulders▼
Drainage of Pavements and Shoulders (IRC SP 50)
Key Specifications & Formulas
1. Surface Infiltration (Clause 7.4.1)
Water infiltration depends on rainfall intensity and infiltration coefficient (f).
Infiltration Coefficients (f):
Surface Type
Coefficient of Infiltration (f)
Earthen Shoulders
0.4 to 0.6
Bituminous Pavement
0.2 to 0.4
Concrete Pavement
0.3 to 0.4
Water quantity to be drained (Q) per meter length:
[
Q = i \times f \times A
]
where
(i) = rainfall intensity (cm/hr),
(f) = infiltration coefficient,
(A) = area contributing to infiltration (m²).
2. Subsurface Drainage (Clause 7.5.1)
Use Darcy’s Law for subsurface water flow:
[
Q = k \times A \times \frac{\Delta h}{L}
]
where
(Q) = flow rate (m³/s),
(k) = permeability coefficient (m/s),
(A) = cross-sectional area (m²),
(\Delta h) = hydraulic head difference (m),
(L) = flow length (m).
Permeability ranges for materials:
Material Type
Permeability (k) (m/s)
Flow Rating
Homogeneous Clays
10⁻¹² to 10⁻¹⁰
Very Slow
Fine Sands, Silty-Clay Mixtures
10⁻¹⁰ to 10⁻⁹
Slow
Clean Sand & Gravel
10⁻⁷ to 10⁻⁵
Moderate to Rapid
Bituminous & Asphalt Courses
10⁻⁹ to 10⁻⁷
Slow to Moderate
For drainage layers, select permeability **10 times
4Riparian Buffers and Vegetated Filters▼
Riparian Buffers & Vegetated Filters (IRC SP 50)
Riparian Buffers (Clause 4.1.4, Fig. 4.4)
Definition: Vegetated strips along flowing water bodies to stabilize banks, reduce erosion, and improve water quality.
Summary: Use 25 mm/hr intensity, rational method for runoff, and design drains per runoff volumes in the table for effective stormwater drainage.
7Subsurface Drainage Systems▼
Subsurface Drainage Systems — IRC SP 50 (Clause 7.5)
Key Points:
Darcy’s Law governs subsurface water flow but natural heterogeneity and anisotropy affect permeability.
Field measurements and geotechnical expertise are essential for accurate design.
Depth and spacing of drains may be adjusted based on flow measurements.
Permeability values guide material selection for drainage or barrier functions.
Darcy’s Law for Subsurface Flow:
[
Q = k \cdot A \cdot \frac{\Delta h}{L}
]
(Q) = discharge (m³/s)
(k) = permeability coefficient (m/s)
(A) = cross-sectional area perpendicular to flow (m²)
(\Delta h) = hydraulic head difference (m)
(L) = length of flow path (m)
Permeability Ranges (Fig. 7.3 summary):
Soil/Material Type
Permeability (k) (m/s)
Rating
Homogeneous Clays
(10^{-12}) to (10^{-9})
Very Slow
Very Fine Sands, Silty-Clay Mix
(10^{-10}) to (10^{-7})
Slow to Moderate
Clean Sand, Gravel Mixtures
(10^{-6}) to (10^{-4})
Rapid to Very Rapid
Bituminous, Asphalt Courses
Very Low (Barrier)
Impervious
Graded Filter & Shoulder Materials
Moderate to High
Drainage Media
Design Considerations (Clause 7.2):
Identify water ingress sources:
Surface infiltration
Lateral seepage through shoulders/verges
High water table or capillary rise
Select drain depth & spacing based on permeability and flow measurements.
Summary Diagram of Subsurface Drainage Flow:
flowchart TD
A[Surface Water] -->|Infiltration| B[Subsurface Soil]
C[Lateral Seepage] --> B
D[High Water Table] --> B
B --> E[Drainage System]
E --> F[Discharge Point]
**Use highest permeability value
8Filter Materials for Drainage▼
Filter Materials for Drainage (IRC SP 50 - Key Points)
1. Aggregate Filters (Clause 7.5)
Purpose: Retain soil, prevent piping, ensure no large voids at soil-filter interface.
Design:
Single-layer for coarse soils.
Multi-layer for fine soils:
Fine aggregate retains natural soil particles.
Coarser aggregate prevents fine aggregate migration into drainage pipe.
Gradation:
Too coarse → large voids → soil particles not retained.
Too fine → poor permeability → hydrostatic pressure build-up.
2. Fabric Filters (Clause 7.5.3 & 7.6)
Made of polyethylene/polypropylene fibers (woven/non-woven).
Key takeaway: Proper filter design balances soil retention and permeability to avoid clogging and hydrostatic pressure, using either aggregate layers or geotextile fabrics meeting specified criteria.
9Drainage at Intersections, Flyovers, and Rotaries▼
Drainage at Intersections, Flyovers, and Rotaries (IRC SP 50)
1. Drainage of Rotaries (Clause 9.4)
Due to super-elevation, water flows toward the center of the rotary.
Water must be collected and drained to the main system.
Minimum outlet width: 600 mm for easy maintenance.
Multiple outlets are recommended if site conditions allow to reduce drain depth.
Refer to Fig. 9.4 for typical drainage layout.
2. Drainage at Intersections (Clause 9.7)
Surface water flow is directed through side drains and PIMs (Paved Interception Manholes).
See Fig. 9.7(a) for schematic flow direction.
Ensure proper grading to avoid water pooling.
3. Drainage at Foot of Flyovers (Clause 9.2)
Provide adequate slope and drainage channels at flyover abutments.
Collect runoff and direct to storm water drains without causing local flooding.
Key Specifications Summary
Feature
Specification/Dimension
Minimum outlet width
600 mm (rotary outlets)
Drain type
Circular drains at rotary center
Multiple outlets
Recommended to reduce drain depth
Side drains & PIMs
Used at intersections
Typical Flow Concept (Mermaid.js)
flowchart LR
A[Surface Runoff] --> B[Side Drain]
B --> C[PIM (Interception Manhole)]
C --> D[Main Storm Drain]
subgraph Rotary Drainage
E[Rotary Surface] --> F[Center Drain]
F --> G[Outlet(s) ≥ 600 mm]
G --> D
end
Note: Design storm water drainage capacity based on local rainfall intensity and catchment area, following standard hydraulic design principles (e.g., Rational Method).
10Stormwater Infiltration and Groundwater Recharge▼
Runoff slowly passes through vegetation/gravel, filtering sediments and pollutants.
Filters include rock/vegetated swales, filter strips, sand filters.
In draining soils, infiltration reduces runoff volume and improves water quality.
2. Groundwater Recharge Strategy (Clause 10.1)
Retrofit existing drains (tertiary, secondary, primary) to allow infiltration starting at roadside drains.
Use infiltration-filter median drains alongside regular drains to capture and infiltrate water.
Stormwater recharge implemented via:
Landscaping (medians, sidewalks)
Bore wells in drains
Porous pavement layers & perforated paving
Detention/retention ponds
Rainwater harvesting tanks on properties
3. Typical Catch Basin with Infiltration Pit (Clause 10)
Layers from bottom to top:
250mm boulders
40mm & downsized WBM
20mm & downsized WBM
10mm & downsized metal
50mm sand bed
50mm Pondicherry pebbles
Brick walls with MS rods and angle frames for structural support.
4. Design Considerations
Retrofit roads should maintain existing drainage slope.
Provide filter media as per Chapter 8 Section 4 (sand, gravel layers).
Excess water to overflow into existing storm drains.
Adjacent properties encouraged to retain and recharge stormwater.
Simplified Infiltration Pit Cross-Section:
graph TD
A[Boulders 250mm] --> B[WBM 40mm & downsized]
B --> C[WBM 20mm & downsized]
C --> D[Metal 10mm & downsized]
D --> E[Sand bed 50mm]
E --> F[Pondicherry pebbles 50mm]
F --> G[Stormwater inlet pipe]
Summary Table: Infiltration Layers Thickness
Layer Material
Thickness (mm)
Boulders
250
WBM
12Maintenance of Drainage Systems▼
Maintenance of Drainage Systems (IRC SP 50)
Key Points from Clause 12.9 & 12.8:
Subsoil Drainage Maintenance:
Inspect twice a year, once after heavy rains.
Observe outflow quality & quantity; muddy water = filter failure, no flow = blockage.
Check inlets/outlets for damage, blockage, scour.
Prevent surface runoff entering subsoil drains.
Maintain marker pegs and pit covers; replace or relocate if damaged.
Keep detailed "as built" drawings for maintenance reference.
Common Deficiencies & Remedies (Table 12.8):
Deficiency
Cause
Remedy
Ponding
Inadequate cross-section, depression, erosion
Deepen drain, refill eroded/depressed areas
Silting
Inadequate invert slope, excess soil entry
Improve slope, check entry points, provide gratings
Blockage (debris/vegetation)
Uneven bed, lack of cleaning
Desilting, cleaning, gratings at entry points
Erosion of bed/cross-section
Steep slope, lack of lateral support
Flatten slope, add drops, provide side support
Maintenance Checklist Summary:
Inspect: Twice yearly + post heavy rain
Clean: Remove silt, debris, vegetation regularly
Repair: Structural damages, scour, pit covers
Mark: Ensure visibility of pegs and drainage features
Prevent: Surface runoff entry into subsoil drains
Conceptual Diagram (Drain Maintenance Cycle):
flowchart TD
A[Inspect Twice a Year] --> B{Check Outflow}
B -->|Muddy Water| C[Check Filter Function]
B -->|No Flow| D[Check for Blockage]
A --> E[Inspect Inlets & Outlets]
E --> F[Remove Blockages & Repair]
A --> G[Check Marker Pegs & Pit Covers]
G --> H[Replace/Relocate if Damaged]
F --> I[Prevent Surface Runoff Entry]
I --> A
This approach ensures effective drainage performance and prolongs system life as per IRC
14Planning and Design of Decentralized Drainage Systems▼
IRC SP 50: Planning & Design of Decentralized Drainage Systems
Key Specifications & Design Approach
Design Basis:
Use rainfall data (50-100 years return period)
Consider soil infiltration rates and aquifer recharge zones
Filtration & Infiltration at Multiple Drain Levels:
Stormwater infiltration should start at street-level drains and continue through tertiary, secondary, and primary drains.
Use of vegetated swales, rock filters, sand filters, and gravel beds to slow runoff, filter sediments, and promote infiltration.
Catch Basin with Infiltration Pit:
Construct catch basins with layered filter media (pebbles, sand, metal aggregates, boulders) to trap and infiltrate water before overflow connects to main drains.
Typical pit includes layers like:
50 mm Pondicherry pebbles
50 mm sand bed
10 mm & downsized metal
20 mm & downsized WBM
40 mm & downsized WBM
250 mm & downsized boulders
Retrofitting Existing Roads:
Retrofit roadside drains with soak pits, infiltration chambers, and filter media.
Use infiltration-filter median drains alongside regular drains to capture and infiltrate pavement runoff.
Additional Measures:
Landscaping in medians, roundabouts, sidewalks.
Bore wells in tertiary/secondary drains.
Porous pavement and pervious paving in parking lots.