Storm & Sewer Water Transmission

Storm, Sewer, Water Transmission Pipeline & Manholes Design

These are the prerequisites for starting the design.

1. Regulatory Framework & Codes

Local Municipal Standards

Specific pipe materials, minimum sizes, cover depths, and construction details.

State/National Codes

IBC, IPC (for sanitary sewers), ASCE standards, state environmental agency regulations.

Design Criteria

The most critical rules (e.g., "Use 10-Year storm for minor system, 100-Year for major overflow").

2. Site-Specific Data

Topographic Survey

A detailed contour map showing existing ground elevations, structures, utilities, and waterways.

Geotechnical Report

Soil properties (infiltration rates, corrosivity) for pipe bedding and trench design.

Existing Utility Plans

Locations of all other underground utilities (water, gas, fiber, electrical) to avoid conflicts.

Land Use & Zoning Maps

Determines population density (for sewer flow) and impervious cover (for stormwater).

3. Hydrologic/Hydraulic Data

Storm Data

Rainfall Intensity-Duration-Frequency (IDF) curves for the project location.

Watershed Characteristics

Area, slope, ground cover (curve numbers or runoff coefficients), time of concentration.

Sanitary Sewer Data

Estimated population, per capita flow rates, industrial flows, infiltration/inflow allowances, peaking factors.

For Storm Sewer Design:

Delineate Drainage Areas

Divide the site into sub-catchments that drain to each inlet.

Place Inlets & Manholes

Locate inlets at low points, along curb lines, and at regular intervals. Manholes are placed at changes in direction, slope, pipe size, or at junctions.

Calculate Runoff

Use a method like the Rational Method (Q = CiA) for small areas or more advanced hydrological models (HEC-HMS, SWMM) for large complexes.

Preliminary Pipe Layout & Sizing:

Assume a slope (often following ground slope for economy).

Manning's Equation (Q = (1.49/n) * A * R^(2/3) * S^(1/2)) to calculate flow capacity in a pipe.

Iterate until pipe capacity ≥ design runoff. Ensure minimum velocity (~2-3 ft/s) to prevent sediment deposition and maximum velocity (~10-15 ft/s) to prevent erosion.

System Analysis & Profiling

Create a hydraulic grade line (HGL) profile to ensure the system has sufficient capacity under design conditions and that inlets do not flood.

Check for hydraulic jumps, surcharging, and impacts on upstream/downstream systems.

For Sanitary Sewer Design:

Define Service Area & Flows

Calculate Average Daily Flow (ADF) from population and industry. Apply Peaking Factors to get Peak Wet Weather Flow.

Layout the Network

Pipes generally follow gravity along streets from upstream sources toward the treatment plant or pump station.

Size for Capacity & Self-Cleansing

Manning's Equation with "n" for sewer pipe (e.g., PVC, HDPE, VCP).

Critical Constraint: Design for full-pipe flow at peak rate to ensure adequate capacity.

Self-Cleansing Velocity: Pipes must achieve a minimum velocity (~2 ft/s) at the anticipated minimum daily flow to prevent solids deposition.

Design Pipe Slope & Depth

Slope is adjusted to meet both capacity and velocity criteria.

Maintain minimum cover (typically 3-4 feet) to prevent freezing and live load damage.

Avoid excessively deep trenches for cost and safety.

KCPM Calculations & Software

Hydrology

Rational Method, NRCS Curve Number Method, Unit Hydrographs.

Hydraulics

Manning’s Equation, Continuity Equation, Energy Equation (Bernoulli), Head Loss calculations (friction, junctions, bends).

KCPM – Standard Software used:

AutoCAD Civil 3D

For drafting, terrain modeling, and basic pipe network layout.

Hydraulic Modeling Software:

EPA SWMM

Powerful for both storm and sanitary, especially for complex systems and water quality.

Bentley OpenFlows (StormCAD, SewerCAD, CivilStorm)

Specialized, user-friendly packages for analysis and design.

Innovyze InfoWorks ICM/InfoSWMM

High-end integrated catchment modeling.

GIS (ArcGIS, QGIS)

For watershed delineation and managing large-scale system data.

Critical Design Considerations & Checks

Constructability

Can it actually be built? Consider trench shoring, dewatering, access for equipment.

Maintenance & Access

Manhole spacing (max ~400 ft), cleanouts for laterals.

Resilience & Sustainability

Design for future land use changes and climate change (higher intensity storms). Consider Green Infrastructure elements (permeable pavement, bioretention) at the source to reduce pipe sizing.

Off-Site Impacts

Ensure your system does not overload or negatively impact downstream systems or properties.

Materials Selection

PVC (common for small sewers), HDPE (flexible), Ductile Iron (pressure), RCP (Reinforced Concrete Pipe for large storm culverts). Choose based on strength, corrosion resistance, and cost.

Easements

Secure permanent legal rights for pipes crossing private property.

Final Deliverables (The "Package")

Plan & Profile Drawings

The essential construction documents.

Plan View: Shows pipe horizontal alignment, locations, structures, and ties to other utilities.

Profile View: Shows ground line, pipe invert elevation, slope, depth, and structures along the pipeline's path.

Detailed Construction Specifications

Standards for materials, installation, testing (mandrel testing for sewers), and backfill.

Hydraulic Calculations Report

Documents all assumptions, methods, and results to justify the design.

Bill of Materials/Quantity Take-off

For cost estimation.

In summary, storm and sewer pipe design is a systematic engineering process that transforms site data and regulatory codes into a buildable, functional, and durable underground system. It balances the laws of physics with practical construction and long-term maintenance, ensuring public health and environmental protection. For any significant project, this is performed by KCPM licensed professional engineer (PE).