MTO Highway Drainage Design Standards

This posting aims to seek comments and inputs from industry stakeholders on the updated Highway Drainage Design Standards.

The Highway Drainage Design Standards were last published in 2008. The edits included in the 2023 update are summarized as follows:

1. Annual Exceedance Probability Terminology introduced and incorporated throughout the document.

2. Memorandum “DCSO #2016‐14 – Implementation of the Ministry’s Climate Change Consideration in the Design of Highway Drainage Infrastructure on Climate Change” and Memorandum “DCSO #2016‐03 Implementing the New Unified Ontario Flood Method for Calculating the Design Flow Rates for Water Crossings” incorporated into standards “SD –1 Design Flows for Surface Drainage Systems” and “WC‐1 Design Flows for Natural Watercourse Crossings (Bridges and Culverts)”.

3. Standard “TW‐1 Temporary Flow Passage Systems and Temporary Drainage Facilities” updated in accordance with the November 2023 update to “OPSS.PROV 517 Construction Specification for Dewatering and Temporary Flow Passage Systems”.

4. References to other manuals and ministries updated throughout the document.

5. Addition/Edit of definitions for Annual Exceedance Probability, Bankfull Flow, Local External Catchment Area, Temporary Flow Passage System, Watercourse, Waterbody and Natural Watercourse and associated edits throughout the document. This includes combining standard “SD‐13 Design Flows and Freeboards for Road Surface Drainage Culverts” into standard “WC‐7 Culvert Crossings”.

6. Reformatting of Tables (with titles and AEP) and figures.

7. Minor editorial corrections throughout the document.