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INTRODUCTION

INSTRUCTIONS

REFERENCE

Hydrology Reports for Water Crossings - MTO Approvals

Guide for Preparing

Hydrology Reports for Water Crossings

MTO Approvals

This task group identifies MTO requirements for preparing and accepting Hydrology Reports at the different levels of planning and design.

The main objectives of this task group are:

  • To ensure that a Hydrology Report is prepared when necessary and that this be identified at the earliest possible stage of development.
  • To make sure all necessary approvals are known and are acquired at the appropriate stage of planning and design.

This task group includes the following tasks:

The MTO Regional Structural Section or Bridge Office may alter requirements presented in this document. The drainage practitioner must demonstrate that adverse drainage impacts to the highway right-of-way and upstream/downstream riparian landowners will not occur. The design of the crossing should be based on runoff conditions anticipated 20 years from the time of design, taking full account of present and probable future municipal controls over increases of runoff from new development.

Determine the Requirements for the Hydrology Report

Definition

A hydrotechnical study will be required when the design of a new water crossing or a replacement/rehabilitation of an existing structure is being considered. The level of detail of the analysis will vary depending on the level of planning and design being undertaken. In the case of the rehabilitation of structures, if the work being proposed will be above the Highway Water Level and the High Ice Level, a Hydrology Report may not be required. This will have to be confirmed with the MTO project manager.

The level of detail of the analysis will depend on the following:

  • The level of structural planning the report is addressing. The Structural Planning Guideline, (MTO 2002) identifies three levels of structural planning:
    The level of detail of hydrology information associated with each of these levels of planning get more detailed as the project moves forward from one level to the other. It is necessary that the proper level of detail undertaken in the hydrology study be commensurate with the level of structural planning the study is intending to complete.
     
  • The type of Hydrology Report being presented. This task is included to identify the level of detail the Hydrology Report is providing. There are possibly two levels of hydrology reporting:
    • Preliminary or
    • Detailed.

    Depending on the level of structural planning, the preliminary Hydrology Report may be prepared in two stages one at the corridor planning stage and one at the route planning stage. On the other hand, for small structures or structural replacement/rehabilitation, the Hydrology Report may be prepared in one stage.

Documentation Requirements

The Hydrology Report should clearly document the following:

  • The level of planning and design being addressed in the report. The details of the information and analysis presented should be commensurate with the level of reporting.
  • The rationale for preparing the report and who initiated the study.
  • The number and locations of the watercourse crossings being considered.
  • Reference to other Reports associated with this watercourse crossing. Careful consideration should be given to the time elapsed between reports to ensure the information in one report, for example the Preliminary Hydrology Report has not become dated by the time the Detailed Hydrology Report is prepared.

The documentation requirements discussed in this section can be included in the Introduction section of the Hydrology Report. Refer to the section "Organization of the Hydrology Report" for the proposed table of contents of the Hydrology Report.

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Approval Requirements

Definition

A number of MTO approvals will be required before the Hydrology Report is finally accepted by MTO. These approvals are:

  1. Approval of the Design Criteria.
  2. Approval of deviations from requirements of the CHBDC (2001), if applicable.
  3. Approval of the Preliminary Hydrology Report.
  4. Approval of the Detailed Hydrology Report.

There is a formal approval process including sign off by the Regional Head of Structural and the Manager of Engineering, for the design criteria and deviations from CHBDC requirements. However, acceptance of the Preliminary and Detailed Hydrology Reports do not require a sign off.

Documentation Requirements

This section should document the following:

  • Approvals received at earlier stages of the planning process, if applicable.
  • Any conditions that were placed by MTO or other authorities and how they have been dealt with.

At some stage in the planning and design of a water crossing it may be determined that one or more of the requirement set by the CHBDC may not be achieved without significant changes to the approach, surrounding lands or other crossings upstream. In such cases a special approval is required to approve the particular criteria that will not meet the CHBDC requirement. The next section describes the process that is to be followed and the documentation requirements.

Approval Requirements for Design criteria not Meeting the CHBDC, 2001

The MTO is governed by the CHBDC in the design of bridge and culvert structures and requires that the code requirement be followed in the design of all structure. However, in some cases, due to site conditions, it may be necessary to consider a design option that contravenes a requirement set by the CHBDC. This section specifically addresses two requirements set by the code, namely: the criteria for clearance at the water crossing and freeboard at the approach to a water crossing.

In the event that such deviations are necessary, MTO approvals will have to be sought before the design alternative can be accepted. The approval will be granted by the Manager of Engineering in the region. In some cases concurrence of the Regional Director may be necessary. A justification/ exception report will be required to document the rationale for proposing the deviation.

The Justification or Exception Report

If a design option that contravenes the CHBDC is being proposed, it is necessary to document the information needed to justify the decision to proceed with such a design. The following information should be included in the report, as a minimum:

  • The design criteria for the structure.
  • A summary of the design considerations to accommodate the impacts of constructing the bridge or culvert structure at a lower elevation. This should also include the impact on maintenance requirements and access to the underside of the structure.
  • Summary of the hydrologic and hydraulic analysis for all the alternatives being considered.
  • Site restrictions and impacts that influenced the decision to consider the contravening alternative. This includes, but is not limited to:
    • Impacts on other bridge or culvert structures upstream and downstream.
    • Requirements of other agencies such as the Conservation Authority, MNR or municipality.
    • Impacts on vertical and horizontal road alignments before and after the structure.
    • The impact on scour at the bridge.
    • The location where relief flow will occur.
    • The impacts on lands and structures within the floodway.
    • Impact on the flood lines.
  • Maps, sketches, photographs and photo mosaics to adequately describe the situation.
  • Cost analysis.

Determining the Cost Estimates

To determine the costs associated with the construction of a bridge or culvert, the costs do not only contain the cost of the structure but also the cost of addressing the impact associated with each design alternative. The cost of constructing a bridge or culvert should include the following:

  • The cost of construction of the proposed bridge or culvert structure and approach.
  • The cost of potential damages to the structure during high flow rate conditions.
  • The cost of added protection to the structure to resist lateral and longitudinal forces due to debris and ice flows and vertical forces due to buoyancy, air entrapment and ice.
  • The cost of potential erosion and scour impacts on the stream channel at the structure and in the vicinity of the structure both upstream and downstream.
  • The cost of compensation for damages to lands and structures if additional flooding is to occur as a result of the proposed design.
  • The cost of future repairs to the bridge approach during flooding events.The cost of replacement of the structure if the life span of the structure is reduced due to more frequent and prolonged submergence conditions.
  • The cost of loss of access at the bridge or culvert during flooding events.

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