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INTRODUCTION

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REFERENCE

Hydrology Reports for Water Crossings - Identifying Drainage Issues

Guide for Preparing

Hydrology Reports for Water Crossings

Identifying Drainage Issues

Before proceeding with the tasks in this grouping, the following tasks should have been completed:

This group of tasks uses the information and data collected to identify the drainage issues that need to be addressed at the proposed water crossing location(s). Some analysis will be required to complete this set of tasks.

MTO recognises that the property of riparian landowners, located upstream or downstream of the water crossing, cannot be damaged by works constructed across a natural watercourse. For this reason, an investigation must be completed to determine if any drainage impacts will occur to the drainage system and surrounding lands

The drainage practitioner will complete the following tasks in this group:

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.

Identify Existing Drainage Problems

Definition

Before proceeding with the design of a water crossing it is necessary to identify any existing drainage problem at the site that may impact the design criteria for the new structure.

Important insight to the drainage problems in the area can be provided from the site inspection and from MTO regional and district staff. Contacting the local conservation authority, municipality, or the local MOE and MNR can also provide further information into the history of the area.

Documentation Requirements

The Hydrology Report should document existing problems with upstream or downstream property to ensure that any liabilities assumed by MTO are clear and that opportunities for corrective measures are addressed early in the design process. This documentation should cover possible problems such as:

  • Upstream or downstream flooding of structures and lands.
  • Upstream or downstream erosion problems.
  • Problems in the roadside ditching system.
  • Beaver dam activity.

In the case of projects that involve the replacement of existing water crossing structures, it is important to also document the following:

  • Incidents where the structure's hydraulic capacity have been exceeded, identifying high-water marks, other signs of overtopping and structural damage, citizen reports and other documented sources.
  • Deterioration of the structure in excess of normal degradation.
  • Signs of blockage due to siltation, vegetation overgrowth or obstruction.
  • Damages to other structures and land in the immediate vicinity.

Having identified existing drainage problems, the cause of the problem should be assessed to determine the potential for further aggravation (refer to the section "Mitigating Impacts to the Drainage System"). If existing drainage problems were found, the Hydrology Report should document the steps taken to reach such a conclusion.

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Identify Issues with other Structures Upstream and Downstream

Definition

Any existing structures on the watercourse, located in close proximity to the crossing site, upstream and downstream, should be assessed for hydraulic adequacy and performance. The assessments should be carried out by reviewing the past history of the structures and by a visual inspection.

It may be necessary to conduct hydrologic and hydraulic analysis to determine the water surface profile without the new crossing in place.

Documentation Requirements

As a part of the Hydrology Report, each existing structure should be documented for:

  • Spans, finished roadway width, skew, distance from the proposed crossing and year of construction.
  • Waterway opening, size, width and height, design flood, velocity, and HWL if available.
  • Hydraulic performance of opening through visual evidence of past floods and channel scour.
  • Any rip rap/bank protection measures constructed or added later and any problem areas and related mitigative measure taken to address these problems. Any monitoring, or maintenance aspects, which should be considered.
  • Any geotechnical considerations, constraints or problems related to the stability of the road or bridge approach fills, settlement problems and the performance of abutments and piers.
  • Any structural/safety problems that may be obvious.

In addition, the waterway opening for each structure should be assessed and documentation provided for:

  • Its past hydraulic performance, identifying whether it was under or over-designed with respect to the structure's performance.
  • The erosion of banks, fill slopes or channel bed, and
  • Any maintenance/repairs carried out in the past.

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Investigate Stability of the Watercourse

Definition

One of the critical considerations when designing a new water crossing is the suitability of the location where the crossing is to occur. It is always preferable, wherever possible, to locate the crossing at a stretch of a watercourse reach that is stable and where shifting of the stream channel or erosion and deposition of sediment will not occur in any significant way during the life span of the structure.

If a stable reach is practically not attainable, additional works to protect the structure and the channel bed and banks will most likely be required. As well, additional maintenance requirement may become necessary over time.

Documentation Requirements

For each of the proposed crossing locations the following should be provided:

  • A geomorphologic assessment of the stream to assess the stability of the proposed crossing location(s).
  • The effect of channel stability on the design criteria of the crossing.
  • Cost implications.

The above information should be supported with the following data and information:

  • A historic record of flooding, channel alignment and erosion problems.
  • Aerial photographs showing the meander pattern of the stream.
  • Soil type for the channel bed and banks.
  • Justification for the distance upstream and downstream, from the proposed location, where the stability assessment was conducted. The drainage practitioner will have to exercise judgement in selecting the minimum distances.

In some cases it may be necessary to realign the stream channel at the location of the crossing. In such cases the following information and analysis should be documented:

  • An inventory of the existing channel and geomorphic characteristics including:
    • Typical width and depth
    • Channel slope
    • Channel form i.e. Bend / reach configuration.
    • Bankful Discharge / Channel Forming Discharge
  • For the proposed channel, the following should be provided
    • Channel characteristics
    • Assessment of impacts
    • Methods of mitigating impacts
    • Approval of other agencies such as MNR, the Conservation Authority and DFO

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Identify Criteria that Regulate the Watercourse

Definition

There are a number of agencies that are responsible for regulating different aspects of natural and man-made watercourses. MTO also has polices and directives that will affect the design criteria of a crossing. Each regulatory agency will determine the criteria that regulate the watercourse within its mandate and will place restrictions on works or structures that interfere with it. These criteria should be documented in the Hydrology Report. These regulating agencies and the associated criteria include, but are not limited to those presented below.

Documentation Requirements

Highway Drainage Design Criteria

The Hydrology Report must identify the design criteria for the components of the highway drainage system (i.e. that form part of the drainage system) whose capacity may be impacted by stormwater runoff discharging from the proposed land development. For details on MTO drainage design criteria refer to PHY Directive B-100 or document "Design of Bridges on Low Volume Roads" for low volume roads (Bridge Office Policy Memo 98-04e). Refer to "Design Criteria for Highway Drainage Works" available from the MTO Bridge Office, St.Catharines, for further details. Other highway design criteria may also be applied. Contact the MTO Regional Structural Section and Planning and Design Section for further details.

Other Drainage Design Criteria

The local Conservation Authority and/or municipality should be contacted for design criteria applicable to the watercourse or water management aspect for which they have jurisdiction.

Where design criteria have been adopted based on a previous drainage study, these criteria should be identified. Refer to the section "Review Previous Drainage Studies" for more details.

Drainage Management Policy of Regulatory Agencies

Provincial regulatory policies for drainage management include:

  • Provincial Policy Statement: Natural Heritage, Water Quality and Quantity, Natural Hazards and Human Made Hazards (Planning Act);
  • Official Plans, Secondary Plans, and Zoning By-laws (Planning Act, Municipal Act); and
  • Fill, Construction and Alteration of Waterway (Conservation Authorities Act).

The above noted policies are recognised by MTO. Where required by the regulatory agencies, the Hydrology Report should document compliance with these policies.

Drainage Management Policy of MTO

Drainage management policies are issued by the MTO under the authority of the Public Transportation and Highway Improvement Act through the following directives.

  • PHY Directive B-100 (PDF - 65 KB) presents design criteria for highway drainage works. Refer to the section "Develop the Design Criteria" for further details.
  • PHY Directive B-63 (PDF - 168 KB) and PHY Directive B-217 (PDF - 91 KB): MTO participation in works administered through the Drainage Act is detailed in PHY Directive B63, and MTO drainage policy for private piped drains on the highway right-of-way is detailed in PHY Directive B217. They should be reviewed when matters related to municipal drains or tile drainage apply to the proposed structure alternative being considered. In such cases, the Hydrology Report must document how the procedure in either directive was followed.
  • PHY Directive B-237 (PDF - 367 KB) presents MTO Drainage Policy conforming to common law. The fundamental basis of this directive is to ensure that stormwater runoff discharging from any highway drainage works will not infringe upon the riparian rights of landowners located upstream or downstream of the highway right-of-way. It may be relevant to issues associated with deck drainage, if the discharge may impact other landowner. It will also identify landowner rights if drainage outlets are going to be affected by the location of a proposed water crossing.

To view PDF files, you will require Adobe Acrobat Reader.

Standards of Practice Identified through Manuals and Guidelines

Manuals and guidelines are prepared to implement the design criteria and regulatory policy of a provincial agency, local municipality, or local conservation authority. Manuals and guidelines present acceptable design applications and/or computation methodologies that conform to design criteria and regulatory policy, and they should be reviewed accordingly. Standard manuals and guidelines that are issued by provincial agencies and are applicable to proposals for water crossing design include:

  • "Drainage Management Manual" (MTO 1997);
  • "The Structural Planning Guideline" (MTO 2003);
  • "Culvert Design Manual" (MTO 1988); and
  • "Flood Plain Management in Ontario Technical Guidelines" (MNR 1987).

This document does not present examples on the application of the various computational methodologies or design applications presented within the manuals listed above; however, references are provided where appropriate.

The local conservation authority and municipality should be contacted for manuals or guidelines that are applicable in their jurisdiction.

Where Conflicts Exist between MTO and the Regulatory Agencies

As an agent of the crown, MTO will not proceed with the construction of a water crossing that contravenes drainage management policies, guidelines and manuals of other regulatory agencies.

Should any design criteria, drainage management policy, guideline or manual of a regulatory Agency conflict with a design criteria, a meeting between the parties may be warranted to resolve the conflict. The design criteria would therefore, have to be approved by MTO Regional management.

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Identify Design Alternatives

Definition

In every project there are usually a variety of options to consider. The number of these options will depend on site conditions as well as on the stage of planning being undertaken. As the planning stages progress and additional information is gathered and analysed, some options will be rejected and others will remain as viable options. Finally, an option will be selected that will satisfy the design criteria, at least the critical ones, and the cost considerations for the project.

The alternatives being considered may differ and could include but are not limited to the following:

  • Different location, orientation and skew.
  • Different spans and clearance, whether or not the structure will interfere with the watercourse.
  • Different type of structure, bridge or culvert.
  • Different structural design.
  • Different material, for example concrete or steel.
  • Different type of foundation.

Documentation Requirements

The type of information to be documented to satisfy this section is primarily a summary of the different alternatives being considered. The complete information for each alternative will be documented as is described under the different sections of this document. Alternatives that will be no longer considered would be documented to the extent where the information was sufficient to make the decision to exclude these alternatives.

For each alternative, the following information should be included as a minimum:

  • The type of crossing.
  • The location of the crossing, height (as accurately as possible) and skew.
  • Spans, type of piers and abutment.
  • Schematics of the proposed structure, showing the layout and dimensions.
  • Hydrologic and hydraulic advantages and disadvantages of the alternative.
  • Reasons for excluding the alternative.

After the design of all alternatives has been completed, the proposed best alternative is to be identified and all the alternatives summarised. Refer to the section "Recommending the Best Alternative".

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