Hydrology Reports for Water Crossings - About this Document

Guide for Preparing

Hydrology Reports for Water Crossings

About this Document

The hydrotechnical design process for a water crossing requires a multi-disciplinary approach that incorporates watershed hydrology, bridge hydraulics, foundation assessments, geomorphologic assessment (stream stability) and highway geometrics. The design also requires a comprehensive engineering approach that involves data collection, hydrologic analysis, formulation of alternatives, evaluation and selection of the "best" alternative according to established criteria, and documentation of the final design

The hydrotechnical design of water crossings for projects within the jurisdiction of the Ministry of Transportation of Ontario (MTO) is to be based on and reflect the principles and procedures identified in the MTO Drainage Management Manual (DMM), the MTO Drainage Design Directives and the Canadian Highway Bridge Design Code (CHBDC), including any Ontario Exemptions. The planning and design approach is consistent with the approach outlined in the MTO Structural Planning Guideline (2003).

This guide identifies the procedure for completing a hydrotechnical design report, commonly referred to as a "Hydrology Report". It provides the detailed documentation requirements for Hydrology Reports prepared for MTO and the rationale for requiring this information. It also provides definitions of the terminology and technical procedures referred to in the document. It is important to note that, technical details or policy statements provided in this document are for clarification only. They are not to be considered as substitute for the original documents or policies. It is the designer's responsibility to refer to the original technical manuals, standards and policies for instruction and guidance.

The documentation of a hydrotechnical design of a water crossing should clearly outline all the assumptions and procedures used, results achieved and conclusions arrived at by the designer so that these could be referred to at any time. The hydrotechnical design documentation may be used for several purposes including:

• Obtain necessary approvals both internal to MTO as well as external.
• Document design hydrologic and hydraulic parameters assessed at the time of design, considering the statistical and dynamic nature of hydrology and the fact that such estimates may change with additional data over the years.
• A permanent record that establishes the baseline of the hydrologic and hydraulic conditions at the time of development of the structure. This can be used to identify the source of any future concerns by others (including any nearby developments/changes), to address legal or litigation matters, and to facilitate future expansion, reconstruction or rehabilitation work to the structure.
• Assessing the performance of the structures especially during future floods.

Purpose of this document

This document is developed to:

• Provide a comprehensive set of MTO documentation requirements that are to be used in the preparation of Hydrology Reports.
• Provide the rationale for requiring this documentation.
• Ensure completeness and consistency in reports prepared for MTO.
• Enable the designer to identify the relevant hydrologic, hydraulic and environmental issues impacting the watercourse, the water crossing, the highway, the surrounding lands and existing structures, at the earliest possible planning stages.
• Provide guidance for the preparation of terms of reference for hydrotechnical studies and for the Drainage component of Request For Proposal documents involving the design of water crossings.

Objectives of this document

This document will provide information to:

• ensure the safety of the travelling public;
• strengthen the management of highway projects by implementing the modern drainage management approach;
• consider the use of alternative and cost effective drainage management techniques that will maintain the integrity of the highway infrastructure throughout its expected life;
• ensure easy access to and consistent application of MTO drainage management practices across all MTO regions of the province;
• ensure that MTO regulatory concerns are addressed in a consistent and comprehensive manner; and
• address issues that are sources of potential liabilities to MTO as a result of the development of water crossing designs for provincial highways.

The Role of the Drainage Management Manual in this Document

The "Drainage Management Manual" (DMM) (MTO 1997) provides the technical reference for this document. It provides the design considerations and computational methods appropriate for use in the design of water crossings in Ontario.

This guide, being procedural in nature, makes reference to the DMM for resolving technical issues. However, the section "Selecting Computational Methods" has been added to provides a brief description of some of the technical requirements referred to in this document. It also provides the linkage to the specific reference in the DMM, where the detailed design information can be found.

The Role of the Structural Planning Guideline in this Document

The Structural Planning Guideline (MTO 2003) provides a comprehensive description of the structural planning stages and processes associated with the development of the structural design of bridges and culverts.

Structural planning includes all activities leading to the completion of the Structural Planning Report and Structural Design Report for the construction of new structures and the rehabilitation of existing structures.

Associated with these structural reports are different Hydrology Studies that are of varying levels of detail. Fundamentally, there are two Hydrology Studies undertaken, a Preliminary Hydrology Study and a Detailed Hydrology study. All these studies are finally documented in the Hydrology Report. The Hydrology Report when completed becomes part of the Structural Design Report.

The Preliminary Hydrology study may be documented in a separate report or incorporated in other Preliminary Design Reports for the structure. It may also be prepared in many stages depending on the level of Structural Planning being undertaken and the information documented as part of other reports. The following are the structural planning stages and the associated Preliminary Hydrology Studies. The breakdown presented here is provided more as a guide rather than a requirement. For this reason, there will be no reference in the remainder of the document as to the level of detail associated with a particular type of study or with each task. The focus will be mainly on identifying the groups of tasks, the actions required to complete each task and the documentation requirements.

Corridor Planning

Corridor planning deals with identifying possible routes within corridors and routes within each corridor. The structural planning activity involves site visits, identification of problems, obtaining preliminary subsoil information and consideration of alternative crossing solutions and structure types, as outlined in Section 4.2. A Preliminary Hydrology Study for Corridor Planning is associated with this level of planning. This study would be of limited detail but address a wide range of issues.

Route Planning

Route Planning deals with the review and cost estimating of proposed structure locations on the selected routes. The Route Planning activity is similar to Corridor Planning but in greater detail, as outlined in Section 4.3 of the Structural Planning Guideline. This level of planning deals with the review and cost estimating of proposed structure locations on a selected route. The structural planning activity is similar to Corridor Planning but at a greater level of detail. A Preliminary Hydrology Report may be prepared at this stage.

Detail Planning

Detail Planning is the final structural planning phase prior to structure design. In this phase all information is gathered resulting in the preparation of the Structural Planning Report and/or the Structural Design Report, as outlined in Section 4.4. The Detailed Hydrology Report is completed for this stage and is the basis of the Detailed Planning.

The Role of MTO Drainage Directives in this Document

MTO Drainage Directives are MTO policies and standards that are to be applied whenever highway drainage works are being designed or may be impacted by works external to the MTO right-of-way. There are three relevant directives:

• PHY Directive B-100: Addresses flood plain management requirements at highway water crossings. It sets the minimum design standards for flow conveyance at highway water crossings. This is the most relevant directive to the design of bridges and culverts.
• PHY Directive B-63: Addresses MTO policy and procedures relating to the Drainage Act. It specifically deals with Municipal Drains. It may be relevant when dealing with bridge or culvert structures crossing municipal drains.
• PHY Directive B-237: Drainage management policy and procedures. It provides direction and guidance relative to stormwater runoff, urban drainage, detention ponds and highway drainage. It may be relevant to issues associated with deck drainage.
• PHY Directive B-217: Addresses MTO policy and procedures on Private Pipe Drains from agricultural lands and individual private residences which outlet onto or cross provincial highway. It may be relevant if the outlets of these drains are located in the vicinity of a propose water crossing site.

The requirements set out in this document conform to these directives. Some portions of the directives have been directly incorporated into appropriate sections (complete with references) for discussion purposes only. It is the responsibility of the designer to refer to the original directive for instruction. Copies of MTO drainage directives can be downloaded from the "Drainage Directives" page of the Drainage Management Web site or obtained from the MTO Regional Offices or local District Office.

About This Document and the TPM process

Hydrology Reports in most cases are completed within the early stages of development of a water crossing design (within the first 30% of the work for detailed structural design). A hydrology report will form part of the Structural Planning Report. In some cases where structural modification require changes to the water opening a hydraulic reassessment of the structure should be done prior to completing the design.

Review These Points before Proceeding

• It is the responsibility of the drainage practitioner to familiarize themselves with the requirements of MTO and provide all information required by the ministry for evaluation, as outlined in this document. Sufficient time should be allowed for the evaluation process and for any approvals required.
• The MTO Bridge Office, Regional Planning and Design Sections and/or the Highway Design Office (Drainage and Hydrology) may alter the requirements presented in this guide.
• MTO may accept a Hydrology Report with a lower level of detail depending on the level of structural planning being undertaken at the time of submission.
• The design criteria will require approval from the Regional MTO Office responsible for the project. Design criteria that do not meet the requirements of the CHBDC will require a special approval and a justification report may be required to identify the reasons for not meeting the code. Refer to the section "Approval Requirements for Design Criteria not Meeting the CHBDC, 2001".

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