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INTRODUCTION

INSTRUCTIONS

REFERENCE

Hydrology Reports for Water Crossings - Finalizing Design and Construction Issues

Guide for Preparing

Hydrology Reports for Water Crossings

Finalizing Design and Construction Issues

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

Before MTO can issue an approval for a land development proposal, the drainage practitioner must complete 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.

Design Bridge Deck Drainage

Definition

Bridge deck drainage may be considered as a special case of pavement drainage. Bridge deck drainage is important to traffic safety in wet weather and in winter.

The hydrologic design criteria for bridge deck drainage is set by Directive B-100, where the return period will vary between 2-10 years depending on the class of road. Bridge deck drainage may not be needed for all bridge structures especially for bridges with short spans.

Documentation Requirements

The design of bridge deck drainage will determine the location and spacing of drain inlets at the approach and on the deck of the bridge. Design examples 4.6 and 6.7 in the MTO Drainage Management Manual (1997) provide a guide to the requirements for the establishment of the design flow rate and capacity of the system.

Accordingly, the following information should be documented in the Hydrology Report:

  • Input parameters identified in the design criteria and from collected data.
  • Design flow rate.
  • The type of hydraulic analysis methods used, whether using design tables or computer software. The discussion should demonstrate suitability of the method(s) used and its acceptability to MTO. Refer to the MTO Drainage Management Manual Chapters 3 and 5, and the MTO Drainage Web document "Evaluation of Drainage Management Software" for details on acceptable methods and the documentation required if the method used has not been evaluated by MTO.
  • Deck Inlets spacing, type and spacing.
  • Down pipe size, number, location and spacing.
  • Ground Level Drainage Outlet locations, type and configuration.

If water surface profile software such as StormCAD is used, refer to the section "Minimum Documentation Requirements" in the MTO web document "Evaluation of Drainage Management Software" for details.

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Complete the Requirements for Erosion and Sediment Control During Construction

Definition

Where applicable, a sediment and erosion control plan stamped by a Professional Engineer should be completed before final approval of a water crossing design. The plan is required to ensure that proper techniques will be used to minimize the impacts on the watercourse and the surrounding environment.

Documentation Requirements

Issues to be addressed and documented in the Erosion and Sediment Control Plan are listed below. For further details on sediment and erosion control during construction, refer to Chapter 6 of the "Drainage Management Manual" (MTO 1997).

  • Construction timing and the proposed construction timeframe and timing constraints for construction (spring, fall constraints) should be noted.
  • Construction phasing and timeframes for the different phases should be included. Indicate whether the entire site is to be developed all at once or whether the proposed land development is to be phased. Sediment control techniques must address both pre-serviced and serviced phases of construction.
  • Stabilization requirements and the allowable timeframe for land to remain exposed before it is stabilized with sod, mulch, or hydro seeding, should be noted. Indicate provisions for the stockpiling of soil.
  • Siltation fencing locations should be located at the site boundary at all side slope and down gradient locations. Siltation fence should also be used to protect significant features (i.e. provides a limit for grading activities) and to control dust, nuisance problems to homeowners in existing surrounding land developments.
  • Access/mud mat locations should be located at each entrance/exit location to the construction site. The mat can be removed once the access locations are paved. The number of access locations to a construction site should be minimized (1 or 2).
  • Catch-basin controls, where used, prevent the migration of sediment into the storm sewers.
  • Rock check dam locations should be located in overland swale systems which outlet to the receiving waters.
  • Siltation basins can be used to service larger drainage areas (stormwater detention facilities can be used as temporary sediment basins during construction, wherever possible).
  • Topsoil stockpile storage locations for soil storage piles and their distance from roads and drainage channels should be clearly shown. Timeframes and proposed works for the stabilization and remediation of topsoil stockpiles should be provided.
  • Inspection and maintenance requirements of the sediment and erosion control works should be noted. Maintenance should be performed as required to ensure the proper operation of sediment and erosion controls, and the works should be inspected after each storm to ensure proper operation.

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Recommending the Best Alternative

Definition

After the design of all alternatives has been completed, a summary of the different alternatives should be provided and the recommended alternative be identified. The documentation of the recommended alternative should be supported with the rationale for the recommendation.

Documentation Requirements

The documentation should include:

  • A summary description of the proposed design alternatives indicating the main features of the each design such as:
    • Description of the structure such as: type, span(s), pier and abutment arrangement
    • Soffit elevation, clearance, road elevation and freeboard
    • Backwater
    • Type of footing, scour depth and scour mitigation measure.
  • A summary of any modifications to the approach, the watercourse, private or public utilities (including drainage outlets), lands and structures.
  • The rationale for recommending the preferred alternative.
  • Cost. The evaluation and selection of a "best" alternate must include an economic analysis to ensure that the selected alternate provides the least total cost from a construction, maintenance, and operation standpoint.

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