Stormwater Management Requirements for Land Development Proposals

Identifying Drainage Impacts

Analyzing the Receiving Drainage System

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

MTO is primarily concerned with impacts to the highway drainage system. Wherever stormwater runoff discharging from the proposed land development may impact the highway drainage system, impacts to the highway right-of-way should be assessed, and the capacity of the highway drainage system must be checked.

However, MTO recognises that the property of riparian landowners located upstream or downstream of the highway right-of-way cannot be damaged by stormwater runoff discharging from the proposed land development. Even though this responsibility is within the mandate of the regulatory agencies, MTO may become liable if the stormwater runoff from the proposed land development is conveyed through a highway drainage system and damages any riparian property located upstream or downstream of the highway right-of-way.

For these reasons, MTO reserves the right to request that the proponent complete a hydrologic analysis and/or a hydraulic analysis of the proposed land development to determine if any drainage impacts will occur to the receiving drainage system, including the highway drainage system, as a result of the proposed land development. This task is completed in:

The MTO Regional Highway Planning and Design Office or the local MTO District Office may alter requirements presented in this document, since an extensive SWM report is not always required. MTO may make provisions to accept a drainage impact analysis that has a lower level of detail associated with it, provided that the proponent submits a plan showing how stormwater runoff from the proposed land development will be conveyed to the receiving drainage system. The proponent must be able to demonstrate that drainage impacts to the highway right-of-way or upstream/downstream riparian landowners will not occur, and that the capacity of the highway drainage system will not be exceeded as a result of stormwater runoff discharging from the proposed land development.


Identifying Components of the Receiving Drainage System

The SWM report should document all the components of the receiving drainage system that will convey stormwater runoff from the proposed land development. Documentation of the receiving drainage system should proceed to a location upstream and/or downstream of the proposed land development, where it can be shown that a drainage impact will not exist.

The SWM report should also include the specific information presented in Table 6: Components of the Receiving Drainage System for all of the identified components of the receiving drainage system.

The SWM report should also present the organisation or person responsible for the operation and maintenance, or stewardship of the identified components of the receiving drainage system. The following organisations or persons could have these responsibilities.

  • MTO (provincial highways): the SWM report should clearly identify which components of the receiving drainage system are part of the highway drainage system (contact the MTO Regional Highway Planning and Design Office for details). The existing highway drainage system could include:
    • highway bridges or culverts;
    • highway storm sewers or roadside ditches;
    • the highway major system;
    • highway stormwater management detention facilities; and
    • highway erosion protection works.
  • MNR (i.e. for crown land).
  • Local conservation authority (where they exist).
  • Local municipality or roads authority.
  • Federal Department of Transportation.
  • Riparian landowners.

Petition awards or municipal drains should also be identified, where they exist.

Table 6: Components of the Receiving Drainage System

Component Relevant Information to be Provided in SWM Report
stream channel systems (natural or man made) cross-section configuration, slope, lining material, alignment/meander pattern
trunk storm sewers tributary area and applicable information presented for storm sewers (see below)
storm sewers material (e.g. CSP, concrete, etc.), diameters, lengths, slopes, inverts, junctions, catchbasin and/or maintenance hole spacing and layout, and inlet/outlet configuration (e.g. head walls, wing walls, flared entrances, flow splitter, etc.)
roadside ditches cross-section configuration, slopes, inverts, ancillary structure (check dams, drop structure, etc.) andlining material
major system roadway surface, median drains, boulevards and storage areas within the right-of-way, swales, and channels or roadside ditches conveying the major storm runoff away from roadway to the receiving streams, channels, ravines trunk storm sewers or ponds
bridges soffit elevation, span arrangement, pier details, abutments, and superstructure
culverts culvert type (e.g. elliptical, box, open footing, etc.), culvert configuration (e.g. single barrel, double barrel, etc.), diameter or span/rise, length, slope, material (e.g. CSP, concrete, etc.), and inlet/outlet configuration (e.g. head walls, wing walls, flared entrances, etc.)
stormwater management facilities type of facility (wet, dry, extended wet, etc.), location and layout, size, length to width ratio, detention time, inlet and outlet configuration, emergency spillway, flow splitter/bypass location, type and capacity, maintenance access, special safety requirements,grading and planting strategy, maintenance procedures/responsibilities , setbacks from highway, and ownership
erosion protection works lining material/cover work, bank drainage, buffers strips, runoff diversions, drop structures, energy dissipators, stilling basins, chutes, retaining walls and check dams
dams size of reservoir, dam height, type, operational rule curve, spillway location, maintenance procedures/responsibilities, and ownership
waterbodies name, location
natural recharges or depression areas volume and location
tile drains location, property ownership

Where a suitable drainage outlet does not exist, and stormwater runoff is conveyed downstream as sheet flow, the sheet flow component should be presented in the SWM report as being part of the receiving drainage system, and assessed accordingly.

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Obtaining an Outlet to the Highway Drainage System

The SWM report should provide the location of the drainage system outlet for the proposed land development, and indicate the legal rights associated with that outlet. Conflicts with existing or future highway drainage works must also be noted.

Documenting Future Highway Drainage Works

Contact the MTO Regional Highway Planning and Design Office for information regarding future highway works. The SWM report should identify future highway drainage works that may be associated with any of the following:

  • new highways;
  • lane widenings;
  • addition of travelling, passing or truck climbing lanes;
  • addition of right or left turning lanes;
  • interchange or intersection improvements;
  • structure replacement and widenings;
  • roadside ancillary facilities; and
  • improvements to the existing highway drainage system.

Documenting if the Proponent Has the Right to Outlet to the Highway Drainage System

This section contains excerpts from PHY Directive B014 (PDF - 367 KB) (Policy Area 2: Drainage of Lands Owned by Others) which have been modified to suit the purposes of this document. This section does not replace PHY Directive B014 (PDF - 367 KB). Refer to PHY Directive B014 (PDF - 367 KB) when evaluating MTO drainage policy matters.

Before MTO permission is given to use the highway drainage system for a drainage outlet, the SWM report should document how the following requirements have been satisfied.
  1. The proponent is a riparian landowner.
  2. The drainage area that corresponds to the proposed drainage outlet is within the natural drainage tributary area (i.e. stormwater runoff is not being diverted).
  3. The proposed land development does not interfere with the rights of upstream or downstream riparian owners (including MTO) to drain their land.
  4. Any stormwater runoff that is proposed to be discharged into a highway drainage system shall not be allowed if the runoff may potentially contravene the mandate of another regulatory agency. If any regulatory agency advises that contravention has occurred subsequent to approval, the source may be disconnected by MTO on written request of that agency.
  5. The proponent has demonstrated satisfactorily that there is no feasible alternative solution.

Where any of the above noted conditions are not satisfied, the MTO reserves the right to reject any land development proposal that may be harmful to its interests (refer to PHY Directive B014 (PDF - 367 KB), Policy Area 2: Drainage of Lands Owned by Others). In such cases, an MTO drainage representative should be contacted for clarification.

Documenting if the Proposed Outlet Conflicts with the Highway Drainage System

The SWM report should clearly indicate whether the proposed outlet will conflict with the existing highway drainage system, or with any future highway drainage works. Where a conflict with future highway works has been identified, the SWM report must document how the conflict was resolved.

MTO does not generally allow drainage works associated with land development proposals to be located within the highway right-of-way, as they should be confined within the land development property boundaries; however where a mutual benefit is recognized, PHY Directive B014 (PDF - 367 KB) provides guidance. The MTO Regional Highway Planning and Design Office must be contacted before making such a recommendation. The following sections should be reviewed.

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Identifying Criteria that Regulate the Receiving Drainage System

Criteria used to regulate impacts to the receiving drainage system should be documented in the SWM report. Regulating criteria are presented below.

Highway Drainage Design Criteria

The SWM report must identify the design criteria for the components of the highway drainage system (i.e. that form part of the receiving 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 Highway Drainage Design Standards 2008 or refer to Design Criteria for Highway Drainage Works. Other highway design criteria may also be applied. Contact the MTO Regional Highway Planning and Design Office for further details.

Where a previous drainage study has been referenced for highway drainage design criteria, refer to Reviewing Previous Drainage Studies .

Other Drainage Design Criteria

The local conservation authority and/or municipality should be contacted for design criteria applicable to the component of the receiving drainage system for which they have operational and maintenance responsibilities.

Where a previous drainage study has been referenced for drainage design criteria related to other components of the receiving drainage system (i.e. other than the highway drainage system), refer to Reviewing Previous Drainage Studies.

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);
  • Provincial Water Quality Objectives (Ontario Water Resources 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 SWM 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 B014 (PDF - 367 KB) presents MTO drainage policy conforming to common law precedents. 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. The proponent must recognise that MTO will not approve a land development proposal if the riparian rights of any landowner may be infringed upon by the proposed land development.
  • PHY Directive B63 and PHY Directive B217: 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 land development. In such cases, the SWM report must document how the procedure in either directive was followed.

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 land development proposals include:

  • "Drainage Management Manual" (MTO 1997);
  • “Highway Drainage Design Standards” (MTO 2008);
  • “Stormwater Management Planning and Design Manual” (MOE 2003); 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 local jurisdiction.

Where Conflicts Exist between MTO and the Regulatory Agencies

As an agent of the crown MTO will not approve a land development proposal that will contravene the design criteria, drainage management policy, or the guidelines and manuals of the regulatory agencies, provided that the integrity of the highway drainage system is not compromised. Should any design criteria, drainage management policy, guideline or manual of a regulatory agency conflict with a design criteria, drainage management policy, guideline or manual of MTO, or vice versa, a meeting between the parties may be warranted to resolve the conflict.

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Identifying Existing Drainage Problems

Before proceeding with an impact assessment, any existing drainage problems that may be aggravated by stormwater runoff from the proposed land development must be identified.

Upstream or Downstream Riparian Property

The SWM report should identify any existing drainage problems, and associate each problem with the appropriate riparian property owner. Existing drainage problems could include:

  • flooding of property;
  • erosion of the stream bed and/or sediment accumulation.;
  • bank slumping;
  • degraded water quality; and
  • lack of a sufficient drainage outlet.

Visit the site, if possible, to assess drainage conditions in the area. Contact the local conservation authority, municipality, or the local MOE, MNR, or MTO office for information.

Highway Right-of-way

The SWM report should identify any existing drainage problems associated with the highway right-of-way, including:

Contact the local MTO District Office for information. Visit the site, if possible (permission from the local MTO District Office may be required).

Documenting Existing Drainage Problems

Having identified existing drainage problems, the cause of the problem should be assessed to determine the potential for further aggravation (refer to Assessing Impacts to the Receiving Drainage System). If existing drainage problems were not identified, the SWM report should document the steps taken to reach such a conclusion.

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Assessing Impacts to the Receiving Drainage System

MTO reserves the right to request that the proponent determine if any potential drainage impacts will occur to the property of upstream or downstream riparian landowners, including the highway right-of-way, as a result of the proposed land development. The SWM report should provide documentation on the following areas.

Hydrologic and Hydraulic Analysis of the Receiving Drainage System

Complete a hydrologic analysis and a hydraulic analysis of the receiving drainage system, for the pre-development scenario and the post-development scenario(s). The level of detail required in the analysis should be considered before proceeding. The goal of the analysis is to identify potential impacts to the property of upstream or downstream riparian landowners (including the highway right-of-way) which may result from the construction of the proposed land development. The analysis should calculate peak flows, water surface elevations and flow velocities, at different reference points and for the frequencies presented in table 7.

Table 7: Analysis of Receiving Drainage System

Reference points in the receiving drainage system: Parameters to be Calculated1 Range of Frequencies2
  1. Immediately upstream of the proposed land development; or immediately upstream of the proposed outlet to the receiving drainage system.1
    - And -
  2. Immediately downstream of the proposed land development; or immediately downstream of the proposed outlet to the receiving drainage system.1
    - And -
  3. Immediately upstream of the highway drainage system.
    - Or -
  4. Along the highway drainage system.3
    - And -
  5. Immediately downstream of the highway drainage system.
    - And -
  6. control point located downstream of the highway right-of-way.
    - And -
  7. Where a known drainage problem(s) have been identified either in the highway right-of-way; and/or upstream or downstream of the highway right-of-way.
  • peak flows
  • water surface elevations
  • flow velocities
  • run-off volumes5
  • low flows4
  • 2 yr
  • 5 yr
  • 10 yr
  • 25 yr
  • 50 yr
  • 100 yr
  • Regulatory Storm

Notes:

  1. Where the peak flows discharging from the proposed land development will be controlled on-site via stormwater management controls at pre-development levels for range of frequencies specified, reference points i), ii) and/or iv) need only be analyzed.
  2. Where the specified range of frequencies or number of reference points in the receiving drainage system is reduced, the SWM report should clearly document the rational used to reduce the level of detail.
  3. May be required when stormwater runoff from the proposed land development discharges directly into the highway surface drainage system.
  4. May be used for water quality controls, fish habitat requirements or for erosion protection works.
  5. Optional: may be required where a sufficient outlet does not exist.

The SWM report must present peak flows, water surface elevations, and flow velocities, calculated for the range of frequencies and reference points presented in Analysis of Receiving Drainage System - Table 7. A table should be presented that compares the results for the pre-development scenario to the results for the post-development scenario(s). Any differences must be clearly presented.

Check the Capacity of the Highway Drainage System

The SWM report should include documentation regarding the capacity of the highway drainage system. Refer to Design Criteria for Highway Drainage Works for more information on appropriate criteria or contact the MTO Regional Highway Planning and Design Office for details. By completing the following tasks, the capacity of the highway drainage system can be checked.

Documenting Computational Methodology

The SWM report should document the computational methodology used to analyze the components of the receiving drainage system, including the highway drainage system (refer to Computational Methods). The SWM report should also document which method was selected, why it was applicable and include any assumptions that were part of the computation. In addition, include the information presented in table 8.

Table 8: Documenting the Computational Methodology

Computational Method Documentation in SWM Report
method used, applicability and assumptions
method used, applicability and assumptions, the selection of input parameters used in the flow rate calculation
the type (synthetic, historic, IDF, continuous, etc.), meteorologic station, storm duration (where applicable) and the discretization time step (where applicable).
method used, applicability and assumptions, performance curves, and input parameters (expansion/contraction coefficients, roughness coefficients, etc.)
method used, applicability and assumptions, input parameters (expansion/contraction coefficients, roughness coefficients, etc.), and starting water surface elevations
method used, applicability and assumptions, and stage-storage-discharge relationship

Identifying Impacts to the Receiving Drainage System

Impacts to the receiving drainage system will not occur if the analysis of the receiving drainage system determined that the proposed land development would not:

  • increase peak flows, water surface elevations, or flow velocities at the reference points and range of frequencies specified in Analysis of Receiving Drainage System - Table 7; or
  • cause the capacity of the highway drainage system to be exceeded.

In such a case, MTO will not require mitigation. The SWM report should clearly document the results of the analysis, and rationalise that impacts to the receiving drainage system will not occur. It should be recognised that mitigation may still be required by other regulatory agencies.

Impacts to the receiving drainage system will occur and mitigation may be required by MTO if the analysis of the receiving drainage system determined that the proposed land development does not satisfy either of the conditions noted above.

Recommending Mitigative Works

The SWM report should clearly present an assessment of the identified impacts with regards to risk. Each impact should be compared against the risk criteria listed below.

Risk Criteria: where each of the identified impacts do not satisfy all of the following risk criteria, MTO will require that mitigation be provided for that impact (the required level of mitigation must then be established):

  • damage will not occur to the property of riparian landowners located upstream or downstream of the highway right-of-way;
  • the structural integrity of the highway right-of-way will not be threatened; or
  • the safety of the travelling public will not be threatened.

The Level of Mitigation: the SWM report must clearly present the following;

Where a conflict with future highway works has been identified, the SWM report must document how the conflict was resolved, which may only be achieved by applying one of the methods presented above.

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