Ministry of Transportation / Ministère des Transports
Text size Enlarge Text Shrink Text
Search Search  |  

Drainage Management - Glossary of Terms

A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z


A

Allowable Headwater Level (for culverts and bridges):
Maximum depth of flow allowed by MTO at the upstream face, measured from the invert, minus the required freeboard.
Allowable Headwater Level (for roadside ditches):
Maximum depth of flow allowed by MTO at the any point along the ditch profile, measured from the invert, minus the required freeboard.
Allowable Headwater Level (for stormwater management detention facilities):
Maximum depth of flow allowed by MTO at the upstream face of the outlet structure, measured from the invert, minus the required freeboard.
Allowable Storage Volume:
The maximum volume of a stormwater management detention facility corresponding to a depth of water up to the embankment of minus the freeboard.
Approval in Principle:
Is a permit or Condition of Approval clearance that is not yet final, and is contingent upon certain conditions that must be met prior to the issuance of the final approval.
AES IDF Curve:
An intensity-duration-frequency curve derived by the Atmospheric Environment Service.
Attenuation of Hydrograph Peak:
A reduction in the peak caused by friction losses and storage in a stream channel, or by the storage in a reservoir, determined by routing the hydrograph through the stream channel or reservoir.

Top of page   Top of page


B

Backwater:
An increase in the water level caused by a downstream constriction or obstruction.
Bankful Discharge:
The discharge that fills a channel to the point of overflowing.
Base Flow:
The flow of water in a watercourse due to soil moisture or ground water.
Bridge or Culvert Outlet:
The cross-section of the bridge or culvert structure after which the water immediately enters the receiving drainage system.
Building and Land Use Permit:
A permit issued by MTO under the jurisdiction of the Public Transportation and Highway Improvement Act, when a structure is to be placed within the highway corridor control area. Contact the local MTO District Office for more details.

Top of page   Top of page


C

Carryover:
The flow in a gutter that overshoots an inlet.
Catchbasin:
A basin of concrete or other material, covered by a grate, and located in a gutter or ditch to intercept stormwater for transmission to a sewer or other outlet.
Catchment Areas:
The total area of land radiating from a reference point, including all drainage work and stream channels, contributing stormwater runoff.
Channel Routing:
A procedure for transferring a hydrograph from one point to another along a watercourse. The process transfers the hydrograph by accounting for storage and friction losses in the stream channel.
CHBDC:
Canadian Highway Bridge Design Code - provides requirements for the design and construction of highway bridges. This design code is adopted in all the provinces in Canada.
Check Flood:
A flood used to check that a bridge designed for the normal design flood will withstand flooding without structural failure.
Check Flow Rate:
The flow rate used to determine whether a waterway designed for normal design flow will withstand a larger flood without embankment or structural failure.
Computational Time Step:
The time interval that the flow rate is continually calculated (during the rainfall convolution process), to produce a series of flow co-ordinates (i.e. runoff hydrograph).
Conditions of Approval:
A condition placed on a Draft Plan of Subdivision or Site Plan that must be satisfied before the proposed land development will be approved.
Confluence:
The location where two or more stream channel systems combine to form a single system.
Constructed Wetlands:
Storage areas that have been designed and constructed to provide wetland function. Such facilities have been reported to be effective methods for stormwater quality control.
Control Point:
A location in the receiving drainage system where the water surface elevation is known.
Corridor Planning:
The planning and implementation of policies that govern the areas adjacent to highway systems.
Critical depth:
Is the depth in a channel for which the specific energy is a minimum.
Culvert:
A conduit, usually covered by fill, whose primary function is to convey surface water through an embankment.
Curb and gutter section:
A roadway gutter section in which the curb and gutter are integral.
Curve Number (CN):
A number between 0 and 100 which indicates the runoff-producing potential of a soil/vegetation combination when the ground is not frozen.

Top of page   Top of page


D

Design Capacity:
The flow rate drainage works is designed to convey based on the design frequency or return period, such that the depth of flow, headwater level or water surface elevation will be at or below the maximum level permitted by MTO.
Design Flood:
The flow frequency criteria used to determine the capacity of drainage works. Refer to Highway Drainage Design Standards (MTO 2008) for more detail.
Design Flow Capacity:
The flow frequency criteria used to determine the capacity of drainage works. Refer to Highway Drainage Design Standards (MTO 2008) for more detail.
Design Flow Frequency:
The flow frequency criteria used to determine the capacity of drainage works. Refer toHighway Drainage Design Standards (MTO 2008) for more detail
Design Flow Rate:
The flow rate that determines the size of drainage works.
Design Storm:
A specified amount of storm rainfall, with its areal and temporal distribution, used to estimate a design discharge.
Detail Design Report:
A report that documents the detailed design of highway works
Detail Planning:
The final planning stage that incorporates all aspects of a project to provide enough information to go through with implementation.
Detention:
The short-time storage of stormwater, such as in ponds or depressed parking lots, as a means of reducing flood peaks. Also the temporary natural storage of flood water in lakes and wetlands.
Detention Facility:
A structure that has the capacity to store stormwater.
DFO:
Federal Department of Fisheries and Oceans.
Directly Connected:
The surface area of a catchment that is connected to a drainage works via a below ground pipe.
Discretization:
The breaking up of a drainage basin into homogeneous sub-components, channels and reservoirs.
DMM:
"Drainage Management Manual" (MTO 1997)
DOE:
Federal Department of the Environment
DPD:
Derived Probability Distribution Method
Draft Plans of Subdivision:
A plan of the proposed land development area that shows the lots that are to be severed from the original property and sold as individual parcels of land.
Drainage Basin:
Synonyms: Catchment area, hydrologic basin; river lake; ground-water basin. The area tributary to or draining to a lake, stream, reservoir, or other body of water
Drainage Impacts:
Damage to property caused by flowing water.
Drainage Management:
The method of managing the flow of water by controlling surface and/or subsurface drainage.
Drainage Outlet:
A segment of the receiving drainage system that will convey stormwater runoff from upstream lands, and convey that runoff to another downstream segment of the receiving drainage.
Drainage Practice:
The act or process used to design drainage works.
Drainage Practitioner:
A professional who is familiar with the drainage practice.
Drainage Problems:
Damage to riparian property caused by flowing water, or any threat to public safety.
Drainage System:
The system of conduits and structures, natural or man made, the purpose of which is to convey water to a suitable outlet.
Drainage Works:
Any structure or object that forwards, holds back or diverts water. These include steam channels, stormwater management control works, major systems, minor systems, truck storm sewers, water crossings and erosion protection works.
Dry Ponds:
An active storage device used to detain water during a storm event, and releasing it at a rate that is selected to minimise water quantity impacts (e.g. flooding).
DTO:
The Federal Department of Transportation.

Top of page   Top of page


E

Encroachment Permit:
A permit issued by the MTO under the jurisdiction of the Public Transportation and Highway Improvement Act.
Environmental Study Report:
A report that documents the alternatives studied, methods used and the recommended alternative, completed as a requirement of the Environmental Assessment Act.
Erosion:
The process by which soil is eroded from land or a streambed and banks (e.g. streambed deepening or bank slumping).
Erosion Protection Works:
Measures that provide protection against erosion. These include grade modifications, lining material/cover work, bank drainage, buffers strips, runoff diversions, drop structures, energy dissipators, stilling basins, chutes, retaining walls, or check dams.
Extended Dry Detention Ponds:
A stormwater storage device that consists of an active storage volume. Unlike a wet pond it does not have a permanent pool. An extended dry pond can only remove solid particles and not dissolved contaminants. The difference between an extended dry pond and a dry pond, is that the release rate of the extended dry pond is selected to mitigate water quality impacts, while the release rate of a dry pond is selected to mitigate water quantity impacts (e.g. flooding).

Top of page   Top of page


F

Final Approval:
The approval granted by issuing a permit or clearing a Conditions of Approval in writing.
Flooding:
The depth of flowing water that can cause damages to structures, or will threaten the safety of the public.
Flood Damage Reduction Program Studies (FDRP):
Flood plain mapping studies completed through a program funded by federal and provincial governments.
Flood Plain:
The area, usually low lands adjoining a watercourse, which has been, or may be, covered by flood water (MNR).
Flood Wave:
Is a wave moving downstream generated as a result of precipitation on a catchment area.
Flow Depth (along the highway surface):
The depth of flowing water along the roadway surface.
Flow Velocity:
The speed of water flowing in any drainage works, measured in units of distance over time.
Freeboard:
A safety factor used in the design of drainage works. It defines the distance between the design water surface and a designated elevation of a structural element (e.g. edge of pavement).
Free Flow Condition:
The flow condition in which water flows in a drainage works unaffected by a downstream condition.
Free Water Surface:
The water surface that is open to the atmosphere.

Top of page   Top of page


G

Grassed Ditches and Swales:
Ditches and swales lined with grass used to improve runoff quality by filtering suspended sediment and heavy metals within the surface drainage system.

Top of page   Top of page


H

Hazard Land:
Property that may be exposed to potential damages from naturally occurring events such as: flood flows in rivers or streams; high water levels in lakes; unstable banks, bedrock and soils; or erosion. Refer to "Provincial Policy Statement, Public Health and Safety Policies 3.1 (MNR, 1997)".
Headwater level:
Is the water level upstream of a culvert or bridge
HEC2:
Hydrologic Engineering Center - 2
HEC-RAS:
Hydrologic Engineering Center's River Analysis System
Highway Corridor:
The limits of MTO jurisdiction as mandated by the Public Transportation and Highway Improvement Act, or permit control area.
Highway Design Office (Drainage and Hydrology):
An MTO Office, part of the Engineering Standards Branch. It is responsible for the development of drainage standards, manuals and policies as well as providing technical assistance to the regional offices and consultants.
Highway Design Report:
A report that documents any design of highway works.
Highway Drainage System:
Drainage works used to convey and treat stormwater runoff from the highway surface and discharge it to a receiver or pass stream flow across the highway right-of-way.
Highway Drainage Works:
Drainage works that form part of the highway system.
Highway Flooding:
Occurs when the capacity of the minor system is exceeded and water begins to flood the highway surface.
Highway Infrastructure:
The systems, structures and elements that constitute the highway transportation network.
Highway Overtopping:
See
  • Northern Region - North Bay;
  • Northwestern Region -Thunder Bay; and
  • Southwestern Region - London.
MTO Regional Structural Section:
The regional office that is responsible for the design and maintenance of local highway structures.
Municipal Drainage System:
Drainage systems that are under the responsibility of a municipality.
Municipal Drains:
Drains that come under the authority of the Drainage Act.
Municipality:
A local government, commonly referred to as a city or town.

Top of page   Top of page


I

IDF curve:
Intensity-Duration-Frequency curves (or tables) that provide the rainfall intensities corresponding to specified rainfall event durations and frequencies of occurrence.
ILLUDAS:
ILLinois Urban Drainage Area Simulator
Impact Assessment:
The process of assessing the potential for damages to property or to public safety as a result of extreme events that are in excess of the design condition(s).
Impervious:
A term applied to a material through which water cannot pass, or through which water passes with great difficulty.
Imperviousness Ratio:
The ratio of the total paved areas connected to the minor drainage system to the total catchment area.
Infiltration Techniques:
Measures used to enhance infiltration of water into the ground. These include infiltration basins, infiltration trenches and porous pavement.
Inlet:
A storm sewer inlet consisting of a vertical opening in the face of a curb into which gutter flow passes.
Interpolation:
A storm sewer inlet consisting of a vertical opening in the face of a curb into which gutter flow passes.

Top of page   Top of page


L

Land Development:
A parcel of land that is to be altered from its current state by the construction of a structure(s).
Land Development Proposal:
A proposal to develop land.
Land Use:
The surface condition of a catchment area (e.g. natural, farm land, residential properties, etc.)
Low Flow Events:
A flow event that has a probability of occurance equal to or less than once every 2 years.

Top of page   Top of page


M

Major Drainage System:
The route followed by runoff when the capacity of the minor drainage system is exceeded. The major drainage system consists of the roadway surface, median drains, boulevards, and storage areas; drainage swales, channels or roadside ditches conveying the major storm; or trunk storm sewers.
Major Flows:
Flows in excess of the minor drainage system capacity, resulting from large storms.
Major Storms:
Historic large storms or rare events (with low probability of occurrence 1-100 year or more) that result in major flows.
Major System:
The route followed by runoff when the capacity of the minor drainage system is exceeded. The major drainage system consists of the roadway surface, median drains, boulevards, and storage areas; drainage swales, channels or roadside ditches conveying the major storm; or trunk storm sewers.
Maximum Possible Elevation:
The highest water elevation the will be allowed under any circumstances after which the impacts cannot be accepted. This is not what the system will be designed to.
MIDUSS:
Micro Interactive Design of Urban Stormwater Systems
MIFM:
Modified Index Flood Method
Minor Drainage System:
The drainage system provided to accommodate relatively minor floods (2 to 10 year return period), and comprising the gutters, catchbasins, storm sewers, and minor channels.
Minor System:
Collects runoff that results from the more frequent storm events (2yr to 10yr), and conveys the runoff to the outlet at the drainage system. In urban settings, the minor system typically consists of curbs, gutters, catchbasin inlets, storm sewers, minor drainage swales and roadside ditches. In rural settings, the minor drainage system generally consists of roadside ditches and minor drainage swales. It can also include curbs, gutters, and catchbasin inlets; however these components are less frequently used in rural settings.
Mitigative Works:
Drainage works used to prevent drainage impacts. (eg. ponds or swales).
MMAH:
Ontario Ministry of Municipal Affairs and Housing.
Modern Drainage Management Approach:
Method of managing drainage systems using the most up to date procedures which take current drainage practices into account.
MNR:
Ontario Ministry of Natural Resources.
MOE:
Ontario Ministry of the Environment.
MTO:
Ontario Ministry of Transportation.
MTO Bridge Office:
The functional office within the Engineering Standards Branch of MTO which is responsible for the different aspects associated with the design of bridges. The office is located in St. Catharines, Ontario.
MTO IDF curve:
Curves (or tables) expressing the rainfall intensities for specified durations and frequencies.
MTO District Office:
Are located in each region of the MTO. They include:
  • Central Region - Manager of Corridor Management Office, Downsview;
  • Eastern Region - District No. 41 (Kinston), District No. 42 (Ottawa), District No. 43 (Bancroft);
  • Northern Region - District No. 53 (Cochrane Area Office), District No. 52 (Huntsville), District No. 53 (New Liskeard), District No. 54 (North Bay), District No. 54 (Sudbury),;
  • Northwestern Region - District No. 61 (Thunder Bay), District No. 62 (Sault Ste Marie); and
  • West Region - District No. 31 (London/Stratford), District No. 32 (Chatham), District No. 33 (Owen Sound).
MTO Documentation Requirements:
Requirements pertaining to design methodology, impact assessment, operation and maintenance responsibilities, computational methodology, statutory mandates, or common law.
MTO Drainage Policy:
Policies that govern the drainage activities of the Ministry of Transportation. It includes policies that are described in Directives, and policy statements.
MTO Drainage Practice:
Practices defined through the MTO Drainage Directives, manuals and guidance tools such as the "Drainage Management Manual" (MTO 1997), and the Web guide "MTO SWM Requirements for Land Development Proposals" (1999).
MTO Drainage Representative:
For all Regions of MTO the drainage representative is the Sr. Drainage Engineer, Highway Design Office (St. Catharines). In Central Region, the drainage representative is the Sr. Drainage Engineer, Engineering Office (Downsview).
MTO Highway Design Office:
The functional office within Engineering Standards Branch of MTO responsible for the different aspects associated with the design of highways. The office is located in St. Catharines, Ontario.
MTO Regional Design Section:
See: MTO Regional Highway Planning and Design Office
MTO Regional Planning Section:
See MTO Regional Highway Planning and Design Offices
MTO Regional Planning and Design Section:
See MTO Regional Highway Planning and Design Offices
MTO Regional Highway Planning and Design Office:
The office in each region of MTO that is responsible for the planning and design of provincial highways. Highway corridor management responsibilities are assigned to designated Corridor Management Officers, except for Central Region where the corridor management responsibilities are assigned to designated Permit Officers. The regional office locations are:
  • Central Region - Downsview;
  • Eastern Region - Kingston;
  • Northern Region - North Bay;
  • Northwestern Region -Thunder Bay; and
  • West Region - London.
MTO Regional Structural Section:
The regional office that is responsible for the design and maintenance of local highway structures.
Municipal Drainage System:
Drainage systems that are under the responsibility of a municipality.
Municipal Drains:
Drains that come under the authority of the Drainage Act.
Municipality:
A local government, commonly referred to as a city or town.

Top of page   Top of page


N

Natural Depression Areas:
Natural areas of varying shapes and sized that trap a portion of precipitation resulting in a reduction in runoff
Natural Drainage System:
A non-constructed drainage system
Natural State:
Unaffected by humans
Natural Watercourse:
A watercourse created by the natural flow of water
Non-uniform flow:
The flow condition in which the velocity and depth of flow for a given flow rate varies along a channel or conduit.
Normal Depth:
The depth of water in a channel under steady uniform flow conditions where the water surface is parallel to the channel bed.
Normal Water Level:
The average summer water level.

Top of page   Top of page


O

Official Plans:
A municipal planning document that sets out general policies for current and future land use for the entire municipality
Oil/Grit Separators:
Are a preliminary treatment device long used in treating stormwater runoff where concentrations of oil and grit are high. Examples of appropriate applications are discharges from restaurant kitchens, abattoirs, meat processing plants and oil refinery storage yards.
OMAF:
Ontario Ministry of Agriculture and Food
Open Channel:
A channel that conveys water with a free water surface (water flows under the influence of gravity).
OTTHYMO:
OTTawa HYdrologic MOdel
OTTSWMM:
OTTawa StormWater Management Model

Top of page   Top of page


P

Peak Flow Rate:
The point in the runoff hydrograph where the flow rate is at its highest value.
Performance curve:
A graph of flow plotted against water surface depths.
PHY:
Provincial Highway.
PHY Directive B63:
An MTO directive issued under the authority of the Public Transportation and Highway Improvement Acts that outlines MTO participation in works administered through the Drainage Act.
 
PHY Directive B217:
An MTO directive issued under the authority of the Public Transportation and Highway Improvement Acts that outlines Private piped drain on the highway right-of-way.
PHY Directive B014:
An MTO directive issued under the authority of the Public Transportation and Highway Improvement Acts that outlines MTO drainage management in highway right-of-way.
Plan of Subdivision
A plan that creates two or more lots or blocks and usually involves the creation of new streets.
Post-development Condition:
See post-development scenario.
Post-development Scenario:
The characteristics of a land development site that reflect the state of the site after the land development has taken place.
Pre-development Condition:
See pre-development scenario.
Pre-development Scenario:
The characteristics of a land development site that reflect the state of the site before the development has taken place.
Preliminary Design Report:
A report that describes the general design approach for a project.
Pressure Flow:
Flow in a conduit with no free surface.
Proponent:
The persons, or a representative, who owns the proposed land development.

Top of page   Top of page


Q

QUALHYMO:
QUALity HYdrological MOdel

Top of page   Top of page


R

Rainfall Time Step:
The time increment to which a storm event duration is divided for hydrologic analysis purposes.
Range of Frequencies:
A range of expected occurrences of an event within a specified period (e.g. 1 per year, 1 every 10 years)
Receiving Drainage System:
Is a drainage works, or a sequence of drainage works, that conveys stormwater runoff.
Recession Constant:
A constant value that defines the shape of the receding portion of a runoff hydrograph.
Recharge Areas:
Areas in which water infiltrated to an aquifer, usually from above
Reference Point:
A location of known hydraulic characteristics.
Regulatory Agency or Regulatory Agencies:
The federal, provincial or municipal organisations having a drainage management mandate as defined in a federal or provincial statute law, or in a municipal by-law.
Regulatory Flood:
The approved standard(s) used in a particular watershed to define the limit of the flood plain for regulatory purposes (MNR). Refer to Highway Drainage Design Standards (MTO 2008) for more more details.
Regulatory Flow:
A flow generated by a storm designated by MNR for flood plain management purposes in a given zone, as outlined in Highway Drainage Design Standards (MTO 2008).
Regulatory Flow Rate:
The flow rate used to determine the limits of the flood plain. It is generated by the regional storms, as defined by MNR. In certain circumstances it can be used as the design flood.
Regulatory Storm:
Storm events that have been selected as the approved standard(s) to be used in particular watershed(s) to define the limits of the flood plain for regulatory purposes (MNR).
Regulatory Storm Flow Rate:
The flow rate for the runoff resulting from applying a regulatory storm to a catchment area.
Relief flow:
The flood flow that bypasses the main structure at a stream crossing by flowing over the roadway or through a relief culvert or bridge.
Reservoir:
A body of water.
Return period:
The average period in years between the occurrences of consecutive events (e.g. rainfall events) of a given magnitude (also termed Recurrence Interval).
Riparian Landowner:
The owner of land along a watercourse, and it relates to rights associated with water, its use, ownership of soil under the stream, accretion, etc.
Riparian Property:
The land along a watercourse.
Roughness Coefficient:
A numerical measure of the frictional resistance of a surface to the flow of water.
Routing:
A procedure for transferring a hydrograph from one point to another along a watercourse or across a reservoir or pond.
Route Planning:
The extensive planning of the placement of highway systems.
Runoff:
See Stormwater runoff.
Runoff Coefficient:
The fraction of runoff that flows through the system after taking into account depression storage and interception factors, such as infiltration and evaporation.

Top of page   Top of page


S

Scour:
Local lowering of a streambed by the erosive action of flowing water. (MTC)
Scour Depth:
The depth of material removed from a streambed by scour, measured from the original bed elevation. (MTC)
Scour Protection Works:
Constructed measures to protect the streambed and banks against localised erosion due to the flow of water.
Secondary Plans:
Similar to an official plan, a secondary plan deals with a specific area within a municipality by providing more detailed land use policies.
Setback:
The distance between the nearest extremity of an object such as a building or structure under consideration for development and the centreline or property line of the highway.
Sign/Signage Permit:
A permit issued under the jurisdiction of the Public Transportation and Highway Improvement Act for any sign that is to be placed within certain distances from the highway right-of-way. Contact the local MTO District Office for more information.
Single Station Frequency Analysis Methods:
Stream flow analysis that utilizes the data from a stream guage station to determine the flows corresponding to different return periods. The analysis also ensures that suitability of the data used in the analysis.
Site Plans:
A plan that indicates specific details of a proposed development including placement of buildings, parking areas, landscaping, onsite lighting, etc.
Soffit Elevation:
The elevation of the lowest point of the undersurface of the superstructure of a bridge or culvert.
Soils Condition:
Type, stratigraphy, cover and degree of wetness of the soil.
Stage-storage-discharge:
Relationship is the mathematical representation of a channel or reservoir determined by quantifying the volume of storage for various stages of depth or elevation; and by the hydraulics of the reservoir or channel to determine flow rates at the various stages of depth or elevation.
Standards of Practice:
Design standard as defined in manuals, peer reviewed documents that have been also adopted for sufficient time.
Starting Water Surface Elevation:
The water surface elevation at a point from which other water surface elevations are deduced using hydraulic calculations
Station Frequency Analysis:
A frequency analysis of flow records at an individual stream gauging station.
Steady Flow:
Flow in which the discharge at a given point remains constant with time.
STORM:
Storage, Treatment, Overflow, Runoff Model
StormCAD:
Storm Sewer Design Modeling Software
Storm Duration:
The length of time during which rain falls is assumed to fall for the purpose of modelling the catchment response (runoff).
Storm Sewer Inlet:
A device used to control the flow of water into the minor drainage system.
Storm Sewer Outlet:
The end works controlling the flow of water from a stormsewer pipe.
Stormwater Management:
The procedures or methods used to design drainage works used to reduce the potential for flooding, erosion, or ensure that the safety of the public will not be threatened.
Stormwater Management Controls:
Storage or conveyance facilities that provide quantity or quality controls of stormwater. These include dry ponds, wet ponds, extended dry detention ponds, constructed wetlands, parking or roof top storage, grassed swales and ditches, infiltration techniques, oil and grit separators, and vegetated buffer strips.
Stormwater Management Detention Facilities:
Storage facilities that detain stormwater for a time and release it gradually. These include dry ponds, wet ponds, extended dry detention ponds, and constructed wetlands.
Stormwater Management Quality Controls:
Storage facilities that provide for improvement to the water quality using physical, biological or chemical process. These include wet ponds, extended dry detention ponds, and constructed wetlands.
Stormwater Management Quality Control Detention Facilities:
Storage facilities that provide improvement to stormwater quality using physical, biological or chemical process. These include wet ponds, extended dry detention ponds, constructed wetlands and other devices.
Stormwater Management Quantity Controls
Storage facilities that retain or detain stormwater for a time and release it gradually. These include dry ponds, wet ponds, extended detention ponds, infiltration devices and constructed wetlands.
Stormwater Management Quantity Control Detention Facilities:
Storage facilities that retain or detain stormwater for a time and release it gradually. These include dry ponds, wet ponds, extended detention ponds, infiltration devices and constructed wetlands.
Stormwater Management Report:
A document that presents the data, methods, procedures and results of the design of drainage works and erosion protection measures.
Stormwater Runoff:
Is the portion of rainfall that moves over the ground toward a lower elevation and does not infiltrate into the soil.
Stream Channel System:
An open channel or watercourse consisting of a number if reaches that are natural or artificial. Generally, natural stream channels have cross-sections of irregular shapes that reflect the geomorphic processes in the stream. Artificial stream channel systems are generally prismatic sections of rectangular, trapezoidal and triangular cross-section and do not vary with distance along the stream channel.
Subcritical flow:
A flow condition where the velocity is greater than the critical velocity and the depth is less than the critical depth.
Sufficient Drainage Outlet:
A point at which water can be discharged safely so that it will do no damage to lands or roads.
Supercritical flow:
A flow condition where the velocity is less than the critical velocity and the depth is less than the critical depth.
A Surcharged Condition:
The condition in which the depth of flow in any portion of a storm sewer exceeds the storm sewer obvert. Causes include a flow rate that exceeds the design flow capacity of the storm sewer or a backwater effect caused by a downstream condition. In surcharged conditions, roadway flooding may occur.
Surcharge:
The flow condition occurring in closed conduits when the hydraulic grade line is above the conduit crown; or the transition from open channel to pressure flow.
Surface Drainage Systems:
The drainage system comprised of the major system and the minor system and may include inlet and outfall structures and erosion protection works.
Surrounding Environment:
The different features and functions in the area around the area in question, which can be impacted of have an impact on the highway or drainage system.
Synthetic Design Storm/Storm Event
A design storm for which the time distribution of the rainfall is derived from generalised data.
SWM Report:
A stormwater management report is a document that presents the data, methods, procedures and results of the design of drainage works and erosion protection measures.
SWMMIV:
StormWater Management Model -4

Top of page   Top of page


T

Tailwater Level:
The water surface elevation immediately downstream from a culvert or bridge structure, measured from the invert of the structure.
TC:
Transport Canada
Time of Concentration:
The time taken for a flow wave to travel from the farthest point of a basin to the location under consideration, the farthest point being determined on the basis of travel time and not necessarily distance.
Time to peak:
The time from the centre of mass of a rainfall distribution to the peak of the resulting flow hydrograph.
Timmins Storm:
A storm that occurred over Timmins in September 1961. It is a 12 hour storm that was selected to be used for regulatory purposes in North and Central Ontario.
Total imperviousness:
The total area within a catchment area in which water runs off the surface without infiltrating into the ground
Total imperviousness ratio:
The ratio of the total paved and roofed areas to the total catchment area.
Tributary Area:
The portion of a watershed contributing runoff to a particular point in that watershed.
Transposing:
A mathematical procedure for transferring the data collected at one location to another location having similar characteristics.
Trunk Storm Sewers:
Sewers constructed to replace natural stream channel systems. They are generally designed to convey runoff from the more severe storm events (25-year to the regulatory storm).

Top of page   Top of page


U

Uniform flow:
The flow condition in which the velocity remains unchanged in both magnitude and direction along a channel.
Unit hydrograph:
A hydrograph resulting from a storm of selected duration that produces unit depth of direct runoff.

Top of page   Top of page


V

Vegetated Buffer Strips:
Grassed or forested vegetation designed to intercept sheet flow and filter contaminants from the runoff prior to the flow entering the surface drainage system.
Velocity Head:
The energy component associated with the motion of water (numerically it is a function of the velocity of flow).

Top of page   Top of page


W

Waterbodies:
Any natural or constructed body of water including: lakes, ponds, streams, channels, wetlands, etc.
Watercourse:
A stream, river or channel in which a flow of water occurs, either continuously or intermittently, with some degree of regularity.
Water Crossing:
A culvert or bridge structure used to cross a water body.
Watershed Areas:
Is the area of land that drains to a single outlet and is separated from other watersheds by a divide.
Watershed, Subwatershed and Master Drainage Plans
Documents that study drainage management issues for larger scale areas, to specify environmental and servicing requirements.
Water Surface Elevations:
The various depths of flowing water, measured to a common datum (e.g. stream channel invert, sea level, etc.), at prescribed locations (e.g. cross-section, catchbasins, etc.) along a water crossing, minor system, major system, or stream channel system.
WSPRO:
Water-Surface PROfile Computational Model
Wet Ponds:
A stromwater management control device consisting of a permanent pool of water that never drains (except during maintenance), and an additional storage space, on top of this pool, to hold the runoff that enters the pond in a storm event. The stored water is gradually released to a receiving water body. The permanent pool provides extended settling time equal to the interval time between storms, and allows the dilution of the discharge during a storm event by mixing the incoming flow with the existing pool of water (clean water).

Top of page   Top of page


Z

Zoning By-laws:
A law passed by a municipal council under the jurisdiction of the municipal Act or the Planning Act.

Top of page   Top of page