Technical Reviews

SNC’s Role in the Planning/Development Approval Process

SNC is a Technical Review Agency to whom  member municipalities (the City of Ottawa, Prescott & Russell, Stormont, Dundas and Glengarry, Leeds and Grenville) delegates  review of material with regard to hydrogeology, drainage, and the natural environment. This can be in the form of Plan of Subdivision Proposals, Official Plan and Zoning Amendments, Severances, Site Plan Controls, and Minor Variances.

Recent amendments to the Planning Act and the updated Provincial Policy Statement (March 2005), has placed greater responsibilities on municipalities related to development. Conservation Authorities assist the municipalities with environmental review, and have staff expertise to provide this assistance.  

Although the Planning Act is the legislation that is most relevant to the land development process, along with the Provincial Policy Statement, SNC also utilizes other guidelines and data that are relevant to our review(s).

Some of the Technical Reports we comment on are:

• Plan of Subdivision Proposals

• Environmental Impact Studies

• Wetland Impact Studies

• Tree Retention/Conservation Plans

• Groundwater Modeling and Hydrogeological and Terrain Analysis

• Stormwater Management Plans

• Sediment and Erosion Control Plans

• Drainage Reports and Assessments

• Slope Stability Reports

• Organic Soils Reports

• Fish Habitat Assessments

• Natural Heritage and Natural Hazard Issues

Stormwater Management

In the past, stormwater management practices involved moving excess stormwater off-site as quickly as possible by using drainage systems to divert to the closest water body. However, this method however is not an appropriate way of dealing with excess water because you are simply moving one drainage problem to another location.

This approach can cause extreme erosion on our stream and river banks as well as causing flooding downstream. This can lead to a reduction in aquatic life, loss of property and human life.

Now, stormwater management mitigates the effects of urbanization on the hydrologic cycle including increased runoff and decreased infiltration of rain and snow melt. The overall volume is not reduced, instead it is detained to promote infiltration (recharging groundwater sources) and to ensure that stormwater runoff does not overload a receiving water body at once with a large amount of water.

Erosion and sediment control is also an important requirement with respect to Stormwater Management design. Erosion control measures include establishing vegetative cover or the use of engineered devices such as rip-rap and gabion baskets. Sediment control is obtained by using silt screens and straw bales to prevent sediment entering a receiving water course and harming aquatic life and potential fish spawning areas.

For more on Erosion and Sediment control please click here.

South Nation Conservation has a commitment and policy to plan and review on a watershed and subwatershed basis. The main objective of our reviews is to determine the project's acceptability from a watershed management perspective with respect to the quality and quantity of the receiving water body. By this we mean that the developer's plans are consistent with any policies that are supported by the CA considering the characterisitics and sensitivity of this water body.

For subdivision and site plan applications, a stormwater site management plan is required for review. Generally, these site management plans include details on best management practices, erosion and sediment control, and details for enhancement and rehabilitation of natural features. Where no subwatershed plan exists, SNC reviews site plans based on our Checklist and Requirements.

Stormwater Management Checklist and Development Requirements (PDF)

Sediment and Erosion Control Plan

Construction activities can adversely affect the aquatic environment as a result of sediment being released to natural receiving waters. The principal cause is removal of the vegetation that has been acting as a protective ground cover, leaving the soil exposed to uncontrolled runoff, wind and rain.

 In Canada, many provisions intended to prevent the degradation of water quality and damage to the aquatic environment are set in place by the Federal, Provincial and Municipal Governments and are also provided in Territorial Acts and Regulations.

Sediment and Erosion Control Plan Requirements
 

Considering the sensitivity of the development area, the Sediment and Erosion Control Plan should address:

• Necessary measures to prevent erosion by effective planning, procedures and water management

• Necessary measures to prevent the mobilization of sediment.

• Necessary erosion control measures to prevent off-site sediment release in the event of sediment mobilization.

• No new or increased erosion on receiving watercourses.

• Prevention of erosion and sedimentation into receiving watercourses during and after construction must be addressed.

• Inspection and maintenance of Sediment and Erosion Measures must be addressed. When, how, and how often (i.e. daily checks) must all be included as well as who will be responsible for inspection and maintenance of ponds, infiltration systems and other Best Management Practices (BMPs).

• The Sediment and Erosion Control Plan should identify location, design and schedule for appropriate BMPs and assign responsibilities for its implementation.

• In order to be effective the Sediment and Erosion Control Plan should be considered a “living document” that may need to be changed or adapted during the life of the project.

Sediment and Erosion Control Plan Checklist

 An Erosion Control and Sedimentation Control Plan should be prepared for all the developments in SNC’s watershed.

The plan will detail the following, but not be limited to: 

•   Soil types for the site

• Slope of all surface water conveyance systems

• An evaluation of potential for erosion based on soil type and velocities from hydraulic analysis

• Proposed sedimentation and erosion control measures to be used during construction as well as any required permanent measures.

• Sequence of installation of sedimentation and erosion control measures (temporary and permanent); and

• Responsibilities for maintenance of the sedimentation and erosion control measures during the construction period and in the long term (e.g. developer, contractor, and municipality).

  

Grading and Drainage Plan

Lot Grading and Drainage Plans are submitted to demonstrate how surface water will be conveyed throughout the study area. This is done to ensure that no low-laying areas are present which will cause problematic ponding of water or other drainage issues.

Grading and Drainage plans are also used as a tool to determine if, during a heavy rain event, a proposed development will have an adverse effect on the environment requiring their stormwater management plan to be revised.

A grading and drainage plan must be completed for all developments. Minimally, it must contain, but not be limited to:

• Both existing and proposed grade at corner of lots

• Final grade at building foundation wall

• Existing and proposed grade for all roads

• Show all drainage for lots and swales, catch basins, etc

• High point and low point of all roads

• Grading of any SWM facility and volume

• Ponding areas on roads, parking lots or rear yards (if any), and

• Plan must show an overland flow route to an adequate outlet. Major system flow must be conveyed without flooding of buildings and maintain a dry access during the 1:100 year flood.

Geotechnical and Slope Stability Reports

Whenever an application has been made regarding lands that are susceptible to erosion or slope instability, alteration to a waterway or development (fill or construction), it must be supported by a geotechnical engineer’s report to ensure that there will be no adverse effect on the “conservation of land” (the meaning of which includes consideration of whether the project will contribute to erosion and slope stability problems).

South Nation Conservation (SNC) acts in a peer reviewer capacity and advises the municipality on the merits of the application vis-a-vis Section 3.1 of the Provincial Policy Statement under the Planning Act.

Additionally, when the SNC is the proponent of an erosion control or slope stabilization project, we acquire the services of a geotechnical engineer to provide recommendations and advice on the design of the project.

The Conservation Authority’s review of a geotechnical engineer’s report is undertaken with the objective of:

• ensuring that the underlying purpose of the study (in a regulatory policy context) has been well understood by the engineer,

• ensuring that the assumptions and limitations of the analysis are well documented,

• confirming that the analytical methods and underlying assumptions are reasonable and appropriate given the situation, and     

• ensuring that the engineer’s conclusions are appropriately applied in the decision-making process.

CA reviewers use the following checklist:

• Has the erosion regime of the watercourse (stream banks and toe of slope) been characterized and accounted for in delineating hazardous areas and recommending safe setbacks?  If the stream banks and/or toe of slope are eroding, there are two basic options:  recommend larger setbacks in anticipation of lateral movement of the slope crest over time, or recommend stream bank or toe erosion protection.

• If stream bank or toe erosion protection works are recommended, has the method of protection been described in sufficient detail to determine whether or not they are appropriate and acceptable from a other perspectives (aquatic habitat management, flood plain hydraulics, riparian zone/valley system protection, etc.)?

• Have the field survey methods that were used been described and were they sufficient?

• Have soil properties been determined based on boreholes or test pits and in-situ or laboratory testing, and if so, was the sampling sufficient to reliably characterize the nature of the soils?  (On sites where there is greater variability in local subsurface conditions, more boreholes or test pits ought to be used).

•  If soil properties information has been “borrowed” from previous studies or empirical data, are the sources of the information clearly identified and has the use of that information instead of site-specific information from field investigations been justified?

• How was the slope geometry determined – from rod and level surveys, use of hand-held inclinometer, or reference to available contour mapping?  Is the characterization of slope geometry reasonable?  Have the most critical (steepest and highest) slopes on the site been used in the analysis?

• How were water table conditions in the slope determined – piezometers in boreholes, observation of moisture in exposed soil layers on slope face.  In the absence of site specific information, was it conservatively assumed that “full saturation” to ground level is a possibility, or was another assumption made and substantiated.

• Have the analytical methods that were used to determine the degree of stability (factors of safety) and appropriate setback distances been described?  Are the methods considered to be “established procedures” or “common practice”.  If the reviewer is not familiar with the method, does the report describe the basis of the method in sufficient detail to justify its application in this situation?  Is the analytical method appropriate given the nature of the soils and the probable mode of failure (cohesive vs. non-cohesive soils, potential for retrogressive failure in marine clays, deep-seated rotational failure vs. surficial sheet slide failure)?   The consultant should explain the rationale behind his/her choice of analytical methods. 

• Has the consultant made a clear recommendation regarding the degree of stability (factor of safety) that needs to be provided?  For new development applications, present guidelines suggest that a minimum factor of safety of 1.5 should be provided.  It should be recognized however that the selection of an appropriate factor of safety for a given situation should take into account the degree of uncertainty that is associated with the site conditions (subsurface soils and their engineering properties, water table, erosion, etc.), as well as the value of the infrastructure that may be at risk.  In cases where there are limited data from site-specific field testing and surveys, or where very expensive or important installations are potentially at risk, greater factors of safety may be warranted.  Likewise, where the infrastructure is more resilient and/or of less value, or where site conditions are known with a high degree of certainty, lower factors of safety may be warranted.  Generally, it is considered to be the responsibility of the consulting engineer to consider and recommend the factor of safety that should be applied in each case, and to substantiate the application of a Factor of Safety which is different from the default value (1.5).

• In cases where the objective of the analysis is to determine appropriate development setbacks, the report should include an explanation of how the setback should be applied in the land use and development control process – what restrictions should apply in the setback zone to provide an appropriate degree of protection to people, buildings and structures against risks associated with erosion and slope failures. 

• The reviewer should compare the setbacks recommended by the consultant with the conservative delineation of hazardous areas obtained by applying the guidelines contained in the Natural Hazards Technical Guidelines (considering toe erosion, stable slope and erosion access allowances).   If the site-specific geotechnical report is recommending less restrictive setbacks than would be obtained from the Technical Guidelines, the basis of that difference should be explainable (e.g. site specific analysis could support a smaller “stable slope allowance” based on a steeper stable slope than the 3:1 slope assumed in the guideline). 

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