Staff Report # 2436/06
November 23, 2006
Memorandum
To: The Chair and Members of the Board of Directors Mississippi Valley Conservation
From: John Price, P.Eng.
Watershed Management Coordinator
Re: Shirley’s Brook Two-Zone Policy
City of Ottawa (Kanata)

Shirley’s Brook is one of two main subwatersheds within the urban portions of the former City of Kanata (see Figure 1.1- Shirley’s Brook/Watts Creek Subwatershed Study - Study Area). It has a total drainage area of 2700 hectares (27 km 2 ) and outlets to the Ottawa River at Shirley’s Bay. The total channel length, along the main branch, is 12.4 kilometres.

The Shirley’s Brook watercourse has several branches with the confluence of the three branches northeast of the intersection of Klondike Road and March Road. The headwaters of Shirley’s Brook are located within the poorly drained wetlands of the March Ridge. The main channel commences west of Goulbourn Forced Road continuing northeast through the Kanata North Business Park and northwest to Klondike Road. The main watercourse then meanders east, parallel to Klondike Road, to the DND property where it follows 4th Line Road (March Valley Road) before turning east to empty into the Ottawa River at Shirley’ s Bay (see Figure 3 – Comparison of Meander Belt Widths & Flood Plain Lines on Shirley’s Brook). The headwaters of Shirley’s Brook is not urbanized and the existing urban area is mainly located along the main branch of Shirley’s Brook on either side of March Road.

Planning History
1) Water Management Plan for Shirley’s Brook, Kizell Drain, Watts Creek and Harwood Creek (1989)

In 1989 the “Water Management Plan for Shirley’s Brook, Kizell Drain, Watts Creek and Harwood Creek – Phases I and II” was prepared by A. J. Robinson and Associates Inc. for Mississippi Valley Conservation (MVC). One of the products of this study was updated flood plain mapping for Shirley’s Brook. The Regulatory (1:100 year) flood plain along Shirley’s Brook is generally confined within the valley section of the brook. The exception to this is the reach of the brook downstream (east) of March Road. For this reach, due to the flat topography, (100 year flow is approximately 30 m 3 /s) the flood plain is wide , shallow and unconfined.

Figure 3 generally shows the existing flood plain for Shirley’s Brook in green. The culvert crossing under the railway line is perched by approximately 0.5 metres which causes an artificially high upstream flood plain elevation. This results in the flood plain width being overly wide and spilling north along the ditch to the next culvert conveying flow east under the railway line. Between the railway line and 4 th Line Road (March Valley Road) the Regulatory flood plain is unconfined with spill areas both north and south.

The Water Management Plan concludes that “With correct planning and drainage design the spill zone through the Kanata North Business Park can be eliminated and the channel and flood plain between Hwy. 17 (March Road) and Klondike Road can be modified to accommodate runoff from future land use conditions”. The Phase II report, identified a flood fringe area where flood
depths are less than 1.0 metres, during the 1:100 year flood, and infilling may be allowed.

2) Kanata North Urban Expansion Shirley’s Brook Watershed Master Drainage Study (1992 )

In April of 1991, Cumming Cockburn Limited completed, on behalf of the City of Kanata and the Regional Municipality of Ottawa-Carleton, a planning study which examined the relevant planning, environmental, servicing and transportation issues associated with expansion of the urban boundary of Kanata to north of Klondike Road. The goal of the study was to examine the existing municipal and regional policies regarding growth and urban expansion, the existing physical features of the study area and the existing and proposed servicing and transportation infrastructure, in order to determine if and to what extent the “Kanata North Urban Area” could be expanded.

The Kanata North Urban Expansion Shirley’s Brook Master Drainage Study, completed subsequent to the original planning study, addressed the drainage requirements associated with the area of the proposed urban expansion identified in Figure 1.2 (Study Area) taken from the report. The Master Drainage Study included a specific encroachment analysis. The introduction
to Section 5.0 Encroachment Analysis of the Master Drainage Study states:
In a previous study completed by the Conservation Authority (e.g. Report entitled “Water Management Plan for Shirley’s Brook, Kizell Drain, Watts Creek, Harwood Creek, Phase II: Water Management Alternatives and Implementation”) it was acknowledged that because of the shallow depths of flooding and the low velocities, infilling within the flood fringe areas would be acceptable provided that a number of concerns are satisfied. They include:
The encroachment analysis is based on the development limits identified on the preferred concept plan given in the Kanata North Urban Expansion Study. The environmental sensitivity of the area was taken into consideration during the preparation of the plan.

Section 7.0 Conclusions and Recommendations of the Master Drainage Report includes several recommendations regarding the potential encroachment into the Regulatory flood plain between March Road and 4 th Line Road (March Valley Road).

7.2 Urban Encroachment
1. All development located within the encroachment area would be protected to the 100 year flood levels. New development would therefore not be subjected to any increased flood hazards. For design of basement elevations the hydraulic grade line would be based on the 100 year computed flood level within the designated stormwater management facility.

2. Encroachment based on the limits as identified on the recommended concept plan for the Kanata North Urban Expansion Area would result in a small loss of natural channel storage under the 100 year design storm event. This could be accommodated by either upgrading Shirley’s Brook to offset any negative impacts or by introducing flow control structure.  Construction of two non-operational flow control structures would offset the impact of encroachment on lost storage along Shirley’s Brook.  Alternatively, the Shirley’s Brook drainage system could be upgraded to offset any negative impacts associated with the loss of available natural storage. This approach would require possible improvements to the CNR and 4 th Line Road culverts.

3. If properly designed the proposed infilling activity to accommodate the proposed development would have no significant impact on the hydrologic, hydraulic and environmental conditions of the study area.

3) Kanata North Expansion Area Phase One Report (1998)

In 1990, a group of landowners in what became the Kanata North Urban Expansion Area (KNUEA) applied to the City of Kanata and the Regional Municipality of Ottawa-Carleton to amend their Official Plans. In response to this, the City of Kanata retained Cumming Cockburn to prepare a concept plan that dealt with land use, development, infrastructure, transportation and
environmental issues. This study was the basis for Regional Official Plan Amendment 41 (ROPA 41) that was adopted by Regional Council in March 1994. The Ministry of Municipal Affairs refused to approve ROPA 41 and it was referred to the Ontario Municipal Board (OMB).  Following the hearing in July 1995, the OMB approved ROPA 41 in January 1996.

The amendment provided a new designation called West Urban Centre Expansion Area and it provided for an expansion of approximately 202 hectares (500 acres) as shown in Figure 1. The OMB approval of ROPA 41 was based on studies being completed as listed in Section 2.4.1,  Policy 8 of the Regional Official Plan as follows:

8. Re-designate the Kanata North Expansion Area shown on Schedule B to allow urban development to proceed, subject to studies to address the matters outlined below to the satisfaction of Council. In the event that the studies are not completed to the satisfaction of Council, the lands shall be re-designated to General Rural. The studies shall address the:
The Kanata North Expansion Area Phase One Report addressed future stormwater systems in Section 2.8.3 of the report. The report references the analysis completed in both the 1989 A. J. Robinson Report and the 1992 CCL report and recommended the adoption of the floodway/flood fringe approach within the study area. There was also a recommendation that Shirley’s Brook should have a 15 metre setback on either side to protect fish habitat identified in the study.

4) Shirley’s Brook Watts Creek Sub watershed Study (1999)

The City of Kanata and the Region of Ottawa-Carleton prepared a subwatershed study plan for Shirley’s Brook and Watts Creek subwatersheds to ensure that planning future development proceeds in an environmentally sound manner. The plan makes recommendations as to how water resources and related subwatershed features and ecological functions should be protected
and enhanced to coincide with existing and changing land use. The subwatershed study identified several structures, in the three subwatersheds, with inadequate conveyance capacity thus having a direct impact on flood susceptibility as the resulting upstream levels upstream of the structure result in an increase to the extent of the land area flooded. Consequently, the report continues,
hydraulic structure improvements including enlargement and/or replacement of existing bridges and roadway culverts should be considered as part of any structural upgrading works initiated by the municipality. The Shirley’s Brook crossing under the railway line is listed as one such structure.

The subwatershed recognizes that development and site alterations proposed in hazardous lands associated with flooding must demonstrate that all of the following can be achieved:
5) Kanata North Environmental/Stormwater Management Plan (2001)

The Shirley’s Brook Watts Creek Subwatershed Study recommended an integrated land and water management approach to development of areas in the North Kanata in the Shirley’s Brook subwatershed. The Subwatershed Study made specific recommendations pertaining to natural area preservation and enhancement and target water quality objectives to guide future
development. Additional detail in the form of an Environmental/Stormwater Management Plan was required to provide a “bridge” between the guidance of the Subwatershed Study and the need for specific stormwater strategies and natural environmental protection measures for the development areas in Kanata North.

The study area for the plan included lands in the Kanata North Urban Expansion Area centred around March Road and Klondike Roads, although existing and ongoing development areas in the Kanata North Business Area immediately to the south were also investigated for opportunities for additional stormwater control or natural environmental enhancement (Figure 1
Kanata North Study Area). Specifically for the Kanata North Urban Expansion Area lands between March Road and 4 th Line Road (March Valley Road) the plan addressed four main issues
Figure 11 ( Kanata North Urban Expansion Area Recommended Facility Locations East of Shirley’s Brook) shows the recommended stormwater management facility locations with two centralized off-line facilities north and south of Shirley’s Brook at 4 th Line Road (March Valley Road). The following flood plain management recommendations were made:

1. The City of Ottawa as the planning authority should recommend to the MVCA that it wishes to pursue two-zone approach to flood plain management for Shirley’s Brook from 4 th Line Road to the confluence of the north and south branch.
2. In pursuing the two-zone option, then as part of the overall site design land developers should undertake hydrotechnical analyses to determine an optimized strategy for alteration of the flood plain of Shirley’s Brook. The analysis should:
Present Development Plans
Subsequent to the completion and approval of the Kanata North Environmental/Stormwater Management Plan, plans for development of the Kanata North Urban Expansion lands have progressed. Figure 2 (Klondike Road Lands - Land Use Plan) shows the proposed land use in the area. A subdivision, indicated in Figure 2 by lotting fabric, has received draft plan approval.
In support of this draft plan of subdivision application, several studies and analyses have been completed to implement and refine the concepts and recommendations presented in the Kanata North Environmental/Stormwater Management Plan.

These analyses include:
These updated models were also modified to assess post-development conditions with respect to changes in land use, proposed filling in the flood fringe areas and proposed new crossings of Shirley’s Brook. The proposed design includes two stormwater management ponds at 4 th Line Road to provide post-development water quality control and erosion control storage for the
subject area. Two dry ponds, located upstream of 4 th Line Road, will replace flood plain storage lost by filling in the flood fringe areas

Downstream of 4 th Line Road (March Valley Road) is the DND property (Connaught Rifle Range). There are further existing spill areas through this property, but no buildings are flooded (open fields) and no future development is expected.

Discussion
As detailed above, there is substantial history through various reports, supporting the application of the two zone concept for flood plain management for the Shirley’s Brook flood plain between 4 th Line Road (March Valley Road) and March Road when the Kanata North Urban Expansion Area developed.

The two-zone concept recognizes the fact that the flood plain can often be divided into two zones: the floodway, where the majority of the flow is conveyed and the flood fringes which exist on both sides of the floodway. 

Section 3.1 of the Provincial Policy Statement (PPS) supports the selective application of the two-zone concept for flood plain management where development and site alteration may be permitted in the flood fringe subject to appropriate floodproofing. Section 3.1.6 of the PPS states in part: 

Development and site alterations may be permitted in those portions of hazardous lands where the effects and risk to public safety are minor so as to be managed or mitigated in accordance with provincial standards, as determined by the demonstration and achievement of all of the following:

a) development and site alteration is carried out in accordance with flood proofing standards, protection works standards and access standards;
b) vehicles and people have a way of safely entering and exiting the area during times of flooding, erosion and other emergencies;
c) new hazards are not created and existing hazards are not aggravated; and
d) no adverse environmental impacts will results.

The analysis that has been completed, demonstrates that these “tests” can be met in the development of this area.

The “Technical Guide – River and Stream Systems: Flood Hazard Limit” states that the extent of the floodway is to be determined based on local watershed conditions, such as critical flood depths and velocity, existing and proposed development and potential for upstream and downstream impacts. Generally, flow depths in excess of 1 metre and/or flow velocities above 1
m/ s can create significant hazards for developments. The average flood depth, during the 1:100 year flood, in the proposed flood fringe areas is approximately 0.4 metres and the average flow velocity is between 0.15m/ s and 0.3 m/ s.

There are reaches of Shirley’s Brook, (e.g. between 4 th Line Road and the railway line) where the 1:100 year flood plain is unconfined and spills uncontrolled both the north and south. Filling in the flood fringe will result in a confined and defined flood plain limit. The area upstream of the railway line, as described earlier, experiences artificially high flood levels and an overly wide
flood plain width. Again Section 4.2 of the “T echnical Guide – River and Stream Systems: Flood Hazard Limit” addresses this situation when it states, in part:
It is recommended that the upstream flood line should make allowances for the backwater effects caused by a structure. Where this assumption results in unacceptable conditions the culvert should be replaced or alternatively, where feasible, the two-zone concept should be introduced.

Although the replacement or enlargement of the culvert crossing is not feasible at this time, a scenario was reviewed where the crossing was removed from the hydraulic model. The result of this scenario was a substantial reduction in the width of the 1:100 year flood plain essentially to within the proposed corridor around Shirley’s Brook to be left after development. The change in riparian flood plain storage, for this scenario, will be addressed by completing additional grading within the corridor.

The proposed design of development along this reach of Shirley’s Brook will include: 
Since the storm sewers discharge to the stormwater management pond at 4 th Line Road The starting 1:100 year water level is approximately 2 metres lower at this location, than upstream of the railway line. This results in basement elevations for dwellings upstream (east) of the railway line that are approxi mately 1.5 metres below the 1:100 year flood plain elevation at that location, however there is no direct connection of storm sewers to the brook at that location. The minimum ground elevation at the lot boundary will be 0.3 metres above the 1:100 year flood level and the at the proposed dwelling location, which is approximately 10 metres from the property line, the ground elevation is approximately 0.5 metres higher than the 1:100 year flood level. The peak water level occurs for approximately 4 hours. This relatively short duration time frame will not cause groundwater levels to rise high enough at the dwellings to impact the basements.
Recommendation:
The Board of Directors approve the application of the two-zone floodway/flood fringe concept for the administration of the Regulatory flood plain of Shirley’s Brook between the confluence of the north and south branch downstream to March Valley Road.

Map references on page 17