Basement Flooding in the
Stag Hill Drive Area
The East York Community Council recommends the adoption of the following report (October14, 1998) from the
Director of Quality Control and System Planning:
Purpose:
This report is to the East York Community Council for its meeting of October 14, 1998. It responds to a request for a
report on the modifications/improvements to the existing sewer system required to solve the basement flooding problem
in the Stag Hill Drive area, and an estimate of the associated cost.
Financial Implications:
The two alternatives to solve the basement flooding problems in the Stag Hill Drive area, and the estimated financial
implications of each are as follows:
Option 1Modification/improvement to the sewer system
Cost: $1,375,000.00
Option 2Installation of back-flow valves with access chambers at the two basement flooding impacted houses.
Cost: $15,000.00
Annual maintenance cost: $200.00
Recommendations:
It is recommended that:
(1)the City use back-flow valves to solve the basement flooding in the Stag Hill Drive area; and
(2)the City enter into an agreement with the two residents experiencing basement flooding to allow the City to install and
maintain back-flow valves at their residences.
Council Reference/Background/History:
Community Council at its September 16, 1998 meeting requested a report on the cost to solve the basement flooding
problems in the Stag Hill Drive area by improvement to the existing sewer system.
Comments and/or Discussion and/or Justification:
Basement flooding in the Stag Hill Drive area, in the block between Leander Court and Hale Court, first surfaced during a
storm on July 10, 1975. To ameliorate/solve the problem, the existing relief storm sewer along Stag Hill Drive was
extended westward to encompass the problem area.
Despite the relief sewer extension, basement flooding persisted. A further review of the problem carried out by Gore and
Storrie (1980) revealed that 'The extent of the flooding in the Stag Hill Drive area appears to have worsened since the
construction of the relief sewer'. The continuing problem was believed to have been caused by the lack of transmission
capacities to accommodate the flow from the relief sewer in both the Glenwood Crescent trunk storm sewer and its outfall
to MasseyCreek. The Stag Hill Drive relief sewer exits to the Glenwood trunk storm sewer. The respective capacities
were calculated to be 1.47 m3/sec for the Glenwood Crescent trunk sewer and 1.98 m3/sec for the outfall, versus 4.44
m3/sec required to handle the runoff from the currently used five-year design storm.
It should be noted that in the last five years, complaints/reports of basement flooding in the subject area were received
from only two residences.
To solve the storm sewer surcharging in the Stag Hill Drive area, and thus the basement flooding problems, it will be
necessary to build a relief trunk storm sewer and an outfall parallel to the existing Glenwood Crescent trunk storm sewer
and its outfall to Massey Creek. The new sewer and outfall will have capacities of about 3 m3/sec. Furthermore, the
drainage from the area upstream of the new sewer must be serviced by a common structure to split the flows. The existing
Stag Hill Drive relief sewer will have to be enlarged and new storm sewers will be installed along Leander Court,
HaleCourt and Glen Gannon Drive.
A precise cost of the required works will be derived during the design stage. In the interim, preliminary cost estimates of
the project components are as follows:
Relief trunk storm sewer from
St. Clair Avenue, East to Glenwood Terrace$ 725,000.00
Outfall from Glenwood Crescent to
Massey Creek$ 245,000.00
Enlargement to the existing Stag Hill
relief storm sewer$ 265,000.00
Installation of storm sewers along Leander Court,
Hale Court and Glen Gannon Drive$ 140,000.00
Total Project Cost $1,375,000.00
The foregoing project had not been included in the current and past capital works programs because of the high cost and
the low number of homes reporting basement flooding.
Two alterative solutions to the basement flooding problems in the subject area, discussed previously, are as follows:
Disconnecting downspouts at homes in the vicinity, advocated and encouraged during the construction and expansion of
the Stag Hill Drive relief sewer, will relieve local sewer surcharging and should still be encouraged. However, this will
not solve local basement flooding, because flows from the Stag Hill relief sewer will not be able to enter the Glenwood
Crescent trunk storm sewer when it surcharges during heavy storms. On the contrary, the Stag Hill Drive relief sewer will
likely act as a relief sewer to the Glenwood Crescent trunk storm sewer during heavy storms. This is the probable reason
for the previously mentioned statement by Gore and Storrie about the worsening basement flooding problem.
The Stag Hill Drive area could be a candidate area, should the City decide to extend the former Cityof Toronto's free
downspout disconnection program city-wide.
In response to inquiries or proposals to use back-flow valves to prevent basement flooding, the then Commissioner of
Works (1987) advised that the former Borough would not encourage or discourage their use because of problems
encountered by other former local municipalities. It is staff's opinion that the foregoing should not preclude their use.
Experience since reveals that despite the possibility of failure/problems, their use in instances where the alternative is very
expensive is appropriate.
Staff have estimated the costs to install and maintain a back-flow valve as follows:
Cost of valve, installation, including
access chamber $ 7,500.00
Annual maintenance cost$ 100.00
Conclusions:
It is much more economically feasible to use back-flow valves to solve the basement flooding problems in the Stag Hill
Drive area then it is to modify/improve the local sewer system.
Contact Name:
Kim Choo-Ying
Environmental Engineer
East York Civic Centre
Tel. No.: (416)778-2218
Fax No.: (416)466-9877
