Neebing - McIntyre Floodway


Location: Thunder Bay, Ontario
Region: Northwestern
Character: Flood Control Resevoir
Activities:
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Neebing - McIntyre Floodway
By Lakehead Region Conservation Authority

DIVERTING STREAMFLOW TO ALLEVIATE FLOODING PROBLEMS
What is it? The Neebing-McIntyre (N/M) Floodway is a large channel extending from the Neebing River at Ford Street and Parkway Drive to the McIntyre River just east of the William Street bridge. The purpose of this engineering feat is to reduce damage from flooding to urban areas in the intercity area and to protect existing floodplain development.

HISTORY
In 1941, Thunder Bay was hit by a fierce storm which caused extensive flooding on the Neebing River. The flood waters rose to the point where they overflowed into the McIntyre River. In an attempt to deal with flooding problems, the community formed the Neebing Valley Conservation Authority (NVCA) in 1954. In 1963 the NVCA was expanded to the Lakehead Region Conservation Authority (LRCA). Since then, the Lakehead has received three major rain storms: 1968, 1971 and 1977. In each of the four major storms, the Neebing River overflowed its banks, causing extensive flooding in the intercity area.
Downstream from Thunder Bay Mall the Neebing River flows through an urban area including residential, light industry and shopping malls. These impervious surfaces prevent absorption during periods of high rainfall resulting in greater runoff of water into the river. Because of the adjacent flat land, the Neebing River easily overflowed its banks and developed a reputation for flooding. The implementation of a flood control system was needed.

In response to citizens concerns, the LRCA initiated and commissioned the construction of the Neebing-McIntyre Floodway. Project planning began in 1973 and construction occurred between 1980 and 1984 at a cost of 15 million dollars. In addition to reducing flooding problems on the Neebing River, the Neebing-McIntyre Floodway benefits the city in the following ways:
Eliminates annual nuisance flooding.
Eliminates flooding up to and including the Regional flood level.
Ensures effectiveness of City's long term sewer separation program.
Increases development capability in the intercity area.
Increases redevelopment opportunities in McKellar ward.
Reduces effect of upstream development on downstream flooding.
Potential for recreation development.

A DIFFERENT PERSPECTIVE
To promote the recreation potential of the Neebing-McIntyre Floodway, the LRCA and the City of Thunder Bay Parks and Recreation Department have constructed over five kilometres of pathways which link to the 28 km network of recreation pathways in the City. Many people use the pathways to exercise pets, enjoy a safe bicycle ride or to stroll to the Neebing Marsh. We suggest using the pathways to tour the main flood control features of the Floodway outlined below. The walk will take about 1.5 hours and covers a distance of approximately three kilometres.

The pathway system includes sections through the Memorial Grove along the Floodway.

Diversion Structure
The diversion structure is the strategic point of the Neebing-McIntyre Floodway. It is at this point where the excess flow of water from the Neebing River is controlled and diverted. The structure is designed with three gates of which only one is used and permanently fixed at an opening of 2.50 m x 2.50 m. The other two gates may be opened simultaneously to relieve build-up of ice or debris. The opening size limits the flow of water through the diversion structure to 29 m3/s which is the maximum capacity of the Neebing River below the diversion structure. Flows in excess of 29 m3/s are diverted down the channel.

The diversion structure forces excess water to go down the diversion channel instead of flooding down the Neebing River.

Diversion Channel
The pathway running parallel to Ford Street offers a pleasant view of the Floodway Channel. The diversion channel is designed to be flooded in order to reduce flood damage to residential properties on the lower Neebing River. Excess flood flows from the Neebing River are 'diverted' along the diversion channel to the floodway channel which begins at William Street.

It is difficult to imagine that this channel, 1.5 km in length, could actually be flooded under 2.5 metres of water. In fact, that is approximately how deep the water in the channel would be if Thunder Bay received a Regional Storm; a storm that would result in 193 millimetres (7.6 inches) of rainfall in 12 hours.

The Floodway's biggest test to-date came during the July 1997 rainfall event. That storm dumped over 90 mm (3.5") of rain in just 7 hours; total rainfall for the event was 119 mm (4.7") over a two-day period. Waters in the Neebing River rose until they were lapping at the bottom of the footbridge near Ford St. However, the diversion structure and Floodway prevented homes downstream from being flooded. The Diversion Channel carried waters up to a metre-and-a-half deep safely out to Lake Superior.

The diversion channel can carry up to 2.5 metres of water, which is sufficient to contain flows from a 'regional storm'.

The Floodway Channel
The Channel is designed to accommodate the excess flows from the Neebing and McIntyre Rivers. The Floodway Channel begins at William Street where the McIntyre River connects and runs through intercity and out to the mouth at Lake Superior. The depth of water in the Channel fluctuates with the water level of Lake Superior.

Cattails and other vegetation grow along the banks of the channel. Seeds and vegetation upstream on the McIntyre River and in the dry channel are carried down and deposited in the slow moving water of the Floodway. The emergent macrophytes (cattails, arrowheads and other plants) along the banks help to stabilize the bank and attract song and marsh birds. The Floodway Channel offers year-round recreation opportunities.

Memorial Grove Program
A recent addition to the Floodway is the Blake Memorial Grove. Under this co-operative program, Blake Funeral Chapel and individuals donate funds to plant approximately 300 trees per year. The Memorial Grove extends along the Neebing-McIntyre Floodway from Fort William Road to the Harbour.