Barrier Management

WHAT IS BARRIER MANAGEMENT?

Barrier management incorporates the environmental effects of natural and man-made obstructions on the health of our rivers and streams. Obstructions in rivers can be vertical structures or water velocity barriers. Permanent natural barriers include geological formations such as waterfalls, chutes and gorges. Man-made barriers include dams, weirs, locks, culverts, pipes and channels. The physical form of our rivers is produced by the surface geology of the watershed. Life in the river has evolved over thousands of years to adapt to natural barriers. Likewise, the animals in a river are adapted to natural disturbances such as beaver dams or logjams. These short-lived barriers have negligible long-term environmental effects on river ecology. Unnatural barriers take the form of dams, weirs, locks, drop structures and culverts. Dams and locks are structures that have the ability to control a volume of water behind them. Typically, small dams are less than 5 metres high and have an impoundment, or on-line pond, less than 40 hectares. Large dams include those used for generating electricity, or for supplying water to our towns and cities. Locks allow for ships and boats to move through a waterway such as the Trent Severn canal system. Drop structures are used for gradient control where the stream has been channelled; they also provide energy dissipation of fast flowing water. Culverts are steel or concrete pipes used to convey water under a road or highway. The physical footprint of unnatural barriers is short-lived, with most structures typically having a life expectancy of 50 years. Some barriers are beneficial to society, while others are functionally obsolete. Regardless of the function of existing barriers, many of these water control structures fail to adequately mitigate the physical, chemical and biological impacts on the forbearing river. It is the manufactured barriers that create significant long-term environmental effects on a river’s biological integrity. In relation to rivers and streams of Ontario, our rehabilitation efforts need to focus on reversing the harm of unnatural barriers. We need to look closely at how we manage man-made barriers and take sensible actions that revitalize our rivers and streams. Dams and locks are structures that have the ability to control a volume of water behind them.

A HISTORY OF CHANGE

The last ice age retreated from Laurentian Great Lakes over 10,000 years ago. Human colonization of North America is thought to have occurred around 9,000 B.C. From the initial colonization to about 1600 A.D., the Native peoples of Ontario lived in harmony with nature, using rivers as travel corridors for trading goods and as a source of food and water. Fish, wildlife and plants were plentiful and harvested from the river valleys, prairies and forests to sustain their lives. Europeans first ventured to North America in the early 1600’s and came into contact with Ontario Iroquois and the Algonquin speaking people. The rivers were used as trade routes supplying furs to the European markets. As the European influence dominated more and more of the Ontario landscape, new diseases from Europe, exhausted food resources and dwindling territories, overwhelmed the Native peoples. By the late 1700’s, pioneers from Europe were moving into Ontario to conquer the landscape. Parcels of Native land were traded for goods and purchased by early settlers. Once acquired, lands were harvested for timber and cleared for farms and roads. The first man-made barriers of the Industrial Revolution were dams, built to harness the power of rivers, for milling lumber and grinding grains or to provide water for logging operations, irrigating crops and livestock. The first dam on record was built in 1782 on the Cataraqui River near Kingston. These early dams were commonly built of elm and pine cribs filled with rock. By the 1860s, dozens of mills existed in the Moira, Ganaraska, Credit, Don, Humber, and Rouge rivers of Upper Canada.Ninety mills were in operation on the Humber by 1860. Communities formed around mills as more settlers came to Ontario from Europe. The dam and pond associated with the mill were important to the livelihood of community because they were the basis of prosperity. With the invention of electricity in the late 1800s, larger dams were constructed to generate a new means of power for industry. This gave rise to the abandonment of smaller private dams because hydro generated electricity became the cheaper source of power for operating mills. Many of these smaller dams and ponds, that once served a worthy societal function, still exist today with some being more than 150 years old. The linkage between the mill, dam, pond and the growth of the community are the basis of the cultural significance expressed by present day historians, when the Weirs have a static volume of water behind them and are typically used for irrigation, monitoring river flows or inhibiting sea lamprey migration.

“Dams are not like the pyramids of Egypt that stand for eternity. They are instruments that should be judged by the health of the river to which they belong”

US Secretary of the Interior Bruce Babbitt, 1998

In 1954, Hurricane Hazel hit southern Ontario hard and eliminated many of the antiquated barriers as the floodwaters swept them away. This flood event caused loss of life, massive property losses and triggered a new way of managing our rivers and floodplains. We became aware that living in the floodplains of rivers was not safe. In response to the flood damage, control structures were built in efforts to solve future threats. Streams were channelized with concrete, new dams were built in headwater areas to store floodwaters, and floodplain protection policies were developed by new regulatory agencies – the Conservation Authorities. By 1973, 72% of the 16,700 kms of streams tributary to Lakes Ontario, Erie and Huron were blocked by dams. Today we have a variety of man-made barriers that have been constructed for mills, generation of electricity, flood control, shipping vessels, irrigation, livestock watering, sea lamprey control, domestic water supply, and recreation. It is estimated that there are 3,000 dams, weirs and other barriers throughout the province, with some watersheds, like the Humber River in the Toronto area, having over 110 man-made obstructions currently existing. The majority of these barriers are located in the headwaters of our rivers. Some of the structures are beneficial to the public, while others are obsolete. Ownership of these structures may be federal, provincial, municipal or private.

In the last decade, many functionally obsolete barriers have come under close public scrutiny due to their outlived intended purpose, risk to public safety and environmental impacts on river ecology. Social values associated with the dams and weirs of our history are slowly changing from the nostalgic to the pragmatic, as the public becomes more informed of the inherent economic and environmental consequences of barriers.

EFFECTS OF BARRIERS ON RIVERS AND STREAMS

The effects of barriers on rivers and streams have been widely studied across North America, Australia and Europe. An extensive volume of science-based information exists. This knowledge has advanced our understanding of rivers and documented the environmental consequences of man-made obstructions in our watersheds. A series of complex physical, chemical and biological processes occur in flowing rivers that link the watershed ecosystem from its headwaters to downstream limit. Longitudinal changes occur in the characteristics of river form, floodplain, substrate and water chemistry, creating physical gradients through a watershed. The ecology of healthy watersheds has adapted to this gradient over thousands of years. Unnatural barriers tend to exhaust reaches of flowing rivers from the natural processes associated with watershed gradients. From this understanding, dams are considered an extreme cataclysmic episode in the river’s cycle of life. Other man-made barriers such as culverts, weirs, and drop structures have similar impacts on a river’s health. The effects of a barrier are directly linked to the physical, chemical and biological processes that occur in a river. It is the combination of process changes induced by an unnatural barrier that cause deleterious consequences. The effects of barriers have been summarized into five categories.