The cost of intensification: watershed gets F grade in urban area

May 29, 2013

Conservation Halton (CH) recently released a report card on the health of Halton’s watershed, measuring surface water quality, forest conditions, impervious land cover and groundwater quality.

Aside from groundwater quality (“A” ranking) the results were sobering, especially for the urban areas. Halton ranks C for both surface water quality and forest conditions, and D for impervious land cover. However, those rankings fall to F in the urban areas, including downtown Burlington.

Impervious land cover

Impervious land cover includes hard surfaces that do not allow water to absorb into the soil, such as roads, driveways, parking lots and rooftops. Runoff can carry pollutants as it runs along these surfaces and reaches local creeks, lakes and aquifers. These pollutants can include gasoline, fertilizers, detergents, salts, pet waste and other toxic chemicals.

Runoff from hard surfaces also increases the amount of water that would naturally occur in a stream, since less is absorbed by the ground. This can cause higher, faster flows resulting in flooding, erosion and habitat degradation. Areas with natural vegetation absorb runoff from rain and snow and help to filter impurities before they impact water quality, quantity and stream health. Natural vegetation also helps to moderate stream temperatures and flows, and supports aquatic life.

According to the CH report, if 10% of a watershed’s land cover is impervious it can begin to result in the loss of aquatic species. By the time you reach 26 to 30% imperviousness, entire aquatic ecosystems can be permanently damaged. Overall imperviousness in our watershed is 21.4% which is a grade of D (F in urban areas).

Forest Conditions:

A minimum of 30% forest cover is typically required to sustain species biodiversity within a watershed, states the report. Forests provide many ecological functions such as wildlife habitat, air purification, erosion control, and recreational opportunities. The overall forest cover in our watershed is 26.4% or a grade of C (F in the urban areas). The majority of large forested areas are located above the Niagara Escarpment.

My Take: This report card is a wake up call for the need to protect trees and greenspace in our urban areas, especially during redevelopment and intensification. As we saw on the Branthaven townhouse project on Ghent, for that one project 100 trees were cut, and greenspace was reduced from 72% of lot coverage to 38%. Residents raised concerns about the loss of trees and greenspace, as well as the impact of ground and surface water runoff into adjacent Rambo Creek. The sought a reduction in the number of housing units to increase the “impervious” ground cover in the area.

Branthaven recently built standard and back-to-back homes on Brant & Plains – a project I voted for. I recently visited again and was struck by the amount of asphalt and buildings, and the tiny amount of greenspace.

Intensification is often pitched as environmentally beneficial, because more compact housing forms take up less land, and prevent development into our rural areas. But intensification can also clearly damage our watershed if care is not taken to the limit impervious land cover and protect tree cover.

Urban development must protect trees and greenspace or the F grade we see is the result.

As I recently wrote in City Talk, pg 13, we can’t sacrifice urban greenspace to protect rural greenspace. Rural greenspace is already protected (by provincial law); city council’s job is to plan intensification in the urban area that respects the health of our communities, the need for urban greenspace and the protection of our watershed, which is clearly already at risk.