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Run-off & Land use Change

Humans have greatly changed the surfaces of the areas that we live and continue to do so. The maps an calculations below take a look at changes on 7-27 North Willard Ave and assess changes in surface types that have significant impacts on water runoff.

1999 Run-off Surface Type 72% runoff

Red-Building, Green-Grass, Grey-Paved, Brown-Dirt, Black-not on parcels

2018 Run-off Surface Type 79

Red-Building, Green-Grass, Grey-Paved, Brown-Dirt, Black-not on parcels

Land

Percent Runoff for each Year

Inches of Runoff for each site with storm types

There has been moderately significant change in surface types in Burlington over the last 20 years. At the site studied on North Willard ave The rate of surface runoff has increased from 72% of the water being runoff to 79% of the water running off rather than infiltrating into the ground water. Though the 1999 map is low resolution and somewhat difficult to differentiate surface types, it appears that though building areas stayed the same, which was expected, there was a transition from green space to paved driveway. This transition from permeable grass and trees to paved driveways accounts for the majority of the change in the average permeability of the site studied and increased the runoff that would occur during a storm. Though this is still only 1/3 of an inch based on a 24 hour period of a 100 year storm, this could have huge impacts when extrapolating this as a trend not only over Burlington but over the whole us and the world.

Either of these sites, compared to pre-European settlement calculations, are terribly altered and are much less effective in capturing ground water. In pre-European times this area would have been heavily forested and with relatively rich well aerated soil that could absorb around 70% of water, leaving only 30% as runoff. This surface type is 2-2.5x as effective at collecting groundwater and avoiding channel incision as the current state of things. The numbers used for calculating the historical land cover may be speculation on some level as well as old growth forest processes may act differently and be more absorbent than the "woods" category used for agricultural lands on the table.

These changes in runoff have the potential to have huge impacts on water quality in Burlington and around the world. If this system naturally only has .3 runoff and has increased to .79, there will be much higher volumes of water and likely higher velocities. This increased runoff can now pick up larger sediment particles with higher velocity and this runoff is now traveling over more impervious surfaces on its way towards lake Champlain. With increased urbanization, this runoff water can be a large contributor to non-point source pollution, picking up a variety of pollutants as it travels through the Burlington area. Road salt, garden fertilizer, pesticides and human and animal waste can all be carried more effectively into the lake, posing a large risk for water quality in the future.