Imperviousness at Brookside School

We all live in a watershed!• A watershed is an area of land that drains into a common body of water.• Everything that happens in a watershed can affect its water quality.

We live in the Passaic-Hackensack Watershed.

This map shows the major rivers and streams. This map shows all the smaller tributaries as well.

This watershed is comprised of two smaller watersheds:• Passaic Watershed• Hackensack Watershed

Allendale is located in the Passaic Watershed,shown here in neon green.

Allendale’s approximatelocation is marked with a red star.

(I actually live in the Hackensack Watershed!)

Inside the Passaic Watershed are even smaller subwatersheds. (sometimes called catchments). Brookside School lies in the Ramsey Brook subwatershed.

The amount of impervious (or impermeable) surface in a watershed greatly impacts the

quality of the bodies of water there.

The more impervious surface, the more surface runoff and the less infiltration. Therefore, there is also less subsurface flow. Infiltration and subsurface flow are crucial for maintaining high water quality.

Permeable Land Surface Mostly Impermeable Land Surface

The results of several studies suggest this relationship between percentage of impervious

cover in a watershed and water quality:

From Rhode Island Dept. of Env. Mgmt.And the University of Delaware.

Percentage of Impervious Surface

Effect on Watershed

< 15 % Protected

15% - 35% Impacted

> 35% Degraded

The highest quality water is found in watersheds with 100% permeable (or pervious) surfaces.

Even 10 – 20% imperviousness alters the natural processes of the water cycle somewhat:

When the level of impervious surface reaches 35%, water quality is negatively affected:

Once the amount of impervious cover reaches 75%, the water can be severely degraded:

Large amounts of impervious surface also increases the chances of both droughts and flooding. Allendale has experienced both extremes in recent years.

Lawn and Garden Watering with both Automatic and Hose

Sprinklers is Limited to:

• Odd House Numbers: Wednesday, Friday, Sunday

• Even House Numbers: Tuesday, Thursday, Saturday

Hurricane Irene: September, 2011.

Water Restrictions: Summer, 2013.

For our next project, we will map our school property to determine the percentage of impervious land surface at Brookside.

Parts of the school property are impermeable, like the parking lots and blacktop play area, as well as the building roof. (left)

Other parts of the school property are permeable, such as the outdoor classroom, the athletic fields, and the area adjacent to the brook. (right)

IMPERMEABLE vs PERMEABLE SURFACES

In your Journal, answer these questions:

1. How does impervious surface impact waterways?

2. How can we determine the percentage of impervious surface at Brookside?

3. Make your own prediction: What percentage of Brookside property do you think is impermeable? Explain how you came up with this amount.