Roads

One measure of urbanization is the length and density of roads in a watershed. As road density increases, so does the total impervious area of a watershed. This is significant in that impervious surfaces impact the hydrological cycle.

Roads are classified in five different categories, according to their functions and width. In Thornton Creek Watershed, the roads occupy 9 sq. km in a 29 sq. km watershed area, roughly 29.5% of the watershed area. The Non-arterial (residential roads) has the highest percentage of total road area with roughly 14%. These roads offer significant although costly opportunities for detaining street water run-off.

 

Road Class
Length
Average number of lanes
Area (km2)

 

Freeway

 

76979.2

 

8

 

1.694

 

Arterial

 

65820.3

 

4

 

0.724

 

Primary

 

105301.7

 

4

 

1.158

 

Non-Arterial

 

877212.8

 

2

 

4.825

 

Minor

 

64348.2

 

1

 

0.177

 

Sub-total of road area

 

8.578

 

Sub-total/watershed area (29.05km2)*100%= 29.5 %

Relationship between Streams and Roads

A map illustrates the spatial relationship between streams and roads.

There is a close relationship between the distance of streams from roads and the possibility for streams receiving water flow and pollution from the surface of streets.

The chart below summarizes the percentage of the creek’s length that falls within a distance of 10 meters, 50 meters, and 100 meters from roads.

Distance (m)

 

Percentage of the creek's length has road within

 

10

 

15.21%

 

50

 

77.60%

 

100

 

94.47%

Fifteen percent (15%) of the Thornton creeks falls within 10 meters from roads. This is significantly high considering scientist have foundthat a buffer width of less than 10 meters is generally considered functionally ineffective (May et al. 1997).

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