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Delineating a Watershed (Video)

Video Transcript

[A maple leaf flies across the screen and lands to the left. A photo of wheat plots fades into the background. Small circles appear containing images relevant to agriculture. The Canada wordmark and the departmental signature fade in. The title of the video appears on screen.]

[No background music for length of video]

Text on screen: Watershed Management - Delineating a Watershed

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[The screen is split vertically into two areas. On the left we see a still image of a river winding through vast vegetation. On the right we see a blue graphic containing many light squares. Text fades in over top of this blue graphic.]

Text on screen: What is a Watershed? Land area in which all streams and groundwater drain to a common outlet - river mouth, bay.

Male narrator: A watershed is an area of land that drains into a particular body of water.

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[The blue graphic from earlier now covers the entire screen. A green square fades in over this blue graphic. In the square we can see branches of a waterway and a white dotted line that indicates the edges of the watershed area. Red, flashing dots appear on screen indicating the high points in the watershed.]

Its drainage network shows first-order streams in the headwaters, at the highest elevation in the watershed.

[The red, flashing dots change locations. They are now indicated the bifurcation points in the watershed.]

Confluences or bifurcations are where streams join each other.

[The red, flashing dots disappear. The white, dotted line begins to flash to indicate the edge of the watershed.]

The white line surrounding or delineating the watershed is the drainage divide or height of land.

[The white, dotted line stops flashing. Blue arrows appear on the waterways to indicate the direction of flow. Another red, flashing dot appears on screen to indicate the mouth of the watershed.]

The flow is to the outlet of the watershed, which in this example is the mouth of the river.

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[The blue graphic covers the entire screen. A green square fades in over this blue graphic. In the square we can see the same waterway as before, including the white dotted line around the waterway. Topographical contour lines are also indicated on the graphic. The roads, buildings and land boundaries are depicted with black lines and squares.]

Text on screen: 1:100,000, 1cm = 100,000cm (1km)

Topographic maps are used to delineate watersheds on paper. They are a simplified graphical representation of the earth's surface projected on a plane. These maps are produced at many scales, typically ranging from 1:25,000 to 1:250,000. For instance, on a 1:100,000 map, 1 cm represents 100,000 cm on the ground, which is 1000 m or 1 kilometre.

[The topographical contour lines begin to flash to draw attention to them.]

On a topographic relief map, brown contour lines depict elevation.

[The topographical contour lines stop flashing. The waterways, indicated with blue lines, begin to flash to draw attention to them.]

Water bodies are depicted in blue.

[The waterway markings stop flashing. The black lines and squares indicating roads, buildings and land boundaries begins to flash to draw attention to them.]

Features such as roads, buildings, land boundaries, etc. are depicted in black.

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[The blue graphic covers the entire screen. A white square fades up over this blue graphic. Two topographical maps are shown: one two-dimensional map with topographical contour lines and one three dimensional map with topographical contour lines.]

This slide illustrates how a topographic map (above) depicts the relief or elevations in the three-dimensional model (below).

[A red circle fades in to indicate the highest point on each map. The intention is to show how the topographical lines translate into a three dimensional model.]

The hill or mountain shown at the right in the model is depicted by a series of circles on the map (above). The streams depicted in blue are in the same location in both the map and the model.

[The red circle fades out. Several blue arrows fade in to indicate the topographical contour lines, shown in brown.]

The contour lines shown in brown connect points of equal elevation.

[The blue arrows fade out. Two new blue arrows fade in to indicate the closely spaced contour lines.]

Steep slopes are shown by closely spaced contours.

[The two arrows fade out and two new blue arrows fade in. The arrows are indicating the widely spaced topographical contour lines.]

Gentle slopes are shown by widely spaced contours.

[The two blue arrows fade out. To small red circles fade in to indicate where the topographical contour lines intersect with waterways.]

Contour lines do not intersect, branch, or cross. Contour lines close on the map or on an adjacent map sheet. When contour lines cross streams, they bend upstream.

[The two red circles fade out. A new red circle fades in to indicate the contour lines that have small lines inside their loops.]

Closed contours appearing as ellipses or circles represent hills. Closed contours with hachures or little ticks inside the circles represent closed depressions.

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[A portion of a map showing an area of Alberta, about 50km southwest of Edmonton, fades up. A stream system has been highlighted in blue.]

Text on screen: © Department of Natural Resources Canada. All rights reserved.

To delineate a watershed on a topographic map, begin by identifying the stream of interest. On this example, the stream has been highlighted in dark blue.

[A red, flashing dot appears on screen to indicate the point where the stream enters another water body.]

Next, determine the point at which the stream enters another water body, a confluence.

[The red, flashing dot fades out. A series of smaller red dots appear around the stream system to indicate the drainage divide for this watershed. Slowly, a red line begins to fade in that connects all the dots.]

Step 3 is to locate the high spots that will identify the drainage divide for this watershed. In this example, the red dots indicate the high spots, which could be hills or ridges. We next connect the dots to draw in the drainage divide.

[The area delineated by the dots and connecting lines slowly turns yellow to indicate the entire area of the watershed.]

The area highlighted in yellow is the gross drainage area of the watershed.

[A grid fades on over top of the map, the red dots and lines, and the yellow area.]

Text on screen: N*L2 = Gross Drainage Area

There are different methods of determining the drainage area, but the simplest is to overlay the delineated watershed with a grid of known scale. Count the number of squares in the watershed. The drainage area will be the number of squares, or N, times the area of the square. This is also known as the Gross Drainage Area.

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[Three circles containing images moving quickly towards the camera. Once full screen they slip off to the upper left and off screen. A grey ribbon moves in behind the circles as they become full screen. The circles line up, zoom out, and center themselves in the middle of the screen. The Agriculture and Agri-Food Canada departmental signature appears below the circles.]

Text on screen: Agriculture and Agri-Food Canada. Agriculture et Agroalimentaire Canada.

[Cross-fade to the Canada with an animated Canadian flag over the last letter in the word.]

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