Video 1 C3: Watershed delineation

Question 1

as engineers, why are we interested in run-off?

Answer 1

because we need to quantify it (know how much and why its there).
It helps in planning to protect our homes and understand the ecosystems around properties (i.e. the performance of the lakes)

Question 2

a major component of knowing the amount of water (in run-off) is knowing…

Answer 2

the area of the watershed thats contributing to a single point

Question 3

what is a watershed?

Answer 3

the area where the run-off converges to a single point

Think of it like a big bowl: everything inside that bowl flows to the lowest point (the outlet).

Question 4

what is a sub-basin? why do we create them?

Answer 4

just a smaller part of a larger watershed; kind of like a tree, where each branch is a sub-basin, and the trunk is the watershed

Question 5

why are sub-basins useful?

Answer 5

• simplifies complex systems
• better flood and flow predictions
• you can pinpoint problem areas in specific subbasins instead of trying to manage the entire watershed

Question 6

what does delineation mean?

Answer 6

drawing boundaries (outlining the edges):

in hydrology, this means finding where the watershed starts and ends based on elevation (high points) and water flow

Question 7

what are the steps for watershed delineation?

Answer 7

1. Identify the study point
2. Identify the general slope of the terrain (which way is going up, which way is going down)
3. Trace the flow lines draining to the study point (flow lines point uphill)
4. Identify ridgelines
5. Start at the study point and draw a line going uphill and perp. to the contours; once you hit a ridgeline jsut keep following it up (ridgelines point downhill)
6. close off the area

Question 8

what is a ridgeline?

Answer 8

a high-elevation line that separates two different drainage areas:

think of it like the roof of a house; when it rains, water runs down either side of the roof. the ridgeline in this case would be the peak that splits the flow

Question 9

what is a saddle? is it acceptable to draw as a boundary? is there a symbol you draw to identify them?

Answer 9

the area between two peaks (of land); yes, it is the only time it is acceptable to draw a contour going from high elevation to low elevation; yes, a triangle is the symbol

Question 10

if any rain fell within the area drawn, then…

Answer 10

it will fall towards the watershed