More of What Is a Watershed Why do we delineate our

watershed? Obtaining Topographic Maps

Online Reading A Topographic Map How to Delineate a watershed

Michele DrostinUNC Institute for the EnvironmentJuly 22, 2014

WHAT IS A WATERSHED?1. The area of land that drains to

a common outlet, such as a lake, river or stream segment.

2. Watershed boundaries are based on topography –highest points are ridges and lowest are valleys and streams.

3. Delineating a watershed provides a bounded area in which natural processes occur AND that people can see and communicate about.

Watersheds are “nested”

All Land is part of a watershed

What• Delineate your watershed and map the land uses and potential

and actual pollution sources. Learn the geography and history of your water body and its watershed.

Why

• The health of your stream, river, lake or estuary is directly impacted by land uses and activities in the watershed.

• You cannot study water without knowing about the land from which the water drains!

When• Every year the land uses in your watershed will change. This

will have a direct impact on your water body of interest.

MAPPING YOUR WATERSHED

• Erosion/Sediment• Fertilizers, pesticides• Animal wastes• Illicit spills and illegal dumping• Leaking septic systems• Runoff from roads, parking

lots and roofs

POLLUTION SOURCES

IMPERVIOUS SURFACE

Impervious coverage Stream health<10% “Protected”

10 to <30% “Impacted” if not mitigated>30% “Degraded” if not mitigated

IMPERVIOUS SURFACE

OBTAINING TOPOGRAPHIC MAPS

Store.usgs.govMap locator and Downloader

• Contours are imaginary line that connects points of equal elevation.

• Contours always connect but not always within the boundaries of your map.

• Contour interval is the vertical distance between contours, generally 10 ft.

• Contour lines never cross each other.

• Contour lines close together indicate steep slope, farther apart, indicate gentle slope.

• Direction of flow is always perpendicular to contour lines.

READING A TOPOGRAPHIC MAP

• Hilltops

• Ridge is an extension of the hill.

• Saddle is a lower area, often on a ridge, between two hills. Where contour lines

cross streams, they form a V that always points upstream.

STEPS TO DELINEATE WATERSHED

1. Place a circle at your outlet.

2. Highlight Jolly Branch and other unmarked low areas that appear to run into Jolly Branch. Follow V all the way until it ends. V indicates valleys or low areas.

3. Identify and mark all Valleys that may flow into Jolly Branch.

4. Now look for hill tops, ridge lines and saddles and mark high points with and X

5. Visualize water flow from direction of high points to determine if water would flow from there to your stream.

6. Connect high points, always crossing contours at right angles.

Streamstats.usgs.gov/north_carolina.html