1. Purpose: To practice delineating a watershed, and to consider methods for estimating the area of a watershed.
Problem: Watersheds are the fundamental hydrologic unit for managing water resources. NYCDEP supplies and manages drinking water from three watersheds within upstate New York, the Croton, Catskill, and Delaware watersheds. Prior to developing these water supply systems, engineers had to delineate the watersheds (area of land that drains water from precipitation into water bodies). Watershed delineation allows engineers to estimate the area of drainage.
You will be completing these same tasks for a small watershed in Tafton, PA. Please complete the delineation by hand using a topographic map and then estimate the area of this watershed online by using computer software.
Go to the USGS website (or MyTopo, or another reliable and free topographic map source) to preview/download a free topographic map at: http://www.usgs.gov/pubprod/. Click on “Map Locator & Downloader.”
In the Search box, type “Tafton, PA” then click “Go.”
Click on the red marker. This should bring up a series of files. Select the “Hawley US Topo” for the year 2016, 7.5 minute by 7.5 minute (27Mb file).
Download to your laptop or desktop, and print a copy of the topographic map. *Suggestion: Zoom in to Tafton on the map and print the “current view” under “Pages to Print…More Options.”
Delineate the drainage area for “Fairview Lake” and “Mainses Pond” using “Fairview Lake Outlet” as the point of interest (PI). Use the steps discussed in class to delineate the watershed. *Suggestion: It may help to do this in pencil first and then go over it in colored pencil, pen or thin marker using different colors to show the steps in delineation.
Estimate the drainage area in acres. Go online and look up Google (ACME) Planimeter, use this computer software as your method for estimating the watershed area in acres. First, locate Tafton, PA and then make sure to select the USA Topo layer. Add markers/points to depict your Mainses Pond delineation. Once all markers/points connect, Planimeter displays the measurement of the drainage area in acres at the bottom of the map. Save (take a screenshot or print and scan) your completed measurement to submit with your homework. *Save a copy of this to your computer, you will need to use this specific Planimeter estimation again for our next homework and in lecture.*
Submission: Each student is required to submit two documents, along with a cover sheet, to Blackboard. Include your full name, class name, homework number, and the date on a cover sheet. With your cover sheet you should submit:
A scanned copy of the printed Tafton, PA topographic map that includes your hand-drawn watershed delineation, using Fairview Lake Outlet as the PI.
A copy of your Planimeter estimation of the same watershed area (this can be printed and scanned or a screenshot photo). Planimeter should display the estimated area of your watershed in acres at the bottom of your delineation, please highlight or circle this number.
Grading: Out of 5 points
Hand-drawn watershed delineation: 2 points
Google Planimeter and watershed area: 2 points
Watershed delineation steps and instructions are properly followed: 1 point
9. The page remembers your most recent position/zoom/map-type for the next time you visit.
10. If you haven’t visited before, it tries to figure out your location based on your internet address.
11. The area computation is done using spherical geometry, so it’s correct for large regions.
12. The lines between points are drawn as great circles, to go along with the spherical area math.
13. Lines that cross the International Dateline do work, with a small gap in the line. (Google Maps applications tend to have problems with theDateline.)Areas that span more than half the globe may display strangely.
14. This used to be called the Google Areometer, because I couldn’t remember the name of the doohickey used to measure areas on a map. Butthe Lazyweb reminded me, so I changed it. Links using the old name will continue to work.