GLS100 Lab Topographic Maps: Part I
GLS100 Lab – Topographic Maps:
Interpreting topography and hydrology from contour maps
Goals and objectives:
The goal of this two part lab is to visualize topography from contour maps. In the process you will learn how to make, read and label contours, obtain map elevation and distance data, and construct and interpret profiles and apply you ability to interpret topographic maps to the landscape of the North Shore.
Introduction to Topographic Maps
Map reading and interpretation is a required skill for all geologists. Field geologists must be able to accurately locate data points. Many features like gravel-bearing deposits, faults, outcrops, landslides, flood plains, and springs are reflected in the landscape and can be located by analyzing topographic maps.
What is a Topographic map?
Topographic maps illustrate 3-D topography on a 2-D sheet of paper. Topography can be represented either by shading or contouring elevation data. Shaded relief maps are easier to visualize, but less detailed and harder to plot and retrieve data from than contour maps. In this lab you will learn to read contour maps.
Terms
Contour: a line connecting points of equal elevation.
Contour interval: The elevation difference between contours
Map Scale: The length on the map that is equal to a given distance on the ground.
Elevation: height above mean sea level.
Relief: Difference between the highest and lowest elevation.
Height: relief of a feature. Measured from the base to the top.
Rules of contours:
1. By definition contours connect points of equal elevation.
2. Contour don't join or cross unless a vertical cliff or an overhang (very rare) is indicated.
3. All points enclosed within an unhachured contour are of a higher elevation.
4. All points enclosed within a hachured contour are of a lower elevation
5. Contours crossing streams V upstream (upslope)
6. Contours crossing ridges between streams V downstream (downslope).
7. The spacing of contours indicates relative slope.
Study the map of the Salem area and answer the following questions:
1. Map properties:
a. Scale: State the relative fraction scale ______and the verbal scale in inches/mile using the bar scale ______.
b. In a sentence state the meaning of the fractional scale:
c. Identify the contour interval:______meters
2. Map area: The map is traverse by UTM grid lines spaced 1000 meters (1 km) apart.
a. Determine the east-west length ______, and north-south length of the map in kilometers.
b. Calculate the maps area in square kilometers? ______
c. Calculate the approximate percentage of the land area that is urbanized? ______
Explain how you determined this value:
d. During storms water flows overland as runoff and percolates into the groundwater table. Runoff enters immediately into streams—a process that is even hasten by sewers. Groundwater will also enter into streams but at a much slower rate. State and explain the effect you think urbanization has on the volume of precipitation ending up as runoff relative to groundwater?
3. Relief is the elevation difference between the highest and lowest elevations of an area.
a. Locate and state the elevation of the highest point of the land in the map area:
i. Describe location:______
ii. State Elevation (don’t forget the units): ______
b. Locate and state the elevation of the lowest point of land in the map area:
i. Describe location: ______
ii. State the elevation: ______
c. Calculate the relief of the map area: ______
Describing the Map Area: Topography and Hydrology
1. Describing the topography:
a. Describe the uplands: Are the hills rounded, flat topped, elongate, asymmetrical, etc.? Do they appear to have a preferred orientation?
b. Describe the lowlands and valleys: Are the valleys long or short. Are they randomly oriented? Are the broader lowlands flat? Well-drained?
c. Glacial ice sheets modify the landscape by disrupting drainage systems, streamlining hills, and plucking the down-ice side of bedrock hills. From your observations make a prediction of the direction of ice flow during the last glaciation. (We will need to confirm this later when we go to Forest River Park.)
2. Drainage and Groundwater Flow:
a. Locate and identify the major streams in the area.
Draining into Peabody: ______, ______, ______, ______
Draining into Salem: ______
b. Are the streams drainage basins well-defined or deranged? (circle one)
b. Is the area naturally well-drained or poorly drained? (circle one)
c. Locating the water table: Lakes and ponds are formed where depressions are deep enough to intersect the water table. Water flows down gradient, therefore the direction of groundwater flow is determined by the slope of the water table.
i. State the elevation of the water table at Breeds Pond? ______meters
ii. State the elevation of the water table at Floating Bridge Pond near Buchanan bridge ______meters
iii. From these and data and elevations of other ponds in the area state the general direction of the regional groundwater flow in the southwestern quarter of the map area. ______
d. What is the approximate elevation of the water table in and around Needam Corner in Peabody. ______meters
e. Is the water table shallow or deep in this area? ______
f. Look at the topography and drainage in and around Peabody Center, where Foster Street and Lowell Street intersect. From your observations offer an explanation as to why this area is so prone to flooding.
g. There are numerous water tanks and tower in the map area. Are these located on hills or in lowlands. (circle one)
Explain:
Final Evaluation (5 pts) : After completing this lab type a one page summary discussion describing the area based on the information obtained from this map.
Include in your summary the following:
1. the percentage of land area that is urbanized and it’s significance;
2. a description of the topography and relationship to glaciation;
3. hydrology, including drainage, depth to water table in lowlands, and direction of groundwater flow; and
4. summarize the factors, of which there are at least three, that contribute to the flooding in downtown Peabody.
I do not want a step by step outline of the lab.
How to submit your assignment:
1. Save as a word.doc that has a filename with your initials (e.g. topolabLSH.doc).
2. Type a statement in the submission box, such as "here is my topolab assignment. It was a lot of fun! "
3. Attach your file. Press the "attach file" button and myWebCourses will take you through the steps.
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