Geomorphology Lab

Part A. Case Study: Elwha River, Washington

For millennia, the Elwha River ran wild, connecting mountains and seas in a thriving ecosystem. The river proved to be an ideal habitat for anadromous (sea-run) fish, with eleven varieties of salmon and trout spawning in its waters. These fish thrived in the cold, clear waters of the Elwha River and historically served as an important food source for the Lower Elwha Klallam Tribe living along its banks.[footnoteRef:1] [1: Text by National Park Service is in the public domain]

American expansion spurred a continual demand for lumber. The growth of the logging industry in the region brought rapid change to the Olympic Peninsula and specifically to the Elwha River with the construction of two dams. The Elwha and Glines Canyon dams were built in the early 1900s, generating hydropower to supply electricity for the emerging town of Port Angeles and fueling regional growth on the Peninsula. However, construction of the dams blocked the migration of salmon upstream, disrupted the flow of sediment downstream, and flooded the historic homelands and cultural sites of the Lower Elwha Klallam Tribe.12 Figure 15.12 provides a locator map of the Elwha River in the state of Washington circa 2010.

Figure 15.12: Elwha River Locator Map.[footnoteRef:2] [2: Figure by USGS is in the public domain]

For over a century, the web of ecological and cultural connections in the Elwha Valley were broken—then the river's story changed course. In 1992, Congress passed the Elwha River Ecosystem and Fisheries Restoration Act, authorizing dam removal to restore the altered ecosystem and the native anadromous fisheries therein. After two decades of planning, the largest dam removal in U.S. history began on September 17, 2011. Six months later the Elwha Dam was gone, followed by the Glines Canyon Dam in 2014. Today, the Elwha River once again flows freely from its headwaters in the Olympic Mountains to the Strait of Juan de Fuca.12

It was the world’s largest dam-removal project. Over the next five years, water carrying newly freed rocks, sand, silt and old tree trunks reshaped more than 13 miles of river and built a larger delta into the Pacific Ocean. Of the 33 million tons of sediment trapped behind the dams, about 8 million tons resettled along the river or at the mouth, and another 14 million dispersed into the ocean. It would take more than 70 dump trucks running 24 hours a day for five years to move that much dirt and debris downstream. Piled up, the sediment would form a cone about one-third of a mile in diameter and taller than a 50-story building (Figure 15.13).[footnoteRef:3] [3: Text by USGS is in the public domain]

Figure 15.13: Size Comparison of Elwha River Sediment.[footnoteRef:4] [4: Figure by USGS is in the public domain]

Figure 15.14 shows the Elwha River delta after dam removal. Notice the brown sediment flowing into the darker colored water of the Strait of Juan de Fuca.

Figure 15.14: Elwha River Delta after Dam Removal.[footnoteRef:5] [5: Figure by Jeff Duda, USGS is in the public domain]

Let’s use topographic maps to explore the fluvial geomorphology of the Elwha River before and after dam removal.

Use the plus (+) sign and minus (-) sign to zoom in and out of the map, as needed. When zoomed in, you can click and drag your mouse pointer to view different portions of the map.

Locate the Elwha River, the Upper Elwha Dam, and the Olympic Power Plant, which is at the site of the Elwha Dam. Note that the Upper Elwha Dam is also known as the Glines Canyon Dam.

1. Does the Elwha River flow to the north or to the south? How can you tell?

2. Where do you find evidence that the Elwha River has changed its course over time?

3. Calculate the gradient of the Elwha River between the Upper Elwha Dam and the Olympic Power Plant.

a. Use the graphic scale at the bottom of the topographic map to find the distance between the Upper Elwha Dam and the Olympic Power Plant. What is the estimated distance in miles?

b. Find the contour line at the Upper Elwha Dam. What is the dam’s elevation?

c. Find the contour line at the Olympic Power Plant. What is the power plant’s elevation?

d. What is the difference in elevation (in feet) between these two locations? Show your work.

e. Divide the difference in elevation by the distance between the two locations. Show your work. Your answer should be in feet per mile.

Use the plus (+) sign and minus (-) sign to zoom in and out of the map, as needed. When zoomed in, you can click and drag your mouse pointer to view different portions of the map.

4. Where does the Elwha River have the steepest channel? At this location, what is the difference in elevation from the riverbank to the top of the cliff at the side of the river?

Keep both maps open in different tabs in order to compare the Elwha River between 1950 and 2020. Refer to the selected topographic map symbols shown in Appendix 15.1.

5. What are three major differences along the Elwha River that you notice between the 1950 and 2020 topographic maps?

Search the Internet to find out about any dams, dam construction/maintenance projects, and dam removal projects in the county where you live.

6. Would you tend to support the construction of new dams in your county? Explain your response in two to three sentences.

Part B Case Study: Louisiana Barrier Islands

Sea level rise and the increased erosion that results is a serious concern for barrier islands. NASA provides a quote from geoscience researcher Matthew Stutz that explains how every barrier island is unique:

"However, rising sea level is not just like pouring more water into a bathtub," Stutz emphasized. Islands react differently based on the geology in a region and how the waves and tides in an area are affected. People tend to assume sea level rise means fewer islands no matter what, but the rate of rise is critical."[footnoteRef:6] [6: Text by NASA is in the public domain]

Decreases in upstream sediment supplies from human activities such as dam construction also play a role in disappearing barrier islands, especially along the Mississippi Delta. The USGS explains that:

Louisiana's barrier islands are eroding so quickly that according to some estimates they will disappear by the end of this century. Although there is little human habitation on these islands, their erosion may have a severe impact on the environment landward of the barriers. As the islands disintegrate, the vast system of sheltered wetlands along Louisiana's delta plain are exposed to increasingly open Gulf conditions. Through the processes of increasing wave attack, salinity intrusion, storm surge, tidal range, and sediment transport, removal of the barrier islands may significantly accelerate deterioration of wetlands that have already experienced the greatest areal losses in the U.S. Because these wetlands are nurseries for many species of fish and shellfish, the loss of the barrier islands and the accelerated loss of the protected wetlands may have a profound impact in the billion dollar per year fishing industry supported by Louisiana's fragile coastal environment.[footnoteRef:7] [7: Text by the USGS is in the public domain]

In the search box, type Louisiana and click the magnifying glass.

Zoom in on one of the barrier islands off the coast of Louisiana (pick any named island).

3. What is the name of the barrier island that you zoomed in on?

Zoom in as far as you are able to.

Click the “Only versions with local changes” box.

4. What is the date of the oldest imagery available?

5. What is the date of the most recent imagery available?

Click on each date available to see how the barrier island landscape changed over time.

6. In two to three sentences, describe the changes that you observe.

7. Use Your Critical Thinking Skills: If the historical imagery at the barrier island that you selected went back 10, 50, or 100 years, what changes do you think you would have observed? Respond in one to two sentences.

Part C. Case Study: Taku and Norris Glaciers

Taku Glacier is a tidewater glacier located in Taku Inlet in the U.S. state of Alaska, just southeast of the city of Juneau. A tidewater glacier is a valley glacier that extends to the ocean. Recognized as the deepest and thickest alpine temperate glacier in the world, the Taku Glacier was 1,477 meters (4,845 feet) thick and 58 kilometers (36 miles) long in 2020.

The map on the following page is of the Juneau Icefield in Alaska. An icefield is a large area that has many interconnected glaciers. You will observe both the Taku and Norris Glaciers, topographic contours, and the positions of the edge of each glacier at different times since 1750. Dates have been provided by using a few different methods, such as aerial photography, survey data, absolute dating of sediment-covered vegetation, and carbon dating of deposited material in moraines. Remember that glaciers naturally gain and lose ice and snow each year. If the amount of ice and snow accumulation exceeds the amount that is lost per year, the glacier will advance (and the glacial mass balance will be positive). If the amount of ice and snow gained is less than the amount that is lost that year, the glacier will retreat (and the glacial mass balance will be negative).

2