GEOL151 Fall 2016: Lab for Week #7 Drainage Basins: Following a River from Source to Sink

Transcription

1 GEOL151 Fall 2016: Lab for Week #7 Drainage Basins: Following a River from Source to Sink Overview As we enter the middle of the course, we move into more synthetic topics and strive to gain an understanding of landscape-scale geomorphology as a whole. We have already studied rivers and river channel processes. However, this week we will take an integrative approach to rivers by assessing how a river evolves throughout a drainage basin, from its headwaters in the mountains to the flat valley floor, and ultimately to its sink. We will visit the Winooski River (and a tributary, the Browns River) in several locations as it flows from the mountains and into Lake Champlain, evolving progressively throughout the drainage basin. Our goals are to assess how a river changes from the uplands to the lowlands and to contemplate how sediment is transported from source to sink in order to gain insight into how drainage basins function. Gear Since this week s trip is more integrative and less quantitative, you should come prepared to primarily think and sketch. We will also bring a few basic tools for measuring water velocity. A camera may be helpful for recording your observations as we progress through the trip. Stops Progressing from the uplands to the lowlands, we will assess four different sites within the drainage basin (Fig. 1). We will visit the first three sites together as a group; you should visit the fourth site on your own using Google Earth. Stop 1: Browns River (a Winooski River tributary) near Underhill Center Stop 2: Browns River (a Winooski River tributary) between Jericho and Underhill Stop 3: Winooski River north of downtown Winooski Stop 4: Winooski River delta in Colchester We will see vastly different channel features as we progress from source to sink. In order to ensure that you can compare between different stops, contemplate the following at each: 1. Is the channel bedrock or alluvial? 2. Are there any interesting channel features (e.g., meanders, woody debris)? 3. How wide is the channel? How deep is the channel? 4. What does the channel look like in cross-section, as best as you can tell? 5. What is the average and range of sediment size? 6. What is the water velocity? 7. Where is erosion occurring and where is deposition occurring? 8. How might the channel be evolving over time? 1

2 Sketching At all four stops, you should sketch both a map-view and a cross-sectional view of the channel (using the attached pages, if desired). Your sketch should seek to depict the overall characteristics of the channel, with an emphasis on showing the processes in operation and addressing the questions above. Each sketch should be oriented both in terms of space (i.e. show a north arrow and flow direction) and in terms of size (i.e. show a scale bar). Don t worry, I am not expecting these to be works of art! I am well aware that everyone has different abilities. The artistry of your sketches is not important; rather, we are interested in the thought process behind your sketches and the choices you make about what to show. You can and should label your sketches thoroughly in order to guide your reader. You should make rough versions of your sketches while we are in the field as a way of recording what you see. However, please make clean, polished versions to turn in with your field report. Either color or black and white is fine; just make sure to keep them neat, well-organized, and easy to read. There are templates at the end of this field guide that you can use for the rough sketches, the final sketches, both, or neither; if you prefer, you can work in a digital drawing program of your choice. Field Report Synthesize your work into a field report focused on how a river channel evolves from source to sink and how sediment is transported through a drainage basin. Refer to the How to Prepare a Successful Field Report handout for more ideas on organization, content, and presentation. Since you will be creating detailed sketches at each stop, these sketches will be able to serve as your observations section. Therefore, your written report should focus on interpretations and on pulling the four stops together with big-picture discussion of channel evolution and sediment transport. Adding a synthetic sketch at the end (e.g., a full source-to-sink depiction of a river channel and a drainage basin) may help guide your thoughts. Please include an introduction and conclusion as usual. I encourage you to work together to discuss your thoughts; however, each student must turn in his/her own field report. Since we will not be meeting for regularly-scheduled classes next week, these reports are due at the beginning of the lab period on Wednesday next week (10/19) in Alison s mailbox in the Geology Department office. 1

3 Figure 1. Location of our four stops, overlain on Google Earth Satellite imagery. For exact stop locations, download the Google Earth file from the class website. 3

4 Stop #1: Browns River near Underhill Center (map view) Stop #1: Browns River near Underhill Center (cross-sectional view) 4

5 Stop #2: Browns River between Jericho and Underhill (map view) Stop #2: Browns River between Jericho and Underhill (cross-sectional view) 5

6 Stop #3: Winooski River north of downtown Winooski (map view) Stop #3: Winooski River north of downtown Winooski (cross-sectional view) 6

7 Stop #4: Winooski River delta in Colchester (map view) Stop #4: Winooski River delta in Colchester (cross-sectional view) 7