Tuesday, October 8, 2013

Field Fridays

Last year at this time, I was spending my Friday afternoons in Morgan Hill State Forest collecting data for a geomorphology field project. My objective was to determine the controls on stream morphology in one valley using field observations.

Left: The study area, in New York State. Right: Morgan Hill State Forest. The study area is the purple rectangle within the State Forest. 

Morgan Hill State Forest is 5294 acres. Once farmland, the land reverted to the state when the farms were abandoned and between 1929-1931 the land was planted with conifers and native hardwood.

The streams in the study area flow into the eastern branch of the Tioughnioga River, eventually reaching Chesapeake Bay via the Chenango River and the Susquehanna River.

A lot of my field work involved walking the study area with a GPS unit, collecting waypoints and tracklines to go along with my observations. I made four transects of the valley to get elevation profiles, walked along two ridges, walked along the streams, and  measured stream orientation at several locations to correspond to the one set of bedrock fractures that were visible in the study area.  It was definitely very rudimentary data collection, but it was enough to get a sense of what was going on in the valley.

I did some statistical analysis on this data as part of a project for a statistics class, and it was great to have the opportunity to go into more detail on the quantitative assessment of the data I collected and its precision.

Left: Data collected with a handheld GPS unit. Large circles are waypoints; smaller circles are part of the recorded tracks. Right: The locations of the four transects used to create elevation profiles, the mapped stream locations and orientations (arrows) and the bedrock orientations. Downstream is to the south.

What I loved about this project was that I got to choose my field area (from one of three possible sites) and decide what to do with it. I learned so much from this study!  Field equipment was limited, because the entire class had to divvy up what was available, so I also had to think about what I could do with the equipment I had. If I was doing the same project again, with the same equipment, there is one thing I would change. I would have walked each track and each route several times so I could average GPS data (lat, long, elevation) and try to increase precision.

My field observations suggest there is a relationship between stream orientation and bedrock fractures. This is assuming that the one exposure of fractures (two sets though) is representative of all fractures in the region. The mean orientation of the stream, calculated from the collected orientations shown in the map above, is equal to the orientation of one of the joint sets.

The stream beds were covered in pieces of shale, and in some places they were even imbricated. My interpretation was that these shale pieces were once part of the bedrock but they've been broken up and moved by streams, particularly during spring runoff. Over time, this process widened the valley upstream (see figure below). Downstream, the valley narrows, interpreted to be caused by incision of a more resistant rock than the shales upstream (although not confirmed because the edge of my study area was also the border of the state forest and I didn't want to go onto private land during hunting season). This produced the ridges/terraces observed at the south end of the study area.

Elevation profiles for the four transects are shown on the left. 5m contours have been added to this map to show the general valley morphology. Recorded elevations for profile C-C' are higher than those upstream and downstream. Contours were not draw through this portion of the map to reflect the uncertainty in this data (this transect was collected when the Garmin battery was low). Downstream is to the south.
This project was definitely my favourite part of any of the course work I've done for my PhD. Not only did I learn a lot, but it was great to see fall developing in the valley over the course of the "field season."

Photo 1 taken at waypoint 017. Photo 2 taken at waypoint 060. Photo 3 taken at waypoint 045. Photo 4 taken at waypoint 051. Waypoint locations are shown on the map above.
Photo 5 taken at waypoint 022 (standing on ridge). Photo 6 taken at waypoint 047. Photo 7 taken at waypoint 065. Photo 8 taken at waypoint 042. Waypoint locations shown on map above.
* This is day 2 of my personal "30 minute blog challenge," where I'm dedicating 30 minutes a day to my blog. This post fit into the 30 minute time frame because all the figures were already done for my report.

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