Summer research comes to an end!

This is the final post of the summer but definitely not the end of this project! Summer totals leave me with 24 fields completed in GIS and I hope to analyze 40 in total. Also, I have 4 fields in both resolutions to test the 10m DEMs and I would like to have 10 total as the larger the sample size, the more reliable the results. We have ground-truthed only 2 fields, it being a very time consuming process and I would like to have the in-field data for at least 5 more fields. I will work on getting this information in September when the weather is gentler and the forest slightly less vegetated. The past few days have been spent writing up the methods I used this summer to get a head start on my thesis and working with the LIDAR data on James City County fields.

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Ground-Truthing

Geology is the study of the earth; however programs such as GIS have allowed geology data collection to move indoors. If you’ve followed my posts you know that my research relies heavily on the data available for use in GIS and the analyses which can be done in the program. In order to do this we needed to determine how closely results from GIS match what’s actually happening on our fields. As I mentioned in the previous post, our task this week was to ground-truth our channel locations. Tuesday this week, a teammate and I visited the cotton-planted field surrounding Peace Hill Bed & Breakfast in Charles City County. Using a GPS unit, aerial photography and a topo map we walked the perimeter of the field marking locations of concentrated flow.

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Charles City County Flow Concentration Analyses

 This week was spent performing drainage analysis on 9 fields in Charles City County, Va. Using the 10m DEMs on the USGS’s Seamless server I was able to determine flow concentration values along the edge of each field. Charles City County is not one of the 11 counties covered by the newly available LIDAR. However, as mentioned in my previous posts, we are able to use this data with confidence after doing comparison analyses on several fields. The 9 fields will also be used in our test of GIS flow concentration areas with actual field observations. I was able to obtain information on the field ownership via the GIS parcel data on the county’s website and am working on contacting the owners for permission to visit the fields. During the visit my teammates and I will walk the parameter of the field and record the location of channels exiting the field with a GPS unit. Then back at the lab I can put these locations into ArcMap and determine their relation to high accumulation locations. This is a key step in our project. If there is a strong relationship between actual channels forming and high flow accumulation values in GIS then these steps can be used easily to find target points for buffer bypassing on a broad scale, without field visitation being necessary.

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Yay New LIDAR!!

The end of last week came with a pleasant surprise of new 1.5m LIDAR being available for several counties in the Coastal Plain of Virginia. This meant I would be able to utilize the most current elevation data with the highest possible resolution. In my last post I explained how the 2m vs. 10m tests proved the 10m to be just as effective as the 2m and earlier this week I performed the same comparison using the new LIDAR. The results were very similar. A plot of the cumulative fraction drained along the field margin with both DEM resolutions showed the two to be matching exceptionally well. The higher resolution sets do allow for more accuracy in tracing the field margin, yet this doesn’t seem to cause a change in determining flow accumulation entering and exiting the field. This is great news! This allows me to analyze flow concentration on numerous fields as I am not restricted by the availability of high resolution data.

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Testing the Accuracy of DEMs in GIS

The first few weeks have flown by here in Williamsburg! The project is fully underway and progress was slow at first but with my methods smoothed out and the data downloaded I’ve been able to pick up speed. As mentioned in my introductory post the majority of my research is being done using Geographic Information Systems (GIS). Beginning the next few days I will be analyzing numerous agricultural fields in the Coastal Plain.

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